The Incredible Mutation (And Restoration) Of The 360 Systems Frequency Shifter

The 360 Systems frequency shifter is a really interesting and fairly rare piece of analog gear, and well suited for use with synthesizers. There are at least two different versions of this device, with the earliest ones housed in a green case...

... and the later versions, sporting some circuit upgrades, housed in a blue case.

I remember first reading about this as part of the equipment listed on the back of the excellent first album by Larry Fast/Synergy "Electronic Realizations For Rock Orchestra". You can see one of these sitting on the top of the Moog Modular 15 in his studio at that time...

 

I had no idea what it actually was, but MAN did it sound cool! FREQUENCY SHIFTER!

Larry not only helmed the many wonderful and inspirational Synergy releases, but also added his distinctive magic to albums and tours by Peter Gabriel, Nectar, Foreigner, and others. A true pioneer.

Thanks, Larry!

My unit is a very early one, I think. A look at the serial number would suggest that it might be made in early 1975, perhaps serial number 8? Maybe, maybe not.

There's quite a bit of rework going on underneath the board. This is often the case with very early boards, as mistakes are discovered and repaired to make the early units sellable. A close examination of this board showed that entire power supply was laid out backwards (!) so all the diodes and capacitors had to be installed backwards to make it work correctly. The blue jumper wires make the proper connections here and there, and parts that were either forgotten or added later to make things work correctly are soldered on back here as well. I really like the 360 logo etched into the board. If you look closely, you can see that they actually used it to connect two traces!

 

The print ad for this (thanks, Riley!!) at the time made some very interesting suggestions about the capabilities of this unit, in typical 1970's flair....

Turn a violin into flannel bass??!??!? What the what? Good God, Y'all!

Those with sharp eyes will note that the case shown in this ad isn't the same case used in either the green or the blue production versions. This picture was probably the original proto unit.

As I mentioned earlier in my blog, I acquired one of the earlier green ones along with my Moog 55, and after a few simple mods and some recalibration, I was able to use it on various projects for a number of years. I remember calling the good people at 360 Systems at the time I got it to see if I could get a schematic, and it took a while for them to actually locate one at the factory! I eventually got a huge blueprint-size schematic in the mail, free of charge. Impressive customer service!

The most useful mod to it at the time was replacing some of the single turn trimmer pots in the balanced modulator sections with 12 turn trimmer pots, to allow for a more accurate calibration (the four green rectangles at the bottom left quadrant).

 

 

Adusting these pots allows you to reduce the amount of background noise and signal bleedthrough, and with the new more accurate trimmers in place, calibrating it was much easier, and improved the performance by a noticeable amount. I also at that time upgraded the generic opamps in the audio path with quieter devices.

In use, there are some pretty interesting effects to be had from this device. As you turn the shift knob, one output shifts things upward by the frequency set on the shift knob, while the other out shifts things down by the same amount. Things can get crazy pretty quickly!

With just a small amount of shift, and the up and down outputs panned hard left and right in a mix, a beautiful chorus sound is created, different from any others. It's said that the swirling "oooh" and "aaah" background vocals on Pink Floyd's song "The Great Gig In The Sky" are treated with a prototype frequency shifter, and that's what it sounds like to me...a sort of growly, swirly wonderfulness.

 

There's also a Ring Modulator output, to create all sorts of clangy, metallic timbres. I read somewhere that John McLaughlin used one of these units in the mid 70's with a footpedal to sweep the oscillator, and that seems likely to me as well...imagine the hyper-speed metallic goodness. Go Johnny, Go!

 

 

Ring modulators were starting to enjoy some well-deserved popularity in the early 70's. Oberheim built a stand-alone effects box type device (dig those crazy graphics!!!)...

 

...and also built a slightly modified version for sale by Maestro (they look quite a bit alike, eh?).

 

Artists like Jon Lord, Joe Zawinul and Jan Hammer were soon using them on their electric pianos and organs to produce a more interesting synth-like texture and create a pitch bend effect for solos.

