RnFR- Thundertone

RnFR · Post by **RnFR** » 08 Feb 2009, 03:44

here's something i churned out the other day. i have been thinking about modeling the Supro Thunderbolt with FETs, but then thought- i just got in these cool new Tesla GE's, why not use those? so that's what it is, the preamp section of the legendary amp used by Page and supposedly Hendrix, done up NPN germanium style. i had to eliminate a few resistors towards the end to bring up the volume and lowered the value of an emitter resistor to up the gain a bit. also, i made the resistor on the input variable so you can adjust the input impedance for guitars with different pickups.

the real gem of this circuit is the tone pot- totally counter-clockwise you get a nice full range tone with plenty of mids. as you go clockwise it goes to a very muffled tone, and as you go even further, it goes to a very thin, cutting tone. there are some very cool sweet spots, and a lot of versatility. i like it better than a regular muff style control, but it does cut plenty of signal- hence the two gain stages after it.

it's a cool sounding circuit. nicely voiced and does a good overdrive type sound. if you don't have the trannys, you could change out the 33K Rc's to trimmers and adjust to taste. i'll make a layout up soon, and hopefully get some clips done.

take it easy!

RnFR · Post by **RnFR** » 08 Feb 2009, 06:34

i just made up this layout in eagle. some of the caps are kind of large in size because i wanted to use some russian ones that i picked up when i bought the trannies. if you've got the lead length, you should be cool. otherwise, if there is any interest for a smaller pcb version, i might be persuaded to do another.

briggs · Post by **briggs** » 12 Feb 2009, 17:10

Looks very nice RnFR, I've just got a stash of Ge trannies

but they are PNP

I think I'll invest in some Ge NPNs too. I built myself a supro clone amp, I should try this and see how it matches up to that legendary tone.

RnFR · Post by **RnFR** » 12 Feb 2009, 21:57

try the master blaster w/ those trannies you got. it's a glorified treble booster/OD. i think i might do a bit more filtering to the high end though. unless of course you've got one of those very dark marshalls or maybe a vox. on my little gibsonish tube amp it was great, just not through my fender super six(twin)- too brite!

Barcode · Post by **Barcode** » 12 Feb 2009, 22:02

i wonder how this would respond to Si trannies? I love the Ge sound, but I'm not down with the temperature instability. If you ask me, the tone is not nearly worth the hassle in some cases. Do you think there would be much tweaking to sub in SI trans?

RnFR · Post by **RnFR** » 12 Feb 2009, 22:16

probably not that much. you could give it a try. might have to adjust the collector resistors. you could try jfets w/trimmers as well.

briggs · Post by **briggs** » 12 Feb 2009, 22:18

I'm getting a new breadboard tomorrow so I can fit even more projects on there. I'll give it a side

FETs with trimmers could work quite well. I'd be tempted to give it a pop with 2N5457s....

RnFR · Post by **RnFR** » 13 Feb 2009, 09:08

very cool!

RnFR · Post by **RnFR** » 05 Mar 2009, 23:19

here's a new layout for more common sized/value parts. this will take NPN GE trannies, switch the battery polarity and elytics for PNP. i'm going to retool the larger layout, but i thought i would add this for people that don't want a monstrous PCB. it's a cool sounding circuit. give it a shot if you get the chance, or at least try the tone control!

pz · Post by pz » 07 Mar 2009, 16:11

Do the Gain and tone pots crackle? You've got DC present there. Then the bias voltage of the second stage depends on the pots positions. I'm not saying it's a flaw, just puts another variable into the sound. One cap between Tone wiper and 2nd stage base would cut out the DC.

RnFR · Post by **RnFR** » 08 Mar 2009, 01:49

that very well could be. i'm in the process of building this one up, so i'll let you know when i get that far. if need be,a cap can be flown off the pot. thanks for the catch, i appreciate the help. i'll amend the schem and layout once i get it figured out.

RnFR · Post by **RnFR** » 27 Mar 2009, 12:43

got this built up last night with the old PCB layout i did. no crackle happening on the pots at all that i can remember. i just have to say again how really nice this circuit sounds. it has a great chimey ring that just made me keep playing and playing. it's not super hi gain, but it does have tons of output. of course i was playing with low output single coils. i'm going to bust out the p90's today and give another listen. it's got a great, balanced, refined kind of thing going on. really nice clarity on all strings. made me want to keep doing that T Rexy bomp bomp,bomp thing up on the high strings. give it a shot if you can. if you don't have the transistors, use any GE's and just rebias to taste.