ACLAM: Mocker (Vox UL Series Fuzz)

I'm a bit of a fan of some of the late sixties / early seventies Beatles fuzz sounds, so I was interested to see this pop-up.  Like the Creepy Fingers Lonely Hearts Fuzz, it's based on the fuzz section built into the Vox UL series amps.  I'm feeling a bit of déjà vu posting this, as it is very similar to the Creepy Fingers - keen to give it a try anyway.

Aclam are of course best known for their Doctor Robert, which is the normal channel of the UL.  I guess by releasing the Mocker, they're completing the family.

Schematic can be found here on PedalPCB.   

ACLAM MOCKER - VERO LAYOUT

Note: the yellow S on the layout should be a B (for bias).  The one on the left above the other bias connection.   

If you don't have BC547A transistors, just use something low-gain.  A 2N3094 will probably do just fine.  Same for the clipping diodes, just use whatever silicon diodes you have handy - the PedalPCB schematic listed voltages at about 0.6v, which is pretty standard for silicon.  Without trying them, it's hard to say what mojo the OA200 diodes provided (if any).

MOCKER VIDEO DEMO

ACLAM MOCKER ON LTSPICE

I noticed that Aclam has left the pair of bias resistors for Q2 quite small - close to the original.  On similar adaptations of this circuit, they're often increased to more familiar values.  Jext Telez has 20k/22k the Creepy Fingers uses 68k/47k 

Trace taken at the Q2 collector - the signal is pretty dirty before it hits the clipping diodes (with sweep on the bias control)

The diodes flatten things out a little and reduce the overall level slightly - apart from a bit of filtering with the tone control, not much else happens to the signal, as the last stage is a buffer

The frequency response is as expected, nothing unusual going on here - slight mid-hump on some settings, tops rolled off.

DATASHEET FOR OA200 DIODES

Aclam used some vintage silicon diodes - here's the original datasheet.   I wouldn't feel too bad if you just dropped in some modern diodes with a vaguely similar spec.   

CREEPY FINGERS: Lonely Hearts Fuzz

I do like some of the Beatles fuzz tones, and coincidentally I have a couple of Gretsch Guitars to match - so when I saw this, I thought I had to give it a try.  

It's very closely based on the preamp from the Vox UL series amps, which were used on Revolver and in some cases Sergeant Peppers.  Hence the name.

The Schematic can be found here, on Pedal PCB.

CREEPY FINGERS LONELY HEARTS FUZZ - VERO LAYOUT

Updated from V1 as it had an error - this layout (V1b) works just fine.   The 1k gate trimmer could be an external pot.  It is quite useful. 

Note that I used a different transistor for Q1, so the orientation is different to the layout above.  I didn’t have a BC319, so I used a 2N3565 instead.  

This is the signal taken from the collector of Q1 - it's dirty from the first stage.

Q2 collector, full fuzz.

VOX: UL Series Preamp

I quite like some of the guitar sounds from The Beatles Revolver album, and after looking at the Vox Supreme, I thought I might have a play with the UL series preamp.

I'm also waiting for the build docs to come out for the Aclam Dr Robert on pedalpcb as a comparison.  It's also a UL730-based pedal - I believe it's the normal channel, and they have also modelled the power amp section.  Keen to see how they have done that.

VIBRATO CHANNEL

Everything below relates to the vibrato channel on the amp, which also happens to be the channel with distortion/fuzz, which is what I'm interested in.

FUZZ / DISTORTION

Strangely there's no control to dial in the fuzz/distortion circuit on the amp itself - it was turned on by a foot switch, and you got what you got.  

The switch increases the gain of T1 & T2 (using T3 and T4 as switches), and at the same time, it ties the OA200 silicon diodes to ground or V+ to create fuzz/distortion.  I'm really not sure which way the diodes connect, as I don't know what's happening with the foot switch.  The schematic is not clear in this regard.  Either way, it all looks about the same regarding wave shapes and frequency response.  

Bypassing the distortion leaves you with a nice clean signal, not unlike the normal channel.

BOOST SWITCH

There's also a boost switch on the front control panel of the amp, but it doesn't appear to do a great deal at the output, maybe a bit of a top boost.

LAYOUT

For some reason, the mid-range control is immediately after the clipping section but before the volume control and gain recovery section (T5 & T6).  The volume control feeds the gain recovery section, with bass and treble controls at the end of the signal chain.  I'm sure they had their reasons at JMI.   This is not a master volume amp either - one volume control per channel, and that's it.

VOX UL SERIES PREAMP SCHEMATIC

VOX UL SERIES PREAMP LTSPICE

This is with a 200mv sine wave at 440Hz, with the distortion/fuzz switched on.  LTspice file is here if that's of any interest.  You may need to change transistors if you don't have the BCs in your library, but the rest should be fine.

Collector T2

Post diode clipping

Output - bass, mid and treble all set to 50%

Output - bass, mid, and treble all set to 50%   Diodes removed from the ground - which I don't believe is part of the normal switching, but I might have to give this a try.  Looks like a rather large square wave.  i.e. a solid fuzz...  

The tone controls are pretty interactive - bass / mid sweep

Mid / treble  sweep

VOX: Frank's Yer Blues Fuzz V2.0

So not strictly Vox, but perhaps it's the easiest way to label this one.  It's variation of the Jext Telez White Pedal done by Frank_NH on Freestompboxes, which is really the brilliant channel of a Vox Supreme.   

Frank made a few changes to keep the feel, while simplifying the design.

• running at 9v

• no wah inductor required 

• germanium diodes instead of germanium transistors for clipping

FRANK'S YER BLUES FUZZ  V2.0 - VERO LAYOUT

Frank also has another more elaborate Vox UL sim on Guitar FX layouts, including a vero layout.  Check it out, it looks pretty cool.