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Moog 701 drum synthesizer - success..!
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Author Moog 701 drum synthesizer - success..!
noddyspuncture
Hi folks,

When I first powered these modules up one kept blowing fuses. It was wired incorrectly, with +12v connected directly to ground..!

So - after a few years of just looking at these Moog 701 drum synthesizer modules... and only ever making a couple of videos of them 'singing away' uncontrollably - but at least I knew that they made *some* noise... I have finally sat down and looked at them in depth.

First I had to build them their own dedicated power supply as the only other one I have is in the Modular. I have drawn out the circuit layout, and from those, the circuit diagrams. I've analysed the workings so to speak and got my head around them. Originally in my previous videos the filter and the envelope generators for both the filter & VCA weren't doing anything.

Bearing in mind the earlier incorrect wiring I found, I investigated and found two more things... the first was a faulty transistor and once I had the EG's doing their thing on my oscilloscope I found that the VCA was still not being controlled. The filter was now being opened and closed - but the module was still sitting there, merrily singing away. The problem, I hate to say, turned out to be what I reckon is a design fault...! The VCA on these things just doesn't shut off.

I trawled the internet for transistor based VCA circuits and found a lot... all basically designed differently to the ones in these modules. So I built my own transistor based VCA going off the designs I found - and now it all works...!

I've played around with the unit and it does some interesting things using just it's own internal oscillators. There are rear connector inputs for white, pink & red noise. I've yet to hook it up to some noise generators - which is where it should really come into it's own... w00t!!

Cheers,
Tom


JohnLRice
Congrats on getting them working! thumbs up I like your "cloud prototyping" too! I've done that before, adds excitement to the adventure! hihi
noddyspuncture
JohnLRice wrote:
Congrats on getting them working! thumbs up I like your "cloud prototyping" too! I've done that before, adds excitement to the adventure! hihi


Thanks John,

By the way here's my first video of it I made tonight... still need to patch in some noise... that'll be the next thing, but for now... hihi



Cheers,
Tom
Dave Peck
Well look at that. I don't think I've ever seen one of these before.

The fact that it's made using hand-wired perf board instead of an etched PCB would indicate it's some kind of prototype or perhaps a released product with an extremely limited production quantity.

How rare is this thing??
noddyspuncture
Dave Peck wrote:
Well look at that. I don't think I've ever seen one of these before.

The fact that it's made using hand-wired perf board instead of an etched PCB would indicate it's some kind of prototype or perhaps a released product with an extremely limited production quantity.

How rare is this thing??


Dave, here is some info I found when I first came across these...

http://olivier-grall.yusynth.net/Moog%20drum%20synth/page%252520moog%2 52520drum.html

Apparently there were only a handful made, and never went into production so you cannot really get any rarer... hyper

Cheers,
Tom
JohnLRice
eek! Wow, sounds great! I don't know about drum/percussion use but I would definitely enjoy making some "end of the world" drones with that! hihi SlayerBadger!
noddyspuncture
JohnLRice wrote:
eek! Wow, sounds great! I don't know about drum/percussion use but I would definitely enjoy making some "end of the world" drones with that! hihi SlayerBadger!


It's the noise element that is yet to be added John. These were never meant as a stand-alone drum synth...!

With either white, pink or red noise and the envelopes set to snappy... I think we will finally hear Bob Moog's definitive 1969 electronic drum sound... applause

And I agree - it makes a fine effects machine as it is. Endless, massive sound effects just pour out of this thing and those little oscillators are fat...!

Cheers,
Tom
noddyspuncture
Here's another video I made of this module...



Cheers,
Tom
Dr. Sketch-n-Etch
That thing sounds awesome. The old Moog stuff always sounds unique, and this is no exception. Are there schematics anywhere?
noddyspuncture
Dr. Sketch-n-Etch wrote:
That thing sounds awesome. The old Moog stuff always sounds unique, and this is no exception. Are there schematics anywhere?


I think the only schematics are the ones I have just drawn out...!?

That's where I started, as these 701's weren't working - in fact a while back one was actually blowing power supply fuses... hihi

Cheers,
Tom
robotmakers
Very interesting!

Cheers,
Roger
Moog$FooL$
thanx for sharing. thumbs up
i'd like to hear/see more about this thread.

just curious if you plan to share your schematic here?
Dave Peck
noddyspuncture wrote:


Apparently there were only a handful made, and never went into production so you cannot really get any rarer... hyper

Cheers,
Tom


Wow! What's the story on how you got this thing??
noddyspuncture
Dave Peck wrote:
noddyspuncture wrote:


Apparently there were only a handful made, and never went into production so you cannot really get any rarer... hyper

Cheers,
Tom


Wow! What's the story on how you got this thing??


