Marshall preamp tweaking suggestions (NOT a tube preamp)

[Xavier]

I have two of these combos

http://www.drtube.com/schematics/marshall/3315-preamp.gif

I only use the normal channel, which has a TL072 on it and some tone stacks. I was wondering if changing the TL072 to whatever OPA2604 or OPA2132 would make an audible improvement. My experience with pedals is that in most of the cases isn't much of a difference, but this is a preamp. What do you think?

I find it to lack some "air". To my ear the high frequencies stop somewhere at 12kHz or so, but I'm not able to identify the treble tone stack. Any suggeston?

[JHS]

First, replace the jacks, the contact pressure decreases with time, yielding in treble loss, or thin treble.

Common guitar speakers have a frequency range up to 7kHz, so if you want to add some more air to your sound make a cap upgrade.
Replace the electrolytics with plain foil types, and the other caps in the amp with Silva Mica and KP-types to reduce the losses, that helps a lot to get a trannie amp alive. Replace the op-amps in the preamp to TI 071PI (only if other manufaturer is used).

JHS

[A.S.P.]

the cw end of the treble-pot is located at the node C3/C4
(to the right of the 2nd opamp, top of the schem)
its wiper goes to the cw end of the vol-pot (further right).

try 470p cap from vol-pot-wiper to treble-pot-wiper,
or a smaller cap from vol-pot-wiper to node C3/C4...

[Xavier]

Wow thanks for the suggestions. As I said, i wasn't able to locate the treble tone stack, so this is of great help. What i don't get is exchanging the TL072 by a TO TL071?

[JHS]

Sorry! TL071 should have been Texas Instruments TL072PI.
I don't know the manufacturer of the ICs Marshall used in the amp but if it is ST, Mitsubishi or other upgrade to original TI.

For me the TI 072PI  is one of the best sounding 072, sweet, warm and clear.

JHS