moog modular vcf?

[numbertalk]

So, at the risk of sounding like an idiot, for those bass patch sounds like TD, Michael Hoenig, etc have used.....is it not at all possible to even begin to *approximate* *similar* sounds with, say, a Prophet 08, putting all ideas of getting the "pure" sound aside? It seems as though it would be possible to somewhat approximate. I can understand how the wave shapes being different/unique (and drifting) would effect the harmonic content/balance and then the character the filter would add on top of that, not to mention the other modules in the signal path, but again, without a ton of experience, so please forgive me, if it's possible to come close with another analog synth, how would you patch this? I've tried using saw-tri waves on my P08 and have not been able to come close, but I would attribute that more to my own inability. What I come up with either sounds too "buzzy" or at the other end the cutoff freq is set so low it's too muddy and muted. And if not with a P08, with, say, Yusynth's Minimoog VCF clone and a non-901/non-Moog Modular oscillator. Maybe it just honestly isn't possible, but again, I'm coming at this as not a 100% purist and even not wanting to really 100% copy such a recognizable sound, but more to know how to do this, just to learn more about patching, and even as a starting point for maybe a similar sound or something.

[yusynth]

[Peake]

[Peake]

[synthetic]

I built my 490 filter. I bought the board, panel and some parts from Synthtech. I went on Mouser and ordered the resistors, caps, diodes, etc. I soldered it together and tested it. I don't see how it's any different from buying a board from someone else on this forum. I think it absolutely counts as DIY.

How is this not DIY?

http://www.wiseguysynth.com/larry/motm/490/490.htm

What's the cutoff for being called DIY? Printing and drilling your own boards and panels? Winding your own transformers? Please, Dr. Peake, let us lowly beginners know so that we will not waste your time again.

[Peake]

I had read long ago that they don't offer kits anymore. Hence, no DIY. Thank you for your attitude and lowering the quality of this thread through attitude and continuous product placement/branding. It certainly does not endear me any further to you, or to the items you are representing. I prefer the positive; you cannot provide it.

Enough of your thread-degenerating attitude. Obviously you and many of your group are -unable- to not waste time and money upon me, so I'll provide the positive example: Let's talk about The Filter instead.

Neh?

[urbanscallywag]

They still sell boards...

[Scott Stites]

[Peake]

[Peake]

[paults]

OK folks, time for 'reality' to rain (yet again) on the Peake Parade Grab yer popcorn and hide the children.

a) I also sold my Moog 55, fully restored to *exact, perfect* factory specs by not 1, not 2 but all 3 of the top Moog repair folks in the world. Why? It was TOO NOISY! The same reason I sold my Xpander (the Xpander was so noisy I thought the Noise Generator was bleeding through). The sound was very 'muffled' to me (like a blanket over the speakers sort of sound). I also owned Moog IIIc Serial #006 at one time (sold because the 901s drifted when I *walked* past them and air blew in the jack holes), and a Moog 15 as well. All 3 were sold because try as I could, the "glamour" of the machine was undone by the sound. Heck, I like my Yamaha FS1r better in that department.

And the Moog modular was the reason I switched from a chemistry degree to a EE degree (well 2 EE degrees). In 1972 I was writing Bob a fan letter every 4 months or so, which he answered every one.

b) but while I had it, I did a little R&D. I used the 2 904As in it, I had 5 other people send me their 904As and I ran all 6 of them on my super-whiz-bang Audio Precision Dual Domain tester. And what I found was

#1 - there is a definite non-linearity in the amplitude versus frequency response
#2 - there is a definite non-linearity in the frequency response versus Q

This got me thinking....hmmm...so I then looked the following "off the shelf" Moog Ladder designs:

Modcan
Doepfer
MoogerFooger 101
.COM

And running the SAME tests for these as the 904As, NONE OF THEM had these 2 particular non-linearities. BTW: the MF-101 was not a Bob Moog design, it was designed by a guy in Canada. It uses crappy CA3046 arrays. Ack!) But I digress.

Well, I thought that was interesting. Here are 4 supposedly clones that did not "measure up" so to speak with the original. So I started running PSPICE circuit simulations and I found the reason. And to confirm it, I just picked up the phone and talked to Bob and he verified my suspicions.

I then got with JH and we worked out how to get that same 'dip in the curve'. Sorry Mike, the caps, Mylar or otherwise, have *nothing* to do with why a 904A sounds the way it does. It's a "company secret" (although not that hard to figure out if you know what to look for and understand transistor theory) but it has to do with adjusting impedances with respect to input levels of the audio (think of it as a separate feedback path).

JH & I then designed the MOTM-490, and I build 10 prototypes with different date code parts to get what's called a Monte Carlo Spread of component values. And I used 3 different caps as well. Running the 10 through the AP, it was verified that the MOTM-490 is the *ONLY* available Moog Ladder VCF that accurately depicts the 904As unique sound.

c) the Mini-Moog VCF's sound depends on 3 things that are interactive:

#1 - the loading impedance of the following VCA, which is a differential amplifier with non-linear input impedance.
#2 - the negative supply is very noisy and the VCF has low PSRR (power supply rejection ratio)
#3 - the unique feedback in the 904A is not exactly the same in the Mini

Lessons learned:

a) careful and thoughtful engineering analysis can show why something sounds a specific way, without resorting to 'floobydust' explanations.
b) one can duplicate a certain audio timbre exactly, without duplicating the circuit *exactly*
c) audio gear designed in 1970 will be noiser than audio gear designed in 2008

If people wish to spend countless hours duplicating pc board traces, then the exact parts to get the exact sound, I say good luck with that. But PLEASE do not think that is the ONLY PATH. It is not.

