Doepfer

Hello, 

Most of my system is doepfer, and I'm only joining now.. Shame on me. 

Question: 

Got myself an A-125, which is very efficient with any frequencies within audio range. 
However it's not dealing very well with LFOs (shift is less than 1/4 of the wave cycle). 

Can anyone confirm this behavior? 
Or could the module be a bit faulty (which I doubt)? 

While I'm at it: if the A-125 is not very good to shift LFOs by design, does anyone know if the A-101-3 any better at this kind of sport? 

Thank you very much.

Thanks for the fast answer!

I knew it! I still have to come across a faulty doepfer module. It just doesn't happen, they just work. 

Ok, so does anyone wants to invent a module that would shift LFOs? 

Would be nice to output CVs (any shape, not only sines from quadrature modules), at a desired phase. 



--- In Doepfer_a100@yahoogroups.com, Florian Anwander <fanwander@...> wrote:

>
> Hi
> 
> > Got myself an A-125, which is very efficient with any frequencies
> > within audio range. However it's not dealing very well with LFOs
> > (shift is less than 1/4 of the wave cycle).
> >
> > Can anyone confirm this behavior? Or could the module be a bit faulty
> > (which I doubt)?
> >
> > While I'm at it: if the A-125 is not very good to shift LFOs by
> > design, does anyone know if the A-101-3 any better at this kind of
> > sport?
> 
> The LFO is simply outside the working range of the Phaser. Phasers are 
> in principle filters - so called allpass filters. Though they seem not 
> to filter the signal at all, they have a center frequency. The lowest 
> possible center frequency is higher than your LFO frequency. This is the 
> reason why the LFO is not shifted.
> 
> I assume it would be the same with the A-101-3.
> 
> Florian
> 
> -- 
> http://fa.utfs.org/
>

Changing the determining capacitors... 

Can't it be variable, some kind of "vari-capacitance"?
And put this under CV control as well! 
And a different CV  for stage 1-6  and stage 7-12 of the A-101-3. 

.. I would buy that immediately. 



--- In Doepfer_a100@yahoogroups.com, Bakis Sirros <synth_freak_2000@...> wrote:

>
> so, if i understand it right:
> 
> if you had a phaser module for low (subaudio) frequencies you could create, from (say) a sinewave lfo, 'out of phase' copies of this sinewave? 
> 
> am i right on this? 
> 
> (for example inverted sinewave, 90 degrees and 270 degrees out of phase sinewave, etc...) like a quadrature lfo, but having not only 4 or 8 phases, but many of them? and this phase offset would be voltage controlled...)
> 
> seems nice....
> 
> 
> 
> 
> 
> 
> ________________________________
>  From: Florian Anwander <fanwander@...>
> To: Doepfer_a100@yahoogroups.com 
> Sent: Friday, June 8, 2012 12:40 PM
> Subject: Re: [Doepfer_a100] Re: Low frequencies phase shift with A-125.
>  
> 
> Â  
> Am 08.06.2012 11:12, schrieb ctujoao:
> 
> > Would be nice to output CVs (any shape, not only sines from
> > quadrature modules), at a desired phase.
> 
> Basically it could be doable with a phase shifter too, you only have to
> change the range to a different range for the center frequency.
> Assumingly this can be achieved by simply changing the determining
> capacitors in the circtuit. Dieter might provide a deeper insight in this.
> 
> Florian
> 
> -- 
> http://fa.utfs.org/
> 
>  
> 
> [Non-text portions of this message have been removed]
>

Hi

> Got myself an A-125, which is very efficient with any frequencies
> within audio range. However it's not dealing very well with LFOs
> (shift is less than 1/4 of the wave cycle).
>
> Can anyone confirm this behavior? Or could the module be a bit faulty
> (which I doubt)?
>
> While I'm at it: if the A-125 is not very good to shift LFOs by
> design, does anyone know if the A-101-3 any better at this kind of
> sport?

The LFO is simply outside the working range of the Phaser. Phasers are 
in principle filters - so called allpass filters. Though they seem not 
to filter the signal at all, they have a center frequency. The lowest 
possible center frequency is higher than your LFO frequency. This is the 
reason why the LFO is not shifted.

I assume it would be the same with the A-101-3.

Florian

-- 
http://fa.utfs.org/

Am 08.06.2012 11:12, schrieb ctujoao:

> Would be nice to output CVs (any shape, not only sines from
> quadrature modules), at a desired phase.

Basically it could be doable with a phase shifter too, you only have to
change the range to a different range for the center frequency.
Assumingly this can be achieved by simply changing the determining
capacitors in the circtuit. Dieter might provide a deeper insight in this.

