Caesar cuts high end

[DAJE]

IMPORTANT - READ FIRST:
I have very carefully triple-checked ALL of the resistors and ALL of the capacitors, and they are definitely all correct. I test all of them before soldering so I know that they're all within spec.

The 3102 and the 3207 have been tested in my other chorus pedal where they function correctly and with plenty of top end.

I also know that the pots are the correct values and in the right places. I might not have tested them before installation so I can't be certain they're within spec.

I have tested all 5 transistors and swapped the positions around. They're all 2N5088s and they're all in spec, as far as I can tell, with a gain between 350 and 450.

I did the mod where you replace D1 and D2 with 2.2uF MLCCs. Neither affects high-end content.

I have adjusted the trimmer very carefully and while it seems to have a slight effect on the high end, there's no point where the highs aren't cut.

The high cut is the same whether or not the PCB is boxed.

It isn't a subtle effect; the pedal is unusably muffled and it sounds like I've zeroed the tone on my guitar and my amp, while my other choruses - one bought, one home made - have plenty of high end.

 

[DAJE]

Did you try adjusting the internal Trimmer to get the sound any better.

I have adjusted the trimmer very carefully and while it seems to have a slight effect on the high end, there's no point where the highs aren't cut.

In the OP. And yes, tried again since then.

You could try lifting a leg on the 4 I have mentioned.

I'll probably do that, might just replace them all while I'm at it.

 

[Locrian99]

Curious did you ever get this figured out ?

 

[DAJE]

Curious did you ever get this figured out ?

I've been busy with other activities, but I should have some free time tomorrow to start investigating the capacitors.

 

[fig]

If it were my build, I'd audio probe from the input through the audio path. That might/could/should reveal the node(s) who are slinging mud at my circuit.

 

[Locrian99]

If it were my build, I'd audio probe from the input through the audio path. That might/could/should reveal the node(s) who are slinging mud at my circuit.

Not nearly as fun as cutting legs off capacitors and scratching your head.

 

[DAJE]

If it were my build, I'd audio probe from the input through the audio path. That might/could/should reveal the node(s) who are slinging mud at my circuit.

I started doing that but audio probing isn't as easy as it looks. Plus I don't really know much about locating the audio path. I might try again tomorrow.

 

[steviejr92]

I started doing that but audio probing isn't as easy as it looks. Plus I don't really know much about locating the audio path. I might try again tomorrow.

Look at the schematic and follow the path and hit each component along the way. Start from the input and work your way through to the output. Again probing all those joints along the way until you hear a weak signal!

 

[fig]

Question; Does the low-pass/hi-cut remain regardless of the BLEND setting?

 

[DAJE]

Question; Does the low-pass/hi-cut remain regardless of the BLEND setting?

Yes, none of the pots has any effect on the high cut.

 

[fig]

I would probe pcb input pad, Q1-2&1, IC1-2&1. Those are the input/output of both and from what I can tell (grain of salt maybe) pretty much the dry signal path of the circuit.

 

[DAJE]

It retains high end up to IC3, so we can forget about everything before that. I'm taking a brief probe break now.

EDIT: I think I've narrowed it down to C18 or 19, so I've pulled them both. But I'm starting to get tired and irritable so I'll come back to it later. I'm hoping I'm not destroying the board.

EDIT 2: C18 was more like 6.2 nF than 6.8 - I have some that are closer to 6.6 so maybe that'll be the answer. If that doesn't fix it I might have to start replacing resistors.

 

[DAJE]

I have replaced C18 and C19, and... didn't fix the problem. The board still works, but I can't pinpoint exactly where the top end cuts out. It seems to be somewhere among the row of resistors from R35 to R40. But I can't tell any more because I'm tired and annoyed again.

I could replace all the resistors there but I'm really not feeling like I can save the board if I keep messing with it. I'm mildly surprised it still works now.

 

[music6000]

I have replaced C18 and C19, and... didn't fix the problem. The board still works, but I can't pinpoint exactly where the top end cuts out. It seems to be somewhere among the row of resistors from R35 to R40. But I can't tell any more because I'm tired and annoyed again.

I could replace all the resistors there but I'm really not feeling like I can save the board if I keep messing with it. I'm mildly surprised it still works now.

Can you confirm what C5 - 47pF says?
It just looks physically large for a small value!
Your PCB may have a pad or trace that is faulty as I have been over the resistors & they all look correct to me.

 

[DAJE]

Can you confirm what C5 - 47pF says?
It just looks physically large for a small value!
Your PCB may have a pad or trace that is faulty as I have been over the resistors & they all look correct to me.

C5 is 100pf. C11 is 47pf.

Pictures show the suspect resistors, C11, C5.

 

[Locrian99]

C5 is 100pf. C11 is 47pf.

Pictures show the suspect resistors, C11, C5.

Quick comparison to color codes in my build they all look the same.

 

[fig]

Welp, if me, I'd swap the IC, just to be certain one channel didn't somehow go bonkers. Then I'd take a closer look at that last cap...C20 1uF, and maybe reflow R41 just for good measure.

 

[KR Sound]

I’ve been following this, but I’m not sure I have anything else to add. However, here is a pic of mine if it’s any help at all.

 

[DAJE]

Welp, if me, I'd swap the IC, just to be certain one channel didn't somehow go bonkers. Then I'd take a closer look at that last cap...C20 1uF, and maybe reflow R41 just for good measure.

I'll do that. I've already swapped the 3102/3207 chips into another chorus pedal where they work normally. Retry that, I guess, and I'm sure I have other TL022s and 4558s in working pedals... just need to do some other things first...

 

[DAJE]

I’ve been following this, but I’m not sure I have anything else to add. However, here is a pic of mine if it’s any help at all.

Doesn't hurt, and yours looks nice

 

[DAJE]

I'll do that. I've already swapped the 3102/3207 chips into another chorus pedal where they work normally. Retry that, I guess, and I'm sure I have other TL022s and 4558s in working pedals... just need to do some other things first...

I swapped the TL022 and 4558 with the ones from my other chorus, and no change to either pedal.