Friday, October 31, 2008

Minimoog mystery solved, maybe

Back in March, I put up this post on the mystery of who owns the first production Minimoog. At the time, there appeared to be two contenders: The Eboard Museum in Austria has a unit that they advertise as being S/N #1001. The Audities Foundation owns one that several third parties who have seen or used it claim is #1001 (the Foundation itself made no such claim, which should have been the first clue, but there was a confounding factor which I'll get to in a moment).

The Moog Archives seems to have resolved the dilemma. It now appears that the Eboard folks do in fact own production #1001. Audities also owns a unit #1001 -- but it's not a production unit; it's a prototype Model C! (All of the vintage production Minis are Model D, except for the handful known as the "Welsh Minis".) The Audities photo that I reproduced in the March post is not this synth. Here is that synth:

Note a few things about it. The big thing is the pitch and mod wheels -- they are completely different from anything that ever appeared on a production Mini. In fact, I'm not sure that they are wheels at all; they may be sliders. Second, note the A-440 oscillator switch; it's a plain toggle switch rather than the typical rocker, and it's a bit to the right of where the production Mini has it. Third, the pilot light: It's higher up on the panel than the production article.

(The thing sitting on the panel that covers the keyboard keys' hinge mechanisms appears to be a ribbon controller of some sort. My guess is that it was added later.)

I had speculated in the March post that Moog may have assigned serial numbers to prototypes and then later re-used those numbers for production units. And sure enough, it appears that that's what happened here. Another clue to the Eboard one is the white-background logo plate, whose legitimacy I had questioned back in March. The Moog Archives now says it's legit; it's the earliest version of the R. A. Moog logo. Unfortunately, we don't have the Audities one to compare to; if it ever had a logo plate, it appears that it was removed when the ribbon controller was installed.

I think we can conclude that the Eboard Museum legitimately has the first production Minimoog. The Audities Foundation has a prototype.

Saturday, October 18, 2008

The Hammond is working!

Started it tonight. At first, I was getting no sound except for a slight hum from the reverb channel. Checking, I found that two tubes in the preamp were cold -- the 12BH7 and the 12AU7. And I thought I had them packed very carefully. However, it got me thinking: I've had problems before with tube sockets not making good contact. So I pulled the offending tubes and pushed them back in, very firmly.

Started it again, and it works! Some of the drawbars are a bit crackly, but I think that will work out with some playing. As usual with this unit, it takes two or three tries with the start switch to get the start motor to engage, but that's no big deal. Everything works and the rotating mechanisms are all quiet.

To celebrate, I hereby present some Hammond-guts porn. The preamp:

The power amp:

The reverb amp:

The run motor, scanner, and flywheel, illuminated by the pilot light:

Wednesday, October 15, 2008

Why does the Juno-60 sound different from the Juno-106?

As you already know if you've been following this blog, I have a Juno-106 that I bought new in 1984. I've always been a fan of its sound, and I keep mine going despite the reliability issues with the 80017A IC's. I've never owned its prececessor, the Juno-60. But many people who have owned both say that they don't sound quite the same -- the words usually used is that the 60 is possibly a bit more mellow (that dreaded means-anything-anyone-wants-it-to-mean word, "fatter"), while the 106 is possibly brighter, "cold" (another one of those non-words), and some people even say it sounds "digital".

So let's start by getting a couple of things on the board out front. The VCO, VCF, and VCA circuits are nearly identical. "How can you say that", you might ask, "when the 106 uses those 80017A's that keep failing, and the 60 doesn't?" Consider: The 60 uses a VCF filter circuit based on the IR3109 quad OTA. It uses a BA662 VCA to control the resonance. A second BA662 serves as the voice's VCA proper. As for the 106? The notorious 80017A is really just an encapsulation of three ICs and some resistors. The IC's? An IR3109 and a pair of BA662s! It's the same circuit, just in a smaller package. A lot of people don't realize that when you look at an ordinary IC, most of what you see is packaging; the actual integrated circuit is a tiny bit of silica embedded in the plastic. Roland bought a bunch of unpackaged 3109s and 662s and had someone encapsulate them, and voila, the 80017A was born. Similarly, the Juno-60's DCO circuit: the counter IC that times the DCO, the reset transistor, and the wave shaping circuitry are encapsulated into the much-less-infamous (because it seldom fails) MC5534 in the Juno-106. The voice circuits are, for all practical purposes, the same.

