ARP Odyssey Oscillators

vtl5c3 · Posted: Mon Dec 14, 2009 6:01 pm Post subject:

I've built three of the deluxe VCOs. Want me to check something with my scope?

Tim Servo · Posted: Mon Dec 14, 2009 11:15 pm Post subject:

Hey Em,

The Thomas Henry circuit should work just fine. I've used simple op-amp stuff like that for level shifting and gain adjustment on several projects. Essentially what you want to do is:
1) Give the circuit a gain of 2. This is adjusted by the ratio of the input resistor to the feedback resistor. Making the feedback resistor larger INCREASES the gain.
2) Add in a small DC voltage to shift the output so that it is centered around 0V. You can add several voltage together using an "inverting summer" circuit. The DC offset voltage is created simply by connecting to +V or -V through a fairly large resistor. The value of the resistor determines the amount of offset (bigger resistor = smaller offset). Remember that the output will be inverted, so add a positive voltage to offset the results in the negative direction.

By the way, I'm the one who is doing the Little Brother clone. We'll be selling a board that is a clone of the waveshaper from the Little Brother at Magic Smoke. Patch in a saw VCO, and you get Saw, Square, Pulse and variable-width Pulse waves out in four octave stops. It also has a built in LFO with delay for vibrato (patch that back to your VCO). The board was designed for us by Harry Bissell, and we've ordered some protoypes for testing. Should be ready for sale in January 2010. Smile

Tim (send in the clones) Servo

emdot_ambient · Joined: Nov 22, 2009 Posts: 667 Location: Frederick, MD

Sweet, thanks!

BTW, what's the word on Magic Smoke's Oddy VCO PCB?

Tim Servo · Posted: Wed Dec 23, 2009 4:57 pm Post subject:

Hey Em,

Well, I'm still working on the Ody VCO. I really have made some progress, but as is typical, I'm juggling four or five or ten projects and trying to decide which ones to complete first. The Lil' Bro, Thomas Henry's new DVD and the VCO Chip Cookbook have been occupying most of my time lately. Still, the Ody VCO is one of my personal faves, and so I'll see if I can push it up on the list a bit. We're looking at a March timeframe maybe? sorry I can't be more specific, but we all know how this stuff goes.

Tim (if you sneak a circus performer across the border, are you a juggler smuggler?) Servo

emdot_ambient · Joined: Nov 22, 2009 Posts: 667 Location: Frederick, MD

That's cool...the Li'l Bro would be sweet, too, since I own two ARP Axxes. Very Happy

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

I'm still having problems with my VCO2 and I'm at my wits' end trying to figure out what the problem is.

Andy suggested I look at the Sync switch and the 4011, but as far as I can see, they're both ok.

Does anyone have any suggestions as to where I should look next?

Thanks!

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

It's been a very long time since I built these VCOs and I STILL haven't got to the bottom of it! I'm still learning electronics as I go so I'm not very experienced at all so any help will be much appreciated!!

I've got the correct Saw and Pulse outputs from VCO1 and the correct Saw output from VCO2, but there's no Pulse output from VCO2.

As I have one VCO of this dual PCB working, I've decided to try and compare the two VCOs to try and work out what's going on. It looks like something is going wrong around the 4011 (a Quadruple 2-input NAND gate). I know this chip is something to do with the Ring Modulator, and also something to do with the buffering the Pulse outputs, but that's as far as my knowledge takes me!

What sort of reading or measurements do I need to post so that some kind soul will be able to help me?

Also, does anyone have a link to the MKIII VCO schematic? I can't find one on the net and the one posted earlier in the thread is for a different version.

I'll be eternally grateful to anyone who can offer even the tiniest bit of help as it's driving me insane!!

Thanks!

Boerge · Joined: Sep 02, 2009 Posts: 82 Location: Germany

The Bad Producer · Joined: Mar 08, 2009 Posts: 282 Location: The Manhole

Hi Letterbeacon,

It probably has nothing to do with it, but I noticed when building JH's Solina Chorus that some 4011's would not work, it was the HEF4011's that were wrong. When I put CD4011 all was okay, I know on some circuits you can use either, some you can't.

I'm sure its not right, but might be worth checking?

