UNIVOX UNIDRIVE build report/rant !!

[MartyMart]

http://diystompboxes.com/sboxforum/viewtopic.php?t=19321&highlight=unidrive

The schem is in this post above.

This rivals the "Jordan Bosstone" ... I'm totally blown away with this little
circuit, it's a 10/10  

I didn't find much posted about this one, odd looking setup but here's
what I changed/discovered :

Ditched that whole "reistors/multi pot" front end - after all, I don't need to
connect to "a piano/hammond/trumpet/cassette tape" etc etc ...
Just went straight in via 1M to ground instead of the 220k to ground, no
pot needed as there's one on every gtr !

The back end looks like volume, but is a "gain/drive" pot coming off the
8k2 link from Q1.
The point of the 10k pot going to ground via the wiper of a 2k pot is lost
on me, so that went, I just used a 50k pot as "normal" wiper to jack and
lug 1 to ground.
Transistors:
My guess is any "medium/high" gain NPN's will work, I went straight to
a pair of 2N5089's Q1/Q2 and an MPSA18 for Q3.

Resistors:
There are two "odd" ones, the 7.55K and the 4K emitter resistors, I used
a 6k8 and a 3k9 for these, also used a 20k trim pot for Q2 from 9v.
Every other value was preserved for resistors/caps
All the 10uf's are 50v electro's and the "50uf" is a 47uf/50volt electro

SOUND:
With the 50k gain pot low, nice almost clean drive - not like a "fuzz" at
all - more like a low gain TS-9 sound.
At higher settings this thing comes alive, sound is a mix between a Jordan Bosstone and a "Blackfire" !!  HUGE !! and bright and full  

SUMMARY:
GO BUILD THIS RIGHT NOW !!!
Try my small changes, you WILL NOT be dissappointed  
:twisted:
( I hope this doesn't come over like a bad "Harmony-Central" review, I'm
just VERY excited by this one, it really is THAT GOOD )

Marty.

[nelson]

you submit a new fuzz build report every three days....how many fuzz pedals does one man need?




























sounds good though, well worth a look, I only have MPSA13 so I will give them a go....

[PharaohAmps]

I actually have a vintage Uni-Drive around the shop somewhere, and it's a truly killer pedal.  The only thing that's kept it off the pedalboard until now is that large foot pedal enclosure!

The 10k / 2k resistor combo is part of the rocker pedal setup.  The 2k pot lets you "preset" the heel down volume, and you get full volume with toe down.  No reaosn not to use a 10k pot by itself there if you want to.

And the back end _is_ a volume control.  The 8k2 resistor is for feedback to the first transistor, probably to keep it from oscillating.

Matt Farrow

[MartyMart]

you submit a new fuzz build report every three days....how many fuzz pedals does one man need?
sounds good though, well worth a look, I only have MPSA13 so I will give them a go....

NOT TRUE !!!  
I've been away for a week, and was working flat out for 8 days before
that ....... !

I guess I'm just getting quick, it only took 1&1/2 hrs to build it !

Totally worth building, though mine is not a "fuzz" sound at all

Perhaps my 50k out pot has changed things, but it doesn't do much of a
"volume" increase, only the last 10%, the whole range seems like "gain"
to me  ??

Marty.

[AL]

Glad you're excited about it... now, where is that schematic exactly? There's a link to the Fuzz Guts page which has a few Univox pedals but no Unidrive. Am I missing something? It's early and I haven't had enough coffee.

AL

[MartyMart]

http://diystompboxes.com/sboxforum/viewtopic.php?t=19321&highlight=unidrive


SORRY !!
Here's the correct link, I'll put it up top also  

Marty.

[AL]

Ahhhhh !!!! Thank you

AL

[petemoore]

I see a "FF". Third transistor and two feedback loops...definitely interesting topology there...
 The front end is for sales to those who couldn't swap input caps/ use with different guitars/bass I think. one, or a selection of two cap values there'd do me.

[Arn C.]

Marty,
  Did you just use a 50k pot or  a pedal with a 50k pot?

Thanks!
Arn C.

[MartyMart]

Marty,
  Did you just use a 50k pot or  a pedal with a 50k pot?

Thanks!
Arn C.

For now, it's just a 50k pot I do have a "crappy" wah which I might use
the case for this, but it works well "set" like a normal OD pedal and will
"clean up" quite well rolling back the gtr vol pot so ........ ?

