Ice pick highs elimination

[ES225]

I have an amp, which is fine except for the ice pick highs that are ripping my ears off. I so bad that I don't even want to play it. I have already changed to a dark speaker.
I read on the internet what the remedy might be but I don't know enough about electronics to locate the location to do the mod.
Here is what was suggested:
"put a Cap across the last plate resistor before the PI. anywhere between .001 and .022. Shunts unpleasant frequencies to ground."
Could someone please point out to me where this location is, so that I could try this cap mod.
I would really appreciate it.

[g1]

First we would have to know the make & model of the amp.
Next we could show you where that is on the schematic diagram, but if you don't read schematics that won't help you.
So we would also need a layout diagram or detailed photos of the insides of the chassis.

[ES225]

Great, thanks for the quick response. It is a Rivera-era Fender Champ II. I don't read schematics well but use the layout diagram instead.
I tried all kinds of mods and nothing changed the high end. I even removed some caps and still no change. I can detail the mods I did make. To my ears no effect on tone.
As I said the amp works perfectly but this high end harshness may have been the turn-off to these amps.

I can give you the link to the schematic and layout.
https://schematicheaven.net/fenderamps/champ_II.pdf
If you would rather email me directly, you are welcome to do so and I can give my email address.

[g1]

I won't comment on the mod or whether it will do what you want, others here may do so.
It is the 100K that connects to pin1 of V2.
If you do put a cap across there, it will need to have a substantial voltage rating, 400V minimum I would think.

[Helmholtz]

This amp is essentially identical to the very good sounding and sought after Rivera era Super Champ (I love mine- no need for mods).
Difference is no reverb section.
To me these amps are classics like BF models.

I think the amp should be able to produce a good Fender clean sound.
Not really meant for distortion but should sound great with a TS pedal in front.

Of course there could be something wrong e.g. with the tone stack.
BTW, there are already 500pF caps between plate and cathode of the preamp triodes.
You might try lifting the 47p cap that connects to pin 2 of V2a.


How much experience do you have with different guitar amps?

Can you post a sound clip?

[ES225]

Thanks again, this helps. Just to be sure, would I solder the cap parallel with the 100K resistor and what value cap would you suggest?
It would be great if this worked. I will wait for your response.

I do have experience with amps. I have enough of them. I have vintage Champs, BF Princeton and P Reverbs, a few 5E3 clones and others. I also have a Super Champ.
The Super Champ had the same issue but its an easy fix on that by just removing the bright cap.

I actually have two of these Champ II and they have the same nasty characteristic of the piercing high end.
I would differ in that these amps don't like pedals at all and they don't need them. That is why they have master volumes.
Everything is fine, except for the lame bright speakers and the ear-killing high end.
Oh, and they are in desperate need of an effects loop.
Any thoughts on an effects loop. Because of the higher gain then a BF, they don't take pedals well up front and as you turn them up it just turns to a mush.

[ES225]

One other thing I was wondering about. There are two ceramic caps on V1, they are both 500 pF. What the heck are these for and what do they do?
I removed both of them, with no change to the tone. I don't know what they were trying to achieve with them.
I have limited experience actually working on amps but would like to learn.

[Chuck H]

Can you post a sound clip?

This would certainly help. What IS too bright or "ice pick"? Since this isn't an amp known to have an undesirable top end character there may be something else to examine. We don't know about the guitar, any effects, interfacing or how anything is set up and being used. With only the amp model presented so far it's a conundrum since the amp wouldn't be the suspect at face value unless it's modified or in need of service.

What kind of guitar? What pickups? Under what circumstances are the unpleasant highs occurring? Are you interfacing this setup for home recording and the highs are in the mixes or are you just listening to a guitar and amp? Are you using any signal processing, pedals or modular units, between the guitar and amp? Does your guitar use a "treble bleed" type circuit and you need to turn the guitar volume down more than usual with this amp? Etc. etc. We don't really have a road map here. Tone encompasses all things in the signal chain. So since the amp isn't immediately suspect for overly bright tone at face value I think that arbitrary modification may not be the proper solution for your problem.

Please offer some details about the above uncertainties and, if possible, a recording as Helmholtz requested.

[ES225]

Its with any and every guitar. I have lots. Its both of my Champ II. Same problem. Compared to a BF or Tweed Fender the ice pick is very noticeable. Its the super high end that pierces write through one's brain. I am not exaggerating. Both of my Champ II are the same and one of them is mint.
Not sure how much experience you have with these. I am using no pedals, except for maybe a bit of reverb from a pedal. That is not the culprit. None of my guitars have a treble bleed.
To give you an idea it even makes my ES175 damage my ears. Its the 3 unwound strings with the high E being brutal.
Trust me I used multiple different guitars and also compare this to other amps.
I am not as enamored with these amps as some might be. I think they have design issues and may be the reason they were not in production long, both the CII and the SC.
That is not to say that they cannot be moded and made great. That is my intention here.

[Helmholtz]

One other thing I was wondering about. There are two ceramic caps on V1, they are both 500 pF. What the heck are these for and what do they do?

These are the caps I mentioned above.
They attenuate treble above 7kHz.
You could try to increase to 1nF or so.
A cap across the plate resistor works the same as wiring it from plate to cathode or ground.

Don't forget about the 47p cap across the 2.2M resistor.

[catalin gramada]

If you speakers ringing no any settings will tame the ice pick out.

[ES225]

I don't understand what you are saying.

[ES225]

Yes, I noticed the 47 pf added even more brightness. I had removed that early on but still remained very bright. I little less but not much.
I removed the two 500 pf from V1 but noticed no difference.

[ES225]

The area g1 suggested must not be the spot. Any cap I but in there makes the amp not omit any sound.
I soldered a .01 and also tried a .001 in the same spot as the 100k resistor.
Now what?

[ES225]

Helmholtz - I think you are onto something. I did remove the 47 pf and then I replaced the two 500 pf with two 1000 pf mica and I believe it worked. The amp still sounds bright, so its not dull but it no longer makes my ears bleed. I am quite encouraged. I might even go higher than 1000 p but I may not have to. I really appreciate your help.
There is a .001 cap near where the 47p was. Would it do me any good to replace that also to higher value maybe. What would that do?