Author Topic: AionFX Andromeda - Loud hum + Pop, goes away when drive pedal engaged after  (Read 184 times)


Hi everyone,

After many builds without issues (or at least issues I could solve by myself), the day has come that I need further help!Hopefully with your support this can be solved before I get grey hair ;)
I'll be as complete as possible.

The build is a kit of AionFX’s Andromeda (kit from Musikding in Germany). It's based on a Nobels ODR-1. I'm getting a loud white-noise type sound, and the pedal pops when engaged/disengaged. More details below.
Thinking I made a mistake building it, I ordered and built a second identical kit. Result: exact same problem. I couldn't find mention of anyone having a similar problem with this pedal, and Klaus at Musikding confirmed he didn't hear about this before.

Here are detailed characteristics of the problem:
  • Constant white noise-type sound when the pedal is engaged; no issue when not engaged- Loud pop when engaging/disengaging
  • Volume of the noise is fixed: independent from the pedal’s Level control, independent from the guitar’s volume pot; and it is there even with no pedals plugged in
  • Noise is about as loud as the guitar playing - i.e. much louder than typical hum/hiss- The louder the amp, the louder the noise
  • Noise goes away when a drive/boost pedal placed after in the signal chain is turned on
  • Noise doesn’t go away when a pedal placed before in the signal chain is on
  • Noise doesn’t go away when a delay/reverb pedal placed later in the signal chain is turned on
  • When the Andromeda is engaged, I am getting a small pop when I turn on my delay pedal (pop doesn’t happen with Andromeda off)
  • Beside the noise, the pedal is working fine, all controls work as expected. It sounds nice, except for the noise :)

What I've tried/done:
  • Testing Andromeda alone, outside of pedalboard: same problem
  • Testing with good 9V battery: same problem
  • Testing with different jack cables and amps: same problem
  • Testing within enclosure, and with a pedal tester (kit from FuzzDogs in the UK): same problem
  • Measure DC voltage between ground and input/output jack tip, with pedal engaged: 0.0v
  • Swapped ICs and transistors for others: same problem
  • Measured components when building (especially for 2nd build): all within tolerances
  • Some voltage readings in the circuit: see picture enclosed -- nothing jumped at me as being an issue, but my understanding is limited. GND in green = continuity with main ground.

Hopefully this gives a good starting point to narrow down the problem...Thanks in advance!


Hi & Welcome.. :icon_wink:

All ICs voltages are fine..
Same for Q2..

Q1 is out-of-order..!!  :icon_wink:
(check for R3 proper connection..)

Q1 Gate seems to get about 1V DC from input..
(place a 10nF - 100nF cap right before R1 and take measurement again..)
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..


Hi Antonis,
Thanks a lot for the reply & the welcome!

I double checked the readings on Q1 after your message, and realized I noted them wrong: I mixed Source and Gate readings - sorry for this!
These are the actual readings on Q1 (with new battery):

  • D: 9.4v
  • S: 0.9v
  • G: 0.0v

Similar readings for the 2nd build (Source: ~ 0.8v).
I also checked R3: 2k96 on both builds, and properly connected to GND and Q1's Source.

I can try adding the cap before R1 this weekend, but not sure if needed considering correcting readings -- there's actually no voltage at the Gate. Also no voltage at input, R1 nor R2.

I'll also try swapping Q1 with others, but I'd be surprised if that's the issue: I already replaced it before with no improvement, and the problem is the same on the 2 separate builds...

Any other idea? Any further voltage readings I can do to diagnose better?
Otherwise I'll try going through the circuit with the audio probe this weekend.

Thanks again!


Q1 Source voltage is low..
(it should lie between 3.5 - 5.5V, give or take..)

Maybe particular 2N5457 transconductance is far apart from (wide spead, anyway..) average one..
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..