Jarman phase-master ever seen one? Pics inside

[John Lyons]

A friend of mine picked this up at a yard sale.
It sounds similar to my Easyvibe, but better!
It looks like an early 70's unit.






There was an input at the front which got moved to the back.
The Speed knob is switched to turn the unit on as well as vary the speed.

The Transistors are 2N5952 for the four in a row and the top left transistor is a 2N4126.
The other transistor is obscured and seems like a house number Z0211??
The caps in a row are all .05 (503)
It sounds really nice!

Anyone seen/heard of one of these before?

John

[Mark Hammer]

Would I be wrong in thinking that the differences between this unit and an MXR Phase 90 are pretty close to....um... negligible?

To whit:

• 2N5952 FETs for control elements
• 4 stages
• 22k fixed resistors in parallel with FETs
• 10k input/feedback resistors and .05uf caps in each stage
• six 741s
• 150k mixing resistors and PNP mixing tranny in output stage

[StephenGiles]

No you would not Mark!

[John Lyons]

I'm pretty green when it comes to phase circuits....
Is the main difference in the Easyvibe/univibe/neovibe etc the caps in the different stages?
Is that were the "wobble" come from?

John

[Mark Hammer]

What you have there is a "phase shifter".  This differs from the "vibes" in that the distribution of phase shift across the spectrum is approximately equivalent across the stages in a phase shifter, and discrepant across each stage in a "vibe".  The result is that any notches created in a vibe are broader, shallower, and less focussed.  The lack of focus to the notches and peaks has a different impact on the listener's attention, by not drawing attention to the notches and peaks.  This adds a kind of background shimmer to the effect instead of telling the listener "Hey! Now the notch is HERE....and now it's HERE!".

Where phase shifters show interesting and pleasing effects of varying resonance using feedback from the output back to the input, vibes do NOT.  Never seen one using a regen/feedback/resonance control, and probably never will.  While the P90 did not have an overt resonance control, it DID provide some moderate feedback from the output back to the input, with the earlier model providing less.  Because I imagine this Jarman thing mimics the early script  P90 with less resonance, that probably why it strikes you as being like a vibe rather than shifter.

[markm]

Ha Ha!!
Either way that this is COOL! 

[John Lyons]

Thanks for the Rundown mark H
I was a bit bummed on the Easyvibe as it seems a bit limp in the depth of effect. It's just not getting the impact that I've heard in recordings or the univibe and neovibe. The Jarman gets pretty close to that psychedelic vibe thing.

Would changing the caps to unequal values such as the univibe creat a similar effect?

How does the Phase 100 compare to the phase 90? (in your opinion)

John

[Sir H C]

Would guess it is from 1974 from the date codes on the ICs.

[Mark Hammer]

Unequal cap values is a major part of the vibe "vibe", but it would seem there is a little more to it than that.  My understanding is that the form of the sweep is a little different, or needs to be so.  I imagine part of that may be because of the different optimal LFO waveform requirements for slower (which vibes never use) and faster (which they do use) sweep speeds, but another part may well be (and this is only an idea not a rule) because the sort of sweep that sounds more interesting when the notches and peaks are very focussed and evident is not the sort that sounds interesting when the dips and bumps are broad and diffuse.

Note as well that, because LDRs are difficult to match, caps have wide tolerances, and the light-source-to-LDR axis is difficult to hold constant across 4 units unless one uses optoisolators, optically-based vibe units are sort of hit and miss, and also subject to variation over time if you have a couple of LDRs wobbling about inside the box.  Don't know about what you're using, but the leads on mine are easily bent, and it is a simple matter for one to be bumped off axis upon installation of the bloard into the box.  Again, remember that you aren't aiming for replication across stages of what you see in one stage, but rather a spread or stagger.  So how do you assure the degree of mismatch time after time?    That's a toughie.

The P100 has 6 swpet stages and 4 fixed ones, plus two width and regen settings.  It is also optical rather than FET-based which lends itself to a cleaner sound.  With more notches, and a little bit more of a number of other things, it is not an easy comparison.  A bit like comparing an MGB and minivan.

[John Lyons]

Yes, It seems that between matching FETs and aligning bulbs and LDRs is the magic in getting these things to sound "correct".

Here are a couple uninspiered clips of the Jarman Phase-Master

Clean through a fender twin reverb Les Paul neck PU
www.mrdwab.com/john/Jarman_clean.mp3

Bridge PU les paul > Fat Gnat OD> Jarman> Slighly distorted marshall.
www.mrdwab.com/john/Jarman_fatgnat_marshall.mp3

John