Red Jekyll & Hyde Squeal Problem

[jwbink1500]

Hi all!!

Hopefully R.G. can give me some advice on this one again.

I just got done modding my Red Jekyll and Hyde pedal and now I have problems. I have a high pitched (smoke alarm pitch) noise coming from the pedal when:
-all pots are dimed,
-at least one side of the pedal is on,
-when the output is run into an amp and
-NO cord going to the input.

The noise increases as the Jekyll knobs increase. Almost sounds like tuning a radio. Hyde side does it as well but to a lesser extent, most prominent on the Jekyll side. When I plug in to the input, the high-pitched squeal goes away and is replaced by a low oscillation. The squeal goes away when I lower the pots on the either side.

I typically check the pedal after each modification so that if I run into a problem, I can retrace. This was no exception. I swapped parts at C7 and R10 for the Hyde side. Worked great at least I didn't hear any Low oscillation. Replaced stock parts and that made no change to the problem.

Trying to audio probe is a pain in the ass because I don't understand the IC TC4053bp. Using the input hot wire and moving around, touching pin 14 on that IC gives me a sound clean of problems. I've searched for solder where it shouldn't be. Checked for cold joints. Those seem to be ok. I'm beginning to wonder if its the TC4053.

Anyone have any suggestions? Where to go from here? 

Let me know if I should post pin measurements of all IC's or only specific ones.

Thanks Joel

[R.G.]

-NO cord going to the input.

I have a cartoon from back in the 70s. It's a picture of a guy in a suit sitting behind a desk. On the desk is a pile of smoking rubble, that being all that's left of a computer terminal. The guy's face and chest are blackened with soot, and the wall behind him is blackened, with a clean space corresponding to where his chest and head blocked the blast of charring.

The caption reads "Gee, it never did *that* before."

Based on my modification experience, I take the caption as the Modder's Mantra.   

If it only happens when the input cord is unplugged, it's likely to be a problem with the input circuitry or the switch chip. I don't see any reason for it to have done that based on one cap and resistor change, so this is likely an unintended side effect of the mod; that's a polite way of saying "could be most anything", especially if you put the original values back and it still has the problem. To say more than that, I'd need to know the age/model of that pedal. There have been several circuit versions of the J&H. Is yours the red folded steel one (the "flat top" model as we call it) or the cast aluminum housing?

[jwbink1500]

Thanks for the reply RG,

I have a cartoon from back in the 70s. It's a picture of a guy in a suit sitting behind a desk. On the desk is a pile of smoking rubble, that being all that's left of a computer terminal. The guy's face and chest are blackened with soot, and the wall behind him is blackened, with a clean space corresponding to where his chest and head blocked the blast of charring.

The caption reads "Gee, it never did *that* before."

Based on my modification experience, I take the caption as the Modder's Mantra.   icon_lol

I would say that's accurate for me.  However, I can usually  back track and fix my screw up. Hey, its how we learn right?

I was fairly sure it wasn't the cap and resistor change that did it, but I swapped back to make sure. It is the red steel folded "flat top" version. Board says VJH1 Version 2D if that's any help. 

On the green side, with all leads disconnected (hot and ground on both input and output) using an audio probe tip ONLY (no audio probe ground) on the output, I get the high pitched squeal. Touching audio probe ground also starts a mid-tone buzz/fizz sound. Both channels are affected though with slightly different tones and buzzes. Bypass functions as it should. Sometimes i can touch the probe on the output, I hear a tone like something charging up. Tone starts low and increases to the mid-tone and stays there.

I do get guitar coming through when hooked up correctly but there is prominent background noise, thats how I found the squeal.

Let me know what to try,
Thanks
Joel

[jwbink1500]

Ok,
I have a really dumb question.
Can the type or quality of wire used to connect jacks to the board cause this problem and/or interference? When I move the wires around the pitch seems to vary with certain locations on the board. Just wondering.

I replaced the original wires to the in/out jacks with slightly longer runs of Radio Shack wire, after that is when I noticed the problem. (forgot to mention that in my first post.) With no input output wires hooked up to the board, and a cord from pedal out to amp in, if I touch the hot output wire to the board i get a similar high-pitched noise. When I touch the ground to the board too, I get the original high-pitched sound. I've tried different section of wire with no luck.

