Saturday, February 27, 2010

Expensive Speaker Wire

I note that inside the Sony APMs I currently own, the wiring, running up to a couple of feet in length, is very thin, nowhere near as thick as lamp AC cord. I wonder if using snooty speaker cable, or even lamp cord inside of them, would improve the sound.

What a bit of work that would be.

I wonder if the really expensive loudspeakers use very thick/quality wiring. These are of course the folks who (correctly) recommend that you place your power amplifier between the speakers and use the minimum amount of wire possible, to keep the signal at its best. If there is an equal amount of low-quality wiring inside the speakers...

Friday, February 26, 2010

Kraftwerk Remasters

I've purchased The Man Machine and Radioactivity. I've only opened TMM out of concern regarding the character of the remastering, and wasn't far off-base...per Kraftwerk, the remaster is (TMM) stately, controlled, and adult, not rocking and bopping and =loud=!

The plusses: A bit louder, fuller, musical in terms of spectral balance. Not overdone.

The Minuses: Perhaps just a touch underdone in terms of punch/volume. Noise reduction was implemented to the extent that it may have caused the character to suffer, and to reduce the treble a bit (not due to the illusion of tape noise adding highs). Perhaps some slight loss of midrange and treble solidity as a result (my only example of this was an LA2a plug-in used with a card DSP engine which provided the LA2a characteristic compression, but caused the image to collapse a bit and definitely caused grain in the treble). It's a digital remaster, after all. Don't expect Manley, Fairchild or Avalon punch and gloss and euphoria. "Expanded Edition" means the booklet contains several pages of photos of the wax versions of the band, doing things like standing at a 24-track analog machine, at a small mixing console, etc. No text in the entire thing, excepting mixing/editing names/studio names etc. on the back.

I didn't want something over-louderized, and it's definitely not that, but it's not rock-and-roll. Or even as punchy as modern techno. I dunno; limiting it as much as they have would definitely increase the already apparrent noise floor to perhaps completely unacceptable levels. I have used high-priced NR hardware during sampling sessions, and a single pass with a decent amount of reduction can cause obvious artefacts. Several passes of slight reduction produced better results, but still ate into the overall character. Shrug...I don't know if I'm even going to open Radioactivity.

Thursday, February 25, 2010

4558 IC in a 2004 CD player...

The Sony CDP-CE375 has a nice character- a bit compressed, lacking a tad of midbass, and the treble is pressed and "audiophile" in a sense. It's not as strong at 10K or so as other players I've auditioned, making it easier to turn way up without strain. The tweeters in my current speakers have bumps at 15KHz and again above 20KHz, so the 375 is not a good match, as it becomes difficult over time.

However...I note that the unit was manufactured in 2004, and it has a 4558 at the audio outputs.



I'll suppose that the circuit preceding it would be perhaps very bright with a modern opamp. Unless I changed my speakers, I wouldn't want to drop in a 2604 or other fast ICs...


Monday, February 22, 2010

On the Moog Taurus 1 and the 904a

Spied on, notes taken from Cary Robert's, regarding the Taurus 1, the legendary Moog which sounds killer and not quite like other Moogs:

-the AC coupling between the VCF and VCA was designed so that the RC product would increase the bass at a corner frequency of 20hz. There is a bass boost built into the Taurus pedals!

-The other element of the bigness of Taurus I pedals is that the filter is driven pretty hard.

Noting that Jurgen Haible has already written about getting a very nice tone out of the 904a by overdriving it. Cary stated that the Taurus 1 uses the 904a design, so it makes sense to run some gain after your 904a (using a 902? Aren't those 2X gain?) and ripping it up.

Saturday, February 20, 2010

Tim Smith on Analog Synths versus Digital Synths

Entered as found except for subtle correction; all italics and bold are in the original.

October of 93

Why do analog synthesizers sound so different from their digital counterparts?

