Author Topic: Gain pot not working  (Read 1064 times)

neiltheseal

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Gain pot not working
« on: January 30, 2023, 09:31:13 PM »
Hello again. I hope you're not getting sick of me!

I just put together the Aion FX Sapphire (Blues driver standard not the galaxie mod) and am having issues with the gain pot. The issue is that it does not work at all.

The pedal works and sounds pretty goo, all of the other pots work fine but there is absolutely no gain and the pot does nothing. Here is a video of what I mean.




Does anybody have an Idea why this might be?

One potentially obvious solution would be the pot itself. As the build docs (https://aionfx.com/app/files/docs/sapphire_documentation.pdf) indicate a dual gang right angled pot, but I could not find one of these so just used a non right-angled one and used wires to connect to the PCB. Although with an audio probe all 6 pins of the pot have an audio signal.

Here are some pics of the inside of the pedal and here is a pic of the schematic with my audio probe tracing. I did not completely audio probe the whole circuit as clearly it makes a sound, however I tried to look around the gain area to see where might be a problem and I am stumped.

https://imgur.com/gallery/umfr1LT
https://imgur.com/gallery/Za6k04A

I ended up removing the pot and replacing it with 2x 220k resistors and also with 2x 470k and still no gain.

I checked continuity per the image below and it all seems fine.

https://imgur.com/gallery/QMI9IXU

I even tried replacing the pot with a new pot and still no gain.

If anyone has an idea I'd love to hear it.

Thanks in advance!

neiltheseal

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Re: Gain pot not working
« Reply #1 on: January 30, 2023, 09:52:33 PM »
I've spent quite a bit of time on this over the last few days and haven't really gotten anywhere. As I said the pedal sounds pretty good and seems to have a reasonable amount of gain through my amp especially when the volume is up (the pedal is LOUD).

However the amount of gain to my ears is the same with and without the gain pot/added resistors.

I've checked continuity on the jfets and it all seems good (as in there is continuity between D,S,G for the next component in the scematic).

One point that may be nothing is that according to the datasheet for the jfets used, it seems the source and drain are flipped to the adaptor (and the PCB). Is this right or is the datasheet perhaps showing the jfet from the bottom up?

Here is a pic with the jfets on the adaptor. Top left has continuity with D, bottom left with S and right with g. These correspond with the relevant holes on the PCB and there is continuity there.

However in the datasheet S it top left and D is bottom left.

https://imgur.com/gallery/Q2pHZNE

https://au.mouser.com/datasheet/2/408/2SK209_datasheet_en_20140301-1594295.pdf

jimilee

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Re: Gain pot not working
« Reply #2 on: January 30, 2023, 10:36:06 PM »
Have you reflowed all of your solder joints and made sure all of your resistors are the right values in the right places?


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neiltheseal

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Re: Gain pot not working
« Reply #3 on: January 31, 2023, 01:29:03 AM »
Have you reflowed all of your solder joints and made sure all of your resistors are the right values in the right places?


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Red I have re flowed solder but no I have not checked resistor values. Will do that right now. Good suggestion.

neiltheseal

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Re: Gain pot not working
« Reply #4 on: January 31, 2023, 04:09:46 AM »
Have you reflowed all of your solder joints and made sure all of your resistors are the right values in the right places?


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This was it!

I put 510 ohm instead of 510k on r9 and r20.

So embarrassing. Thanks for your reply!

jimilee

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Re: Gain pot not working
« Reply #5 on: January 31, 2023, 11:12:45 AM »
Have you reflowed all of your solder joints and made sure all of your resistors are the right values in the right places?


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This was it!

I put 510 ohm instead of 510k on r9 and r20.

So embarrassing. Thanks for your reply!
Fantastic, glad you got it working. We all still do it after all these years.


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Pedal building is like the opposite of sex.  All the fun stuff happens before you get in the box.