HELP! Sansamp GT2 squeals like hell

[zener]

I just built a Sansamp GT2 from Tonepad. At first, it was nice. It only squeals when the high control is at 70% of the slide ( slide pot) and the amp is British.

When I was about to put in an enclosure, I noticed that I wired lugs 1 and 3 of the pots. The length of wires are just exact so I have to desolder the wires of lugs 1 and 3.

After soldering back again, the monster squeal came. It comes with the high control at just 30-40% both at British and California. It squeals at Tweed when high control is at 70-80%. I checked the joints and there was none. After all I only changed the wiring of pots, which is away from components.

It's like the high control was turned into squeal control.

I used 3 TLC2262 and a TL072 as what Vasiliok said before.

[free electron]

hi!
Common problem with hi-gain distortion units without clipping diodes, something that keeps signal at lower amplitudes. I spent a lot of time to solve that problem in GT2 type effects. I made 2 surface pcbs with shielding ground plane, every wire was shielded and it squealed.. The problem lays in stomp switch, you can shield everything, but in the end you have input and output very close to each other. Rise treble, gain and you've got an oscillator.
There's one trick in original GT-2. Bypass signal is taken from the first buffer, also - signal goes to notch filter (Fender type sound which has less gain). And this buffer acts like one-way valve here. Signal from output simply cannot go to the input of the hi-gain part of GT2. And it stops squealing.
If you can sacrifice truebypass, take the signal from out of the first buffer and after DC isolation (10u, 100k to gnd) use it as bypass signal.
That's the only one efficient sollution I figured out.
Regards
Peter

[Athin]

actually I've never had a problem with bypass - I use a 4066 chip and it workes great. I also had a problem with squeal - It turned out that after cleaning the board from soldering paste (which just happens to be in the solder as well) it stopped. Hell knows, maybe I've moved something or whatever, but if you get paste between the 9v and signal input legs of the opamp things like that may happen.

[zener]

Thanks!

Sorry Peter, I'm still quite a newbie. I don't know what exactly to do. Is the buffer your talking about is the first opamp circuit or another buffer circuit? What notch filter? Also I can't see any 10u and 100k to ground in the schematic I used http://www.tonepad.com/getFile.asp?id=79.

Thanks a lot :wink:

[free electron]

Zener:
There are no 10u and 100k I mentioned on Tonepad's schem, you have to add them in a way like this one.
U1a - that's the buffer
C4,C5,C6,R7,R8,R9 - notch filter that cuts out some mid frequencies.
regards
Peter

[zener]

Is the proposed 10uf and 100k to ground is only for a GT2 that squeals when bypassed? Mine squeals when the effect is engaged. The squealing comes from moving either or two or all of the following: level, gain and especially high. The low control seems to be the only thing that supresses the squeal slightly but it is helpless to the high control that can easily bring on the squeal monster.

Thanks for any help :wink:

[free electron]

No, these changes help to remove oscillations in every state, bypassed and engaged.
There's one more thing. Used often in hi-gain tube applications and generally in tube preamps. It is good to mute signal somewhere inside the effect when it's bypassed. When you set max gain, max volume and bypass effect you can sometimes hear a silent distorted signal in the background. Usually shorting signal to ground near Gain pot is enough to deal with that problem.
In GT2 we can use for that the second section of switch, the one that lights the LED. Schematic.
Regards
Peter

[zener]

BTW, mine doesn't still have a bypass switch on it. The jacks are connected to the circuit.

All I did is just put the 10uf-100k-470 trio from pin6 & 7, the 100K to the ground and the end of 470 will be the bypass signal which of no use to me yet since I still don't have a bypass switch.

Did i miss anything?

I'll try to hook up a bypass switch as soon as possible

Thanks.

[free electron]

it squelas without bypass? Something else is wrong in that case..
try to use shielded wires for Gain pot and input switch (amp type), try to separate input signals from output.
The one I made without bypass was very quiet, also used Tonepad's layout.
Regards
Peter

[zener]

I just hooked up a bypass switch and still the same. The 10uf-100k-470 input doesn't work when effect is engaged.

I'll try to find a shielded wire ASAP.

[zener]

Sorry, the first trick proposed by Peter worked, contrary to my earlier post. The squeal was significantly REDUCED. It's a lot better now. But the squeal was seems to be replaced by hiss-like that sounds like a shower of water or a rain outside. The hiss is a bit louder than the usual hiss from high-gaon distortions. Thw squeal is just when you fully crank up the high and gain and it's no longer an ear-piercing one.

I'm about to replace the jack wires with a shielded one. I hope it helps.

[chuckschuldiner]

Use only  EMG pickup..

The squeals sound have disapear......