Univox Unidrive...... hmmmm.... this doesn't sound right

[Bernardduur]

Hey all!

I am busy building a Unidrive as some posts on this forum stated it ROCKED

So I had to find out myself


Now my problems; I noticed that the original scheme had no polarity marks. How should I position the 10 uF caps so it works??

Second, I checked my stuff over and over again, but my unidrive I build now sounds horrible; a huge misbiased fuzz like sound. Hmmm.... this doesn't sound right at all. This couldn't be normal. I had no 7.5k so I used a 20k and 12k in parallel; the 4k turned out to be a 3.9k. I used a 10k trimmer + 10k resistor in series for the collector of Q2...........

I use 5088's; original one had transistors with a Hfe of around 230

Where should I look first??

[Sir H C]

The Unidrive is a booster.  You could be over boosting, try turning the gain control down.  Schematic would help in telling how to place the 10uF cap.

[Bernardduur]

I used this schematic

No gain control; I used both low gain as high gain transistors.

Bias can't be gotten over 4.23V

I tried replacing the 10 uF caps with smaller ones (1 uF /  100 nF) but the problem remains

[aron]

WOw, that looks like a fuzz face with an output buffer.

[Phorhas]

Yeah, a bootstrapped fuzz face (?)

BTW, the "gain" control is the rotary switch at the input... man you made me want to build one as well and check it out

[Bernardduur]

Hmmmm.... dunno! The sound I get is not what I expected to hear

Topic about one MartyMart build one and left out the whole front unit and claims it would sound from clean boost to somewhat gritty. All I get now is a misbiased fuzz

[Mark Hammer]

That "Range" control looks odd, and oddly placed.  All it really seems to do is to alter how much attenuation occurs via the "Pedal" control, and not in any particularly useful way.  Given that pedals of that era (or any for that matter) are/were reticent to employ additional controls that didn't do anything that might increase their marketability enough to justify the extra production cost (knob, pot, machining, etc) I'm thinking that the one unconnected lug in the diagram probably goes somewhere else in the circuit.  The question is: where?  There is a reasonable likelihood that it provides some sort of tonal alteration, and that perhaps it compensates the output volume pot ("Pedal") level for what it might take away in signal elsewhere.

Keep in mind I'm just guessing here.  I would be curious in hearing from anyone who actually HAS or has used one of these.  Does the "Range" control do anything audible, and does it do anything besides change the overall volume level?  If it does NOT change the volume, but alters the tone, then clearly the schematic shown here is in error, even though it appears to comedirectly from UNivox.  Of course it would not be the first time a "factory schem" was incorrect.

[Sir H C]

The Range at the output sets the minimum volume that you can get out.  Since it is a wah-like pedal the problem is getting the pedal to stop at the minimum volume you want out, so the range sets this point.

[Mark Hammer]

Ah!  Now I get it.  Had I looked at the physical package, that would have made a great deal of sense.  I was thinking purely in terms of a standard stompbox and not a foot-treadle operating unit.

never mind!

[Barcode80]

Second, I checked my stuff over and over again, but my unidrive I build now sounds horrible; a huge misbiased fuzz like sound. Hmmm.... this doesn't sound right at all. This couldn't be normal. I had no 7.5k so I used a 20k and 12k in parallel; the 4k turned out to be a 3.9k.

i think parallel would give you 32k, would it not? that might be your problem, as 32k is way out of tolerances as a sub for a 7.5k

[Sir H C]

Second, I checked my stuff over and over again, but my unidrive I build now sounds horrible; a huge misbiased fuzz like sound. Hmmm.... this doesn't sound right at all. This couldn't be normal. I had no 7.5k so I used a 20k and 12k in parallel; the 4k turned out to be a 3.9k.

i think parallel would give you 32k, would it not? that might be your problem, as 32k is way out of tolerances as a sub for a 7.5k

Series would be 32k, parallel would be around 7.5k

[Barcode80]

hehe, that would explain 2 of my unsuccessful builds in the last two weeks, got confused

[MartyMart]

Hmmmm.... dunno! The sound I get is not what I expected to hear

Topic about one MartyMart build one and left out the whole front unit and claims it would sound from clean boost to somewhat gritty. All I get now is a misbiased fuzz

Hi, using the mods suggested in that thread really makes the Unidrive a "little cracker" !
Changing the FB 8k2 to a pot, turns it into anything from almost clean FAT boost to a nice Fuzz/OD pedal.
Mine is still in use in it's old "Wah" shell but you could easily use it as a normal stompbox with gain/vol controls.
Hope you solve the bias problem ! - worth persuing as it does have it's own special "sound"
MM.

[Bernardduur]

FINALLY, I am done

The error I could not find..... so I just rebuild mine. And yes, this thing ROCKS!!!!!! I added the input stage although I got nice results with turning the volume down. The input stage makes it easy for me to switch between guitars and variate a bit without turning the thing down.

I'm sold! I used BC547B's for trannies as the original stated for silicon ones with a low Hfe (230). These are around 300 and do sound really good

I can make a new schematic if persons like it with the right (??) orientation of the elco's

[MartyMart]

GREAT ! glad that you finally got one working correctly
MM.

[stopstopsmile]

does someone have a schematic for the modified version?  I am looking for a 1 knob dirty boost and that can get crunchy and rock and cleans up.  If someone can PM me a schematic and mods-much appreciated.

[DougH]

The rotary switch was used to select input Z for different kinds of musical instruments.

Interesting ad copy:

http://i14.photobucket.com/albums/a320/Doug_H/Other/unidrive_ad.jpg

http://i14.photobucket.com/albums/a320/Doug_H/Other/unidrive_catalog.jpg

[Bernardduur]

Anyone knows which instruments they biased these settings on?

[wlrs]

Anyone knows which instruments they biased these settings on?

It is supposed to sound like a cello.
Yes please post a schematic I would like to give it a try as well.
Thanks.
wlrs

[MartyMart]

Anyone knows which instruments they biased these settings on?

It is supposed to sound like a cello.
Yes please post a schematic I would like to give it a try as well.
Thanks.
wlrs

Well, not quite, that's a photo of Mr Page using a "bow" on his Les paul !!
It's not actually going to sound like any cello that I've heard
Input section is for connecting either guitar/keyboard etc.