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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
MFOS 10 Step Sequencer not sequencing
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Cato



Joined: May 29, 2014
Posts: 43
Location: uk

PostPosted: 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. Very Happy
All my builds had various issues and needed trouble shooting before success, the mfos 10 step has got me stumped. Confused


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)
Cool 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 Mad
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: 1535
Location: Chicago
Audio files: 14

PostPosted: Sat May 31, 2014 10:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

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: 43
Location: uk

PostPosted: Sun Jun 01, 2014 5:42 am    Post subject: More info on mfos 10 step issues
Subject description: think i'm barking up the wrong tree
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Thanks for reply, Very Happy pretty sure negative power is good.
I've added image showing what power the chips are getting.
I've also added this link, short video of sequencer in action.

www.youtube.com/watch?v=wwW0WVffULM&feature=youtu.be

I think I am missing the obvious Embarassed


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pin out readings.
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elmegil



Joined: Mar 20, 2012
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Audio files: 14

PostPosted: Sun Jun 01, 2014 8:49 am    Post subject: Reply with quote  Mark this post and the followings unread

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: 43
Location: uk

PostPosted: Sun Jun 01, 2014 9:46 am    Post subject: MFOS 10 Step Sequencer not sequencing Reply with quote  Mark this post and the followings unread

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: 43
Location: uk

PostPosted: Sun Jun 01, 2014 9:51 am    Post subject: MFOS 10 Step Sequencer not sequencing Reply with quote  Mark this post and the followings unread

For info here's a link to my 8 step build

www.youtube.com/watch?v=PvYwCeKF210
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Cato



Joined: May 29, 2014
Posts: 43
Location: uk

PostPosted: 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



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PostPosted: Sun Jun 01, 2014 11:05 am    Post subject: Reply with quote  Mark this post and the followings unread

That would certainly cause some interesting problems Very Happy
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Cato



Joined: May 29, 2014
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PostPosted: 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



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PostPosted: Sun Jun 01, 2014 12:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

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 Smile
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Cato



Joined: May 29, 2014
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PostPosted: Sun Jun 01, 2014 1:26 pm    Post subject: MFOS 10 Step Sequencer not sequencing Reply with quote  Mark this post and the followings unread

Thank you for all your help. Very Happy 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 'Embarassed' but not defeated. Very Happy
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elmegil



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PostPosted: Sun Jun 01, 2014 2:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Sun Jun 01, 2014 9:57 pm    Post subject: MFOS 10 Step Sequencer not sequencing Reply with quote  Mark this post and the followings unread

Thanks for all your help and advice. Very Happy
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Cato



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PostPosted: Tue Jun 17, 2014 1:11 pm    Post subject: Still Stuck
Subject description: Automatic sequencing
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Confused 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? Shocked
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elmegil



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PostPosted: Tue Jun 17, 2014 1:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Tue Jun 17, 2014 2:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Tue Jun 17, 2014 2:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

I assume by your reply that it should be sequencing automatically?
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elmegil



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PostPosted: Tue Jun 17, 2014 2:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

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:

Posted Image, might have been reduced in size. Click Image to view fullscreen.
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Cato



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PostPosted: Tue Jun 17, 2014 2:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

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 Smile
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elmegil



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PostPosted: Tue Jun 17, 2014 3:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

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 Smile
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Cato



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PostPosted: Wed Jun 18, 2014 2:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

I have used scope and all outputs are correct
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Cato



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PostPosted: Wed Jun 18, 2014 2:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Wed Jun 18, 2014 2:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Fri Jun 20, 2014 3:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

Some scope images for clarity


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Cato



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PostPosted: Fri Jun 20, 2014 3:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

These two scope images are readings from the cathode and anode of D18


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