This is a subject I delved into with some detail in Mark Vail's book 'Vintage Synthesizers'. (Available through Keyboard Miller-Freeman Publications.) Mark made an excellent contribution to the history of electronic music by compiling this text. I peruse it often. In the interview with Mark, I explained some of the basics of audio electronics. I'll try to present a comprehensible overview of this subject again here. Let's look at the Moog- mini Moog. When this instrument was invented, designing with IC op amps was in its infancy. There were very few available, and if one was any good, it was really a monolithic device constructed out of discrete transistors, resistors, capacitors, etc. Maybe encapsulated in epoxy, etc. The device that was available commonly was the UA741 op amp. The UA741 device was used in the mini-moog, but it was used only in the Logarithmic amplifier circuits that convert the linear control voltage from the keyboard and other sources into an exponential current suitable to produce the doubling of the sinusoid's response necessary to produce a musical octave. (This current was used to control the charging current in the integrator that is the basis of the oscillator in the mini). As a result of the lack of IC op amps, the mini design team designed almost everything with discrete circuit configurations, much like high end audio designers would have done in hifi gear. The result? A very hifi sounding synthesizer!

The point that I'm trying to get around to is this: The mini-moog had no IC op amps anywhere in the audio signal path. Thank goodness, or I'm certain that it would not be teh legendary instrument that it is today. I think it's important to point out that the Moog modular instrument's system I, II and III had no ICs in the signal path either. The Moog System 15, 35 and 55 had very few op amps in the signal path, I think around 1. (Edit: IIRC there are opamps in the outputs of each oscillator waveform and also one in the CP3a mixer). If you had the good fortune of reading Mark Vail's article about Emerson's Moog system, you may have noted his reference to changing the op amps in this system and the very positive effect it had on Emerson's Moog! (They used National's LF411, 412 Types, a quiet, stable op amp of more contemporary design). The 741 type op amp designs would have ruined the sparkling, sweet highs that made the mini and the early modular instruments so famous. The 741 is not suitable for use above a volt or so about 6KHZ, so you can see why.

Op amps from this period and even some modern ones act like low pass filters in an audio circuit, or worse, when pushed to their limits, generating slewing induced distortion- a very unmusical sound, some folks describe as a smearing of the signal. Until recently the best Pro audio and HiFi equipment did not use ICs either. That's right, in 1993! Some engineers will probably never accept op amps in the IC form from a purist's point of view. There is not a small number of poeple that are convinced that Vacuum tubes are the finest form of sonic amplification and they certainly have a point. However tubes are of little practical value in Voltage controlled synthesis circuits.

The lack of acceptance for IC op amps by engineers and careful listeners in the High Fidelity and high end audio fields is not without reason. Until recently, thay have not had very good sonics, or if they had a nice warm sound they were somewhat noisy. Thankfully this is no longer the case. But unfortunately, even today's great digital synth companies are not using the best op amps they could. There are other factors in the mini-moog that are important, like the Moog lader VCF, who would dispute this? Also the frequency response of the mini is more or less flat out to 35KHz. I recently fired up my Arp2601/3620/2500 system and was re-shocked at the fat, rich sound that comes out of this system. It has two 2500 series 1407 multimode filters and 1 of the early Arp copies of the Moog VCF installed and a total of 11 VCOs. It's 2 note duophonic but I usually just use the monophonic mode. What a note! My poor sample playback machines are somewhat sad in comparison, but certainly have their own merits. I've upgraded all the op amps in my analog systems (I have 3 souped up 2600s along with the 2500 system). It made a very real difference! Remember; old, slow op amps are Low Pass Filters.

So what's the difference between old analogs and new analogs, or old analogs and new digital instruments? Let's start with old analogs versus new analogs, or particulary the polyphonic analogs like the Prophet 5, ESQ-1, the Oberheims with Curtis ICs in them. They are all constructed with IC versions of the synthesizer module, VCOs, VCFs, VCAs etc. The most prolific are the Curtis ICs. I can tell you for certain that they are sonically much inferior to the early synths, particulary modular synthesizers. I have had scores of folks tell me the same thing!

Why? These IC synth functions do not have the simple, unobtrusive signal path that the modular machines did. They have relatively high THD, usually more than 1% (odd order unfortunately) and they have what I usually descrive as a flat, 2-dimensional, pinched sound. So what happened? In the change from discrete "hifi" type circuits to the IC form, something was lost. The early Moog and ARP VCAs (2500-2600-900 series Moog) had discrete design with greater than 90dB of dynamic range. Digital before Digital!

What changed when we went to digital, relative to analog? If you read Mark Vail's article about Emerson's Moog, you may recall one of the technicians who modified this instrument mentioning that the Moog's response was extending out to 50KHz or so. All digital synths have a BRICK WALL filter at exactly 20KHz. Is there a sonic difference to these two systems? I sure hear one! Let's face it, a Moog 55 can demand nearly every dollar it sold for on the day of its manufacture. Now that's lasting value. It isn't just because it's a pretty synthesizer either! (Although it certainly is!) ARPs in excellent shape can demand the same arrangement, especially the 2500 system.