I changed IC5 (TC4053) and IC4 (TL072) and got no change in the problem. Could it be another IC, the wire or another component?

When I jumped C14 (0.1nf) with my pliers, the sound disappeared (Not sure if that means all sound or not), but changing the component did not fix the problem.

Since the sound is altered by both green and red sides of the pedal I would have thought it was IC 4 or 5.

Any suggestions?

Thanks
Joel

[twabelljr]

I replaced the original wires to the in/out jacks with slightly longer runs of Radio Shack wire

I think you should keep these as short as possible and try replacing them with shielded wire.

[R.G.]

My first, knee-jerk reaction is that the power and/or ground is not being decoupled correctly. I have occasionally run into situations where I accidentally damaged a capacitor while doing other stuff.

I would replace all the electro caps on the board, carefully observing polarity and value, just as a shotgun first step.

[Paul Marossy]

Seems like the easy fix is to plug a cord into the input. When do we play pedals with no cord in the input anyway?

It sounds to me like it is self-oscillating when nothing is plugged into the input. If your mods have to do with increasing the gain, then it may have pushed the circuit(s) over the edge as far as stability is concerned.

[jwbink1500]

Wow, thanks for the response everyone!!!

I may order some shielded wire and try that as well as changing all the electros. Should I stick with electrolytics or change type or does it really matter other than size and Voltage rating?

Paul, I see you point. But there was some noise prominent while playing after the last mod that caught my attention and revealed the squeal after more looking and prodding around. Reverting mods back to pre-noise state did not remove the noise as I hoped.

Soooooo, that just means I screwed something up.

Back to the wiring issue. When I plugged in tonight strum the guitar, the noise disappears shortly when the guitar notes sounds. As the notes fade out, buzzing and noise fade in. Touching jacket of the hot (red) wire going from the jack to the board makes the pitch of the noise change. Could this a shielding problem after all?  Moving the wire in different locations near the board also changes the pitch

Let me know what you all think,

Thanks,
Joel

[Paul Marossy]

I may order some shielded wire and try that as well as changing all the electros. Should I stick with electrolytics or change type or does it really matter other than size and Voltage rating?

You could replace any electros in the signal path with other types. But you're limited to a maximum size of 1uF in film type caps. Power supply caps should remain a polarized type.

Paul, I see you point. But there was some noise prominent while playing after the last mod that caught my attention and revealed the squeal after more looking and prodding around. Reverting mods back to pre-noise state did not remove the noise as I hoped.

Soooooo, that just means I screwed something up.

Hmm... probably. I've modded a few of them and haven't had this problem, yet anyway.

[R.G.]

I may order some shielded wire and try that as well as changing all the electros. Should I stick with electrolytics or change type or does it really matter other than size and Voltage rating?

There is no particular need to change types. The circuits in there are conservatively designed, and good electros will work fine. Get the same capacitance and voltage.

But there was some noise prominent while playing after the last mod that caught my attention and revealed the squeal after more looking and prodding around. Reverting mods back to pre-noise state did not remove the noise as I hoped.

RF oscillation sometimes appears as a hiss in the audio sound. It is possible that the mod lets it oscillate at RF.

Back to the wiring issue. When I plugged in tonight strum the guitar, the noise disappears shortly when the guitar notes sounds. As the notes fade out, buzzing and noise fade in. Touching jacket of the hot (red) wire going from the jack to the board makes the pitch of the noise change. Could this a shielding problem after all?  Moving the wire in different locations near the board also changes the pitch

That description is consistent with a low level RF oscillation that gets swamped by an incoming signal.

There is no good way to debug this by discussing it. Replace the electrolytics. That will do *no* harm, and my cure it. If this persists, then shield the input wire; it is possible that twisting the input lead with the ground lead to the jack will do almost as well. Um, you *did* leave the ground wire to the input jack intact, right?

[jwbink1500]

Hi guys,

Sorry it took a while to get back. Had to order parts and then got caught up in life. 

Anyways, I replaced the 2 - 100uf 25v caps and the 50v 10uf cap and got no change. Also, twisted the input wires together and the output wires together. And as you asked RG. I do have ALL input and output wires connected correctly. I get sound when playing guitar through it.

