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 Post subject: ParaEQ hiss and high Q
PostPosted: Mon Jun 27, 2016 9:50 pm 
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Any support troubleshooting the following would be greatly appreciated.
First, there's a lot of noise/hiss associated with the High boost/cut pot. Second, the High Q freaks out when turned fully counter-clockwise. For example, there is a loud pop accompanied by a high-pitched squeal when dialed all the way to the left.
All the other pots seem fine - no issues with with the low/mid portions of the pedal - just the two upper pots on the high freq. channel. The clearance seems ample between the pots and the circuit board.
So far, I've re-flowed the solder on all pots and footswitch.
The pedal is usable providing I don't cross that threshold on the Q knob, although I would like to minimize the hiss and have the pedal fully function as designed.
My gut feeling is that the soldering is solid, though I will certainly keep resoldering if necessary just to make sure. My guess is that there is something not quite right in the treble section of the circuit. I'll double-check to make sure all of the resistors and caps are correct.
Here are a few pics:


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PostPosted: Mon Jun 27, 2016 9:53 pm 
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A few more pics...


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PostPosted: Mon Jun 27, 2016 9:54 pm 
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...


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PostPosted: Mon Jun 27, 2016 9:55 pm 
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Last ones...


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PostPosted: Tue Jun 28, 2016 6:00 pm 
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Update:
I tried it with the IC4 op amp (TL074) out of the circuit and the the squeal and hiss are gone. I'm will re-solder the op amp points when I get a chance and see if this makes any difference when the op amp is reengaged.


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PostPosted: Tue Jun 28, 2016 6:53 pm 
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Might be the IC itself.

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PostPosted: Wed Jun 29, 2016 4:38 pm 
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Ok - I swapped out ICs (not the sockets) and re-flowed the solder on the IC4 socket (after removing the IC). No luck, same issue. How often do these sockets fail?


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PostPosted: Wed Jun 29, 2016 9:02 pm 
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Hard to tell exactly from the pictures but it looks like your R36 might have the wrong color code?


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PostPosted: Wed Jun 29, 2016 10:50 pm 
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I did double check all the resistors and they are all correct, including R31 (it's color code is orange/orange/black/black brown, though the black bands do look kind of blue in the pic). Thanks for looking.


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PostPosted: Thu Jun 30, 2016 8:08 am 
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bryansbizaar wrote:
How often do these sockets fail?

Unless grossly abused with a soldering iron, I've never seen that happen.

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My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2


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PostPosted: Fri Jul 01, 2016 8:21 am 
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What else should I try next beyond re-soldering all the joints?


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PostPosted: Fri Jul 01, 2016 4:34 pm 
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Maybe you could tip up the pot covering the bottom of the socket and take a clear photo there. Also, if there is excess solder flux on the the board you could try cleaning it off with flux solvent or isopropyl alcohol and a soft plastic brush. Makes it easier to see the actual solder joints and sometimes the flux itself has been reported to cause problems. Other than that, if the only symptom happens when you turn the pot, you could try swapping pots or measuring the pot with an ohm meter. If nothing else, it may take some test equipment to sort out the problem.


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PostPosted: Mon Jul 04, 2016 3:33 pm 
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Update: I think it might be fixed. Here are a few things I did:
*re-touched all the solder points (and removed the 3 boost/cut pots so I could access the 3 x TL074 sockets' solder points)
*cleaned most of the flux
I can't say which of the above did the trick, but if I had to guess, I'd say it was re-heating the socket points. Anyway, I'll keep my fingers crossed!


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