akai

AKAI VX600 MATRIX SYNTHESIZER

The VX600 is a quite rare analogue synthesizer made by AKAI in 1988. The VX600 has 6 voices, each containing two oscillators with square/pulse, saw and triangle waves plus white noise on VCO2. Real voltage controlled oscillators, mean a tune is required to keep them in sync. It was marketed at players of the EW1000 series wind instruments.Each voice can be assigned to a different MIDI channel for multi timbre operation.The GLIDE, BREATH and VIBRATE controls seem to be redundant if not using the EW controller. BEND works though. Add the following to the MOD matrix to control filter cutoff.

  • (EW.BEND) (+50) (CUTOFF)

The filters consist of 6 low-pass resonant (up to self-oscillation), keyboard tracking VCF's and 6 high-pass filters (no resonance this time). the low-pass filter can also be modulated by VCO2. The VX609 uses Curtis chips 3378 (VCF/AMP) and 3374 (VCO).

two LFO's (with delay) both LFO1 and LFO2 have a range of waveforms: triangle, positive sawtooth, meg sawtooth plus square wave. It has three ADSR envelopes. or ADDSRs , every envelope has two decay settings. the EG's can also be delayed. The LFO can be a bit slow for some, so add this line (even multiple times) to the MOD matrix controllers to add more speed

  • (KEY GATE) (+99) (LFO-1 SPEED)

I purchased this in later 2017 from eBay. It cost a small fortune. I saw the superb Jexus videos on YouTube and when one came up for sale I just went for it. It's a US version with 120vAC. Overall it was in good condition. Display is 40x8 LCD. The back light had been replaced, although it still seem washed out and faded. The inverter also makes a high tension whine.

VX backlight, old one and new LCD version bought in 2018

unfortunately this does not cure the high pitched whine noise on many VX600's

It's actually the yellow pulse transformer (2e16-1001-01) making the noise, not the display. I may desolder it as the new LCD doesn't use it.

display

card

It takes about 15 minutes for the synth to stabilise before doing a VCO tuning calibration. I looked at this on a DVM and found the voltage sits at .22v then rises up to 2.5v over a period of 9 minutes. Why this happens is unclear. I have found that if the auto calibration doesn't complete, or takes an eternity you my need to check the DAC voltage. It should be 2.5v DC. Procedure is in the service manual. If your VX600 sounds bad this is possibly the reason.

If you cannot set the DAC voltage at 2.5v, check the SSM2300 multiplexer IC's. These are roughly equivalent to 4051's but differ in that they have S&H and internal capacitors I believe. This means you can't do a direct swap in the Akai. I discovered a bad SSM by removing them all, plus all the voice cards. I monitored the DAC voltage with a meter and inserted the SSM's one by one, turning the synth off of course whilst doing it. I notice one IC caused a voltage drop and this turned out to be a bad IC.

Some pictures of the insides:

old LCD

inverter

 

Battery/CPU/ROM

processor

 

Voice Cards x6. Voices play from bottom to top, when first powered on. The synth calibrates top down.

voices

 

Below the voice cards. Opamps and multiplexers

vb

 

Power Supply

If servicing, watch you don't bend the 2 regulators in the middle of the image too much as they can just break off as must have happend previously on my synth. The heat sink is not supported

psu

 

There was some UV damage to the side panels. I'm not a fan of nicotine yellow so I must try and restore these.

uv

EWI3020m

In 2018 I bought a EWI3020m synth module and the 3020 wind instrument on eBay. The main reason I purchased these is not become an electronic KennyG, but to get replacements for the CEM3374 and 78 chips for my VX. The EWI module has 1 of each. The EWI modules is essentially a single voice, similar to the VX. The module is pretty cool in it's own right and the wind instrument may turn out to be fun

 

ewi

The synth can have 6 separate outputs. I believe back in the day the VW-X6 DIN/PHONO cable was available. It possible to make your own using a 13 pin cable similar to those found on old Atari ST monitors, Digikey part number CP-1013-ND. The pinout for the VOICE OUT connector is shown below.

sep

 

 

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