Project files: OPA+BUF preamp/headphone amp

What is it?
This is a small universal preamp/headphone amp based on a single opamp of your choosing and the BUF634 buffer. This circuit has fallen out of favour with DIY’ers over the last few years but with the right opamp it does sound very good – in fact I think that for many people this would be all they really need 🙂

How big are the boards?
The board measures app. 3.3″x2.3″ or 84x59mm.

What is the status of the boards?
This board is in version 2.0 because it is based on one of my earlier layouts that has been recently updated. It has been built and tested and seems to be working fine.

Does it use any special/expensive/hard-to-find parts?
No, not really. My recommended opamp for this would be the LME49710 as the best value for money, but you can easily go overboard with something more esoteric (= expensive) if you want. For all-out quality I’d probably prefer the OPA627, but that’s a personal preference and there are many other options as well (AD797, AD843, AD8610/OPA827/LME49990 on SMD-adapters etc.).

Anything else I need to know?

• The BUF634P used to be very hard to get, but should now be manageable to find again with Mouser, Digikey etc.

• The bandwidth limiting cap (C3) is intended to be mounted inside the socket for the op-amp. If you are not using a socket, you can mount it on the back of the board. The footprint is for a 2.5mm leaded type but a 0805 SMD cap should fit between the holes as well without issues.

• Note that in my picture I have used Wima MKS-02 decoupling capacitors (the small red ones). This was just because I had them available and they look nice – in reality 100nF X7R multilayer ceramics will be just as fine if not better.

Downloads:
Download design files here

Edit May 5th 2016: Download a BoM from here.

Related information:
Note: Always read the “intro post” for additional important information about my designs.
Read the BUF634 datasheet for more information about this design as well.

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