Booster +

markm · Post by **markm** » 24 Sep 2007, 22:23

I found this circuit on one of the Japanese blogs.
This thing sounds Fantastic!!

Layout;

https://i17.photobucket.com/albums/b72/ ... YOUT-1.png

Transfer;

https://i17.photobucket.com/albums/b72/ ... er_PNP.gif

Schematic;

https://i17.photobucket.com/albums/b72/ ... ooster.gif

MoreCowbell · Post by **MoreCowbell** » 25 Sep 2007, 02:05

Looks like it shares some similarities with the Keeley Katana.

(I should really check the Katana schematic before I make that statement, but oh well.)

bajaman · Post by **bajaman** » 25 Sep 2007, 03:25

nice touch with the current stage (bipolar transistor) after the second jfet

I am sure all those ROG amp sims would sound better too, with bipolars for current gain and lower output impedance drive capabilities, after each fet stage.
bajaman

DougH · Post by **DougH** » 25 Sep 2007, 11:18

John Greene ?!?

bajaman · Post by **bajaman** » 25 Sep 2007, 11:28

he must have moved to Japan

jg · Post by jg » 25 Sep 2007, 12:55

DougH wrote:John Greene ?!?

https://www.diystompboxes.com/smfforum/ ... ic=56303.0

DougH · Post by **DougH** » 25 Sep 2007, 13:30

Ok, so you reversed it from the PCB. Gotcha...

Amazing- I could actually access that thread. Most of the diystompboxes threads you guys link I cannot access since I don't have my acct anymore. Since I'm not a member I can't search or whatever. Funny how that one worked.

jg · Post by jg » 25 Sep 2007, 13:46

DougH wrote:Ok, so you reversed it from the PCB. Gotcha...

Amazing- I could actually access that thread. Most of the diystompboxes threads you guys link I cannot access since I don't have my acct anymore. Since I'm not a member I can't search or whatever. Funny how that one worked.

markm · Post by **markm** » 26 Sep 2007, 02:49

Sorry guys, guess I threw you off a bit with that one!
Interesting comment about the BiPolar Trans in there Steve, perhaps it woud be worth adding something like that just to see what it would do to an ROG build?

jg · Post by jg » 26 Sep 2007, 03:09

markm wrote:Sorry guys, guess I threw you off a bit with that one!
Interesting comment about the BiPolar Trans in there Steve, perhaps it woud be worth adding something like that just to see what it would do to an ROG build?

?
Steve? Bipolar Trans? wut?
You just really threw me off...

markm · Post by **markm** » 26 Sep 2007, 03:15

bajaman wrote:nice touch with the current stage (bipolar transistor) after the second jfet
I am sure all those ROG amp sims would sound better too, with bipolars for current gain and lower output impedance drive capabilities, after each fet stage.
bajaman

Sorry John

Q3 in the schem!

jg · Post by jg » 26 Sep 2007, 03:36

markm wrote:
bajaman wrote:nice touch with the current stage (bipolar transistor) after the second jfet
I am sure all those ROG amp sims would sound better too, with bipolars for current gain and lower output impedance drive capabilities, after each fet stage.
bajaman
Sorry John
Q3 in the schem!

AH! And Bajaman's first name must be Steve?(my biggest confusion)
But I don't think it's really a 'current' stage since it is a PNP configured for gain but yet is providing feedback into the FET. But I think it is positive feedback. So, it is wandering into the fields of instability, nice place to be but probably very sensitive to component selection, would be my guess...

bajaman · Post by **bajaman** » 26 Sep 2007, 10:45

It is a modified version of the infamous antisymmetric pair configuration, using a fet instead of an npn transistor. This circuit was very trendy in the early 70s but did have a tendency to be a wee bit unstable though.
Nevertheless this is an interesting circuit snippet and is worthy of further investigation and analysis - it could be very useful in better emulating triode valve characteristics on low voltage (9v) supplies. It is certainly a huge improvement on just a single j201 fet stage.
bajaman

ps: thanks John and mark for bringing this little gem to our attention!!!

bajaman · Post by **bajaman** » 26 Sep 2007, 11:36

Hi folks
I ran that fet /pnp snippet through my simulator - it performs just like a unity gain high impedance buffer - signal is in phase too, but no overall voltage gain whatsoever - just an elaborate high impedance input buffer stage with a low output impedance. I will have a hunt through my old notes from the 70's and post a suitable voltage gain antisymmetric pair when I find it.
cheers
bajaman

Post by **modman** » 13 Oct 2007, 21:35

bajaman wrote: ps: thanks John and mark for bringing this little gem to our attention!!!

Thanks for the explanation Baja.
I'm still wondering where this originally came from: DIY or Boutique origin? It's remarkable at least on the level of originality...

Should consult our Japanese members!

N0F1 · Post by **N0F1** » 03 Nov 2007, 16:23

I think there might be a similar fet/tranny arrangement in the marshall bluesbreaker II from 1998, except it's an NPN instead of the 3906.

Looks like in the mind of the marshall designer(s), that circuit emulates a cathode follower to drive the tonestack (think bassman/JTM45 circuit).