Oscillation in bypass mode

[Ciaran Haslett]

Sorry man...been flat out all week.  Yeah something's not right with that pot.  Sounds like either the wiper is lifting and dropping or there's DC on it.

I should have asked this much earlier but can we have voltages?  I'd be a bit suspect of the cuts near the mids pot.

Also that wire doesn't sound right.  Shielded wire wraps around the "signal" wires to catch RF.  Try the ghetto solution if you don't have the right wire.

[Marbles]

Ah crap, ok, I'll ghetto it till I have proper wire.
And please, don't apologize, I really appreciate the time and effort you put into my problem. I should owe you one :D

Ok, these are my voltages:

OPA2604AP:

7.19      14.37
7.19        7.19
6.51        6.19
0.00        7.15


TL072CP IC2:

8.42    16.93
8.42    16.36
4.20    16.37
0.00     0.07


TL072CP IC3:

8.43    16.93
8.43      8.42
8.34      8.42
0.00      5.71




I check the cuts and take a picture of that. It's not the Mid-pot btw, but the Midrange pot. I will try and look if I have a replacement pot laying around. Guess that would not be a probable cause for the oscillation? :D



Edit: Midrange wire next to 18v wire... Makes you think :D

[Ciaran Haslett]

Yip...IC2 isn't right.  Pin 5 is connected to a divider through the mid range pot so should read around 8-9v.  Pin 6 and 7 are also very high.  Really starting to suspect your cuts/placement now.  I'll have another look over your pic but better ones will help

[Marbles]

Really?? Darn..

I knifed a lot, and the midrange doesnt pop anymore, but still squeel

THis is the bottom:






And another. Hard to tell though:





The one in the middle left is a piece of plastic btw, not a bridge

I checked it multiple times, but possible that I overlooked something of course

[Marbles]

Ok, I'm afraid the measurements were done after my hacking slashing.
I think you'll like my new voltages :)

8.46     16.87
8.47       8.46
4.22       8.46
0.00       5.70

I secretly hoped this problem was also the cause of the squeeling haha. No such luck eh?

[Ciaran Haslett]

Deffs looking better.  There's a few things you can do now that you have it open and out.  

Definitely no shorts now?  Ground and MidR 1 looks suspect.
Reflow some of those joints.  Please tell me thats not lead free?!?  haha...you know how we feel about that stuff!

Experiment....lift the wire from MID 2 off the pot.  That will remove the mid gyrator altogether.  Still squeal then?

Try swapping the IC's around.  Half of IC 2 and 3 are the mid/bass gyrators.  Maybe that previous short hurt IC2.  Might be worth swapping the charge pump IC too.

Finally...shielding.  I'd start with MID 2....then all of them lol.

The quest continues.....

[Marbles]

Ciaran,

You're a god amongst men. The ordeal is over! If we ever meet, drinks are on me that night :D

i ghetto shielded like a madman and it looked horrible. Still the same.

Ordered parts to build an Openhaus cause I was done with this. But had not read your last comment yet. Played on it a bit and apart from the squeel was really enjoying the gain of this pedal, so decided to give it one more shot.

Changed the 2 TL072cp to 2 TL072ip, but the same problem. Also thought the cp sounded better, but that must've been in my head. Changed them back to cp anyway.

Reflown all the joints, all of them. Checked every wire for damage. Even though i rebuild the charge pump from scratch with different parts, it did not sit right with me. Cause the peeeep got a lot louder when touching the bottom row (and capacitor).

Ordered another bag of 7660scpa's and: Presto! I could touch it without squeeling.. Super cautious I screwed everything back in the enclosure, and plugged in my guitar... Low gain sound.. wtf!*&^*&

Got everything out again only to realise the volume pot of my guitar was almost all the way down grrr...

Long story short: It works! There is about 2 roles of duct tape inside (i packed everything) and it is dead silent. Well, feedback on high volume of the guitar, but normal, good, enjoyable feedback.

So thanks, everyone and especially you Ciaran for the amount of patience and guidance through this drama haha. Really, really appreciate it. Really.

The dominator lived up to his name.

[Ciaran Haslett]

Haha....RESULT!  Nail the lid shut and never open it again!  

Might be worth posting where you got your good and bad batches of 7660S too.

Glad she's up and running lad.  Enjoy!

[Marbles]

Thanks :)

Yeah, this one won't be opened again... ever