Note to SH101 modders

[Solderman]

This is really one for the archives and not a Help request per say.
Shortly after I modded my SH101 with various mods found on the web, (namely Novamod 1 and Mixer mods) it started acting weird. The sequencer/arpeggiator button LED's would light up at completely random intervals, and lock out the keyboard, often making the pitch go crazy or just going silent, as well. Over time the lockout intervals became more and more frequent until it was unusable, even only with CV/Gate, after just a few minutes.

The problem has turned out to be the ground pin on the CPU. I still don't know if some of the mods caused a floating ground somewhere on the circuit board, but the solution is to solder a nice long wire directly between pin 20 of the CPU on the underside of the main board and the negative battery terminal. No other solder points will work, not even the pads adjacently connected to the CPU's ground pin.

So far it appears to be working perfectly after several hours use. I will update this thread should any other problem(s) arise.

And now for the shameless demonstration of what my mods can do: http://67.18.24.4/~murmurbe/music/noodl ... TheMod.mp3

[Mooger5]

Thanks for sharing. I don´t plan on modding my 101 so soon but that´s good info. Something in the service notes reminds of what you described: "The CPU may overrun if excessive static electricity is fed through the jacks, etc. To prevent this, the GND on the GATE OUTPUT jack in the Jack Circuit Board and the GND lug on the Keyboard are connected with a larger wire."

By the end of your demo, is that the VCO or the LFO modulating the filter at audio range frequencies?
I checked the block diagram regarding the LFO/clock rate and the sequencer sync from the CPU and I´m not sure what will happen if I change the rate to go further up in the audio band. Some interesting noises can be made, but how stable would the sequencer be when running on its own at very high speeds?

[Solderman]

By the end of your demo, is that the VCO or the LFO modulating the filter at audio range frequencies?
I checked the block diagram regarding the LFO/clock rate and the sequencer sync from the CPU and I´m not sure what will happen if I change the rate to go further up in the audio band. Some interesting noises can be made, but how stable would the sequencer be when running on its own at very high speeds?

LFO. It has its speed range extended. From memory, I think it's R15 you replace with an SPDT switch with a resistor on each throw to switch between the two ranges. I haven't messed with the sequencer at high speeds, but everything else works fine with it. I would assume if it got fast enough, the fall time of the gate would not reach a note-off point and it would just be like a constantly open gate.

[Mooger5]

Thanks. Any special reason it´s the resistor and not C20 (the 1u cap)?
About the sequencer running too fast for the gate, that means the adsr cv will keep cycling, right? Any crazy sequence running at very high speeds may behave like a unique waveform modulating the filter through MOD and KYBD. Of course the VCO will sound at a steady pitch, like a constant drone (or whatever would come out) but it must be possible to play simple melodies using the key transpose function. I hope this makes sense...

moog rogue.mp3 - 5.52MB

This is the first mod I made to my Rogue: replaced the timing cap (6.3u) with a 100n poly. There´s no sequencer, just the synth´s Auto-trig running. It sends too fast signals for the attack and decay to comply with, but the resulting CV sent by these two to the filter and the OSC Sync keeps going, if stepped at times. Sounds very interesting and useful. I managed to get some sounds from the early Kraftwerk albums.

[666]

stop synth rape now, before it's too late!

[Solderman]

Any special reason it´s the resistor and not C20 (the 1u cap)?

That was the Novamod recommendation. Seems to work well, although I didn't do the 150k in series at the CB like they did. I put it on the switch.

About the sequencer running too fast for the gate, that means the adsr cv will keep cycling, right?

I finally tried this. You can get that intro to Spacelab up to a certain speed, then the gate has this "aisling" effect on the tempo where as you increase the LFO, the sequence starts to slow down. A little further up more and the sequence stops. A little further up still and it speeds up again. The cycle repeats in a very tight circle until you get to the maximum LFO speed.


666, it was purely consentual I assure you.

[Mooger5]

I finally tried this. You can get that intro to Spacelab up to a certain speed, then the gate has this "aisling" effect on the tempo where as you increase the LFO, the sequence starts to slow down. A little further up more and the sequence stops. A little further up still and it speeds up again. The cycle repeats in a very tight circle until you get to the maximum LFO speed.

That´s what I was thinking. That aisling effect is more or less predictable at high unmodded lfo rates and it certainly has to do with the sequencer speed coinciding with the adsr. Whenever it starts to sound "too weird" for musical purposes I guess all it´s needed is to tweak the envelope time.
Could you post an audio sample, please?

