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 Forum index » DIY Hardware and Software » The layout factory
ERIC ARCHER DIY LOWPASS VCF LAYOUT
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PHOBoS



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PostPosted: Sat Apr 04, 2015 2:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

if you get sound out that's a good sign that means it's at least passing through the LM13700.
Could you measure the voltage on pin 7 of the TLC2262 while turning the CV pot ?
You should get a voltage varying somewhere between 5V and 9V.

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tokyomatik



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PostPosted: Tue Apr 14, 2015 9:33 am    Post subject: Reply with quote  Mark this post and the followings unread

i'm trying with a 12v psu at the moment and from the 2262 when i turn the freq pot i get a voltage variable between 11.58v and 7v....
is that ok?
where should i look now??
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breadman



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PostPosted: Tue Apr 21, 2015 7:52 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm having pretty much the same issue as tokyomatik-- fine unfiltered sound, no filtered sound. I've only tried it with this fresh 9v which is actually supplying 9.58v, but right now pin 7 on the 2262 is reading between about 6.2v and 9.4 as I turn the freq pot. I've got the scope fired up, but would love to know if anyone has any ideas!
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tokyomatik



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PostPosted: Sun Apr 26, 2015 3:06 am    Post subject: Reply with quote  Mark this post and the followings unread

still mumbling about the reason why the filter is not working....
did u solved it?
any ideas?
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PHOBoS



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PostPosted: Sun Apr 26, 2015 4:03 am    Post subject: Reply with quote  Mark this post and the followings unread

tokyomatik wrote:
i'm trying with a 12v psu at the moment and from the 2262 when i turn the freq pot i get a voltage variable between 11.58v and 7v....
is that ok?
where should i look now??

That sounds ok to me.

breadman wrote:
I'm having pretty much the same issue as tokyomatik-- fine unfiltered sound, no filtered sound. I've only tried it with this fresh 9v which is actually supplying 9.58v, but right now pin 7 on the 2262 is reading between about 6.2v and 9.4 as I turn the freq pot. I've got the scope fired up, but would love to know if anyone has any ideas!

hmm interesting that you seem to have the same problem. Just to make sure do you get any sound out of it when the mixpot
is turned to the filter (so just unfiltered sound) or no sound at all ?

the voltage on pin 7 tells me that the CV control part is ok (or at least it does something), so the current control
for the OTAs works. If you get any sound out than the signal also flows through the OTAs. So I'm not sure why it
wouldn't be working.

maybe if you (both) take some clear photos I can spot something. Rolling Eyes

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tokyomatik



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PostPosted: Sun Apr 26, 2015 6:58 am    Post subject: Reply with quote  Mark this post and the followings unread

actually the mix pot pass the sound but unfiltered, with pot completely close i have no sound at all
i could try to take picture of the board later if i find the battery for the camera
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PHOBoS



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PostPosted: Tue May 05, 2015 9:25 am    Post subject: Reply with quote  Mark this post and the followings unread

oh dear I clicked the wrong button, sorry Embarassed Rolling Eyes

anyway your reply was
tokyomatik wrote:
i found the battery, later some photos
could be that i used lm741 instead of ua741(this board doesn't look design for tle246)....??

That shouldn't matter. Actually any single opamp would probably work, it just creates a fake ground at half the supply
voltage which is the same thing as the TLE2426 is used for. You could measure the output voltage (pin 6) to see if it
works but since the CV section seems to be working it should be ok. Do you have a scope ?

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tokyomatik



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PostPosted: Tue May 05, 2015 10:10 am    Post subject: Reply with quote  Mark this post and the followings unread

yep i have a scope
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tokyomatik



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PostPosted: Tue May 05, 2015 11:04 am    Post subject: Reply with quote  Mark this post and the followings unread

i checked pin 6 and i have 4.46v.... i should have 0v... ?
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PHOBoS



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PostPosted: Tue May 05, 2015 11:38 am    Post subject: Reply with quote  Mark this post and the followings unread

no, ignore the label 0V in the schematic. It's a bit confusing since it would be 0V with a real dual supply,
but in this case it's a fake ground at half the supply voltage so with a 9V supply 4.46V is a good value.

