Valhalla issue

[PKRPedals]

I have noticed a couple quirky things with my Valhalla since building it. It has the same squeal/oscillation that my pineapple has when the gain is up around 2 oclock. Also when turning down the eq section all the way, it kills the volume. I run my cable from the power amp out to the front of the amp, it actually sounds better to me this way, and the pedal acts like a mute when you switch it off, but this my be normal for it to do that. Just thought I would bring it up. I have used all my guitars with this pedal and the pineapple and they all cause the squeal. I thought my Les Paul was different but turns out it does it to. These are the only 2 pedals that I have this issue with and I can't seem to figure it out. I reran my cables in the pineapple with shielded cables and that may have helped a bit, but it still has the squeal. My Thermionic and Thermionic Deluxe don't have the squeal. Now with all that said, these pedals sound amazing but I have to roll off my volume just a bit to make the squeal go away. I can deal with it but would rather it work properly. Any ideas?

 

[PKRPedals]

Are you using 9v or 12v to Power it? Make sure your Charge Pump is TC1044S or 7660S.
Someone @ FSB also suggested trying a buffered pedal before it as it worked with their Clone PCB squeal.
Using shielded cable on Input & Output Jacks is also suggested by another.

I checked my charge pumps and they are 1044s and 7660s. I swapped the 1044 for the 7660 and it still squealed. I did put my boss pedal in front and that stopped the squeal.

You aren't the first person to have oscillation issues with this circuit. (and the issue seems to affect several different vero / PCB layouts)

As music6000 mentioned, at least one person found that a shielded input wire helped. It's odd that a buffer in front helps, considering the first stage of the circuit is a unity gain buffer.

Just a random thought, make sure R29 and R31 are both 10 ohm and not 10K by some chance.

I was very careful with the resistors on this build, I’ve had that bite me before. I can put my ds 1 in front of it, just plugged in and not on, and there is no squeal at all. It is almost completely quiet. It’s a great sounding pedal aside from the squeal.

 

[Chuck D. Bones]

I usually think that shielding the input wire is overkill, but in this case it may be necessary. For shielded wire to to be most effective, the separated center conductor and shield leads at each end must be as short as possible. You should be able to keep each under 1/2 inch or so. If you don't have shielded wire, twist the green & black input wires tightly, like 5 turns per inch, and see if that helps. Twisted wires are not as effective as shielding, but it's a whole lot better that individual wires. Shielding the output wires (both pairs) could also help, but try the input side first.

The DS-1, or any other buffered bypass pedal, helps because it presents a low impedance source at the input to the Valhalla. Any stray signal that would be picked up on the Valhalla's input gets shunted to ground by the preceding pedal's output buffer.

The input buffer is unity voltage gain, but it has extremely high current gain. It can be thought of as a very sensitive receiver with the input wire as the antenna.

 

[PKRPedals]

I replaced the input with shielded cable and it still squeals. I think it may just be one of those that squeal. Could a buffer be installed on the input instead of using another pedal to solve it, maybe?

 

[music6000]

I usually think that shielding the input wire is overkill, but in this case it may be necessary. For shielded wire to to be most effective, the separated center conductor and shield leads at each end must be as short as possible. You should be able to keep each under 1/2 inch or so. If you don't have shielded wire, twist the green & black input wires tightly, like 5 turns per inch, and see if that helps. Twisted wires are not as effective as shielding, but it's a whole lot better that individual wires. Shielding the output wires (both pairs) could also help, but try the input side first.

The DS-1, or any other buffered bypass pedal, helps because it presents a low impedance source at the input to the Valhalla. Any stray signal that would be picked up on the Valhalla's input gets shunted to ground by the preceding pedal's output buffer.

The input buffer is unity voltage gain, but it has extremely high current gain. It can be thought of as a very sensitive receiver with the input wire as the antenna.

I was looking at the Original PCB guts & the LM2940CT-12 is bent at right angles & screwed down to the PCB through the top hole, Does that need to be Grounded.
Also the jacks are PCB mounted so no leads!

