View Full Version : Ming-Da MC34-B


DanTana
04-03-2005, 08:56 AM
Chinese made equipment suffers from a stigma, they cost less so the perceived quality is also less. I have not found this to be true in this case. Politics aside, the Chinese can do what no other country can right now, sell decent made and good sounding equipment for a fraction of others. The Ming-Da MC34-B falls into the category, inexpensive for a tube amp of this quality, and definitely a very good sounding unit.

First I want to thank Thor for giving me the opportunity to try this and eventually buy it from him, I wasn't expecting much, except I had seen pictures and knew it looked nice, but I was in for a shock when it came to the sound quality. It arrived in it's factory box and packing and in perfect shape, first thing I immediatly noticed was it's heavy weight. I wasn't expecting something that small to weigh that much. I was very taken with it's good looks, polished stainless steel and black krinkle finish transformer covers and a very thick faceplate. The "pagoda" cover I call it, keeps small hands and fingers away from the hot tubes. The whole amp has a feeling of being well built, solid and heavy feeling, the cover has a thick plexiglass top with air holes drilled and polished trim around the outsides. It press fits into the chassis with rubber grommets to hold it in place. The next thing was to bias the output tubes, removing the bottom plate I found the same quality of material, a fairly thick steel bottom, thicker than what you'd even find in the highest of quality Japanese gear. I was very impressed with what I found next, the internal wiring and component layout, was one of the most intelligently thought out of anything I've seen before. All the wires were twisted together, and every component seems to be used as support for the others. The leads of the resistors, capacitors, diodes, are used as supports for the rest of the circuits, the bias pots and wiring points. All resistors are 1 watt rated except the cathode resistors which are 5 watt rated, the capacitors are Rubycon, SME, Samsung, and the coupling caps are "Ming-Da" brand. The bias pots are easy to get to underneath, one nice feature would of been to place these to access from the outside. After biasing the tubes, it was time to finally listen.

At first I was very impressed with the sound, nice deep bass, fairly linear extension to the treble. However, I wasn't as impressed with the midrange, it was a little muddy and not as clean as I like. I also noticed that in certain passages, female voices and horns seemed a little harsh and edgy. It had 6L6wxt+ Sovtek tubes and after learning I could put in EL34's that was the next logical step. Installing and rebiasing the EL34's were straight forward, I set the bias to 35ma and began listening again, what a difference!! The midrange was now much cleaner sounding, the bass although not as deep, was very tight and detailed. The highs had a nice extended and smooth sound, but at times I still had that slight hardness and edginess. The driver tubes and preamp tubes were 6N1 and 6N2, both using the same pinouts as the 12AU7, 12AX7 tubes except 6 volt filaments. This limits the available tubes to try in this amp, so I first rewired the preamp socket to 12 volt. This wasn't too difficult, and I purchased two JJ Tesla 12AX7's to try in it.

Now to try the new tubes, first powered it on to make sure it didn't start smoking or other mistakes, and rechecking the bias it was time to listen again.
Changing out the 6N2's to the JJ Tesla 12AX7's was the next biggest sound improvement, the hardness was now gone, the midrange more detailed and the highs extended very nicely. The EL34's I had used were the new Russian issued Mullards, I purchased these from Triode Electronics and they arrived very quickly, from the outset I could tell these tubes were winners. The next steps I had taken was two fold, I bought some high voltage metal film capacitors and decided to try these new tubes in triode mode. After wiring these in triode and rebiasing once again, time again to hear the difference.

Once again, another impressive improvement in the sound quality, in triode mode these new Mullard tubes just seemed "sweeter" sounding, more detailed and the midrange was very clean and natural sounding. The highs seem to be more effortless in it's presentation, and at times certain instruments seem to just float in the air. However, one thing seemed lacking somewhat, and that was just a little more inner detail in the music, now much improved I felt it could do a little better. Now at this point normally listening was a joy, no listener fatigue at all, compared to the out of the box listening sessions, I just wanted to listen to every album over and over again, the amp finally captured what my turntable and cartridge was capable of delivering. Being a perfectionist, I was first considering the new "supertube" 6H30pi that could be a drop in replacement for the 6N1, the 6N1 is not a bad tube by any means, but I also had been reading how the new JJ Tesla ECC99 was an outstanding driver tube, made especially for driving high powered triode tubes like the 300B.

I made a trip to Triode Electronics next, wanting to buy two 6H30pi's and unfortunately, somebody had just purchased 24 of them and they were sold out. What next...well they had the ECC99 JJ Tesla's and for backup, I also bought two RCA clear top 12AU7's. Now to get home and rewire the driver socket from 6 volt to 12 volt and try the ECC99. This wasn't as drastic as an improvement as changing the preamp from the awful 6N2 to the 12AX7, but the sound seemed to clean up noticably, detail mainly was improved. The linearity of the tube was from deep bass to the treble. This driver tube seem to be much more transparent sounding, making the preamp swaps more noticable. Now it is much easier for me to hear the difference between the EH, JJ and other preamp tubes I've tried. I think these new ECC99's are also a winner. The biggest comment I can make about them, is they just seem cleaner sounding. Subtle details are now more noticable and hearing soft passages are easier, during some listening sessions when a loud instrument might be playing, I can still hear the drummer lightly hitting his cymbal. I tried the RCA clear tops and it's no contest between the ECC99 and them. The JJ's win hands down. The JJ's are that much cleaner sounding and detailed than the RCA's to hear a difference.

