Minipre in a box…

A while ago I presented my “MiniPre”-project of a simple op-amp based preamplifier. Now I’ve had occasion to put it into use as a small standalone preamp/active monitor controller.

The design is very simple, so not much to be added there (whatever you need is probably already in the original post), but it’s basically a standard dual op-amp in non-inverting configuration.

The power supply will be in the form of a small DC-DC converter (a continuation of my previous experiments) so that I can feed the box from a single 5V supply and keep the case size down. Because of this I’ve managed to cram everything into the smallest available hifi2000 case, so it will fit nicely on a desk 🙂

The advantage of this simple design is the the selection of opamp tends to have a noticeable influence on the sound signature, so this is one place where there is room to experiment whether different options have better synergy than others.

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Project files: Universal Mini-preamp

A few weeks ago a reader was commenting on simple buffers/preamps and also asked about ebay-kits to use since I haven’t posted anything with a volume control yet. That got me searching to see what was actually out there and very quickly came the realisation – “I can do this better” 😀 Not sure if I did, but I at least tried 🙂

What is it?
A very simple opamp-based buffer/pre with an onboard volume control that can be used as a “buffered volume control” with a power amplifier module, a real preamp with or without gain or even a “CMoy”-style headphone amp. The board has space for a DIP-8 dual opamp, polypropylene input caps and a full-size Alps volume control and still manages to be very compact. I’m showing the board now as I already have a couple of applications for it in the pipeline myself which you will see later 🙂

How big are the boards?
2″x2″ (app. 51×51 mm) – a theslowdiyer standard size (TM) 😉

What is the status of the boards?
The board file is v1.0. I’ve built a prototype and everything seems to be fine.

Does it use any special/expensive/hard-to-find parts?
None, really. You can get what you need from Mouser/Reichelt and similar places and most of the component values aren’t that critical anyway.

Anything else I need to know?

  • The opamp should be a dual-type with standard pinout. My recommendations would be either the LME49720 (sadly discontinued in DIP) or the OPA2107 (still available but fairly expensive), but there are loads of other options. The board layout should be suitable for using adapters as well (for DIP/SO-8 singles or SO-8 duals) and if you want to go all-out there’s even a discrete option from Burson that should fit as well.
  • The only surface mount components are the optional (but recommended) 1206 bandwidth-limiting caps on the bottom – otherwise it’s through-hole all the way.
  • The PCB should be happy with just about any (regulated) dual power source – linear PSU, switching PSU or even a pair of 9V batteries.

Downloads:
Download design files here

Related information:
Even though this is a basic opamp circuit and I can just about draw the schematic and recite the parts values from memory, I went back to look at it once more to try and read up on the theory behind. If you aren’t very familiar with the basic schematic already I can absolutely recommend the old but still excellent articles from Headwize/Head-fi member Tangent here and here. Tangent’s pages also have a ton of other useful information and although the site isn’t updated any more (and it’s quite old) there’s still plenty of good stuff even for inexperienced diy’ers.

If you are more technically inclined then probably the best resource is the “Opamp Applications Handbook” from Analog Devices and edited by Walt Jung.

Note: Always read the “intro post” for additional important information about my designs.

RIP…

Just read over on Innerfidelity that the founder of the Headwize site and namesake of the CMoy headphone amplifier, Chu Moy, has passed away recently.

As a relatively early member of Headwize, I can remember discovering a site with an active discussion forum and a lot of inspiration for a novice audio diy’er like myself. Apart from the direct contribution of the Headwize forum (including the projects gallery that I have mentioned several times in the past), Headwize of course also spawned head-fi.org and many other international and local headphone forums that still run today.

Headwize was also the birthplace of the first community headphone amplifier build projects (like the ones from Tangent and AMB) that have helped others get started in this new hobby. I am sure there are quite a few people out there who first experienced the elation of playing music through a self-built amp via one of these projects 🙂

Although I never knew Chu Moy personally and he was out of the “spotlight” for many years, I am very grateful for his contribution to the audio hobby and of course for being one of the reasons why I am in this at all 🙂

Full story by Tyll Hertsens