 

[PKRPedals]

I looked at that also but it is grounded through the middle leg. I put my meter on it and it's showing ground. That's interesting about the PCB mounted jacks. I know there was one guy on here that built one and said he had no issues, so I don't know what he did different. There was also another guy that had the squeal. I watched the one video on Youtube for this pedal and it squealed around 2 o'clock.

 

[music6000]

I looked at that also but it is grounded through the middle leg. I put my meter on it and it's showing ground. That's interesting about the PCB mounted jacks. I know there was one guy on here that built one and said he had no issues, so I don't know what he did different. There was also another guy that had the squeal. I watched the one video on Youtube for this pedal and it squealed around 2 o'clock.

Some have upped the 47pf cap to 560pf to get rid of Squeal but it muddies the sound.
Apparently the Original has a Ferrite Bead resistor type which is used to shield unwanted noise.
Try putting some over the Input & Output leads, There are Hollow type & Clamp type available.

 

[Robert]

Could a buffer be installed on the input instead of using another pedal to solve it, maybe?

Ideally I'd like to find out what in the heck is plaguing these things (because it's not just you)....

But, as a last alternative, I will get some mini buffer PCBs worked up today that can be inserted into effects like this. (or any other case where you might need a tiny buffer).

 

[PKRPedals]

I would love to find out and not use a band-aid for it. But there are apparently other guys that are building these with different pcb's and they are having the same issue.

 

[Chuck D. Bones]

Here's the thing about the squeal. It's an instability. It's non-linear. A circuit can be right on the edge of oscillating and not oscillate. A circuit can be just past the edge and oscillate like a &^*#$@#.

You can measure the resistance of a wire from the jack to the board and read a number close to zero. But that's not the whole story. There can be some inductance in the lead and that might make the difference between oscillating and not oscillating. Board-mounted jacks have significantly less lead inductance.

I can see how Vero boards can have oscillation problems because they don't have ground planes. I've built a few Vero boards and so far (knock on wood) I have been pleasantly surprised by a lack of oscillation and noise problems.

Try the ferrite beads. Might just be the ticket. Dialing back the bandwidth a little on each stage might help too.

 

[PKRPedals]

I’ll try the bead first and get back with you. Hopefully it will work but if not, that will be one more thing tried

 

[music6000]

I know there was one guy on here that built one and said he had no issues

I'm assuming they plugged into their pedalboard & had a Buffered pedal in Front & are probably in for a Surprise as a Stand Alone pedal!

 

[PKRPedals]

That could be very true. I'm going to install the ferrite bead tomorrow and see what that does. Maybe Pedalpcb will come up with a small buffer to add to the input so that an extra pedal isn't needed to kill the squeal.

 

[Chuck D. Bones]

Adding another buffer inside the box may not help.

 

[PKRPedals]

You don’t think adding it in the input would work? I don’t know if it would or not, I was just thinking the the boss pedal going in stopped the squeal so surely adding a buffer at the input would.

 

[Chuck D. Bones]

It really depends on the coupling mechanism. If the stray coupling that causes oscillation is on the board itself, then a buffer inside the box will fix it.

 

[PKRPedals]

I tried the ferrite beads and they didn't work. I also did a buffer on breadboard, the basic buffer from muzique. It stopped the squeal but was really noisy.

 

[PKRPedals]

I did a breadboard circuit of a Klon style buffer and put it in the input and that stopped the squeal. Maybe something to think about adding it to the board on the front end?

 

[Chuck D. Bones]

Yes Chuck, But after the pulling & squeal stops, will the pedal still work.

No, but that's not the point. We're pulling IC1 as a diagnostic to help us narrow down where the problem lies.

 

[Chuck D. Bones]

The fact that adding an off-board buffer helps makes me think the squeal is stray coupling on the board, probably due to the proximity of traces. I can't find anything suspicious on the top layer of the board, but maybe there is something on the bottom side.

 

[PKRPedals]

It could be. When you look at the original, it is spread out on a much larger board.