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 Forum index » DIY Hardware and Software » Thomas Henry designs
The Thomas Henry VCA-1 Page Is Up
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a.b.o.z.



Joined: Feb 07, 2007
Posts: 351
Location: Zagreb, Croatia
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PostPosted: Sat Apr 05, 2008 1:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

crashlander42 wrote:
Speaking of a Thomas Henry ADSR, I stumbled across this this very simple ADSR which seems very Thomas Henry influenced. In fact there is a pleading for Thomas Henry's return to the internet on the page.
question.


Hei,
do you maybe have parts placement diagram for that one?
It seems to be missing form that link.
Anyone?

Thnx

Ivan
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macumbista



Joined: Sep 12, 2007
Posts: 394
Location: berlin
Audio files: 3

PostPosted: Wed Oct 22, 2008 8:55 am    Post subject: Reply with quote  Mark this post and the followings unread

Howdy all. I just tried breadboarding this, and found that I couldn't really get any audio input unless I connected directly to pin 3 of the 3080, and even then it's super quiet. Source is normal VCO.

Also, no matter how much I mess with the offset trim and initial level, I still get some huge thumps from the LFO. I'm running it on +/-12V currently since I don't have a 15V PSU yet. Would that make a difference? Any obvious things I check in my breadboard? Tear it up and start over?
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philpeery



Joined: Nov 08, 2006
Posts: 137
Location: new jersey, usa

PostPosted: Wed Oct 22, 2008 9:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Mac,

I've built this one successfully on breadboard, with the pcb layout from Scott's site (TH's layout I assume), and a variation of that layout that I did myself. My layout includes MTA156 power connectors, slightly different input and output connection scheme. If there is interest, I will dig it out and post it.

So are you sure that IC2 isn't blown or bad? Check to make sure that pin 3 is connected to a good ground, I've had that bite me in the past. Also, for testing purposes, you might try eliminating the switch, cap, and pot on any of the audio inputs. Also check your pins for Q1. If these are backwards, you will get no CV to pin 5 of your OTA!

Since you say that even when you connect directly to pin 3 of the 3080 you get very low output, I would suggest swapping out IC2.

Hope this helps!

Phil
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Luka



Joined: Jun 29, 2007
Posts: 1003
Location: Melb.

PostPosted: Wed Oct 22, 2008 10:12 am    Post subject: Reply with quote  Mark this post and the followings unread

phil can you post it
i would be interested

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macumbista



Joined: Sep 12, 2007
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PostPosted: Wed Oct 22, 2008 10:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Phil,

thanks for the tips! One other change I made from the original schemo was to use a TL074 for ICs 2 and 3. I guess using seperate ICs might cut down on some crosstalk later, but I can't see it being the cause of my troubles now.

I'd like to see your layout if you can find it, because I'm going nowhere with this version right now. Thanks much if you can post it!

Derek
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macumbista



Joined: Sep 12, 2007
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PostPosted: Wed Oct 22, 2008 11:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Update: removing R1 (22 Ohm from IC1 pin 3 to ground) gives me almost expected behavior. I can hear the input audio modulated by the LFO, and by adjusting R22 (initial cv) and R21 (variable cv attenuation) I can sort of get rid of the CV thump. R17 (offset trim) doesn't do anything. And the overall output levels are still extremely low, as under -30dB on my desktop mixer! I know it's pretty difficult to check long distance. Now would be the time to EBay up a scope I guess... But if anyone has further suggestions I'd love to hear them. I'm especially curious why removing R1 suddenly gives me audio input...

EDIT: Never mind all that.... My mistake was almost too silly to admit...like forgetting to power the 3080 Embarassed

Last edited by macumbista on Wed Oct 22, 2008 1:44 pm; edited 1 time in total
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macumbista



Joined: Sep 12, 2007
Posts: 394
Location: berlin
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PostPosted: Wed Oct 22, 2008 1:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

Think I got just about everything working. Clean input, no thump, smooth modulation. Just one last bugger...

In spite of all the successful troubleshooting so far, my output levels are still very low (-30dB on the mixer when the input level peaks at about -4 dB). Is this normal? Again, could this have something to do with the 12V power supply? What is the normal output level of this VCA, for those of you that have built it?
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Danno Gee Ray



Joined: Sep 25, 2005
Posts: 1349
Location: Telford, PA USA

PostPosted: Wed Oct 22, 2008 3:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

To err is human...To report it to the world so the rest of us can learn from it...IS Divine!
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Blue Hell
Site Admin


Joined: Apr 03, 2004
Posts: 22815
Location: The Netherlands, Enschede
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PostPosted: Wed Oct 22, 2008 5:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

macumbista wrote:
forgetting to power


I used to do that all the time ... then I forced myself to always do the power lines first and to use sockets for ICs ... after doing the power lines connect the power, check the power ... then switch the + and - ... and only then make the rest of the circuit and plug in the ICs. That pretty much always worked ... but it's boring Laughing

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macumbista



Joined: Sep 12, 2007
Posts: 394
Location: berlin
Audio files: 3

PostPosted: Thu Oct 23, 2008 4:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Checking my Analogue Systems VCA, I see that the levels which come out of it are also quite low. Is this just a "feature" of most VCAs, that you don't get nearly the level you put into them out again after modulation? How do most folks deal with this when the output goes to a line level audiomixer? Cranking up the gain in the mixer adds a lot of noise when the signal from the VCA is quiet.

Derek

EDIT: second silly mistake was assuming that a cap marked .22J would be 22pF, obviously it wasn't! Values between 10-22pF for C2 give me proper levels out, with very little difference in sound between the values. Live and learn, unfortunately in that order.
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