ARP Odyssey Oscillators

elmegil · Posted: Wed May 29, 2013 7:48 pm Post subject:

The attenuation switch will switch it from 1X to 10X, usually. I believe it makes them higher impedance which should minimize their effect on the circuit.

prgdeltablues · Posted: Thu May 30, 2013 8:42 am Post subject:

I'm seen that sort of distortion of square waves on my scope, using the probe on x1. Switching to x10 often sorts it out. It's caused by a mismatch between the RC constant of the probe and that of the scope input -using probes with trimmers (which is a pF variable capacitor), you adjust the trimmer until a square wave looks right. Not the only possibility of course, but worth checking out.

Peter

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

Turns out this was the problem after all! When I select 10x attenuation the wave shapes are as expected.

Thanks for your help!

isak · Posted: Mon Jun 03, 2013 9:30 am Post subject:

Hi guys.

I used this scheme to increase the output Vpp of the ody vco and it works great.

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

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

Can I use the same scheme for LFO or ADSR etc to increase the Vpp as well?

Cheers.

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

Sorry to drag this up again, but I still don't think my saw and square waves are correct!

On the previous page I thought my waveshapes were a little 'wonky' looking. They used to be perfect square and saw waves, but after getting my synth out of storage where it had been languishing for a couple of years, I noticed that they were wonky.

I thought it might have been my oscilloscope that was playing up, and using the attenuator on the probe it looked like the problem had gone away. But I've just recorded my synth straight out into my computer and took a look at the waves in my DAW. They're still wonky! In both oscillators!

I guess I'll have to start poking around the 4011 seeing as that's the component that both oscs share.

isak · Posted: Sat Jun 29, 2013 9:12 pm Post subject:

Hi

How does they look in the scope?
Are they look ok in your scope and in your computer they look wonky?
If yes that's normal.
I have the same thing with mine.
On the scope looks as they should, when connect to the soundcatd (RME FF400) look wonky, it's very obvious when at low freqs.

Cheers.

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

Well they look wonky on my scope, until I use the attentuator switch on my probe, when they then appear as expected. On the previous page of this thread it was said that this was an impedance issue.

My problem is though is that if my square and saw wave look wonky in Cubase, after going through my FF400, then surely I'm not able to compose/ record with perfect square and saw waves?

I've attached some screenshots of the audio clips so you can see what I mean by wonky.

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isak · Posted: Sun Jun 30, 2013 2:10 am Post subject:

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

Ok, if you're sure...!

isak · Posted: Mon Jul 01, 2013 2:18 am Post subject:

It's an AC DC thing.
Not sure why it's happening but it does.
I was in the same situation, with the scope it was perfect shapes.
With the comp scope like yours.
Besides that...the sound is the same sound, nothing to worry about.

Q..
What input of the FF400 you use?
Did you tried to connect to the back of the FF400 inputs or only to front inputs?

numbertalk · Posted: Mon Jul 01, 2013 8:30 am Post subject:

I know I forget this as well but just as important is how does it sound? If it sounds ok then it's very likely ok.

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

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

Apologies if this has been asked before, but is anyone running this on +/-12v at all?

Do I need to re-calculate some resistor values for it to work, or should I be fine just plugging it in?

Thanks!

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

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

That's good to know, thank you.

What sort of value would you recommend?

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

I havent tried modding mine yet, but the value i will try when doing so will be something around 180K - 220K.

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

Great, thanks a lot!

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

isak · Posted: Mon Oct 14, 2013 1:03 pm Post subject:

Hi steffensen Smile

Back then I think we talked about the 56k of the PWM, not the 274k..
If I remember correctly one should add 16.5k to the 56k in the 12V version.
So when you turn the PWM all the down you will get the square you want.

Just found it in one of our emails...

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

isak · Posted: Mon Oct 14, 2013 8:47 pm Post subject:

Hhoo...
Got your point Smile

Cheers.

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

If I wanted to be able to control the pitch of each oscillator separately, which trace should I cut?

Looking at the PCB layout posted on page 1, it looks like I need to cut the trace that goes from the 1v/Oct to the VCO2 Scale trimmer. Does that sound look right?

xpmtl · Joined: Aug 10, 2007 Posts: 158 Location: Brussels, Belgium

Working on SMD version of this great little module.

So far it sounds great, need to verify tracking and stability and also how it performs on 12V.

I'm tracking 4-5 octaves (the fifth is a bit sharp) with unmatched trannies.

How does yours track? how many octaves?

I'll add pads for Thru-hole transistors for the expo pair in next revision, just want to know if i'm having the same results.

Cheers,

X

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isak · Posted: Fri Jan 10, 2014 1:47 pm Post subject:

Hi

that look nice, good job.
I can track mine with no matched transistors up to 9 fully octaves.
It perform great with 12V although the signal is a bit low comparing to 15V.

cheers,
Isak E.

xpmtl · Joined: Aug 10, 2007 Posts: 158 Location: Brussels, Belgium

Thanks Isak

What did you use as trannies for the expo pair?

I'm wondering why I only get 4 good octaves when you get 9, must be something else perturbing the thing.

Back to testing I guess Smile

cheers,

x