Resurrecting the MacBeth Elements Synth

[Markyboard]

For those not familiar this is the MacBeth Elements synth - version 1:

 

 

 

Ken Macbeth is well known in the modular circles for his highly prized modules and a couple of larger format semi modulars. He also developed the Micromac - D, his clone of a mini which sounds phenomenal (just ask Carlo). He then designed and hand built just over 100 of these Elements back in 2015ish in which he actually took on the assembly part himself in his apartment after his outsourcing fell through. It's a wonderful sounding 3 oscillator mono that barely qualifies as a semi modular. But still this thing sounds incredible and is the true essence of the word boutique with a price tag to match. Version 2 followed 2- 3 years later sacrificing midi for individual VCO CV outputs and a few other desirable features.

 

But 5 years later there's a problem; there are no schematics, no documentation (he never even wrote a user manual) and repair shops have no clue based on what I've read from other owners with problems. On top of that Ken Macbeth has left the building (literally) and is no longer reachable on FB for those that used FB to correspond with him in the past. Rumor has it he went off to make wine although another recent rumor indicates he's coming back at some point.

 

My Elements started acting up a couple of months ago where VCO1 would continuously drift and never stayed on one pitch for more than a few seconds at best. While I can fix most analog synths I need schematics and so this is the moment I had been dreading. I really had no clue whether I would encounter unrecognizable or un-labeled parts and be able to fumble my way through. Turns out after opening the unit a couple of weeks ago it uses all common discreet parts; no CEMS, SSMS or anything fancy other than standard transistors, op amps, resistors, caps etc.

 

This was a relief but after a few wrong guesses I was back to now what I do? Well the answer was reverse engineer the VCO board. I had no idea how time consuming this was since I've never had to do it. I had to learn KiCad, a schematic capture tool (and more) that was very frustrating to use at first. I even tried another program but quickly returned to KiCad realizing there's a learning curve to this - deal with it. After a couple of days I started to get the hang of it and it got easier and faster as I went.

 

"Buzzing out the connections" is tedious and easy to make a mistake. Even easier to miss a connection. I was constantly back and forth between buzzing out a few connections at a time and going to my computer to capture the latest. Even with the right connections laying it out on a schematic into recognizable circuits is challenging. However 9 days later I had a schematic - of the VCO1 path only! Fortunately VCO2 and VCO3 follow the same architecture with some of their own unique features and routing between them and the filter board., I'll worry about that when/if the need arises.

 

 

And no, I will not be putting the rest of the schematic on line unless Ken says it's OK (highly unlikely). Anyway once I had the schematic in hand it was easy to fix the problem I caused when I blew out a CA3083 transistor array . Soon after I discovered the source of the drift was a flaky VCO1 frequency pot. The thing is no amount of exercising that pot changed anything and the problem was there over the entire frequency range. Well live and learn.

 

Here's the VCO board:

 

 

This is the signal that controls the frequency. Notice the fluctuations which are very small (20mV scale) but enough to cause havoc.

 

Here's the identical signal used by VCO2:

 

 

After isolating the problem to the pot itself (last thing I suspected) I was able to swap with VCO2 and confirm that VCO1 was stable and VCO2 was now drifting. I sprayed Deoxit into the pot case opening, worked the pot a bunch and now no more drift. Still I ordered replacements just in case.

 

Well that's it. Assuming I can get this thing back together .

[mate stubb]

Ken's stuff always sounds great. That's such a cool synth!

[Ockeghem]

Elementary, my dear Watson. â Sherlock Holmes

Easy for you, difficult for me.â Señor Wences (?)

(subsequently quoted by Alan Hale aka 'Skipper' on Gilligan"s Island, Mel Blanc aka Speedy Gonzalez, others?)

[Marzzz]

Sometimes I wish I had majored in EE.

[ProfD]

For those not familiar this is the MacBeth Elements synth - version 1:

 

Well that's it. Assuming I can get this thing back together .

Brotha Mark, there's no doubt in my mind that you will be able to put MacBeth back together just fine.

[Markyboard]

For those not familiar this is the MacBeth Elements synth - version 1:

 

Well that's it. Assuming I can get this thing back together .

Brotha Mark, there's no doubt in my mind that you will be able to put MacBeth back together just fine.

 

Thanks Prof. I have been discussing with a fellow owner/user up in Maryland on getting those vernier dials for the VCO frequency controls lined up right and matching each other. He had a hell of a time and warned others on GS several years ago. Turns out he disassembled the vernier mechanisms when he didn"t need to and I think that was most of his problem.

 

I"ve got mine almost fully assembled now since last posting and no problems.

[Paolo Di Nicolantonio]

Glad you found the source of the problem, Mark! Aaah, the joys of analog synths. On a semi-related note, I noticed the Macbeth website altogether seems to be gone as well, at the moment https://www.macbethstudiosystems.com

[Markyboard]

Thanks Paolo. Had to open it up again for a quick reverb tank fix and a fine cal adjust today but all good now. Interesting that his website is gone. On the other hand this is his first web update in 7 years.

[nursers]

Sometimes I wish I had majored in EE.

 

Agreed - I admire the hell out of people that can do this - even you Mark

[Markyboard]

Ouch!