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Opamp unity gain/buffer PCBs?

post #1 of 12
1/19/10 at 4:24pm
Thread Starter 
Does anyone offer an opamp buffer PCB? I've looked around for awhile, and I'm surprised I can't find one.

I need to drive a DSP with a low input impedance (6K) with the output of either a tube or passive preamp. This DSP will only operate below 200hz, so I do not need incredible resolution, but I do want good bass. I have a few OPA2132's and OPA2134's. I know I could P2P a buffer from them, but at this point I'm not sure what I'm going to do for an enclosure and I'd like the buffer to be fairly flexible in terms of mounting and placement. I've got a nice little regulated supply and a pile of wall warts. All I need is a cute little PCB to make build and mounting easy. Any ideas?

Paul
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post #2 of 12
1/19/10 at 4:34pm
Perfboard CMOY
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post #3 of 12
1/19/10 at 4:58pm
Thread Starter 
Perfboard would certainly work (I've used it to do P2P cascoded mosfet CCS's for my tube amp), but I just figured I'd check and see if there was something out there I am missing. I know I can cut perfboard down, but a dedicated PCB could be really small, have nice mounting holes, etc. If such a thing doesn't exist, I won't be too disappointed.

Paul
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post #4 of 12
1/19/10 at 5:27pm
Might want to check out the JISBOS buffer. It's a nice little discrete JFET/bipolar buffer that should be well suited to the task.

AMB was selling boards for them but apparently they've been discontinued. Zaubertuba recently bought some though I don't know from whom. You might want to send him a PM and ask.

Good luck!

se
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post #5 of 12
1/19/10 at 5:29pm
Quote:
Originally Posted by Paul J. View Post
Perfboard would certainly work (I've used it to do P2P cascoded mosfet CCS's for my tube amp), but I just figured I'd check and see if there was something out there I am missing. I know I can cut perfboard down, but a dedicated PCB could be really small, have nice mounting holes, etc. If such a thing doesn't exist, I won't be too disappointed.

Paul
Sound like a reason to learn Eagle/Diptrace or other program and use BatchPCB.
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post #6 of 12
1/20/10 at 6:19am
Quote:
Originally Posted by Koyaan I. Sqatsi View Post
Might want to check out the JISBOS buffer. It's a nice little discrete JFET/bipolar buffer that should be well suited to the task.

AMB was selling boards for them but apparently they've been discontinued. Zaubertuba recently bought some though I don't know from whom. You might want to send him a PM and ask.

Good luck!

se
I got mine from glass jar audio not too long ago.

Another pcb you might try is Monofied Sijosae Buffer PCB [PCB107A4O] - $2.00 : Seeed Studio Depot, Arsenal for interaction engineering . If you're just looking for something simpler you could find a cmoy pcb and just adjust the gain resistors for unity gain.
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post #7 of 12
1/20/10 at 6:30am
sjostromaudio.com - Home look for the SSB01 its a discrete unity gain diamond buffer PCB and its tiny. small enough that i'm using them in place of BUF634 in my portable and made from fairly cheap parts. very good performance IMO
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post #8 of 12
1/20/10 at 8:54am
The Sijosae buffer is an open loop buffer so you would have issues with DC offset, unless used in loop with an op-amp. It does sound very nice in my Pimeta.

It looks like the SSB01 is an open loop buffer as well, so it would have the same potential issue with offset.
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post #9 of 12
1/20/10 at 9:58am
yes unless its in the feedback loop as I have used it you have to inject current into the input to get rid of offset

heres mine


and for scale



and in my FiQuest



sounds great!! of course I needed to find a convenient ground which isnt included in the DIP8 socket, but I wired a DIP8 socket to the star ground under the board with thick silver and brought it up top-side and plug my ground wires into that to allow me to still roll opamps and buffers without a soldering iron. I also use the ground socket for plugging in the ground wires for decoupling the cool opamp adapters i'm using
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post #10 of 12
1/20/10 at 12:50pm
A simple and very good buffer would be a complementary JFET buffer with SK170 and SJ74, open loop but with adjustable DC-offset. Only 5 parts/channel. A single end JFET buffer with SK170 as both buffer transistor and current source à la Nelson Pass's B1 preamp could also be made with adjustable DC-offset.
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post #11 of 12
1/20/10 at 7:25pm
There are some other alternatives like RJM's buffer RJM Audio - Szekeres VE Headphone Buffer and the Pass derivate DAO which could be interesting.

There's a PCB ofr the later here.
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post #12 of 12
1/26/10 at 12:39am
Thread Starter 
Somehow I missed a bunch of posts! I just tossed together a basic unity gain buffer with a OPA2132 I had lying around. I had the power supply in my parts bin (the Bugle power supply from John Hagerman). It might be overkill, but what could that hurt?

It seems to work fine. I haven't scope'd it. It does not sound great. I can't hear obvious distortion, but it is less detailed and sort of "dead" in comparison to not using it (tried it between CDP and amp). It blunts transients and the soundstage. Of course, it also introduces some old yucky jacks and the closest extra IC. I wouldn't expect adding an opamp with 100% feedback to improve things though! I have a fairly transparent system.

It should do what I need it to. The bass sounds fine, and I suspect it will be plenty happy driving the DSP. I may revisit the buffer, but not until I have the rest of the system working.

thanks all!

Paul
LL
LL
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