From benjamin.kuris@compaq.com Thu Oct 31 13:33:28 2002
Subject:Tube gain thoughts-- slightly OT

I suggest the "howlers" check on the various web resources aimed at
guitarists (www.amptone.com, www.ax84.com) for more insight on tube
topologies for gain.

I've become quite obsessed with the subject and many of the
discussions on this board mirror longstanding guitarist tricks

Some examples are: adding clean boosts before a tube stage, pre-post
gain equalization techniques, pre-amp/poweramp distortion.

I've just finished mod'ing a $50 Kalamazoo model one amp (schematic
is on the web) whose topology is:
input->preamp triode-> tone control->gain control->preamp triode-
>master volume control (I added this)->power tube (EL84 in single
ended class A)->mic'd Speaker or load w/direct output) to be a
keyboard recording amp/preamp and educational tool-- its very
interesting to compare the sonic differences of the various
combinations of source volume, gain, and master volume.

Once you sort of get a sense of the controls, you can start playing
with different preamp tubes. Personally I love the way a 12DW7
sounds (thanks for the tip, Steve) for clean to overdriven, and the
traditional 12AX7 for high gain fun. In all cases getting real
power tube overdrive is key to complex sounds once you start getting
into high gain configurations-- its like adding a texture to a
drawing.

I could be wrong, but I think a crucial part of the speakeasy preamp
is to use a single ended transformer output stage (like the EL84
mentioned above). This topology also crops up at the output of the
AO28 preamp on a b3. I use a V5 into the speakeasy and then into a
leslie 145. I can't imagine wanting more gain... w/my V5 flat out
and the speakeasy at 3/4 volume I can drive my leslie silly. Then
adding in some solid state distortion from the once neglected
overdrive knob on V5 puts me in Rock-grind land. When I really want
to turn heads, I hit an a/b switch (actually a hacked Danelectro $25
EQ pedal) and feed some of my V5 through a resonant filter + hard
distortion and then into my *non* organ amp signal path (I'll use the
same path w/out the resonance to tighten up the lows of my leslie).

Once great thing about keyboard amplification is that you really
don't need a closed loop like a guitarist playing feedback style--
much of the black magic (er... complexity) in a guitar amp is based
on getting things to be just barely under control. I actually mod'd
out the reverb channel of my traynor YGL-3 (twin) so I had 2 clean
channels as the extra tube gain stage wasn't playing well with my
keyboards. Whereas most guitarists prefer yet another gain stage for
a mesa boogie sound. I think you'll also see more keyboardists using
Twins then Bassman amps for this reason.

Anyway my final comment is that Steve and Speakeasy should add a 6W,
EL84 output option to their products (w/speaker out jack shorting to
a 8ohm load resistor)-- they would be a steal as single ended point-
to-point recording amps!

Or one could buy a lexicon 284-- but you wouldn't get the service and
customization that speakeasy provides.

-Ben