So assuming that there is a difference in sound (and I've heard enough reliable witnesses say there is), where could it be coming from? Let's take a look at the rest of the audio processing: the portion that follows the summing amp, which combines the six individual voice signals into a single mono signal. A lot of Juno players don't realize that there is not a highpass filter per voice; Roland cleverly placed the HPF switch on the panel to suggest that the HPF precedes the VCF, but it isn't so. There is only one HPF circuit for the whole synth, and it works on the summed mono output of the voice circuits. Following the HPF is a seventh VCA, which is tied to the VCA level control on the panel (that bit looks like a kluge; maybe I'll write about it later), and then the chorus circuit, which takes the mono input and produces a stereo output. There's a bit more stuff for the master volume control and the various outputs, but all of that is bog-standard IC amp and buffer circuits.

The chorus circuit on the two synths looks the same; there may have been minor improvements that have eluded my quick scan of the circuits, but they both use the same bucket brigade ICs, the same control circuits, and the same gain make-up circuits (there is no noise reduction, which anyone who has heard either synth on headphones has already realized). However, I found some differences in the HPF circuits. First of all, on both synths, the HPF is not a voltage-controlled filter. It's basically a set of four passive RC filters. The panel or recalled setting controls an 1-to-4 analog demux which routes the signal through one of the four.

The one on the Juno-60 is pretty straightforward. Here's the portion of the schematic:

The four outputs of the analog demux are on the right (the two inputs from the control CPU are on the bottom, and the mono signal enters at the top left at pin 3). The pins are labeled as to the corresponding position of the HPF switch on the panel. As you can see, going up from output 1 to output 3, the signal gets routed through progressively smaller-valued capacitors; the smaller the cap, the higher the cutoff frequency. The output for position 0 has no cap; it's just a straight wire, so position 0 of the HPF is actually no filter at all. It's straight through.

Now here's the corresponding circuit from the Juno-106:

As you can see, it's more complex. First things: I am pretty sure that the CPU is sending the two input signals, A and B, inverted. Therefore, the pin labeled "Y0" corresponds to position 3 of the HPF switch, "Y1" is position 2, etc. The opposite interpretation doesn't make sense when you look at the circuit.

Now note the first difference: The straight-wire output corresopnds not to position 0, but to position 1. The circuits for positions 2 and 3 look pretty similar to the ones on the Juno-60. But what's all that business connected to the position 0 output, around IC4b? Well, it sort of looks like a Sallen-Key filter, as used on the Yamaha GX1. What's it doing? Note C8, the 0.01 uF cap shunted to ground. That's a lowpass filter! This part of the circuit is acting like a bass boost. (C6, I think, is just there to keep IC4b from self-oscillating.)

Second difference: Note IC4a. In both the 60 and the 106, the "seventh" VCA that I mentioned earlier immediately follows this HPF circuit. Although the VCA is an oddball part ("uPC1252"; the only data sheet I've found is in Japanese, but some Googling reveals that it was manufacturered specifically for dbx), it doubtless is based on an OTA circuit, and like all OTA circuits, it loads the input some, particularly as the gain is decreased. The Juno106 uses IC4A to buffer the input to that VCA. The Juno-60 doesn't have that buffer; it couples almost directly, only separated by a DC-blocking capacitor. That means that the 1252 VCA is loading down the outputs of the passive filters on the 60, which introduces high-frequency rolloff. So the HPF actually acts a bit more like a fairly wide bandpass filter, particularly as the VCA level control on the panel is turned down and the input impedence of the 1252 decreases. That doesn't happen on the 106 because the buffer amp provides a constant high input impedence for the HPF output.

Third difference: The analog mux used is a different part. The Juno-60 uses a 14051; the 106 uses a 4052. They work basically the same way, but possibly the properties of the analog portions of the two circuits are different. I need to look into that some more.

To me, the biggest difference is in the configuration of the filters, with the 106 providing one "high pass" position which is actually low pass. And, the loading of the filter circuit on the 60 is probably significant; circuits with some rolloff above 8KHz or so are often perceived as "warmer" by listeners. Maybe I'll have to get a 60 so I can compare them myself.

Tuesday, October 14, 2008

Bringing in the Hammond

Last weekend, my stepson came over and helped me move the Hammond in from the garage to the new studio space. Before we moved into the new house, it was stored in (climate-controlled) storage, and then it had to wait in the garage for a while. All in all, it hasn't been played in about 2-1/2 years. So there are a few things that need to be done first.

