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 Forum index » DIY Hardware and Software
ARP Odyssey Oscillators
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steffensen



Joined: Jul 11, 2012
Posts: 85
Location: Sweden

PostPosted: Thu Mar 21, 2013 10:45 am    Post subject: Reply with quote  Mark this post and the followings unread

AndyR1960 wrote:
Oh dear, not this old thread again Smile

Last week, I finally got off my a$$ and did some work before zooming off for a few weeks.

I'm glad to report that this VCO works fine with +/-12v with no modifications. No problems at all with 1v/Oct scaling or tuning. Unfortunately my scope is down at the moment, so I can't properly check the waveforms, but they sound fine to me, just a slight adjustment on the pulse width to bring it to 50% - I'll check when I'm back home.

I've been meaning to test this for ages - got a new PSU, so I was able to try it before re-calibrating to +/-15.

Hope this helps.


I can only agree with Andy here. Working just perfect.
Actually, i planned to find the PW value and replace my crappy trannys next week or so. Working on thinning out the backlog atm..
If you figure it out before i get to it, thats allright by me. Wink
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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
Location: London, UK

PostPosted: Mon Apr 29, 2013 3:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've had my dual oscillator board running for a few years now. The other day I noticed that the mild steel bracket I used was getting a bit rusty, so I replaced it with a aluminium one. Fine. Everything appeared to work ok after I'd replaced it.

However, I didn't check the 1V/Oct at the time. I've just tried using it and now I can't get it to change pitch by applying a CV to the 1V/Oct jack at all. Neither oscillator will change pitch.

Now logic tells me, it MUST be where I've broken a connection or something when I changed the bracket over, but I can't see anything wrong at all.

If both oscillators aren't responding to the 1V/Oct jack, whereabouts do you think I should start looking on the board?

Thanks for your help!
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steffensen



Joined: Jul 11, 2012
Posts: 85
Location: Sweden

PostPosted: Tue Apr 30, 2013 2:02 am    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:
I've had my dual oscillator board running for a few years now. The other day I noticed that the mild steel bracket I used was getting a bit rusty, so I replaced it with a aluminium one. Fine. Everything appeared to work ok after I'd replaced it.

However, I didn't check the 1V/Oct at the time. I've just tried using it and now I can't get it to change pitch by applying a CV to the 1V/Oct jack at all. Neither oscillator will change pitch.

Now logic tells me, it MUST be where I've broken a connection or something when I changed the bracket over, but I can't see anything wrong at all.

If both oscillators aren't responding to the 1V/Oct jack, whereabouts do you think I should start looking on the board?

Thanks for your help!


And you have checked the solder joints from where the CV is coming in to the board with the Continuity test i guess? Should be easy to find if doing this i would guess.

Btw, i asked this in the "ghost-thread" about this build but thought id ask here as well now - How did you guys solve the VCO's locking in to each other?
I get as much as they shouldnt share the same Ground trace, but when using a aluminium panel, its hard to avoid.
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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
Location: London, UK

PostPosted: Sun May 12, 2013 1:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

steffensen wrote:
And you have checked the solder joints from where the CV is coming in to the board with the Continuity test i guess? Should be easy to find if doing this i would guess.


It turns out I managed to ground the CV input -all fixed now.

However, I have just noticed another problem. I thought something sounded a bit strange with the audio out, so I took a look on the oscilloscope.

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

As you can see, the bottom of the square wave is wonky. When I first built this module years ago, this was straight. This occurs on both oscillators. Where should I start looking to rectify the problem?
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isak



Joined: Dec 13, 2009
Posts: 627
Location: Israel
Audio files: 18

PostPosted: Sun May 12, 2013 1:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

what is the rate your playing?
the scope is on ac or dc mode?

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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
Location: London, UK

PostPosted: Sun May 12, 2013 1:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

It's in AC mode, and I don't know the rate. It's the same shape no matter the rate, I think.
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steffensen



Joined: Jul 11, 2012
Posts: 85
Location: Sweden

PostPosted: Sun May 12, 2013 2:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

I had the same scope results when i was troubleshooting mine before.. dont really remember how i got this result, but it was when altering the resistor values. Gonna think about it, see if i can remember.. might be in the schmitt trigger area.. Seems the most obvious right now.

