Reducing high frequency before clipping in Metalzone

[ZebCahan]

Hello,
I have a question concerning the filters before the clippingstage in the Metalzone.
I have already done alot of modding to it after reading alot of the threads in this forum and I think that it sounds much better now.
But one thing i would like to get rid of is the fizz in the upper frequencies.
I tried to put capacitors over the clipping-diodes but since they are after the gain-ompamp they just make it sound more dull with the fizziness still there.
Taking a look at the schematic :

http://www.freeinfosociety.com/electronics/schemview.php?id=138

I cant really find anything that I can change to make this happen.
I thought of the filter 47n and 10k right after the first opamp but when using a filter calculator I get 388hz so its already reducing highs before the clippingstage.
Any suggestions would be welcome.
Maybe putting a 4.7nf capacitor to ground directly after the 10k in the inputstage?


/Sebastian

[dschwartz]

- play with those 47pF and 100pF caps at the opamp´s fedback..like doubling them all..
- try softening the distortion a bit, put a 5k trimpot between the diodes and ground, and trim to taste
- make the treble cap from 10nF to 22nF or 33nF

one or all of this mods may help you..if you find that the problem is Fuzz instead of fizz, lower that 10uF cap on the gain opamp..try lower values (1uF, or even lower, experiment)

[earthtonesaudio]

Maybe increase the 47p cap to anywhere from 100p to 470p, in the "gain" op-amp stage.

Oops, Daniel beat me to it.  I agree with his other suggestions.  I would also recommend concentrating your efforts in the circuitry before the bass/treble tone section.

[ZebCahan]

Wow thats two fast answers! Thanks!
Danel :
I thought the 47p together with the 1k formed a highpass filter? Or am I reading it totally wrong? Im reading as much and trying to learn as much as I can so if you can explain this to me I would be very happy.
I will try to increase them as well.
If you mean c44 as the treble-cap(?) I tried to change the resistor r61 instead, a while ago and it helped a little bit.

Earth:
Do you mean around the IC4 after the diodes?

/Sebastian

[earthtonesaudio]

I meant the one with the gain control potentiometer, directly before the clipping diodes.  But the op-amp directly after the diodes would be a good candidate also.

[dschwartz]

Wow thats two fast answers! Thanks!
Danel :
I thought the 47p together with the 1k formed a highpass filter? Or am I reading it totally wrong? Im reading as much and trying to learn as much as I can so if you can explain this to me I would be very happy.
I will try to increase them as well.
If you mean c44 as the treble-cap(?) I tried to change the resistor r61 instead, a while ago and it helped a little bit.

Earth:
Do you mean around the IC4 after the diodes?

/Sebastian

if you see the 47pf with the 1k alone, yes, they are a high pass filter.. the trick here is that high pass filter goes to the inverting input of the opamp, then it substract highs..the bigger the  cap, the more treble you are taking away..that´s the beauty of opamps, yiou can add and substract frequencies..

[ZebCahan]

Oh! Very good info.
What would happen in a inverted opamp?
Thanks for taking the time to explain!

/Sebastian

[rogeryu_ph]

Hi sebastian,
Maybe this would help, I haven't tried yet. Just read his mod recommendation.
http://www.bossarea.com/forum/topic.asp?TOPIC_ID=5613

[ZebCahan]

Thats a good thread. 
Thank you all for the help!


/Sebastian