I was told, by a mutual friend of Mr.Emerson's, of an R.A.Moog modular system being sold in Florida back in March 2013. Took me about 3 months to secure and have it shipped back here to the UK. It included numerous prototypes - hand built. One was built into a 901 VCO case. I have since used the case for my own home built 901B - but the insides have been surgically removed exactly as they were. No one knows what that module was meant to do. And I have had quite a few current and ex Moog technicians look at it...!

Four of the prototypes that came with this thing were the 701 & 702 drum and percussion synths - two of each. They've been sitting on the shelf as I've been busy restoring the Modular. I've finally gotten around to looking at them. The 702's need more work - I've just drawn out those circuits too.

Here's a photo of the whole thing I got.. there is also a ribbon controller not in the picture... note the sign up top..! That is a one-off. Used by David Van Koevering to promote the Minimoog in Florida around the early 70's... cool

And below is how the thing looks now...



Audiohub
VERY VERY cool, Tom!
I hadn't realized that this was the synth used at the "Island Of Electronicus!"
There was a nice writeup about it in the Analog Days book. It's nice to see it still making such great music in your performances.

I had the pleasure of meeting David Van Koevering sometime in the late 80's, although at the time I didn't quite realize the part he played in Moog history.

Tom, is it possible that your modular might be one of the special systems created for the MOMA performance? woah

Apparently one of them went to Keith to eventually be built into the behemoth we all know and love, but I've never heard any more about the other ones.

It sort of makes sense that one might have gone to David for promotion purposes, along with those two rare drum modules...
noddyspuncture
Audiohub wrote:
VERY VERY cool, Tom!
I hadn't realized that this was the synth used at the "Island Of Electronicus!"
There was a nice writeup about it in the Analog Days book. It's nice to see it still making such great music in your performances.

I had the pleasure of meeting David Van Koevering sometime in the late 80's, although at the time I didn't quite realize the part he played in Moog history.

Tom, is it possible that your modular might be one of the special systems created for the MOMA performance? woah

Apparently one of them went to Keith to eventually be built into the behemoth we all know and love, but I've never heard any more about the other ones.

It sort of makes sense that one might have gone to David for promotion purposes, along with those two rare drum modules...


Do you know - that never actually occurred to me but I suppose, given the extra modules that came with it, it does actually make sense..! By the way I actually have four of these rare modules... two 'drum' and two 'percussion'... cool

Cheers,
Tom
Squattamolie
GREAT JUMPIN' JEHOSEPHAT is that COOL!

Wow! jawdrop

And how can one not love a Minimoog tucked inside of it like a little marsupial!

I'm sure I'm the only one wishing someone was able to reproduce these. hihi

Edit - I just realized how freakin' wacked I am. I've had that part 3 video on in the background as I worked on stuff, and I suddenly realized I WAS ENJOYING THE TESTING AS MUSIC - oh my God I'm such a geek. I actually like the testing as a piece of music. HELP ME!!
Audiohub
So, what are the various modules in your system?
Some I know, but others are not familiar to me, and I can't make out the printing in these pictures.

Some close-ups of the various sections would be appreciated, if possible.

Theres a few pictures floating around the web of the MOMA machines, but nothing I found with enough quality to get a good look at all of the different models.

It's pretty cool to think that yours might be one of them!
noddyspuncture
Audiohub wrote:
So, what are the various modules in your system?
Some I know, but others are not familiar to me, and I can't make out the printing in these pictures.

Some close-ups of the various sections would be appreciated, if possible.

Theres a few pictures floating around the web of the MOMA machines, but nothing I found with enough quality to get a good look at all of the different models.

It's pretty cool to think that yours might be one of them!


If you look at the picture above, the one with the R.A.Moog sign on top... the modules are, top left to bottom right...

Two of the 701 drum synths (which I have just got working), custom headphone amplifier/ A440 source, 901C output stage (serial 1001 hand built on pegboard!), two 702 percussion synths (2 of only 3 know to be in existence - even rarer than the 701's, 8 of which can be seen on the MoMA photos)

Early VCA case housing a hand-built circuit on peg-board which is a pitch changer/octaver - and works!, 991 filters and attenuator, 911A dual trigger delay front panel only (I have since built my own circuit and it is now complete), Custom Delays Mixer (from the CEMS system), 907 FFB, 905 reverb, 902 VCA, 912 envelope follower

2x901A oscillator controllers and 4x901B oscillators, 901B oscillator case housing an unknown hand built peg-board module still to be identified (I have since built my own 901B circuit and used the case for it), 903 noise generator, 901 oscillator, 904A LPF, 3x 911 EG, 2x 902 VCA, 994 multiples

Bottom row is obscured, but has a CP3 mixer and two system 10 mixer panels. I have since had two CP3A mixer panels made and built my own circuits for them and also a CP4A panel made and filled it with all the relevant switches and sockets. Of course I had to also wire this little lot together...!

