Thunderchief build report

[Benny]

I just finished the Thunderchief from runoffgroove.com.  This is an amazing pedal... it has a very nice range of distortion, and goes from bluesy to crunchy to metal.  Many thanks to the guys at runoffgroove, great job!

There has been some discussion here about getting the transistor in the third stage to bias correctly.  I tried a handful of Siliconix and Fairchild J201's and the gate and source pins were all 1-3 V above the published test voltages with the drain at 4.5V.  I'm not sure at what point this starts to affect the operation of the circuit, all the transistors I tried sounded fine to me as long as the drain was at 4.5V.

There is a small problem with noise (hum/hiss) when the gain is turned up.  I noticed that placing a buffer (bypassed TS-9) between the guitar and the 'chief almost completely eliminated the noise.  Anyone else notice this, or can anyone explain it?  I double-checked my wiring around the first FET but I didn't see any mistakes (but that doesn't mean they aren't there!)  I should also note that it's not boxed up yet, that will probably help with the noise.

Lastly, I tried 3 different types of JFET's in the circuit: Siliconix J201's, Fairchild J201's, and Fairchild 2N5457's.  The 2N5457's sounded pretty weak, even at max gain there wasn't much distortion.  The Siliconix J201's sound great.  The Fairchild J201's sound identical to the Siliconix ones to me (and they're 1/3 the cost from Mouser!)

Benny

[Alpha579]

Cool, sounds great...Might have to make them...
So placing a buffer before the gain stages elimanates noise? Was there any tone/dist loss? If not, ive got a heap of high gain designs that hiss like hell... Cant explain why that would work, but thanks for the info  

[petemoore]

My ThunderChief doesn't do metal, probably is a little less gainy [4 of 4 Jfets], and could use some  more Q tryouts.
 Great voice though, I put an old Wah nonTB switch [I dunno...has three leads Dpst?] to switch out the last little cap, what an EZ and quite nice mod, which of course tapers off the highs, in an amount I see no need to tweek.
 Yes the choice of transistors seems critical on this one, I need more J201's I think to get the Max Gain happening, sounds just superb tho as it sits.
 The noise floor is quite low till near max gain pot settings, which I don't find myself using much with my rig, my TC does the super DirtBoost with the gain knob low, I'd not call it a Fuzz...sounds best IMO doing the 'too big for your own britches' tube amp thing...it does that amazingly well.