Help. Aion Anubis Gain Issue

Started by Blooze, December 20, 2021, 09:51:04 AM

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Blooze

I soldered up an Aion Anubis (Scarab Deluxe) and for the life of me can't get the Gain (Fuzz) pot to do anything. I get bypassed signal fine and processed signal fine.  The Fat, tone, volume, and bias all seem to work.

I first checked all the component specs and didn't see any that were incorrect. The only substitutions I made was to parallel a couple resistors (1k/3K) for the 750R and used a 100n film cap instead of an MLCC in the power supply filtering.

I reflowed all the solder joints. There's plent of solder now  ::) I hate doing that as to me they looked very good initially.

I then checked the voltages. Set my bench supply to give me 9.00V at the PCB after the diode and filtering. Here are the voltages I got.

Q1c: 3.70
Q1b: 1.13
Q1e: 0.523

Q2c: 1.30
Q2b: 0.70
Q2e: 76 mV

Q3c: 4.50
Q3b: 1.30
Q3e: 0.699

Q4c: 9.00
Q4b: 4.50
Q4e: 3.90

I audio probed the circuit. Lots of volume increase on Q3c and Q4B/Q4e. Probed the Gain pot and it goes from non existant sound at min to just barely audible maxed.  This is all with the tone/fat pots set to noon, bias at 4.5V on Q3c, and volume pot at max. I get volume before C3 (100n) but virtually none at the base of Q2). I keep looking at that voltage after C3 though.

I've swapped out transistors trying new 2N5088's, BC109's, 2N5089's, etc. for no change..
I un-soldered the gain pot thinking maybe it was bad.  It wasn't, but I checked a new one and soldered the new one in.
I un-soldered the 4u7 cap and checked it on my little Gm328.  it was fine, but replaced it as well while I had it out.
I originally didn't have a 750R resistor, so paralleled a 1K and 3K. removed those and put in some SIP sockets.
I took out the Q3 1K bias resistor and socketed that as well so if I got this thing working I could adjust the bias sweep a bit.

Any help would be appreciated. I've built a few fuzzfaces and such on perf and tag board as well as a hot chilicon (which this basically is) and other PCB based effects without too much trouble, fwiw.


















toneman

Looks like lots of cold (looking) solder joints on all of the pots.

Reflow iwith a little more heat and fluxcore solder.

8)
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TONE to the BONE says:  If youTHINK you got a GOOD deal:  you DID!

duck_arse

#2
remove the 47R you have fitted at R7 and replace with 47k. what are the colour bands on your R12?
You hold the small basket while I strain the gnat.

Blooze

Quote from: duck_arse on December 20, 2021, 10:31:46 AM
remove the 47R you have fitted at R7 and replace with 47k. what are the colour bands on your R12?

Why is it always something stupid like 47R instead of 47k  :o I feel like a doofus.

I believe R12 is a 4.75k. Yellow,purple, green, brown, brown. Must of thrown it back into my 4.7K bin as I just had 3-4 of them.

Blooze

Replaced the 47R and touched up the pot connections. Holy $*%#!  This thing smokes.

Gonna have to mess with the bias resistor a touch and see if I can get a better sweep out of it, but other than that it's good.

Thanks so much guys for putting a second set of eyes on this.

duck_arse

#5

easy. mind, that green band really threw me, didn't quite know which way to read that one.


it's a funny thing the way some people say what's wrong wit me pedal blah blah help me fix, yet post no photos or circuits. takes a few minutes to spot a gold band, takes longer to type up what you've found. but they'll never learn.
You hold the small basket while I strain the gnat.

Blooze

Quote from: duck_arse on December 21, 2021, 08:57:40 AM

easy. mind, that green band really threw me, didn't quite know which way to read that one.


it's a funny thing the way some people say what's wrong wit me pedal blah blah help me fix, yet post no photos or circuits. takes a few minutes to spot a gold band, takes longer to type up what you've found. but they'll never learn.

I figure if I didn't show photos, the schematic, and the board layout it wasn't going to help anyone be able to help me. It's not like someone with a fresh eye can see what's going on without them. I'm just thankful there are folks like yourself willing to take the time to look things over and discover the mistakes. If you can believe it that's the first time I've done that with a resistor that I can remember. I checked each one before populating the board. Obviously I was not paying attention and grabbed out of the 47R drawer.  Yep, it measures 47 ohms, good to go! So I got the right part, just not the correct one because I obviously can't read.  :icon_rolleyes: