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TZFM SAW VCO
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frijitz



Joined: May 04, 2007
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PostPosted: Fri Oct 17, 2008 10:21 am    Post subject: Reply with quote  Mark this post and the followings unread

widdly wrote:
I'd like to see some PWM control on there. Then it would really cover a lot of bases...FM, sync and PWM from one VCO.
Hi Widdly --

This is the kind of question we stew about all the time. The main goal is to make a good solid TZ VCO that can be put out at a reasonably low price. Added features will add to the price. A Pulse output is a reasonable feature to think about. But we cannot just keep piling on feature after feature. In the end what we include will depend on how panel space is allocated. If a popular feature would not increase the panel width, then it would probably be worth putting in. We could also put the circuitry on the board and let folks who do their own panels choose whether to populate and connect it. That will depend on how the board layout turns out.

Thanks for your suggestion! We are looking for lots of input like this. Now is the time.

Very Happy

Ian
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Funky40



Joined: Sep 24, 2005
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PostPosted: Fri Oct 17, 2008 1:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
The main goal is to make a good solid TZ VCO that can be put out at a reasonably low price.
Very Happy

Ian

I don't think that a TZ is this thing you should go first for low price.
would you go and look to the price at first when you design a Ferrari ?
Look that it is good to drive Wink


No, don't save on a ZEro !
fine when you can keep the electronics on a somewhat simple level
but don't save on functions.............make it full blown please as long it will be a not too complicated board.

make the Ferrari be a Ferrari and not a Fiat Wink
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jnuaury



Joined: Feb 28, 2008
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PostPosted: Fri Oct 17, 2008 1:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

but is PWM necessary?
it seems like a TZFM waveform converted to a pulse wave wouldnt sound any different than a non-TZ VCO but I am not certain

also, there is a lot of waveshaping circuits you could always use to get a pulse output

Im trying to imagine a 5pulser mangling this VCO......

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Fetafarmer



Joined: Jul 29, 2007
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PostPosted: Fri Oct 17, 2008 3:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:

I'm wondering how to do the Initial Frequency (bias) control. Right now it is just a pot. Would a multiposition switch be preferable? The continuous variability doesn't really seem necessary, although it works fine. Fixed levels would make it easier to to explore different modulation depths and to get back to previously dialed-in sounds, but It would be an additional expense.

Opinions?

Very Happy

Ian


It's hard to say without being able to try it out, but I can't imagine a switch helping all that much in terms of repeatability. And I expect that I'll be looking to this oscillator more for free exploration of timbre, anyhow, with little concern for repeatability. Given that perspective, and the fact that a rotary and pot take up the same general amount of panel space, I'd personally opt for having Initial Frequency/Bias as a pot.

Cheers, and thank you for bringing this into being in the first place,
Kevin
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bridechamber



Joined: Oct 06, 2007
Posts: 64
Location: Saint Paul, MN

PostPosted: Fri Oct 17, 2008 6:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

If bias is just a matter of voltage division, is there a simple, elegant way to give the builder the option of pot OR rotary?

As far as pulse width, etc -- could you use a comparator to get the same pos- and neg-going pulses as the core, and would that sound any harmonically different than a standard VCO's pulse? Please forgive the complete ignorance in that question. Wink
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frijitz



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PostPosted: Fri Oct 17, 2008 8:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
If bias is just a matter of voltage division, is there a simple, elegant way to give the builder the option of pot OR rotary?
Genius! The divider resistors could be soldered onto the switch terminals so that it looks like a pot. You would just need the same size mounting hole. The panel graphics could be general enough to cover both cases. thumleft

Quote:
As far as pulse width, etc -- could you use a comparator to get the same pos- and neg-going pulses as the core, and would that sound any harmonically different than a standard VCO's pulse?
Hmmm... Need to think more about that one. What you are asking would a bit of circuitry. Standard PW/PWM off the regular Saw would be easy and probably quite rich though -- if we have enough panel space.

Very Happy

Ian
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bridechamber



Joined: Oct 06, 2007
Posts: 64
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PostPosted: Fri Oct 17, 2008 10:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

[quote="frijitz"]
Quote:
What you are asking would a bit of circuitry. Standard PW/PWM off the regular Saw would be easy and probably quite rich though -- if we have enough panel space.
Ian


What do we have so far?

Pots:
coarse freq tune
fine freq tune
initial freq
lin FM level
expo FM level
sync level

Jacks:
1v/oct
lin FM
exp FM
sync
saw out
sine out?

If that's where we're at, we have room for a PWM jack, PWM level pot and initial PW pot.
I think there is also room for a dynamic FM VCA. Personally, I think this would be more valuable than PWM. If we need to shave one pot, I'd shave the PWM level pot, and combine that with the initial PW pot (normal the PWM jack to +V).

