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Bare SAW VCO interest?
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Sell a simple, cost-effective, stable, accurate VCO?
Where have you been all my life -- this is exactly what I have been waiting for!
77%
 77%  [ 21 ]
No, I have too many VCOs already.
0%
 0%  [ 0 ]
No, I only like VCOs that drift and don't track over more than 3 octaves.
3%
 3%  [ 1 ]
No, your external waveshapers are too weird.
7%
 7%  [ 2 ]
No, we don't use VCOs around here.
7%
 7%  [ 2 ]
What's a VCO, and why would I want one?
3%
 3%  [ 1 ]
Total Votes : 27

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frijitz



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PostPosted: Thu Sep 04, 2008 10:32 am    Post subject: Bare SAW VCO interest?
Subject description: Or no?
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Several people have asked if it would be possible to have a board for a barebones SAW VCO for use in poly systems, for stacking or for systems emphasizing external waveshapers. I'd like to get some idea of how much interest there would be. The circuit has my latest version of the integrator with reset method and uses a MOSFET discharge switch driven by a special pulse shaping network to reduce the reset deadtime to about 200 ns. I'm surprised there was no discussion when I asked this the other day, but maybe an actual survey will help.

Very Happy

Ian
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Peake



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PostPosted: Thu Sep 04, 2008 10:37 am    Post subject: Reply with quote  Mark this post and the followings unread

You had my interest up until this: "stable, accurate..."

My Selector VCOs are plenty good for such things, if I need that. The TH VCO-1 is cheap and with an added saw shaper, is just fine, and is exceptionally interesting as a VC LFO with very wide range.

BTW, how could it be less expensive than the ARP Odyssey oscillator currently offered here? Looks like a pair would cost much less then $20.00 to build.

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Rykhaard



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PostPosted: Thu Sep 04, 2008 10:49 am    Post subject: Reply with quote  Mark this post and the followings unread

My 2nd VCO built for my current modular in early 2006 was a stripped down version of Ian's VCO that were up on his web page then. I even substituted cheaper opamps as I didn't have the 'big bux' then to buy the more expensive OP opamps.
And my self-made stripped down version of Ian's VCO from then (even with a metalized polyester film cap.) is working WONDERFULLY!
Many credits to Ian for that design back then. I was going to build more of them, but have since switched to Ken Stone / Ray Wilson PCBs for my VCOs.

I may be looking at the new sliders based one. Cost dependant though.

And now a stripped down version redone from Ian, I'll be watching the price for. If it's compatible with my wallet, I may then shift to them. (I'm again as I did in the 90's, building my own wave shapers, into a separate panel.)
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Peake



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PostPosted: Thu Sep 04, 2008 10:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Actually, those ARP VCOs would make decent VC LFOs, without mods...Hmmm..
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Dave Kendall



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PostPosted: Thu Sep 04, 2008 11:53 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Ian.

I guess this would be a cut-down version of one of your VCOs, but with the dial-a-tempco thing? or simpler....?

I like cheap, stable and accurate. Smile
(I'm sure if Tim servo had written that, it would appear at the end, albeit slightly different Very Happy )

cheers,
Dave

edited, 'coz I just found the thread. Right. Coffee. Now... Embarassed
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bugfight



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PostPosted: Thu Sep 04, 2008 12:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

hehe i wonder who voted option 3?
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filterstein



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PostPosted: Thu Sep 04, 2008 12:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

If it is really simple, so you can use it easily as an add-on, i'd buy a few.
There's almost too much to build lately, but a simple vco that you could stack on a system, something like a sawtooth sub oscillator by way of speaking would be nice.
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Peake



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PostPosted: Thu Sep 04, 2008 12:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

bugfight wrote:
hehe i wonder who voted option 3?


The world may never know.

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frijitz



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PostPosted: Thu Sep 04, 2008 2:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

Peake wrote:
You had my interest up until this: "stable, accurate..."

Oh well, we can provide options to degrade it. I even can show you how to deliberately add a *variable* amount of drift! Just requires one extra resistor (and possibly a trimmer to vary it.)

Quote:
The TH VCO-1 is cheap and with an added saw shaper, is just fine, and is exceptionally interesting as a VC LFO with very wide range.

I can guarantee you that mine has a greater range, if that matters to you. (Although I don't like using a Saw core for an LFO.) The VCO-1 is basically the same as an old Electronotes design, BTW. I happily used a couple of similar circuit for many years, until I developed better ones. But we're getting away from the point, which is to provide a barebones Saw VCO without waveshapers. Of course the McMoog crowd generally won't be interested in that.

