MXR/Dunlop M68 Univibe

[Big Monk]

Rare wishlist request for me. Been interested as of late in trying a Vibe with FETs in the phase section ala the P90 and reading through the literature, this seems to be partly that.

 

[Feral Feline]

A newb, I understand, but an ol' PPCB-hand such as yourself.
I guess you never saw my Wish List postal...

 

[Big Monk]

A newb, I understand, but an ol' PPCB-hand such as yourself.
I guess you never saw my Wish List postal...

To the search function!

 

[Big Monk]

Still don’t see it. Thread stands!

 

[Giorfida]

Wouldn’t be surprised if the m68 is essentially the phase 90, but with the phase shift capacitors using the unitive values (all stages different) vs the phase 90 values (all 4 the same)

 

[Big Monk]

Wouldn’t be surprised if the m68 is essentially the phase 90, but with the phase shift capacitors using the unitive values (all stages different) vs the phase 90 values (all 4 the same)

From the sound samples I’ve heard, I think it’s more along the lines of what I’ve been trying, which is what you said, but also the Univibe LFO and something approximating the Univibe preamp.

It’s got more motion and throb than just a Phaser with different caps.

If you’ve ever played a UniVibe type pedal against a “Univibed” P45/90, the difference is pretty significant.

In short, the staggered caps don’t make a Phaser have that lopsided throb. Not that the M68 stands right up there with a LDR/Bulb unit either but it’s got something interesting about it and gets close to that sound with a phase section not dependent on LDRs and a light source.

Which in the end is a bit more “future proof”.

 

[Giorfida]

From the sound samples I’ve heard, I think it’s more along the lines of what I’ve been trying, which is what you said, but also the Univibe LFO and something approximating the Univibe preamp.

It’s got more motion and throb than just a Phaser with different caps.

If you’ve ever played a UniVibe type pedal against a “Univibed” P45/90, the difference is pretty significant.

In short, the staggered caps don’t make a Phaser have that lopsided throb. Not that the M68 stands right up there with a LDR/Bulb unit either but it’s got something interesting about it and gets close to that sound with a phase section not dependent on LDRs and a light source.

Which in the end is a bit more “future proof”.

Makes sense. Definitely would be curious to see the schematics at the very least. Ehhh who am I kidding, it gets done as a project and I’m building it lol

 

[juice886]

I had an original unit at some point and wasn't impressed with a vibe depth. But maybe there is a deviation from unit to unit, who knows.

 

[Robert]

I kinda want one of these, just because, so maybe we'll have to check one out.

It also appears to be opamp based unless those are transistor arrays.

 

[Giorfida]

I kinda want one of these, just because, so maybe we'll have to check one out.

It also appears to be opamp based unless those are transistor arrays.

View attachment 70405

My guess, only by the numbering, is in the lower right you see q6-q9, as standard SMT transistor packaging, but bottom row, just right of the switch pads we have q10 which is what I’d guess to be a transistor array. The other dip components are labelled q so I’d guess your observation that it’s opamp based is correct!
Betting similar to a phase 90 then, with opamps with FETs modulating.

what got me at first was seeing the transistors starting with QQ… then I noticed bottom left corner just To the left of the switch, what looks like thru hole transistor pads (q5 maybe?), and in the upper center what looks like 4 sets of thru hole transistor pads (q1-q4 maybe)?

Makes me wonder if these are the matches FETs (I’d be curious as to how Dunlop matches for production quantities!).

But this is just my very uneducated guess- I can count on both hands how many SMT circuits I’ve tried to figure out!

Very curious to see how this traces out!

 

[Feral Feline]

Good thread so far…

 

[Robert]

MXR uses an awful lot of (arguably) bloat for bypass, LED switching, and power conditioning in almost all of their pedals.

Because of how close those transistors are to the footswitch my guess is that they're part of the switching. This is the Custom Badass 78 Distortion, for example:

 

[Big Monk]

I think the thing that interested me most about this is that the Turning a FET phaser into a UniVibe is lackluster but make a FET Univibe seems to have more potential.

And I’ve liked the clips I’ve heard so I’m sure there is wiggle room in the circuit to make it more Vibey than it already is.

Plus, future proof.

 

[Big Monk]

@Robert

Did you just buy the Univibe on my Reverb watch list for $89.99?

 

[Robert]

I did not, but I'm probably going to grab one soon.

 

[Big Monk]

I did not, but I'm probably going to grab one soon.

I might as well. I just want to play one and get a feel for it.

 

[giovanni]

I haven’t built a Univibe yet and when I do, I’d like it to be this one.