XR-2206 VCO problems

Conboy · Joined: May 01, 2009 Posts: 24 Location: London

Hi
I'm not a newbie to synth building so I may be a little embarrased here.. Smile

I have just got hold of a bunch of 2206 chips after purchasing a copy of Thomas' VCO Chip Cookbook.

I have tried breadboarding both of the simplest VCO setups for this chip. Currently I have the "standard arrangement" set up. All I am getting however is a lot of distorted noise... vaguely tuneable distorted noise mind! Obviously something is wrong.

Tuning the 1M variable resistor I get howling noise over most of the range, but a small section of the range with a cleaner very high pitched tone. The amplitude trimmer seems to have no effect on the level at all.

Could I have bought a bunch of dodgy chips?

I have checked and double checked everything... and as I say I have built plenty of complex circuits before so I am a little puzzled.

Anyone got any ideas???

thanks

elmegil · Posted: Wed Jan 30, 2013 10:45 pm Post subject:

I assume you've tried multiple different 2206 chips?

I don't have this one handy (well, I have an el Cerrito VCO, but not quite the same thing), so I can't really say much else....

LFLab · Posted: Thu Jan 31, 2013 2:22 am Post subject:

Built two of these on Bugbrands' layout, both worked fine from the start. Did have some tuning problems later on due to a "el cheapo" IC socket failing.

Conboy · Joined: May 01, 2009 Posts: 24 Location: London

I have tried several from the same batch. Maybe I'm just being an idiot and missing something.

It is a shame thought that all the VCO chips in Thomas's book are discontinued - it's a great book and highly educational. The only place to buy any of these chips is eBay which doesn't give me the same confidence as Farnell etc.

elmegil · Posted: Thu Jan 31, 2013 6:18 am Post subject:

It takes some digging, but EBay isn't the only place for all of them.

I got my XR-2206's from this place, Unicorn Electronics:
http://198.170.117.30/IC/GENERATORS.html

Conboy · Joined: May 01, 2009 Posts: 24 Location: London

Thanks - unfortunately I am in the UK so dont fancy paying the postage and duty on a few little IC's!

I have plenty of other parts about so I may try to build a VCO from a CA3080 (I have a bunch of them) - I have just got a copy of Thomas's 3080 book .

I'm just building a VCO as part of a ring modulator so trying to keep it simple but still reasonable quality.

Mind you everyone seems to be looking for the elusive "simple VCO" design but I'm beginning to think there isn't one! Not one that is half decent anyway.

magman · Joined: Feb 04, 2009 Posts: 351 Location: Liverpool, UK

If you want to get a chip from a reputable supplier in the UK, the Cricklewood Electronics look to have them in stock, here:

http://www.cricklewoodelectronics.com/Cricklewood/search.php?mode=search&page=1

Probably quite a bit more expensive than what you have paid already, but still worth having a known good chip to check against.

Regards

Magman

Conboy · Joined: May 01, 2009 Posts: 24 Location: London

Thanks Magman

They look like a very handy supplier. Might just get one as you say just to test

I have managed to breadboard a pretty decent VCO using the 3080 anyway so I'm going to run with that for the time being

Paradigm X · Joined: Feb 15, 2011 Posts: 251 Location: Null and void

I also got 2 2206s from T**** for not a lot...

Cheers
Ben

edit, mine appear to have the same date code as the ones warned about below, caveat emporer...[/b]

Tim Servo · Posted: Tue Feb 05, 2013 11:36 am Post subject: XR-2206 VCO problems

Hi All,

I've run into a similar problem with a bunch of NOS 2206 chips I bought. One thing you might try is running the chip on a lower supply voltage. Try 11 or even 10 volts. I found that did the trick, although it does mess with the output levels. Something tells me that these chips we're seeing don't work as well with higher current levels. I'm experimenting with changes to the El Cerrito (keeping the PCB the same, just changing a few Rs) to see if I can come up with a fix for these chips, so we'll see. Also, in the US, Jameco sells the 2206 for about $6. I have a few of these that I'm going to try to see if they behave okay at 15V.

Tim (back to the ol' breadboard) Servo

Sodium · Joined: Feb 11, 2012 Posts: 13 Location: Sweden

I run my chips on 12V.

According to the data sheet:
Single Supply Voltage Min 10 , Max 26 V
-> Split-Supply Voltage Min +5, Max +13 V

Thomas_Henry · Joined: Jul 24, 2009 Posts: 108 Location: N. Mankato, MN

Hi,

Sodium · Joined: Feb 11, 2012 Posts: 13 Location: Sweden

roglok · Joined: Aug 28, 2010 Posts: 124 Location: uptown

Just finished one using the Bug Brand layout - with a 15V supply i'm getting harsh noise on the output. On 12V it all seems fine except that I can hear a rather prominent crackling noise on frequencies between 500Hz and 3kHz - I've tried 3 different chips from this batch:

2206CP
F0919

Also on 12V the wave morphing works but doesn't go all the way to a perfect saw shape. I guess this is due to the lower supply voltage...

A great design, but the crackling is really annoying...

NoizeToyz · Posted: Fri Mar 15, 2013 6:35 am Post subject:

Hi All,
I recently built the Mega Percussive Synth and I get the same problem from the XR2206 CP.

The 'Shell' voice is created by the 2206, but all I get from it is distorted noise, which seems to go into self oscillation at higher frequencies.

I also got my XR chips from ebay and was thinking that they might be dodgy.

I'll try the UK supplier you recommend Magman.
Cheers.

NoizeToyz · Posted: Mon Mar 25, 2013 9:12 am Post subject:

Hey,
Anyone have any joy with their XR2206 circuits?
I just completed a second Mega Percussive Synth (to be 200% sure that I'd not soldered badly, or messed up the wiring) and it acts exactly like the first - the Shell generator just creates noise rather than the triangle wave.

The chips I'm using are XR2206CP F0919

I've ordered some more from Cricklewood Electronics so will let you know once I've swapped out the chips...

roglok · Joined: Aug 28, 2010 Posts: 124 Location: uptown

Hey chivaros - I can confirm that those chips are dodgy. I was getting bad results from that batch as well. Yesterday I received a military grade XR2206 in ceramics package, which performs very well in Thomas Henry's XR-VCO.

My advice is to stay away from XR2206CP F0919 chips!

NoizeToyz · Posted: Tue Mar 26, 2013 4:40 am Post subject:

Thanks roglok,
That's good to know as it was driving me crazy!

*Edit*

Just got delivery of chips from Cricklewood, and they work perfectly.
They are batch numbers: F0630 and 0519

MC1495 · Joined: Mar 24, 2009 Posts: 14 Location: baltimore

on a slightly different tack -
if i wanted to build this exponential converter for split-supply and remove the linear FM option - what would be the right approach?
do i just tie q1 and q2's emitters to ground?

Tim Servo · Posted: Thu Mar 28, 2013 10:44 pm Post subject: XR-2206 VCO problems

It's good to know there are SOME date codes that are okay. I've been through several chips, and the only one that works properly in the "El Cerrito" XR VCO is an F0747 date code. It might also be worth noting that this one has a small stamped indentation at the OPPOSITE end from the Pin 1 notch. All of the ones I have that only work on lower voltages have the stamped indentation at the same end as the Pin 1 notch.

Tim (notches? we don't need no stinking notches) Servo

marcmarc