And now... the "Twender"

[majormono]

After tweaking and rebuilding some tube-amps I thought why not pack all what I
like about Fender amps in one little FET-box and see what comes out?
Well obviously I did exactly that and the result ist what I call unimaginatively
"The Twender", with a little bit of tweed, a little bit of blackface and a
*little* look at some ROG stuff...
Much to my suprise I really like this little beast quite a lot (and too bad I
don't like country-licks ;-) with all that sparkle and twangyness.
Not too bad for being "tubeless"!

If you like the fendery way why not try something alike? Maybe you're as
surprized as I am...

Take a look at the schematic if you like:


There's even a quick-done little soundfile on my site but I would urge you not
to listen to it (bad playing right after finishing it late at night, you know
... ;-).
Hey, this was real fun to build (too bad terms start again soon)!

grol
www.grol.de/diy

[stm]

Thanks for sharing this!

Looks very promising.

I like the way you implemented the presence control.

Love twangy and bright sounds too.

STM

[Marcos - Munky]

Looks interesting. I like to hear soundclips of it.

[Mark Hammer]

Neat.

Go here - http://www.ampwares.com//ffg/ - and check out the schematic of the 6G6 "Blonde" Bassman.  It has one of the more interesting control configurations of Fenders, splitting up the tone stack, or rather the tone controls, such that treble comes downstream, AFTER the middle, bass and volume controls and 2 more gain stages.

I've never had the opportunity to try one of these in real life, and I'm curious about what it might sound like at higher drives.  Like STM, I was pleased to see the implementation of a presence control, although one wonders if it is effective.  Keep in mind that the presence control in actual amps is supposed to use variations in negative feedback AFTER the output transformer to alter the production of harmonic content.  Lift one end of the feedback resistor (which would be the 27k part in the Twender) to cancel all negative feedback, and you hear a huge jump in bite and grit.  If there is no transformer to produce such added harmonic content (and remember this is a "weakness" of the output transformer) BEYOND what comes from the circuit itself, then there is not really any added harmonic content to cancel with negative feedback.  I'm not suggesting it won't produce ANY effect, but the presence control here would not likely function identically to that in the actual amp, as much as the tone stack does.

On the other hand, this does provoke some thinking about how one *could* use variations of negative feedback to adjust final harmonic content in an emulator situation.  Is there perhaps any room for using a cheap output transformer (e.g., Mouser 10k:10k) as a source of "transformer error"?

[majormono]

Well, as I said I started this thing to simply throw together several things I like about different amps... obviously the tonestack is BF based but not the "power" amp (so "Twender" might be a bit misleading ;-). I was not my intention to clone some specific model, but a complete tweed version is scheduled now.
I didn't expect the presence control to work at all but it does!
Much to my suprize the thing worked the first time I tried it and so does the presence - not too different from a "real" presence control. I don't know why it does but so it is... and to try such silly things I build this thing after all (that's what I like DIY for).

Actually it sounds best connected to a fx-return, but man that thing sparkles better than I ever hoped (even in my strange little clip ;-).
I tried it with my Boogie MkIV, Acoustic G60T and 70's AC-30 and it's different on all of them.

If you like to try it yourself I can send you the PCB layouts...

grol
www.grol.de/diy.htm

[petemoore]

You could try reducing the value of the 100k preceding the third transistor for more gainy sound. It may be possible to 'press a lower value R' across the boarded 100k resistor for a quick test.

[RedHouse]

Adding a couple low-pass filters on the back end (after neg feedback) might tame some "sparklyness" a bit, most of the ROG amp-sim's have 'em.

[majormono]

Thanks for all your ideas but actually the thing is great as it is, I just wanted to share it in case anyone could use it ;-). There is nice overdrive when gain is maxed and more ain't suitable I think.
I thought about every part before I started building and have some experience with "real" amps and was curious...
If I want a different sound I build another design instead of endless fiddling with this one (and certainly destroy it in the end, oh I know about that ;-).

The sparkle-factor is quite controllable with the presence trimpot / brightswitch and I like it the way it is (it won't suit everything though as is *is* very sparkly). Maybe later...

Just go build one and tweak the hell out of it, I'd be interested about any opinion.

[Mark Hammer]

Finally listened to the sample.  That's one terrific sound, IMO.  A little bit of compression up front (or even afterwards) would make it a killer module for just about anything with single coils.  Should I assume the top end sheen we hear is *with* the presence control turned "up" or is there more ice-pick-through-the-forehead obtainable?

[majormono]

Uh, so much praise for such a short mediocre clip ;-)
I have the presence trim between 10-14 o'clock all the time and the mid trim at 14 o'clock so there's still something to make an icepick from.

I used my cheapest guitar to record the clip (Stagg strat clone with a mix of Duncan and Dimarzio SCs), but it matched much better than my more serious guitars...
The speaker is convolved from a pro junior (10") as is the springverb.

I said I was amazed...

[george]

Hi majormono

I notice you don't use trimpots on the JFET drains to adjust for variations between J201s, like the ROG guys do.

Did you have to try a few different J201s or did it sound good first go?

Cheers

[Jason Stout]

majormono, in your schematic I see that XXX is a pot but, what does XX and X represent?

[cb]

Twackface

That's my vote for what to name it. :wink:

[majormono]

In Eagle (that's what I use) an "x" represents a wirepad so the other are in, out, switches...
I adjusted the bias with the Rs marked with an ~ for 4.5V at the drain, you have to do it for every single FET again (just don't wanted 4 trims extra so I choose the closest match after adjusting with an external pot).

grol

[majormono]

If anybody is still wondering why I called this thing Twender, take a look at is cousin still in planning: The Twinder (the name should be obvious this time - it's a 5D8 clone).
Twender was simply finished earlier but named later ;-).

Preliminary schematic:


And if anybody cares to give the Twender a try I prepared the PCB and Layout files (but please do not redistribute them unrestrained ;-):
//www.grol.de/diy/Twender-LAY.gif
//www.grol.de/diy/Twender-PCB.gif

grol