I’m looking for suggestions for a small, cheap and simple DIY compressor design. I’d like to build 8 into a shallow 1U rack, hence the small, simple and cheap. More if I can fit them.
These would be used on individual analogue drum voices, pre-mix. Something dead simple as far as user controls go too - like one knob per channel ;D or none …
Line level synth type signals, not guitar, but range would be an advantage. Running from DC power would be nice.
One thought I’ve had is to mod the Oatley valve pre kit with gain and volume. The board might look big but 2/3 of that is the power supply, which will run 2 pres. It’s a little pricier than I was hoping, and they’ve taken the schematic and PCB artwork down from the site >:(
That’s not a bad suggestion. The 4301 is available in DIP. Profusion have them for ~5 UKP in small quantities. And there are two unassigned op-amps on board (hello filter?)
combines in a single IC,all the active circuitry needed to construct a wide range of dynamic processors. / exponentially-controlled VCA, a log-responding RMS-level sensor and three general purpose op-amps.
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The combination of exponential VCA gain control and logarithmic detector response (‘decibel-linear’ response) simplifies the control path mathematics of the dynamics processors. This makes it easy to design audio compressors, limiters, gates, expanders, de-essers, duckers, noise reduction systems and the like./
Sorry, but the two op-amps in the chip are available to transform the log RMS-level sensor signal in a compression level signal to feed to the internal VCA… IIRC you need one op-amp to compare to your compression threshold and one to adjust it according to your compression level. Just look at the typical application in the datasheet.
However this makes a simple compression to build. This chip is so great! This is also on my todo list I would like to make a digitally-controlled compression. So if you go the That way please share your experience!
Let’s say I wanted the ultra-ultra-cheapest comp possible: a light bulb and an LDR? optocoupler design?
/edit/ The DOD 280 optical comp from tonepad fits the bill. And it’s pretty darn small.
Yeah I do agree But that is a pity there is no adjustable attack and release time in their typical design
Check out their “full featured compressor” PDF
they are designed for guitars but you can just adapt them easily
What’s the difference, and what’s involved in making the change? The word “impedance” springs to mind…
Now I’m picturing a 1U case with in/out jacks on the back panel, soldered to an edge connector … small FX boards plug in to the edge connectors. Another edge connector on the front end of the card connects to unlabelled pots on the front panel, with a scribble strip above them for labelling.
After discussions in chat (thanks bugfight and stryd_one) it looks like a combination of the DOD 280 and Ken Stone’s Stomp Box adapter is a reasonable build
I am interested in building Ken Stone Adapter myself but seams all the links from the page are broken. Are these PCBs artworks freely available as that DOD 280 compressor? Somebody tried DOD 280? Is there any other tonepad FX that some of you liked using with synths?
EDIT: Are there any disadvantages using LED and LDR instead of optoelement?
As this Stomp Box Adapter PCB is pretty simple I redraw it in Corel and EPS file is attached in this post. I dont know is it legal as I didnt find PCB artwork published, but as the schematic is free I hope this could be too. Hope You`ll find it useful.
Yucky. What about the what comp? that looked much nicer.
Sure. But unless I can get this under $30 a channel, it’s not worth the bother. I might as well pick up a few Borrowerhingers. I might stretch the budget a bit to go tubular
I’ve just built the stereo for final mixes and live work - a really good piece of design, (though contains a few mad resistor values). Pro quality kit, boards have good part spacing, proper ground planes, and go together well.
I would like to make a digitally-controlled compression. So if you go the That way please share your experience!
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