Florian

-- 
http://fa.utfs.org/

Ha! 
Do you think it would be suicidal to have the 2 types of capacitors (10 & 470, for each of the six) under the control of a switch? 
I'm getting excited, now... 


--- In Doepfer_a100@yahoogroups.com, <yahoo@...> wrote:

>
> > > Would be nice to output CVs (any shape, not only sines from
> > > quadrature modules), at a desired phase.
> >
> > Basically it could be doable with a phase shifter too, you only have to
> > change the range to a different range for the center frequency.
> > Assumingly this can be achieved by simply changing the determining
> > capacitors in the circtuit. Dieter might provide a deeper insight in this.
> >
> > Florian
> 
> Right ! One has to change the values of the six capacitors C3, C5, C7, C9,
> C11 and C13. The factory value is 10nF. To obtain LFO range one has to
> increase the values. I'd try 470n or 1u. Pay attention that foil capacitors
> (no electrolytic capacitors) have to be used.
> 
> Best wishes
> Dieter Doepfer
>

so, if i understand it right:

if you had a phaser module for low (subaudio) frequencies you could create, from (say) a sinewave lfo, 'out of phase' copies of this sinewave? 

am i right on this? 

(for example inverted sinewave, 90 degrees and 270 degrees out of phase sinewave, etc...) like a quadrature lfo, but having not only 4 or 8 phases, but many of them? and this phase offset would be voltage controlled...)

seems nice....






________________________________

 From: Florian Anwander <fanwander@mnet-online.de>
To: Doepfer_a100@yahoogroups.com 
Sent: Friday, June 8, 2012 12:40 PM
Subject: Re: [Doepfer_a100] Re: Low frequencies phase shift with A-125.
 

  
Am 08.06.2012 11:12, schrieb ctujoao:

> Would be nice to output CVs (any shape, not only sines from
> quadrature modules), at a desired phase.

Basically it could be doable with a phase shifter too, you only have to
change the range to a different range for the center frequency.
Assumingly this can be achieved by simply changing the determining
capacitors in the circtuit. Dieter might provide a deeper insight in this.

Florian

-- 
http://fa.utfs.org/

 

[Non-text portions of this message have been removed]

What about 6 different switches to mix and match? 
That would give improbable combinations of filtered bands... 
Or each stage is a LP and HP filter, and with certain capacitor values, I might just end up filtering all frequencies at a single stage?



--- In Doepfer_a100@yahoogroups.com, <yahoo@...> wrote:

>
> > Ha!
> > Do you think it would be suicidal to have the 2 types of
> > capacitors (10 & 470, for each of the six) under the control of a switch?
> > I'm getting excited, now...
> 
> That's possible but it will be difficult to find a sitch with 6 layers. The
> wires should be short as possible to avoid additional hum noise. Maybe
> shielded cables are necessary.  One has to try it out.
> 
> Best wishes
> Dieter Doepfer
>

> > Would be nice to output CVs (any shape, not only sines from
> > quadrature modules), at a desired phase.
>
> Basically it could be doable with a phase shifter too, you only have to
> change the range to a different range for the center frequency.
> Assumingly this can be achieved by simply changing the determining
> capacitors in the circtuit. Dieter might provide a deeper insight in this.
>
> Florian

Right ! One has to change the values of the six capacitors C3, C5, C7, C9,
C11 and C13. The factory value is 10nF. To obtain LFO range one has to
increase the values. I'd try 470n or 1u. Pay attention that foil capacitors
(no electrolytic capacitors) have to be used.

Best wishes
Dieter Doepfer

> Changing the determining capacitors...
>
> Can't it be variable, some kind of "vari-capacitance"?
> And put this under CV control as well!
> And a different CV  for stage 1-6  and stage 7-12 of the A-101-3.
>
> .. I would buy that immediately.

One could probably make very much money with the design of a voltage
controlled capacitor VCC :-) This would revolutionize the whole electronics.
I know only such designs in the HF electronics (with capacitors in the pF
range, e.g. with varactor diodes). I don't know any VCC circuit with values
in the 10nF range.

Best wishes
Dieter Doepfer

Hi

> Ha! Do you think it would be suicidal to have the 2 types of
> capacitors (10&  470, for each of the six) under the control of a
> switch? I'm getting excited, now...
You need either a 6-folded mechanical switch or six electronic switches.
Electronic switches like CD405x-Series have a little resistance (~120 
Ohms) in "on"-mode. I cannot judge how much this would affect the effect.
If you want to be on the safe side, then you might use reed relais.