Now anybody buying one of these amps may or may not feel the stock amp would need changing, but at least there is a good enough foundation to work with that allows this kind of tweaking and deliver this high of sound quality. I could tell immediately this amp had potential, and I wasn't wrong. I think out of the box, this amp sounds good but can be fatiguing after long sessions due to some of the harshness of the 6N2 preamp tube. Other than a 6AX7 there isn't much choices here, possibly the 6DJ8, but these don't impress me either. For some people who maybe shy about modding, this may not be a good amp to buy, you may not be happy with the sound out of the box. For the ones who aren't afraid to do a little soldering and swapping in better tubes, then you will be rewarded with a very decent sounding, inexpensive amp that will provide you hours and hours of enjoyment.

zincman
04-03-2005, 10:49 AM
Nice review Dan, well written. As an owner of chinese stuff along with US made, they are hard to beat on the value for sound dollar. Although my Dareds lack the top quality materials I just remind myself how much they cost. Thanks again for a nice review.

DanTana
04-04-2005, 10:48 AM
Thanks zincman, these amps sort of remind me of the value of the old Dynakits and Heathkits of the 50's and 60's. One thing I didn't mention in the review, was the fact this is an integrated amp, and allows for two inputs, and has a headphone output and volume control. The volume works with the headphones connected or not, so you can adjust the gain as you like. Two mods I am considering next, replace the coupling caps with something "known" like Auricaps, and bypassing the integrated functions to shorten the signal path like a dedicated amp.

DanTana
04-20-2005, 10:09 AM
Just an update on the latest incarnation, picked up four "Orange Drop" caps, film and foil type, put those in and added a resistor to the negative feedback loop to the input tube. The Orange Drops were only about $2.00 each and probably the best deal on capacitors anywhere. I replaced the "Ming-Da" caps and the Orange Drops were nearly twice the size, a bit of a hassle getting one in but the rest installed fine. The resistor I just matched the size of the existing one, and soldered it in series.

As soon as I powered it on I knew it was different, it was so much clearer sounding and the highs were very clean. Even the bass seemed stronger, although maybe not lower, but more controlled might be the best term to use. Sometimes you never know what your missing until you change it, and I realized I wasn't hearing as much as the music as I should be. The midrange is now where during certain songs, I can make out the lyrics much better. I wasn't always sure if it was my source devices, my phono cartridge or CD player that sometimes seem lacking, not knowing it was my amp. Having changed it from Ultralinear operation to Triode, feedback isn't needed, or at least as much. Now I can tell that something designers use to reduce distortion, can reduce detail and clarity also.

teapot97
05-07-2005, 11:40 PM
I owned a mingda MC 34B. How can I rewire to 12v to accomodate 12ax7 tubes ? Any photos to follow ?

Many thanks.

DanTana
05-08-2005, 07:59 AM
This should help : http://www.triodeel.com/images/rb6n2pcv.gif

Pin 9 will be soldered to ground, unsolder it and place the wire that was on pin 5 to pin 9.

Solder a jumper over pins 4 and 5.

Andyman
05-08-2005, 09:27 AM
Dan:
Nice reviews. Have you had a chance to audition that almarro A205A yet? I wonder how it compares to the Ming Da.
Let us know!

DanTana
05-08-2005, 10:24 AM
So far that little Almarro has been a pleasant surprise. I wouldn't think a little SE EL84 amp could put out so much power and sound as nice as it does.

Andyman
05-08-2005, 11:59 AM
I sure love mine. One thing about the power though is that someone in the other link stated that a lot of the gain is loaded into the bottom of the volume pot. I've never had mine past 10:00 on the La Scalas, and things change fast from 9 to 10, so that wouldn't surprise me at all. It definitely has more volume at equivalent settings that the 22 wpc Harman Kardon 430 it replaced. It may run out of gas after 12:00, but unless I get a bigger house, I'll probably never find out!

THOR
05-08-2005, 12:11 PM
Glad your enjoying Dan! Someday I'll have to get another and try the things you've done. That is if the Miata ever gets done ;)

DanTana
05-08-2005, 12:30 PM
Chris, So far, the Ming-Da has been one of the best audio purchases I have ever made. Thanks again...and get that Miata done now that the weather is improving.

craigcook
05-08-2005, 11:02 PM
just curious, who sells these? I saw an ebay listing by jim60815, not sure if it was legit ($528 + $145 shipping).

DanTana
05-09-2005, 10:29 AM
You can find it here among other places including EBay.

http://www.cattylink.com/engproducts-P9.htm

teapot97
05-11-2005, 07:24 PM
Thanks for the diagram. Do I need to rewire all four preamp tubes 6n1 and 6n2 ? By the way, on the four preamp which is 6n1 and 6n2 ? ther is no label. After rewiring it, all four would be 12ax7 tube or 2 tube 12ax7 the other tube could 12at7 etc.

teapot97
05-11-2005, 07:28 PM
On the diagram to convert to 12ax7 on pin 9 need to attached the wire from pin 5 and jumper 4&5. Do I have to do on all 4 tube sockets ?

trickytree
05-12-2005, 12:27 PM
I have had my Ming Da MC34-B for about a month now and it is an amazing little amp. I have had this valve itch for some time but have never taken the plunge and tried one. This one came up secondhand so was even more of a bargain and I must say it is possibly the best amplifier that I have owned. In my system it does all that my previous Naim pre-power combination did and then some. Amazing.
Apart from a set of Sovtek 5881's that are available as an option when buying the amp from Edenlake (http://www.edenlake.com/) it is standard at the moment but I must admit that it is great that Dan has done so much work that we can all copy, cheer's mate!
I must say I just luuuurve the look of those Mullardesqe EL34's so i'll get me a set of those and also have a go at modding for the 12AX7's but will not be in any great hurry, i'm enjoying it as it is thank you very much!