I guess only one kitchen sink will fit : )

Scott
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Rykhaard



Joined: Sep 02, 2007
Posts: 1290
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PostPosted: Fri Oct 17, 2008 10:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

bridechamber wrote:

As far as pulse width, etc -- could you use a comparator to get the same pos- and neg-going pulses as the core, and would that sound any harmonically different than a standard VCO's pulse? Please forgive the complete ignorance in that question. Wink


Positive and Negative portion width control of a PWM, DOES sound very different. Smile
The later VCOs that I was building the mid 90's, using my dual PW / PWM and Splitwave modification for the VCO's waveforms, allowed modulation of the positive and negative portions of the combined PW waveforms. It produced a harmonic movement that I'd not experienced anywhere else previously.

I'll be following this route again, when I start building my wave shaping modules. Smile (I'm currently Sawtooth only, until I get more VCOs built.)
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Funky40



Joined: Sep 24, 2005
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PostPosted: Sat Oct 18, 2008 12:09 am    Post subject: Reply with quote  Mark this post and the followings unread

jnuaury wrote:
but is PWM necessary?
.

i should mention that my post was not related to PWM.
It's a matter of fact that i allways use the 5Pulser whenever i like to have a Pulsewave running Smile
And i think i never used the pulse out on the zero i must admit

What i like to see is:
two lin FM inputs
A VCA i would not want, because i prefer to use an LPG.
as an option two 1V/oct inputs would be great too
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Luka



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PostPosted: Sat Oct 18, 2008 12:16 am    Post subject: Reply with quote  Mark this post and the followings unread

i think you need a special VCA for these those funky. I remember readin on the cynthia zero osc that it comes with a dedicated VCA to enable some extra range. i could be wrong, it has been a while since ive been over there
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jnuaury



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PostPosted: Sat Oct 18, 2008 2:48 am    Post subject: Reply with quote  Mark this post and the followings unread

im sure the built in VCA wouldnt be after the VCO where you might want a LPG but for the modulation source so the VCA control the "index" or depth of modulation

a lot of FM sounds become more interesting when the depth is controlled dynamically

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phdinfunk



Joined: Jun 04, 2008
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PostPosted: Sat Oct 18, 2008 6:05 am    Post subject: Reply with quote  Mark this post and the followings unread

jnuaury wrote:
im sure the built in VCA wouldnt be after the VCO where you might want a LPG but for the modulation source so the VCA control the "index" or depth of modulation

a lot of FM sounds become more interesting when the depth is controlled dynamically


I'm pretty sure that using an LPG on the FM inputs would be pretty cool. Since we can FM these oscs with anything from a sine to...<?>...well anything. If you're modulating with a sawtooth it would be cool to dial in a little mod with low harmonics and hit it with more harmonics at higher mod levels... I'd personally like the input VCA left off so I can experiment with what I feed it for modulation.

--Jonathan
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phdinfunk



Joined: Jun 04, 2008
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PostPosted: Sat Oct 18, 2008 6:08 am    Post subject: Re: Don't quite comprehend... Reply with quote  Mark this post and the followings unread

"In an analog TZ VCO the frequency is determined by two different input voltages. This is a bit awkward to use, which is one of the reasons I am thinking of using fixed switchable bias levels.

The base frequency of the oscillator is determined by the product of the usual expo current and the dc level at the FM input (called "bias", or "initial"). So lower bias levels require more expo current to get to the same base frequency."

[...]

"It's lots of fun to use! But if you want to make a one-to-one correspondence with your Yammy settings, there is a bit of work involved.

Please let me know if any of this is unclear and I'll try to do better."

I think I basically get it. If I want to do more intense FM, I'll need to set the bias lower, and if I'm donig more subtle FM I'll start with higher settings on the Bias control, and pitch tracking will be better. Is that right?

Does that mean that for each setting of "Bias" there is a range of possible modulation depths?

This seems like a very cool osc to play.

Thanks for this project, Ian.

Jonathan
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phdinfunk



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PostPosted: Sat Oct 18, 2008 6:17 am    Post subject: Reply with quote  Mark this post and the followings unread

"I'm pretty sure that using an LPG on the FM inputs would be pretty cool. Since we can FM these oscs with anything from a sine to...<?>...well anything. If you're modulating with a sawtooth it would be cool to dial in a little mod with low harmonics and hit it with more harmonics at higher mod levels... I'd personally like the input VCA left off so I can experiment with what I feed it for modulation."

On second thought, CV bleedthrough is a huge deal with an FM patch like this since it would pull the patch out of tune, right?

An LPG might be ideal since, where could CV bleedthrough with a Vactrol? (maybe I'm not understanding some possible bleedthrough sources here, so forgive my ignorance)...

Otherwise, maybe we actually DO need a special VCA on the FM input in order to help avoid CV bleedthrough, or perhaps Ian could just reccomend a good VCA design...

Any thoughts?

