Roland MKS-50 modifications unofficial

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Roland MKS-50 modifications unofficial

Postby jxalex » Tue Dec 20, 2016 12:06 pm

Here I thought to share my experiments and to share it in hope that some others will contribute too or check over, evaluate these modifications.

I have some thoughts about this particular rack synthesizer and I begin to post here as the work progresses which cover about
*memory patches

1, Envelopes attack time can be faster.

When looking at the service schematics then there are C56 and C58 which can make the signal attack time faster.
At first I replaced these to 1uF and then I replaced to 0.1uF. In my synthesizer these are 4.7uF,
Havent heard any unpleasant artefacts, Oscilloscope showed faster over 5x attack time however it has some steps in it.
Can someone other try out this modification too and report how it sounds to their ears?

In fact on Juno-106 the envelopes are so fast that it is clicking when using the fastest attack time.

2. DCOs modification -- these can sound fatter.
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Re: Roland MKS-50 modifications unofficial

Postby jxalex » Wed Jan 04, 2017 3:12 pm

2. About DCO driving modifications in progress. It is just a concept of the idea if it works.

The DCO circuit does not need to be exactly at the same frequency as the CPU clock, 12MHz, so what if to do, the different clock generator for this and to modulate its frequency?

I made a VCO which frequency with transistors, with frequency region 10..14Mhz, without any quartz, frequency was changed with varactors. Feeding the DCOs with it -- no difference compared to XTAL osc. SO, it does not have to have the exactly the same phase. Also changing the external generator frequency changes the pitch and in quite affordable limits. So far so good. Also the generator itself had harmonics at -30dB level. :)
Now the thoughts are:
HOW and with which signal to modulate that 12Mhz clock in order to get the oscillators signal fatter?

experiment 1.
1. modulating the VCO with external signal generator with frequency between 2Hz...700kHz, deviation changing 100kHz... 2Mhz, center frequency 12Mhz --- result: the only audible effects resulted in LOW MODULATING FREQUENCIES below far below 100Hz ! Modulating with high frequencies just added hiss in the tones, but did not made the effect like tone is going fatter, whatever deviation.

experiment 2,
2. the VCO modulating with wideband noise generator -- no audible effect. Again, only low frequencies had audible effect.

So far the positive result is that with low modulating frequency it gives vibrato effect.
lowering the feeding 12Mhz clock signal CHANGES the signal fatter, but it was quite hard to control at the steady

So, where I went wrong?

next experiment would be with low frequency noise generator
feeding with the modulated pulse width.
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