SOLVED Cobbler treble piercing?

[harmaes]

I just build the cobbler and noticed that the top range of the treble control is extremely piercing.
I checked some demos on YouTube and my build is sounding comparably except for the treble knob.

Since there’s no schematic yet I tried tracing the components around the B1M treble control:

- The A1M bass pot lug 3 connects to a 22nf which connects to lug 1 of the treble pot.
- Lug 2 of the treble pot goes to 2x 470k resistors after which it goes to a 4n7 cap to lug 3 of the cut control and also into a 10k resistor to a 1uf cap to the 3v3 zener clipping into the TL072 opamp.
- Lug 3 goes into a 100pf and 100k resistor

I used 1/4 watt 470k resistors, could that be an issue? I also used silver micas for the pf values.

If someone can help with calculating the sweep of the treble pot based on the component values and validate if this is correct and results in a very high treble range (seems to be above 10k)? It also interacts with the cut control. If the cut is set to max the treble pot will oscillate above 1 oc. in my build.
I haven’t put the build in an enclosure yet so grounding can reduce something but I guess something isnt correct yet.

@Robert: are the 470k resistors correct and what would the upper range of the treble control be in this circuit? I think that the 2x 470k resistors are in parallel right? I checked an AC30 schematic and it has a 220k resistor which is close to the 2x 470k in parallel. The Wampler 30 something and the Vox use a 50pf instead of a 100pf but that should even be brighter.

 

[mybud]

Just a suggestion: see if an improvised earth ground of some kind affects the squealing.

 

[harmaes]

Just a suggestion: see if an improvised earth ground of some kind affects the squealing.

I will box it tomorrow so I’ll know if this improves it! Thanks.

 

[harmaes]

Using the TSC in the web (http://www.guitarscience.net/tsc/info.htm) for the Vox tone stack I noticed that the treble indeed goes way over 10k.
The 100pf is normally 47pf which reduces the treble somewhat:



I see a zener with a 717 ohm value. How can I measure if the zeners I used of 3v3 are working correctly?

So the RL on the right is using 2x 470k resistors in the Cobbler circuit coming out on 940k or parallel to 235k?

 

[Synchrony Pedalworks]

I double checked my Cobbler this evening. I am not getting a piercing treble sound when the treble knob is maxed. I wish I could help you more with the electrical component, but hopefully, some of the gurus will “chime” in.

….sorry for the bad pun, dad joke, etc.

 

[Locrian99]

What are you using for your charge pump? If I remember correctly I ended up with a whine from using a a 1044cpa instead of an scpa. And I bought an scpa off eBay once that I believe was just a remarked cpa because it did the same.

 

[harmaes]

I used a TC1044S(CPA) so should be fine.
I just boxed the pedal and the oscillation is indeed gone. It sounds quite good only when the cut is moved to around minimum or 9 oc and the treble is raised it really sounds horrible IMO. With the cut to max and treble to max it's working as expected with a vox and you can increase cut by turning it down and decrease treble to get the balance. I reduced the 100pf in the B/T tone stack to around 50pf and I'm using NE5532AP opamps now instead of the TL072CP.

Overall there's quite a lot of high end around and above 10k that I don't like and it also is obvious when digging into the strings. But in general I can get some chimey sounds which was the reason I build it. So all good.

 

[Feral Feline]

Glad you got it sorted. Mark it solved, @harmaes !