Charlie

Boerge · Joined: Sep 02, 2009 Posts: 82 Location: Germany

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

Thanks for your replies!

I am using an HEF4011 so I am going to order some CD4011 from eBay tonight to try in there. VCO1 seems to be working fine though, which suggests that the HEF4011 is ok. I'll order some CD4011s just in case though.

I've just checked continuity between the pins of the 4011 and, apart from the ones that are supposed to be linked, there are no shorts.

Thanks for the link to the schematic - it makes things a lot clearer now. I'll see if the 4011 is presenting the inverted signals when I get my oscilloscope out later on this evening.

Thanks again for your help - I really appreciate it!

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

So I had a go with the oscilloscope yesterday evening and this is what I've got.

Each vertical square = 5 volts.

First up are readings from the healthy VCO1 - ie. the one that works.

Output from VCO1 Pulse Out:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

This looks like a healthy 0-5V square wave.

Output from HEF4011 Pin 2:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

An inverted 2-5V square wave.

Output from HEF4011 Pin 3:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

A 0-15V square wave.

Now, here's VCO2 - ie. the VCO that doesn't work.

Output from VCO2 Pulse Out:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

As you can see, it's just outputting 5VDC.

Output from HEF4011 Pin 12:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

A saw wave about 0-2.5V.

Output from HEF4011 Pin 11:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

15VDC although there's NO continuity between that pin and the positive rail.

Where do you think I should go from here? I traced back the signal of the VCO2 to before it gets to the 4011 and it's very different to the corresponding signal on VCO1 which I think means it's not the 4011.

I'm really just making stabs in the dark here! Any more help will be much appreciated!

Boerge · Joined: Sep 02, 2009 Posts: 82 Location: Germany

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

The VCO core being the two transistors with the TempCo resistor next to it, correct? Because the Saw wave appears fine, it points to problems in the Square wave waveshaper circuit, I think. Would you be able to point me in the right direction of the waveshaper circuit?

Thank you!

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

I got my CD4011 chips today and unfortunately they haven't made a difference.

I traced the wave forms back this morning and it looks like something's going wrong around the 3086 area. I've tried swapping VCO2's 3086 with VCO1's 3086, but that had no effect, indicating that the chip wasn't the problem. I can't see any shorts round that area and all the resistors have the correct colour codes on them.

I'm pretty stuck again! Does anyone have any suggestions at all???

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

I fixed it!!

I'm almost too embarrassed to say, but the problem turned out to be me not soldering one leg of a resistor Embarassed

It works great now! Thank you very much for everyone who suggested solutions!

blue hell · Posted: Sun Sep 05, 2010 8:17 am Post subject:

Broadwave · Posted: Mon Sep 06, 2010 1:16 am Post subject:

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

Thanks for a great project -the ring mod sounds amazing!

I have noticed one thing with the FM inputs however:

I have switching jacks which go through a passive attenuator wired pot and then to the PCB. If I turn up the pot with nothing connected to the jack I can hear the pitch of the VCO change slightly. As they are switching jacks, should I wire the jacks so the inputs are normalled to ground when nothing is inserted in them? Would this stop the slight pitch change?

Thanks!

Broadwave · Posted: Tue Sep 07, 2010 12:59 am Post subject:

numbertalk · Posted: Fri Sep 10, 2010 5:40 am Post subject:

peng · Posted: Fri Sep 17, 2010 9:46 am Post subject:

1234 · Joined: Nov 14, 2010 Posts: 11 Location: Bulgaria

Hello to everybody here!
I'm new in this forum and decided to start with this VCO (thank to AndyR1960 for adapting this for such affordable building!).
To make it short - I already finished the VCO and think its sound is wonderful, but i have some bleed trough from one to the other oscillator. This could be observed on both VCOs, does not matter which output you listen, always the other oscillator is in the background - it is not loud, but one can hear it anytime. I already changed the ring mod IC, but didn't find any improvement (this was shot in the dark Smile

).
Is this the normal behavior of these VCOs?
I will try to post some examples when I find some time.

blue hell · Posted: Tue Nov 16, 2010 5:50 am Post subject:

1234 · Joined: Nov 14, 2010 Posts: 11 Location: Bulgaria

Thank you for the notice!
Doubleposting was not intentional, just pushed wrong button... Embarassed