Aion Electronics Lab Series L5 Build - Compressor issues

[bsas]

Hi all!

So, I just finished the "Aion Electronics Lab Series L5 Build" and I am having some weird stuff and an obvious issue on the compressor that I just can't figure it out. If anyone can help me, thanks! :D

Here is the project schematics/docs:
https://www.dropbox.com/s/dnizjzbetec84gu/aion-lab-series-preamp-documentation.pdf?dl=1

Here is my issues as I described at "DIYStompboxes":
http://www.diystompboxes.com/smfforum/index.php?topic=113954.msg1082893#msg1082893

Issue:

1) Children boards LEDs behavior:

First I tried to wire the LEDs in the standard "on/off" mode where you "link" both small boards by the "CH" lug. The LEDs never turned off. The weird thing is that both 3PDT were working fine and doing what there were suppose to do but the bypass LED and the channels LED were always on.

Then I removed the link and I wired the CH from the channel select board directly to ground (the "always on channel LEDs option) and all LEDs work fine now, with a small exception that the bypass LED is never fully "off". It is like very weak light while off and very strong while on.

2) Compressor muting the note attack instead of compressing:

The pedal sound OK, I guess, and everything looks like it is working but the compressor is very weird. Basically I can see it acting and it's LED blinks when it grabs a high peak note as expected, but sound wise, instead of compressing the signal, it mutes the attack of the note and the volume comes back slowly. It almost sounds like a buggy noise gate.

3) Low output:

Being a preamp pedal I was expecting a monster amplification, but, for me I need to put volume at 12 and master almost at 12 to be kind of unity level. Am I missing something here?

4) A lot of heat from voltage regulators:

The voltage regulators run quite hot all the time. I already measured the +|- 15V pins and they measured perfectly. Is that expected?

Interesting findings:

- I can measure voltage on the Q3(MPSA13) pins, but, if I remove it, the sound of the compression stays the same (AKA bad). Seems to me that somehow it is getting ignored. I already tried to replace the MPSA13 with a couple others and it doesn't help.

- Also, when I turn the unit ON the compressor LED lights up and fades out slowly...

[bsas]

I noticed something interesting: If I apply 1kHz 50mV sine wave on the circuit input, with my current configurations, I can measure 450mV across C38 if the compressor switch is OFF. If I turn the compressor switch ON and set the LIMIT where it can kick in constantly, the voltage across C38 drops to 17mV!!!

[bsas]

Here is my detailed and boring voltages:

1) Knobs for ALL measurements:
- All knobs are at noon, except both Volumes which are MAX, Master is MAX, and Limit is around 2:00 (according to calibration instructions);
- Bright switches OFF, Input at HI

2) What I did to calibrate:
Following instructions AS IS, I pumped 1kHZ 30mVA on IC10:PIN2 and I was able to calibrate:
- IC10:PIN6: 4.41 VA (4.337 VA with Comp ON)
- PIN_OUT to 1.171 VA with Comp ON

3) I already measured the D4 and D5 diodes (from Mouser) and they both check -0.6V drop.

4) The Comp LED blinks on the expected moments, when I make a hard attack on my notes, and it fades out as expected too, while the note fades out. The problem is the sound. I am expecting my note to squick (compress) but instead if literally mutes the note completely on the attack and if "fades in" if I let the note ring. Almost sounds like if the moment the Comp LED blinks, my guitar volume drops to zero, and then slowly comes back like I am sweeping the volume knob back to 10 (tricky to explain).

5) Measurements:

- All are made with 4 possible scenarios:
A - 1kHZ 30 mVA on IC10:PIN2 / Comp ON (this is where the problem happens, and the Comp LED is always ON).
B - 1kHz 30 mVA on IC10:PIN2 / Comp OFF
C - 0 mVA on IC10:PIN2 / Comp ON
D - 0 mVA on IC10:PIN2 / Comp OFF

- If I use (...) I mean voltage AC, If I don't, means DC:

IC10:
  | A       | B       | C       | D       |
1 | (0.09)  | (0.09)  | (0.152) | (0.152) |
2 | (0.03)  | (0.03)  | (0)     | (0)     |
3 | 0       | 0       | 0       | 0       |
4 | -15     | -15     | -15     | -15     |
5 | -14.32  | -14.32  | -14.32  | -14.32  |
6 | (4.33)  | (4.41)  | (0)     | (0)     |
7 | 14.96   | 14.96   | 14.96   | 14.95   |
8 | (0.130) | (0.130) | (0.130) | (0.130) |

IC9:
  | A      | B      | C       | D       |
1 | (0.23) | (0.69) | (0)     | (0)     |
2 | 0      | 0      | 0       | 0       |
3 | 0      | 0      | 0       | 0       |
4 | -15    | -15    | -15     | -15     |
5 | 0      | 0      | 0       | 0       |
6 | 0      | 0      | 0       | 0       |
7 | 0      | 0      | 0       | 0       |
8 | 14.96  | 14.96  | 14.96   | 14.96   |

IC11:
  | A       | B       | C       | D       |
1 | (0.117) | (0.117) | (0.117) | (0.117) |
2 | (0.22)  | (0.05)  | (0)     | (0)     |
3 | 0       | 0       | 0       | 0       |
4 | -15     | -15     | -15     | -15     |
5 | -14.32  | -14.32  | -14.32  | -14.32  |
6 | (1.25)  | (3.9)   | (0)     | (0)     |
7 | 14.96   | 14.96   | 14.96   | 14.95   |
8 | (0.130) | (0.130) | (0.130) | (0.130) |

IC12:
  | A       | B       | C       | D       |
1 | (0.74)  | (0)     | (0)     | (0)     |
2 | (0.067) | (0)     | (0)     | (0)     |
3 | (0.067) | (0)     | (0)     | (0)     |
4 | -15     | -15     | -15     | -15     |
5 | 0       | 0       | 0       | 0       |
6 | 0       | 0       | 0       | 0       |
7 | (0.74)  | (0)     | (0)     | (0)     |
8 | 14.96   | 14.96   | 14.96   | 14.96   |

Q1 - 2N5457 (this guy I wasn't sure to measure AC or DC, so I did both):
  | A              | B            | C           | D           |
D | 0              | 0            | 0           | 0           |
S | (1.17) / -0.17 | (3.7) / -3.9 | (0) / -0.42 | (0) / -0.42 |
G | (1.27) / 0.32  | (4.1) / -3.4 | (0) / 0.03  | (0) / 0.03  |

Q2 - 2N3906:
  | A      | B      | C      | D      |
C | 0      | 0      | 0      | 0      |
B | -0.58  | 0      | 0      | 0      |
E | -12.3  | -14.4  | -14.4  | -14.4  |

Q3 - MPSA13:
  | A      | B      | C      | D      |
E | -15    | -15    | -15    | -15    |
B | -13.76 | -14.3  | -14.3  | -14.3  |
C | -14.32 | -0.385 | -0.385 | -0.385 |

I measure 100F - 120F :O. I hope that is expected...

[bsas]

Fixed! Just basic miss adjustment on the trim pots. :(

Check the original post for amazing info about this limiter circuit. :)