DanTana
05-19-2005, 07:19 PM
Teapot, Sorry for the late reply, I've been out of town the last week. You do not HAVE to do all 4 sockets, but if you do then your correct with using say...12AU7's where the 6N1's were and 12AX7's where the 6N2's were. I've tried 12AU7's, 12AV7's, ECC99's and 5965's in that spot and to me, the ECC99's, sound best, but have less gain, the 12AV7, 5965 sound very good too, and have more gain. I've got RCA 5965's and GE triple mica 12AV7's that are pretty darn good sounding also. I've also put the 12AV7's in the preamp spot and they were pretty good there too. Of course the gain is far less, but they seem to not color the sound very much. Right now though I'm sort of mixed between the new GT Mullard copy 12AX7's and the new Svetlana silver plate 12AX7's. The Svetlana has some outstanding bass and nice highs, Mullards seem more neutral. At least with the mods, you can have many more choices with your tube swapping. One thing I wish I had done before wiring the driver sockets, is trying the 6H30pi Russian tube, someday I may change it back and give that tube a try.

Trickytree, Glad your enjoying yours, it truly is one of the best bargains in tube audio out there.

trickytree
06-11-2005, 04:23 PM
Dan,

I'm wondering if you would be kind enough to talk me through how to set the bias on the Ming-Da? I bought mine secondhand and only got the following photo with it....no instructions. Although I have done a bit of DIY before I have never had a go at a valve amp.

My amp is the same as pictured apart from the cathode resistors that are square ceramic 5w 10ohm.


http://img297.echo.cx/img297/1516/34bbiasing9qw.jpg


TIA,

Paul.

DanTana
06-11-2005, 05:57 PM
That's a decent picture to go by. Use your DMM and place the negative on "B", then put the postive on either "A" or "C", then you'll adjust the pot "D" if your probes are on "A" and "B", you'll adjust pot "E" if your probes are on "B" and "C". At first move the pots very slightly so you can get which way increases and decreases the voltage. You didn't say which tubes you were using so I'd use 25mv for 6L6 and 30mv for EL34. Your probes will be on either side of the resistor when your adjusting the voltage, you'll have to go back and forth many times until it steadies. One side effects the other so it will take a good 10-15 minutes probably, maybe longer. First you may want to do a quick check on the voltage to see if any of the tubes are way out of spec, and do those first. Also, I'd give the amp a good 10-15 minutes at least to warm up, so if everything is good, just leave it on until then and recheck. Also, I use a 8 ohm 20 watt resistor across the speaker outputs. You can get those at Radio Shack, that will protect it in case of oscillation.

trickytree
06-12-2005, 11:49 AM
Thanks very much Dan, much appreciated.


Paul.

SOUNDASAPOUND
08-25-2005, 08:42 AM
HI,I am the proud owner of a Ming-Da EL34-A ,'it is an excellent amp' I have already replaced the valves with the russian Mullards and replaced the 400v 0.10uf caps with black gates they have improved detail and made the sound more immersive and thats before they have berned in, I am also waiting for some Auricaps to be deliverd from the US.
I have bypassed the selector switch and removed the pre amp circuit so it is virtuley a power amp now and it sounds great.But I would like to add a triode mode
do you no where I could get some info and diagrams to help, ming da dont give them out understandabley and they dont give info on biasing with the amp,please could anyone help...

DanTana
08-25-2005, 10:12 AM
If you look above you'll see a picture and a description on how to bias the "B" model, which I'm assuming isn't much different from your "A" model. As far as triode mode goes I simply soldered a 100 ohm 1/2 watt resistor across pins 3 and 4. Removing or reducing the amount of feedback will also improve dynamics. Make sure you remove the UL connections before you wire it in triode, or if your ambitious you could add a switch for UL/Triode. I can't remember which preamp/driver tubes the "A" used, but I wired the heaters for 12**7 tubes. I had good success with both the ECC99 and 12BH7 for driver. I'm curious though, you said you removed the preamp circuit? How did you wire it afterwards?

SOUNDASAPOUND
08-26-2005, 08:13 AM
Thanks for the info . :thmbsp:

SOUNDASAPOUND
10-29-2005, 06:49 AM
I would like to add a triode mode to my Ming-Da mcm34-A but I whant to use the
pre amp switch as Ive removed the preamp cuircuit so the switch is now redundant,it would be very usefull if I could make use of this but I dont know where to start could anyone help.Ive whanted to do this mod for ages..
Alan

DanTana
10-30-2005, 05:54 PM
You'll have to wire the #4 pin to both ultralinear and to a 100ohm resistor to pin #3. You maybe able to do that through the stereo/headphone switch, but I'm not 100% sure. The circuit for UL will just be the #4 pin, but triode will be both #4 and #3 pins.

SOUNDASAPOUND
10-31-2005, 12:27 PM
THANKS!! IM GETTING THE IDEA BUT IM NOT SURE WHAT MAKES UP THE UL CONNECTON'S,DO THEY GO FROM PIN 4 TO THE NEXT VALVE AND IS IT JUST ON THE EL34'S.DO I NEED TO TOUCH THE ECC82'S/ECC83'S?. :thmbsp:

DanTana
10-31-2005, 01:22 PM
The ultralinear connections go from the output transformers to the output tubes on pin #4. Triode connects pins #3 and #4 with a 100ohm resistor, removing the ultralinear connection on pin #4.