For many artists at the time, this often served as a gateway (or at least a sideways entrance) to using synthesizers like the Minimoog or the Arp 2600, as they became more readily available.

 

 

I loaned my 360 Systems Frequency Shifter out to a friend, who at some point apparently decided that it was now his. When I finally got the unit back, he had proceeded to remove the circuit board, discard the case, and mount it into a single rack space casing. Like most of his (always very nicely made) devices, it was basic black, and all knobs, jacks and switches were unmarked. Feh.

After a number of phone calls, I was luckily able to track down the original case languishing in the back rooms of a recording studio (thanks, Roger!), and decided that when I got the time, I would restore it to its former 70's glory. The case had faded and discolored somewhat with time, but I still loved the sheer weirdness and funky mojo of the overall package.

GREEN! It's really an underused color.

My original schematic had gone missing, but after some sleuthing, I found a copy on the internet. I'll publish it here for those who might be interested. This would seem to be the scematic for the later model blue Frequency Shifter, as it differs in some areas from the components used in my unit, and the date on the print is from 1976. It was however plenty close enough to allow me to identify all of the necessary wiring locations on the circuit board to successfully transplant the board back into the original enclosure.

This looks remarkably similar to a schematic I saw in Electronotes back then for this type of device. It's certainly possible that one might have inspired the other...

 

Some important parts were missing. The original power transformer was gone, as was the cool green illuminated power switch and original potentiometers.

This also seemed like a good time to replace the electrolytic capacitors, as they were now 40+ years old, and the rubber seals were dried and cracked. The opamps in the audio path had already been upgraded a number of years ago, and I also wanted to extend the frequencies of the shift oscillator, and provide better CV control of the shift frequencies so I could easily control it from the Moog 55 and other devices.

The original unit had line level and instrument level outputs ( just the line level outputs scaled down with a resistor divider). I thought that the panel space for the instrument level outs would be better served by making them the inverted phase versions of the line level jacks. This could make for some interesting stereo effects during shifting.

I found a transformer from Mouser Electronics that fit the same mounting holes, and was just a bit larger voltage-wise than the original. I also found a functional green illuminated power switch...nowhere near as cool looking as the original, but it would certainly do until a better replacement could be found. These were fitted, along with a new power cable and strain relief.

 

The front panel was cleaned, and the new power switch, jacks, knobs and pots were installed. You can see some of the discoloration around the screw holes, but it still looks pretty good, I think.

 

 

Adding the parts for the output inverters and the improved CV scaling would require the addition of a small board to hold the necessary circuitry, so I built everything on a small perfboard and mounted it to the inside front panel of the unit. This made wiring up the various outputs easy and kept the lead lengths short.

When I fired it up initially to take a look at everything, I found that that the transformer voltage was indeed too high. This made the voltage regulators on the main board overheat since they now had to dissipate the extra power to bring this higher voltage down to the required level at the main board.

I added a couple of small 5 watt resistors to each side of the transformer outputs to soak up the extra voltage, and secured them to the top of the transformer with some silicon rubber adhesive. This reduced the power dissipation of the regulator, and now things were running nice and cool again. I also upgraded the 12 turn trimmers to grey 20 turn trimmers, since one had gone intermittant after all these years.

 

 

 

 

To extend the frequencies of the shift oscillator, I bought a 5 position rotary switch to replace the original 3 position switch. Now I had a position below and a position above the original panel marking. I added the appropriate capacitors to the shift oscillator circuit for the two new positions, and that gave me a lower and higher shift range, as compared to the original circuit.

After a bit of wiring to connect all of the front panel controls, and some tesing to verify that all of the various circuits were functioning correctly, it was time to reassemble the board into the original case, and recalibrate the system.

 

The unit is still missing its unusual gigantic radio tuner dial to set the shift amount, but I believe that it's merely biding its time hiding in my storage space. Until it returns, I did manage to find a smaller version to keep the front panel from looking too barren.

