Alpha Dog Problems

[spwilson218]

Hello guys and gals!

I've just finished building the Alpha Dog for a friend, it was a pleasure to build from beginning to end with no real issues to speak of. I'm now at testing, and bear with me because this is difficult to explain.

I'm getting signal when plugged in with unity on the volume knob at around 12 o'clock on the dial, I can hear the Fat/Soft/Hard/Filter knobs all doing what they're supposed to but the gain knob is giving me issues. With gain at total 0 there is hardly any volume, turn it up ever so slightly and then a huge amount of volume kicks in along with a tiny bit of overdrive, keep turning and nothing changes for the whole sweep of the pot.

I've given the board a big blast with contact cleaner, I can't find any birdges between the pads and I've reflowed everything I can, just in case.

Has anyone else had a problem like this? If so, how did you fix it? HEEEEEEEEEELLLLLLLPPPP!

[mauman]

Welcome!

Pictures of your build would be very helpful. 

Until then, (1) the Gain pot is specified as a 1 meg "A" taper, which gives a gradual run-up in resistance.   Is it possible you installed a 1 meg "B" taper, which would give you a much faster increase?  (2) Is the BS170 installed in the correct orientation?  Putting it in backwards will change the clipping.

[benny_profane]

This issue is confusing. How can the SOFT and HARD controls be operating properly if you only have a tiny bit of overdrive? Those controls determine the clipping characteristics of the circuit.

[madbean]

If the gain kicks up super quick my first suspicion is a bad wafer on the pot. But a pic so we can put more eyes on your resistors is a good idea.

[spwilson218]

Welcome!

Pictures of your build would be very helpful. 

Until then, (1) the Gain pot is specified as a 1 meg "A" taper, which gives a gradual run-up in resistance.   Is it possible you installed a 1 meg "B" taper, which would give you a much faster increase?  (2) Is the BS170 installed in the correct orientation?  Putting it in backwards will change the clipping.

The BS170 is definitely orientated the correct way. The pot that I've installed is the D1M that was provided with the PCB. I wouldn't mind if it was the difference of having a log or lin taper to be fair, but when I say the taper is weird I mean it goes from 0 to 60 in the space of a millimetre!

[spwilson218]

This issue is confusing. How can the SOFT and HARD controls be operating properly if you only have a tiny bit of overdrive? Those controls determine the clipping characteristics of the circuit.

The volume jump is so drastic and coupled with the small amount of overdrive you can the hear the slightly different nuances that the hard and soft controls provide.

[spwilson218]

Here are photos of the board as requested!

https://drive.google.com/drive/folders/1JR9BdYND62vDrfIWdkDDj81YDYqg158f

[spwilson218]

Looks like I have to do this individually.....

[spwilson218]

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[spwilson218]

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