I’m knitting this with hot needles, so please be patient for further and proper documentation and descriptions of modifications. 🙂 The following first….
Digital noise hotfix
While I did not notice any significant digital garble/noise in the signal path of my unit, some people on the interwebs (including an Audiopilz of fame) take issue with what is assumed to be digital bleed. This seems to be present on the main out only while the headphones output remains clean. I cannot reproduce this issue on mine, so part of me thinks this is overblown interwebs dynamics, but just in case, here’sa potential fix.
In the following I show how I rewired my unit to resemble the circuit of the Roland SH101, a synthesizer probably entirely unrelated to the L1 but a model of a synth nevertheless!
As you can see, that SH101 is hardcore – direct VCA out wired to a potentiometer that is followed by a repeating OPA buffer (IC1 on the SH101 schematic pic above). The L1 practically does the same, and it also shares the “twice around the world”-style wiring from VCA out to volume pot and back to main out we can find on the Roland synth.
On the way to that out socket, some folks’ units seem to pick up noise. To repeat: I don’t have this on my unit at all. Testing TP4 against my modification in place, I get the same sonic qualities. Also, before considering this mod, note that you can always use the HP output – neither harm nor shame in that.
Most importantly, if you’re testing this with overly pulled up preamps or phones in order to hear better what’s going on, note that the 101/L1 filter+VCA have some noise floor. OTAs work in a way that relies on heavy signal reduction at the input side and heavy amplification on the output side (that’s one reason them synth designing folks tend to use modern stuff like them 2164 IC and what have you). TLDR: some noise is normal here; what you shouldn’t hear is digital garble/bleep. Here’s what I get (beware, loud saw at beginning), which is a tad dirty, but that’s what these old circuits are…
Does my L1 need output therapy?: simply check U42, Pins 6+7 in comparison with the main out socket. (Don’t put a cable directly there but use some small value resistor in between, and keep the L1 on the same ground as your mixer/sound card.)
FIX: If your signal is much better at that point than at the main out, consider the following fix. That fix requires slight disassembly, trace cutting and wiring a cable onto a SOIC IC. If you don’t have SMD soldering experience, consider paying a local solder person for the job (might be much cheaper than wasting an entire L1). Pics are below…
- Unscrew the bottom lid. Simply keep all 13 screws in their holes and pull off the bottom lid and place it somewhere safe. Much easier to reassemble later.
- Take out the I/O board as follows: take out the three screws and then pull the board out. Note that the larger output sockets are tightly fit against the main PCB, so gently lift and pry, if need be (very softly! no excessive force needed, simply patience).
- If need be, take out the zif connector on the main PCB side, then cut the trace as seen on the picture below. Be careful with stanley knives and stuff that can slide off the PCB and into your body parts or stuff. I use a bit of a shoddy pockets knife with a broken off/cerated tip and scrape very gently until the surface layer is off; then stronger in order to separate the copper trace. Put in the I/O board afterwards.
- Connect as per picture below your new output: 1k resistor (and 100k resistor to ground) connected to the cathode of a 10uf electrolytic capacitor. The anode of that capacitor to U42, Pins 6+7. Put some heatshrink aroudn the open parts of the capacitor and resistors. Done.
- Test, test, test that sound. TP4 versus your new main out. If that’s better, then..
- Put the bottom lid back on. When turning the screws back in first turn them a little bit anticlockwise (to the left) once you feel a slight bump, start turning clockwise. This way, the screws go back into their previous grove rather than digging new burrows into the plastic.
- Donate something to the Women’s Audio Mission and/or the Trevor project, and follow me for more modding recipes…
Behold the lid! 13 screws for 13 dancefloor bangers per release!
I/O board: Understand the zif saftey mechanism first before pulling the cable, please.
The I/O board taken out & the trace to cut. sorry for the blurry picture and the absence of wooden bowls or dried flowers for ambience, but you’ll find that trace easily!
Backside of the I/O board with the new output connection in place.
New output connection soldered onto the OPA buffer. NB OPA buffer, meaning operational amplifier buffer, are easy to mix up with other designs, so…
Again, this little “hotfix” should be considered only if you tested U42 against the main audio output and found the former of better sonic quality.