I'm not saying that the frequency response as a singular spec is the whole answer; it's not. I believe that a major factor is this; In high end hifi design schools, simple topologies (circuit layouts) are widely believed to have the most desirable sonics. The less nonlinear nodes (connection points) that a signal has to go through, all the better. Hence Vacuum tube designs with their very straightforward topologies, and next best- discrete FET designs, then Bipolar transistor designs, and the least desirable topology? ICs (integrated circuits). But I must say, today's op amps are changing minds and the rules. There are some really excellent-sounding devices around now, as good as the best discrete designs in my opinion. Let us install some of these marvels in your system!

Can our mods make your digital synth sound more analog? Well, sort of. We are certainly speeding up the response time of these circuits (slew rate, settling times, etc.) . We are also electively raising the frequency response in the Reconstruction Filters, and if there are electrolytic capacitor in the signal path that aren't rerquired and are causing unnecessary low freq. roll offs and phase shifts, we can remove them! If they are required, we can correct their unpleasant effects. So at least these machines are performing at their very best. These mods are standard fare in the HiFi mod world. We are just bringing them into the Pro Audio, electronic music world.

Will these mods make your Vintage Keys (or other type) module sound like a Moog modular or an ARP modular? (I love mine, it sounded quite nice before new op amps, and even smoother and warmer after new op amps were installed). This would be an extreme claim to make, but let's say this: The sound of a digital synth with the best possible op amps and if necessary an extension of its frequency response certainly gets you closer! I think a lot closer. And our customers agree! The lastest audio op amps are discrete, monolithic designs. It's a good age for op amps, they are finally up to snuff! When you hear or read about people saying their old analogs are much warmer and fatter sounding, they are not just hearing things (no pun intended). They are REALLY HEARING THINGS!

Another point I would like to make is that almost every digital synteh has a very sharp (24-30dB per octave) filter set at usually no higher than 20KHz. There are studies that show while we may 'not hear' abouve 20KHz, there is EEG activity above this frequency in certain folks. There is a perception of energy above this point. Plus if you will look at the gain/phase graphs (showing the changes we make to the RCF Filter) I have provided in this brochure, you will see significant phase shifts well within the Audio Bandpass. If you extend the frequency response of a digital synth's circuits you move this phase curve further away from the ear's perception. This is helpful. Well, if you're still awake and not entirely confused, I hope this has given you something to chew on. Thanks for taking the time to read my dribblings.

Timothy C. Smith

Weyer/Smith Labs

The Audio Clinic

Tim Smith on Sound Quality, the 2604 opamp.

From Tim Smith's 1993-ish papers.

"The following discussion is provided, recognizing that not all measured performance behavior explains or correlates with listening tests by audio experts. The design of the OPA2604 included consideration of both objective performance measurements, as well as awareness of widely held theory on the success and failure of previous op amp designs.


The sound quality of an op amp is often the crucial selection criteria- even when a data sheet claims exceptional distortion performance. By its nature, sound quality is subjective. Furthermore, results of listening tests can vary depending on application and circuit configuration. Even experienced listeners in controlled tests often reach different conclusions.

Many audio experts believe that the sound quality of a high performance FET op amp is superior to that of bipolar op amps. A possible reason for this is that bipolar designs generate greater odd-order harmonics than FETs. To the human ear, odd-order harmonics have long been identified as sounding more unpleasant than even-order harmonics. FETs, like vacuum tubes, have a square-law I-V transfer function which is more linear than the exponential transfer function of a bipolar transistor. As a direct result of this square-law characteristic, FETs produce predominantly even-order harmonics. Figure 9 shows the transfer function of a bipolar transistor and FET. (Bipolar shows strong second, third, fourth and fifth content; the FET shows only a second harmonic, one-half the strength of the bipolar). Fourier transformation of both transfer functions reveals the lower odd-order harmonics of the FET amplifier stage.


TheOPA2604 uses FETs throughout the signal path, including the input stage, input-stage load, and the important phase-splitting section of the output stage. Bipolar transistors are used where their attributes, such as current capacity are important and where their transfer characteristics have minimal impact.

