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Built Xoxbox // NO SOUND
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Re: Built Xoxbox // NO SOUND

by sequentialmood on Thu Apr 25, 2013 6:51 pm

Ok, sorry, i should have misconfigured my oscilloscope software...

Here is the signal on R62:
LEG 1:
Image
LEG 2:
Image

Sounds strange ? :?
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Re: Built Xoxbox // NO SOUND

by MMM on Fri Apr 26, 2013 10:19 am

Something's wrong here - but I'm not sure if this is a measuring issue.

One side looks pretty good (although the signal should be significantly stronger - about 5V peak-to-peak - but this could have something to do with the soundcard scope).
However the signal on the other side should be much, much weaker (about 150mV max) and will also look very different.

The side towards the oscillator should be the "strong" side and the side towards the filter the "weak" side.

What type of oscilloscope are you using?
You may also want to measure the resistance across R62.
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Re: Built Xoxbox // NO SOUND

by sequentialmood on Fri Apr 26, 2013 10:32 am

Thanks for the answer MMM !
So it sounds that the VCF block is not working as it should (?).

I'm currently using my Mac book Pro built in soundcard as an oscillo with a software called "Signal Scope Pro", but i'm planning to buy a true oscillo to make the debugging easier.
I'll also change R62 to see if it change anything.

I'll let you know. :)
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Re: Built Xoxbox // NO SOUND

by MMM on Fri Apr 26, 2013 10:41 am

sequentialmood wrote:Thanks for the answer MMM !
So it sounds that the VCF block is not working as it should (?).


That's hard to say since the signal seems not to make it into the filter. I'll think about it a little more. The voltages for the actual filter ladder looked ok to me.
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Re: Built Xoxbox // NO SOUND

by sequentialmood on Sat Apr 27, 2013 7:34 pm

Hello,
I've changed R62, here are my new tests on the VCF.

leg 1 on R62 (VCO side):
Image

leg 2 on R62:
Image

on the res pot, when a key is pressed on keyboard:
With res at Zero:
Image

With res at max:
Image

but still no sound...
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Re: Built Xoxbox // NO SOUND

by MMM on Sat Apr 27, 2013 7:41 pm

That's more like it. So the signal makes it through the filter - good!

Check at the "-" side of C38. You should get a signal there when pressing note buttons (in keyboard mode).
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Re: Built Xoxbox // NO SOUND

by sequentialmood on Sat Apr 27, 2013 8:09 pm

Ok.
here is what i get on C38, when i press a key.

Image

Many thanks, MMM!
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Re: Built Xoxbox // NO SOUND

by MMM on Sun Apr 28, 2013 3:34 am

OK, so there's essentially nothing.

Check with the oscilloscope on pin1 and pin2 of IC15B; you should have a very weak signal there (without having to press note buttons)

Check with the multimeter at R146 what happens when playing notes. Check similarly at D34 and D35.
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Re: Built Xoxbox // NO SOUND

by sequentialmood on Sun Apr 28, 2013 1:54 pm

Hi,

on IC15B:
on Pin 1, when i do not press anything. the signal reacts to Cutoff/Res/Env Mod values changes.

Image

on pin 2, i do not have any signal.

When a key is pressed:
on R146 (leg1/leg2): 0.64V / 4.94V

on both D35 and D34: 11.75V
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Re: Built Xoxbox // NO SOUND

by MMM on Sun Apr 28, 2013 2:27 pm

We're getting closer.

Please measure with a multimeter the DC offset at IC15B:

pin 1, pin 2, pin 6, pin 8

Please measure what happens at IC15B pin 4 when playing a note.
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Re: Built Xoxbox // NO SOUND

by sequentialmood on Sun Apr 28, 2013 3:55 pm

here are voltages on IC15B:

seems good on pin 1, 2 => 5.33V

pin 6 => 5.33V
pin 8 => 5.38V

pin4 => 8 mV (i guess near null signal, even if i press a note on the keyboard.)
Last edited by sequentialmood on Sun Apr 28, 2013 4:05 pm, edited 1 time in total.
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Re: Built Xoxbox // NO SOUND

by MMM on Sun Apr 28, 2013 4:05 pm

The plot thickens.

Theory: The volume envelope is missing or doesn't make it to the VCA (IC15B).

Please measure with the multimeter the behaviour when playing a note at the cathode of D27.
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Re: Built Xoxbox // NO SOUND

by sequentialmood on Sun Apr 28, 2013 4:13 pm

nothing on D27 cathode when a note is pressed.
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Re: Built Xoxbox // NO SOUND

by MMM on Sun Apr 28, 2013 4:24 pm

...which means no volume envelope.

Please measure both sides of D36 when playing a note. Since we are dealing here with rapidly changing voltages you'll possibly not get much information from the multimeter; it could appear as a small positive "dip" at the anode and a longer one at the cathode. You may also want to try to measure this with the oscilloscope.
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Re: Built Xoxbox // NO SOUND

by sequentialmood on Sun Apr 28, 2013 4:39 pm

ok, i've just resoldered few points on D27.

here are my results:
- on cathodes on D27 and D36, voltage raises when i press a key, the value depends on how i press the note button (0.2v/0.5V)
- now i've also got a raise on pin 4 of IC15B, which is around 11.8V (pretty high??)

Thanks.
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