Pete :
I't's more akin to the "coloursound OD" than any type of "Fuzz" - unless
you put in some NPN germaniums of course  :wink:
It is a "Unidrive" after all !!
Don't get the use of all those input resistors, just "level" control ??
A BMP tonestack/Superfuzz notch would make it even more "fun"

Definate "keeper" and will be on the pedal board quite a lot I think

Marty.

[barret77]

hey, post a simple sound clip if you have a chance... I'm curious on how it sounds...

[Arn C.]

Thanks Marty!!!!      


Arn C.

[brian wenz]

Hello Hello---
     Jeez Marty, I was just thinking that you don't build ENOUGH fuzzes!
This is interesting......I've had this schematic for years and never built it.
Is  the MPS 18  higher gain then the 5089??   [Just wondering if the "higher gain in Q3"  relationship needs to be observed for this circuit.]
Brian.

[nelson]

the MPSA18 is a darlington NPN, V high gain.

good for ampeg scrambler clones...

[MartyMart]

Hello Hello---
     Jeez Marty, I was just thinking that you don't build ENOUGH fuzzes!
This is interesting......I've had this schematic for years and never built it.
Is  the MPS 18  higher gain then the 5089??   [Just wondering if the "higher gain in Q3"  relationship needs to be observed for this circuit.]
Brian.

The MPSA18 is probably overkill ! It's a VERY hot output !!
I'm busy 'til monday, but I'll get a sound clip done then and also try some
less "gainy" transistors, at the moment it's breaking up my amps a bit
which is adding to the "crunch" some what !!!  :shock:

BC549's or 2N3904's/2N5088's may be a better bet.
If someone has time over the weekend, please build one and tell me how
you like it ?

Marty.

[PharaohAmps]

It really doesn't matter what the last transistor is, with regard to hFe.  It's used here as an emitter follower and doesn't provide voltage gain, only current gain and a low-impedance output.  If you want higher gain from this circuit, use your MPSA18 for Q2.  Q3 could be a 2N3904 or 2N2222 with no real effect on the sound or response.

The sound of the vintage unit I have is NOT fuzzy at all - it's a fairly clean boost with some hints of transistor overdrive.  It's really designed to pummel the preamp of a tube amplifier into submission, and it does a great job at that.

For folks who'd like to clone this in a non-rocker pedal format, I'd say:

Ditch the rotary switch up front, change the 220K to a 1M, change the input cap to a 1uf NP (if you can't get a 1uf NP, then a .1 film or poly cap would work, don't use an electro on this one.)

The 7.5K resistor can be replaced with a 20k and a 12k in parallel.

Ditch the 2K pot, just run the 10k pot's 3rd lug to ground.

One knob, no waiting.  A super-loud boost that sounds great and will crunch up your amp with no complaints.

Matt Farrow

[MartyMart]

Thanks Matt, that's about what I have, I guess that using 2x2N5089's is
giving me that extra "crunch" to the circuit - which I like BTW
I'll ditch the first electro on monday and use a 1uf NP poly cap.
I can't detect any "noise" though at present, its very quiet !

It does "blast" my valve amps in a VERY nice way !!
Could a "Fuzz" pot be added, a bit like a FuzzFace arrangement ?
That would give some nice control around Q1/Q2   ?

Marty.

[bass_econo]

soundclip soundclip soundclip!!!

[vortex]

Thanks for the heads up Marty!

I just built the Unidrive using Matts suggested substitutes and 2N5089 trannys. This is a ballsy booster! Very nice bite and definition to the notes, scary amount of boost. No fuzz to speak of.

I am testing it out on my Boss VF-1 modeling preamp tonight but hopefully will get to crank it up with an amp tomorrow. I am certain the preamp tubes will get a surprise.  

A very cool circuit ... thanks Marty and Matt!

[petemoore]

For the caps marked 10v, I'd use 16v or 25v....
 The input and output caps at 10uf are quite large, and should pass bass guitar source inputs N/p.
 Have you Tried smaller ones for less bass ?
 That whole input thing is like a big ol volume [input gain] pot made from fixed resistors. It looks like a rotory switch would be used, I'd replace that with a 'rotory' pot, or eliminate it...maybe just insert series resistance there.