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Arp 4072 self osc clipping
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isak



Joined: Dec 13, 2009
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PostPosted: Tue Jun 18, 2013 3:36 pm    Post subject: Arp 4072 self osc clipping Reply with quote  Mark this post and the followings unread

Hi

does the self osc suppose to clip when i put the reso all the way up?
it reaching to the red lines in my sound card, but hard.
is there any way to reduce the gain of the self osc?
one more thing...it seems i cant get more then 14.5khz when self oscillating.
can i get it to 20khz?

cheers,
Isak E.

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yusynth



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PostPosted: Wed Jun 19, 2013 4:19 am    Post subject: Reply with quote  Mark this post and the followings unread

1-No I don't remember it would clip, normally it's a nice sinewave but with a very large amplitude.

2-That's the normal behaviour of this filter

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isak



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PostPosted: Wed Jun 19, 2013 8:37 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for replying.

I just read in your site that that you manage to get to 20khz, this is why I asked.
I know it not suppose to clip, is there any way to reduce the amplitude of the self osc?
Beside the small issues it works well I think.

Oohhh I remembered what I wanted to ask...
When rising the reso is it normal that the general vol is getting lower?
Meaning reso up vol down, reso down vol up, its the same like in the tb303.
I'm asking cause I don't own an arp synth.

Cheers.

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isak



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PostPosted: Thu Jun 20, 2013 3:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

ok, i did some tests and pics..

this is the pic of the clipping..

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

and this is the sine wave in different freq position.. (no VCA, straight from VCF).

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

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

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

any idea or help please?

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yusynth



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PostPosted: Thu Jun 20, 2013 11:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK, therefore the auto-oscillation is not clipped in the filter but by your audio recording board. If you look at the scope you'll see that the signal level is something like 8 to 10V peak to peak, this correspond to an audio level of something between +10dBU to +14dB.That's completely normal, signals and CV in modulars are way up the so-called audio-range. That is the output signal of a module MUST be attenuated (at least 8 times) before being fed to a normal audio device.

Now I am puzzled by the waveshape you show for the highest frequency auto-oscillation getting a quasi triangle shape.

Which type of power-supply are you using ?

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isak



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PostPosted: Fri Jun 21, 2013 1:56 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks.

So at the output of the VCF do I need to increas the output resistor (R42)?

I'm using the MFOS wallwart power supply.
15V.
http://www.musicfromouterspace.com/analogsynth_new/WALLWARTSUPPLY/WALLWARTSUPPLY.php

In another MFOS VCF it's all ok, no prob at all at high freq.

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elmegil



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PostPosted: Fri Jun 21, 2013 6:14 am    Post subject: Reply with quote  Mark this post and the followings unread

A common way to attenuate for audio inputs is to put a 10k pot to ground for your output, and take the signal to your board or other audio device from the wiper. Then you can use the pot to adjust to the point where you get the best sound from whatever the input is expecting.
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isak



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PostPosted: Fri Jun 21, 2013 2:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the tip elmegi.

Could I replace the pot by resistor after getting the results I want?
The sad thing about putting a pot at the output is the low output I'll get for the actuall audio through the VCF after attenuate the self OSC.

Yves,
Could the shape be like that cause of bad transistors matching?
Or maybe the lm3900 is bad?

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elmegil



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PostPosted: Fri Jun 21, 2013 3:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

The idea is that it's a voltage divider. You could replace it with *two* resistors, one representing the resistance from wiper to the signal out, and one representing the resistance from the wiper to ground.

I don't understand why this is a "sad thing", you can always turn the pot all the way up and get exactly the same signal you would have gotten without... ?? If you used fixed resistors, not so much.
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isak



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PostPosted: Fri Jun 21, 2013 9:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

Now I see, we creating a voltage divider.
I'm still learning here Smile

The output suppose to go to the VCA, as I see in the VCA schem there is a 100k pot at the input, so I'll try connect directly and see if It will help.