About the organ: It's an A100, one of the spinet styles that Hammond produced mainly for the home market. Despite that, it's a full-up tonewheel organ, with exactly the same layout, sound generation, and controls as the venerable B3. In fact, if you are looking for that B3 sound but find the price tag daunting, you can pick up an A100 and get that exact same sound for $500-1000 less. I don't know why it is that the A100 should sell for that much less than the B3 when they both use the same components. The only difference is that the A100 contains a built-in power amp (two, actually) and speakers, so you don't have to have an external tone cabinet to play it. (Despite that, it does have a socket for connecting a Hammond tone cabinet, or with the proper adaptor, a Leslie.)

The A100 weighs about 350 lbs., and this one has a magnetic attraction for my toes. I actually dropped it on my toes once! So, of course, as we were moving it in, my shoe got stuck in a gap in the floor between the hallway and the room, and it nearly ended up on my toes again. But I eventually got myself unstuck, and now here it resides in all its glory:

Once it was in place, the first step, after a good vacuuming, was to unlock the generator's locking bolts. The generator, and all of the rest of the rotating mechanism, is suspended by a set of springs for mechanical isolation while in use. For transport, it has to be locked down to avoid damage. Here is one of the locking bolts, protrouding from the underside of the generator shelf:

Next step: oiling the generator and motor/scanner assembly. The generator has two funnels on top of it. To oil, fill each one of these funnels with Hammond oil once, and then let it drain. The oil runs into a resevoir and from there to a bunch of little cotton threads which convey it, via capillary action, to the many bearings inside the generator. I don't have a good shot of the funnels (there will be a video of this part up next week), but here is the front of the generator:

The motor/scanner assembly has a little pot on top of the motor which contains a cotton pad. To oil, squirt oil on the pad just to the point of saturation. More will not do any good; it will just wind up all over the place and possibly crud up the contacts of the scanner. Here's a shot; the motor is the square box, with the oil pot on top of it. The scanner is to the left:

Note that this is the run motor. The start motor is at the other end of the generator; it doesn't require regular oiling. However, while I was in there, I put a bit of oil on the mechanism that couples the start motor to the generator shaft. This particular organ has always had a bit of trouble with the start motor not engaging the shaft, and some oil seems to help.

Now, since the organ hasn't been started for a while, I'm going to wait a few days for the oil to propagate through the mechanism. As it happens, I had to go out of town for a few days on business anyway.

The next step was to reinstall the tubes, which I had removed and packed away before the organ was moved from the old house. This organ has a bunch of tubes carrying the Hammond brand. Now, Hammond didn't actually make its own tubes. I'm not sure who made them. They are all noted "Made in Holland". Here's a 6Y5 full-wave rectifier tube, from the reverb power amp:

And a 12AX7 from the preamp:

So when I get back, it will be ready to attempt to start. Before I do that, since it hasn't been on for a while and the filter capacitors are likely completely discharged, I need to come up with a way to limit the power inrush the first time it's turned on. I think I know where I can borrow a variac, but if I can't find one, the backup plan is to plug together all of the long extension cords I bought while were were building the house, about 200' worth, and plug the organ into that. That much wire should do a fairly decent job of limiting the inrush. I'll turn on the run switch for a few seconds, without trying to start it (I'll bet it won't start with that much voltage drop). Then I'll get rid of all the extension cord and attempt to start it.

A few glam shots: Some of the drawbars.

The start and run switches. Older Hammond tonewheel organs have a run motor (the one in the photo above) which is an old-style synchronous motor. It does a fine job of regulating speed once it's started, but it does not have enough torque to start by itself. So there is a second, compound motor which does the starting. It's sort of like starting a car: You switch on and hold the start switch (it's spring loaded) for about six seconds, while the start motor cranks it up. Turn on the run motor, wait a second or two for things to stabilize, then let the start switch go.

Something that a lot of Hammond players don't know about: This is the patch panel that alters the fixed presets (the reverse keys that don't correspond to a set of drawbars). You change them by moving the wires from one terminal to another. Hammond put a paper sticker on the back of the generator compartment cover that explained how. I was surprised to find this still intact when I first took the back off of mine, and I preserved it. I'll summarize it in a post next week. Note the little white cloth sack hanging from the far edge; it contains spare terminal screws. I've got some special plans for this panel, which I will explain in a future post.

Sunday, October 5, 2008

Synth pop, circa 1961

A VSE thread today pointed me towards Max Crook's Musitron, with which he recorded (among other things) the keyboard solo to Del Shannon's 1961 pop hit "Runaway". Reading further, it seems that the Musitron, a custom instrument constructed by Crook, was based on the guts of a Clavioline. The Clavioline was one of several almost-organ, almost-synth type devices designed between 1940 and 1960, which can be regarded as predecessors of the Minimoog. Other such instruments included the Ondioline, the Maestrovox, and the Hammond Solovox.