I have to do some tests with a scope myself to see what's useful. It might be a bit tricky since the levels
are very much attenuated throughout the circuit and boosted later on in the mixer section. But you should probably
be able to see the input signal on pins 8 and 9 (if it's working that is). Best would be to test with a noise source
although some music will probably work too as long as you have something with a wide frequency range.

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tokyomatik



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PostPosted: Tue May 05, 2015 12:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

funny...for the test i'm using exactly a noise source....
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tokyomatik



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PostPosted: Sun May 31, 2015 7:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Finally a picture of the board, still not working..... Sad should i take a picture of the copper side too??


IMG_1011.JPG
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IMG_1011.JPG


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PHOBoS



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PostPosted: Mon Jun 01, 2015 4:22 am    Post subject: Reply with quote  Mark this post and the followings unread

tokyomatik wrote:
should i take a picture of the copper side too??

yes please, and maybe a photo that shows how the pots are wired although I don't really doubt you did that correct.
(but have to rule everything out) the resolution is great! thumleft

I will take a look at it this evening and maybe do another test with my scope. Last one wasn't very succesful because
the levels are very low and there is a large DC offset voltage throughout the circuit. So I couldn't really get it into view
on my (old) scope and the AC setting seemed to screw it up. What's the level of your noise source ?, so I can use a similar
level.

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Last edited by PHOBoS on Mon Jun 01, 2015 8:43 am; edited 1 time in total
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tokyomatik



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PostPosted: Mon Jun 01, 2015 4:33 am    Post subject: Reply with quote  Mark this post and the followings unread

later i will take another picture of the copper side Very Happy
as noise source i use the white noise of my ms20 and the noise source of my sn76477 voice, so if i'm not wrong should be -+5v for the ms20
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PHOBoS



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PostPosted: Mon Jun 01, 2015 4:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm not 100% sure but it looks like you used a 4K7 resistor instead of 47K for R5. It's attached to pin4 of the LM13700
and on your photo it's in the top left corner between the 1nF and 22pF capacitor. Brown and red look a bit alike
though so measure it to be sure. The rest of the components are correct from what I can tell.

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tokyomatik



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PostPosted: Tue Jun 02, 2015 8:25 am    Post subject: Reply with quote  Mark this post and the followings unread

I checked R5 and is 47k, so it's correct
but I start to think that maybe the wiring of the pots could be wrong...
let's see


9v vc lpf silkscreen.jpg
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PHOBoS



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PostPosted: Wed Jun 03, 2015 12:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

If you look at the pots from the backside that would be correct. Otherwise they are reversed but then the filter would
still work, just the pots rotating in the opposite direction.

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tokyomatik



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PostPosted: Wed Jun 03, 2015 4:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

So....what do u mean with watching from the backside? back or front pin 1 is pin 1, pin 2 is pin 2 and so on...this is to say that also the pots are ok?

now the only option left is to take a picture of the copper side
but my camera is dead and i have to ask to a friend( the one that took also the other picture)

and when also that is correct...well..... then i will give up this filter and move on
to the acoustic side of music and maybe gardening
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PHOBoS



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PostPosted: Wed Jul 08, 2015 10:35 am    Post subject: Reply with quote  Mark this post and the followings unread

I just did a test with a +/- 5V noise source and an oscilloscope. Although the amplitude isn't very large (±1 Vpp), you should
be able to see the noise signal at pins 5, 9, 12, 8 of the LM13700 with the frequency pot turned to GND (no filtering).

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Paradigm X



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PostPosted: Tue Aug 04, 2015 2:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey

This filter looks very interesting. Does anyone know if its possible to extract a high pass response as well?

Cheers
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PHOBoS



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PostPosted: Thu Aug 06, 2015 2:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmm if you invert the output and mix it with the input signal you get a HP filter. I just took another look at the schematic
and the output is actually already inverted because of the output mixer,. so if you mix that with the source signal it could work.

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Paradigm X



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PostPosted: Thu Aug 06, 2015 3:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Interesting, many thanks. I forgot you could fudge a HPF like like.

Im deciding between this and the WASP filter. This is simpler, but the wasp does everything i want, including distortion.

Cheers for the reply.

Ben
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