DanTana
01-11-2006, 08:40 AM
A few months back I did a circuit change that transformed this amp into a different category, I replaced the typical cathode bias setup, resistor and bypass capacitor, with a single AA 1.5v NIhM battery. I put one on each side per preamp tubes. The noise floor dropped, the clarity improved, and even frequency response seems to be better. Bass seems to go very deep now. This was almost like putting in a new amp it made it sound that much better.

DanTana
01-11-2006, 08:48 AM
Here's a link to the article I wrote on the battery bias I did on the Ming-Da a couple months ago, I highly recommend this mod.

http://audiokarma.org/forums/showthread.php?t=47389

MikE
01-15-2006, 02:20 PM
I just ran across this thread... Thor I'm surprized you sold the Ming. Was that the same one that Rob "custom built" for you? The pictures are gone [now] but from what I remember it sure looked like a keeper to me. I thought you were very happy with it. What happened? You said you may "get another one" but will you be able to get one exactly like Rob put together for you? Did the amp just not provide long term enjoyment or did a change in components make it no longer compatible? Or did your listener priorities shift? Just curious.

MikE

THOR
01-15-2006, 03:13 PM
No Rob didn't custom build it he imported it for me via his US distributor and gave me a deal on the price.

I was very happy with the look and sound of it, it was in need of a bias adjustment after using it for a year and I was also strapped for cash with my Miata restore. Since I had 5 very good Luxman SS amps I figured I could offload the Ming Da to subsidize my car project and not have to deal with a bias adjustment ;)

Someday I would like another tube amp, on top of the sound they are great conversation pieces when folks see them. They don't see tube gear at the local Best Buy and Circuit City.

MikE
01-15-2006, 04:14 PM
Someday I would like another tube amp, on top of the sound they are great conversation pieces when folks see them. They don't see tube gear at the local Best Buy and Circuit City. Pearching to the choir on that one brother! :D I sometimes haul my amp / crate to work just to hear "what's THAT?" hehe MikE

TWantiques
04-30-2006, 05:40 PM
Last weekend I was able to get one of the MV34-A amps. At the time, I knew nothing about it (I only have SS) other than it sounded pretty good with a cheap CD player and a pair of bookshelf Wharfdales. I listened to several tube systems at the Atlanta AK meet we had in March and was quite impressed. Have been thinking about how to get started with a tube amp.

The guy that had it works for a company that sells them. I am an antique dealer and I was able to trade him an old fan for it! I didn't think it too much of a risk, got a great deal without having to layout any cash.

I was very pleased and not surprised to search AK and find this thread. Looks like I didn't buy a pig in a poke. I am going to get it hooked up in the next few days and give it a good test run. I like the idea of the mods DanTana has suggested so I'll make a run at some of those. Currently they are beyond my skills but I need to learn.

A new audio experience, should be fun!

Terry

DanTana
05-01-2006, 09:46 AM
First thing your going to want to do is check the bias, this will have to be done with the power on at operating temperature. I think 35mv is the correct setting. You need a DMM with clips and a small screwdriver to adjust the pots. You must be VERY careful when doing this only because there is high voltage inside. Use the one hand rule and keep the other hand away to avoid lethal shock. It really isn't too dangerous, but one slip and it could be. The bias points are very well diagrammed in this thread. Get a good baseline listening to this stock before you consider any mods. The mods are not that difficult either, those will be done with the power off. Still you must be careful, one bare wire can cause a short and poof. Radio Shack sells plastic alignment tools which will make adjusting the bias a much safer affair. It will include a small plastic flat screwdriver. I put 8ohm resistors across the outputs lean it back for easy access, take off the bottom cover, turn it on and let it warm up awhile. Then adjust.

TWantiques
05-01-2006, 09:38 PM
Thanks Dan, I'll follow your advice closely. This electrical work is new to me so I am going to take my time. As it is now I'm going to be out of town for the next week and a half so it will be later on in May before I can get started.

If you don't mind I will be looking for your help from time to time.

I'm looking forward to this project.

Terry

davehanc
05-15-2006, 04:53 AM
I first came across the MC34B on ebay, and was intrigued by Dan's review and experience of modding. I bought one about a month ago when I found a local distributor. So far I've switched to JJ EL34s (wired for triode a couple of days ago) and ECC83s and Winged C 61NPs - I have some Sovtek 6H30pi from an unfinished Hagerman kit, and will try those before I decide on the ECC99. I 've seen some negative responses to Dan's questions elsewhere on using the 6H30, but from what I can see the higher heater curent may be the only problem. I tried them in the amp as the first change with the other original chinese tubes, and it seemed fine - I'll let you know how I find them when I've had longer to listen to the triodes and done a few more of the mods you suggested - battery bias, NFB. Mine came with Solen MKP coupling caps which are decent, but will eventually be replaced. Have to say this is probably the best audio buy I've ever made.

From what I've read on the MC34A, it seems to come with 12AU7/12AX7/EL34 (and maybe triode/UL switching?) so TW is probably part of the way there already.

Thanks
David

DanTana
05-15-2006, 05:39 AM
The 6H30pi is probably an excellent choice, just a little pricey is all, changing to 12v opened up a plethora of options. Good luck.

davehanc
05-17-2006, 07:59 AM
Dan,
I can't convince myself that I'm sure about the exact location of the resistor to duplicate in series to reduce NFB. Could you confirm which part of the circuit to look at? What is the R in your amp?

