SH-101 Envelope Sustain/Release Issue. Help!

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The Goob
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SH-101 Envelope Sustain/Release Issue. Help!

Post by The Goob » Sun Aug 07, 2016 7:05 pm

I'm trying to fix an SH-101.

Issue is:

When both the sustain and release sliders are set above minimum and the envelope is modulating the VCA, notes do not fully decay. If sustain is set to minimum, AD&R all work fine with any settings, and if release is set to minimum, AD&S work fine with any settings. Combining the two produces a perpetual drone.

I know the sliders are a common point of failure, so I thought replacing the S&R sliders would fix the problem, but I swapped them both out and the drone persists. :hmm:

Everything else on the synth works fine.

Has anyone else had this issue where a slider replacement didn't fix an envelope problem? Any ideas?

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Post by The Goob » Wed Aug 10, 2016 7:56 pm

Noticed something else when testing further.

With decay set @ maximum, the sound will decay (slowly) even as a key is held and sustain is at maximum (and release is non-zero too).

I replaced C59, which did not help anything.

Is anyone willing to help explain the 101 EG circuit to me? I understand that C59 is the integration cap, but I'm a little lost beyond that.

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Post by The Goob » Mon Aug 15, 2016 6:52 pm

Alright...got a chance to check some voltages this weekend and was pretty sure I had it figured out but that doesn't appear to be the case. :confused:

My understanding is that op amp 16a acts as a comparator in this circuit. So without a gate, its output should be low, which would disconnect the DS part of the circuit and allow R to sink current from C59 - pulling the EG output voltage down. That's not happening here so I replaced the op amp thinking it had gone bad. It didn't change anything. Same readings as before and the synth still drones when S and R are up.

Here are the voltage readings. Can anyone help? Am I completely off on how the circuit's supposed to work?

Image

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Post by The Goob » Fri Aug 19, 2016 6:41 am

I guess I'll bump this one last time before the weekend :help:

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Post by guest » Fri Aug 19, 2016 12:22 pm

your analysis is correct, U16A should be low when there isnt a gate. and, since you replaced it, something else must be preventing it from going low. there are a couple of options here:

1. check to see if its getting warm. its possible that there is a short (or shorted out resistor) at the ouptut of the opamp, that is forcing the output. if possible, you can desolder the IC, lift the output leg out of the hole, and solder the rest back in. then you can see if it does the right thing without the rest of the circuit effecting it.

2. the opamp is the wrong kind. what was the original, and did you replace it with that kind?

3. the opamp has a bad ground connection. its possible that the opamp can not go to ground, because this has a broken trace or something. measure the resistance from the leg on the opamp, to the ground plane somewhere a decent distance away on the board. it should read 0ohms.

4. the inputs arent connected. set the synth up where it is constantly droning, and measure the voltages directly on the opamp legs. hold the meter on the legs for a few seconds and listen to the sound to see if it goes away. sometimes a part is bad (like the diodes in this case) and putting your meter across that part allows current to flow through the meter, making the circuit work while you are measuring, so all your readings are ok, but it is still broken once you remove the meter.
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Post by The Goob » Sat Aug 20, 2016 12:25 pm

Thank you for your response. It helped me solve the problem and the 101 now seems to be working correctly.

Seems it was misbehaving due to the use of an incorrect op amp. A TL072 was initially installed in the EG circuit and I replaced it with another TL072, but the schematic calls for a IR9022s - same pin designation, but lower current draw than the 72. Someone must have replaced the original IR9022 with what they had on hand and left it at that. I tried swapping in a TL062 I had on hand and the EG circuit is now working! I should have tried that before but thought the 72 would be fine.

Looks like TL022 is the currently available IR9022 sub, so I'll go with that.

Thanks again. I'm thrilled to have this sorted out.

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Post by guest » Sat Aug 20, 2016 4:08 pm

glad to hear you got it sorted. honestly, i was a little puzzled as to what could be causing the issue. since the attack section was working, the opamp must have been able to go low when the gate is high. but, when the gate is low, it wasnt doing the right thing. sounds like a phase inversion problem with the opamp. the TL022 is identical to the 9022, and makes a good substitute. if the TL062 works, its actually a better opamp as it has lower bias current, so the integration capacitor wont lose charge over time. its pretty much identical to the 022, except it uses JFETs for the input stage instead of BJTs.
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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by makhho » Fri Sep 11, 2020 4:21 pm

Okay, I got a weird issue with my SH101 that sounds similar to Goob's.

