Carbon Squish (Custom Diamond Compressor)

[MattG]

Build Rating

5.00 star(s)

As I mentioned previously, my recent Aion Quartz build was mostly just to have a reference circuit handy for any necessary debugging of my own custom PCB spin of the Diamond Compressor. This build, my Carbon Squish is my first take on that circuit. Turns out I didn't need the debugging reference, as it worked on first power-up. However, it was nice to be able to take advantage of the various additional functions the Quartz offers (switchable EQ center frequency, high cut enable/disable, and EQ defeat). My intent is to make a simplified or "opinionated" Diamond Compressor, so that build definitely had value in helping to form my opinions.

No issues or self-sabotage (like my last build). The comments I made about the Diamond Compressor circuit in the Quartz build report still hold, so nothing to add on that front.

One thing I realized: this circuit has two internal buffers, that use two BJT transistors: one for the buffer, and one as a constant-current source. In some cases, the constant current source can lower distortion. It seems most people say this is overkill in a guitar effect circuit - but I appreciate overkill. However, according to Rod Elliott, just about any modern opamp makes for a better buffer than most discrete transistor circuits. So I already have a revision of the Carbon Squish queued up that replaces the discrete transistors with opamps. While it's cool that it theoretically improves noise performance, the main benefit is that it lowers part count and PCB space. My ultimate goal is to fit this in a 1590B or - if I'm feeling brave - maybe even a 1590A. So anything that reduces the circuit footprint is a step towards my goals.

The enclosure is from Tayda, it's "lawn green" IIRC. I recycled the steampunk compressor clip art from my Median Compressor build (note: that's not my artwork, I found it on the web).

The attached mini-PCB at the bottom is my buffered electrical MCU-based quasi-IC bypass module.

Edit: see post #3 below for a build with an updated PCB.

 

[bluedmc777]

I love my Diamond comp. Many have come but only one has stayed!

 

[MattG]

Just finished the updated version I hinted at above. It's the same circuit, but the discrete BJT-based buffers have been replaced with opamp buffers. This allowed me to shrink the PCB a bit. Everything worked on first power-up! The enclosure is "Cosmic Lilac" from @StompBoxParts. I used SprayMax 2k matte for the final clear coat, which somewhat muted the factory finish. Like my recent Timbre Man v2.0, I kind of like slightly-dulled look of the matte on a shiny factory finish.

Per the AionFX Quartz documentation, the Diamond Comp uses the uber-expensive OP275, which is similar in specs and price to the OPA2134, around $8 (USD) currently. This is crazy! When I built my Quartz, I originally tried to get away with a TL072, but when I swapped in either an OP275 or OPA2134, I feel like there was a noise improvement at higher compression levels.

So tonight I compared my previous Carbon Squish build, with an OPA2134 opamp, to the new one with NE5532 opamps. I could quickly switch back and forth, and with the gain and volume maxed (i.e. the noisiest setting), I couldn't hear any obvious difference. The NE5532 is an old opamp, but still has decent specs - not quite as nice as the uber-premium OP275 or OPA2134, but impressive for a 30-year old design. And they are cheap and readily available. At any rate, I generally only use this for a bit of volume, EQ, or very mild compression, so at these conservative settings, the opamp really doesn't make a difference. NE5532 it is!

Edit: I forgot to mention, this Cosmic Lilac finish took four tries for the film-free decal to transfer completely, that's a new record. I got a bit more transfer on each subsequent attempt, so my working theory (further elaborated here) is that some factory finishes simply don't take the transfer as well. Additionally, each subsequent attempt is a little better due to the acetone removing whatever aspect of the finish inhibits the transfer. For this enclosure, I leaned into that idea a bit after the third failed attempt, and really went to town with the acetone. And indeed, after that - the fourth attempt - I got nearly 100% transfer.