DanTana
05-17-2006, 08:40 AM
The negative feedback circuit will begin at the speaker output, if I remember right it will be soldered to the 8 ohm positive post. You can just add another resistor right there if you wish. Trace the wire back and you will see a 100K resistor, a good starting point might be to double the value, you can remove the old reisistor increase the value you want. I don't use any negative feedback. A little feedback didn't sound bad, but the music detail seemed to increase as I decreased feedback.

davehanc
05-20-2006, 09:48 AM
Dan,
I wondered how far you'd gone in reducing NFB. I've just removed it completely, and the improvement in detail is not subtle - I'm listening now and I can hear something which was totally masked before - when the vocal channel is unmuted on the mixing desk just before the voice comes in, the ambient soundstage changes as the vocal mic images the studio. Amazing.
Battery bias is next.

DanTana
05-20-2006, 08:16 PM
First I added another 22K resistor which reduced by half roughly, then I added a 100K resistor, then connected the wire to the 4 ohm terminal. Finally I removed it completely.

davehanc
05-26-2006, 08:26 AM
Battery bias is done. I measured 1.18V at the cathode before removing RC, and the charged NiMh batteries measured 1.44V out of circuit - the sound after installing was a darker background (increased downward dynamic range) with increased sibilance on vocals, cymbals etc. This has improved day by day and a week later, the batteries measure 1.35V in circuit and the sibilance is still there, but much decreased (perhaps I've become acclimatised to how it sounds?!!). Overall, it's an improvement on the standard bias setup. I'll try a pair of Nicad batteries to get closer to 1.2V - I'm thinking the higher voltage = current through the 12AX7 is outside the optimum range.

The Sovtek 6H30pi and the Winged C 61NP are very close; overall I prefer the 6H30 but on some recordings the extra gain required makes the background hash more noticeable on headphones, but still below the ambient threshold on the main system.

DanTana
05-26-2006, 11:08 AM
That's a nice write up there Dave. I'm using 12ax7 or 5751's in the input stage. The lower noise floor was amazing after I put the batteries in. I haven't notice any sibilance like you mentioned. What I'm considering doing is putting 2 AA's per side, so I can increase the available amperage. I can't give any impressions with the tubes your using. Let us know if the use of Nicad improves it.

davehanc
05-27-2006, 04:45 AM
The 5751 looks interesting - how do you like it compared to the 12AX7? Which one are you using?

DanTana
05-28-2006, 12:07 AM
I like it very much, a little less gain, but I think it's a little more dynamic. I'm using a Sylvania JAN right now.

davehanc
06-04-2006, 08:13 AM
I think the EL34s have been running too cold at 30 to 35mv across the cathode resistor. I measure plate voltage as 420v so with max plate dissipation of 25w, 80% of max bias current is 47.6ma - so 47.6mv across the cathode resistor (476mv across the 10ohm resistor indicated on the DMM) should be correct, and it sounds richer and more detailed at this bias point. Any comments about this method of determining bias?
I've gone back to the 6N1P - what was immediately impressive about the 6H30pi ultimately caused fatigue, and the 6N1P is more musical, equally detailed but less forward.
Thinking about trying the JJ KT77.

manolito
06-12-2006, 11:31 AM
Nice thread DanTana and others. I would like to clarify the change from 6L6's to EL34's. Do I need to make any modificationd to hardware: resistors, connections and so on? I understand that bias will be adjusted of the potentiometers as adviced earlier but how is it with the wiring and components connected to the tubes?

Thanks a lot! I am just waiting for my new MC34-B, but I feel that the mods are quite soon on the schedule.

DanTana
06-14-2006, 01:56 PM
No change of hardware required. Just readjust the bias.

manolito
06-14-2006, 03:57 PM
Thanks DanTana.

manolito
08-01-2006, 11:53 AM
Hi again,
Can I use 6DJ8 instead of 6N2 in MC34-B without any mods in hardware?

DanTana
08-04-2006, 03:38 PM
I have tried it at one time, and although it wasn't one of the highly regarded versions of the tube, I wasn't impressed. I like the ECC99 or 12BH7 now that I'm using much better, but then you have to change the wiring for 12v heaters.

manolito
08-05-2006, 02:04 PM
Thanks again. I have a large set of 6DJ8/E88CC tubes used in other devices. I put Tesla E88CC instead of 6N1 and Siemens E88CC for 6N2. The sound was much more better with Revel Performa F30 speakers; big floorstanders. Next I will put EL34 tubes for 6P3P.

sorenj07
08-05-2006, 05:48 PM
Sounds pretty sweet. Does anyone have the schematic, so I can take a peek? I'm currently using some 6L6WXT+'s myself in a DIY tube amp and the ability to rebias to take EL34's or 6550's would be cool.

manolito
08-06-2006, 10:43 AM
Sorry for the question discussed a lot earlier, but I wish to clarify the mod to triode mode in MC34-B. Shall I need to do anything else than to connect pins #3 and #4 by a 100ohm resistor in every four output tubes (6L6 or EL34)?

