Lower gain on Fender Tonemaster? Submitted by Geoff G.
Well Geoff, you said you have tried lower gain tubes, some cap
and resistor swaps etc. After checking out the schematic, I notice there is no presence circuit. Now you may wonder what does
the "presence" circuit have to do with headroom? Well, the presence circuit introduces negative feedback into the
amp, in the process this causes phase cancellation of certain freaquencies and therefore you get more 'presence" as you
add more negative feedback into the driver. Negative feedback makes the power amp have less distortion or "headroom".
You can add a presence circuit two ways, fixed or adjustable. If you don't want to add a pot simply locate the 4
ohm tap on the output transformer "the green wire" and add a resistor anywhere between 27k to 100k. connect
that to the .1uf cap that joins with the 47k resistor that is tied to ground on the tail of the driver. between ground
and the .1uf / 47k junction add another .1uf cap from ther to ground. That's it. I would start with 100k and if not enough
work my way down to 27k which will add the most negative feedback. If you want the presence to be adjustable, install
a 20k linear taper pot and instead of tying your .1uf cap to ground, take a wire from the .1uf / 47k junction put
it on the left hand lug of the pot, add a 4.7k resistor from that same lug to the back of the pot (ground) add
your .1uf across the center lug and the right hand lug of the pot and solder the other end of the cap to ground. This is the
classic Fender/Marshall presence circuit. again if you gpo this route experiment with the resistor values comming off the
speaker tap from 27k (Plexi / Fender Bassman) to 100k (Modern Marshall). Remeber the lower the reistor value the more negative
feedback, the more clean headsroom you will get out of the amp. Adding this circuit willmake a dramatic difference in clean
headroom. You should be able to get the master volume up to around 2 - 3 o'clock before the power section starts to break
up. Hope this helps.
Why no cathode follower on clean channel of Soldano X88R? Submitted by Michael
Hello Michael. Thank you for your question. I cannot claim
to know what Mr. Soldano was thinking, but my quess is is would have required the adition of another tube, and he would have
needed only half the tube. There is no gain in a cathode follower stage. The main reason it is used or was invented is there
is higher current from a cathode follower than a the grid, and the signal taken from a cathode follower will be the same phase
as the signal fed into it, unlike a regular grid stage, where the signal going into the grid, comes out of the plate out of
phase with the original input signal. A cathode follower is by no means mandatory, at any stage. I believe the cathode follower
is used universally because most amp designers are trying to take the original Fender / Marshall tone and gain (overdrive)
and effects loops and such, but stick to what is known to work (if it ain't broke, don't fix it). In fact Soldano is the only
designer I know of who uses a cathode follower after the recovery stage of his effects loop designs (SLO) as apposed to merely
adding a gain stage, and sending that output to the phase inverter. I use both methods. If I have a free stage when I modify
an amp that has a loop or I am adding a loop, I will use a gain stage recovery amp with a cathose follower to the phase inverter
which keeps the signal current the same as a marshall (Marshall takes the tone circuit from a cathode follower and then out
to the phase inverter as you know). If I would have to ad a tube just to get a cathode follower I will
use a single gain stage and take that right to the phase inverter. There is really know difference in tone. The cathode
follower will give more headroom (volume) but not that much. I think Mike ran out of tubes, so skimped knowing players where
not buying a Soldano for the clean but the overdrive. But I think Soldano has a fantastic clean on all his amps.
Hope
this helps.
Dino
2:42 am edt
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