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 Forum index » DIY Hardware and Software » Thomas Henry designs
XR-2206 VCO problems
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Conboy



Joined: May 01, 2009
Posts: 25
Location: London

PostPosted: Wed Jan 30, 2013 8:19 am    Post subject: XR-2206 VCO problems
Subject description: Can't get basic circuit to work!
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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
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elmegil



Joined: Mar 20, 2012
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PostPosted: Wed Jan 30, 2013 10:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

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....
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LFLab



Joined: Dec 17, 2009
Posts: 200
Location: Rosmalen, Netherlands

PostPosted: Thu Jan 31, 2013 2:22 am    Post subject: Reply with quote  Mark this post and the followings unread

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.
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Conboy



Joined: May 01, 2009
Posts: 25
Location: London

PostPosted: Thu Jan 31, 2013 3:07 am    Post subject: Reply with quote  Mark this post and the followings unread

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.
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elmegil



Joined: Mar 20, 2012
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PostPosted: Thu Jan 31, 2013 6:18 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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Conboy



Joined: May 01, 2009
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Location: London

PostPosted: Thu Jan 31, 2013 6:30 am    Post subject: Reply with quote  Mark this post and the followings unread

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.
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magman



Joined: Feb 04, 2009
Posts: 361
Location: Liverpool, UK

PostPosted: Fri Feb 01, 2013 3:29 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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Conboy



Joined: May 01, 2009
Posts: 25
Location: London

PostPosted: Fri Feb 01, 2013 3:57 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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Paradigm X



Joined: Feb 15, 2011
Posts: 286
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PostPosted: Mon Feb 04, 2013 10:11 am    Post subject: Reply with quote  Mark this post and the followings unread

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]

Last edited by Paradigm X on Tue Apr 30, 2013 8:22 am; edited 1 time in total
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Tim Servo



Joined: Jul 16, 2006
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PostPosted: Tue Feb 05, 2013 11:36 am    Post subject: XR-2206 VCO problems Reply with quote  Mark this post and the followings unread

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
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Sodium



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

PostPosted: Wed Feb 13, 2013 1:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

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
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Thomas_Henry



Joined: Jul 24, 2009
Posts: 129
Location: N. Mankato, MN

PostPosted: Wed Feb 13, 2013 8:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi,

Sodium wrote:

Single Supply Voltage Min 10 , Max 26 V


And indeed the +15V single supply I specified is well below (by 11V) the spec sheet claims. So that's certainly not the problem.

Thomas Henry
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Sodium



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

PostPosted: Thu Feb 14, 2013 12:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Thomas_Henry wrote:
Hi,

Sodium wrote:

Single Supply Voltage Min 10 , Max 26 V


And indeed the +15V single supply I specified is well below (by 11V) the spec sheet claims. So that's certainly not the problem.

Thomas Henry


I haven't built any of these cards yet, guess I assumed it was split supply. Sorry for that.
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roglok



Joined: Aug 28, 2010
Posts: 163
Location: uptown

PostPosted: Sat Feb 16, 2013 11:39 am    Post subject: Reply with quote  Mark this post and the followings unread

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...
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NoizeToyz



Joined: Jan 09, 2010
Posts: 23
Location: Brighton
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PostPosted: Fri Mar 15, 2013 6:35 am    Post subject: Reply with quote  Mark this post and the followings unread

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.
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NoizeToyz



Joined: Jan 09, 2010
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Location: Brighton
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PostPosted: Mon Mar 25, 2013 9:12 am    Post subject: Reply with quote  Mark this post and the followings unread

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...
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roglok



Joined: Aug 28, 2010
Posts: 163
Location: uptown

PostPosted: Mon Mar 25, 2013 9:34 am    Post subject: Reply with quote  Mark this post and the followings unread

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!
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NoizeToyz



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PostPosted: Tue Mar 26, 2013 4:40 am    Post subject: Reply with quote  Mark this post and the followings unread

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

Last edited by NoizeToyz on Wed Mar 27, 2013 3:36 am; edited 1 time in total
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MC1495



Joined: Mar 24, 2009
Posts: 19
Location: baltimore

PostPosted: Wed Mar 27, 2013 3:21 am    Post subject: Reply with quote  Mark this post and the followings unread

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?
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Tim Servo



Joined: Jul 16, 2006
Posts: 924
Location: Silicon Valley
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PostPosted: Thu Mar 28, 2013 10:44 pm    Post subject: XR-2206 VCO problems Reply with quote  Mark this post and the followings unread

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
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marcmarc



Joined: Mar 31, 2013
Posts: 2
Location: Amsterdam, Netherlands

PostPosted: Sun Mar 31, 2013 6:22 am    Post subject: Power supply 11V or less
Subject description: faulty XR2206 batch
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Thomas_Henry wrote:
Hi,

Sodium wrote:

Single Supply Voltage Min 10 , Max 26 V


And indeed the +15V single supply I specified is well below (by 11V) the spec sheet claims. So that's certainly not the problem.

