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Mailist to discuss all issues regarding the Digitech GSP-2101 Guitar FX Processor

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Message

RE: [gsp-2101] Tube circuit technical question.

2004-12-10 by M M

I also use and recommend a BBE (although I use an older 422A). Not only
does it cut the mud but it can be handy for a quick treble or bass
boost/cut change to cut through the mix,
 
Mark
 
-----Original Message-----
From: jason stanley [mailto:jsnstanley@...] 
Sent: Thursday, December 09, 2004 9:36 PM
To: gsp-2101@yahoogroups.com
Subject: Re: [gsp-2101] Tube circuit technical question.
 
Highly recomend using a BBE Sonic Maximizer on the other side of the
2101 (882),  That will get you out of the mud!   Rock On 2101 User!
p.s. (SansAmp PSA-1 to supplement distortions if needed.)

saber540ltd <saber540ltd@...> wrote: 

Knowing that some people consider the 2101's tube pre-amp as being 
mediocre and somewhat muddy (though I get somewhat decent results by 
placing an EQ between my guitar and the 2101), I was looking at the 
schematic of its tube circuit , wondering if anyone ever tried 
changing some of the filtering in the tube stages. I'm hoping maybe 
that Dieter could enlighten me on this topic. The following are a few 
characteristics of the actual tube distortion circuit:

1) Before reaching the tube stages, the signal goes through a 
different hi-pass RC filter depending on which tube distortion is 
selected. One filter cuts the lows below around 600Hz which I assume 
is for the Saturated Tube setting to reduce muddiness. There's a less 
extreme one of around 90Hz which may be for the Distorted Tube. 
There's one just below 25Hz, probably for Clean Tube. And also, C112 
can be switched in to cut everything above 2.4kHz in certain 
settings. All this filtering occurs before the signal reaches the 
tube stages.

2) Between tube V2's two stages, C128 and R210 result in a low-pass 
cornring at around 3.3kHz. I've seen something similar in "lead" 
sections of a Mesa pre-amp circuit.

3) After the last tube stage of V2, there appears to be an op-amp 
filter only for Distorted and Saturated Tube settings. It seems to 
contain a gyrator circuit built around Q30 but I'm not familiar 
enough with gyrator circuits to say for sure. Does anyone know this 
filter's exact characteristics or purpose?

I'm just wondering if anyone is known to have experimented with or 
improved the tube pre-amp by fiddling with these or other elements. 
And BTW, what is the Blue Dream Upgrade link supposed to be on 
Dieter's website; does it have anything to do with improving 
distortion quality?

Larry




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