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 Forum index » DIY Hardware and Software
An idea for a new kind of DIY VCO
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Uncle Krunkus
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PostPosted: Thu Apr 27, 2006 6:47 am    Post subject: Reply with quote  Mark this post and the followings unread

Okay,
First, the PSU I was running it off was humming. (I pulled the 4066 and there was hum irrespective of the main frequency control)
It disappeared when I went to a 9V battery for power. (I'll fix this soon)
I also noticed that there are plenty of sub sonic power fluctuations getting through to the output no matter what the speed of the clocks is. Jan, I reckon this might be causing those curves between samples on the trace. I'm gonna do a quick sketch of the clock circuit as well just in case you can see something amiss there. Maybe I need bypass caps. But how many? And where? And what value? .01uF seems to be popular for bypass caps.

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Blue Hell
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PostPosted: Thu Apr 27, 2006 11:20 am    Post subject: Reply with quote  Mark this post and the followings unread

Sounds like a mistake in the grounding ... told you I heard hum Very Happy

But WTH do the subsonics come from ... could you post a sketch of the PSU maybe ?

Hmm, wish I could simply see and touch the thing ... that would help maybe ... this can be hard to say something sensible about.

Could also be that excessive current is drawn by the circuit for some reason.

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Blue Hell
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PostPosted: Thu Apr 27, 2006 11:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Missing bypass caps should give glitches, not hum. You didn't connect an electrolitic capacitor reverse biased somewhere ?
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Uncle Krunkus
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PostPosted: Thu Apr 27, 2006 3:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

No, the hum is separate. Caused by an unregulated crapola 9V adaptor. I'll knock up a little regulated PSU for it today. Forget the hum.
The sub sonics (or what look like large curves on my 300ms updating Winscope) are being made by the number of digital chips across the power, I'm almost sure of it.
Stop Press!!
I think I just spotted a reversed electro! Jan you're a genius!! Very Happy
I'll get back to you.

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Uncle Krunkus
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PostPosted: Thu Apr 27, 2006 3:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry, false alarm.
It was just a trick of the stripboard. Confused

I've designed a little sub board that plugs in to where the 4520 chips are and works as an auto reversing dual 4 bit counter. Lucky I have the reality of a new baby to distract me, cos I think I could easily drive myself insane! Laughing

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Uncle Krunkus
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PostPosted: Sun Apr 30, 2006 5:09 am    Post subject: Reply with quote  Mark this post and the followings unread

New PSU and the hum is gone.
I'm still a bit sus about the output though. When I change from the DC coupled output to the cap (.01uF) the squared off wave turns into a series of spikes. Why can't I uncouple the DC and retain the shape of the wave?
Is it just because I'm "looking" at the waveshape through my mixer and into the soundcard?
Anyway, I'm working on the reverser mod now, as I know it will improve the sound by a long way.

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PostPosted: Sun Apr 30, 2006 4:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

Uncle Krunkus wrote:
(.01uF)

That might be a bit smalish, it depends on impedances driving from and driving into, but yoy might even need an electrolitic one. Increasing it to .47 uF will improve things.
Quote:

Why can't I uncouple the DC and retain the shape of the wave?

Because your ;etting through high frequencies, for a first order high pass RC filter you'll have signal drop of 6 dB / Octave below the cutoff frequency (fcutoff=1/(2*pi*R*C) . This will distort the wave, noting you can do a bout that. But the good news that below a certain frequency you can't hear the signal anymore, so typically one would try to set the cutoff frequency around 20 Hz or so. What C is needed for that depends on the R you have, which is somewhat hard to estimate but the imput impedance of the input you put thes signal in might be in the manual of the device in question.

When you need a large capacitor, either from calculation or from experimentation, it might have to be an electrolytic type, in that case connect the plus side to your circuit using the minus side as the output.

Maybe read the section 'time domain considerarations' at http://en.wikipedia.org/wiki/RC_filter and have a look at the graphs there.

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PostPosted: Sun Apr 30, 2006 6:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

Congratulations,on your arrival,Uncle K.
Just skimming through here,(i can't see the sch. on this linux-stem)but noticing you're using a 4520 counter in the sketch.I've found them to be most pedantic about their clock pins!

I followed Ken Stone and put a filter in there,4k7 series,33n pin to earth.Cleaned it up no end.

Robert
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Uncle Krunkus
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PostPosted: Mon May 01, 2006 3:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Well, looking back I've got the output of the TL071 as a voltage follower. Looking forward I've got a line in on a Behringer MX1602 mixer. I figure they should both be pretty high, yeah?
Hey Robert,
what do mean by "pedantic about their clock pins" ? I haven't had any hassles with the 4520. (Although I am about to replace them with a DIY auto reverse clock made of 4024s and 4030s)

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PostPosted: Mon May 01, 2006 7:17 am    Post subject: Reply with quote  Mark this post and the followings unread

fussy!

