#1
Hi all,
I built the thunderchief guitar effect, and I hear this crackly hiss sound, even if the guitar is not connected.

I also have another problem with it, that it sounds great one time , and another time it sounds like it is kind of blocked or muted notes.

This effect has 4 100k trimmers, and I wanted to know if that could cause this kind of problems?

Thanks a lot,

NirBenda
#2
Check your solder connections
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#3
it wont be the trim pots, that would only adjust the sound not make it sound crappy, check your grounding
Quote by Deliriumbassist
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#4
Ok guys.. .will do check the soldering and ground again...
btw.. when I do set the trimmers there is a noise going out as I change them, but I think this is because the DC voltage changes while turning it.

Thanks for your reply...
Hopefully it will work.. I'll let you know.

NirBenda

(myspace/nirbenda)
#5
Quote by rancidryan
it wont be the trim pots, that would only adjust the sound not make it sound crappy, check your grounding

Yes it could very well be the trim pots. I wish people wouldn't give advice if they have no idea what they are talking about.

TS the DC voltage on the FETs drain is supposed to change when you alter the trimpot. Your description definitely sounds like mis biased FETs. They are probably very sensitive right now at the way you have biased them, hence the inconsistent sound.

Bias the drains to approx half your supply voltage (if using a 9V supply then 4.5V).

Crackly hiss is either bad grounding or lack there of or it is DC leaking into your signal path (thats a bit unlikely though). Bad solder joints can also create hiss and crackle. What are you using as an enclosure? Have you hooked up all the grounds?
#6
hi kurtlives91,
I have set the trimmers exactly around that voltage.

I have taken the schematics from:
http://runoffgroove.com/thunderchief.html

Where they say that:
"Fixed resistors were used to approximate the trimpot value"

So I guess this is one way of solving it. (although I would prefer having the trimmers to play with)

I haven't been using an enclosure yet, because it not yet to be working well and it is still on the uncut perfboard.

I think that the easiest thing for me right now is to check the soldering again and recheck the grounding connections on the board, before replacing all the trimmers.

Thanks for the replay,

NirBenda

(myspace/nirbenda)
#7
Once you have the voltage that suits you best on the drains. Remove the trimmers and measure their resistance. You can then replace the trimmers with fixed resistors. You then get a bit more consistent sound over time and the floor noise is reduced quite a bit. That's what ROG is saying basically.

I bet your problem is you have nothing to shield the circuit and get rid of RF frequencies. I think when you put it in a metal enclosures your problems will be fixed.
#8
Great man, thanks a lot,
Seen your site, pretty cool looking stuff there, respect!

NirBenda

(myspace/nirbenda)
#9
Quote by kurtlives91
Yes it could very well be the trim pots. I wish people wouldn't give advice if they have no idea what they are talking about.



sorry


guess im still learning ill know for next time though

its what you get for being 1/4 way through a 2 year long electronics course

*puts on dunce hat*
Quote by Deliriumbassist
Antisocial Behaviour Order. A chav's equivalent of GCSEs.