The topology consists of a single folded-cascode gain stage followed by a unity-gain output stage. Differential input transistors J1 and J2 are special large-geometry, P-channel JFETS. Input stage current is a relatively high 800uA, providing high transconductance and reducing voltage noise. Laser trimming of stage currents and careful attention to symmetry yields a nearly symmetrical slew rate of +/-25V/us.

The JFET input stage holds input bias current to approximately 100pA, or roughly 3000 times lower than common bipolar-input audio op amps. This dramatically reduces noise with high-impedance circuitry.

The drains of J1 and J2 are cascoded by Q1 and Q2, driving the input stage loads, FETS J3 and J4. Distortion reduction circuitry (patent pending) linearizes the open-loop response and increases voltage gain. The 20MHz bandwidth of the OPA2604 further reduces distortion through the user-connected feedback loop.

The output stage consists of a JFET phase-splitter loaded into a high speed all-NPN output drivers. Output transistors are biased by a special circuit to prevent cutoff, even with full output swing into 600 ohm loads.

The two channels of the OPA2604 are completely independent, including all bias circuitry. This eliminates any possibility of crosstalk through shared circuits- even when one channel is overdriven.

Friday, February 12, 2010

Again: Specifications or Music?

I note that famed amplifier designer Nelson Pass says:

"There has been a failure in the attempt to use specifications to charaterize the subtleties of sonic performance. Amplifiers with similar measurements are not equal, and products with higher power, wider bandwidth, and lower distortion do not necessarily sound better. Historically, that amplifier offering the most power, or the lowest IM distortion, or the lowest THD, or the highest slew rate, or the lowest noise, has not become a classic or even been more than a modest success.

For a long time there has been faith in the technical community that eventually some objective analysis would reconcile critical listener's subjective experience with laboratory measurement. Perhaps this will occur, but in the meantime, audiophiles largely reject bench specifications as an indicator of audio quality. This is appropriate. Appreciation of audio is a completely subjective human experience. We should no more let numbers define audio quality than we would let chemical analysis be the arbiter of fine wines. Measurements can provide a measure of insight, but are no substitute for human judgement."

And another quote on art:

"...this is what art is supposed to do-- shake you up, make you think differently. Make you sweat. Doing its job. God, yes." -Gregory Frost, "Madonna of the Maquiladora"

Sunday, February 7, 2010

Remaster, or Remix?

Some vinyl has made the jump to CD in different form, disappointingly. No mention is made of any alteration from the original. The most evident examples in my collection, are:

-Yello, "You've got to say Yes to another Excess".
-Robert Fripp, "Exposure".
-Skinny Puppy, "Mind: The Perpetual Intercourse".
-Klaus Schulze, "Drive Inn" and "X".

Yello lose the viny version of "I Love You" and include a different version with a gong. Feh. The Fripp is a complete remix, not for the better. Puppy trade the vinyl version of "Dig It" for the 12" vinyl version- Inferior! The Schulze have since been repaired in the new reissues, so avoid any earlier versions, the ones without the booklets. Congratulations to Klaus and his team that the originals have been so well-represented in the new issues! Big grin for "X" fans!

Note that the vinyl version of "Dig It" is seemingly only available on Alternative Press' "Industrial Strength Machine Music".

Note that the KMFDM remix of "Godlike" found therein is also seemingly not on any other media, and is wonderfully bass-heavy. Bliss!

But back to remasters...

I note that everyone from Synergy through Ultravox, Kraftwerk, Dead Can Dance and others have reissued older material with remastering. I haven't heard any of the above, but am very curious about the differences from the original material. I have several of the Yello reissues and they have nice booklets, and rare singles included, which is wonderful as some are very hard to find. (The original John Foxx issues of "Metamatic" on CD, although in two slightly different versions, contain many related singles, which is also, quite wonderful, and extremely welcome. Now to create a single CDR of both versions, containing all of the rare singles!).

By the way, if you have the technology available, play Ultravox's title track "Rage in Eden"...backwards. Check the chorus.

Monday, February 1, 2010

The 1.22V standard for audio signal voltage

I don't know current, ohms, and all of that stuff so I may likely fall flat on my face in attempting to express this, which is okay as I seek answers, and the questions may lead to them. Of course, correct me where I'm wrong, but do so in a manner allowing me to learn.

I have heard recently that the consumer-level 1.228 VRMS standard (CD player outputs, and most importantly, Technosaurus, Moog, and Buchla oscillator signal outputs, close and in general) is from the days of tubes.