All of these were variations on an idea: a monophonic instrument employing a single oscillator, generating a harmonically rich waveform (usually a square wave, or close to it). Divide-down circuitry produces 3-6 octaves' worth of notes from this. Then, a set of 10-15 fixed high pass and low pass filters can individually be switched in or out of the circuit by stop tabs or other controls usually mounted on the front of the keyboard, below the keys. Various combinations created formants that could, if one listened with an optimistic ear, approximate various string, brass, and woodwind instruments. Other combinations could produce then-novel tones. (A few types also had primitive envelope generators. More often, a knee lever was provided for the player to control the envelope manually.) The filters were usually basic, single-pole passive RC or LC types. Combining them could result in a number of complex response curves. It is not clear how the different values of the filters were arrived at by the designers, and there is surprisingly precious little design data available on the Internet. Presumably the filter combinations were developed empirically, so as to approximate the tonal characteristics of the instruments being imitated, although they may have had means available to research body formants of those instruments. Or perhaps they just guessed. In any event, with no buffering, switching in various combinations would have caused the filters to interact, probably leading to a lot of cut-and-try guesswork.

The resemblance to a analog subtractive monophonic synthesizer can be seen. An oscillator generates a harmonically complex waveform, and filters remove parts of it to produce a desired tone. Of course, the filters are fixed, there is no voltage control, and no proper VCAs, so the analogy only goes so far. Nonetheless, these instruments did have another component which was to appear in synths much later: the low-frequency oscillator. It was hard-wired to vary the frequency of the audio oscillator, and only a few rates and 2-3 depth settings were available.

Of course, all of the circuitry was tube-based, transistors having not been invented yet. No doubt this limited what could be done, not only from a strictly technological standpoint, but also based on cost, portability, and what the customer was prepared to put up with. The fully polyphonic Hammond Novachord was no doubt an impressive technological achievement in 1940. Owing in part to the number of tubes it contained, it's probably also true that it was very expensive (in retrospect, it's rather remarkable that Hammond was able to sell 2000 of them), capable of heating a small house, and, most importantly, it probably only ran a few hours at a time. Given the average operating life of most type types in those days, multiplied by 146 tubes, it probably averaged a tube failure every 10 hours or so. This may have been what ultimately killed it, and perhaps explains why only a handful of Novachords survive today.

One obvious way to address all this is to make a monophonic version. For that, you only need a few tubes; it ends up being a lot more portable, and most importantly, a lot less expensive. The inability to play chords didn't matter so much if the instrument was intended to be an adjunct to a piano, and many of these instruments were designed so that they could be fastened to the underside of a piano keyboard, in addition to being played on their own stands. And this is most likely how several designers arrived at fairly similar instruments.

Generally, the keyboard came with a combo amplifier which was an integral part of the instrument, providing power to the keyboard as well as amplification. Further, the amplifier was designed to perform wave shaping and other types of distortion and non-linear frequency response to further shape the instrument's overall sound. The amplifier was usually designed so that it and the keyboard could be fastened together to make a single enclosed case, for transporting.

The Clavioline was featured on several early rock hits, in addition to the aforementioned "Runaway". Max Crook himself had several minor hits under his own name, performed on the Musitron, as well as using it on nearly all of Del Shannon's songs. Producer Joe Meek had a Clavioline, and he used it to play the distinctive keyboard melody on The Tornadoes' original version of Telstar. (Answer to a trivia question: "Telstar" was the first song by a British group to reach #1 on the USA Billboard Hot 100 charts.) Among the groups The Tornadoes beat out for that honor were The Beatles, who later featured the Clavioline on "Baby You're a Rich Man". Jazz musician Sun Ra made frequent use of the Clavioline. Meanwhile, Crook continued development of the Musitron. He started by adding a spring reverb, made from hardware-store springs. Later, he gutted a reel-to-reel tape recorder and used it to incorporate a tape echo system into the Musitron, which also provided some effects capability by means of varying the tape speed. Crook went on to devise a more advanced instrument with true percussion sounds as well as a real-time pitch bend capability. Additional development continued in other quarters. The Ondioline had its keyboard mounted on a mechanism that allowed left/right movement of the key bed; using a guitar-like finger vibrato, the player could add vibrato or other effects to the sound. Selmer in the UK produced a version of the Clavioline with selectable sub-oscillators. Harold Bode developed a range extension for the Clavioline, and later developed a polyphonic version dubbed the Tuttivox.

