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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
VCO/BINTIC
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neandrewthal



Joined: May 11, 2007
Posts: 672
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PostPosted: Mon Dec 01, 2008 12:29 pm    Post subject:  VCO/BINTIC
Subject description: They won`t do bass.
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So, I`ve built 40 modules over the last year and they all work, but these two are killing me. They both have the same problem and basicaly the same design, so I must be doing something wrong, or have a faulty batch of a particular component or something.

Both of them have a frequency range starting in the medium range, and ending way above audio Confused The VCO can come close to what you might call a `bass` tone, but the BINTIC can`t. I don`t know how low the bintic is supposed to go, but I know the VCO is supposed to be able to go well into the sub-audio range.

I`ve greenlined everything in both of them and can`t find anything wrong, even a wrong resistor value.

The components I used are TL072 for the op-amps, SSM2210 for expo pairs, PN4391 for the fet and polystyrene caps for the 2n2`s

I tried increasing the cap in the BINTIC, but it took much bigger caps to make a noticable difference, and when it did, it stopped clocking the filter.

Any ideas what could cause this? I give up Evil or Very Mad

Thanks.

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Blue Hell
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PostPosted: Tue Dec 02, 2008 2:36 pm    Post subject: Re: VCO/BINTIC
Subject description: They won`t do bass.
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neandrewthal wrote:
polystyrene caps


A while ago there was some issue here with someone soldering the polystyrenes too hot which caused trouble, maybe that's the problem here as well?

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neandrewthal



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PostPosted: Tue Dec 02, 2008 10:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks, I did take note of this. Actually, I originally had a polyester cap in the BINTIC and I changed it to polystyrene(being extremely careful) to see if it would make a difference. It didn't. I suppose it wouldn't hurt to try a new one in the VCO.
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Blue Hell
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PostPosted: Wed Dec 03, 2008 11:31 am    Post subject: Reply with quote  Mark this post and the followings unread

I see the VCO (when I picked the right one?) and the BINTIC are basically the same re. the oscillator ... having the same issue in both looks like a reproducible mistake ... you did use the 3140 (and not a TL072 for it)? You did put in the tempco (and if not a 1 K resistor instead)? Do you run 'm on 12 or on 15 V?

Not that I know what the problem is, just some questions that came up looking at the schematics.

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neandrewthal



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PostPosted: Wed Dec 03, 2008 11:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Oops, I should have been more specific. Yes, the GGS48 is the right one and I did use CA3140 in both. I meant I used TL072 for the dual amps. I have tempcos on both of them, right over the SSM2210's and I'm running on 15v.
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Blue Hell
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PostPosted: Wed Dec 03, 2008 12:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok ... I've looked into lm384 vs ssm2210 compatibility, looks ok also into pn4391 vs 2n4856 .. I don't know too much about fets, but looks ok to me.

The oscillator runs too fast, or fast at least, so either too much current is used to charge the timing capacitor or the capacitor is shorted too fast I'd think ... and I can find no reasonable explanation sofar, maybe one of the vco gurus here knows ...

Do you have a way to see the amplitude of the signal at the output (pin 6) of the 3240? When there is not much amplitude the switching could be happening at the wrong (output) level maybe.

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fluxmonkey



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PostPosted: Wed Dec 03, 2008 2:33 pm    Post subject: Re: VCO/BINTIC
Subject description: They won`t do bass.
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neandrewthal wrote:
The components I used are TL072 for the op-amps, SSM2210 for expo pairs, PN4391 for the fet and polystyrene caps for the 2n2`s.


you might want to check the orientation of the FET; PN vs the specified 2N versions i think may have different footprints... and i seem to remember that sometimes even different mfgs of the same part number can switch things around?

b

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neandrewthal



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PostPosted: Wed Dec 03, 2008 9:22 pm    Post subject: Re: VCO/BINTIC
Subject description: They won`t do bass.
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Blue Hell wrote:

Do you have a way to see the amplitude of the signal at the output (pin 6) of the 3240? When there is not much amplitude the switching could be happening at the wrong (output) level maybe.


Unfortunately not. Maybe I rig up some sort of PC scope setup.

bbob wrote:


you might want to check the orientation of the FET; PN vs the specified 2N versions i think may have different footprints... and i seem to remember that sometimes even different mfgs of the same part number can switch things around?

b


Yes, that is too true. I have a bag of backwards BC550's here that wreaked havoc until I discovered their little secret. I tried reversing the PN4391 in the BINTIC, though, and it stopped working altogether.

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otherunicorn



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PostPosted: Thu Dec 04, 2008 4:00 am    Post subject: Reply with quote  Mark this post and the followings unread

I expect the PN footpring would match the outline on the PCB. The 2N footprint is mirror image. In an ideal world, the FET will discharge the capacitor instantly, so that is not your issue. The frequency should relate directly to the capacitor value - double the capacitor to halve the frequency (drop 1 octave). Try feeding a negative voltage into one of the inputs. I usually find these have a range from ticking to supersonic, as built, so I don't know what is going wrong for you. Most likely a part common to both that is peculiar to your build, or a consistant error you make.
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RF



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PostPosted: Mon Dec 08, 2008 10:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm having the same issue with my Bi-N-Tic.
Version 1.1 board.
12 VDC, 1k res instead of tempco, LM394, CA3140.
I've been troubleshooting for a while now...confusing.
I'm putting it away for tonight - back at it tomorrow with more information...

bruce

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neandrewthal



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PostPosted: Wed Dec 10, 2008 8:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the suggestions everyone. I went up to .47uf in the VCO and I have no bigger capacitors. It still won't go low enough when the Zero trimmer is set properly. I give up. I just cranked it down to -15v and I'll have to forget about v/oct tracking for now.

