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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
10 step sequencer problem
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Hubaswift



Joined: Jul 06, 2016
Posts: 91
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PostPosted: Fri Dec 16, 2016 7:15 pm    Post subject: 10 step sequencer problem
Subject description: start/stop buttons does not start the sequence properly
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I finished building the sequencer, and everything works except the actual sequencing. I checked the TL072 clock circuit and it's outputting a saw wave as it should, but when I press the start/stop sequence button, it just resets to the first step and doesn't sequence. Any pointers on where I should look first?
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elmegil



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PostPosted: Fri Dec 16, 2016 9:11 pm    Post subject: Re: 10 step sequencer problem
Subject description: start/stop buttons does not start the sequence properly
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Hubaswift wrote:
I finished building the sequencer, and everything works except the actual sequencing. I checked the TL072 clock circuit and it's outputting a saw wave as it should, but when I press the start/stop sequence button, it just resets to the first step and doesn't sequence. Any pointers on where I should look first?


So, you need to approach this methodically.

1) when you say "everything works", does the step button work?

2) You have a saw from U3-A, but do you have pulses from U3-B?

3) Are all the various steering diodes where the step button and clock come together oriented correctly?
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Hubaswift



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PostPosted: Fri Dec 16, 2016 10:43 pm    Post subject: Re: 10 step sequencer problem
Subject description: start/stop buttons does not start the sequence properly
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elmegil wrote:
Hubaswift wrote:
I finished building the sequencer, and everything works except the actual sequencing. I checked the TL072 clock circuit and it's outputting a saw wave as it should, but when I press the start/stop sequence button, it just resets to the first step and doesn't sequence. Any pointers on where I should look first?


So, you need to approach this methodically.

1) when you say "everything works", does the step button work?

2) You have a saw from U3-A, but do you have pulses from U3-B?

3) Are all the various steering diodes where the step button and clock come together oriented correctly?
Thanks for the quick reply!

1) Yep, it works fine.

2) Yes, they're extremely quick pulses though.

3) Double checked all the diodes on the board, they're all oriented correctly.
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elmegil



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PostPosted: Sat Dec 17, 2016 12:14 am    Post subject: Reply with quote  Mark this post and the followings unread

The pulses are expected to be very narrow (as seen in Ray's daigram). That really points to something being wrong with D18. D16 is fine, because the clock oscillator works. D19 is fine because the step button works, and all the stuff driven by the clock is fine, because the step button works. D18 is the link between the oscillator output and the clock input to the 4017. Make sure you don't have any cold solders....

I suppose the pulses could be *too* narrow to clock the 4017. I'd consider verifying R23, R28, R29, and R32 values, and then with it powered on, see that you're somewhere in the neighborhood of 8V at pin 6 of U3.
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Hubaswift



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PostPosted: Sat Dec 17, 2016 11:03 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
The pulses are expected to be very narrow (as seen in Ray's daigram). That really points to something being wrong with D18. D16 is fine, because the clock oscillator works. D19 is fine because the step button works, and all the stuff driven by the clock is fine, because the step button works. D18 is the link between the oscillator output and the clock input to the 4017. Make sure you don't have any cold solders....

I suppose the pulses could be *too* narrow to clock the 4017. I'd consider verifying R23, R28, R29, and R32 values, and then with it powered on, see that you're somewhere in the neighborhood of 8V at pin 6 of U3.
Ok, I just noticed the weirdest thing. My oscilloscope probe is hooked to ground, and then the other probe I put on pin 5 of U3, When I probe it the whole sequencer starts to work and actually sequences. I take my probe off of pin 5 and it stops.