For starters, I stupidly plugged in a 12VDC center positive 2A walwart meant for another unit instead of the regular PSA 9-12VDC center negative one I use to power the 101.
This reverse polarity walwart was plugged in momentarily, however there was damage done to the 101 that I am trying to sort out.

The new behavior after this episode is like this:
12VDC center negative PSUs makes the unit hum now, when it didn't before.
However, the unit powers on fine with a 9VDC-12VDC CN PSU, and the control switches operate fine except that the VCA is not properly responding to the ENV section when triggering the SEQUENCER with internal clock rate or EXT CLOCK IN.

When running the sequencer with EXT CLOCK IN. or internal clock, the VCA just HOLDS on notes and drones until the next step in the sequence is triggered. The release in the ENV section does nothing to the dynamics.

Held arpeggios function in the same way -- internally clocked by the LFO rate, the ENV does not properly modulate the VCA.
Attack, decay, and sustain seem to be the only parameters in the ENV that are modulating the VCA.

The VCA gets the correct ENV routing/settings (ADSR fully modulate the VCA) when I trigger a note on via the keyboard or external gate in.

I replaced the protection diode D8 and switched out the dodgy power switch -- checked all my voltages coming from the jack board to the main board; everything seems normal.

I replaced IC16 and all transistors in the ENV section, but I am still getting this VCA hold issue.

I replaced IC4 and IC5 in the trigger section, TR8 between the CLK line and LFO section, TR28 in the VCA section, TR11 between the EXT CLOCK INPUT and CPU, and TR12 between the HOLD INPUT and CPU.

Nothing.
It is like STEP 6 "CLOCK CHECK" of the CPU function diagram, found in the service notes, is not executing properly, NOR does it seem that STEP 10 "PLAY", STEP 11 "ARPEGGIO" function properly.

Did I burn the T1 transformer coils partially?
Did I fry part of the TMP80C49 controller?
Is this a D/A issue?

@Guest - Is this where I should start looking for shorted components in the ENV section that are keeping IC16 from sending the ENV to the VCA?

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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by guest » Fri Sep 11, 2020 6:22 pm

quick question: does the envelope still effect the filter? if yes, does the release section work on the filter?
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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by guest » Fri Sep 11, 2020 6:27 pm

also, was D8 blown? and how do all of yoru powersupply rails look? there are like 5 or 6 rails in this thing, be sure to check them all. and if you have a scope, use that as well to make sure there isnt any excessive ripple on the rails.
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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by makhho » Fri Sep 11, 2020 7:09 pm

Guest, thank you for getting back to me!

The ENV does not "fully effect" the VCF, as release does not change any of the VCF characteristics. Only ADS of the ENV appear to modulate the VCF. So I guess to answer your question yes the ENV partially effects the filter.

All the 8 rails on the main board were just triple checked -- they are fine. As are the voltages on the JACK board leading to the mainboard. The +4.5V measurement on connection 51 of the jack board, as well as 104 on the main board are jumping around, but they stabilize to the +4.5V when measured at the cathode of D15. Otherwise, everything seems fine.

The protection diode was not blown, but nevertheless I replaced it.

Don't have a scope atm, so can't check for excessive ripple in the rails.

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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by guest » Fri Sep 11, 2020 9:57 pm

since the protection diode wasnt blown, there is a good chance there wasnt much damage other than what youre seeing. sounds like a problem before the ENV section. im going to have to dig a bit to see what the differences are between the gate signal with the sequencer running versus not.
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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by guest » Fri Sep 11, 2020 10:04 pm

does the envelope behave any differently depending upon its control switch (GATE+TRIG, GATE, LFO)?
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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by makhho » Sat Sep 12, 2020 10:06 pm

Yes.

When ENV control is switched to LFO, ENV behaves fine and the release actually does something.

When switched to "GATE+TRIG" and "GATE" the ENV does not modulate the VCA or VCF fully (held note, ADS are only working, release does nothing as described above.)

I'm not sure what GATE IN, KBD triggering, and LFO control have in common, but they do make the ENV behave properly.