And so here it is, in all of its Mighty Green 70's glory, its Mojo and Mighty Shifting Powers intact!

Good God, Y'all!

 

 

 

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Sequential Circuits Artifacts

Sequential Circuits ran a number of interesting print ads back in the 70's and 80's. I was a big fan of their products for a number of years, and in the early 80's I was finally able to purchase one of the first Rev 3 Prophet 5's. I was taking weekly synth lessons from P5 co-designer John Bowen who told me to wait a bit to get the upcoming Rev 3 model, a decision that has served me very well (thanks, John!). I remember driving down to San Francisco and picking it up along with a blue Roadrunner hard case from Don Wehr's Music City on Columbus St. (A great place, now long gone, sadly).

I remember this seeing this ad (probably in BAM magazine) by Mattos...one of my favorites!

 

The address would indicate that this was from before they moved into their official headquarters on North First Street in San Jose.

I was fortunate enough to make some good friends there, and visited from time to time to update the software on my machine, gawk at all the cool stuff being built, catch up on the latest happenings and discuss such weighty matters as adding Midi or a remote keyboard to my system. Good Times, Great People.

At some point, I picked up this set of road case stickers for various products, including my favorite..the P5 Sphinx. I think that there might have originally been a few others, but these are the ones that remain. I haven't really seen these around much, so I thought I'd post them here, before they vanish for good. Hope you enjoy them!

 

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Gettin' Some Serious Control Of The Moog 55 Modular!

The next round of modifications For the Moog 55 came about to increase the system's usefulness in studio and live performance.

Although the 55 looks like a very large and powerful system, there are some things about the way it's implemented that limit its abilities, and not always in ways that are immediately apparent.

Well, some are obvious. Seven VCOs and ONE lowpass filter? I mean, C'MON.

But hey, that's a pretty obvious one, and you knew the job was dangerous when you took it.

Sure there's also a highpass filter, but on its own, it doesn't give a lot of flexibility for voice shaping. There's a set of 6dB/octave lowpass and highpass rotary switches that I still haven't figured out much use for even after all these years (and I'm certainly open to suggestions here).

There's other things that are less obvious, but pop up as annoying limitations as you use the system more and more.

For instance...

Hey, there's no real dedicated LFO. Sure, there's the big standalone 921 oscillator, but using it as an LFO seems like a criminal waste of its many capabilities. It's the only oscillator in the system that can be hard synced via the Clamp input, and who wants to give up an incredible audio oscillator as a lowly LFO anyway?

On the other hand, it is syncable and resettable when used as a clock, and the adjustable differential auxiliary output makes for great stereo panning effects when patched to a couple of VCAs, it has a reverse sawtooth output...maybe it IS just a very capable (and expensive) LFO. It's puzzling. At any rate, where are the simple LFOs? Not here...

 

The 921B oscillators can be set low enough to be an LFO, but each of the two banks of 921B oscillators are tied to a single 921A controller. You can't use the other two oscillators as audio oscillators tracking the keyboard without the third (LFO) oscillator tracking the keyboard as well. What the what??!??!

 

Yes, that's right...there is NO way to control these oscillators individually! There's no separate CV tracking inputs, and no way to separate them from the 921A controller. So in reality, instead of having 7 oscillators in the system, you have 2 groups of 3 oscillators that must track the same pitch CV (so basically you have two fat oscillators) and one super oscillator that will, in most instances, end up being an LFO.

Erg.

This was a sobering realization as I started trying to create larger independent patches.

Another hidden limitation is that all three 921B oscillators in a group share the same pulse width, and the same amount of PWM if applied. If you set the 921A controller so that one oscillator is a square wave, all three are square waves. There are no individual CV inputs for pulse width on the 921B modules. When you consider just how useful poly PWM is for creating lush animated leads and pads, this becomes a baffling omission for a top of the line system.

