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Another Super High End Phono Stage! No expense spared...

Bsabel: It looks like you have selected the 33K input loading resistor rather than the 47K. Was this intentional?

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One suggestion I'd make for any future run of the PCB would be to lengthen the board enough to add another pair of 4-pos dip switches for input caps: 50pF, 100pF, 150pF and 200pF. Or at least 3-pos switches connected to 50, 100 and 200pF. This would allow 0-500pF (or 0-350pF) by 50, depending on which switches are on. The cabling (to cart) on my TT's varies from 85pF to 170pF. Recommended capacitance for my carts varies quite a bit as well. Shure recommends 200-300pF for the M97xE and 400-500pF for the V15-III, and I think 250pF for the M110HE. Pickering recommends 300-400pF for the XSV. I don't know what AT recommends for my 140ML, or ADC for the PSX30. The point is, adjustable capacitive load can be just as important as resistive for MM. Naturally, I need different capacitance for each of my table/cart combos.
 
I heard Fasterdamnit's CNC Saturday night in my system, with my cart/arm/table. I know a few guys who HAVE to have one of these, me included.

I cobbled an RIAA preamp together with Op-Amps over 30 years ago and it wasn't pretty sounding. Looking at the specs on today's Op-Amps I'll attribute the huge improvement in sound to at least a couple of specs that have really improved. The slew rate is now insane. The gain bandwidth product is even greater extending to RF.

Not to mention the noise is imperceptible. This is one quiet preamp. Just amazing.

BTW, I'm planning on SLA 12V batteries that I recharge.
 
My CNC is dead in the water - no signal getting thru. This is probably a result of my probing with an oscilloscope.

The P/S voltage is still getting thru my TT relay fine and I am reading +8.4vdc and -8.25vdc on the board. I reversed the +,-&G wires going into the board and have them entering from the bottom. Left about 1/16" protuding above the board so I can chech them w/o having to remove the board.

I used the scope to verify that I have the small signal from the TT getting to pins 3 & 5 of the first stage, but there is not enough coming out to measure.

The meter reads ~300mv at pin 1 of the second stage but no reading at pin 7. There is no "click" or "pop" sound thru the speakers when the CNC is turned on or off.

With basically "0" into 2nd stage, how am I getting what should be a normal signal level out of one side, and why is this not getting to the receiver?????

Have a dental appointment today (6 mo checkup) on the other side of Baltimore. Fortunately this takes me by the exit for Baynesville Electronics - one of the few brick & mortar stores left in the area, not counting RS. I'll get another set of opamps and see if I can keep my fat fingers & probes off the board.
 
The board should be good. It takes more voltage or current than you have to mess up a trace. (lightning does quite a job, I'll post a picture)

So it comes down to either connections or components. You just measure the resistance from RCA jacks to a chip leg or trace to verify the connections to the outside world. They measure easily (pull the chips first to open the other paths) except the ICs themselves. Since you are getting another set of ICs today that ought to get you there.

BTW, thanks for reminding me. I have an electrical supplier here I can get a number of components from. (not any really good caps, sadly)
 
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ghazzer said:
My CNC is dead in the water - no signal getting thru. This is probably a result of my probing with an oscilloscope.

The P/S voltage is still getting thru my TT relay fine and I am reading +8.4vdc and -8.25vdc on the board. I reversed the +,-&G wires going into the board and have them entering from the bottom. Left about 1/16" protuding above the board so I can chech them w/o having to remove the board.

I used the scope to verify that I have the small signal from the TT getting to pins 3 & 5 of the first stage, but there is not enough coming out to measure.

The meter reads ~300mv at pin 1 of the second stage but no reading at pin 7. There is no "click" or "pop" sound thru the speakers when the CNC is turned on or off.

With basically "0" into 2nd stage, how am I getting what should be a normal signal level out of one side, and why is this not getting to the receiver?????

Have a dental appointment today (6 mo checkup) on the other side of Baltimore. Fortunately this takes me by the exit for Baynesville Electronics - one of the few brick & mortar stores left in the area, not counting RS. I'll get another set of opamps and see if I can keep my fat fingers & probes off the board.
Click to expand...

Op amps are relatively simple to troubleshoot. If you have proper supply voltage and good signal into it you will have something out unless the chip itself is blown or shorted somehow. They may not be very robust under static shock conditions so that is a possibility.

Measure the DC voltage at pins 4 and 8. Should see your -8 and +8 volts. If you don't see both that would be your problem.

If good, unplug your turntable and use the scope to look at the signal directly at the RCA Connectors. Plug them back in and check the signal strength at pins 3 and 5 (positive inputs to the Op Amps). The voltage level should be much the same as the unplugged connector. If not, there is a short, open or low resistance path to ground somewhere in the input.

If the signal to the input is good and the supply voltages are good, and still no signal on the output check for DC voltage on the output. If it is up near the positive supply voltage or down near the negative or alternating between the two (check with scope on DC for 1 or 2 volts/div) there is a problem in the feedback circuit. Without proper feedback almost any signal into an Op Amp will run the output as close to the rail power voltage as it can reach. If the DC out is not close to 0, the feedback circuit is probably either open or shorted to ground.

If all this checks out, check to see if there is a short at the output to ground that is shorting out the output. If there isn't, then try swapping out the Op Amp to see if another one works.

If all of that doesn't show up the cause then you need the help of someone a lot smarter then me cause that's the extent of what I know about troubleshooting these things.

