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 Forum index » DIY Hardware and Software » YuSynth
Inverted Output on the VCA PCB
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vcfool



Joined: Jun 19, 2008
Posts: 23
Location: Barcelona

PostPosted: Mon Mar 30, 2009 6:36 pm    Post subject: Inverted Output on the VCA PCB Reply with quote  Mark this post and the followings unread

Hi,

So I built the Yusynth VCA some days ago and I like it so far. But I found the output was inverted.

After checking the schematics vs. the PCB, I noticed that on the schematics R10 goes to U1b pin 6 (inverting input) and R11 to pin 5 (non-inverting input).
For what I see, on the PCB these connections are swapped.

I crossed those resistors on my module and the output got right. Maybe not a big deal for audio signals but definitely better for CV ones.

Another great module...
Thanks!
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yusynth



Joined: Nov 24, 2005
Posts: 1219
Location: France

PostPosted: Tue Mar 31, 2009 12:01 am    Post subject: Re: Inverted Output on the VCA PCB Reply with quote  Mark this post and the followings unread

vcfool wrote:
Hi,

So I built the Yusynth VCA some days ago and I like it so far. But I found the output was inverted.

After checking the schematics vs. the PCB, I noticed that on the schematics R10 goes to U1b pin 6 (inverting input) and R11 to pin 5 (non-inverting input).
For what I see, on the PCB these connections are swapped.

I crossed those resistors on my module and the output got right. Maybe not a big deal for audio signals but definitely better for CV ones.

Another great module...
Thanks!


Thanks I will correct the PCB as soon as possible

Yves

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Sebo



Joined: Apr 27, 2007
Posts: 534
Location: Argentina

PostPosted: Tue Mar 31, 2009 6:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

If I remeber correctly, when I calibrated the VCA, I connected the input to
one channel of the oscilloscope and the output to the other channel and
overimpose the two signals to do the calibration, and the signals where
on phase (non inverted).
I built the VCA using the PCB layout at the Yusynth site.

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yusynth



Joined: Nov 24, 2005
Posts: 1219
Location: France

PostPosted: Tue Mar 31, 2009 11:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Sebo I will check this tonight Wink
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vcfool



Joined: Jun 19, 2008
Posts: 23
Location: Barcelona

PostPosted: Thu Apr 02, 2009 7:25 am    Post subject: Reply with quote  Mark this post and the followings unread

Sebo wrote:
If I remeber correctly, when I calibrated the VCA, I connected the input to
one channel of the oscilloscope and the output to the other channel and
overimpose the two signals to do the calibration, and the signals where
on phase (non inverted).
I built the VCA using the PCB layout at the Yusynth site.


I also built the VCA self-etching the PCB layout on YuSynth's website and my output was definitely inverted. If yours is not, then I would say that something is different between our modules.

I don't have a dual channel scope, I had to manage with a single channel one:
Input a Ramp and got a Saw - Input a Saw and got a Ramp.
With some positive DC offset I got a negative offset at the output. I am using a switch to bypass the AC coupling caps. I mounted them on the panel and used 10uF electrolytic bipolar, not tantalum. Looking at the picture of Sebo's module (great job btw!), the only difference I can spot are these AC coupling tantalum caps on the signal inputs. I used the 2SC1583, one LF442 and one LF411.

You all know much more electronics that I do, so most important is: Follow the tracks on the PCB and compare it to the schematics. I think you'll see the difference that I pointed out: Connections going from Q1/Q2 to U1b are crossed. Just rechecked it... once more.
Wink
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Sebo



Joined: Apr 27, 2007
Posts: 534
Location: Argentina

PostPosted: Thu Apr 02, 2009 5:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi vcfool:
I can't check the schematics right now, I will do it soon.
But I'm not saying you are wrong, I'm just saying what I remember, and I
might be wrong (memory could play tricks sometimes).
I used a TL072 and a LM741, I also built the AC version.
It's great that you like the module I built, thanks for your kind words.

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yusynth



Joined: Nov 24, 2005
Posts: 1219
Location: France

PostPosted: Fri Apr 03, 2009 7:24 am    Post subject: Reply with quote  Mark this post and the followings unread

vc fool is saying right, it is very simple to modify the PCB to fix that. I have redesigned a PCB that I will publish this week end.

Cheers

Yves

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Sebo



Joined: Apr 27, 2007
Posts: 534
Location: Argentina

PostPosted: Fri Apr 03, 2009 10:54 am    Post subject: Reply with quote  Mark this post and the followings unread

Ahhh!!! I was wrong.
Or my memory plays me tricks or maybe one of the oscilloscope channels
was inverted.
I don't want to correct the PCB, the oscilloscope was borrowed, and I can't
calibrate the VCA again.
I build the AC versions to use with audio signals only, so I think is not relevant
if I remember that the output is inverted.
I plan to use the dual ringmodulator as VCAs for control signals, do you
think it will perform well? If not I will build some DC VCAs with the new PCB.
Thanks.

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Sebo



Joined: Apr 27, 2007
Posts: 534
Location: Argentina

PostPosted: Thu Jan 21, 2010 11:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi:
Today I was making a patch with my modular and remembered this thread,
so I tested my 4 VCAs with a PC oscilloscope, and they aren't inverting
the signal. Also I added the signal before and after the VCA in the mixer
and the signals are not cancelling each other, just doubling the output level.
I didn't do any mods...

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