And did you make the Novamod external filter input too? How does it sound if you feed it with the phones output (a la Minimoog)?

Cheers.

[Solderman]

Whenever it starts to sound "too weird" for musical purposes I guess all it´s needed is to tweak the envelope time.
Could you post an audio sample, please?

http://67.18.24.4/~murmurbe/music/demos ... astSeq.mp3
It's hard to demonstrate that final bit where the speed cycles as you go up. You can sort of hear it drop once. If I were to have tapped the slider with my fingernail or something, it may have been easier to hear it actually stop.

And did you make the Novamod external filter input too? How does it sound if you feed it with the phones output (a la Minimoog)?

I did but I can't use the headphone out because I couldn't get an input gain level pot to work properly so it's whatever amplitude the source is. What I do instead is use a mixer's effects send directly to the 101's filter input, and send the 101's channel back to it that way so I can control the level. The example below is regular first, then I press the cable into the effect send jack and play the feedback version:
http://67.18.24.4/~murmurbe/music/demos ... edback.mp3
Pretty disappointing, actually. There isn't much play on the mixer knob between what you hear there and complete muddy, overdriven feedback tone. I'd much rather mess with the VCA overdrive mod.

[stalLion]

This is really one for the archives and not a Help request per say.
Shortly after I modded my SH101 with various mods found on the web, (namely Novamod 1 and Mixer mods) it started acting weird. The sequencer/arpeggiator button LED's would light up at completely random intervals, and lock out the keyboard, often making the pitch go crazy or just going silent, as well. Over time the lockout intervals became more and more frequent until it was unusable, even only with CV/Gate, after just a few minutes.

The problem has turned out to be the ground pin on the CPU. I still don't know if some of the mods caused a floating ground somewhere on the circuit board, but the solution is to solder a nice long wire directly between pin 20 of the CPU on the underside of the main board and the negative battery terminal. No other solder points will work, not even the pads adjacently connected to the CPU's ground pin.

So far it appears to be working perfectly after several hours use. I will update this thread should any other problem(s) arise.

And now for the shameless demonstration of what my mods can do: http://67.18.24.4/~murmurbe/music/noodl ... TheMod.mp3

I have this problem with my 101, which isn't modded. Thanks Solderman, I might have to crack it open on the weekend and see if this fixes if for me.

[Solderman]

I have this problem with my 101, which isn't modded. Thanks Solderman, I might have to crack it open on the weekend and see if this fixes if for me.

You probably already know this, but try making the connection with mini-clips first. This is how I discovered the solution.

[Mooger5]

Whenever it starts to sound "too weird" for musical purposes I guess all it´s needed is to tweak the envelope time.
Could you post an audio sample, please?

http://67.18.24.4/~murmurbe/music/demos ... astSeq.mp3
It's hard to demonstrate that final bit where the speed cycles as you go up. You can sort of hear it drop once. If I were to have tapped the slider with my fingernail or something, it may have been easier to hear it actually stop.

And did you make the Novamod external filter input too? How does it sound if you feed it with the phones output (a la Minimoog)?

I did but I can't use the headphone out because I couldn't get an input gain level pot to work properly so it's whatever amplitude the source is. What I do instead is use a mixer's effects send directly to the 101's filter input, and send the 101's channel back to it that way so I can control the level. The example below is regular first, then I press the cable into the effect send jack and play the feedback version:
http://67.18.24.4/~murmurbe/music/demos ... edback.mp3
Pretty disappointing, actually. There isn't much play on the mixer knob between what you hear there and complete muddy, overdriven feedback tone. I'd much rather mess with the VCA overdrive mod.

Thanks for posting.

The sequencer doesn´t sound as fast as I had imagined. In time I´ll experiment with really low values for the timing capacitor in the order of a few nanofarads.
If we take an lfo waveform at a very fast rate as unity, any sequence of four notes (for instance) must be four times faster to be perceived as a single-cycle waveform at the same rate. It would allow for some creative FM modulations, but possibly entering into "overclock madness" territory. Maybe some heatsinking to the cpu is in order, low-profile of course.
Just thinking out loud...

About the audio input mod example, is that the synth line or the phones out, through fx send? It´s not too obvious, but perhaps better results could be obtained by sending the phones out to the fx send of a different channel, leaving the line out for monitoring only? I think there could be better separation, preventing the entire synth/mixer combo from feedbacking the feedback...