Good Luck

Shelly_D
 
ghazzer said:
Bsabel: It looks like you have selected the 33K input loading resistor rather than the 47K. Was this intentional?
Click to expand...

Not really. I was testing the switch to make sure everything was connected properly and that's what I had it on when I snapped the pic. 47k is the best for my current setup.
 
Shelly_d: Thanks for the excellent suggestions. I will try them tomorrow (ops, later today). I did measure V+/- at pins 4 & 8 of each opamp - OK.

Electronics store did not have the opamps I asked for, or suitable subs either. I'll have to order some. Think I will first make a summary list of the opamps that are listed as having been tried in he CNC.

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ghazzer said:
Shelly_d: Thanks for the excellent suggestions. I will try them tomorrow (ops, later today). I did measure V+/- at pins 4 & 8 of each opamp - OK.

Electronics store did not have the opamps I asked for, or suitable subs either. I'll have to order some. Think I will first make a summary list of the opamps that are listed as having been tried in he CNC.

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Click to expand...

I already did that. Here is the list I compiled - in no particular order:

LME49720

LM4562


AD823


AD797 sugested as added stage for MC preamp


LM833


OPA627/637


OPA2314, NE5532, TL072, AD823


lm4562, ad823, 5532


OPA 2604.


OPA 4134


OPA2134


LME49990 Could be a VERY quiet one


I was looking for items that Mouser carried. I found 2 withen my budget:

OPA 2134

and

LM833 (That's almost a throw away purchase at $0.56 each. Also have a supply of 5532's I picked up from Jameco at $0.25 each that I could try.

Good Luck

Shelly_D
 
HypnoToad said:
AD797 & OPA627/637 are single circuit op amps and you need two on an adapter to work with the CNC. The power pins are 4 and 7 not 4 and 8 like on the dual circuit ones as well.

Adapters like these (no affiliation):


http://www.ebay.com/itm/2x-DIP-DIP-Dual-Mono-Opamp-PCB-Adapter-OPA627BP-/220788700790?_trksid=p4340.m263&_trkparms=algo%3DSIC%26its%3DI%252BC%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%26otn%3D15%26pmod%3D350414669117%26ps%3D63%26clkid%3D2912752133852481040
Click to expand...

Thanks for that. I had not looked at their data sheets yet. Just compiled the list from the thread.

Shelly_D
 
I only have 10X probes for the scope, so Merrylander helped me make a 1:1 probe from a coax with a BNC connector. It is quite sensitive, and definitly uncalibrated, but I am only looking for relativity between measurements so It should be OK.

I plugged the right channel into the phono stage of the receiver so I could listen to the balance test on a Shure test record. Monitoring the left channel plug I could definitely see the signal on the scope when the test record was playing to the left channel, and "background" at other times.

Then I plugged the left RCA into the CNC and put the probe on the center conductor on the inboard side of the CNC - NOTHING. Also got nothing when I put that RCA into the right ch jack, so something is shorting or loading down the input. Could still hear the right ch playing thru the speaker so that tells me when to expect to see a signal.

Will have to TS this further when I get home tonite.

WOW - I just went over 500 posts.

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ghazzer said:
I only have 10X probes for the scope, so Merrylander helped me make a 1:1 probe from a coax with a BNC connector. It is quite sensitive, and definitly uncalibrated, but I am only looking for relativity between measurements so It should be OK.

I plugged the right channel into the phono stage of the receiver so I could listen to the balance test on a Shure test record. Monitoring the left channel plug I could definitely see the signal on the scope when the test record was playing to the left channel, and "background" at other times.

Then I plugged the left RCA into the CNC and put the probe on the center conductor on the inboard side of the CNC - NOTHING. Also got nothing when I put that RCA into the right ch jack, so something is shorting or loading down the input. Could still hear the right ch playing thru the speaker so that tells me when to expect to see a signal.

Will have to TS this further when I get home tonite.

WOW - I just went over 500 posts.

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Click to expand...

Glad you narrowed down the cause. Check the usual culprits like solder bridges and low spec termination resistors, possible shorted cap on the input. It it also possible that the dip switches on that channel are inserted incorrectly and you have the 47 K off and all the others on? That could give you pretty low input to the Op Amp.

Just a few thoughts here.

Shelly_D
 
sachu888 said:
Hi,

I am planning to power my CNC on some higher capacity batteries,which one of these would be a better option:
http://in.element14.com/ever-ready/pj996/battery-pj996-6v/dp/3055905
http://in.element14.com/ever-ready/601162/battery-pp9-9v/dp/300159

Or can anyone suggest me a good power supply option for CNC.

Regards,
Sachin
Click to expand...

Sachin I use 4 of those 6v lantern batteries in the first link and find they are fine for my phono stage, it gives +12v, 0 , -12v.

Hope this helps.
 
Depending on the Op-Amps you select you could use 6 - 6V batteries for +/- 18V supplies or 4 - 9V batteries for the same voltage. The 6V batteries have a higher mAH rating. They could last the rest of your life (just joking!).

Of course if you are thinking of either a 6V or 9V supply you greater headroom with the 9V supply.
 
6v batteries

HypnoToad said:
Sachin I use 4 of those 6v lantern batteries in the first link and find they are fine for my phono stage, it gives +12v, 0 , -12v.

Hope this helps.
Click to expand...

Hi Phillip,
I am seriously considering using 4 of these 6v batteries,does this come with any type of connector or I will have to solder on spring.

Regards,
Sachin
 
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