Aion FX Gaia MK 1 - No Audio  [SOLVED]

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imwaltraud
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Post by imwaltraud »

This is my first post. Please be gentle :-)

I am currently building a Ain FX Gaia Mk. I pre amp pedal based on a Catalin Bread CB30 and simply can't get it to work. There is basically no audio output at all. When you really crank the amp you can hear a faint signal but that is it. The original build instructions call for 2n5457 JFETs or the SMD equivalent. At first i was using MMBF5457 SMD JFETs. This was my first attempt at soldering SMD components so when the pedal didn't work i automatically assumed that i screwed up the soldering job. I then replaced them with BF245As which are supposed to be a drop in replacement for the 2N5457. Pin out is different that is why they are upside down. Replacing the JFETs didn't change anything though.

I traced the circuit with an audio probe and there is a proper signal up to R22. Right before R22 the audio signal is still there after R22 its gone. I also measured the JFETs (I only measured and probed the circuit after replacing the SMD JFETs.) This is what I got ->

Q1
G faint audio signal 0v
D clear audio signal 4.975v
S very faint audio 0.46v

Q2
G clear audio signal 3.971v
D no signal 8.30v
S clear signal 4.972v

Q3
G faint audio signal 0.535v
D clear audio signal 4.751v
S very faint audio signal 0.8v

Q4
G clear audio signal 3.988v
D no signal 8.31v
S clear audio signal 4.750v

Q5
G faint audio signal 0.481v
D clear audio signal 4.419v
S no audio signal 1.027v

Q6
G clear audio signal 3.976v
D no audio signal 8.30v
S clear audio signal 4.419v

After R22 the signal is gone

Q7
G 2.240v
D 4.407v
S 2.750v

Q8
G 3.959v
D 8.30v
S 4.411v

I attached the schematics and to pictures of the PCB.

I must say I am totally at a loss here. Any help would be greatly appreciated.

Thanks

Martin
Attachments
Schematics.lpg.jpg
IMG_5735.jpeg
IMG_5737.jpeg

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mauman
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Post by mauman »

Welcome! Thanks for the very detailed analysis and photos. I think you've narrowed it down to R22, so I'd focus there. The color code on R22 looks correct for 470k, and the traces look OK, so maybe:
- resolder both ends of R22
- with power off, check continuity and look for 470k between the terminals of C20 and C21 that face R22
- replace R22

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imwaltraud
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Post by imwaltraud »

Thanks for the quick reply.

I replaced R22 and checked continuity before and after replacing the resistor. Everything seems to check out ok. I measured 470k between the terminals at C20 and C21.

Still no output though.

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mauman
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Post by mauman »

Of course, that would have been too easy! But you gotta check the simple things first.

Next, you've got 2.24 V of DC on the gate of Q7 that shouldn't be there. The circuit around Q7 is essentially the same as Q1, Q3 and Q5, and all of those gates are close to 0V since there's no DC path from +V to the gate. Check the caps that should be isolating the Q7 gate from +V (C21 & C23), one may be faulty or there may be a solder bridge/wire clipping. Also check voltage on both ends of R23 & R24, and look for a solder bridge around the gate of Q7. Or Q7 itself may be faulty.

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imwaltraud
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Post by imwaltraud »

Its's working ! :applause:

I compared the circuit around Q7 with the other parts of the pedal and discovered that R24 had basically no impact on the voltage supplied to the gate of Q7. Seems like you cannot substitute a 3.3M resistor with a 3.3k one :slap:

I replaced R24 with the correct value and bingo.

Thanks a million for your help!
:worship:

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mauman
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Post by mauman »

Congrats! I can't tell you how many times I've done just that, last week I subbed a 100k for a 100R in a UniVibe and then couldn't understand why that lamp just wouldn't light up...

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