Quote:
BTW, how could it be less expensive than the ARP Odyssey oscillator currently offered here? Looks like a pair would cost much less then $20.00 to build.

Why do you think it couldn't be? Seems kinda arrogant, to assume you know how much it would cost.

Very Happy

Ian
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Danno Gee Ray



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PostPosted: Thu Sep 04, 2008 2:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

How much would it cost?
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frijitz



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PostPosted: Thu Sep 04, 2008 2:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

Dave Kendall wrote:
I guess this would be a cut-down version of one of your VCOs, but with the dial-a-tempco thing? or simpler....?
I like cheap, stable and accurate. Smile

Thanks for your interest!

Right now I'm thinking simple: just an ordinary tempco-compensated expo converter plus my new Saw core.

Two opamps for the expo, one for the integrator, an IC comparator and an output amp for level shifting and gain. Also a pair of 5 V subregulators.

Inputs for 1V/Oct, coarse and fine frequency, lin mod and expo mod.

Possibly optional circuitry for sync and maybe a simple Tri shaper.

On the panel two frequency pots, one FM level pot (user connect to either expo or lin), jacks for 1 V/Oct, FM and output.

I'm sure it won't be possible to make everybody happy with the level of features.

To keep the cost down, the user can choose less expensive opamps (sacrificing some performance.) I don't have cost estimates yet, but the more interest there is, the less expensive the boards.

Very Happy

Ian
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Peake



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PostPosted: Thu Sep 04, 2008 2:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

The TH VCO is a triangle core, just right for us McBuchla fans.

No offense intended, but the recent announcement of the ARP oscillator boards makes this slightly bad timing? The ARP look to cost less than $10.00 per oscillator, or so, unless the boards are over $7.00. We are cheapskates. We want more VCO for less money. Whatcha got? Sorry if I'm putting attitude into this. More oscillators are good, in general...

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frijitz



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PostPosted: Thu Sep 04, 2008 4:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

Peake wrote:
The TH VCO is a triangle core, just right for us McBuchla fans.

Understood. I have been asked about doing a Saw VCO.

Quote:
No offense intended, but the recent announcement of the ARP oscillator boards makes this slightly bad timing?

Huh? You lost me again. When was that announced? As far as I can see mine was first. Besides, we live in the US of A where the free enterprise system is still in effect, at least for the time being. Nobody would be forced to buy either.

Quote:
We are cheapskates. We want more VCO for less money.

I suggest you speak for yourself. I think plenty of folks would pay up a couple of dollars more for improved performance.

But we will see. For now I'm just looking to see what kind of interest there is. If there isn't enough I really don't care. Again I'm responding to requests I have got from several people.

Very Happy

Ian
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widdly



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PostPosted: Thu Sep 04, 2008 7:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm interested in your design Ian, although I don't usually buy pcbs.

I've started on a similar idea for a stacked detuned saw osciallator using three or four of the 4069 oscillators from rene schmitz. They are hard to beat in terms of simplicity but the v/oct input needs some work.

Last edited by widdly on Thu Aug 05, 2010 10:07 pm; edited 1 time in total
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fonik



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PostPosted: Thu Sep 04, 2008 11:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
I think plenty of folks would pay up a couple of dollars more for improved performance.

i just started doing that, i already bought the components for the saw core from your site, including the burr brownies and the LM329s.

i am very interested in reliable and stable VCOs i can depend on. i use my modular for live performances, my ears are very sensible to the (de-)tuning and that's why i am still looking for a better VCO than the ones i have.

ian, does your new version provide more stability than your origin one?

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EdisonRex
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PostPosted: Fri Sep 05, 2008 12:28 am    Post subject: Reply with quote  Mark this post and the followings unread

One can never have enough oscillators. I'd be interested in a couple of boards, were they to become available. It would be helpful to have a lead on any hard to obtain parts though, especially for us outside-the-USA-types.
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Ricko



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PostPosted: Mon Sep 08, 2008 9:57 am    Post subject: Reply with quote  Mark this post and the followings unread

One nice thing about just having a basic saw is that it might spur other people to design some more interesting waveshappers: it seems like Ian is the only person doing any new work here (not to knock the efforts of the revivalists).

Any chance of having a layout that also allows NTCs as well as Tempcos? Ignoring the values, space for the extra two components seen in the bottom diagram of
http://www.uni-bonn.de/~uzs159/expo_tutorial/index.html
would be great. At Futurelec, NTCs are about 35c; tempcos are about $4: I know it is not a great absolute price, but it all adds up.

Also, even though this perhaps goes against the "basic", any chance of full wave rectification of the linear (and expo?) CV inputs, to allow quasi-through-zero operation?

