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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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Posted: Sat May 31, 2014 10:07 am Post subject:
MFOS 10 Step Sequencer not sequencing Subject description: Stuck Can anyone Help please |
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Hello I am new to electro music, have found it a useful resource when stuck. I am now Stuck and out of ideas.
I am a amateur hobbyist, I got into electronics about 2 years ago and have built an 8 step 555 / 4017 based sequencer with APC oscillator and a portamento. Plus a 16 step sequencer 555 / 2x 4017 with APC oscillator. I bought and loved building the mfos noise toaster and have built a Thomas Henry VCA.
All my builds had various issues and needed trouble shooting before success, the mfos 10 step has got me stumped.
What works
1) start/stop push button
2) step push button
3) reset push button
4) last step selector dial all steps
5) stop/reset/10 steps switch
6) clock rate (audible oscillation)
7) CV output range (I can hear a slight change in tone)
LEDs light up with each step
What does not work
1) no sequencing
2) all gate switches, whether on or off, the LEDS stay on
3) no portamento
I originally had C8 and C11 the wrong way round, did'nt know about tantalum cap polarity, removed and replaced with new ones.
All ICs have power and ground seems ok
Have since swapped out all chips and have replaced Q11 2n5457 3 times. The last time I soldered a cut down piece of socket and 'plugged' the jfet in, to avoid soldering it, still no luck
Q11 shows -2.4v on gate, 0v on drain, 5.4v on source. When taking these readings placing the probe on the Gate starts the LEDs sequencing !! but no change to clock sound.
Can anyone help or advise ?
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Area of concern is U3 and Q11 jfet. No voltage on source |
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Last edited by Cato on Sun Jun 01, 2014 8:42 am; edited 1 time in total |
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
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Posted: Sat May 31, 2014 10:01 pm Post subject:
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It's really not clear what you are saying about the clock. You say that the LEDs light in sequence, but you've focused on the FET in the clock oscillator section, as if the clock is not oscillating. But then how could you hear audio??
My suspicion if the clock is not working is that your -12V rail is not correct. You should have -12V, not ground, at pin 4 of U2 & U3, and pin 11 of U6. These are the only three chips that use the -12V rail, and if the clock isn't working all three sections controlled by these chips are down--the -12V supply is the obvious thing they have in common. |
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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
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Posted: Sun Jun 01, 2014 8:49 am Post subject:
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Are we listening to the raw CV out in your video? CV's are meant to control other synths, not be sound sources in themselves. If that's not what we're listening to, I think it would help me understand to know what we *are* hearing.
I'm kind of baffled how we would hear the clock out on the CV out at all. What should be happening is the clock is doing the same thing as the step button--moving each step forward.
Here's a similar sequencer I built; I'm using the soundlab mini synth built into a cigar box as the sound source.
[video]http://www.youtube.com/watch?v=8sdn6WWC8xg[/video]
The only really signficant difference with Ray's is that he's using a "real" oscillator rather than a 555 chip.
If I had to guess at this point, I'd say you have some portion of the clock circuit shorted to somewhere after the CV pots going into the output section. Not clear how that could happen, the circuit sections are on opposite sides of the board, but.... |
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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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Posted: Sun Jun 01, 2014 9:46 am Post subject:
MFOS 10 Step Sequencer not sequencing |
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The same sound is emitted from all CV outputs plus external start gate out and trigger out. I'm baffled. is'nt the external start an input?
Plus the step LED is confusing, surely if I switch off a gate its LED should go out too.
its plugged into a audio spliiter (sound card interface design by Ray Wilson) and then in to a Lepai amp. |
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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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Posted: Sun Jun 01, 2014 10:03 am Post subject:
MFOS 10 Step Sequencer not sequencing Subject description: new idea |
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Its just ocurred to me that all the jack sockets may be wired back to front, the ground and signal wires are, i think, the wrong way round. |
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Sun Jun 01, 2014 11:05 am Post subject:
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That would certainly cause some interesting problems |
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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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Posted: Sun Jun 01, 2014 11:07 am Post subject:
MFOS 10 Step Sequencer not sequencing Subject description: switched jack wires |
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Yes I had wired the jacks back to front. Now no sound from external start, 'bass' sound through gate out, lighter 'ticking' sound from trigger out, and no sound from any of the CV outputs.
All the other issues remain, am thinking I may have shorted something somewhere because of this obvious error. So I had the ground wires connected to the signal of the jack and the signal wires connected to the jacks ground. |
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Sun Jun 01, 2014 12:11 pm Post subject:
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You aren't supposed to get sound out of any of those jacks!
They are control voltages, not audio.
The gates will make a sound in time with the clock, and the triggers will be a thinner sound because they're pulses, not square waves. But you're supposed to use those as inputs to an envelope or other "triggered" function in your synth.
The control voltages are then used to control the pitch of a VCO, which is external to the sequencer. Do you have any VCOs?
Everything you describe in this most recent post sounds entirely what I would expect from a correctly functioning sequencer.