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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by guest » Sat Sep 12, 2020 10:58 pm

can you probe the gate out and see what it looks like in keyboard mode versus sequencer mode? its generated by the microcontroller in both cases, so it doesnt bode well if it does the wrong thing in one of the modes.
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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by guest » Sat Sep 12, 2020 11:01 pm

does the octave range switch function right?
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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by guest » Sat Sep 12, 2020 11:07 pm

check that D26,27 are good.
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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by guest » Sat Sep 12, 2020 11:14 pm

is the hold button selected?
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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by makhho » Sun Sep 13, 2020 10:50 pm

Octave range switch works as expected when playing notes on the keyboard, with gate in, sequencer triggered via LFO, EXT. CLK IN, and INTERNAL clock.

D26 and D27 are fine

Hold button is not selected.
And it does appear to work as expected, since it can "hold" the arp function, as the arp is being internally clocked. Though as mentioned before, ENV does not route to the VCA properly in ARP mode when clocked externally or internally.

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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by makhho » Sun Sep 13, 2020 11:07 pm

Probing the gate out pin 38 on the controller shows a difference in pulse shape and time duration for keyboard vs sequencer/internal clock use.

When doing nothing, pin 38 hovers at +4.5VDC constant.

Gate out voltage on keybed presses show an inverted pulse that drops from +4.5VDC to 0VDC for the duration of the key depression.

When a sequence is programmed and you hit play, the gate out voltage drops to 0VDC (for the duration of playing the sequence) and on each advancement of the sequencer a +4.5VDC pulse of 5ms occurs.
Last edited by makhho on Mon Sep 14, 2020 6:42 am, edited 1 time in total.

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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by guest » Mon Sep 14, 2020 1:20 am

what is the voltage on pin1 of the microcontroller? should be 5V.
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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by makhho » Mon Sep 14, 2020 6:31 am

Yup! +5VDC at pin 1

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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by guest » Tue Sep 15, 2020 2:39 am

i dont have a 101, so this may be a silly question, but are arpeggios supposed to be held? i was reading through the manual, to look for some clues, and it has a diagram showing the gate not being retriggered during an arpeggio.

the odd thing to me, is that it seems like everything is physically functioning. the envelope generator section works fine, if it is given an appropriate gate signal that shuts off. the microcontroller can put out both high and low signals for its gate, but it is not doing this for arpeggios and programs, instead its just blipping off for a short enough time to reset the attack cycle. it would be truly odd if something in the program memory fried, and this was the result. it seems far more likely that either (A) this is what its supposed to be doing given the current set of inputs, or (B) one of the inputs to the microcontroller is being misread due to a trace being bad or a diode being shorted. so in my mind, the question is, is this a reasonable behaviour for some set of inputs? thats why i was asking about the hold function. maybe portamento? the manual isnt super detailed, so im having a hard time figuring it out.
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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by makhho » Tue Sep 15, 2020 11:28 am

Yeah, you get into arp mode by hitting up, down, or up/down then hold keys down on the keybed with one hand and then hit the HOLD button and the internal clock runs through the ARP depending on direction you selected.

You can also just hold down keys in one of those three modes (up/down/up+down) without the HOLD being latched and the internal clock will run through the arp you are holding.

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Re: SH-101 Envelope Sustain/Release Issue. Help!

Post by makhho » Tue Sep 15, 2020 12:00 pm

I've had this 101 long enough to understand unusual behavior, as I've used it almost every day for music/sound work for the past 8 years; it definitely is not functioning properly.

The ENV release should absolutely be responding and modulating the VCA and VCF when sequencing a pattern using the INT CLOCK and advancement of the sequence using an EXTERNAL CLOCK INPUT source. And it should be responding like this when in GATE and GATE+TRIG mode.
The fact that the ENV is functioning properly with full ADSR parameter control over the VCA and VCF when triggering notes via the keyboard and gate input suggests that the issue is in fact not in the ENV section.

So where does that leave us to look?
This all makes me think that it is controller issue since sequences are getting into memory and notes are advancing, but the ENV control over the VCA and VCF is not working properly when each successive note is being triggered via internal or external clock. The VCA just drones and sounds like it is being held until the next step in the sequence is triggered. This really doesn't make any sense if we're talking about anything other than the controller.

I am tempted to get a replacement controller, maybe something like what Tubbtec is offering to test it out. I always wanted long term memory storage for patterns anyway, though I am still sold on this being something else.

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