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 Forum index » DIY Hardware and Software » Thomas Henry designs
XR-VCO build report and praise!
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Coriolis



Joined: Apr 11, 2005
Posts: 616
Location: Stilling, Denmark

PostPosted: Sun Mar 09, 2008 12:04 pm    Post subject: XR-VCO build report and praise! Reply with quote  Mark this post and the followings unread

I just finished up my first XR-VCO last night, and just wanted to say a few words about this great circuit.

Built it from the Bugbrand pcb layout and had no problems, other than accidentally reversing the +V and -V leads to the board !!! pale
Only a low hum came out...
Thankfully I have LED indicators on both rails of my PSU, and something was clearly wrong there. Also, the quad opamp got pretty hot, but none of the other chips did. So FYI - it seems this vco will take that kind of abuse for at least 10-20 seconds... Embarassed

Fixed that, and it worked. Calibration was a bit weird though, I followed instructions from Scott Stites' site and had the vco hooked up to winscope (freeware software scope) - heavily attenuated of course. Soundcards don't like 10V PP signals, I think.
Adjusting the trimmer for sine/tri offset did nothing visible or audible. Left that as it was. Waveform appeared to be well centered around 0 anyway.
Sine round trim got me pretty close to what sounded like a sinewave (still a bit of hollowness to the sound tho), but this was where I discovered that winscope was rather useless. I could a difference to the waveform turning the trimmers, but I couldn't see it. In fact, the waveforms looked heavily quantized on the display, so little changes would probably not even be visible! Crap.
Adjusting for 1V/oct didn't make much sense either, but this is down to me being a newb. The only controller I have that could possible be adjusted to octave steps, is my Baby 8 sequencer. With my DMM I set up a 3 step seq, jumping from 1 to 2, to 3 volts. Sounded reasonable.
Then adjusted the 1V/oct trimmer. This seemed to offset all 3 octaves at once - I kinda figured I would hear the scale stretch or shrink instead...?
Left that alone as well.

This is only my second vco, first one is a TH VCO-1 (also nice), But I gotta say, I'm in love. Wonderful bottom end in this thing, and the skew function is so great. Like it better than PWM on the VCO-1.

Squarewave is much louder than sine/tri though, but I guess I could try fiddling with a resistor value or something...

Thanks to Thomas Henry for this one (and Tom Bugs for this particular layout)!!! props respect thanks

C
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Funky40



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PostPosted: Sun Mar 09, 2008 1:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi, Coriolis, try this one maybe :

http://www.zeitnitz.de/Christian/Scope/Scope_en.html


i think i used this one once to calibrate a VCO.
It seems to have a little a asymmetrie on the Waveforms ( S-shape----left/right) ( had a short look now )

another one was Visual analyser 8. I think this was mentioned here at EM from G2Ian.
But it's not running stable on my computer


ok, compared it to my ( crappy) Scope.
Seems to be good or useful ( that from zeitnitz). Was a tip in a german forum.



funky
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Coriolis



Joined: Apr 11, 2005
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PostPosted: Sun Mar 09, 2008 3:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ah, thanks - I will try that one.

C
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a.b.o.z.



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PostPosted: Tue Jun 17, 2008 9:32 am    Post subject: Reply with quote  Mark this post and the followings unread

I've just finished mine. This thing is really cool. It is my first VCO (beside sound labs) so I really enjoy it. It worked from very first power up. I'm still waiting for 394 to come so I used two 547s (not matched Very Happy ) instead. No tempco either. Here is a little clip I recorded. Only Klee and XR.
Invert B on. A output controling 1Voct and B controlling Skew. This is fun.
Thanks to Thomas and Scott.

Ivan


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fluxmonkey



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PostPosted: Tue Jun 17, 2008 1:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

a.b.o.z. wrote:
I've just finished mine. This thing is really cool. It is my first VCO (beside sound labs) so I really enjoy it. It worked from very first power up. I'm still waiting for 394 to come so I used two 547s (not matched Very Happy ) instead. No tempco either. Here is a little clip I recorded. Only Klee and XR.


FIRST a Klee, THEN a VCO? wow, talk about diving into the deep end of the pool! i had to start with the easy stuff. impressive!

b
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a.b.o.z.



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PostPosted: Tue Jun 17, 2008 3:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

thnx
i've started about 5 years ago with guitar effects. then stoped a bit. then did apc then discovered soundlab and mfos and at the end this great place.
and i've always wanted a modular so.... Smile
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a.b.o.z.



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PostPosted: Wed Jun 18, 2008 3:07 pm    Post subject:   Reply with quote  Mark this post and the followings unread

Hmmm
I've run into strange thing I don't know how to solve.
I've hook XR to Visual analyzer http://www.sillanumsoft.org/prod01.htm
and tried sine wave to rampoid wave skew like Scott did here: http://mypeoplepc.com/members/scottnoanh/thomashenrysxrvcoskewedwaveforms/
I've got it inverted??? Am I right? Because when I tick "invert" check on Visual analyzer I get what Scott shows here.
Any ideas what I did wrong?
Is it got to do with 547s instead of 394???
Help me I'm a noob Very Happy
Thnx

Ivan


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Blue Hell
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PostPosted: Wed Jun 18, 2008 4:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

I think the invert button is there because some sound cards invert the audio signal, which does not result in an audible difference BTW.
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also .. could someone please turn down the thermostat a bit.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
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a.b.o.z.



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PostPosted: Wed Jun 18, 2008 4:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

Oh I see. And this is the case. Soundblaster inverts signal, terratec does not. Cool. I feel satisfied on good build Very Happy
Thnx
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slo



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PostPosted: Thu Jun 19, 2008 6:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
FIRST a Klee, THEN a VCO? wow, talk about diving into the deep end of the pool! i had to start with the easy stuff. impressive!