The only other electros on the board are C8 C25 and C30. C25 and 30 can be found on the Jekyll side of the schematic but the C8 has me lost. On my Schematic I have IC's 1-5 My board has an IC6 and C8 seems to be tied in some how. I don't know if this could even be the issue.

Correct me if I am wrong but C25 and 30 are on the Jekyll side and should not be causing interference on both sides, right.

The problem, to me, sounds like it could be a cap. When I have the output cord hooked up and I get the squeal noise, if I unplug the POWER SUPPLY cord for about 10 seconds and then plug it back in, the sound starts quiet (squeal absent) and increases to the squeal noise within about 2 seconds and then stays there. Maybe I am way off here though.

This is getting difficult to troubleshoot without an updated schematic. I have a version that says REV.: 1.1 Date Juli 2005 Drawn by KHE. I emailed Visual Sound for a schematic a while back and they would not send me one. Kinda irritating since the basis of the pedal is the Tubescreamer and Shredmaster. Anyone have a schematic?

What to try next?

Thanks,
Joel

[R.G.]

Sorry it took a while to get back. Had to order parts and then got caught up in life. 

No problem. I'm forced to sing that song a lot of the time.

Anyways, I replaced the 2 - 100uf 25v caps and the 50v 10uf cap and got no change. Also, twisted the input wires together and the output wires together. And as you asked RG. I do have ALL input and output wires connected correctly. I get sound when playing guitar through it.

Sorry about that. It was my best guess at the time.

The problem, to me, sounds like it could be a cap. When I have the output cord hooked up and I get the squeal noise, if I unplug the POWER SUPPLY cord for about 10 seconds and then plug it back in, the sound starts quiet (squeal absent) and increases to the squeal noise within about 2 seconds and then stays there. Maybe I am way off here though.

That's my guess, too, unless something is getting hot and you're getting a thermal heating/cooling effect causing the oscillation as something heats up. It's rare in pedals, but does happen sometimes. You might be able to find it by using freeze spray or just feeling parts with your hands to see what gets hot - if anything.

This is getting difficult to troubleshoot without an updated schematic. I have a version that says REV.: 1.1 Date Juli 2005 Drawn by KHE.

That schemo is one drawn by someone outside the company, so I don't know if it's accurate or not.

I emailed Visual Sound for a schematic a while back and they would not send me one. Kinda irritating since the basis of the pedal is the Tubescreamer and Shredmaster. Anyone have a schematic?

There are no schematics for that released outside the company, as a matter of policy.

However, we *do* try to make repairs as quick and inexpensive as we possibly can, even on out-of-warranty items, and even on units which have been modified by the owner and no longer work right. If you'll contact support@visualsound.net you can get some estimates of what,  how much, and how long. Any incoming repairs that they can't handle (which are few and rare, thankfully!) come to me personally.

DC-voltages troubleshooting is very powerful, but when something mostly works but oscillates (that is, an AC-only problem), you're kinda stuck with needing to go to an oscilloscope of some kind to find out what's happening.

[jwbink1500]

Thanks a lot RG!

That may be the route I take. I can usually work through my mod mess-ups. I usually test after each modification not matter how small. That way I don't get 17 mods done and realize "SHIT! Now what's wrong?"  I'm just lost on this one. All the things that I thought it could have been have turned out to be fine. So it seems anyway. Its starting to reach the point that the board is getting messy at a few copper spots have peeled and I had to jumper.  As, I said I still have sound so that's good. 

As for overheating of parts, the effect seems to be instantaneous upon connection to power, aside from 2 second effect that I mentioned. Could overheating still be a problem?

Anyways, this is soooo frustrating.  I'll probably change C8 and see if that does the trick. After that I'll probably email Visual Sound.

Thanks RG

Joel

[R.G.]

As for overheating of parts, the effect seems to be instantaneous upon connection to power, aside from 2 second effect that I mentioned. Could overheating still be a problem?

It could still be overheating, although I'm grasping at straws here. The small parts on that board will have thermal time constants (that is, the fundmental rate at which they heat up) in the 1-3 second range, so that matches the timings you mention. That's all I had to go on.Things that happen faster than 1 second are usually electronic, slower than 1 second generally thermal. There are *many* exceptions though.