thunderchief fixes

[electrictabs]

well after some experiments i made the thunderchief work...
here is some solutions if you can't find or can't afford J201(in Greece it costs 15€ per unit so i used SK118)
the most common problem is that the third jfet doesn’t bias right with the 470 ohm resistor. I replaced it with a 10K resistor and biased again all the fets with the 100K trimpots .Sounds very good
here are the voltages of the third fet before and after replacing the 470 ohm resistor

before:

d  4.52
s  4.45
g  0.05

after:

d  4.45
s  1.00
g  0.20

I would also recommend you to use a linear 1M gain pot instead of a log…

I think SK118 is too gainy for my taste I would try another type less gainy...Any suggestions???
I have also some noise (not too much but noticeable) when the gain is from middle to max…can anyone help me to fix that???

[Eddie]

Good idea!
I will try the 10k resistor next week!
Thanks for posting it!

Eddie

[Eddie]

ok I could not wait to try it out.I tried first a 5 k resistor but i could not bias the Fets (got over 9 volts Source??). After that i tried the 10k resistor.After rebiasing all the Fets(BF245A) i got 1 Volt at the Source of the third Fet.
But I still have  the misbiased Fet sound. I think that I will order the J201 and (hopefully) quit the experiments.



BTW what are your experiences with the thunderchief?
How does it sound?Really like a Plexi/VH..?How does it compare to other pedals?Purplexed?Guvnor?

And to runoffgroove: To my knowledge Eddie Van Halen never used a speaker Simulator for recording.Just used the Palmer to get line level for effects after the PowerAmp.All the albums have a real miked
cab.

Very good site for the early VH Sound: http://www9.ocn.ne.jp/~evinda/english.html

http://www.legendarytones.com/typical_early_edward_van_halen_setup_diagram.htm

Eddie

[electrictabs]

well probably you ve done something wrong

i also had the sound of misbiased fet with 470 ohm resistor but now it sounds great. great distortion ,has lots of guts.i put it in my transistor amp and it sounds a lot tubey. But i'm a classic rocker and i'm thinking of replacing the sk118 with something less gainy...
question:
after replacing the resistor did you bias all the fets again???
if not then this is your problem...
if you did and still have problems check again your circuit for mistakes
(i know that you've done it a lot of times but believe me i have found mistakes after the 20th check in some of my circuits)
then if you still have problems use transistor sockets and throw other types in...

hope i helped you a lot

[Eddie]

I rebiased everything.I ordered the J201.
I think that this shop delivers to Greece too:
http://www.banzaieffects.de/parts/transist.htm

50 cents for one J201!Good price!

To Runoffgroove:

Is the Thnderchief a distortion pedal or a direct recording device?
Why do you included filtering "like a Celestion speaker"? :idea:
Sorry I`m a little confused.

Thanks!

Eddie

[Gary]

You can try direct recording with the 'Chief.  Actually, we've intended this to be used as an overdrive pedal, but you may find other uses.

The reason for shaping the sound is to estimate the sound of the speakers, regardless of your setup.  This circuit is intended for a clean amp.  The flatter the response of your amp, the better the 'Chief will sound.

EVH was reported to use the Palmer for live play.  Since I don't know him personally, I can't say for sure.  The thing we agree on is, he used a load box so he could turn the amp up full.  This is what we wanted to simulate so we could get an approximation of the sound without all the volume.

Check this site to see the inspiration for some aspects of the Thunderchief:
http://www.amptone.com/eddievanhalenrig.htm

I'm glad you are finding how to get the circuit working for your particular jfets.  You should find the J201 jfets will work fine.  Remember that jfets are highly variable.  You may find some that will not bias correctly, even though it is a J201 from the same lot.  Always buy more than you need and sort until you find ones that will work.