DIY Simple Active Preamp

No problem this is what's it's all about.

More than enough gain, if I connected my phono pre to my power amp I think the roof would lift off.

I have the order for Mouser done already, just need to hit okay.:D

Hopefully RussellC will chime in with his thoughts on the B1.

I am seeing it this way, my phono stage is fine, my power amp is fine and all my preamp is doing is getting in the way.

I have one question though, am I better getting two single ganged pots or going for a stepped dual gang, I know which way is cheaper.:D

B-1 is very nice, warm, transparent, excellent bass, but no gain. There is a thread here somewhere I lifted from diyaudio forum about a simple gain stage for the B-1, utilizing more SK170 J-fets of course. While I may try this yet, I am more inclined to try the J-fet BOZ.

If you have plenty of gain to bring your power amp to a good level in the passive mode, you will have plenty for the Job. With the F-5 only having 15 db, a little gain is a good thing for any speakers under 90 db or so.

The main feature of the B-1 is that it is a buffer. A circuit that presents high input impedance making it extremely easy to drive, eliminating problems presented by very long interconnect cables and so forth. Very easy to drive, then the circuit presents a very low output impedance, allowing it to easily drive power amp input impedances. Wide bandwidth, transparency, great bass, are all excellent features of the B-1, just no gain.

However, all that said about gain, it will usually get most of my speakers, including the big E waves to more than loud enough levels. (The F-5 I'm currently using only has 15 dB of gain, so a little preamp gain is handy when slightly less efficient speakers are being used.) Nelson describes the B-1's gain situation as "going 55 with the gas pedal to the floor." He feels if it is loud enough, then good, and feels well about not wasting gain that the amplifier would have to make up, full throttle is good...

Sorry for the OT, and hope this helps.

Russellc
 
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The DIY Audio thread for the "hot rodded" version of the B1, which I am putting together, is here:
http://www.diyaudio.com/forums/group-buys/147075-gb-dc-coupled-b1-buffer-shunt-psus.html
The group-buy thread where I got my PCB and parts bundle (from member Teabag) is here:
http://www.diyaudio.com/forums/group-buys/147075-gb-dc-coupled-b1-buffer-shunt-psus.html

EDIT:

Here are some good build threads with pics showing everything:
http://www.diyaudio.com/forums/blogs/tea-bag/296-salas-dcb1-blue-edition.html
the following is step by step:
http://www.audiocircle.com/index.php?topic=85001.0

DOUBLE EDIT:

There are guys still building the "standard B1." That can run off of a wall-wart and does not need heat sinks IIRC. Those boards are available at the PASS DIY store. Why Hot Rod Hypnotize? Since I have not heard either, I can't tell you. I am doing this in a leap of faith. Should be fun if I don't smoke the components.

Those hotrodded DCB1 versions also allow the removal of a few caps in the signal path, so some DC sensing blocking circuit can be used for ultimate speaker protection from DC if something goes wrong. The hotrod versions have a much different power supply as well and a much more complicated Shunt style regulator. The hotrodders turn up the bias on the big mosfets as high as they dare.....several different levels have been experimented with.

I have both a half built mesmerize and a half built Hyptotize as well. Need to pull them out and finish them!

Russellc
 
Sorry for jumping on your thread like this.
I am building one currently, almost all the parts are here.
RussellC built like 15 of them.
If you have enough level running your sources straight to power amp, the B1 would do it for you, as it would only provide attenuation. I have no idea how it sounds, but I like the philosophy behind it.

It does a little more. It properly loads the sources, it has a low output impedance and it has current capability that any passive doesn't have.

These are a few of the reasons that active preamps didn't die out when the "passive preamp" appeared so long ago.
 
Does anyone know the answer to the question, comment, on the first page about unbalanced battery supplies? Say your positive power supply is 1 or 2 volts off of the negative supply does that mean you will have a DC offset and require an output coupling cap?

They don't really stay matched as they wear down.
 
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HypnoToad,
Your pre might be the bee's knees. So maybe get that pot as was suggested by Pio1980 earlier. I think it's very cool you built it, using parts on hand, to boot.
 
You can run the J-Fet Boz off the same supply as the B 1, Nelson tested the Boz on 12vdc and it ran fine so 18vdc will be more than adequate.

I have enough parts laying around to make a simple 18v regulated and well filtered PSU that will run both:

18vdcSinglePSU.jpg


Or use 3 of my 6v lantern batteries.

