Raspy treble from 2203 amp

[Mark]

I plugged into my friends 2203 and it sounded dreadful. It was overly compressed and the treble is raspy.

The compression was due to the 100K cathode follower resistor measuring 880K. I replaced it and the amp sounded much better. The amp still has raspiness which goes away when I turn the volume up.

I’m wondering if I should consider the Kevin O’Conner mod where you put a 100K resistor in series with the master volume wiper connection.

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http://site.triodestore.com/JCM8002203Stock.pdf

This Triode circuit diagram has a 100pF cap across the first stage and I believe that Dave Friedman does put a 0.002uF across the cathode follower 100K resistor.

Thoughts on raspy treble response?

Thanks for your assistance.

[bepone]

Speaker is v30? Change the speaker?
Some other guitar problem?

[Mark]

Speaker is v30? Change the speaker?
Some other guitar problem?

I used a EVH MIM guitar, and I also used my Strat. The box is a Fender Bassman box with Kendrick Blackframe speakers in it. I have previously used the box with a 1959 and it sounded fine. The speakers aren’t overly bright.

[Mark]

Mystery double post.

[Littlewyan]

That master volume mod doesn't actually help, I did some tests on this a few years ago with a spectrum analyser and found it made no difference. But YMMV.

Dave Friedman puts a 500pF cap across the cathode follower 100K, lowers the first coupling cap to .0022uF, adds a 22uF to the final stage cathode and lowers the NFB resistor to 47K on 4Ohm tap. This is what he did to the Jake E Lee amp anyway. If you're looking to tame the raspiness I would start with the first and last mods personally, or even try removing the second 500pf treble peaker.

[cdemike]

That master volume mod doesn't actually help, I did some tests on this a few years ago with a spectrum analyser and found it made no difference. But YMMV.

Dave Friedman puts a 500pF cap across the cathode follower 100K, lowers the first coupling cap to .0022uF, adds a 22uF to the final stage cathode and lowers the NFB resistor to 47K on 4Ohm tap. This is what he did to the Jake E Lee amp anyway. If you're looking to tame the raspiness I would start with the first and last mods personally, or even try removing the second 500pf treble peaker.

Agree with these. I also would suggest experimenting with potentially adding a resistor to ground after the second peaker (sort of simulating adjusting the normal volume control when plugged into only the bright channel on a 4-hole amp).

What was the cause of the 880K CF resistor? Was it damaged or was it a mistake? Either way, it might be worth checking other component values also to see if they might be contributing.

[Mark]

That master volume mod doesn't actually help, I did some tests on this a few years ago with a spectrum analyser and found it made no difference. But YMMV.

Dave Friedman puts a 500pF cap across the cathode follower 100K, lowers the first coupling cap to .0022uF, adds a 22uF to the final stage cathode and lowers the NFB resistor to 47K on 4Ohm tap. This is what he did to the Jake E Lee amp anyway. If you're looking to tame the raspiness I would start with the first and last mods personally, or even try removing the second 500pf treble peaker.

Agree with these. I also would suggest experimenting with potentially adding a resistor to ground after the second peaker (sort of simulating adjusting the normal volume control when plugged into only the bright channel on a 4-hole amp).

What was the cause of the 880K CF resistor? Was it damaged or was it a mistake? Either way, it might be worth checking other component values also to see if they might be contributing.

Thanks for taking time to reply to my thread/post.

The 100K went high over time. The 100K on the valve socket is measuring 120K so it’s going too.

I think it’s the old Fender issue where they used 1/2 watt resistors on the anode/plates of the valves when they should have used 1 watt resistors. I replaced the resistors with 1 watt ones.