Presence control for LXH2 Marshall

[Yazoo]

The presence control on the LXH2 Marshall simulator (a really great solid state emulation of the real tube amp) tends to work more as an additional gain control and from what I've read, it's meant to work like the equivalent treble boost on the power amp stage of the real thing.

I saw an old post about the presence control modification for the Marshall LXH2 and visited Krister Sundstrom's site where he reproduces a part of an older Marshall LXH2 schematic he found with a different layout for the presence control. I had problems understanding the changes and added an extra 10K resistor connecting the output of stage 3 to the wiper,pin 2, of the presence control. I left everything else as it was. I then looked at the schematic again and realised I had misunderstood, but the way I did it does also work quite well. Has anybody else tried this modification and if you have, could you post the way you did it please?

[km-r]

i really loved the sound of my marshall LXH2 and have been very sad abandoning the project...
i did the modifications made by Krister and it worked quite fine, more like a presence control and a little less gain control.

i think the modifications were really made to make it act like a presence control but i can no longer find Krister's schematic for that, would you mind pointing me to it?

when can i find time to resurrect my LXH2???

[Yazoo]

Krister has a fragment of the schematic  dealing with the presence modification reproduced as ASCII text on his main LXH2 page near the bottom here:

http://hem.passagen.se/amps/

If you can merge that with the main LXH2 schematic and reproduce it here I'd be grateful.

[slacker]

From looking at the ASCII scheme I think it goes like this. The 0.033uF cap gets moved to between the output of opamp 3 and the 3.3k resistor. The left hand side of the 10k resistor that was connected to the 0.033uF cap gets connected to the output of opamp 3. Everything else stays the same.
This makes opamp 4 into a treble booster, the output of which then gets mixed with the rest of the signal by opamp 5. So the presence control should now add more treble as it's turned up.