Troubleshooting help needed - Aion Andromeda 125B (Nobels ODR-1)

[Hanzo]

Hello - I'm new to the forum and this is also my first build; my knowledge and skills are pretty low, but I'm here to learn so I can eventually build my entire pedalboard.  I've put a couple evenings now into trying to find where my mistakes are but I'm stumped at what these observations mean.  I'd appreciate any insights.

https://aionelectronics.com/wp-content/uploads/2018/08/andromeda_documentation.pdf

- Pedal works in bypass mode.  When engaged it goes quiet but there is an extremely faint overdriven signal there.
- I'm using all mouser and small bear components.
- No mods except I put jumpers in for D6 and D7, and a couple caps had to go to the next voltage higher due to availability.
- I've attached a schematic with voltage readings I took, and I will of course happily take any more requested.
- Interestingly (to me) is when I fed a sine wave in, I picked it up on the input side of R9 but very very weak on the output side.  So I bypassed R9 which got me a signal at the output jack.  So then I plugged in a guitar and amp and it played OK at certain settings but I got all kinds of weird sounds when I turned the spectrum and bass knobs.

What additional information would be helpful?

[thermionix]

Double check the value of R9 with your meter.  Pretty easy to put 120K or 1.2M in there instead of 12K.  Or you could read the bands backwards, or it could just be bad.

[duck_arse]

welcome to the forum, Hanzo, if nobody's yet said.

get the manufacturers datasheet to suit your particular Q1, check very carefully the pinout, then check/compare the build docs. I think that part might be wrong facing. and seeing as you have no signal past the point where you have ?linked across all the diodes? open one of those links, fit at least one diode. if you want max level/least clipping, leave all the diodes in one direction empty and unlinked. you don't want to be shorting the signal to ground, you want it to flow past that point to the output.

all yr other voltages look about ok, I think. can we see photos of your build, please?

[Hanzo]

Thanks for the welcome.  R9 checked out (12K).  Here is a photo.  I will check Q1 when I get home from work.  I don't quite follow the diode idea... are you suggesting I bypass all of them?

[duck_arse]

what I can gather from your diagram is that you've left out one string of diodes, and replaced them with wire links. this is bad, the links will short ALL your signal to ground. all of it, gorn. if you don't want to fit one or both strings, leave those spots empty, and unlinked. power off the circuit and test with your meter. set to the ohms range and meter between the R9/R10 point and the R27/R28 point. I rekon it will read nought or close to.

[Hanzo]

I think I follow you now.  Would you mind checking out page 6 under "clipping diodes".  I followed the instructions to jumper D6 and D7 (after I made a mess trying to hit the little jumper pads).  It says they are in series.

But when I think about your explanation and read the schematic, D6 and D7 are in parallel with the other diodes and would seem bad to jumper like you said.  Further confusing me is they go to vB and not ground.

https://aionelectronics.com/wp-content/uploads/2018/08/andromeda_documentation.pdf

[PRR]

> Further confusing me is they go to vB and not ground.

For audio signals, vB "is" ground.

vB is usually grounded for AC(audio) and some bias voltage (often +4.5V) for DC.

When you want to dump some signal (like rounding high peaks), you need an AC/audio ground. Whether this is common ground, or vB, depends on the needs of the DC part of the circuit. Since the entire clipping section is typically between two op-amps biased to +4.5V, dumping to vB may make more sense.

[Hanzo]

Ah, so D5 and D6 are the first stage that round the + and - peaks off to ground, and D4 and D7 are really the second set in the series that I'd want to either use or jumper.

I'll try making that change tonight.

[Hanzo]

Bingo!  duck_arse was right.  Also thanks PRR and thermionix for helping me eliminate other issues.  My lesson-learned is to spend some more time up front studying how the circuit works before jumping into the build.

I just A/B/C'd the pedal with an Open Road and ODR-1 and it actually has slightly lower noise and better note separation, but the bass control alone makes this the king.

Aion, what a great project, thank you!  Check documentation on page 6, you might want it to say D4 and D7 there instead of D6 and D7.

[duck_arse]

nice work, it's a good looking box, too.