Thomas Henry


Dear all,

I recently tested a batch of XR2206 (I do not know the batch number anymore) and came to the conclusion that something has changed
in the design or production process. They also gave a lot of distortion
with the power supply set to +/- 7V5.
The I made a base setup with a single supply and noticed the distortion
disappearing at 11V5.
I then realized that two chips I bought in 2002 (batch 0044 = 2000 week 44) which I at the time wanted to use for the TD Cross Generator were
put aside by me as not good. I rested them with 11V and they were OK.

I looks like that the ones I bought in the early eighties worked fine
with +/- 12V.

Conclusion: If you want to use the Thomas Henry design, I suggest you lower down the supply voltage to 11V.

Note:
Thanks to Thomas for his great work, in particular for the SKEW option, which I now implemented in a modified way to the TD Cross Generator.

For all the XR2206 fans:
1984:
http://marcmarc.home.xs4all.nl/ele/fff/index.html
batch 8109

2002:
http://marcmarc.home.xs4all.nl/ele/td/index.html
batch 8538

Regards,

Marc Marc
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jpmaus



Joined: Jan 16, 2014
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Location: Austin, MN
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PostPosted: Mon Feb 17, 2014 6:11 am    Post subject: Reply with quote  Mark this post and the followings unread

I am having a nightmare of a time getting the TH XR-VCO running. I must've etched six+ boards now and ruined at least four+ of them. Have a look at (only some) of the wreckage and cringe:

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

I am at my wits end with the thing, and so I thought I'd attach a close-up of the last board I soldered in the hopes that someone might be able to tell me (a newbie) exactly what I'm doing wrong.

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

A few notes in relation to the close-up. On this particular board, the TL074 becomes extremely hot upon power up. (On an earlier board, the TL074 would always just snap like a firecracker!) The tempco is also moved out of the way intentionally here, in order to make the LM394 more visible. In any case, all the resistor/capacitor values have been checked and triple checked, as has the solder underside (for any possible shorts). All of the semiconductors/ICs have been replaced numerous times. I've tried running +15V (red wires bottom left) and -15V (black wires bottom center): no sound out (from orange wire on the top, third from the right, nor from purple wire on the bottom). I've tried running +15V & -15V with all of the DPDT wires properly attached to a DPDT switch, still, no sound out. I've tried hooking up the coarse and skew in addition to everything just mentioned, still no sound. I've tried hooking up ALL of the pots in addition to everything mentioned, still no sound (out of the sine or square outputs).

In short, then, I have been unable to get this thing to make any sound, and I wonder what the hell I'm doing wrong! (Something with the power? The diode orientations? The IC orientations? Etc.) Please don't laugh at me if it is something obvious, I've lost more than few nights sleep trying to get the XR-VCO going. Hopefully someone can tell me what I'm doing wrong, but if not, I should have some El-Cerito boards on the way once Magic Smoke returns from moving. It's just, I figure, if I can't get /this one/ going, how am I supposed to manage anything else! Please let me know... Thanks...
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elmegil



Joined: Mar 20, 2012
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PostPosted: Mon Feb 17, 2014 7:10 am    Post subject: Reply with quote  Mark this post and the followings unread

It looks like the foil you're using for etching is the one from Birth of a Synth?

Have you confirmed that the etching process is ENTIRELY complete? could there be tiny shorts?

That kind of behavior in the TL074 could indicate that you've got shorts to places that shouldn't have them.

A picture of the solder side would would be helpful.
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bubzy



Joined: Oct 27, 2010
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Location: United Kingdom
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PostPosted: Mon Feb 17, 2014 8:39 am    Post subject: Reply with quote  Mark this post and the followings unread

are you sure you have the power rails wired up the correct way around? the quad opamps really don't like the power reversed.

the layout looks ok (comparing it to the one on birthofasynth)

try it one chip at a time, starting with the opamp. that way you can see at least if they are interfering with one another.

also (although im sure you have done this) check the etched side for possible shorts

_________________
_Richard_ Smile
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jpmaus



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PostPosted: Mon Feb 17, 2014 3:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks guys... I just can't tell you how frustrating this has been. What I /wanted/ to do is post all sorts of cool photos of the finished the instrument, not etch six+ boards, solder five of them, and not get a single one of them to work!! I've checked my power supply with TWO multimeters and it reads +15V coming in (black to black / red to red). Now, I'm including a photo of the solder-side:

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


I know it isn't pretty. But any scratch that is evident in this photo has been tested and it isn't stopping the flow of current. The same goes for the joints, they've all been checked. In other words, given that the same thing has happened now with FOUR+ boards, it has to be that I'm doing something extremely wrong, something unrelated to the PCB, something unrelated to the soldering, but something ABSOLUTELY wrong.
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