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Dr Gris
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Post by Dr Gris » Wed Dec 05, 2018 2:51 pm

I'm no EE but from my preamp racking days the trickiest part was to get minimum magnetic influence on my input transformers.
If they were tube, you also had the heater wiring to think about (elevated or not), although you can do it with DC.
Most of the times an external PSU worked best.
Also, most of the modular PSU's I see here don't use toroidal core transformers that supposedly emits less stray than El core.

Interesting that the UTC transformers "only goes down" to 200 Hz, that's not very low.
Of course they will produce sound lower than that, but I wonder if they feel "weak" in the bass registers?

//M

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CZ Rider
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Post by CZ Rider » Wed Dec 05, 2018 5:37 pm

Dr Gris wrote: Interesting that the UTC transformers "only goes down" to 200 Hz, that's not very low.
Of course they will produce sound lower than that, but I wonder if they feel "weak" in the bass registers?

//M
Always wondered how much the transformer choice affected the frequencies the ring modulator can produce.
The original Harold Bode ring modulators use UTC A-20's. These are rated at 10Hz to 50K Hz. Bob Moog also used the A-20 for mixing transformers in his polyphonic oscillator bank and the 700 series percussion modules. Definitely high quality transformers with shielded enclosures.
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noddyspuncture
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Post by noddyspuncture » Wed Dec 05, 2018 6:36 pm

CZ Rider wrote:Bob Moog also used the A-20 for mixing transformers in his polyphonic oscillator bank and the 700 series percussion modules.
Hi Terry,

I'm intrigued as to where you found this info...?

Reason I ask is because my 701's or 702's didn't have any transformers in them..!

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Post by CZ Rider » Wed Dec 05, 2018 9:27 pm

noddyspuncture wrote:
I'm intrigued as to where you found this info...?

Reason I ask is because my 701's or 702's didn't have any transformers in them..!
From studying Bob's schematics and various photos.
There would be only one A-20 transformer at the final output. The function of the transformer being mixing the many 700 series module audio outputs together.
Can see here in Bob's hand drawn 701 schematic, top right the penciled in transformer. Labeled "outputs" at pin 20 and 21.
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Can see the single A-20 in the back of the Eric Siday 700 series system. Right side in the middle of the rear photo.
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A BMF posted schematic of the polyphonic oscillator bank shows how Bob wired these up. The 61 oscillator outputs +/- are all tied together to the A-20. The oscillator outputs are hot at +/- 11.5 volts each and would short out if connected to any audio. Would guess the 700 series are very similar with hot outputs ment to use the A-20 as a mixing transformer.

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Eric Siday commissioned Bob to custom build the 700 probably late 1967 to early 1968. Can only guess Eric needed several percussion sounds simultaneously and purchasing five or more Moog systems was not an option. He had one large system. So Bob shrunk down the basic elements needed in a cost effective package and created the 700 series for Eric and a way to trigger them. Bob built one of the first electronic drum/percussion machines. I imagine at that time Eric needs this machine kept as a trade secret, so no one knows of it's existence until years later. Bob never gets credit for creating one of the first drum machines. But Eric's recordings prove otherwise.
Bit of Moog history. :mrgreen:

PS: Back OT, here is an original R.A.Moog made ring modulator for the modular systems. It is pasive as all the extra functions on the Bode model can be patched via existing modules. Just a pair of A-20's and 4 germanium tophat diodes with balancing pots. 2 inputs 1 output. Very old school.
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Post by jjsynth » Thu Dec 06, 2018 3:16 am

I too have a Synth-Werk Ringmod and I also have the 50Hz hum problem. Gerhard advised me to shield my power supply with mu-metal foil. I'm using a synthesizers.com power supply and his assumption was that the magnetic field of the transformer causes this. I have placed the ring mod farthest away from the power supply with dubious success. I will try to replicate Johns experiments.
:hmm:

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noddyspuncture
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Post by noddyspuncture » Thu Dec 06, 2018 6:57 am

CZ Rider wrote:
noddyspuncture wrote:
I'm intrigued as to where you found this info...?

Reason I ask is because my 701's or 702's didn't have any transformers in them..!
From studying Bob's schematics and various photos.
There would be only one A-20 transformer at the final output. The function of the transformer being mixing the many 700 series module audio outputs together.
Can see here in Bob's hand drawn 701 schematic, top right the penciled in transformer. Labeled "outputs" at pin 20 and 21.
Thanks for the reply Terry..!

I had actually noticed all those points you listed. Spotted the T/X on the schematic and also the T/X in the Paris museum photo.

When I got my 701's running I did indeed use a transformer on the output - that schematic is actually for the 701. I experimented with a few small transformers until I found one that worked.

There isn't really any place inside the 700's for a T/X - especially one as large as the A20 - unless it was "suspended" between the two compartments, but there are no signs of any provision for that. So they must all have been mounted outside in the rack..!? Actually, thinking about it, that makes sense because the outputs feeding the T/X do appear on the rear connector..!