I did the same thing, built the Klee then the voices, still only have a TH-VCO1, I am gearing up to build the XR so it's nice to see the successfull builds of it. My rational in building the Klee first was to do it while the forums were still very active for it, helps a lot, this site is indispensible.
Congrats on a new VCO!

George
ps. Just completed a successfull SuperController build, but my hardware scope blew up, so again a handy thread!
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creatorlars



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PostPosted: Thu Jun 19, 2008 8:04 am    Post subject: Reply with quote  Mark this post and the followings unread

I am halfway thru building four of these, and also use a computer oscilloscope -- so thanks for sharing your notes!
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Broadwave



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PostPosted: Fri Jun 20, 2008 9:26 am    Post subject: Skew on XRVCO Reply with quote  Mark this post and the followings unread

OK, finally got round to building one of these things - All is fine except for the manual skew... I just can't get a true ramp waveform.

The problem is that the second ramp peak (created as you turn the skew pot towards +ve) never gets to the same amplitude as the first half of the cycle.

I want to use these as VCLFO's, but because of this problem I'm not getting an even modulation, and it sounds sick (that's sick in the original sense i.e. not well : )

I'm running it off +/-12v... could this be the problem? Should it be +/-15v?

Hope somebody can help.

Andy.


(Additional) - Just tried a +/-15v PSU, problem still there... am I expecting too much?

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zthee



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PostPosted: Tue Aug 12, 2008 1:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

I just spent the last hour calibrating my second XR VCO!

It's the VCO I use the most - the skew function is just great!
- But my manual skew knob only starts to give affect at about 12 o'clock - any thing I can do to fix that?

The skewed part of my triangle is also a bit lower (Like AndyR1960's is) - is this related to my sine being a bit lower aswell? (need to fix that - but it doesn't really bother me - so I'll keep it as it is now!) Wink

It's still a great VCO!!!
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a.b.o.z.



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PostPosted: Tue Aug 12, 2008 1:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

zthee wrote:

- But my manual skew knob only starts to give affect at about 12 o'clock -

I've got same thing with mine..doesn't bother me too much but if it's fixable..why not. Smile
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zthee



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PostPosted: Tue Aug 12, 2008 1:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

a.b.o.z. wrote:
zthee wrote:

- But my manual skew knob only starts to give affect at about 12 o'clock -

I've got same thing with mine..doesn't bother me too much but if it's fixable..why not. Smile


It really doesn't bother me either - but I thought if I'm going to fix the amplitued problem (sine vs. triangle) - why not fix this at the same time.. But since the amplitued problem really isn't bothering me it might take a while.. Very Happy

I'd just do it so the whole thing is perfectly functional Cool
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creatorlars



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PostPosted: Tue Aug 12, 2008 2:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm super-happy with my first XR-VCO and have no issues besides the same complaint about the manual-skew (doesn't bother me.) Let me know if you find appropriate resistor values and I'll make the "fix" too.
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zthee



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PostPosted: Tue Aug 12, 2008 2:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Since the manual skew is connected between -15V and +15V and only starts to work at 12. Could it be that the -15V part does nothing?

Maybe it should be connected to ground instead?
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widdly



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PostPosted: Tue Aug 12, 2008 7:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

I think you are correct zhee. From the schematic, it looks like after the summer, it is run through a diode.

But if you had a positive skew VC, the manual skew would work in the negative direction?

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Scott Stites
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PostPosted: Tue Aug 12, 2008 9:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Seems to me Thomas left some slop in the controls to offset things when one were using CVs. I don't recall this effect when I had it on the breadboard. You could try putting a 100K resistor between the -15V and bottom of the manual skew to see if that gave you more range, then work from there? Even try a pot (wired as a rheostat) to test how much resistance put the full anti-clockwise position to just where you wanted, then measure the resistance of the pot and select a resistor to match. Usually I just clip in with alligator clips when I'm doing that kind of thing.

Cheerios,

Scott

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zthee



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PostPosted: Tue Aug 12, 2008 11:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Scott - I'll try it out and report back! Smile
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Coriolis



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PostPosted: Tue Aug 12, 2008 11:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi guys - mine also has a sweet spot on the skew control, where most of the action happens. I ran into the same situation recently with my wavefolder build (Yusynth), where everything happened on the shape pot about mid-travel, and replacing with a smaller value (20k vs 50k originally) gave a more even sweep. Something to try perhaps. Though, if the action is bundled up at one end of the pots travel, Scott's suggestion makes more sense.

C

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bugbrand



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PostPosted: Wed Aug 13, 2008 6:18 am    Post subject: Reply with quote  Mark this post and the followings unread

I think Scott has the right idea..

But if, indeed, you did want to make more use of the centre range of the pot you could raise the value of R40 (the summing resistor). This would effectively reduce the range of the Initial Skew control.

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Scott Stites
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PostPosted: Wed Aug 13, 2008 6:38 am    Post subject: Reply with quote  Mark this post and the followings unread

My worry there was if the pot currently has control from center all the way to CW, then reducing the value of the summing resistor might make the manual skew not skew all the way CW. If, however, there's still some slop on full CW, it will bring more of the control over to the CCW side of the pot.
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creatorlars



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PostPosted: Wed Aug 13, 2008 8:04 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm going to try Scott's suggestion next time I pull out my panel for maintenance, and I'll report my results in this thread.
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a.b.o.z.



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PostPosted: Wed Aug 13, 2008 8:37 am    Post subject: Reply with quote  Mark this post and the followings unread

Scott Stites wrote:
You could try putting a 100K resistor between the -15V and bottom of the manual skew

errr where is that?
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