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 Forum index » DIY Hardware and Software » Thomas Henry designs
TH’s Quadrature Function Generator sync mod
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funkyfarm



Joined: Jan 21, 2007
Posts: 583
Location: France
Audio files: 3

PostPosted: Wed May 16, 2007 7:54 am    Post subject: another Doepfer rip off Reply with quote  Mark this post and the followings unread

mono-poly wrote:
funkyfarm wrote:
Adam-V wrote:
Doepfer have got a VC Quadrature LFO planned for release in July.
Cheers,
Adam-V

Yep ! but surely with sine waveforms...
maybe the same as Jim Patchell’s VC Quadrature Oscillator ? Wink


I wouldn't be surprised if it would be another Doepfer rip off.


sorry for my english, but what does it mean ?

Doepfer has a genius trick to create triangle waveform ?
it's a fake announcement ?
patchell clone ?
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Dan Lavin



Joined: Nov 09, 2006
Posts: 620
Location: Spring Lake, Mi, USA
Audio files: 21

PostPosted: Wed May 16, 2007 8:37 am    Post subject: Reply with quote  Mark this post and the followings unread

funkyfarm:

He is referring to the accusation some DIYers have against Doepfer: that Doepfer 'copies' designs from the DIY community without permission, royalty payment, etc.

I personally do not know his designs and have no experience with them, so I can not say either way. However, these accusations have been made on a number of forum topics (here and elsewhere). I recently purchased a MKE midi keyboard pcb from him a few months ago, so I am keeping an open mind about it.
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funkyfarm



Joined: Jan 21, 2007
Posts: 583
Location: France
Audio files: 3

PostPosted: Wed May 16, 2007 10:20 am    Post subject: Reply with quote  Mark this post and the followings unread

Ahh...

So, I hope Jim P gonna be rich this time Very Happy

are there only "sine waveforms" available for a VC design ?
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toppobrillo



Joined: Dec 10, 2005
Posts: 766
Location: oakland, ca
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PostPosted: Wed May 16, 2007 5:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
are there only "sine waveforms" available for a VC design ?


you can add this quadrature wave shaping stuff on to any VCLFO circuit with a "triangle" core you find [provided it sweeps from - to +]

i currently have on the breadboard a VC modulator with a complimentary waveform output that can be swept continuously [via VC] through all phase relationships, 0 to 360 [0]..

it becomes a large circuit when you add all the waveshaping for both outputs [12 OP-AMPs!] and is obviously cool, but is it worth the complexity?? i was inspired to try it by the similar virtual module in the G2 demo.

what do you all think? well, i am gonna build it anyways. Wink

josh
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Tim Servo



Joined: Jul 16, 2006
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Location: Silicon Valley
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PostPosted: Wed May 16, 2007 8:50 pm    Post subject: TH’s Quadrature Function Generator sync mod Reply with quote  Mark this post and the followings unread

i currently have on the breadboard a VC modulator with a complimentary waveform output that can be swept continuously [via VC] through all phase relationships, 0 to 360 [0]..

it becomes a large circuit when you add all the waveshaping for both outputs [12 OP-AMPs!] and is obviously cool, but is it worth the complexity?? i was inspired to try it by the similar virtual module in the G2 demo.

what do you all think? well, i am gonna build it anyways. Wink

josh[/quote]

*****************
Hey Josh, is your design continuously variable from 0 to 360, or are you cross-fading between 0, 90, 180, etc? If your design is continuously variable, then that truly is an acheivement! If not, it still sounds very cool. Let us know how it works out when you build it.

Tim (continuously loony) Servo
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funkyfarm



Joined: Jan 21, 2007
Posts: 583
Location: France
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PostPosted: Fri May 18, 2007 3:02 am    Post subject: Reply with quote  Mark this post and the followings unread

can we imagine a circuit that will take any audio (or DC) signals, and shift it to 90, 180, 270 and 360° ?

ONE INUT
FOUR SHIFTED OUTPUTS


for sure TH would have already done it...
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Thomas Henry



Joined: Mar 25, 2007
Posts: 298
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PostPosted: Sun May 20, 2007 3:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Note that the quadrature function generator is truly a function generator, and not an oscillator is the usual sense of the word. This is what makes it so stable with respect to frequency as well as amplitude.

