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Diaz mods


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12/6/1998 7:19 PM
Anthony Stauffer
Diaz mods
I just read an article in one of my old guitar magazines that was about SRV's amp's and it had some quotes and suggestions from Cesar Diaz on what he did to get Stevie's Amps to sound the way they did. Two of the mods he did were to 1) Disconnect the first channel from the phase inverter circuit, and 2) to disconnect the tremelo by snipping the wires at the intensity control. According to the article this serves to 'unload' the amp, thus warming up the tone somewhat. Has anyone done these mods and if so how is the first one accomplished and also IYHO how much differece can be heard?
 
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12/7/1998 7:52 AM
MJ Harnish

>1) Disconnect the first channel from the >phase inverter circuit, and 2) to disconnect >the tremelo by snipping the wires at the >intensity control. According to the article >this serves to 'unload' the amp, thus >warming up the tone somewhat. Has anyone >done these mods and if so how is the first >one accomplished and also IYHO how much >differece can be heard?  
 
#2 increases the gain of the amp some since the trem circuit, even when off, eats up signal. This is mentioned in just about every amp book as an easy, reversible mod. On my deluxe reverb I *think* I prefer the sound of the amp with the trem attached since the amp seems to lose a bit of its clean sparkle with it disconnected (I'm still experimenting).  
 
For #1, I guess you'd just unsolder the 220k mix resistor right before the phase inverter for channel one and tape it up. Theoretically you should be able to remove the other 220k too and run a straight wire here (since you no longer have to mix the two channels) which would have some noticeable effect on the tone (should increase highs and gain?); I think Weber mentions this in his first book as a way to improve "fidelity."  
 
Both of these would be easily reversible if you didn't like them; if you decide to disconnect the trem controls and want to get a little more radical (without altering the amp at all in a damaging, non-reversible way) you could use one of the pots to add a presence control (if you're so inclined; I've found that it helps my DR cut through better in a band situation when I can adjust the mids and the presence).  
 
MJ
 
12/17/1998 6:06 AM
Matt D

Diaz' amps are also known to utilize:  
.68uf bypass on 2nd triode stage in place of 25uf  
silverface-spec phase inverter  
HIGH plate voltages, around 500+VDC B+  
 
These amps do what he suggests- clean/tight bass and crunchy top end. Pretty clean in the mids (i.e. bright).  
Matt D
 

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