DanTana
08-09-2006, 08:31 AM
Manolito, you also need to remove the ultralinear wire that is connected to the pin and tape it up securely. Then solder the 100ohm resistor to pins 3-4. I used a 1/2 watt 5% carbon film resistor you can buy Radio Shack.

manolito
08-09-2006, 08:48 AM
Thanks. Yes, that was also my doubt after reading quite many articles of the triode mode connections compared to ultralinear using pentodes, but I wanted to be sure of the matter.

platinum
08-30-2006, 04:39 PM
Hello Dantana,
I have been following your experiences with the Ming Da MC34B with great interest as I have owned one for about 18 months and I was so pleased to have found your threads.
I have changed the preamp tubes to ECC83 (re-wired accordingly) and the main tubes to EL34.
The driver tubes are now ECC88. Today I snipped the NFB wires at the +ve speaker terminals and I was rewarded with an amazingly clear liquid sound.
However, a hum was then audible on both speakers, one louder than the other.
What can I do to prevent this? Should I carry out the Triode Conversion to the EL34 Tubes first or should I just reconnect the NFB with an additional High resistance?
e.g 1Mohm.
Thanks for your assistance.

DanTana
08-30-2006, 09:51 PM
I would recommend doing the triode conversion first. I think you will like it better although less power than Push-pull. If you still experience hum after that, something else is wrong. I didn't totally remove NFB until after I wired in triode. I believe PP sort of needs some NFB to cancel out distortion. I don't believe triode requires any NFB.

platinum
08-31-2006, 02:48 AM
Thanks for your prompt reply and your helpful information. Reduced power should not be an issue as I seldom go beyond 11 'o' clock on the volume control (replacement ALPS Blue (50K)), however my speakers are Uni Q and rated at 6 ohm, will this impact on the load? Will move forward with the Triode conversion. After this, which mod would be most beneficial? the Battery Bias, Capacitor Upgrades or another in order to extract the most music out of this amazing amp. Thanks again.

davehanc
12-18-2006, 07:56 AM
Context: MC34B driving a pair of Bohlender Graebner 28.1 planar magnetics after an active digital crossover at 250Hz - no passives between amp and driver. The BG is somewhat 'cool', and I've been loking for extra 'warmth' without losing detail. Things I've tried in the last 6 months:

6H30pi at input and/or phase splitter positions
Etched detail, closer to a SS sound. I've heard this tube sound good in other circuits, and I suspect it's not getting the heater current it needs. Back to the JJ ECC83S.

JJ KT77 replaced JJ EL34
Smoother midrange, extended top end.

EH 5751 replaced JJ ECC83S
Less gain so less hum, which is good - don't want to feed any more LF to the drivers than is necessary. Also more delicacy - something like the change from pentode to triode.

GE JAN 12AT7WC replaced EH 5751
Tried this after reading the El Cheapo thread on the Decware forum (thanks Eli and Jim ) - the basic idea is that PP amps cancel most of the 2nd harmonic, making the 3rd dominant. Perhaps a fundamental difference between SE and PP amps? The story goes that the 12AT7 has overall higher distortion than other 12A*7 types, but it is mostly the 2nd harmonic and after PP cancellation the distortion 'waterfall' sounds better. It worked for me.

Jensen Copper/Oil coupling capacitors replacing Solen/SCR MKP
Wow. This is the single largest improvement I've heard from all the tweaks. If you do nothing else, my recommendation is to find room to fit better coupling caps. The circuit is good enough that this is a reward.

David

DanTana
12-18-2006, 08:20 AM
Nice write up Dave. One thing that will eliminate hum is to use battery bias. Ever try different driver tubes? The JJ ECC99 works great there. RCA clear tops are good too, I've even used 12bh7's, as far as preamp tubes I've used the Sylvania 5751's and liked those very much. I also have some Sylvania 7025's that work really nice.

davehanc
12-19-2006, 04:43 AM
Dan,
I have battery bias on the phase splitter positions, and it does work well. Are you using it at the driver positions as well?
I haven't converted the driver positions to 12v yet - probably next on the list.

David

DanTana
12-19-2006, 09:12 AM
Yes, I'm using it on the driver/preamp position now, I haven't done it at the phase splitters because I believe they would require about a 22v battery for proper bias? The 12ax7 only needs about a 1.5v bias. I would definitely consider battery bias on the first stage and the 12v heater conversion for the second.

Andywardle
02-28-2007, 05:22 AM
Hi there, great thread - looking forward to getting my mitts on the 34B and seeing what it'll do. I have just bought one (waiting deliviery) from Ornec.

I am to be driving KEF Q15's (6ohm), and wonder which Impedance seeting to run them on? Common sense says the 4ohm tap will work best. Am I right?

Which of the mods will reap the best reward the quickest?

Andy

Yamaha1
03-01-2007, 01:37 AM
I am waiting for some Chinese made SS dual mono amps, also some exotic material speakers, going by China's history, they are fully capable of making fantastic stuff, also SOA.

davehanc
03-12-2007, 08:40 AM
Andy,

The Q15 dips to about 3ohm at 8-9kHz, and the Q15.2 also at 200Hz - have a look at the curves at:
http://www.pcavtech.com/techtalk/wire_size/index.htm#Q15-mag-lo
Try both to see which you prefer, you won't hurt anything; I'd guess the 4ohm tap may be better.

Mods which most improved the amp for me were changing the output tubes to KT77 with triode connection, getting rid of negative feedback (if so, you must do the triode thing as well), and upgrading the coupling caps - I'd regard these as the mods with the best bang for the buck (sub EL34 for KT77 if you're nervous). If you go further and delve into battery bias, different input and phase splitter tubes etc you need to know more about what the circuit does, and you start getting into DIY territory. Once you cross that border, abandon all hope - you may become addicted to working out what's wrong with the MC34B circuit, and how it can be done so much better...

