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Observations on Dumb-bell preamp clone

5/10/2000 1:27 PM
DominikObservations on Dumb-bell preamp clone
Hi there,  
now that the preamp is finished I got around to tweak it some and play around with it. A friend of mine was blasted away by the sound, altho up to now, the thing is only running over my Leslie 145 (motors stopped).  
I found some things I would like to change or ad:  
 
The bright caps of the dumbleator circuit (on the send and return pots) are not really what I need:  
The 1 nF cap on the send pot is way too bright and the 270 pF on the return is not really doing anything. I plan on putting 470 pF on both and see whether that suits my needs.  
I plan on putting a 39 pF or 47 pF cap across the 1M master pot (after the preamp stages, before the dumbleator input.).  
I have the feeling that the Clean channel of the skyliner (1997 Rev1.2) is not as bright as the 70s Clean. Maybe something is wrong , but I have to turn up the treble to almost 10 to get enough highs in the clean mode. The tone stack (not the one after OD2) of the skyliner is not very effective when in OD mode. I tweaked around the tone stack after OD 2 to get more mids and succeded. It seems to me, that the skyliner OD has more crunch to it, and is much smoother, but lacks some definition (mids??). I used a 100k resistor before the OD input trim. The 70s OD is more in the face and with lots of definition altho a bit harsh. I used a 220K in front of the input trimmer here. Maybe I should experiment with a 500k trimmer after the OD2 decoupling cap. Channel switching is abusletly noiseless now. I found that running the volume/gain on both channels on 5 or 6 yields the best sound.- Going higher makes the skyliner OD a bit to extreme (the input trimmer is set conservatively). I like the OD sound when the Drive is set to approx 3 - 5, with the Drive Master wide open. Maybe I will put a 1 nF cap across the plate resistor of OD2. I definitely will do a follow up project: a combo modeled after the skyliner series. I would like to add onboard tube reverb a la Fender, but will have to see where to implement it. As Gil suggested, I will stick closer to the Dumb-bell layout next time, but found that my layout resulted in a fine sounding amp.  
 
Dominik