Need help debugging a Sinamp project

Started by hooya, June 07, 2010, 10:33:44 PM

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hooya

I've got the board all wired up with the specified components.  Using 3P4T rotary switches (limited to three turns) for the switches and regular ol' pots.  Using the suggested IC's and transistor for now until I fix this annoying problem.

The thing has a VERY loud high pitch squeal.  Especially when I'm not playing but it's still present when signal is going into the unit.  I can change the pitch and tone of the squeal with the MOD and MIC switches.  The squeal is also effected especially by the High potentiometer.  So it seems like something is creating the high pitch sound.  When I turn the Drive all the way down it gets very extreme.

I've poured over the circuit board and can't find any errors, but there obviously is one.  I etched the board myself and it was pretty messy but I cleaned it up pretty well.  Would a missed contact or a bridged connection cause this issue?  I've gone over the switch wiring a dozen times and I'm sure it's correct.  I notice the red 1M resistor from the IN to Ground... I'm not sure why that is red in the schematic.  Could that have something to do with it?

Any ideas?

hooya

No ideas from anyone on this?

Upon further questing on this project I've decided the squeal sounds just like feedback.  And just like feedback it goes away when you actually put a real signal into it.  So would a bridged connection cause that problem?  I think that must be the issue but haven't found any missed or bridged connections anywhere.

Any help or just thoughts/ideas on what the issue could be would be very welcome.  Again, I'm using all totally spec parts.  I'm sure I'm wiring up the switches correctly, unless I'm completely misunderstanding how they are supposed to work.

Brymus

Read "what to do when it doesnt work" at the top of the board.
Then post back after going through the list.
Someone might be able to help you after that.
I'm no EE or even a tech,just a monkey with a soldering iron that can read,and follow instructions. ;D
My now defunct band http://www.facebook.com/TheZedLeppelinExperience

hooya

Other than measuring all the voltages, I'm not sure what information I'm not giving that is requested in that post.  I'm trying to be as forthcoming and complete as possible.  What further information would be useful at this point?  I'm just hoping anyone here has actually built the circuit.  It's possible noone active here has.

MikeH

I built it.  But mine did not have a high pitched squeal.  What you are probably hearing is some oscillation possibly due to wires being too close together, sloppy lead dress, solder bridges, bad joints, incorrect component, etc etc etc etc etc.  It could be caused by almost anything.

But it's pretty much impossible to narrow it down without some voltage readings.

The red resistor to ground is an optional pulldown resistor to eliminate pop noises when using true bypass switching.  It's red because it wasn't in the original schematic (because the original unti was not true bypass, and didn't need it)
"Sounds like a Fab Metal to me." -DougH