GSSL bus compressor with Turbo Mod build

This is a build I’ve been wanting to do for a long time. I just love SSL buscompressors and SSL’s in general, so being able to build one myself intrigued me big time. After reading through a post on I bit the bullet and ordered the GSSL kit from PCBGrinder. The kit’s page has both an assembly & wiring guide on it, if you’re as inexperienced as me that’s a great help.

GSSL Kit, knobs and VU meter

On top of the kit itself I ordered a case and a ready-made frontpanel from and the turbo mod. The latter makes the GSSL behave more like a real SSL buscompressor in which each channel has its own sidechain circuit.

say howdy to the new and neatly packaged front panel

I’ve been working on this build for several months (I think I first started in February) and had to tackle a few obstacles, which I’ll describe here, it might help out someone.

Final GSSL assembly with Turbo Mod and Sidechain HPF

So, here goes the list of things that caused me to work longer on the GSSL than expected:

  • Life in general ūüôā
  • The standard GSSL itself worked virtually right away. Make sure this is working properly before starting mods.
  • Don’t forget bridge all the “white lines” on the PCB with trimmed leads.
  • Distorted sound at some ratio’s: this was a problem with the Lorlin switches. Make sure the stop-pins are in the right pinhole!
  • Bad soldering, especially after bolting on the turbo mod. Reflow or resolder if a continuity test using your DMM fails or sounds rather funky.
  • Because my frontpanel allowed for a sidechain HPF filter, I wanted the compressor to retain this functionality, even after adding the turbo mod (it might have some use for bass-heavy material). So, I needed to replace the kit’s SPST switch with a DPDT switch and an extra cap. I went with the same value as suggested in PCBGrinder’s assembly manual: 100nF, which makes for a 160 hz high-passfilter. Explained more eloquently over at this GroupDIY post.
    IMG_20160714_160147 IMG_20160714_160139
  • Although the case and frontpanel are of of excellent quality, the frontpanel’s not secured in the middle and will bend a bit. Solved that by glueing some extra metal profiles to the frontpanel’s backside and tightening them on the bottom plate with screws.
  • Changed standard LED with a blue one. No rocket science there, but it sure looks pimped-out. The VU meter’s red leg gets a cool glow-in-the-dark kind of feel when the LED’s on in the dark.
  • It took me ages to realize that for turbo mod installation the 100R resistor did not need to be lifted, only the 47K resistor. No wonder my sidechain HPF didn’t work and the readings were way off.
  • Level drop of +-6dB on one of the sides where it worked before: after taking out and working on the PCB, reseat the IC’s properly
  • Screwed up a solder pad on the turbo board: curse yourself and your friggin’ hobbies and recreate the traces to the component’s leg in the broken pad with small pieces of wire.

List of materials/sources:


“Starting out with DIY” rhymes on “Bo Hansen DI”

Disclaimer first: I'm NOT an electronics expert, far from it. I'm simply an enthusiast starting out with DIY audio, learning along the way and wanting to share my findings with other enthusiasts, hoping to infect others with the DIY bug ;-)

I’d been eyeing DIY audio websites and forums for a while now, and wanted to build a GSSL compressor and Classic API preamps for myself, but not without some practice first. I never soldered on a PCB before, the toughest thing I ever soldered was a Bantam patchbay, so I thought I’d get my feet wet with a rather basic yet high quality¬†build first. sells PCB’s and kits, and just before the BODI28 kit went out of the store I ordered one. The kit is¬†sadly no longer available, if it were I’d build me some more of these DI’s.¬†Forgot to took pictures along the way, suffice it to say the build actually went very smooth and the circuit worked right off the bat.

Here’s a picture of the inside:
BODI28 guts


The kit contained two PCB’s, so I ordered all components required from Mouser and a case from Modushop, and built myself another one. The metalwork on the XLR connector – i know, i know – isn’t too¬†¬†smooth but the entire package feels very sturdy nonetheless. Most important, it sounds a gazillion times better than any DI at the price point of this kit.

BODI28 finished

This first build definitely got me interested in building more and consequently, more kits and PCB’s are on their way to what is now my DIY corner of the house. Don’t be afraid to try it yourself, start with an easy kit and go for it. It’s fun to build and learn about electronics and hearing your own work actually work is pretty kick-ass too.

You’ll need some tools that are adequate for the job though. What I used¬†to finish this very build was :

  • A good temperature-controlled soldering iron. I was recommended this Velleman soldering station by a friend with a lot more soldering miles on his sleeve than me.
  • Decent¬†solder.
  • A third hand of some kind. I’ve got this one from Conrad.
  • Multimeter for measuring resistance values and verifying solder connections (continuity test). I dived into the Velleman¬†catalogue again and got me the DVM 851.
  • Some basic cutting and stripping tools (I bought a Jokari stripping tool for this which is extremely convenient) to get wires cut to the right size.
  • The drilling work on the case could be prettier, but a standard electric drill with metal mills¬†did the job for me.

Up next is a GSSL with Turbo mod and a CAPI VP28!