Either way I am going to make both the B 1 and the BOZ and have a shootout. I will etch some boards this week and probably have them both up and running on the weekend.
 
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Cool!
Do you think I can I run the JFET BOZ as a gain boost module at the end of the B1?

I might buy a board from you. :D
 
Cool!
Do you think I can I run the JFET BOZ as a gain boost module at the end of the B1?

I might buy a board from you. :D

There is a different circuit I have posted from DIY that is designed to be a gain circuit for B-1. Similarly, it uses SK170 J-fets.....it requires a seperate and somewhat more elaborate PS however. As to J-fet BOZ, Not to beconfused with regular BOZ, Seems I read Nelson saying distortion was lower at 12-13 volts, I'll have to recheck. Be interesting to see J-fet BOZ tagged onto B-1! Dont know if aboard is required, low parts count...could probably be put together on a board from RS.

I think the B-1 gain circuit was on the input, but I may be remembering wrong.:scratch2:

Russellc
 
I use ExpressPCB and ExpressSch. I usually just make the design in ExpressPCB as I can print it out for etching, I wouldn't use it for a commercial board as not many companies accept the files.

I removed the balance control and took out some other parts in the output, it resembles the output stage of the CNC now. I just wanted something simple to see if it would work, I measured the outputs and there is no DC. It's virtually just a low gain stage with a volume control at the front.

You can add different inputs if you like.


I am still not sure about the volume control as it is very sensitive. If anyone has any ideas about implementing it better let me know.

Not trying to insult your intelligence, but I was just curious what type of pot you are using, logarithmic (log) or linear?
 
Not trying to insult your intelligence, but I was just curious what type of pot you are using, logarithmic (log) or linear?

Don't worry you won't insult my intelligence as I have none.:D

It was a Rat Shack one I had laying around and has A100KX2 on the back which I took the "A" as being an Audio or Log taper.
 
There is a different circuit I have posted from DIY that is designed to be a gain circuit for B-1. Similarly, it uses SK170 J-fets.....it requires a seperate and somewhat more elaborate PS however. As to J-fet BOZ, Not to beconfused with regular BOZ, Seems I read Nelson saying distortion was lower at 12-13 volts, I'll have to recheck. Be interesting to see J-fet BOZ tagged onto B-1! Dont know if aboard is required, low parts count...could probably be put together on a board from RS.

I think the B-1 gain circuit was on the input, but I may be remembering wrong.:scratch2:

Russellc
C man, did anyone make a board for one of these B1's with a gain stage? Can you find the link to the thread at DIYaudio that shows the circuit?

As to the power supply needs, if a B1 builder already has an 18 v (or larger) supply, a simple regulation circuit should take care of the lower voltage needed for the Jfet BOZ.

Am looking forward to Hypno's shootout results. Go Toad!!
 
C man, did anyone make a board for one of these B1's with a gain stage? Can you find the link to the thread at DIYaudio that shows the circuit?

As to the power supply needs, if a B1 builder already has an 18 v (or larger) supply, a simple regulation circuit should take care of the lower voltage needed for the Jfet BOZ.

Am looking forward to Hypno's shootout results. Go Toad!!

All the parts have arrived for the B1 and the Jfet BOZ, I have the boards etched and drilled so over the weekend it should be working. I think the B1 is probably going to be what I need as the output from the Phonoclone 3's is comparable to that of a CD player. But it will be interesting to see what the difference is.
 
My main 'A' system uses a minimalist C-J Motif MC-9 as the control center. A mere 4 milspec FETs, a lot of custom C-J film caps, Tiffany grade connectors, the best control units, and no elytics whatsoever in this glorious 10 dB gain largely empty box of costly-when-new air. E-Bay was definitely my friend on this one. The HypnoToad'ed 640P is it's phono front end.
 
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Put the 18vdc PSU unit together this evening, Schottky fast acting diodes, 2 x 2200uf 35v caps as filters and a ten ohm resistor for lower noise and it works! The PCB is only 3" x 1 1/2". Will assemble the B1 and Jfet BOZ tomorrow.

18vdc.jpg
 
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That is great work! A while back I bought some 0.47F (no micro there) 5V caps. I'm thinking that I can series parallel them and use them on a CNC power supply. It will look messy but will run for 5 minutes when I disconnect the batteries.
 
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