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elmegil



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PostPosted: Fri Jun 21, 2013 10:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yah, you ought to be able to use the 100k on the input to limit the output down to something usable Smile

It's all down to where is it clipping.....
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isak



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PostPosted: Fri Jun 21, 2013 11:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks Smile

BTW can you maybe help me to understand something?
Yves said..
Quote:
If you look at the scope you'll see that the signal level is something like 8 to 10V peak to peak

how he was able to see it on the scope?
i'm all new to the scope thing, just bought it Embarassed
if i center the signal on the scope screen how can i see the peak to peak and how will i know via the scope the Vpp?
there is no mark on the screen to that.
i can also make the signal larger or smaller in the scope screen even the 5V signals so how he knew its 8 to 10V peak to peak?

sorry for newbi question, as said still learning.

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gdavis



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PostPosted: Fri Jun 21, 2013 11:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

isak wrote:
thanks Smile

BTW can you maybe help me to understand something?
Yves said..
Quote:
If you look at the scope you'll see that the signal level is something like 8 to 10V peak to peak

how he was able to see it on the scope?
i'm all new to the scope thing, just bought it Embarassed
if i center the signal on the scope screen how can i see the peak to peak and how will i know via the scope the Vpp?
there is no mark on the screen to that.
i can also make the signal larger or smaller in the scope screen even the 5V signals so how he knew its 8 to 10V peak to peak?

sorry for newbi question, as said still learning.

"P10x>2V" displayed on the scope indicates 2V per division (the black horizontal lines printed on the screen). Count the number of lines the signal spans from top to bottom, multiply that by two and you get the peak-to-peak voltage of the signal. When you change the scale the 2V number should change to another number representing the volts per division the scope is set to.

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yusynth



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PostPosted: Sat Jun 22, 2013 12:53 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi

I have just checked the auto-oscillation behavior of the yusynth ARP filter with my oscilloscope and I obtained a perfect sine wave from 21Hz up to 19,4kHz (corresponding to the full range of the cut-off potentiometer).
Concerning the peak to peak amplitude it rises from 8Vpp at 21Hz to 20Vpp at 19,4kHz.
Freq shape amplitude
21Hz sinewave 8.0Vpp
100Hz sinewave 9.0Vpp
500Hz sinewave 10.4Vpp
1kHz sinewave 11.6Vpp
5kHz sinewave 15.6Vpp
10kHz sinewave 18.2Vpp
19,4kHz sinewave 20.0Vpp

Are you sure that you are using your oscilloscope correctly ? Are you using a X1 probe or a x10 probe, in both case have you calibrated your probes ?

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Last edited by yusynth on Sat Jun 22, 2013 12:25 pm; edited 2 times in total
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isak



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PostPosted: Sat Jun 22, 2013 7:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Using X1 not X10.
I didn't calibrated my probes, I got my scope few weeks now, still learning about the scope.
I found the calibrate thing but it's not with a crew driver, it's something strange.
Looks like I need to hook something over there, it's a metal thing with a hole in it.
my next question will be...
How come the MFOS SVF comes out ok and the arp and the vca not?
Not that I'm trying to say something here, I'm just looking for logical explanation, Why is that?
BTW...really not sure I'm using my scope correctrly, this is what happens when I jump over my head try to learn as much as I can without really understand what I'm doing and expect to get the best in minimum time Rolling Eyes

in the manual it says..

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

this is the probe adjust..(should i try to turn it left or right?)

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

one more thing, i found this pot (Variables), what its suppose to do?
can i "adjust" the probe with this as well?

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

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Blue Hell
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PostPosted: Sat Jun 22, 2013 7:48 am    Post subject: Reply with quote  Mark this post and the followings unread

isak wrote:
Using X1 not X10.
I didn't calibrated my probes, I got my scope few weeks now, still learning about the scope.
I found the calibrate thing but it's not with a crew driver, it's something strange.
Looks like I need to hook something over there, it's a metal thing with a hole in it.


You hook up a probe to that thing and then there is a little trimmer screw on the probe or on the plug-blob connecting to the scope - you use that one to make a nice looking square wave.

