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previous: Steve A. Bruce:   &nb... -- 7/3/1998 12:29 AM View Thread

Re: Tube AMPS for low volumes

7/3/1998 5:57 AM
GFR
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Re: Tube AMPS for low volumes
Steve, just to remember that thread:  
 
A speaker electrical impedance has a peak at a low frequency (~100Hz) and then increases with frequency (begining at around 2KHz). This increase with frequency is because of the voice coil inductance. The peak is important and happens because of the paper cone, air, cabinet, etc.  
 
Also, if you mimic the load of a guitar speaker and slave the signal to a PA or HiFi amp, it won't sound like the speaker did. You have also to mimic the frequency response of the speaker, that is a different thing from its impedance.  
 
References: Plate to Plate, LHX2, Pittman's patent on the GT Speaker Emulator, and the papers of Thiele and Small (this last one requires engineering background).  
 
Also take a look at Pittman's book. A lot of Marshalls there have compensated direct outs (taken from the phase inverter, however) with a lot of caps. Some boogies there also show a single cap compensated direct out, but the cap values are not shown.  
 
The resistive divider approach suggested earlier in this is what the Scholz "Power Soak" uses. Its nickname "Tone Soak" speaks for itself.  
 
I've seen good reviews of a recording system that is basically a big sealed box with a small cabinet and a mic inside it. Because the cabinet is sealed you can crank the amp and and apart from a little leakage, in total silence.  
 
GFR