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Early version non-potted phaser module disassembly. Click to view larger images.

There's a lot going on there. Two different circuit boards? Thanks for posting, Mike.

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Great info and data thanks for sharing.

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Always give thanks for everyday, It may be your last so Rock On Semper Fi!!

Yes, that's sometimes called a daughter board, or a sub board. The component leads from some devices on the upper board are used to both connect the circuit and support the daughter board. They just didn't have enough surface area on a single board to fit all the required components. I believe the Flanger module is probably the most complex circuit of the set. I'll see if I have more info on that.

Notice too, they've scraped off the part numbers on the chips in effort to guard against other companies copying or reverse engineering the circuit.

After some investigation of the schematics I can confirm that the MPC phaser is extremely close to the original E-H Small Stone. Chips are the CA3094 OTA. Different layout, obviously, to accommodate the unique form factor of the MPC module, but pretty much the same circuit. Right down to the matching NPN/PNP transistor pair at the input and the "color" switch.

The phaser in the photos above stopped working a while back. It used to work fine, then one day it would not pass any signal at all. That's the reason I opened the box.

I finally got around to troubleshooting it and found that the large silver electrolytic capacitor had failed. It was shorting V+ to ground so there was no power supply voltage getting to any of the circuit. It's a 500uf/15v cap, and the phaser actually worked fine when it was removed. I did manage to find a 330uf/16v to replace it. Sounds great now.

Another MPC module saved from the trash heap!

Good job. Caps will go and it is close on to 30 years old.

If you are implying that I "copied" the circuit on the Phaser, you're right! After about 20 breadboards and noise out of this world, finally settled on the final design. The first ones done were fully potted and after potting failure of about 10%, Karp figured out that the catalyst was interacting with the a couple of the components. We changed the pot mix and fixed the failure but still had to burn in the boards prior to potting since the ICs were not stable. The daughter board gave us a little breathing room on the etch. After we went to a wave machine, there was a lot of discussion about doing another design but we finally got most all of the noise out and it was a pretty nice phaser. You'll note that that envelope is a little different on the molded white boxes. We changed the sweep point - and compromised a little 2k audio on the fold but really cleaned up the interaction of the pot ... AND killed most of the 10k hiss.

The Flanger and prototype delay is another story. I worked my butt off with Amerel trying to get production lot of the Reticon SAD 1024 bucket brigades. Reticon seemed to think that 1000 lot runs were small potatoes. I signed so many releases that you'da thought we were building Triton missles! That's a whole 'nother story.

I'm not implying anything... just comparing at the schematics!

It's a good one to copy, though! Pretty much the best sounding phaser pedal circuit of the era, as far as I'm concerned.



I'm listening...

This is great stuff!!!

I believe that we're all watching and listening for more ..............

RCSBlues

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RCSBlues

Thanks again for the knowledge you share with us. You can see that we enjoy playing around with the gear and we are wiling to learn. Thanks.

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Always give thanks for everyday, It may be your last so Rock On Semper Fi!!

From what I've seen so far; I could learn from you guys! It's hard to imagine that when I was first envolved in the brand, we, SLM, didn't have the test equipment to really determine what audio properties were being produced and there was no platform in place to gather "consumer" information. Opinion was the operative word. "I think that pickup has more mids than I like, the other one has a hole at 1.5k" ... Opinion. That changed very quickly as I did have some of the equipment to measure actual response characteristics and put some of the opinions to bed.

The SLM guitar shop really matured very quickly in the late '70s and a few of the guys there became R&D staff rather than "setup" staff. It was really fun!

I could bring in a concept, drawing/mechanical or prototype and run it through the shop and they'd either love it, hate it or mess with it and we'd determine if the design was viable.

A lot of the front end work was done at home by many of us since we were all engaged in keeping our dealer base happy and alive. Alvarez was the bread and butter of the shop and the "Electras" were the edgy cousins. We would rob R&D funds from Alvarez - sorry Gene - and stick the money in Electra, be it for finishing equipment, wood blanks etc. Now, 10 years later, I can also say that I gave away "traded" several Alvarez to guys that would get us parts or do some contract work for us on the electrics.

I'm really happy to participate and honored be part of these discussions!

Tom

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The "prototype" delay never hit production. The closest thing that we had was the Flanger module.

The bucket brigade chips were voltage suckers and SLM Electronics (Amerel) could likely have made it happen if we'd have equipped the MPC with dual supplies but there were issues with that as well.

Shortly after the MPC concept was abandoned, digital technology hit more of a mainstream. Karp hired Greg Geerling (spelling may be wrong) and he was a wizard with digital designs. He did a bunch of smaller boards - reverb, flange, delay etc. These appeared first in the Crate 40 watt DSP amps. Had we had Greg and the technology, I'd imagine that you'd see a bunch of digital MPC modules.

By that time, I was all over MIDI and trying out all kinds of different analog to digital circuits and physical transitions. I tried light optics fired at the string at the bridge, quartz inserts at the saddle and attempting all sorts of ways to speed up the response. At that time, none worked well and I decided to consentrate on other elements. Roland was already beginning to market their Fuji made guitars and I simply gave up the project.

The other production "give up" on the MPC was the wireless. I REALLY wanted this to come to reality. My vision was to integrate a wireless module. Every time I turned around the FCC would block any attempt at public band width. On one occasion, I tried a business band circuit in a Vulcan on a gig at Mississippi Nights in St. Louis and ended up listening to some foul mouthed cab driver on the landing. It wouldn't have been so bad but it was in the middle of one of Steve Lynch's solos during a clinic! I think that was strike 3 and out!

Tom