Preamp Suggestions For Marshall JCM 2000 Dual Super Lead

[rockstephan]

I just bought the Marshall JCM DSL 100 watt head. I'm looking for some help finding the right pre-amps to put in my amp. It currently uses the ECC83 and I'm looking for more gain and more sustain but, I don't want to loose the Low end as well. If you have any suggestions to throw at me, please do.

Stephan

[tubeswell]

You mean "pre-amp valves/tubes" right?

EEC83/12AX7 is highest gain in that family. You could try one that has a long plate/spiral filament - supposed to offer more 'gain'.

Other ideas that spring to mind (from my recent experience with fiddling with the pre-amp gain stages in my amp) include making adjustments to the resistors and caps in each gain stage i.e.

raising plate resistor values from 100k up to 150k (or even 220k)

Lowering the grid stopper values down to 1.5k (or even 100 Ohms, or nothing) - but not on the first stage - better to keep that between 33k to 68k

Playing with the cathode resistor + cathode bypass cap combinations. Higher value bypass caps (e.g. 10uF or 22uF - as opposed to .68uF or 1 uF) or inserting cathode bypass caps where there are none, generally increases the gain. So does lowering cathode resistor values (but don't go below 820 Ohms, otherwise you might get the amp cutting out when you hit a big chord).

Changing the attenuation between gain stages, (i.e. by altering voltage dividers, or grid leak resistor values) to get more or less signal going into the grid of the next stage.

Raising the B+ and/or B++ voltage (you need to watch your maximum plate voltage if you do this)

Increasing the coupling cap values e.g. from 1nF to 2nF or 4.7nf between gain stages can increase the bass (and hence 'gain'/distortion) Too much bass here can result in 'farty bass' syndrome.

Some peeps will be angry with you if you do all these at once and report problems. Best to try them one at a time, so if you encounter problems, you can easily undo your experiments.

[Amp Kat]

Have you considered a stomp box in front like the tone bone british. That amp allready has a lot of gain in the ultra mode but adds noise and treble also when engaged. Increasing plate resistance will add noise and so will lowering cathode resistors. It is however possible to find a right combination of preamp tubes to get what you want but NOS would be the way to go and it could be costly.