--Jonathan
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frijitz



Joined: May 04, 2007
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Location: NM USA
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PostPosted: Sat Oct 18, 2008 8:13 am    Post subject: Reply with quote  Mark this post and the followings unread

bridechamber wrote:

What do we have so far?

Pots:
coarse freq tune
fine freq tune
initial freq
lin FM level
expo FM level
sync level

Jacks:
1v/oct
lin FM
exp FM
sync
saw out
sine out?

Scott -- That's pretty close. We actually need all three waveforms out: Saw, Tri and Sin.

Very Happy

Ian
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frijitz



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PostPosted: Sat Oct 18, 2008 8:20 am    Post subject: Reply with quote  Mark this post and the followings unread

Rykhaard wrote:
Positive and Negative portion width control of a PWM, DOES sound very different. Smile
Yes, I'm familiar with that. Laughing

But remember, we would be working with the FMed Saw, so it wouldn't really be like ordinary PW/PWM. Look at the screen shot in the first post and imagine it driving an ordinary PW/PWM circuit.

Very Happy

Ian
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frijitz



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PostPosted: Sat Oct 18, 2008 8:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Luka wrote:
i think you need a special VCA for these those funky.

No, you do not. You can use your LPG or a ring modulator or whatever you like. That's one of the reasons I am leaning away from including a VCA.

Very Happy

Ian
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frijitz



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PostPosted: Sat Oct 18, 2008 8:29 am    Post subject: Reply with quote  Mark this post and the followings unread

phdinfunk wrote:
I'm pretty sure that using an LPG on the FM inputs would be pretty cool. Since we can FM these oscs with anything from a sine to...<?>...well anything. If you're modulating with a sawtooth it would be cool to dial in a little mod with low harmonics and hit it with more harmonics at higher mod levels... I'd personally like the input VCA left off so I can experiment with what I feed it for modulation.

Yeah, that's pretty much how I'm looking at it. But, of course, if we did put it in we'd make sure it could be bypassed.

Very Happy

Ian
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frijitz



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PostPosted: Sat Oct 18, 2008 8:35 am    Post subject: Re: Don't quite comprehend... Reply with quote  Mark this post and the followings unread

phdinfunk wrote:
I think I basically get it. If I want to do more intense FM, I'll need to set the bias lower, and if I'm donig more subtle FM I'll start with higher settings on the Bias control, and pitch tracking will be better. Is that right?

Does that mean that for each setting of "Bias" there is a range of possible modulation depths?

Yep, you got it. With 5V bias you can only go to zero frequency (-5V modulation). With .2V bias you can (roughly speaking) go to 5/.2 = 25 times the base frequency (pos or neg). And so on.

Very Happy

Ian
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frijitz



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PostPosted: Sat Oct 18, 2008 8:58 am    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
bridechamber wrote:

What do we have so far?

Pots:
coarse freq tune
fine freq tune
initial freq
lin FM level
expo FM level
sync level

Jacks:
1v/oct
lin FM
exp FM
sync
saw out
sine out?

Scott -- That's pretty close. We actually need all three waveforms out: Saw, Tri and Sin.


Oooopsie, missed one. We need a switch to select AC or DC coupling for the modulation input.

Ian
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frijitz



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PostPosted: Sat Oct 18, 2008 9:06 am    Post subject: Reply with quote  Mark this post and the followings unread

phdinfunk wrote:
On second thought, CV bleedthrough is a huge deal with an FM patch like this since it would pull the patch out of tune, right?

Good point. CV bleedthrough will indeed contribute to the pitch. But since you are making big dynamic changes in the pitch anyway would this be a big problem in practice? I'll try to play around some with this when I get a chance.

Very Happy

Ian
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frijitz



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PostPosted: Mon Oct 20, 2008 4:49 pm    Post subject: Tracking results. Reply with quote  Mark this post and the followings unread

Here is how the TZ VCO is tracking as of today.

For maximum bias (+/-5 V)
Code:

Octave starting    % error     % error
 at (Hz)           downramp    upramp

25                 +0.2        -0.2
100                --          --
2000               -0.1        --
4000               --          -0.1
8000               +0.1        +0.1
15000              +0.2        +0.1


So tracking to within 0.2% from 25Hz to 30kHz. ( Shocked Can your VCO do this?)

Accuracy decreases at lower bias, because the expo source must supply more current for a given frequency. For a bias of 2V, tracking is better than 1% up to 8kHz. I think this is pretty good, since at high modulation indices you will either want clangorous sounds or will need to use the sync feature.

Very Happy

Ian
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widdly



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PostPosted: Mon Oct 20, 2008 7:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Nice!

I am almost as excited as you are Ian! Laughing

Can't wait to build a few of these.

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



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PostPosted: Tue Oct 21, 2008 7:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Great project!
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loss1234



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PostPosted: Tue Oct 21, 2008 12:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

i am getting sweaty palms i am so excited!!!
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