Anyways, to answer your questions, The diode looks fine, and the probe sequence thing tells me that the diode probably isn't the issue. I checked all of those resistor values and they are correct. One thing I should have noted at the start that I just realized is that I'm running this off of +/- 15v rather than +/- 12v in case that makes any difference. I don't have my meter on me at the moment, but I'll check pin 6 when I do. Again the sequence only when probed thing makes me think this probably isn't the issue.
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Hubaswift



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PostPosted: Sat Dec 17, 2016 11:26 am    Post subject: Reply with quote  Mark this post and the followings unread

I also just noticed that even though the notes don't sequence, it still repeats the gate and trigger outputs from that step.
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elmegil



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PostPosted: Sat Dec 17, 2016 12:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hubaswift wrote:
elmegil wrote:
The pulses are expected to be very narrow (as seen in Ray's daigram). That really points to something being wrong with D18. D16 is fine, because the clock oscillator works. D19 is fine because the step button works, and all the stuff driven by the clock is fine, because the step button works. D18 is the link between the oscillator output and the clock input to the 4017. Make sure you don't have any cold solders....

I suppose the pulses could be *too* narrow to clock the 4017. I'd consider verifying R23, R28, R29, and R32 values, and then with it powered on, see that you're somewhere in the neighborhood of 8V at pin 6 of U3.
Ok, I just noticed the weirdest thing. My oscilloscope probe is hooked to ground, and then the other probe I put on pin 5 of U3, When I probe it the whole sequencer starts to work and actually sequences. I take my probe off of pin 5 and it stops.

Anyways, to answer your questions, The diode looks fine, and the probe sequence thing tells me that the diode probably isn't the issue. I checked all of those resistor values and they are correct. One thing I should have noted at the start that I just realized is that I'm running this off of +/- 15v rather than +/- 12v in case that makes any difference. I don't have my meter on me at the moment, but I'll check pin 6 when I do. Again the sequence only when probed thing makes me think this probably isn't the issue.


12V vs 15V shouldn't matter.

This is like a problem I've heard before. Usually it's probing one of the pins of the 4017 though.

try using something non conductive to poke at the pin in question. If that also works, you have a cold solder joint there. It might not be a bad idea to touch up all the joints on that one anyway.

Did you use sockets? Spring leaf sockets or milled? I've had spring leaf ones also cause problems where the chip wouldn't make solid contact.

What do you see on pin 14 of U1? Is it an anemic pulse that isn't enough to trigger the chip, or is it just flat nothing? Does probing that pin also make things work (a possibility)?
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Hubaswift



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PostPosted: Sat Dec 17, 2016 2:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
Hubaswift wrote:
elmegil wrote:
The pulses are expected to be very narrow (as seen in Ray's daigram). That really points to something being wrong with D18. D16 is fine, because the clock oscillator works. D19 is fine because the step button works, and all the stuff driven by the clock is fine, because the step button works. D18 is the link between the oscillator output and the clock input to the 4017. Make sure you don't have any cold solders....

I suppose the pulses could be *too* narrow to clock the 4017. I'd consider verifying R23, R28, R29, and R32 values, and then with it powered on, see that you're somewhere in the neighborhood of 8V at pin 6 of U3.
Ok, I just noticed the weirdest thing. My oscilloscope probe is hooked to ground, and then the other probe I put on pin 5 of U3, When I probe it the whole sequencer starts to work and actually sequences. I take my probe off of pin 5 and it stops.

Anyways, to answer your questions, The diode looks fine, and the probe sequence thing tells me that the diode probably isn't the issue. I checked all of those resistor values and they are correct. One thing I should have noted at the start that I just realized is that I'm running this off of +/- 15v rather than +/- 12v in case that makes any difference. I don't have my meter on me at the moment, but I'll check pin 6 when I do. Again the sequence only when probed thing makes me think this probably isn't the issue.


12V vs 15V shouldn't matter.

This is like a problem I've heard before. Usually it's probing one of the pins of the 4017 though.

try using something non conductive to poke at the pin in question. If that also works, you have a cold solder joint there. It might not be a bad idea to touch up all the joints on that one anyway.

Did you use sockets? Spring leaf sockets or milled? I've had spring leaf ones also cause problems where the chip wouldn't make solid contact.

