Ready again…

Recently I checked the mod boards in the SE1X to find out that there still was some level mismatching. The intended 0.775 volts RMS on any stage output and external input were not yet achived.
So I removed the boards and did some additional modifications. Here’s a photo of the updated boards. No, these are not the boards for 6 SE1X’s but the complete mod for one single unit!
And it’s not even the full mod, the controller board shown above as well as some meters of additonal wiring belong to the upgrade too.

During re-assembly I will check the levels starting at the VCA back to the VCOs and have the last missing parts installed, once the required values have been determined. Stay tuned!

Stacking it up

As circuit design is finished and most PCBs are populated now, it’s time for assembly.
First of all the controller boards need a place:

Here you can see the Controller Board on top of the original SE1X CPU and analog boards.
An additional copper-cladded PCB should prevent digital noise from the new microcontroller to disturb the analog board, although the small ATmega @1MHz with no fast clocked outputs would not make much EMC trouble either. The Controller Board gets its +/-15 volts supply directly from the PSU, all other voltages (+/-12, +/-7, +5) are generated on board.

The board lying on the table is one of three VCO jack boards. The functions of its 8 jacks is alrady outlined in the previous post.

I thikn it’s time to wire & fire things up…

The MIDI jacks from the SE1 CPU board have been removed and extended by shielded cable to allow the DIN jacks to be fitted in the new rear panel, same will apply to the IEC power connector.
Yes, it’s supplied from an isolation transformer, and yes, the open frame PSU is a nasty little devil and will be replaced by something more safe and silent.

The VCO1 Jack Board is now connected to the Controller Board by several (yellow) cables, carrying control voltages of different kind. The two shielded cables are hooked up to the analog board – one in between the VCO output and VCO Amount VCA input, the other one delivers the triangle output to the sine converter on the Jack Board. The sine wave is mixed to the VCO output under control of the Controller Board, eventually overriding the command from the SE1 CPU.

On the photo above I was adjusting the Middlebrook & Richer triangle to sine converter that any of the 3 VCO Jack Boards features to allow all three VCOs producing sine waves. I was quite surprised that I got the 2nd harmonic down to -50dB and the 3rd to -40dB, measured at 440Hz. Overall THD will be in the 1.5% range, maybe even better when final adjustment are made.

 

 

Synclavier Sample-to-Memory – getting serious…

The NED Synclavier is an awful combination – complex circuitry built up of hundreds of (mostly TTL) ICs and no documentation in the wild.

So there’s no way around getting intimate with circuitry to understand how things work to make my latest project possible. First of all I needed an idea how everything is timed – a most important point in a serially operating system. Similar to the Able processor itself, the Sample-to-Memory unit makes use of an unidirectional 16 bit parallel bus on which control information, memory addresses and finally data are sequentially transfered.

All information propagate through the daisy-chained modules PSF, PSADC, PS(B)MC, DDDAC and then back to PSF, while the four timing signals into which all communication is framed traverse the chain in the opposite direction. To learn how this actually works, I’ve hooked up a minimal memory chain setup consisting of only the PSF and a PSMC. As the PSF gets the actual timing from the PSSRGA, the latter board is also installed in the poly bin:

The analyzer probes bring some color into the bin.

It was a quite succesful session so far, the bus timing is no secret to me anymore.

Stay tuned for the next steps on a long way…

SE1 goes modular

Studio Electronics’ SE1X is a nice 19″ synth module featuring 3 VCOs based on a Moog concept, one Moog-style 24dB ladder filter and a 12dB Oberheim-like switchable lowpass / bandpass filter. The VCOs are capable of sawtooth, triangle and variable-width pulse waveforms; with the addition of a triangle-to-sine converter according to Middlebrook & Richer, the SE1X version generates a sine output instead of triangle on VCO2. Everything  is mixed together by classic LM13700 OTAs and finally controlled by two cascaded discrete Moog-style VCAs.

So far everything was strictly analog. The control of all the analog circuits including LFO and envelope generation resides in the digital domain of the central microcontroller. Although the D/A converter used features rather high resolution for internally generated signals, MIDI-only control restricts the actual precision to 7 bits for external control.

Needless to say that the SE1 needs an option for external CV control, stricly analog. Once we started drilling some holes, why not making the whole thing modular? To cut the story short, after all the component count of the modified SE1 has doubled, a new rear panel was necessary to allow 43(!) jacks to be fitted and 7(!) additional circuit boards to be installed.

Ready for a peek inside?

Two out of 43 1/4″ jack holes in the new laser-cut aluminium rear panel grant a peek on the old circuitry

How modular it finally got is probably best described with some photos – stay tuned!