And soft/hard sync?

I'd certainly be interested in getting some saw VCOs that had all that!
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julianw



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PostPosted: Mon Sep 08, 2008 10:07 am    Post subject: Reply with quote  Mark this post and the followings unread

I'd buy some if the boards were really small and you could stack a load of them behind a panel (I'm thinking 8 Shocked) for a monstrous 'unison' oscillator, (maybe with an 'global detune' option) actually come to think of it, (like widdly's project) if you could fit two or four of them on a single PCB, that would make things a lot easier.

Just my 0.2Hz Very Happy
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Dave Kendall



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PostPosted: Mon Sep 08, 2008 10:25 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
for a monstrous 'unison' oscillator, (maybe with a 'global detune' option)


The CGS 37 CV cluster looks like an ideal one-knob-global-detune jobbie - add a voltage divider pot between +V and GND, with wiper connected through a 100K resistor to IC1 pin 13 of the CGS37, outputs A thru K to VCOs as needed..... Smile
http://www.cgs.synth.net/modules/cgs37_cv_cluster.html
That way the CV for external control is there as well as the pot....

cheers,
Dave
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loss1234



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PostPosted: Tue Sep 09, 2008 4:00 am    Post subject: Reply with quote  Mark this post and the followings unread

i will want some of these (at least 2) for sure if the price is right. if not, maybe only ONE but i will want AT LEAST ONE

none of your designs have ever failed me and i think it would be fun to try to make my own waveshapers.

thanks again!

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machine.cuisine



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PostPosted: Thu Sep 11, 2008 5:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

I am interested. Like someone said above, you can't have too many VCOs.
A 'triangle shaper' and/or a 'sync' option would put it over the top.

Thanks, Ian.

PS- I must of missed this big ARP VCO thing...?
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v8pete



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PostPosted: Fri Sep 12, 2008 12:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Ian - sounds like a nice design Smile

Interested to hear that it has a Mosfet discharge switch - just wondering how you've managed to deal with the generally much higher leakage compared to a Jfet? Have you managed to find a really good device, or is there some clever circuit trickery at work Smile Smile

Pete
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frijitz



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PostPosted: Fri Sep 12, 2008 12:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

v8pete wrote:
Interested to hear that it has a Mosfet discharge switch - just wondering how you've managed to deal with the generally much higher leakage compared to a Jfet? Have you managed to find a really good device, or is there some clever circuit trickery at work?

Pete --

Good question. I was confused about this point for many years. If you look carefully, I think you will find that the high leakage you are refering to is at *very* high voltage. At normal voltages the impedance is extremely high. This is why an inexpensive MOSFET opamp like the CA3140 outperforms all but the most expensive JFET opamp devices.

A bigger problem is that most MOSFETS are designed for high current. Because of this they have large areas which leads to a large capacitance. I found that the VN0104, which is fairly common, to have low capacitance and good performance. But the BS170 also works just fine. I did make a little pulse shaping network to drive the gate to the correct voltage with a nice rounded pulse. This helped get rid of some strong ringing.

Thanks for your interest!

Very Happy

Ian
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v8pete



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PostPosted: Sat Sep 13, 2008 1:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the reply Ian - that's interesting ! Actually , taking a look at the BS170 DS it doesn't actually look that bad anyway, specified for a Drain current of 0.5uA at Vgs=0 at 25V - I think its better than quite a few of the more modern very low Rds-on P-channel devices that I looked at recently. Do you still have the same basic reset configuration as the Jfet circuit, (ie. Source connected to summing junction) but with the integrator output ramping up (as its an N-fet)?

I was going to run with the usual Jfet circuit for a 3-oscillator synth that I'm working on at the moment, but certaily sounds like its worth spending a bit of time investigating the Mosfet idea if I get the chance!
Pete
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frijitz



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PostPosted: Sat Sep 13, 2008 9:44 am    Post subject: Reply with quote  Mark this post and the followings unread

v8pete wrote:
Do you still have the same basic reset configuration as the Jfet circuit, (ie. Source connected to summing junction) but with the integrator output ramping up (as its an N-fet)?

Yes, right. What is different is that the MOSFET is an enhancement-mode device, so the gate has to be driven positive to turn it on. To do this, I power the LM311 comparator between Gnd and ~7V. I also use a 1V peak ramp, to reduce slew-rate limitations.

If you try this you might want to buffer the Saw with a TL071 (etc.) and check for excessive ringing at its output. Speeding up the discharge leads to more ringing than in the usual circuit -- make sure this is acceptable in your design. Here's a shot of a pretty good ramp reset taken directly at the integrator output.

Very Happy

Ian


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