Paragon squeal is driving me mad!!

[KevTom23]

Hi all.
I've built the full size Paragon. I was lucky enough to be able to source genuine Panasonic MA856 and Toshiba 1s1588 diodes from European / UK suppliers, and I am absolutely blown away by how the pedal sounds. up to a point.
There's a squeal at the pedal's extreme settings that I can't get rid of, so looking for guidance.
The business diodes are socket mounted, as are resistors R3 (1k) and R17 (100k).
So far, I’ve swapped out the charge pump and both opamps for compatible versions, and shortened the diodes’ legs so that they sit flush berween the socket posts (I initially left them longer than they needed to be).
The squeal persists.
it’s only there when both sides are on and the pots are near maximum all round.
Boards are connected with trimmed header pins and none of the cables to the jacks or 9v are axcessively long. Jack sockets are open Neutrik jobbies.
Pots and 3PDTs are Alpha.
Any ideas on where to go next?

 

[Robert]

This should be avoidable, but possibly not very easily with an existing PCB layout...

As a sort of band-aid you could probably add one of the mini buffer PCBs to the input.

 

[clarisso11]

Thanks for chipping in! That sounds reasonable.

If in fact the original doesn’t squeal but the clones do (FuzzDog, PedalPCB), I can only imagine that coming from differences in the way the PCB is laid out (not component differences).

So unless the PCB is revised, is seems like the additional buffer is the way to go. Or accept it and never play with the controls turned up. Although I wouldn’t want to be taken by surprise by that oscillation, especially at high volume, it gets pretty piercing.

 

[JamieJ]

Do you normally play the pedal with all controls dimed?

For me they sound best in and around 2 o'clock range for all controls on my paragon mini. I often set my pedals and amps up by listening how to pot reacts when there is a high level of ground hum. I normally put my guitar against the amp so that it makes some ground hum then I adjust the pot and listen to where it starts to react and add to the hum. I then adjust from there to taste. With the paragon it should not be that they are most responsive at fully CW on the pot - if that's the case there is a problem with the circuit. If you can find the sweet spot this way and it doesn't squeal then all should be good in the world.

 

[Robert]

I definitely want to build one of these and determine if a revision is needed to the PCB layout.

The circuit is basically two Bluesbreakers, there's no excuse for oscillation.

 

[clarisso11]

I would buy a revised version
I noticed that all the clones are routing the tracks closely together, where the main board and footswitch board are connected, maybe that’s part of the problem?

 

[Feral Feline]

A momentary stomper that dimes all the controls would be part of my ideal KOT.

 

[Popnfreshbass]

I mean…. If you dime two stacked overdrive pedals, it’s gonna squeal right?