Florian
-- 
http://fa.utfs.org/

> Ha!
> Do you think it would be suicidal to have the 2 types of
> capacitors (10 & 470, for each of the six) under the control of a switch?
> I'm getting excited, now...

That's possible but it will be difficult to find a sitch with 6 layers. The
wires should be short as possible to avoid additional hum noise. Maybe
shielded cables are necessary.  One has to try it out.

Best wishes
Dieter Doepfer

Am 08.06.2012 14:35, schrieb ctujoao:
> What about 6 different switches to mix and match? That would give
> improbable combinations of filtered bands
Nope! That will be ending in a very flat and ineffective sounding phaser.

> ... Or each stage is a LP
> and HP filter, and with certain capacitor values, I might just end up
> filtering all frequencies at a single stage?
again: No. These allpassfilters do not have anything to do with a LP or HP.


Florian

-- 
http://fa.utfs.org/

And now , I'm confused: how do the sweeping notches in the frequency spectrum are created (I'm just referring to the manual)? 
I'm googling like a maniac, but it's less and less clear. 


--- In Doepfer_a100@yahoogroups.com, Florian Anwander <fanwander@...> wrote:

>
> Am 08.06.2012 14:35, schrieb ctujoao:
> > What about 6 different switches to mix and match? That would give
> > improbable combinations of filtered bands
> Nope! That will be ending in a very flat and ineffective sounding phaser.
> 
> > ... Or each stage is a LP
> > and HP filter, and with certain capacitor values, I might just end up
> > filtering all frequencies at a single stage?
> again: No. These allpassfilters do not have anything to do with a LP or HP.
> 
> 
> Florian
> 
> -- 
> http://fa.utfs.org/
>

Thank you very much to make the effort of trying to enlighten ignorants such as
myself.

This is where I'm lost:
What I think I know: the phasing effect is one signal being sent out of phase and mixed with its original version.
Now: isn't the phase shift of this shifted signal, due to the physical effect of passing through some sort of filter (something like notch or BP)?

Then the mix of the two would create some level of interference (destructive or constructive), which are function of the amount of phase shift (and the nature
of the filter used to create the phase shift)... no?


--- In Doepfer_a100@yahoogroups.com, Florian Anwander <fanwander@...> wrote:

>
> Am 08.06.2012 18:05, schrieb ctujoao:
> > And now , I'm confused: how do the sweeping notches in the frequency
> > spectrum are created (I'm just referring to the manual)? I'm googling
> > like a maniac, but it's less and less clear.
> 
> Those created by the phase cancelation, when the phse shifted signal is 
> mixing with the original signal.
> 
> Set the A-125 to zero "resonance" and "mix" fully clockwise (no original 
> signal), sweep the "shift": you don't hear any notch and not 
> phaser-effect at all.
> Now turn the mix back to 12oclock position, but still zero "resonance" 
> and sweep "shift": you will hear the notch now.
> 
> if you add "resonance" you will have also some kind of mix. That is why 
> you hear the notch with resonance and mix fully clockwise.
> 
> 
> To explain in detail this I would need some graphics. Maybe I will do 
> this some other day.
> 
> 
> -- 
> http://fa.utfs.org/
>

Am 08.06.2012 18:05, schrieb ctujoao:
> And now , I'm confused: how do the sweeping notches in the frequency
> spectrum are created (I'm just referring to the manual)? I'm googling
> like a maniac, but it's less and less clear.

Those created by the phase cancelation, when the phse shifted signal is 
mixing with the original signal.

Set the A-125 to zero "resonance" and "mix" fully clockwise (no original 
signal), sweep the "shift": you don't hear any notch and not 
phaser-effect at all.
Now turn the mix back to 12oclock position, but still zero "resonance" 
and sweep "shift": you will hear the notch now.

if you add "resonance" you will have also some kind of mix. That is why 
you hear the notch with resonance and mix fully clockwise.


To explain in detail this I would need some graphics. Maybe I will do 
this some other day.


-- 
http://fa.utfs.org/

Dear sir, you made my day!
I will go to bed a bit less stupid tonight. 
I didn't think trough the filtering of other frequencies, with anything other than all pass. 

Thank you very much for the explanation. 


