DBM 39_V1.1.gif

SIR #39 Mod

DBM – does R9 really need to be there?
– It’s not necessary for the circuit to function. I put it in because I read that it was part of the #39 circuit. 
On the presence control is the 4.7k there to lower the 25k pot’s resistance down instead of using a 100k NFB & 5k pot?
– Correct.
Lastly, the .68uF cap there instead of the usual .1uF – what difference do you hear w/ this?
– The .1uf affects only very high frequencies. The .68uf affects also the midrange. Since I have a 47k feedback resistor I thought the .1uf made the sound very shrill. On the other hand, the amp gets very loud with the .68uf when the presence control is fully turned up. 

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