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I'm stumped, is there a way to invert audio signals in 200e?
MUFF WIGGLER Forum Index -> Buchla, EMS & Serge  
Author I'm stumped, is there a way to invert audio signals in 200e?
mritenburg
I'm looking over every 200e module and I cannot find a way to invert an audio signal. Is there some esoteric functionality buried in a module that can invert an audio signal?
Kent
Fuzzy memory here, but:

IIRC the 227e sub-mixer's internal mix bus is reportedly of flipped polarity.

Read this thread for more, dear sir.
rkilman
Kent wrote:
Fuzzy memory here, but:

IIRC the 227e sub-mixer's internal mix bus is reportedly of flipped polarity.

Read this thread for more, dear sir.


That’s a fascinating thread!
mritenburg
rkilman wrote:
Kent wrote:
Fuzzy memory here, but:

IIRC the 227e sub-mixer's internal mix bus is reportedly of flipped polarity.

Read this thread for more, dear sir.


That’s a fascinating thread!


Fascinating indeed!

Seeing that the 292e has two sets of outputs for each channel, I'm wondering how difficult it would be to add passive inverters to one output of each channel? Maybe this is a diy question?
papz
I'm not sure what you mean by "passive inverter".
An opamp-based inverter should do the job and is very easy to DIY.


Both resistors with the same value will give a gain of -1, which is what you want.
Absolute value is not critical, can be 10k, 33k, 100k...
Navs
If the 200e has a ring modulator you can use it to invert your signal. Patch a negative voltage into one side of the mutliplier and your signal to be inverted to the other.
batchas
mritenburg wrote:
I'm wondering how difficult it would be to add passive inverters to one output of each channel? Maybe this is a diy question?

I don't know any other passive solution than using a transformer to invert the signal, but for audio it might no be ok... IMO no guarantee of sound quality. Afaik it's far "better" and not complicated to go active (invert. opamp, FET etc).
Now where to put this is the next question (would need small pcb etc etc).
Yeah... The DIY section might answer your question more accurately.
mritenburg
Navs wrote:
If the 200e has a ring modulator you can use it to invert your signal. Patch a negative voltage into one side of the mutliplier and your signal to be inverted to the other.


200e does have a balanced modulator that can do ring modulation, but the separation of audio from CV in the Buchla system renders this technique impossible. Inverting a CV is easy in Buchla as there are several ways to do it already.

Which brings my next question to mind: could a pair of tinijack-to-banana cables be used to send audio to the 256e for inversion then return the audio to the signal path? Or are the DA/AD or MCU in the 256e too slow/noisy for audio?
Navs
mritenburg wrote:
Navs wrote:
If the 200e has a ring modulator you can use it to invert your signal. Patch a negative voltage into one side of the mutliplier and your signal to be inverted to the other.


200e does have a balanced modulator that can do ring modulation, but the separation of audio from CV in the Buchla system renders this technique impossible. Inverting a CV is easy in Buchla as there are several ways to do it already.

...


Of course. I hadn't considered that. How do Buchla users find this separation - is it of value or a hindrance?
Kent
Navs wrote:
How do Buchla users find this separation - is it of value or a hindrance?


Both. Yet it is easily circumnavigated in many cases (not all) by using a format changer.

The intentional omission of negative voltages in all but the Verbos 254V module does cause one to think harder as to how to achieve certain things.
ersatzplanet
Navs wrote:
If the 200e has a ring modulator you can use it to invert your signal. Patch a negative voltage into one side of the mutliplier and your signal to be inverted to the other.


This also only works if the Ring Modulator is not AC coupled, I don't know the Buchla's are, but seeing how they separate the CV and Audio via jack types, it wouldn't surprise me if it was. Many RM are AC coupled.
Peake
The 106 mixer channels inverted, not sure if the 206 did as well. Buchla said he separated CV from audio because distortion is unimportant to CV signals and IIRC one more reason; it's not a hindrance but as mentioned above there IS a specific mindset in using his designs. Not everything going on in a module is brought to the front panel. Serge went there with patch-programmable modules and a mixture of CV and audio.
Drillionaire
ersatzplanet wrote:
Navs wrote:
If the 200e has a ring modulator you can use it to invert your signal. Patch a negative voltage into one side of the mutliplier and your signal to be inverted to the other.

This also only works if the Ring Modulator is not AC coupled, I don't know the Buchla's are, but seeing how they separate the CV and Audio via jack types, it wouldn't surprise me if it was. Many RM are AC coupled.

The signal input is AC coupled, but the modulator input is not, and is okay to accept a signal within the ±15v power rails. (This is not true for any of the banana CV inputs, and negative voltages should never be applied to CV inputs on a 200e module for risk of damaging the digital components.)
The circuit is designed to accept line level audio present in the buchla standard, so you probably wouldn't need -15v to get a -1 gain signal on the output.
mritenburg
Peake wrote:
The 106 mixer channels inverted, not sure if the 206 did as well. Buchla said he separated CV from audio because distortion is unimportant to CV signals and IIRC one more reason; it's not a hindrance but as mentioned above there IS a specific mindset in using his designs. Not everything going on in a module is brought to the front panel. Serge went there with patch-programmable modules and a mixture of CV and audio.


The other reason, according to the Don was DC offset not being a concern in the audio path where it was a major concern in the Control path.
Peake
That's it, thank you. Couldn't remember it verbatim.
Navs
mritenburg wrote:
The other reason, according to the Don was DC offset not being a concern in the audio path where it was a major concern in the Control path.


Try telling that to anyone attempting dynamic linear FM with 'dirty' signals hihi
Peake
Proportionally unimportant, not entirely unimportant. Audio-rate FM paths on the 258 and 259 are cap coupled. Of course, enough DC offset through a sound system capable of producing a DC output will kill loudspeakers. Or cause the classing thumping in the 2600 mixer to VCA path.
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