The BINTIC is completely out of commission, unfortunately because I tried to see what would happen if I turned the FET backwards(this was several months ago) and it stopped working completely. I don't have any left except MPF-102 and everyone seems to say those are no good in the BINTIC.

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neandrewthal



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PostPosted: Sun Dec 14, 2008 12:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Ok, I've resurrected the BINTIC by finding a used PN4391 on the junk heap that still works. I switched the cap to 47u and the pitch is a little lower now, but it no longer clocks the filter. I traced the sound all the way to the BC547 that goes to the 4024, but nothing is getting to the CLK input. Any idea what is going on here? Why would the BC stop passing the sound after the cap is lowered?
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Sine



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PostPosted: Mon Dec 22, 2008 6:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

I have been messing around with the oscillator circuit of this thing on my still to complete bintic board to find out why the VCO's of my asm2 where acting so strange. ( both use the same oscillator core )

I found that with the fet I used the vco oscillated at a higher frequency than it should and that the amplitude of the sawtooth was way to small.
And when you go up in frequency the problem gets bigger ( so the amplitude gets lower )

This could come to a point where the signal is too small to get a clock signal through to the 4024 in the bintic

An other fet solved this problem ( faster and with a lower on resistance ) but introduced a new one ( this one might be too good Wink ) so I ordered a few 2N4856's to see what they do, elby uses a J108 in the ASM2 so that may be a valid replacement.

But it is clear that my 2N45-something is no good, and a J105 is problematic as well, unless you like a badly deformed sawtooth.

I'll let you know what my results are when the fets are in.
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neandrewthal



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PostPosted: Tue Dec 23, 2008 12:08 am    Post subject: Reply with quote  Mark this post and the followings unread

Sine wrote:

I found that with the fet I used the vco oscillated at a higher frequency than it should and that the amplitude of the sawtooth was way to small.
And when you go up in frequency the problem gets bigger ( so the amplitude gets lower )


This is encouraging to hear. I hope it works out for you and I am looking forward to your report. Hopefully I just need a new FET as well.

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Sine



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PostPosted: Tue Dec 23, 2008 1:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

And since images say more than a thousand words I took some pics of the scope.

http://picasaweb.google.com/lh/photo/_eskxpmBtsrO1ybwPDocKw?feat=directlink
The VCO core at approx 20kHz with a J105 fet.

Great clock pulses, but a very deformed sawtooth, especially the flat end bugs me.

All settings on the scope and the the same and the fet swapped for a mpf102
http://picasaweb.google.com/guidomennen/ASMBiNTikVCOFilterSynth#5283086263429370770

The frequency has more than doubled, the sawtooth is much higher above 0 and the amplitude has almost halved.
This makes for very wimpy clock pulses to the counter and could cause your problem.

Even when I tune it back to 20kHz the pulse is way too small for a mos counter.

-edit-
Okay, my web host is on the fritz and google web albums don't allow linking ( Booo.. ) so i replaced the images with links, sorry
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Rykhaard



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PostPosted: Wed Dec 24, 2008 7:23 am    Post subject: Reply with quote  Mark this post and the followings unread

The only difference that I'm able to provide is for the JFET tranny. I've always been using the J112 for my VCOs and have never had any troubles.

I HAD my Bi-N-Tic up and running with my dual VCA addition modification (for the Cutoff controls) and all was swell. Though I liked the sonic possibilities from the unit, I didn't find it useful enough. I stripped it down to the Sawtooth only. (Which I increased to 10vPP output.) I'm doing the same thing with my 2nd one.
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Sine



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PostPosted: Thu Dec 25, 2008 7:20 am    Post subject: Reply with quote  Mark this post and the followings unread

I found J112's on some old industrial process control boards and they work perfectly !
Gotta love old junk Razz

In the deep end it oscillates at a few Hz and it starts clocking at about 20Hz with a almost perfect sawtooth to over 50kHz.

Thanks for the tip ryk

So the verdict so far

No go :

J105
mpf102
2N5457

So far confirmed go :

J112

Probbably ok :

2N4856
J108

Seems I could have known about the MPF102, Ken writes on his site :

Quote:
The MPF102 is reportedly causing some oscillators to fail or be very weak. As such, it may be best to avoid using them as the FET. I originally used them in my VCOs because it was all I could get locally. I have not tried them in the Bi-N-Tic, instead assuming they would suffice, as they had in the VCOs. These days I use 2N4091.


So a 2n4091 should work as well, it seems I managed to pick among the few that won't work in this circuit ...

Last edited by Sine on Thu Dec 25, 2008 1:42 pm; edited 1 time in total
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neandrewthal



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PostPosted: Thu Dec 25, 2008 12:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Excellent, definitely picking up some J112's on my next digi-key order.
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Rykhaard



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PostPosted: Thu Dec 25, 2008 1:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Excellent to read! Smile I haven't a clue as to where I learned of the J112 from, but it's the one that I've been using since October '05, when I built successfully, my first discrete VCO. Smile

IIRC as well - whomever I'd learned it from had said that the J110 family (J110, J111 and J112 would all work). I barely know a thing myself about JFET trannies, except for their basic operation method. Due to that I'm not able to give any further advice. Confused

On a happier note: Happy Season every1 Smile
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Blue Hell
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PostPosted: Fri Dec 26, 2008 5:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sine wrote:
I found J112's on some old industrial process control boards and they work perfectly !


Cool good work!

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