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921b clone ?

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921b clone ?

Postby rarecomponent » Mon Apr 02, 2012 11:17 am

Has anyone successfully cloned the 921b Osc.?

I wonder if the module would work without the uA 796 Sync section? (a rarecomponent ...but allowing for +12v connection and various resistors to SAW out.)
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Re: 921b clone ?

Postby EMwhite » Mon Apr 02, 2012 1:05 pm

Check MOS-LAB, located in France. Said to be among the best: http://www.youtube.com/watch?v=SMTouJJP51A
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Re: 921b clone ?

Postby rarecomponent » Mon Apr 02, 2012 1:35 pm

yes...familiar with these thanks...but I'm more interested in the home made attempts..
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Re: 921b clone ?

Postby MC » Mon Apr 02, 2012 2:48 pm

You need the companion 921A in order to get v/oct response

The 921 would be a lot easier to clone than the 921A/921B, parts are easier to get.

I've seen 921 clones that are based around the CEM3340 VCO, that isn't even a faithful clone.
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Re: 921b clone ?

Postby Kevin Lightner » Thu Apr 05, 2012 11:41 pm

A common 1496 ring modulator IC will work in place of a uA796, I think.
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Re: 921b clone ?

Postby rarecomponent » Fri Apr 06, 2012 7:21 am

Oh ???? thanks Kevin..thats given me a new lead..I was going to emit the ua796 but now thats something else to follow up.
The 921b and 921 are very similar but deviate around this chip..but both complicated circuits...quite a marathon.
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Re: 921b clone ?

Postby Kevin Lightner » Fri Apr 06, 2012 6:00 pm

You might consider just building the base design of the 921/921B and omit the sync features.
While it's usable and nice to have, it's overly complicated and isn't worth the trouble for the amount it's usually used.
Remember, no matter what design you build, you will still need a tempco resistor and high quality cermet trim pots.

Fwiw, when I was building up Hans Zimmer's huge Moog, he had a system delivered that was previously owned by UCLA.
That system had some DIY 921A/B sets that were built by JL Cooper.
On the boards it said "Moog via JLC"
So it IS possible to dupe them, but they're not an easy project and certainly nothing for a beginner.
I very much suggest prototyping them beforehand on breadboard or other temporary fixture.
It is also high recommended that you borrow someone's 921(s) to compare things to.
Schematics and photos can only go so far.
Good luck!!
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Re: 921b clone ?

Postby rarecomponent » Sun Apr 08, 2012 8:29 am

thanks again Kevin for your kind help ...the 1496 you suggested is a replacement for the 796 by the looks of it so its down to different case but I should sort it OK..that was a great tip. I would like to stick to the original Moog module if possible. Ive begun the design and have taken Moogs original layout and circuit plan (this Ive done from the few photos Ive gleaned..I wont be able to get a hands on of a 921b here in the UK) but the top layer tracks are proving elusive as the components cover the copper in most places but if I work from the schematics I should be able to get there eventually. (I hope) The 921a is a doddle but this 921b is the most difficult Moog Ive cloned so far but it will be superb to have the 901s and 921s in my system. I'll keep everyone posted but I reckon this is gonna take a good 6 weeks or so. (then theres the set up!)
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Re: 921b clone ?

Postby jpdesroc » Tue May 08, 2012 9:53 am

I just found this topic about Moog 921b clones..
Nice info from you guys !
I'm in a System 55 clone project myself since a while..
The clone won't be a 'perfect' clone but VERY similar
estheticaly speaking. I'll also add some new modules
of my own like this MIDI interface:
http://www.arcenson.com/projects/modula ... Interface/
I already started a 12 VCO's job aimed for a futur MIDI
guitar controler.
So I needed:
4 x 921a VCO drivers clones (called M103A in my system)
http://www.arcenson.com/projects/modula ... %20driver/
and
12 x 921b VCO's clones (called M103B in my system)
Not yet uploaded on my ftp but for info:
My 921b clones have the exact front panel design as 921b's
except for the RANGE steps..
Mine are 32',16',8',4',2',1' instead of the original LO,32',16',8',4',2'
AND one major thing is the inner circuit...
The VCO CORE is an exact copy of the famous
MOTM UltraVCO MOTM300 completely PCB redesigned
with stuff I removed and stuff I added around for front panel component uses.
For copyright reasons I won't be able to share any schematic
original & modif but some photos will be available.
To be followed..
The following link shows some modules ready to share.
http://www.arcenson.com/projects/modular/

I'll be uploading my 921b VCO's detailed files very soon
in this ftp space.
Anybody who has the same Moog system 55 cloning goal
are very welcomed to share ideas!
Cheers,
J-Pierre
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Re: 921b clone ?