Cheers
David

Andywardle
05-17-2007, 05:45 PM
Hi folks,

I got my ming da :banana:

Sounds great, but now i'm getting a bit twitchy, and am going to insert some JJtesla e34l EL34s.

Anybody got a good Bias setting that I can start with for these new valves?

Going over the DIY threshold is one of the reasons that I got the amp! :thmbsp: but thanks for the heads up Davehanc!!

Andy

ian99
12-30-2007, 08:05 AM
Andy,

Did you try any mods?

I am still sifting through the contents of this extremely-informative thread, planning to try one thing at a time, and take my time doing it. Need to draw up a plan first. I bought an MC34-B a couple of months ago and very happy with it out of the box (I'm no audiophile but might get converted one day). Sounds like there are many improvements to be made and I love tinkering. First thing I guess is to draw out a full schematic for the stock amp, building on Dan's schem that he thoughtfully posted. I am definitely hooked on the valve sound for the simple uncluttered music that I mostly like. Glad I gave the valves a go.

Ian.

petrucci
04-28-2008, 05:51 AM
Hi...i'm new to this forum. I'm intereted in modding and biasing the Ming da mc 34 B amp. Would like to ask some questions. Which pins should i measure when biasing the amp( Changing the original 6p3 tubes to EL34 tubes)? and can i use KT-66 tubes instead of EL34 tubes? Thank you very much.

vonswedge
06-30-2008, 03:22 PM
Hello everyone,
I am new to the technical world of amp mods and I'm wanting to modify my MC34-A to triode. I have bought the 100 ohm resistors and I don't know which pins are #3 and #4. I feel that I shouldn't even attempt this because of my lack of experience. But I don't know of a local service that would preform this mod for me so I want to try it. It sounds easy enough remove #4 on all valves and connect 3 and 4 together with the resistor. My amp looks just like the picture in the previous post. I just cant see to follow the wires from the transformer to the output tube. There is a copper wire linkage that runs across 2 valves on one pin. Then there are 2 baby blue resistors that bridge between 2 valves on another pin. Please help, and forgive me for being so technically challenged. Cheers!

PDRCanada
06-30-2008, 07:26 PM
New York Sound has a ton of 'em....look under Hi-Fi products Meixing...$397.00 + shipping:yes:

TWantiques
06-30-2008, 09:24 PM
Hi...i'm new to this forum. I'm intereted in modding and biasing the Ming da mc 34 B amp. Would like to ask some questions. Which pins should i measure when biasing the amp( Changing the original 6p3 tubes to EL34 tubes)? and can i use KT-66 tubes instead of EL34 tubes? Thank you very much.

Hello everyone,
I am new to the technical world of amp mods and I'm wanting to modify my MC34-A to triode. I have bought the 100 ohm resistors and I don't know which pins are #3 and #4. I feel that I shouldn't even attempt this because of my lack of experience. But I don't know of a local service that would preform this mod for me so I want to try it. It sounds easy enough remove #4 on all valves and connect 3 and 4 together with the resistor. My amp looks just like the picture in the previous post. I just cant see to follow the wires from the transformer to the output tube. There is a copper wire linkage that runs across 2 valves on one pin. Then there are 2 baby blue resistors that bridge between 2 valves on another pin. Please help, and forgive me for being so technically challenged. Cheers!

Gentlemen, while there are numerous AK'ers who could probably answer your questions I know DanTana was quite familiar with this amp and the OP of this thread. He isn't online as often as in the past so I suggest you PM him referencing this thread and I'm sure he will respond the next time he signs in. Good luck.

Terry

agronk
09-18-2009, 04:01 PM
:thmbsp:Very very interesting mods from DanTana specially
I`m already ordering or purchasing (sory for my english)
MC34-B but after a careful look in their web page and receiving their
price list I came with conclusion why baying another tubes when the Chinese already put them in amp. EL34 x4(JJ)、12AU7 x2、12AX7 x2
and it is about Euro100 expensive than MC34-A
any suggestion?
Agron:yes::yes::yes:

diskvask
04-23-2012, 04:36 PM
Does anyone have the picture to measure/adjust bias on the mc34-b? :)

The image link in post #18 is broken...

DM101
06-08-2012, 07:21 PM
354904

Here you go, assuming I've used the attachment facility correctly.

psyopwak
06-11-2012, 09:35 PM
I agree with DanTana that Chinese audio has a stigma. Some of the quality seen in the Hi-Fi suffers, but not all. I think there are some (companies) that are having better QC and overall visibility on the manufacturing process than other companies who are letting counterfeit and stealing of parts take place.

Also I think that some Chinese companies are doing the same thing many Japanese companies were doing in the 1970's and 80's in the American auto industry. They see that they can make a quality product that can compete in the world market. Honda and Toyota starting making very good cars and very decent prices in America. I have an amp by Line Magnetic Audio and I like it more than a Cary I listened to for double the price!

It's also made to a very high standard.....

Inventor
03-17-2013, 04:47 PM
Realizing this is a very old thread, I have searched for a schematic for the MC34-B, yet have had no success.

Reason: My amplifier had a catastrophic tube failure while playing: a right channel 6L6 lit up internally, and thankfully blew the fuse. After installing a matched quad of JJ 6L6's and adjusting the bias, the right channel is without a sound. Swapping preamp and output tubes does nothing.

Both my Vandersteen 1's are perfectly functional with a NAD test amp.

The outputs measure proper resistances through the ground, 4 Ohm, and 8 Ohm taps.