How does the Saw look like? Can you scope the output from pin 3 of the 3086? (or the closest leg of any component on the trace from it)
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isak



Joined: Dec 13, 2009
Posts: 627
Location: Israel
Audio files: 18

PostPosted: Sun May 12, 2013 2:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

try to put it on dc mode and lower the pitch, see if you get the same results.
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elmegil



Joined: Mar 20, 2012
Posts: 1345
Location: Chicago
Audio files: 14

PostPosted: Sun May 12, 2013 6:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yah, what Isak said. I have an AC/DC switch on my VCF inputs and I was looking at them with the scope the other day, and a wonderful square wave input was immediately warped to have slopes top and bottom in AC mode. And there were definitely audible effects of same, even with the filter wide open.

I would hope a scope's AC input would be less prone to such things, but....
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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
Location: London, UK

PostPosted: Mon May 13, 2013 6:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the replies!

So in AC mode, the higher the frequency, the less wonky the bottom of the square wave. So lower frequencies have more of a wonk.

In DC mode the square wave is normal, as I expect a square wave to look. However the wave jumps down to bottom of the display meaning I have to use the DC offset knob to bring it back to the centre.

Does this mean there's a significant DC offset on my sound waves?
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steffensen



Joined: Jul 11, 2012
Posts: 85
Location: Sweden

PostPosted: Mon May 13, 2013 6:03 am    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:

Does this mean there's a significant DC offset on my sound waves?


These VCO's have a DC offset, thats right. Not sure if anyone in here did try to buffer them? Curious on the result.
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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
Location: London, UK

PostPosted: Mon May 13, 2013 12:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

I thought the DC offset was just on the ring mod out?

Hmmm, so it's all ok then? The problem was my oscilloscope?
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AndyR1960



Joined: Feb 16, 2007
Posts: 275
Location: Manchester UK
Audio files: 5

PostPosted: Wed May 15, 2013 11:21 am    Post subject: Reply with quote  Mark this post and the followings unread

I know it's not much help, but I'm not getting any problems, the square waves are flat top & bottom in AC or DC on my scope (which is way past it's best!!). Also got a clean saw wave.

I've rechecked all my boards, and there's nothing that I've added or changed... the files I uploaded are exactly as I use here at home.

All the components I use are exact (no substitutions) and I use Hydro Flux Solder (water soluble - leaves no flux on the board once cleaned with a toothbrush and water!)

I wish I could be of more help... I feel a bit useless not being able to.


ARP Sq AC.JPG
 Description:
ARP VCO Square AC
 Filesize:  165.42 KB
 Viewed:  102 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

ARP Sq AC.JPG



ARP Sq DC.JPG
 Description:
ARP VCO Square DC
 Filesize:  161.96 KB
 Viewed:  98 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

ARP Sq DC.JPG



ARP Saw DC.JPG
 Description:
ARP VCO Saw DC
 Filesize:  144.38 KB
 Viewed:  88 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

ARP Saw DC.JPG


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isak



Joined: Dec 13, 2009
Posts: 627
Location: Israel
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PostPosted: Thu May 16, 2013 4:13 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Andy.

Thank you for your amazing work!
Btw is there any chance you will do the vca section some where in the near future? Wink

Cheers man and thanks again!!!

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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
Location: London, UK

PostPosted: Thu May 16, 2013 9:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Andy,

I built the VCOs nearly five years ago now, and at the time they worked perfectly. I put my modular in storage for a couple of years and have now got it out again.

I noticed a bit of corrosion on the PCB, and used some isopropyl alcohol to scrape it off. Measuring the DC offset and the wonky square waves must mean that something is still wrong, as I'm sure I used to have normal waveforms and no DC offset before.

So you posting those wave shapes means that I'm not going mad, and it is possible that I had perfect wave shapes a few years ago.

It's strange that I get the weird wave shape on both oscillators. Do the square waves share some circuitry? I think they share the ring mod section, don't they? Maybe I need to look there. Actually, the ring mod has a DC offset doesn't it? Maybe something's gone wrong around there, and the DC offset is added from there.