Postby forbin » Wed Jul 18, 2012 1:22 am

Hi -- interested in your cloning of the 921B/921A pair -- i have almost finished doing this and had a fair amount of success so far. I still haven't got the sync circuitry with the multiplier going completely and had to "tweek" the design a little bit to as i just cannot get a dual fet at anything approaching a reasonable price. You can see the rather slow progress here: http://forbinthesynthesizer.blogspot.co ... lives.html I am just in the throes of getting back into it and will try for a dual foot print for the multiplier along with fixing up the transistor array stuff up! Got a nice e-mail from a lady at Moog music that they are quite happy for me to post the layout (single sided and reasonably easy to etch your self + 2 x regulators so can run from +-15V) when i had finished as long as it didn't say moog all over it and purport to be from them. She basically said that they weren't really very interested in anything prior to Bob getting the company back in the mid 90's...
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Re: 921b clone ? + 921a clone

Postby jpdesroc » Wed Jul 18, 2012 7:46 am

Sorry, my last post had bad links to my projects pictures & files..
Here it is again when the corrected links. Just have a look..
Sorry again.
JP

I just found this topic about Moog 921b clones..
Nice info from you guys !
I'm in a System 55 clone project myself since a while..
The clone won't be a 'perfect' clone but VERY similar
estheticaly speaking. I'll also add some new modules
of my own like this MIDI interface:
http://www.arcenson.com/projects/Modula ... Interface/

I already started a 12 VCO's job aimed for a futur MIDI
guitar controler.
So I needed:
4 x 921a VCO drivers clones (called M103A in my system)
http://www.arcenson.com/projects/Modula ... CO_driver/

and
12 x 921b VCO's clones (called M103B in my system)
http://www.arcenson.com/projects/Modula ... _UltraVCO/

My 921b clones have the exact front panel design as 921b's
except for the RANGE steps..
Mine are 32',16',8',4',2',1' instead of the original LO,32',16',8',4',2'
AND one major thing is the inner circuit...
The VCO CORE is an exact copy of the famous
MOTM UltraVCO MOTM300 completely PCB redesigned
with stuff I removed and stuff I added around for front panel component uses.
For copyright reasons I won't be able to share any schematic
original & modif but some photos will be available.
To be followed..
The following link shows some modules ready to share.
http://www.arcenson.com/projects/Modular/

Anybody who has the same Moog system 55 cloning goal
are very welcomed to share ideas!
Cheers,
J-Pierre
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Re: 921b clone ?

Postby EricK » Wed Jul 18, 2012 4:39 pm

So, your Moog© 921b clone is really an exact copy of MOTM© Ultra Vco©, but for copyright reasons you won't post pics of the pcb? :wink:


The panels look good!
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Re: 921b clone ?

Postby thealien666 » Wed Jul 18, 2012 5:17 pm

In looking at the specs for your MIDI-to-CV interface, I noticed there is only 12 bits of resolution for a 10 octaves range. That will result in some notes being of approximate value. Wouldn't have been better to use at least 14 bits, or better yet 16 bits for such a wide range ? 16 bit D/A converters aren't that expensive these days, are they ?

With 12 bits, you have 4096 different voltage values divided by 120 semitones (10 octaves), which yields only 34 possible different voltage values per semitone. Even though you can get a precise 1 volt per octave out of this, some notes in between will suffer from imprecise voltage for accurate pitch.

With 16 bits, you'd get 65536 different voltage values divided by 120 semitones, which would allow 546 different possible voltage values per semitone. You'd be assured of perfect pitch for every single note !

Anyway, if I was making a MIDI-to-CV interface, I would make sure to build the absolute most precise one I can. Because what's the use of having ultra precise and stable VCOs if only to send them approximated pitch control voltages ?

My take on it.

Although, your panel and PCB look mighty professional there. 8)
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Re: 921b clone ?

Postby Kevin Lightner » Wed Jul 18, 2012 9:52 pm

"So, your Moog© 921b clone is really an exact copy of MOTM© Ultra Vco©, but for copyright reasons you won't post pics of the pcb?"

I saw that too.
They will be a decent oscillators, but it won't be quite the same as real 921s.
Every circuit has natural characteristics where only the same design and execution can yield the same results.
921 sync is especially unique to the 921, but also the motms are probably quicker to process modulation.
They likely have a bit lower noise floor overall too.
But I do understand that finding / affording real 921s is difficult or impossible.

The Forbin board is probably closer to a real 921, albeit a bit bigger board.
I wish he'd have asked me for dual FETs, I could have saved him some grief. ;-)
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Re: 921b clone ?

Postby analogmonster » Thu Jul 19, 2012 4:39 am

Hi cloners,

reading the threads concerning the 921 clones and studying the schematics I've not understood yet why a "ringmod" - chip is used for syncing. Hard sync is easy: just reset the oscillator core in the middle of the cycle by an externel reset signal. Soft sync is a bit more tricky, determine the amount of impact of the external signal on the oscillator core. Soft sync can be achieved by a pot and/or transistor solution.

So a question to all 921 owners (originals or clones): What does a sync of a 921 do differently compared to hard or soft sync? If you need the modulator circuit just for "leveling" the external signal there might be easier solutions to achieve this.
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