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ARP Odyssey Oscillators
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AndyR1960



Joined: Feb 16, 2007
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PostPosted: Sat Aug 30, 2008 9:14 am    Post subject: ARP Odyssey Oscillators Reply with quote  Mark this post and the followings unread

Sorry, me again...

I've just built a clone of the ARP Odyssey Oscillators (MkIII), including the Ring Mod - All works great, very pleased.

...except that the oscillators are locking together when I get close to unison.

I've heard of this problem before, especially when two Osc's are built onto one board, and particularly when (for example) a quad op-amp is shared by both osc's.

I've removed any flux off the PCB, it's very clean and I know the PSU is fine.

Unfortunately, I just don't know enough about the theory of electronics to know what I can do about this locking.

As I mentioned before, it's an exact copy of the Oscillator section of the PCB, and no component substitutions have been made, apart from using good quality WIMA 680pf timing caps instead of polystyrene and multiturn trimmers.

Any suggestions?

Andy

PS. You may be wondering why the hell I've built Oddy Osc's... It's all to do with the sync and ring mod combo, I've tried several VCO's/RM circuits in the past and never been able to get that distinctive Oddy sound.


ARP Oddy Osc.jpg
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urbanscallywag



Joined: Nov 30, 2007
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PostPosted: Sat Aug 30, 2008 10:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Congratulations, that's a cool project. I have an Odyssey and would like to build some modular Odyssey VCOs. They do have a unique sound.

It doesn't look like there are any decoupling capacitors around your opamp.
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AndyR1960



Joined: Feb 16, 2007
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PostPosted: Sat Aug 30, 2008 10:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Ah, now then... this is the problem you see : )

There are no op-amps - there's a couple of 3086 tranny arrays, and a CD4011 which is used for the osc's integrators and the ring mod.

All the de-coupling (not that there's much... if any!!!) on the PCB is identical to the original. I can only presume that its all the switching that the discrete FET's are doing that's causing the lock-up.

Will have to have a long hard think, and see if I can somehow de-couple the FET's.

Andy.
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urbanscallywag



Joined: Nov 30, 2007
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PostPosted: Sat Aug 30, 2008 11:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Ah, I see. I saw the 2 chips on the sides weren't op amps, I couldn't tell what the center chip was (and then you mentioned quad opamp...).

Hmmm. Can you just add an electrolytic and ceramic decoupling capacitor to each rail on the actual board? (never mind I see the tantalums)
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urbanscallywag



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PostPosted: Sat Aug 30, 2008 11:12 am    Post subject: Reply with quote  Mark this post and the followings unread

You could still decouple the 4011 right?
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Peake



Joined: Jun 29, 2007
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PostPosted: Sat Aug 30, 2008 11:37 am    Post subject: Reply with quote  Mark this post and the followings unread

Is the overall layout the same as the original?

The SEM uses a 3086 (IIRC, the Prodigy as well) for a pair on the same board, and they have both avoided the locking issue. I have no idea how. If someone can open an Odyssey and send you a photo of the oscillator section it might help.

Very nice board, by the way.

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AndyR1960



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PostPosted: Sat Aug 30, 2008 12:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

Peake wrote:
Is the overall layout the same as the original?


Yup, I copied the PCB foil from the service notes and just removed the S&H and LFO sections.
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bubblechamber



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PostPosted: Sat Aug 30, 2008 3:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

when i've encountered this problem it was often coming from using the same ground for both oscillators. and there's always the possibility that they are meant to do that and it's a "feature"...
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AndyR1960



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PostPosted: Sat Aug 30, 2008 3:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've decided to look at the power and ground rails to each osc, maybe try to separate them a bit better.

If that fails, I'll re-design the board so each of the 3 parts (2 oscs and the ring mod) has it's own supply.

It's late I'm off for some shut eye.

Andy.
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AndyR1960



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PostPosted: Sun Aug 31, 2008 2:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Bubblechamber - Thanks, that's what the problem was!

I thought I'd be clever and extend the ground trace to make it easier to wire up the pots... I didn't realise that I'd created a loop between the two oscillators.

Working really well now Very Happy

I thought about uploading all the details, but I'm not sure what the legal aspect of this would be as I guess someone, somewhere still has a copyright on the design?

