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FDP Forum / Amp Mods, Repairs, and Projects / How to mid boost DR

Mars Hall

USA NW Indiana

Jun 13th, 2018 10:52 AM   Edit   Profile  

I have a 75 SFDR. How can I boost the mids? I’ve seen a mid boost mod on a BFDR with a mid pot on the back of the amp. However, I’d like to just make the change on the board and leave it.



Jun 13th, 2018 09:24 PM   Edit   Profile  

Try changing the 6.8k resistor, on the bass pot of the Vibrato channel, to a 10k.



Jun 14th, 2018 01:56 AM   Edit   Profile  

Yes, though how much of a boost is desired?
With reference to the mid control of a AB763 Twin Reverb, the stock 6k8 of your DR is equivalent to setting the TRs mid to ~8, 10k equivalent to turning it up full, >9.
If you want more than that, ~22k is the practical limit before the mid scoop becomes so shallow that the range of the treble and bass controls may seem to become rather limited.
Perhaps try modelling it in the tone stack calculator.


Mars Hall

USA NW Indiana

Jun 14th, 2018 06:04 AM   Edit   Profile  

What I would like, is it to sound more like my 66 Super Reverb. I do run the mud control of the SR right around 8.



Jun 14th, 2018 09:59 AM   Edit   Profile  

Well, on the face of it, the value of that resistor may not need to go much higher, 10k, 9k1 or 8k2 may get you there.
However, the SR AB763 has a 22nF mid cap, c.f. the 47nF of the DR, so the SR will have more low mids even with the same value of mid resistor. Again, TSC may be helpful in getting your head around this.
But then the different speaker arrangements of the 2 amps are significant in regard of their overall tonal balance, as is the likelihood of the actual value of at least some of the components in the amps drifting away from nominal over time.

FDP Forum / Amp Mods, Repairs, and Projects / How to mid boost DR

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