It depends upon having access to the derivative (or negative derivative) of the triangle wave. An outboard unit generally won't give you this free of charge.

On the other hand, a circuit to give quadrature outputs for any sine wave already exists: it's the old all pass filter used in a phase shifter. The trouble is, the four outputs usually don't hit 90 degrees or multiples thereof right on the mark. For example, the phase shifter that will be appearing in An Analog Synthesizer for the 21st Century hit something like 700 degrees total, not 720 degrees if I recall aright.

Anyway, the function generator approach is simpler and more stable than the oscillator approach. But do keep in mind that the Mankato lowpass filter does a pretty good job when put into self-oscillation. Of course, it's considerable more complicated than the function generator method we're discussing here.

For what it's worth, I'm working on a new version of the quadrature function generator at this very moment.

Thomas Henry
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toppobrillo



Joined: Dec 10, 2005
Posts: 766
Location: oakland, ca
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PostPosted: Mon May 21, 2007 12:46 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Hey Josh, is your design continuously variable from 0 to 360, or are you cross-fading between 0, 90, 180, etc? If your design is continuously variable, then that truly is an acheivement! If not, it still sounds very cool. Let us know how it works out when you build it.


yes the compliment moves from 0 to 360- the technique that is used was first described by bernie hutchins, i believe, and is found in your 'sawtooth animator' type circuits.. i've seen a few designs published, elektor and maybe ETI? [i believe the digisound system had one of these modules] if i can find a link to one, i will put it here-

anyhow, this type of circuit only works properly with a sawtooth input- when you apply different offsets at specific times you are able to effectively build a new ramp at any time between resets [of the original signal] the way the offsets are timed in is by way of a comparator that looks at the input and compares it with a [variable] offset voltage.

in the waveform animator circuits i've seen, a few of these "wave multiplier" circuits are fed outputs from a 3-phase LFO circuit and mixed together to simulate the sound of a multi-oscillator synth with pitches slightly detuned to get that phased sound. it's a really cool effect.

the circuit i have been playing with has incorporated this idea with a modulation source in mind- plus all the waveshaping techniques known to mankind Laughing

josh
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funkyfarm



Joined: Jan 21, 2007
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Location: France
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PostPosted: Wed May 30, 2007 5:46 am    Post subject: Reply with quote  Mark this post and the followings unread

Back to the QFG !

LOW SWITCH :
note i've added a switch that puts 680nf in parallel with stock 330nF, for real slow oscillation...

MASTER OFFSET POTENTIOMETER :
I am also about adding an OFFSET stage, with pot and bicolor LED, one common control for all outputs.

The trick is to generate positive or negative offset with a pot, and adding two mixer in order to blend this new voltage with both main output. (0° and 90°)
Then it had to be inverted for the two last outputs.
At least, a single resistor is required for those 180° and 270° outputs (third and forth) to be blended with this new "inverted" signal.

I know it's not clear, but quite missing here. Wink
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Thomas Henry



Joined: Mar 25, 2007
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PostPosted: Wed May 30, 2007 10:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hello all,

I tried, I really tried!

After reading the above messages, I thought I might be able to come up with a new Quadrature VCO based on the 566, 8038 or XR-2206. After three weeks of travail, I can honestly say---it just ain't worth it.

I won't bore you with the details, but essentially I was always able to hit 90% elegance with each of these chips, only to have the remaining 10% fall flat and screw the whole thing up, chip-count-wise.

However, for the DIY-ers out there, note that the VCO-1 (described elsewhere on this Forum) is more or less the same topology as the Quadrature Function Generator as described in my book Build a Better Music Synthesizer. Hence, one should be able to combine the two easily for a voltage controlled Quadrature VCO. I don't think the 566, 8038 or XR-2206 are going to go anywhere in this project. As for sync, what about bridging the timing cap with an MPF-102?

But, I'm sick of this project, so someone else can take it on!

Thomas Henry
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