Even the MiniMoog lets you set separate pulse widths for each oscillator, and even though they don't have PWM, there are certainly some classic sounds to be had there.

Now, to be completely fair, all of these things I've listed here as limitations actually tend to underscore what was still the main purpose for this system back in 1974.

It was designed as a studio instrument, where you would use recording techniques like overdubbing to build up a complex sound, instead of having lots of individual control of all the basic elements. While I could see and understand this approach to using the instrument, I was increasingly missing the touches that would further unlock the many capabilities that lurked beneath the surface, tantalizingly out of reach. And for live performance, having this kind of flexibilty greatly increases the usefulness of the system, since it can be patched to do more at once.

So, here's what I did about it (deep breath).

 

The schematics show that each 921B already has the necessary circuitry to be controlled by multiple CVs for both the pitch and the pulse width. The only thing required would be a summing opamp circuit for each, an easily implemented circuit. This would duplicate the actions of the summing circuits in the 921A...in essence giving you two (or more) separate control inputs to these oscillators. This seemed like a promising place to start...

 

I also needed to create some jacks as inputs for these new CVs, but the oscillator panels are already filled with jacks, and I didn't want to lose any of the current sync or FM capabilities.

My solution was to replace the mono jacks used here with TRS stereo jacks. Now, if I plugged a cable in halfway (first click) then the incoming signal would go to the original sync or FM destination. If I plugged the cable all the way in, then the signal would go to the new pitch or PW destinations. I could use a TRS splitter to drive both destinations at once if desired, and best of all, the mods would be invisible from the front panel.

 

 

I designed and built the additional summer boards using surface mount technology. This gave me a very small footprint, as the circuitry is fairly simple, and allowed me to use some very beneficial components.

With pitch inputs to summers, the input resistances must be very closely matched to tolerances of .1% or better to get proper tracking from multiple CV sources (like if you planned to drive an oscillator from a sequencer and also a keyboard to make transposition changes). Companies back in the day like Emu Systems or Sequential Circuits often had someone dedicated to measuring and binning vast quantities of 100k ohm metal film resistors all day long to feed production needs, using accurate test meters or a specialized test setup.

For my summers, I opted to use precision surface mount thin film resistors from Susumu that are already factory matched to .01%. These excellent resistors cost a little more, but the end results are worth it. I also chose a surface mount precision low drift dual opamp for my design that served as both the pitch and PW summers. All of this was built onto a Surfboard 9161 prototype board including a fine tuning trimmer for the pitch CVs.

Now, I know that there are some people who are wary of their abilities to solder surface mount components, but with good equipment, practice and patience, it's not really that difficult, and the end results can be quite good.

 

There was even enough room at the bottom to drill a small hole to allow for mounting the boards on the oscillator module via a stick-on nylon standoff.

 

As I thought about how I might use this, it occurred to me that it would also be useful to be able to disconnect the CVs coming from the 921A to increase the amount of independent control for each oscillator. For this, I decided to add a set of small switches to each 921B for the pitch and PW controls coming from the 921A. This way, each oscillator can be controlled from an external CV, the 921A, or both!

Hey, now we're gettin' there!

 

 

After carefully selecting and drilling the locations on the oscillator front panel, I installed a pair of short bat toggle switches. Using a nice dress nut instead of the standard supplied hex ones made them look more like original equipment on the panel.

These switches connect or disconnect the pitch and PW summing signals from the local 921A module for each oscillator.

After a bit of tweaking and tuning, each oscillator worked great, and was now completely addressable from any internal or external CV sources.

 

And, everything looked great installed back into the system as well, I think.

 

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The Oberheim SEM Modular Project

Over the years I've collected several of the original Oberheim SEM modules, and quite a while back a friend gave me an abandoned Oberheim case for a two voice extension. This had a supply built in...

