New at runoffgroove.com: Thunderchief

[Ammscray]

Excuse the stupid questions, but what amp did you guys use to prototoype this pedal with, and how did you have it set?

Second stupid question: how come you guys don't post soundclips with amps and pedals?  The convenience issue aside, how really is a pedal played through a simulator and/or preamp recorded direct supposed to give one an accurate idea how the box will sound in the "real" world?

Please no offense I just don't understand, I just have yet to hear a pedal recorded direct that sounds even remotely close to when it's cranked through an amp and the tubes are hot and the speaker is pushing air...

thanks for your thoughts

[Ge_Whiz]

I don't know about what Marshall might have tried over the years, but British transistor amp manufacturer HH were using overdriven JFETs to provide their "Valve Sound" emulation very successfully back in the late 1970s. I wish I had a circuit to share with you, because this works really well in the HH, but they jealously guarded the technology by incorporating it into an encapsulated black box called the 'Tone Correction Module'. Since MAJ Electronics bought out the rights, they manufacture spare HH TCMs and, sensibly, see no reason to share the secrets of the TCM, which appears in the service manuals only as a box with numbered pins.

If the TCM in my HH ever fails, I'll replace it and reverse-engineer the old one, but I suspect it won't contain any major surprises. It's off-on only, but sounds magnificent. Mind you, their SS amps were state-of-art in the 70s/80s. I have to say that with sounds this good, I don't need the hassle of valves.

[amz-fx]

The idea of imitating amp models has been around a long time...  that's actually part of the attraction of the Fet Muff...  you can switch the diodes in and have a harsher type clipping or take them out for a softer amp-like overdrive.

The Mini-Tubes preamp with its 2-stage or 4-stage minibooster sections was designed with tone shaping from a Marshall Lead amp for a better distortion model and high-gain sounds.

The simple jfet CS stage idea has been adapted by at least one boutique builder for a line of pedals that imitate amplifiers.

But if you look at some of the solid-state amplifiers made by Fender, Marshall, etc.,  they have in some cases used the same procedure to make a solid-state amp.  I don't have the exact models in front of me but if you trace through a couple of them you can see the influence from their tube amps.

-Jack

[Gary]

Ammscray,

The amp that I used to prototype is an old Randall RG35 SS deal.  It's the least "coloring" amp I have.  All tone knobs were set full up on the clean channel.

To answer the second question, we use cab sims to give a common reference point.  Yes, there is sometimes drastic coloring of the sound with certain amps.  There comes a point where it's hard to tell what is the amp and what is the pedal.  To avoid this, we use cab sims direct to recorder.  It's our attempt to provide an apples to apples comparison.

[Doug H]

Come to think of it- how come Marshall never did this themselves? Seems they went mostly the diode clipping route with their stompboxes, didn't they?

Kerry M

Interesting question...

I'm guessing their opamp approach has a lower parts count, for one, although I haven't sat down and counted the parts. The other issue is consistency, real important for large scale production. The CS jfet circuits sound great, but the jfet stages have to be biased individually due to variations in ea piece. This is fine for diy or even boutique/garage production, but my guess, once again, is that the labor involved here could be prohibitively expensive for a large scale production that competes with the likes of Boss, et. al.

Doug

[amz-fx]

I don't have the exact models in front of me but if you trace through a couple of them you can see the influence from their tube amps.

I found a quick example of a nice amp...  the Ibanez GX-20:

http://www.mif.pg.gda.pl/homepages/tom/files/gx20.gif

-Jack

[Doug H]

Thanks for the link, Jack. That's a nice site.

Doug

[ian87]

any word on that PCB?

[B Tremblay]

any word on that PCB?

Yes, it's now available on the Thunderchief page: http://runoffgroove.com/thunderchief.html

[ian87]

any word on that PCB?

Yes, it's now available on the Thunderchief page: http://runoffgroove.com/thunderchief.html

stoked.... placing parts order today ..... rubbing hands together in villainous fashion ....

[Eddie]

Thanks for the Thunderchief!!!
Great idea.

I built one today but i used the BF 245. I adjusted the drain voltage to 4,5 (+- 0,3 V).
I have a biasing problem. The distorted sound fades away with some crackling at the end. Like a misbiased FET.
Especially on a low gain setting, at higher gain it is nearly ok.

Could someone post the Fet`s voltages?Is the BF 245  the wrong Fet?
Or should I use a different drain voltage?


THANK YOU!!!


Eddie

[changes]

well this thing looks great...although i m new to this i want to build one...
some questions...this circuit will give you the preamplification (the tone) of a marshall super lead.right?the gain in the schematic is the distortion of the super lead?any schematic for adding an eq to this...?

does anyone know other amp simulators like the super lead...somethin like fender or vox ac30???

[Paul Marossy]

I like the name (and the way it sounds). Wasn't the Thunderchief a fighter jet from the 50s?

[Eddie]

My voltages on the BF 245 Pinouts, starting with the first, "left" BF 245:

1:
D 4,5 v
g 1,4
s 0,0

2.
d 4,6
g 1,15
s 0,0

3.
d 4,5
g 4,4
s 0,4

4.
d 4,46
g 1,146
s 0,0


Ist the gate voltage of the third BF 245 too high?


Please help me to find the mistake.
I measured all the resistors and checked the layout.


Thanks for any help!!


Eddie  :?:

[B Tremblay]

Wasn't the Thunderchief a fighter jet from the 50s?

Correct! http://www.globalaircraft.org/planes/f-105_thunderchief.pl

However, I suggested it to Gary based on a friend's story of mistaking the AC/DC lyric "done dirt cheap" for "thun-der-chief."

We figured it was a pretty bad-ass and fit the pedal well.

[Joep]

To Eddie:

Make sure you use BF245A. B & C will not work (properly).

Did you used sockets? Can you switch around with the fets, to see it this makes any difference?

Try turning the pot of Fet 3 a bit to raise the voltage to 6 or 7 volts. Does this change anything?

Bye,

Joep

[Paul Marossy]

"However, I suggested it to Gary based on a friend's story of mistaking the AC/DC lyric "done dirt cheap" for "thun-der-chief."

He he... that's funny.    Dirty deeds thun-der-chief!

[Eddie]

@Joep: I used Fairchild BF 245 A Fets. I had a look on the datasheet for the FET`s orientation. I checked it 20 times now.

If I raise the voltage to 6-7volts the sound disappears/fades away...


Thanks!

Eddie

[Joep]

No wiring mistake? The circuit is a bit complex around the 3rd fet....

Joep

[Joep]

BTW you can try raising the supply voltage to 15V. The turn-on voltage of the BF245 might be a bit to high.

Ajust all the trimmers to 7,5 now.