Looking at cgs.synth,you'll see in his sequential switch he implements this...
Quote:
I had some trouble on the prototype unit with some brands of 4516 counters. It seems some of them are pedantic about the speed of the rising and falling edges of the clock pulse. The problems experienced were: the counter advancing on both rising and falling edges of the clock pulse, skipping steps, or stepping back and forwards between two steps. The offending devices were Mitsubishi and Fairchild. The National Semiconductor device worked perfectly.


I made a mistake above,i breadboarded with 4520(a ST HCF4520BE) putting a 3n3 in series with a 4k7 to earth.It stopped playing up and divided the clock nicely as a 2/4/8 divider.

Robert
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Blue Hell
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PostPosted: Mon May 01, 2006 11:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Uncle Krunkus wrote:
I figure they should both be pretty high, yeah?


Opamp output should be near zero omhs, that's good and it can be ignored. For mixer in lets assume 47 kE. And lets say you want 20 Hz for the cutoff frequency, so :

20 = 1 / (2*pi*47e3*C) or C = 1 / (40*pi*47e3) = 17 uF ... hmm bit higher than expected.

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Uncle Krunkus
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PostPosted: Mon May 01, 2006 1:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Jan,
I'll give it a go.
And let you know!

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PostPosted: Tue May 02, 2006 8:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes!
We have liftoff!
I changed the output cap to a 17uF electro.
I changed the 3K9 in the DAC to exactly 4K to keep it accurate.
But most of all, I found that my bit lines were still messed up!!!!! I fixed 'em, and all of a sudden I can hear harmonic content smoothly moving into the sound and then dropping out. The wave is squared off. It sounds really good, well compared to before! Now it's worth making the reversers!!
I is a happy man! Very Happy

PS in the attached mp3: - sample1 is moving quite fast (it's the beating sound at about 2hz) sample3 is going at about 3/4 speed and the rest are set to their slowest rate of change. It's easier to see what it's doing in Soundforge.


SupSub3-5-06.mp3
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Download
 Filename:  SupSub3-5-06.mp3
 Filesize:  144.39 KB
 Downloaded:  599 Time(s)


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PostPosted: Tue May 02, 2006 10:19 am    Post subject: Reply with quote  Mark this post and the followings unread

Uncle Krunkus wrote:
Yes!


Phew Very Happy

& sample sounds waay better indeed.

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PostPosted: Tue May 02, 2006 12:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yep, sounding very good!
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PostPosted: Thu May 11, 2006 3:05 am    Post subject: Reply with quote  Mark this post and the followings unread

I've almost finished two auto reverse Gamera chips. The first one sounds good already. Two should make it even smoother!!
As for the front end, I'm wondering how to make an input which will kick over the 4017 from any constantly recurring signal in, whether it be sine, saw, square etc. and anywhere from 160Hz -> 100Khz. I s'pose a schmitt trigger will be in there somewhere. Some kind of pre-gain/diode clamping kind of thing to square it off maybe?
Any ideas would be much appreciated.
I also realised that it could be simplified a lot to make it easier for a DIY project. You really only need 4 clocks; 2 ramps & 2 reversing, then a rotary switch for each sample (Cool and you could dial up which clock fed each time slot. That pulls the chip count down to just 15! Rolling Eyes

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PostPosted: Fri May 12, 2006 7:25 am    Post subject: Reply with quote  Mark this post and the followings unread

Here's the latest sample.
I'm begining to think that this project's ends don't justify the means.
I think maybe I should do some work finishing my Soundlab and get back to it later.
I'm satisfied with it so far. I think I'd like to hear it backing up the rest of the synth to work out how much more time is worthwhile investing.

"A creative person makes a lot of stuff. An artist knows what to keep."

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PostPosted: Fri May 12, 2006 9:10 am    Post subject: Reply with quote  Mark this post and the followings unread

I think you forgot to add the sample... Surprised
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PostPosted: Fri May 12, 2006 2:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yeah. Whachoo doin? Holdin' out on us? Very Happy
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Uncle Krunkus
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PostPosted: Fri May 12, 2006 5:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry dudes,
I've got the nappy brain!! Very Happy
Here tis


SSub130506.mp3
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 Filename:  SSub130506.mp3
 Filesize:  492.62 KB
 Downloaded:  566 Time(s)


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PostPosted: Fri May 26, 2006 5:24 am    Post subject: Reply with quote  Mark this post and the followings unread

cool project! For kicking the 4017, i once dit this with an lm358 as a comperator and a diode to get ground and high. Worked well for playing my sequencer with the bassguitar.
I saw some shematic how to use a phased lock loop with an divider in it´s feedback to multiply an incoming wave. Might be useful to clock this with slower signals.
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