What do you think?
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AndyR1960



Joined: Feb 16, 2007
Posts: 275
Location: Manchester UK
Audio files: 5

PostPosted: Thu May 16, 2013 9:54 am    Post subject: Reply with quote  Mark this post and the followings unread

@LetterBeacon

The only component I can think of that's shared is the 4011, maybe start there... check the square waves before they go to the 4011 too?

Are your Saw waves OK?
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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
Location: London, UK

PostPosted: Thu May 16, 2013 9:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes the saw waves are fine, although I think they have the DC offset on them.

Unfortunately I won't have a chance to check anything until early next week, but I'll keep you posted.

Just to confirm, is this the correct schematic for this version of VCO: http://www.arpodyssey.com/schematics/ody_36.gif
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steffensen



Joined: Jul 11, 2012
Posts: 85
Location: Sweden

PostPosted: Thu May 16, 2013 10:12 am    Post subject: Reply with quote  Mark this post and the followings unread

steffensen wrote:

How does the Saw look like? Can you scope the output from pin 3 of the 3086? (or the closest leg of any component on the trace from it)


AndyR1960 wrote:
@LetterBeacon
Are your Saw waves OK?


LetterBeacon wrote:
Yes the saw waves are fine, although I think they have the DC offset on them.


If the Saw is ok, then the core of the VCO's are ok. Which is good to know, and makes it easier to track down.
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AndyR1960



Joined: Feb 16, 2007
Posts: 275
Location: Manchester UK
Audio files: 5

PostPosted: Thu May 16, 2013 10:30 am    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:


Just to confirm, is this the correct schematic for this version of VCO: http://www.arpodyssey.com/schematics/ody_36.gif


You're in the right area... but wrong page, that's the link to the VCF/ADSR etc Wink

You need the schematics for board BII, the MKII/III Oddy VCOs
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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
Location: London, UK

PostPosted: Mon May 27, 2013 10:59 am    Post subject: Reply with quote  Mark this post and the followings unread

AndyR1960 wrote:
@LetterBeacon

The only component I can think of that's shared is the 4011, maybe start there... check the square waves before they go to the 4011 too?

Are your Saw waves OK?


I just checked my saw waves (pin 3 on the 3046) and in AC mode there's a tiny little curve to the triangle slope, so it looks like my saw waves aren't healthy!

I get a 'rounded' square wave measuring just over 2V with a 2V offset going into the 4011 on (pins 2 and 12).

I then get a 15V square wave -normal looking in DC mode, wonky looking in AC mode- at pins 3 and 11 of the 4011.

I've attached photos in case they help at all...!


Photo 27-05-2013 18 53 31.jpg
 Description:
This is the saw with a slightly bend on it, measured from pin 3 of the 3046.
 Filesize:  2.72 MB
 Viewed:  161 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

Photo 27-05-2013 18 53 31.jpg



Photo 27-05-2013 18 42 06.jpg
 Description:
This is the square wave going into the 4011.
 Filesize:  2.77 MB
 Viewed:  156 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

Photo 27-05-2013 18 42 06.jpg


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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
Location: London, UK

PostPosted: Wed May 29, 2013 8:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Because this is an issue with both oscillators, could this be a test equipment problem? Could the AC input on my scope be warping the waveforms?
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elmegil



Joined: Mar 20, 2012
Posts: 1345
Location: Chicago
Audio files: 14

PostPosted: Wed May 29, 2013 8:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes, actually I've seen that with my scope, which admittedly is probably a lower-end device.
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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
Location: London, UK

PostPosted: Wed May 29, 2013 8:36 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmmm, that's interesting.

My one is a secondhand one I found on a classifieds ad, so I don't think it's particulary high end.

It looks to be the model below Andy's, although he's posted perfect wave shapes.
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LFLab



Joined: Dec 17, 2009
Posts: 179
Location: Rosmalen, Netherlands

PostPosted: Wed May 29, 2013 12:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

The probes you use with the scope are also of influence, do the ones you use have a trimmer cap inside (adjustment screw)?
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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
Location: London, UK

PostPosted: Wed May 29, 2013 4:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

Interesting. They don't have a trimmer, but they have an attenuation switch.
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