Andy.
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julianw



Joined: Jul 30, 2007
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PostPosted: Sun Aug 31, 2008 7:34 am    Post subject: Reply with quote  Mark this post and the followings unread

AndyR1960 wrote:
I thought about uploading all the details, but I'm not sure what the legal aspect of this would be as I guess someone, somewhere still has a copyright on the design?

Andy.


I'd go ahead and upload the info, pcb layout etc. I just checked here and apparently ARP went into liquidation 27 years ago.

If you have a pcb layout I'll probably have a go making one, I had a jam session last weekend with my modular and a friend playing his Oddy, I really liked the bass sounds he got out of it.
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synthmonger



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PostPosted: Sun Aug 31, 2008 7:39 am    Post subject: Reply with quote  Mark this post and the followings unread

so how did ya make a separate ground?
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AndyR1960



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PostPosted: Sun Aug 31, 2008 8:44 am    Post subject: Reply with quote  Mark this post and the followings unread

synthmonger wrote:
so how did ya make a separate ground?


I didn't have to...

The ground trace went from the power connector to osc 1 then on to osc 2 and back to the power connector.

I just cut the ground track between the seperate Osc circuits, so each oscillator had it's own ground with a common point at the power connector, And following Urban's advice, I also added a decoupling cap across the 4011 to be on the safe side.

I'll get some PDF's/Audio samples up after I've had a rest.

Andy.
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creekree



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PostPosted: Sun Aug 31, 2008 9:02 am    Post subject: Reply with quote  Mark this post and the followings unread

AndyR1960 wrote:


I'll get some PDF's/Audio samples up after I've had a rest.



yes, please!
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rjd2



Joined: Sep 02, 2007
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PostPosted: Sun Aug 31, 2008 12:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

2 questions:

1-which vco version did you clone off of? i understand there are slight differences in the topology of the odyssey vco's.

2-so....anyone wanna make a run of these pcb's? i'd be in for 4-8, at least... Very Happy
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urbanscallywag



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PostPosted: Sun Aug 31, 2008 1:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Wow, glad the power routing solved the problem. Cool
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AndyR1960



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PostPosted: Sun Aug 31, 2008 3:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

rjd2 wrote:
2 questions:

1-which vco version did you clone off of? i understand there are slight differences in the topology of the odyssey vco's.


The VCO's are from the Mk 2 & 3 - The Mk 1 Osc board is double sided and I don't have enough experience making DS boards at the moment.

There are a few odd and hard to get components, I got mine by trawling around ebay and got some very good deals.

Andy.
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Zodiak



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PostPosted: Sun Aug 31, 2008 5:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

julianw wrote:
AndyR1960 wrote:
I thought about uploading all the details, but I'm not sure what the legal aspect of this would be as I guess someone, somewhere still has a copyright on the design?

Andy.


I'd go ahead and upload the info, pcb layout etc. I just checked here and apparently ARP went into liquidation 27 years ago.

The maybe the site you have used for research http://www.rhodeschroma.com/?id=arp and it says that CBS bought the inventory in 1981, but it doesn't mention the intellectual rights. You could always write and ask I suppose. Question

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Peake



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PostPosted: Sun Aug 31, 2008 8:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've never cared for the sound of any ARP oscillators after the 2600, but this thread has caught my attention.

Service Manual, page 45, 7.7 Board B-II:

2N5485:
Central Semiconductor at Mouser: 610-2N5485, .55 singly.
Fairchild at Mouser: 512-2N5485, .12 singly.

2N5910/PN5910: Eep, 6 in stock at americanmicrosemi at $6.25. Doesn't show up at my favorite places. Mouser crosses the PN to the NTE106. I've never had much luck with substitute components. $15.90 on ebay for the PN version, quantity of six. Try:

H&R ENTERPRISES, 1060 in stock.
All Parts Sales, 200 in stock.
Digitron Electronics, 300 in stock.

2N:

WE Express United States 2N5910 MOTOROLA 625
Perfect Electronics Ltd United Kingdom 2N5910 MOTOROLA 3500
Digitron Electronics United States 2N5910 FAIR 127

Can't identify Q5, and 6,7,13,14. You'll have to figure out how they selected the various transistors...