[RF]

[JohnLRice]

Nice info Paul, thanks!

[Peake]

[Peake]

[paults]

#1 reason should have read: frequency response versus amplitude

Meaning: if you set the Fc knob to a value (with resonance at '0') and then do a frequency response plot (ie plot the low-pass response), you will see that with different input amplitudes, the 'flat part' of the frequency response is not flat at all. There is a pronounced 'dip', and the intensity and shape of that dip varies with input signal level.

[paults]

Mike:

You only need matched pairs for the 'top pair' (where the output is tapped off) and suggest using the Analog Devices SSM parts over the THAT, because you will get better results. For the other 6 transistors, use BC550 or BC560s because they have 2-3 times the gain and 1/2 the noise of say 2n2222 or 2n3904s.

With regards to a 901:

a) use a polystyrene cap, or at the least do a 'dual footprint' on the pc board for each type (all you need to do is add 1 hole).
b) use RN55E resistors throughout. You can get these cheap enough at Mouser, they will not effect the sound 1 iota

(a) and (b) will NOT eliminate the drift, but it could make the thing useful over more than 2 octaves for more than 5min at a time

[paults]

One more little tidbit:

One of the 'great tricks' of the 904A is to use it *after* a VCA in a patch, not before. The input amplitude of the signal really has a great effect on the sound. Placing it in the 'traditional' spot after a VCO will only feed it a constant amplitude. You can get a bit of timbre shift by messing with the amplitude going in (a mixer in front), but a lot of really interesting tones can be had by using the VCF last.

The only downside is the possibility of more noise, assuming an 'off' VCA is quieter than a VCF sitting there with no input. The MOTM-490 is very quiet

And Mike, I prefer my Mark Levinson 383 amp with the B&W speakers, thanks.

[paults]

After reading all the posts, some final thoughts:

a) the MOTM-490 is not temperature compensated, as to be 'bad' in this regard as the Moog is. As a side comment, MOTM is the only company that does temperature compensate the VCFs, which is another discussion

b) the main reason a 901 has a different sound is the sawtooth is really a sort of distorted triangle, which then makes both the Sine and Triangle 'not perfect'. Pulse is pulse Does this add something? Sure, but not to the extent people think. I will bet that the *output amplitude* of a 901 is different than a 921, and THAT makes the sound out of the 904As different

c) the CA3080 in the 921 is not used in a critical part of the VCO core. It's used as a differential amplifier. The improvements with respect to temperature drift would be

#1 - replace the LM308 op amp in the CV summer with a better part
#2 - replace all the LM741s with TL071s
#3 - use RN55E 0.1% 10ppm resistors in the CV summer
#4 - replace CA3086 with MAT02EH in the exponential converter

This is for a redesign, not to 'drop in' an existing 921. These changes will not alter the sound at all. but it will make it less drifty.

I like less drifty. Robert Rich has toured extensivedly with his 8 MOTM-300 VCOs and 6 MOTM-310s uVCOs and has stated several times that he can tune the system up at home in CA, put it in the back of the van, drive across the US to NYC, set it up on the stand and after a 10min warm up, *never have to touch a single VCO knob*. It's STILL IN TUNE.

d) I am in design of a DVCO (digital VCO) that has a temperature sensor on the board. There is a jumper option to allow ambient temperature 'to drift' the DVCO's pitch.

[Scott Stites]

[suitandtieguy]

[frijitz]

[elhardt]

The B.S. never ends. One of the biggest problems with these forums is that people don't seem to learn anything. We've been down this road several times. The Moog 901 waveforms don't look different than others, as I had Andrew Sanchez record some specifically for me to analyze. I also grabbed one or two that Mike Peake himself posted. I wanted to hear the magic he claims is there, but there was none. There were audio files posted comparing the Moog to the Arturia MMV for drift comparisons, I posted some comparing the Moog to the Technosaurus and a straight digitally generated sawtooth with measurements of cycle to cycle jitter down to the nanosecond range (another goofy theory that didn't pan out, since the Moog had 3 times less than the modern Technosaurus), and there was no magic. And it keeps being pointed out that drift can be patched in, as some of us do often, but they don't want to listen. In nature noise/drift is usually of the 1/f type. Nothing magical about that.

Go ahead and ask Peake or anyone who won't let go of the Moog osc dogma to post audio files where we can actually hear the Moog magic and you will see that they can't do it. It's all talk and nothing physical or aural to back it up.

I still have up online an audio file that switches back and forth between a 901 Moog sawtooth and one generated in Cool Edit Pro (link below). These are on the two opposite ends of the spectrum. They're as far away as I could possibly get, and still there is almost no difference at all. No magical interesting Moog waveforms, or magic power supply noise, or magic jitter here.

http://home.att.net/~elhardt2/Sawtooths.wav

-Elhardt

[Peake]

[Peake]