Your sequencer takes the place of the keyboard in the diagram on this page:
http://www.musicfromouterspace.com/forums.html?MAINTAB=SYNTHDIY&PROJARG=ELECTRONICS/analogsynth101.html&VPW=1321&VPH=670
It generates control voltage (pitch, usually), trigger (key press) and gate (key hold), not audio |
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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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Posted: Sun Jun 01, 2014 1:26 pm Post subject:
MFOS 10 Step Sequencer not sequencing |
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Thank you for all your help. I had a sinking feeling that it now worked and needed to be plugged in to something else. So off the top of my head a VCO will trigger the sequencing?? Need to study Rays build notes again and again.
A quick look at the schematic confirms? that U5 CD4013 SET (pin6) is where the VCO signal goes to, via external start socket, and thus triggers Q and NOT Q. Is this right?
A VCO was planned to be my next build. I have been frustrated but I have learnt a lot with this build. Now for some reading and thinking. After all I am a noob at this '' but not defeated. |
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Sun Jun 01, 2014 2:42 pm Post subject:
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So there is some confusion here still I think.
The clock circuit (U3 + Q11) is, technically, a VCO. It is an oscillator, being used as a clock, and it is controlled by voltage.
This is not the same as a VCO you would be using for voicing the "notes" you are playing with the sequencer.
Pin 6 on the 4013 is for an external START. Basically rather than only having a switch control "is the sequencer running or not" you can do that under voltage control as well--a pulse to the start jack will turn on the 4013, which will start the sequencer running, assuming it was stopped (and not stopped with the manual switch, which holds the flip flop in reset).
I really think that the Synth 101 pages at Ray's website (I liked into the middle of it, but there's a lot of good material there) would be good reading before building much more. |
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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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Posted: Sun Jun 01, 2014 9:57 pm Post subject:
MFOS 10 Step Sequencer not sequencing |
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Thanks for all your help and advice. |
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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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Posted: Tue Jun 17, 2014 1:11 pm Post subject:
Still Stuck Subject description: Automatic sequencing |
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I am just plain confused, quoting Ray Wilson below.
"The main idea of a sequencer is to provide an automatic means of sequentially stepping through a series of adjustable voltages to drive a VCO (or any other voltage controlled device)"
Before I go further on fault finding....
With only the power connected, should the sequencing start automatically ? i.e. no other cables connected whatsoever. I now understand the voltages driving VCO bit.
I know I have got the start, stop and reset working correctly, but just by hitting start should it not start to sequence automatically through each gate/step? |
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Tue Jun 17, 2014 1:26 pm Post subject:
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U3 is a VCO that is supposed to supply the internal clock.
What's your clock rate pot set to? If it's way low, perhaps it's just not got the VCU running? |
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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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Posted: Tue Jun 17, 2014 2:03 pm Post subject:
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clock rate high or low (0 to 10) no change.
readings at pot ;
CR1 at 0 rate -9.8v, at 10 -8.4v
CR2 at 0 rate 0v, at 10 -8.4
CR3 at 0 and 10 rate 0v |
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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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Posted: Tue Jun 17, 2014 2:08 pm Post subject:
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I assume by your reply that it should be sequencing automatically? |
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Tue Jun 17, 2014 2:20 pm Post subject:
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Yes it should. It isn't even capable of having an external clock, so if you hit start it should be going.
Does step work?
You should look for clock signal at pin 7 of U3; that goes through a diode to the actual clock "bus".
If Step works but it doesn't self-clock then you have a problem in the oscillator that is built around U3.
If Step doesn't work either, then you have a problem downstream in the clock bus itself.
Here's what you should see on the various points in the clock area:
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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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Posted: Tue Jun 17, 2014 2:32 pm Post subject:
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Yes Step works.
I will check and probably replace diode D18 and digest your info.
I am convinced the fault is in the U3 area, have read and re-read Rays info and it all points at pin 7 of U3 not triggering pin 14 of the 4017.
Thanks |
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Tue Jun 17, 2014 3:01 pm Post subject:
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Why do you suspect D18?
Have you verified that there is actually a clock signal coming out of U3-B? If the oscillator isn't oscillating the diode won't do you any good |
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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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Posted: Wed Jun 18, 2014 2:04 pm Post subject:
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I have used scope and all outputs are correct |
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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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Posted: Wed Jun 18, 2014 2:29 pm Post subject:
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However U3B scope signal seems to be weak compared to the other signals. Clock rate was set at 9 when I did this.I will post images to support findings as soon as I can. |
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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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Posted: Wed Jun 18, 2014 2:30 pm Post subject:
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However U3B scope signal seems to be weak compared to the other signals. Clock rate was set at 9 when I did this.I will post images to support findings as soon as I can. |
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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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Posted: Fri Jun 20, 2014 3:15 pm Post subject:
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Some scope images for clarity
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Cato
Joined: May 29, 2014 Posts: 44 Location: uk
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Posted: Fri Jun 20, 2014 3:20 pm Post subject:
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These two scope images are readings from the cathode and anode of D18
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