Cant remember if X1 probes need calibration ... Rolling Eyes

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PostPosted: Sat Jun 22, 2013 7:51 am    Post subject: Reply with quote  Mark this post and the followings unread

Oh, and re. the 2nd image - you seem to have set X1 / X10 on auto - that is the probe will determine what happens with some contact on the probe connector on the scope - this will only work if you have suitable probes (i.e. the original probes) and otherwise you need set it manually to the X1 or X10 value that is mentioned on the probe itself.
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isak



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PostPosted: Sat Jun 22, 2013 8:41 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks blue hell.

on my probe its on X1.
the variables is like an endless turning pot, how do you know its on auto mode?

it not the trimmers, i really dont know where they are.

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

thous are the only trimmers that on the front panel.
ive checked the back and there are no trimmers there.

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

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yusynth



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PostPosted: Sat Jun 22, 2013 10:17 am    Post subject: Reply with quote  Mark this post and the followings unread

No these trimmers have nothing to do with probe calibration and you must have them set to the resting (default) position. The probe calibrating screw is on the probe itself (not on the scope) either on the probe handle or on the probe plug.

See it on this photo :
Posted Image, might have been reduced in size. Click Image to view fullscreen.

and on this video
http://www.youtube.com/watch?v=uOAzRlhrnYE

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gdavis



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PostPosted: Sat Jun 22, 2013 10:54 am    Post subject: Reply with quote  Mark this post and the followings unread

Another thing, the dark grey knob in the middle of the volts/div knob needs to be all the way clockwise to the "cal" position. The ">" in the P10x>2V display should go away.

The 10x thing is kind of confusing (been trying to understand it in the manual). It sounds like it always defaults to 10x. In order to change it to 1x you need to go into the "variables" section and select "HPOS" (with the "cursors" button? Not sure), then hold the "select" switch down and turn the knob counter-clockwise. The P10x should go away.

But you should double check that the probe really is really 1x, the manual sounds like they expect you're using a 10x probe.

You really should sit down and read through the manual to understand how to operate the scope. There are little things that can easily throw off a measurement (like not having the knob set to cal).

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PostPosted: Sat Jun 22, 2013 12:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

yusynth wrote:
No these trimmers have nothing to do with probe calibration and you must have them set to the resting (default) position. The probe calibrating screw is on the probe itself (not on the scope) either on the probe handle or on the probe plug.

See it on this photo :
Posted Image, might have been reduced in size. Click Image to view fullscreen.

and on this video
http://www.youtube.com/watch?v=uOAzRlhrnYE


thanks Yves.
i adjusted my probes perfectly Smile
for the Arp...well...still the same.
ive checked at 1X and 10X, dosent matter, its the same.

Hi gdavis and thanks.
Quote:
Another thing, the dark grey knob in the middle of the volts/div knob needs to be all the way clockwise to the "cal" position. The ">" in the P10x>2V display should go away.

that worked.

Quote:
The 10x thing is kind of confusing (been trying to understand it in the manual). It sounds like it always defaults to 10x. In order to change it to 1x you need to go into the "variables" section and select "HPOS" (with the "cursors" button? Not sure), then hold the "select" switch down and turn the knob counter-clockwise. The P10x should go away.

EDITED:

worked as well, defiantly on 1X and still the same.

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

Last edited by isak on Sat Jun 22, 2013 12:23 pm; edited 1 time in total
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yusynth



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PostPosted: Sat Jun 22, 2013 12:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Do you have a scope function in your recording software ? How do look the waveforms (without clipping of course) ?
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yusynth



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PostPosted: Sat Jun 22, 2013 12:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK doesn't seem to be a problem with the probe. I am puzzled. Can you post photos of your PCB (good resolution) so we can check there's no mistake.
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isak



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PostPosted: Sat Jun 22, 2013 12:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

yusynth wrote:
Do you have a scope function in your recording software ? How do look the waveforms (without clipping of course) ?


2 kinds of comp scopes, no clipping.

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

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PostPosted: Sat Jun 22, 2013 2:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

yusynth wrote:
OK doesn't seem to be a problem with the probe. I am puzzled. Can you post photos of your PCB (good resolution) so we can check there's no mistake.


for sure! thank you for that.
i hope my old Minolta camera will do the job


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