...and aside from the space for the two SEMs, there was a small panel for a mono mixer/headphone amp, and a cool-looking blank panel with a nice plastic badge and the Oberheim "marching musical note" logo holding a spot that could accommodate the Oberheim mini-sequencer.

I was never able to find one of those sequencers that I could afford (a friend had one, and I thought that it was pretty cool) but more recently I started to think about turning that blank panel into a nice patch bay for the unit, making it easier to interface it with some of my other synths, especially the modular system.
It already had a few patch points on the back panel for oscillator CV in and a gate, but one of the truly beautiful things about the SEM is that there are a large number of patch points inside the unit that can be accessed by connecting wires and a Molex connector the the appropriate spot. It's easy now to find a copy of the schematic on the web, and a quick look will show the large number of useful spots that you can take advantage of, in essence turning this already useful module into a mini modular system of sorts. The voltage levels available will likely play very nicely with other components in your setup, and give you lots of cross-patching capabilities.

Although I've seen other patchbays of this sort that employ the smaller 3.5mm jacks for interfacing, my requirements are strictly old school, and I decided to use typical 1/4" jacks for my project. This means that there would be fewer total jacks in the space, but it would make for easier connections to my gear. I found a source for TRS Neutrik jacks with both connections normalled at a very good price, so I purchased a supply of these for my project. This type of jack configuration would give me the most flexibility for any type of connection that might be needed, including normalled inserts, if desired.
Using the front panel washer for these jacks, I started trying different physical layouts for the panel, trying to get the desired connections with most flexibilty without the panel being too crowded.

I had already made a list of what connections I wanted brought out to the panel, and used that as a guide to start with so I wouldn't miss any important ones. I also started to think about what connections should be normalled, so bringing in one oscillator CV would drive all the oscillators on both SEMs, unless I wanted to patch in at other points to separate things. This same idea was also applied to other CVs for the filter and the external CV busses, as well as the gate signals. The final connection of the normalled chain was on the back panel, so I could connect cables here that could be out of sight in my system to reduce the front panel clutter.

Once I found the layout that I was happiest with, I covered the blank panel with masking tape and carefully marked the drill locations for all the holes. When drilling the panel on a drill press, I started with a small drill bit to allow me to more accurately locate the desired position, then cycled through several progressively larger sizes until I reached the 3/8" hole required for mounting the jacks.
I removed the masking tape, cleaned the panel, and tentatively installed the jacks so I could apply the lettering for the various patch points.

For this part of the project, I used an old Brother labelmaker, and printed labels using black letters on clear tape.
Using a pair of sharp scissors, I cut away all the excess tape from around the borders of the actual lettering, which made the finished project look much more like it had actually been silkscreened instead of done by labels. Using an X-acto knife to hold the edge of the labels allowed me to more precisely poistion each one before I applied pressure to bond them to the panel.

The finished panel looked pretty good, so the next step was creating the wiring harness complete with Molex connectors.
I set the case and panel on my bench so I could estimate how long each individual Molex cable had to be, and put a temporary tape label on each one with the name of the connector it would eventually mate with.

This allowed me to create a less cluttered wiring harness that would fit more easily inside once the system was assembled. Once everything was cut and measured, the Molex connectors were attached to one end, and the appropriate jacks were wired to the other. The normalled connections for the jacks were made at this time, and a separate small harness and connectors was created to make the necessary connections to the back panel.

The little mixer panel was originally set up to provide a mono output, but it seemed like it would be really useful to have separate outputs for each SEM module. I added a bit of wiring and a couple of extra jacks to allow for individual outputs which really opened up a lot more possibilities.

Everything was connected, the jacks were all tested for proper operation, the tape markers were removed, and the unit was finally completely assembled and retested.

The final unit worked just like I had hoped, and will be used for several planned projects linking the Oberheim, Moog 55, and my Prophet 5 keyboard together as a system.

A future modification will add an internal noise source and a sample and hold module for each SEM...I added these a few years ago to a standalone single SEM I have, and really liked the added flexibility.


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