Sample and Hold, etc:

2n3958 dual FET- Didn't think that I'd see this outside of Buchla design (it's in the 259 waveshaper and the 291 dual BPF). I believe that Mark Verbos replaced it in his 291 clone with an opamp: http://www.simple-answer.com/bandpass.jpg
There's another 291 version on the net, link here on E-M in this forum, with another substitution, but this time a tranny. BF245 replaces 2N3958.

BF245 (c version): Mouser 512-BF245C, .13 each. a and b versions, same price.

2N5459: Mouser 512-2N5459, .15 singly.

LM1458: Mouser 512-LM1458N, .33 singly. Very slow opamp; replace if used to buffer audio outputs.

LM301AN: Mouser 512-LM301AN, .30 singly. Slow, but clips nicely.


Board A, if anyone is interested:

2N4392: Mouser 610-2N4392, $1.64 singly, but the Fairchild PN version is 512-PN4392, .13 singly.

2N6076: Mouser 512-2N6076, .09 singly.

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"IC 741. Sometimes you don't want fidelity." -Small Bear Electronics Catalog
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AndyR1960



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PostPosted: Mon Sep 01, 2008 12:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Peake wrote:

Can't identify Q5, and 6,7,13,14. You'll have to figure out how they selected the various transistors...


Q6/7 and Q13/14 are 2N3904/06 pairs for the exponential converters - I read in the old SynthDIY archives that ARP never actually bothered to match them, so neither did I... no problems at all, tracking very well over 5 octaves.

I guess I got lucky with the 2N5910's (ebay a year ago, 50 for 20USD).

Rapid, here in the UK, stock all the odd value resistors (61.5k, 88.7k, 49.9k etc.).

The 1.87k Tempco may be problematic. I got mine from Vintage Planet, but I'll take another look at the schems to see if I can sort something out for the more commonly available 1K.

Andy.
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AndyR1960



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PostPosted: Mon Sep 01, 2008 5:02 am    Post subject: Reply with quote  Mark this post and the followings unread

OK, It's pretty rough and ready... but it works Smile

There's plenty of info around the web if you need the schematics.

Enjoy,


Andy.


ARP Odyssey Dual VCO.pdf
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PCB Layout and Component Placing.
Build at your own risk :)

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Peake



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PostPosted: Mon Sep 01, 2008 8:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Is this the oscillator board? Looks like the heat-sunk pair have some level of matching/selection:

http://www.arpodyssey.com/odybfrnt.jpg

1.87K Tempco? And people chide me for liking the uA726 Wink

Thanks for the project!

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"IC 741. Sometimes you don't want fidelity." -Small Bear Electronics Catalog
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loss1234



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PostPosted: Mon Sep 01, 2008 9:33 am    Post subject: Reply with quote  Mark this post and the followings unread

wow

thanks a lot!

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AndyR1960



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PostPosted: Mon Sep 01, 2008 10:08 am    Post subject: Reply with quote  Mark this post and the followings unread

Peake wrote:
Is this the oscillator board? Looks like the heat-sunk pair have some level of matching/selection:

http://www.arpodyssey.com/odybfrnt.jpg

1.87K Tempco? And people chide me for liking the uA726 Wink

Thanks for the project!


NP. I almost used the pics from arpodyssey.com for the project (those pics are from the Mk1 white faced Oddy).

I think I could have made the board more compact using a double sided board, but I wanted to keep things simple, which is why I went for the MkII/III version.

Seriously though, don't bother matching the expo pair as it works fine without.

I must find a workaround for the tempco's as I've only got 2 left Shocked (but loads of 1k's)

Last time I used a 726 was in '77 - I tried to build the Formant... Hmm, 'nuff said! Smile

Andy.
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/mr



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PostPosted: Mon Sep 01, 2008 3:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

urbanscallywag wrote:
I have an Odyssey and would like to build some modular Odyssey VCOs. They do have a unique sound.

Unique in what way? Smile

(I have no experience of the Odyssey (but I do have a strong belief that "VCO character" is an overrated thing, that's why I'd like to know!))
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