The advent of performance synthesizers like the Minimoog (1971) probably would have killed off the Clavioline and its kin, but it appears that they were already out of production by then. What may have happened was that players in the mid-'60s discovered that combo organs could cover the most useful territory, cost about the same, and had the advantage of being polyphonic and more reliable. ((This was ironic since the first successful product of the Jennings Musical Industries company was a version of the Clavioline called the Solovox. The company later went on to produce the iconic Vox Continental combo organ.) It does not appear that anyone ever built a solid-state version of the Clavioline: by the time such a thing would have been practical, there was no point, as Moog and Buchla had already gone beyond it with their early voltage-controlled oscillators and filters.

The Clavioline-type instruments filled a gap between the first electronic instruments, and the availability of musician-affordable synthesizers in the early 1970s. They may seem crude and cheezy now, but at the time they were regarded as radical by popular music listeners used to the familiar timbres of guitar, sax, organ, bass, drums, and strings. They helped popularize the idea of new and unusual sounds, and helped pave the way for the use of synths in rock, jazz, and pop music.

Thursday, October 2, 2008

Got a few extra minutes? Why not build your own polysynth?

VSE contributor "adamstan" designed and built his own analog polysynth from scratch. Holy cow. The spirit of DIY lives! Here's some info from the thread on VSE:

"I consider it to be a 'Poor mans Memorymoog' with a little bit of Prophet 5 thrown in . It features:-

  • 5 voices- 2xVCO per voice
  • 3xEG per voice (hardwired to pitch, cutoff and volume)
  • 3xLFO (pitch, cutoff and PWM)
  • Moog ladder VCF
  • Noise source
  • Ring Modulator
  • Patch memory (128 user patches)
  • MIDI
  • Mono mode with selectable note priority (High/Low) and triggering (single/multi) and with portamento
  • Unison with adjustable detuning
  • VCO A offers sawtooth, square and triangle.
  • VCO B offers sawtooth and square waves.

"It's built using only standard off-the-shelf components - no CEM or SSM or similar chips inside - only typical opamps, switches, transistors etc."

"Case (together with keyboard) was salvaged from some crappy 70's combo organ."

It uses a scanned keyboard and microprocessor control of the panel. It has what appears to be a two-line X 80-character backlit LCD display. Adam wrote the firmware himself. Here's a photo (it's the one on the bottom, below the Siel):

The guts:

A close-up of 4 of the voice boards, mounted edge to edge. Note how small they are:

This, needless to say, is one heck of an accomplisment. To build an analog polysynth, at a time when none of the Curtis/SSM component ICs are available any more, and one can barely find a simple OTA -- a great piece of work, absolutely terrific. Adam says it cost him $1600 in parts. VSE contributors are comparing to the $2000 (price via Sweetwater) Prophet 08, and wondering how much it would cost to mass produce. That's a hard question to answer; a company like DSI could certainly get the parts cheaper and realize economies from mass production, but that would be offset by the cost of the labor (Adam's labor was obviously free to himself; he hasn't said how many hours he has into it), and the fact that Adam used a gutted combo organ for the keyboard and case (hence the funky reverse keys in the bottom octave). My back-of-the-envelope calculation is that with the R&D cost already sunk, a rack mount/tabletop version could be manfactured for about $800 and retail would be around $1300.

Here is a link to sound samples, many of them. As I wrote on VSE, the basses and leads are quite Moog-ish, which is no surprise since the synth uses the Moog transistor ladder VCF design, but the pads and strings have more of an Oberheim vibe to me. The ring modulation is a plus and it lets the synth do a lot of things that most vintage polysynths can't do. The synth apparently doesn't have an auto tuning function, as the author mentions that it drifts some, and that can be heard in some of the samples. (It does have variable detuning in unison mode, so don't let the lead samples throw you off.) I personally am not a big fan of synths that don't stay where I put them regarding tuning, but it's what a lot of synthesists want these days, at least from an analog synth. My only other complaint, judging from what I've seen and heard, is that I don't like where the pitch and mod wheels are placed; I'd rather have them to the left of the keyboard. (They are where they are because the recycled combo organ case didn't have room.)

All in all, a brilliant piece of work. I can't help but wonder how much it would cost to get someone like Ken Stone or Bridechamber to mass produce the circuit boards and sell them as kits.