What do you see on pin 14 of U1? Is it an anemic pulse that isn't enough to trigger the chip, or is it just flat nothing? Does probing that pin also make things work (a possibility)?
Non conductive didn't do anything, it's not a cold solder joint. I didn't use any sockets. I see nothing on pin 14 of U1, and it doesn't make anything work. I accidentally shorted U3 A, but probing U3 pin 5 still makes the circuit work. If I touch the pin with my finger it also works, so it probably has something to do with the pin discharging. I'll go replace U3 and check again in case the short damaged the chip. There was a spark but no smoke so I doubt anything surrounding got damaged.

Edit: Ok, I think I've found the problem. I replaced U3, on U1 pin 14 there is just dc now. On U1 pin 12, there is a clock signal, but I noticed that when I put my finger/probe on U3 pin 5, the clock signal voltage increases, so I think it's probably that small increase in the clock voltage that is making it trigger when I put my finger or probe on U3 pin 5, so then my question is, What component would I want to change in order to slightly increase the clock voltage? Should I change R29?
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Hubaswift



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PostPosted: Sat Dec 17, 2016 3:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

I got it working. Changing R29 to a lower resistance seems to do the trick. Odd considering it was the right value to begin with. When the sequence is really slow it still doesn't trigger, so I think I just need to play around with the value of R29 more. Another small issue, though it may be normal is that the portamento range is really, really small. Is there a something I could change on the board to give the portamento a bigger range?
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gdavis



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PostPosted: Sat Dec 17, 2016 4:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

When you touch it with your finger or the probe, you're increasing the capacitance. Based on your earlier statement that the pulses are very quick, I'm guessing the pulse is too short to allow it to reach full amplitude. The increased capacitance lengthens the time of the pulse allowing it to reach the higher voltage.

Lowering the value of R29 increases the hysteresis which also lengthens the pulse. Increasing the value of C2 should lengthen the pulse as well without affecting the hysteresis.

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Hubaswift



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PostPosted: Sat Dec 17, 2016 9:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

gdavis wrote:
When you touch it with your finger or the probe, you're increasing the capacitance. Based on your earlier statement that the pulses are very quick, I'm guessing the pulse is too short to allow it to reach full amplitude. The increased capacitance lengthens the time of the pulse allowing it to reach the higher voltage.

Lowering the value of R29 increases the hysteresis which also lengthens the pulse. Increasing the value of C2 should lengthen the pulse as well without affecting the hysteresis.
I actually already increased the value of C2 thinking the same thing. the sequencer seems to be working great now. It seems that this wasn't even my error, but rather a design flaw, but it makes me curious as to why others don't seem to always have this problem.
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Grumble



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PostPosted: Sun Dec 18, 2016 12:56 am    Post subject: Reply with quote  Mark this post and the followings unread

I like to help ppl out who have problems from a electronic/technical nature, but it would very much help me if the thread starter would at least provide a link to the diagram in question!
I'm sure there are a lot more willing ppl, but like me who don't first like to search for info about the question (at least: this keeps me from digging into the problem...)
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wackelpeter



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PostPosted: Sun Dec 18, 2016 5:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Hubaswift wrote:
It seems that this wasn't even my error, but rather a design flaw, but it makes me curious as to why others don't seem to always have this problem.


Wouldn't see it as an error in the design.

Had similar problems with the comparators in my 2 quantizer builds... getting the correct treshhold is a bit tricky there... But i'm sure plenty of others build them without having troubles and they used the same components and values but then you still have all the tolerances of the parts and so on... Don't worry, now you know where to look at when you have similar problems again, as opamps or comparators are used in many other circuits as well...

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Hubaswift



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PostPosted: Sun Dec 18, 2016 1:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Grumble wrote:
I like to help ppl out who have problems from a electronic/technical nature, but it would very much help me if the thread starter would at least provide a link to the diagram in question!
I'm sure there are a lot more willing ppl, but like me who don't first like to search for info about the question (at least: this keeps me from digging into the problem...)
Needlessly, I've already solved the problem thanks to others help, but linking to MFOS site can be odd since all the different projects on the left list have the same url, so I can't really link to the 10-step sequencer page in specific, instead it will go to another random project page with the same url. That's why I didn't link, but it's easy enough to search "MFOS 10 step sequencer" and scroll down to the schematics.
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