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Re: Rick E. ?


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7/13/2004 5:28 PM
D. Re: Rick E. ?
Hi Chris,  
 
thanks for your input. By the resonance control you mean the "Depth" mod, sort of like a NFB bass boost?  
 
Can you elaborate a bit more on the T-Filter? This term is new to me.  
 
I imagine a resistor cap to ground resistor thing (which would cut highs?) or a cap resistor cap thinggie??  
 
Thanks for any insight!  
 
Cheers,  
 
Dominik
 
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7/13/2004 5:40 PM
Chris - CMW amps

Hi D./Dominik  
 
resonance=depth :)  
t-filter : used in some old Gibson amps ( GA series )  
 
for building : give it a try and trust your ears  
 
Hope Rick sees this post too,  
 
Chris
 
7/14/2004 11:43 AM
Dominik T-Filter!
Hi Chris,  
 
seems like I found something:  
 
"T filter":  
 
C1  
------+---------
 
7/14/2004 1:34 PM
Matt
Dominik,  
That looks very similar to the midrange control/circuit on a Matchless Cheiftain. Check the schematic but I think the values are 150k for R1 and R2, 560pF for C1 and .01uF for C2 with the midrange pot between C2 and ground. Something like that. That at least might give you some idea of the order of magnitude of those values.
 
7/14/2004 1:54 PM
Dominik
Matt,  
 
thanks for your reply!  
 
I will try your values and report back!  
 
Dominik
 
7/14/2004 2:16 PM
Terry Shipman

Hi Chris/Dominik,  
 
This is getting interesting.  
 
I have looked up a few Gibson GA schematics and found that the values vary on different models with:  
 
C1 500 pF  
C2 0.0047 uF and 0.003 uF  
R1 and R2 220 kOhms  
 
Looking at this with limited knowledge, if I understand this correctly, with C2 at 0.0047 uF the lower corner frequency is 154 Hz and the upper corner frequency is 723 Hz, so I guess the mid-cut would be the band between these two frequencies.  
 
With C2 at 0.003 uF the lower corner frequency is 241 Hz and the upper corner frequency stays the same giving a narrower band of mid-cut.  
 
It seems to make some sense that adding this circuit in front of V2a the tone could be shaped and the signal reduced by the loss in the filter.  
 
If I have got any of this wrong, please tell me.  
 
Terry
 
7/14/2004 2:56 PM
Dominik
Hi Terry,  
 
with the TSC I come to the following conclusion:  
 
The normal Fender TS gives a Mid Scoop at around 450 Hz (-25db, with all controls on 6).  
 
The Marshall TS gives a Mid Scoop at around 600Hz (-10db, all controls on 6).  
 
I think one should get close to these values with the right values of the T-Filter. Unfortunately one cannot generate a T-Filter with the TSC. I tried to do an apporximation with the Fender TS but the results are not that good.  
 
Dominik
 

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