That's good enough for me (so long as your filters and VCAs and Oscillator FM inputs are sensitive enough for this signal level to produce massive depths of modulation- The Moog does not; the VCA expects 5V from the envelope, so tremelo is a problem; the Buchla oscillators and filters DO have FM inputs optimized for this audio signal level, providing extreme goodness in this department. The Buchla VCAs only accept DC signals, as the control and audio paths in that machine are separate, which is not a problem. It provides for another way of looking at things and thus, doing things.)!

Integrated Circuit IC Upgrades

I remember and respect the great, late Tim Smith for his among other things paper and work regarding upgrading synth signal paths and digital synth D/A sections/reconstruction sections. Thank you Tim for the great information and friendship, and God bless and keep you always.

Tim was into the Analog Devices OP275 dual opamp and IIRC the Burr-Brown 0604 as well. He made the ARP 2600 into a new beast through this and other modifications.

I am sorry to have to eventually slightly differ on this, but taste is for each person and there are many choices. Tim and I start with the early discrete machines as a reference, such as the Moog 901 series oscillators, which he called "as close to listening to current as is possible" (again, IIRC, close paraphrase). The Moog and Buchla second-generation and later version oscillators went to early ICs on the outputs (CBS Buchla 158 has LM301A). Going discrete in these cases would be wonderful, but for those with these items, upgrading the ICs is of interest.

I note that the TL071 was created (indicated in the specs) to directly replace the 741, as a direct drop-in, hopefully at least in audio-related circuits (check the paperwork). This should be easy to try on the Moog 921 series oscillators, for example.

I recommend the 071 to at least try as it is much faster than the 741 (and you may only wish for 741-style phase and bandwidth characteristics in vintage phasers, delays, and not in oscillators). In some cases the bandwidth limiting etc. may be required for desirable spectral balance, the Oberheim FVS Four Voice etc. being a possibility, would have to hear the new next to the old to decide. The later opamps have slew rates of 25V per microsecond and over, and depending upon the circuit in which it is used, can result in tight, closed-sounding, controlled, slightly hard or glossy treble and overall character. You might like this. I am tending to the middle ground 07X type, as the discrete oscillators do not sound closed, controlled, tight, etc.

Again, I'd have to listen to two versions side-by-side in order to decide. I'm willing to do so :)

It's a very interesting question, especially regarding oscillators and filter signal paths.

I am of course aware of those who will mock the use of earlier opamps. They should be aware of the effect such opamps have in the signal path of early effects devices compared with their modern counterparts. Some phasers etc. can become too clean, and lose that gut-level musical "Yeah!" result. The same with synthesizers.

Overall spectral balance, especially on a multitimbral device, is very important. You may have seen the EQs in mastering labs; they may have 0.5dB adjustment increments. A musician will be able to hear these adjustments as they are made. A mastering engineer knows where to make these adjustments resulting in an overall musical improvement. I venture that the same occurs in synthesizers.

When I was at Alesis, a musician brought back a prototype of a new version of the QS line, saying that there were (specific problems) in the audio, compared to the older version. We craned our necks and cupped our ears listening for it, and it was there, subtle but definitely measurable on the test equipment. Yes, it was slightly brighter, and yes, this made a difference in overall character and musicality (spare me the "QS sucks!" remarks; I'm well aware, and was working to improve them while I was there, which was part of my personal goal at the company.).

Subtle changes in spectral balance can produce large musical results. Or the inverse.

Pasted from a thread:

Of course I don't recommend swapping the high speed devices into circuits made for the early low-speed devices, without planning ahead regarding optimisation, although it's worth doing blindly in circuits featuring the mid-level ICs such as the 072, just to see what happens. Even in "correctly designed" circuits, I find that the new ICs aren't quite for me, re-read the comments regarding even subtle spectral shifts. Big spectral shifts from "upgrading" or using "new" parts may provide lots of treble, but this immediately reminds me of hi-fi stores back in the day, selling speakers with graphic equalizers set to a "smile" configuration so that it was all boom and zizz. Perhaps impressive to some on a showroom floor, yet useless when considered over time. Some speakers were perhaps even made to this curve...shameful.