Power supply: I have good filament Voltage, and find myself wondering if the right channel plate Voltage is nothing. Not sure if I have no high Voltage there, or a blown output transformer.

I would like to test high Voltages, and of course the windings in the tube side of the output transformers, as well as trace the input circuits.

Thanks to anyone for assistance, I am profoundly appreciative in advance.

Jon

DanTana
03-23-2013, 07:06 PM
Sorry I've been very very busy lately and haven't had time to find the old schematic. I think I still have a copy of it somewhere and will upload as soon as I can find it. I think I wrote the makers of the amp to get the original copy from them, but I used some schematic program and made a nicer copy. Give me a a couple weeks to find it.

Thanks,
Dan

DanTana
03-23-2013, 07:11 PM
Your lucky day, I found this in an old mail archive. This isn't the cleaned up version, but the one the Ming-Da engineer sent me.

DanTana
05-20-2013, 08:48 AM
I've had several requests for a schematic, I had the original one I was sent by the engineer at Ming-Da and it was handwritten and hard to read. I cleaned it up and posting it here.

saratoga
05-30-2013, 02:01 AM
and how many tubes did you buy?
how much did you spend?
i would rather buy PRIMALUNA INTEGRATED AMP

tailskid
12-22-2013, 06:52 PM
I have, what I believe to be a rebadged Mingda mc34 b integrated amp, its now called an M-Star. Was listening the other day and it just went dead. No power light, nothing. What gives? Bad power supply maybe? Any feed back would be greatly appreciated.

DanTana
12-24-2013, 11:54 PM
I would get a voltmeter and start checking the voltages on the PS outputs. Careful I believe a couple are around 500v-550v. The rest I believe are 12v. If those are good then maybe your bridge rectifier might of died.

needlestein
01-17-2014, 05:14 PM
Hi everyone,

I don't know if I've ever posted on this site yet or not, but based on the info in this thread, I got a Ming Da MC34-B and it's fantastic. I changed out the caps, modded to 12AX7 and installed Gold Lion KT66 tubes and I can tell you that this thing ROCKS.

I played it stock for about five years and was always impressed with the sound. I upgraded the tubes a couple times. 6L6 tubes can sound very different as you all know. The stock Chinese ones were a little lean and pale sounding. I added some Sovtek WXT+ and that was a good sound, full, rich, but somehow technical. I threw in some Soviet tubes (you know, those military ones) and I think they sounded the best for a long time.

But now, with the KT66, new caps and JJ 12AX7's (which I could say I made the mods myself, but I have to give all the credit to Larry Smetana at Accutech in East Hartford, CT) it's a totally different and better sounding amp all the way around. I don't want to make this an ad for Larry's shop, but let's just say he charged me for parts and two hours of labor to do the job. Since I have a nine-week old baby girl, there is no way I have the time have made these upgrades--but anyone easily could using the information right here in this thread.

The sound is so full now that I turned off the subwoofer that I used to use when playing this amp. Larry says the sound will get even better once the tubes burn in. That transformation is almost hard to imagine.

So, anyway, for the guy who was wondering why his amp wasn't playing at all? There is a fuse in the amp that's probably blown. I brought my amp to Larry because something happened to the map--one of those military tubes might have died or maybe one of the caps blew. I was playing it as usual and I heard sort of a low pop, the right inboard 6L6 began double or triple in illumination and I ran over to switch the amp off. I replaced the tubes and tried to power it up and it was totally dead. The fuse blew.

I decided to have Larry have a look at it and make upgrades that he thought would be best--I don't know if he read this thread or not, but he did all the ones that DanTana said to do except he put in the KT66 instead of el34.

Larry also mentioned that it's a solidly made amp that's stuffed pretty tightly, so the mods weren't as easy as they might have been on some other amps, and the point-to-point wiring makes it a little more challenging. The other reason I'm glad I had him look at it was because he said that while the build quality is very good, he did find more than a couple of bad solder joints on the inside that he also repaired.

Who knows? Maybe him fixing those bad solder joints has much to do with the improved sound, too. I wouldn't know. It was a dead silent amp at full volume and no input before I handed it over for the repairs/mods--no hum or anything, so maybe the bad solders, probably cold joints, didn't have such a bad effect, but I'm glad they're repaired nonetheless.

I love this amp. Sounds great, looks great, bargain price--can't beat it.

Inventor
03-11-2014, 09:28 AM
I did fix the MingDa MC34B amplifier, and now it sounds wonderful. The Amp suffered a severe power supply breakdown, fortunately it did not take the iron with it. The AC input fuse did blow.

The bridge rectifier was found shorted: both AC inputs were shorted to ground AND the DC output.

The large DC filtering capacitor was shorted.

Two ground wires in the signal path were not soldered to the grounding lugs. A very slight left-channel hum cleared up after soldering these.

One of the right channel output tubes had very low gain. The other one blew violently. A new matched quad of 6L6's were installed and biased. The left tube with the best gain (testing with my B&K Precision 747) had a bias resistor burned open.

The bias resistors were very low grade units. The open resistor crumbled easily, evidencing it had run hot before failing. All four were replaced with high grade 25 Watt ceramic wirewounds.

The bias pots were replaced with Bourns units. Bias was carefully equalized. After playing for an hour, bias drifted slightly (I use 4 meters at once) so I re-biased and it settled down nicely. I have 171 hours on those tubes now, with no bias drift.

Every solder joint was heated up, and the slightest touch of Kester 60/40 microwave-grade non-corrosive solder was added.

Thanks for the schematic and the good advice.

Jon