I also got a 951 keyboard and a 956 ribbon controller with the system along with the perspex R.A.Moog sign... wink

applause

Cheers,
Tom
ahmo
Wow! I would love some samples of this thing with the 3 types of noise patched in, anf the 702's as well.

Would you consider it, nothing fancy!
noddyspuncture
ahmo wrote:
Wow! I would love some samples of this thing with the 3 types of noise patched in, anf the 702's as well.

Would you consider it, nothing fancy!


Yeah no problem... but I would need to get those 702's up and running as well first...! help eek!

Cheers,
Tom
Moog$FooL$
noddyspuncture wrote:
ahmo wrote:
Wow! I would love some samples of this thing with the 3 types of noise patched in, anf the 702's as well.

Would you consider it, nothing fancy!


Yeah no problem... but I would need to get those 702's up and running as well first...! help eek!

Cheers,
Tom


what's wrong with them??

a few posts back dr. sketchy was asking about these.... perhaps check with him for some help . he's pretty good with osc. & filter design amongst other analog issues. hmmm.....
noddyspuncture
Moog$FooL$ wrote:

what's wrong with them??

a few posts back dr. sketchy was asking about these.... perhaps check with him for some help . he's pretty good with osc. & filter design amongst other analog issues. hmmm.....


Although I've gotten the 701's working nicely now, the 702's are a different challenge. The two 702's I have here are only half built...! The oscillator board is complete but the wiring to some front panel potentiometers looks to have connections missing. And I am working *blind* as there are no schematics, except for the ones I have drawn out.

I have managed to get the oscillators running but the 'Pitch Vernier' and the 'Bandwidth' control aren't fully wired - or at least I don't think they are and therefore don't work - yet...!

Also the 'other side' enclosure along with it's board is missing - but the controls on the front panel are there, again with no wires to them. But I have sussed what would be on this missing section. The front panel controls give a clue - there are Attack & Decay... which would indicate that there's a EG and an associated VCA on there. And then there is the 'Repetition" section with 'Rate' & 'Regularity' controls. The oscillators don't seem to be designed to be running constantly - unlike the 701. They would appear to be controlled by this onboard oscillator, or LFO - ie: turned on & off.

So it would make sense that this oscillator is a square wave LFO type thing and the "Regularity" would be the PW setting. There is one other control - a 3 way selector labelled "Excitation" - selecting either Pink Noise, Multiple Impulses or Single Impulse. As the noise section on the 701 has all the noise inputs on the rear connector, I can assume that the Pink noise here would also be a similar rear connector input.

But it's the "Impulse" part that confuses me. This LFO will need to be 'Excited' by Pink noise and Impulses which I can't yet get my head around... very frustrating

Anyway that's a way off yet as my first task is to get these oscillators running properly... confused

Cheers,
Tom
RichardC
noddyspuncture wrote:

But it's the "Impulse" part that confuses me. This LFO will need to be 'Excited' by Pink noise and Impulses which I can't yet get my head around... very frustrating


Could it be that the LFO is only related to the "Multiple Impulses" switch position (there is a line linking that position to the LFO controls on the front panel)?

Just a thought from looking at a closeup of a front panel here:
[url]
http://olivier-grall.yusynth.net/Moog%20drum%20synth/MOOG%20drum%20syn th%20702.jpg[/url]
noddyspuncture
RichardC wrote:
noddyspuncture wrote:

But it's the "Impulse" part that confuses me. This LFO will need to be 'Excited' by Pink noise and Impulses which I can't yet get my head around... very frustrating


Could it be that the LFO is only related to the "Multiple Impulses" switch position (there is a line linking that position to the LFO controls on the front panel)?

Just a thought from looking at a closeup of a front panel here:
[url]
http://olivier-grall.yusynth.net/Moog%20drum%20synth/MOOG%20drum%20syn th%20702.jpg[/url]


Actually it should be: "Random Impulses" - my bad originally... cool

Yeah, I see the 'line' you mention - the way I read it though was that the the whole "Repetition" thing, which is basically the LFO, is subject to 'Excitation'... via Pink Noise, Random Impulses & Single Impulse...?

Would that make sense? But is still doesn't answer what these 'Impulses' would actually be or where they originate...?

Cheers,
Tom
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