"More treble" is not automatically "better". I've long since stated this regarding the spectral balance of certain discrete vintage modules, and stand by it from a long-proven musical perspective. ADAMs, anyone? And again, listen for that closed, tight treble in circuits using the fast ICs. Some call it "audiophile"; I call it "closed and tight". Depends upon what experience you define as "music"...and to reiterate from the above: ..the discrete oscillators do not sound closed, controlled, tight, etc.

The 4558? It's in the TR808, good enough for me. Nice that you and Jurgen have listened to me regarding the need for such "slow" ICs as used in vintage FX, to provide that vintage FX sound. Thanks for listening. I see 741s in Jurgen's Schulte phaser clone, so that it will sound that close to the original. Very, very good. The 4558 is only just better than the 741, I -will- look into substituting it out in my CD changer, but will replace it if nothing sounds better -to my ears-.

Also, don't overlook the J-FET chips such as the LF353. Very useful for good-sounding upgrades of early chips, but not "too far" into the changes described earlier. Same sort of slew rate as the 072.

I am however perplexed at the need to use a $4.00 opamp to achieve the frequency reponse, dynamic range, and musicality of the old discrete transistor output sections, which are far less expensive and already a standard of sorts...

Isn't the 748 in the output sections of the Moog 921 and 921b? Don't have time to refer to the schemo. Yep, that should be replaced (by whatever is to you, musical). I'd prefer some sort of cheap, discrete transistor output as it's established and less expensive than some opamp choices.

luka wrote:

i agree re: 4558s in 808 jeff found that in mb808 using tl072 made the sounds to clean and lost the 808 vibe. 741s in the schulte phaser sounded great

I replied: Interesting about it "losing vibe". Yes, I agree (and many high-end stereo designers also agree) about vibe or musicality being first, being the goal. Yesterday I was reading a review about a particular Pass amplifier, about it being supremely musical (paraphrasing?) and that this negated its weaknesses. I'm in that school of things.

the bad producer:

071s are a good idea, as listed in its paperwork. Drop them right in without worry of any sort. You'll likely get a much cleaner sound, which you might or might not enjoy. I find that I prefer phasers to have that "vintage" midrange blur and whoosh. It gets me to say "yes!" and is to me musically inspiring. The Moog is the only recent phaser which causes in me a grinning musical response. I wonder what they're using, and how much is the result of the excellent overdrive circuit.

Muff wrote:

Well put, I think that's the heart of it. If one person likes a sort of character to sound, and another likes it differently, neither is wrong. Preferred musical style is the same. We do this for fun and enjoyment! I don't understand people who deride the preferences of others when it comes to subjective things. No matter what the test equipment may or may not say, if you like it one way, you like it that way. Simple as soup.

This is an interesting thread. Many may not realize that parts of their gear can easily be swapped in and out to change the sound character. This is fantastic for those who like to tweak, explore, tailor things to their liking. There's no wrong move if it is an improvement to the ears of the owner. Thanks for posting this Mike.

I replied:

IIRC in the DIY world there is a preamplifier which allows the user to select the opamp they most prefer, and a number of ICs are suggested for review. I really love this idea, and would love to see it take hold in the synthesis field. Including discrete opamps such as the inexpensive kits on Doesn't the Cirroco synth use discrete opamps? I wonder what that would do, on oscillator outputs, summed together, of if that doesn't do much, on the oscillator mixer and VCA outputs.

Using the Minimoog with CV converter velocity signals

Thanks to the Minimoog pro for confirming this insight/suspicion.

The Expression pedal input is to a VCA separate from the Output VCA connected to the corresponding ADSR. You'll have to read the manual and look at the schemo, but I surmise that there is a +5V signal normalled through the Expression input jack which is broken when a pedal jack is patched in.

You can use a stereo male plug to use a 5V velocity signal with this input. To add an Amount control, get a pot and crossfade between the 5V and the CV signal. Have a tech do this if you have any doubt about your ability here. Don't screw it up :)

From a response at

"The external volume input on the back of the Mini has a switching jack that disconnects a fixed voltage going to the second VCA. The schematic shows +10v applied through a 33K resistor, giving it about a 0 to +6 volt working range. So any voltage source in that range will work. My test indicated +5 volts was not quite 100% volume."

I see that the Studio Electronics MIDIMoog has a velocity feature, but it's a switch for on/off for each, VCA and VCF. I don't know if this imparts "full" velocity or not, but evidently, these good folk knew about this possibility from the beginning. Cheers to Greg and the rest at Studio Electronics!