1. The controller board

The controller board for the additional circuitry sitting on the SE1 analog board, waiting to be fitted.
By chaining into the 40 conductor flat cable between the SE1 digital and analog boards, the new board has full control over all analog control voltages and digital switch controls signals.
27 OP Amps and 18 CMOS SPDT switch functions take care of proper signal routing. Almost all analog CVs are buffered and routed to output jacks. Each CV has an input jack assigned, followed by protection circuitry and an input buffer. The mechanical contacts in the jacks do not get in touch with the CVs, but control the CMOS switches. Each VCO has an additional CV input which allows to override the internal waveform setting. The same applies for the VCF; a dedicated CV determines whether to use the internal setting or override to one of the three filter types. For ease of A/D conversion of those latter four CVs, the controller board features a small Atmel AVR microcontroller.

 

2. The VCO jack board (1 out of 3 identical boards)

A VCO jack board in a not fully populated state. Most parts reside on the bottom side.

Each VCO gets one of these jack boards with the following features:

VCO CV OUT – a buffered version of the internally generated VCO CV (pitch, frequency, whatever you like)
VCO CV IN – override the internal VCO CV by an external 0..5V control voltage
WAVE SELECT – override the internal VCO waveform setting by an external CV. With this jack board, all three VCOs now offer saw, tri, pulse AND sine and any combination thereof!
WIDTH CV OUT – the internal version of the pulse width control for rectangular wave form. Dim your studio light with it under MIDI control…
WIDTH CV IN – externally control the pulse width of rectangular wave
VCO RAW OUT – the raw output of the VCO, buffered to 0,775Vrms into 10k ohms in triangle mode
MIX IN – disconnects the VCO from the internal mixer and allows an external signal to be inserted (or an effects enriched version of the raw out)
AMOUNT IN – an external 0..5V CV overrides the internal VCO amount setting

There’s no amount out as this control is not modulated or influenced by the envelope generators, but only a representation of the 0-to-63 value set in the SE1’s menu. Too low resolution to be of real use, sorry.

Important: all intermediate outputs (read: all except the main output) are trimmed to 0,775 volts RMS with a triangular signal at 440Hz.
The inputs are adjusted the same, to a patch wire from any intermediate output to its adjacent input will not change the overall signal amplitude.
This allows for transparent insertion of effects, assuming they provide a 0 dB gain.

 

3. The RMOD/Noise Jack Board

This is the smallest out of the six jack boards of the mod. It provides the following features:

RMOD RAW OUT – the raw output from the ring modulator, trimmed to 0,775 volts RMS with an 440 Hz square wave (50% duty cycle)
RMOD MIX IN – allows to insert an external signal to the RMOD amount VCA, instead of the ring modulator
RMOD AMT IN – override the internal RMOD AMT control by a DC CV of 0..5 volts
NOISE MIX IN  – disconnects the noise generator from its amount VCA and replaces it with an external signal (like the external input on a stock SE1X)
NOISE AMT IN – override the internal noise amount control by a DC CV dod 0..5 volts
MIX OUT – a buffered copy of the “master mix”, the sum of the amount VCAs of OSC1..3, RMOD and noise, right before it enters the VCF

 

4. The VCF jack board

Here’s the board with all the filter controls and signals, look here for its capabilities:

VCF IN  – remove the VCF input from the “master mix” and insert an external signal – 0,775V RMS, input impedance 10kOhms, nothing new here…
VCF TYPESEL – a control voltage on this jack selects the VCF operating mode, one out of 12dB LP, 12dB BP or 24dB, overriding the internal setting
CUTOFF OUT – a buffered version of the internal cutoff control voltage (in the range -5..+5 volts!)
CUTOFF IN – overrides the internal cutoff control, same voltage range as for the output of course
RESO OUT – a buffered version of the internal resonance/Q control voltage (0..5 volts)
RESO IN – overrides the internal resonance control
VCF OUT – the buffered and normalized output of the VCF before it enters the VCA

 

5. Final! The VCA board

Although two parts are missing, here’s the VCA jack board! Featuring those features:

VCA IN – disconnects the VCA input from the VCF output and allows to insert an external signal. 0,775V RMS, you may have guessed it.
FUZZ AMT – something new: the SE1X’s Fuzzzz has gone variable. Apply a 0..5 volts CV here to control the amount of distortion
VCA1 CV OUT – the internal control voltage for the 1st VCA (controlled by ADSR)
VCA1 CV IN – overrides the internal VCA CV for envelope control
VCA2 CV OUT – the internal control voltage for the 2nd VCA (which is mainly the volume knob’s position)
VCA2 CV IN – overrides the internal volume control
OUTPUT – finally, here’s what you are listening to. The level remained unaltered, which means it is normally somewhat lower than 0.775V RMS.