The 702's I have were incomplete and in completing them I assembled circuits as a result of my google-ing - so transformers weren't needed. Would like to know what the exact circuitry should be in the missing halves of my 702's..!

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Notron fn
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Post by Notron fn » Sat Dec 08, 2018 10:36 am

I snagged a SW 6401M off of facebook several months ago.

I guess I'm lucky--or I just slotted it far enough away in my case from the PSU. No hum here.
Insert pithy statement here

JohnLRice

Post by JohnLRice » Thu Apr 18, 2019 2:16 am

jjsynth wrote:I too have a Synth-Werk Ringmod and I also have the 50Hz hum problem. Gerhard advised me to shield my power supply with mu-metal foil. I'm using a synthesizers.com power supply and his assumption was that the magnetic field of the transformer causes this. I have placed the ring mod farthest away from the power supply with dubious success. I will try to replicate Johns experiments.
:hmm:
Did you have any luck re-positioning your ring modulator to avoid the hum, jjsynth?

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Post by jjsynth » Thu Apr 18, 2019 2:56 am

Yes, I did three things:
- I did what you did: mount it upside down. Now the metal case faces the power supply.
- I mounted the power supply in a new position so that the transformer is now parallel to the ring mod.
- I tried to add additional shielding. I'm not sure, whether this helped, but it didn't seem to hurt either....

JohnLRice

Post by JohnLRice » Thu Apr 18, 2019 3:19 am

jjsynth wrote:Yes, I did three things:
- I did what you did: mount it upside down. Now the metal case faces the power supply.
- I mounted the power supply in a new position so that the transformer is now parallel to the ring mod.
- I tried to add additional shielding. I'm not sure, whether this helped, but it didn't seem to hurt either....
Ahh good, I'm glad you got it resolved or at least improved enough to be usable! :tu:

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synthetic
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Post by synthetic » Thu Apr 18, 2019 6:34 pm

The Synth-Werk isn’t in a big metal shielded box like the rest of their modules?

JohnLRice

Post by JohnLRice » Thu Apr 18, 2019 7:08 pm

synthetic wrote:The Synth-Werk isn’t in a big metal shielded box like the rest of their modules?
Yeah but it's open on one side. I don't know if that's why flipping it upside down helps in certain situations or if it's just the general positioning of the transformers or other sensitive parts?

If the metal enclosure is helping shield things, maybe at least for the ring modulator and maybe the FFB it would be a good idea to have them completely enclosed?

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synthetic
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Post by synthetic » Thu Apr 18, 2019 9:27 pm

The front panel says "Programm Input?" I wanted one until just now.

JohnLRice

Post by JohnLRice » Thu Apr 18, 2019 10:42 pm

synthetic wrote:The front panel says "Programm Input?" I wanted one until just now.
:eek: :lol: I don't think I ever noticed that! I just went into the other room to check mine and it is spelled that way too. :hihi:

But it appears that the spelling is correct for the German language so it's cool. 8-) More info here:
http://baxtercommunications.nl/is-it-pr ... LlC--hKhPY

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josaka
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Post by josaka » Thu Apr 18, 2019 11:36 pm

...you would possibly think they might have noticed if it was an error.. :) :deadbanana:

JohnLRice

Post by JohnLRice » Thu Apr 18, 2019 11:55 pm

josaka wrote:...you would possibly think they might have noticed if it was an error.. :) :deadbanana:
Well, there have been panel labeling errors that have slipped through before with more then one manufacturer I can think of so it's not unheard of. :hihi:

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CZ Rider
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Post by CZ Rider » Fri Apr 19, 2019 4:04 pm

JohnLRice wrote:Well, there have been panel labeling errors that have slipped through before with more then one manufacturer I can think of so it's not unheard of. :hihi:
A continuation of tradition? Back in the summer of 1969, when Bob and company were cranking out modular instruments in Trumansburg, NY. This one slipped by.
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My CP7 panel reads "ENVLOPE". :hmm:
Interestingly I found another CP7 from 1970 that has the correct spelling.
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Certainly makes it unique. :hihi:

JohnLRice

Post by JohnLRice » Fri Apr 19, 2019 7:57 pm

Other's that come to mind:

There was a Synth Tech module that had a "Coarse" pot labeled as "Course" but I can't remember if it was a MOTM, FRAC, or Eurorack module and if it made it to production or if it was just an error on the pre-production rendered image.

The initial run of the Modcan 40B VCF had the resonance attenuators labeled "0 - 0 - 10" instead of "0 - 5 - 10"
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The first Krisp1 MU run of the Oakley Croglin VCF had the "Duality" pot labeled "Durality".
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The first (only?) run of the Encore Electronics MU version of the UEG had the Linear and Log graphics for the Slope switch reversed:
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