 

White and Blue for the Wave Two

Recent HD44780 based LCDs fit directly to Wave2.3s and can easily be installed into Wave 2.2s. By removing the old HD43160A display controller and adding a 7421, a modern display will work just fine. The 2.2 and 2.3 firmware already have the proper intialization procedures and only need to be convinced to use them by a simple jumper wire.

PPGs Wave 2 was excluded from this upgrade so far because the EPROM code can only deal with the original HD43160A LCD controller. So the old chip has to go at first

HD43160 removed from Wave 2 TAS board

Although the addressing and chip enable signals to the TAS board of the Wave 2 are somewhat different from the TAS82/83 in the 2.2 and 2.3, a valid enable signal for the LCD can easily be generated by addition of a 7421 chip as well.

Wave 2 LCD Wiring

But there’s still the problem with the firmware…

Fortunately, the HD43160A as a predecessor of the HD44780 uses a subset of its command set. Assuming the power-on-reset circuitry of the HD44780 on the new display works well, it would require one additional initialization command to be issued and another command to be modified. The space required for this modification including another delay loop was gained by removing the memory size checks for 6kByte and 32kByte borders, as all Wave 2s known to me have 12kBytes of RAM (excepting the sound RAM). So the memory test has been modified to check whether 12kBytes of usable RAM are available, otherwise throw a ‘9’ to the display to indicate an error.

There are two more locations in the firmware causing trouble: the HD43160A obviously needs the cursor to be re-enabled after some other operations, which is a command 04hex for the 43160. For the 44780 this means to write the characters from right to left, so these commands had to be found and were simply removed for now, as it does not seem necessary for the HD44780 to re-enable the cursor anymore.

Finally it was worth the trouble:

Wave 2 with new display

 

 

 

MIDI for the Synthex

The later Elka Synthex models had a small MIDI interface built in, consisting of not more than a serial interface device (Motorola 6850), some glue logic and the obligatory photocoupler. The original boards are quite rare, and therefore rebuilds showed up over the years.
I’ve also designed a small board, using SMD components where possible for the ease of assembly and availability of components. Since the firmware used is still the unmodified original, the modern MIDI board suffers from the same problems as the original does – more messages than note on/off would probably screw up the small CPU of the Synthex.

Enough requests provided, a replacement CPU board allowing to MIDIfy the whole synthex (except the LFO section, because it’s strictly analogue) would be a possibe future products. So come on guys…

Oh sure, you want some tech stuff. Here it is, small enough to hide below the 24 wire strip cable:
MIDI board for the Elka Synthex

A Mega Cartridge for the DK Synergy

This Synergy ROM cartridge does not only behave like an easter egg, it also has some eggs inside

Megacartridge for the Synergy

Here the Mega Cartridge resembles the VCART6 cartridge, but that’s by far not the end. The initiator of this nice little project, Fabian Draeger, has just made a short video showing the prototype in action:

Right after inserting, the Mega Cartridge says hello and then immediately switches to the module last used.
In the video the VCART6 and the Wendy Carlos 1 are shown, but the memory inside is big enough to keep all official cartridges ever released. Depending on your interest, the Mega Cartridge will soon be available in quantities as fully built PCB. To compile your individual ROM, I would need proof of your ownership of the original cartridges for copyright reasons.

For the tech guys here's of course a photo of the inside

Mega Cartridge inside view

Old, new, white, blue

Something old – a PPG Wave 2.2 or 2.3,
something new – a 40×2 LCD,
something white – the LED backlight,
something blue – the background color

That’s the recipe for replacing a fading or just boring display in a PPG Wave, and here is how it looks like:

This is a drop-in replacement for all 2.2/2.3 that are already using the new HD44780-compatible display. It can be easily recognized – it is somwhat smaller than the old ones, revealing the metal frame on the front panel, and is mounted on some metal. Old 2.2 with the TAS82 require the on-board controller to be removed and some additional circuitry installed. The firmware is aware of both types.
Even refitting of Wave 2’s will be possible soon, I’m working on a firmware patch to allow the new type to be used with the Wave 2 as well.

And as a special gift, you get rid off that squealing noise of the inverter 🙂

To give you an impression how it would look like in ePaper-style – black on white – I’ve mounted  another display in the Wave. This type requires drilling some new holes, otherwise the LCD appears shifted to the right:

Wave 2 with backlit display…

A How-NOT-to-do-it guide

This Wave 2 owner decided that his PPG also requires a backlit display.
No problem so far. But the datasheet of the EL foil backlight stating that it need 200 to 250 volts AC obviously led to a very wrong decision:

What we see here is an AWG28 2-wire cable ripped off from some flat cable, soldered to the primary lugs of the mains transformer -or, in other words – directly to the 230 VAC mains.
The other end is connected to the EL foil behind the LCD. Even the cheapest alarm clocks from the 70’s running EL illumination from the mains had at least a protective resistor in series.