--- In Doepfer_a100@yahoogroups.com, Florian Anwander <fanwander@...> wrote:

>
> Hello
> 
> > Now: isn't the phase shift of this shifted signal, due to the
> > physical effect of passing through some sort of filter (something
> > like notch or BP)?
> No.
> 
> What we call a "filter circuit" is a circuit which has two 
> characteristics, which are both related to the center frequency, and 
> which change above and below the center frequency.
> 1.) The phase of the output signal in relation to the input signal
> 2.) The level of the out signal in relation to the input signal
> 
> In both cases this is not an abrupt change, but the change starts slowly 
> somewhere below the center frequency and ends somwhere above.
> Both characteristics change at "the same time".
> 
> We know five kinds of filters: Lowpass, Bandpass, Notch, Highpass, and 
> Allpass
> 
> All of them have the phase behaviour in common.
> 
> But only four of them have the level behabviour in common:
> * Lowpass: the output level above the center frequency is less than below
> * Highpass: the output level above the center frequency is more than below
> * Bandpass: the output level around the center frequency is more than 
> below and above
> * Notch: the output level around the center frequency is less than below 
> and above
> 
> The allpass does not change the level, but still changes the phase.
> 
> You could use e.g. a Lowpass also for a phaser, but since there is also 
> this level-thing, the phaser effect would stop soon above the center 
> frequency: one ocatve above the center frequency there is nothing to mix 
> with the input signal anymore - it is filtered away already. Same for 
> all other types of filters. With exception of the allpass: The allpass 
> provides the wonderful phase shift, wothout spoiling the game by muting 
> the shifted frequencies.
> 
> A phaser works only with an allpass - nothing else. But the other way 
> around: a phaser never can be used as a filter.
> 
> Florian
>

Hello

> Now: isn't the phase shift of this shifted signal, due to the
> physical effect of passing through some sort of filter (something
> like notch or BP)?
No.

What we call a "filter circuit" is a circuit which has two 
characteristics, which are both related to the center frequency, and 
which change above and below the center frequency.
1.) The phase of the output signal in relation to the input signal
2.) The level of the out signal in relation to the input signal

In both cases this is not an abrupt change, but the change starts slowly 
somewhere below the center frequency and ends somwhere above.
Both characteristics change at "the same time".

We know five kinds of filters: Lowpass, Bandpass, Notch, Highpass, and 
Allpass

All of them have the phase behaviour in common.

But only four of them have the level behabviour in common:
* Lowpass: the output level above the center frequency is less than below
* Highpass: the output level above the center frequency is more than below
* Bandpass: the output level around the center frequency is more than 
below and above
* Notch: the output level around the center frequency is less than below 
and above

The allpass does not change the level, but still changes the phase.

You could use e.g. a Lowpass also for a phaser, but since there is also 
this level-thing, the phaser effect would stop soon above the center 
frequency: one ocatve above the center frequency there is nothing to mix 
with the input signal anymore - it is filtered away already. Same for 
all other types of filters. With exception of the allpass: The allpass 
provides the wonderful phase shift, wothout spoiling the game by muting 
the shifted frequencies.

A phaser works only with an allpass - nothing else. But the other way 
around: a phaser never can be used as a filter.

Florian

Ok, so I tried the cap modifications (mounted them in parallel with the 10nF ones, straight onto the board): 

=> 470nF=> Efficient phase shifting from around 1kHz, down to 50Hz
=> 1MF... shift efficient down to less than 20Hz, but goes south around 120Hz

I'm staying with 470. 

Thanks guys!


--- In Doepfer_a100@yahoogroups.com, "ctujoao" <ctujoao@...> wrote:

>
> Dear sir, you made my day!
> I will go to bed a bit less stupid tonight. 
> I didn't think trough the filtering of other frequencies, with anything other than all pass. 
> 
> Thank you very much for the explanation. 
> 
> 
> --- In Doepfer_a100@yahoogroups.com, Florian Anwander <fanwander@> wrote:
> >
> > Hello
> > 
> > > Now: isn't the phase shift of this shifted signal, due to the
> > > physical effect of passing through some sort of filter (something
> > > like notch or BP)?
> > No.
> > 
> > What we call a "filter circuit" is a circuit which has two 
> > characteristics, which are both related to the center frequency, and 
> > which change above and below the center frequency.
> > 1.) The phase of the output signal in relation to the input signal
> > 2.) The level of the out signal in relation to the input signal
> > 
> > In both cases this is not an abrupt change, but the change starts slowly 
> > somewhere below the center frequency and ends somwhere above.
> > Both characteristics change at "the same time".
> > 
> > We know five kinds of filters: Lowpass, Bandpass, Notch, Highpass, and 
> > Allpass
> > 
> > All of them have the phase behaviour in common.
> > 
> > But only four of them have the level behabviour in common:
> > * Lowpass: the output level above the center frequency is less than below
> > * Highpass: the output level above the center frequency is more than below
> > * Bandpass: the output level around the center frequency is more than 
> > below and above
> > * Notch: the output level around the center frequency is less than below 
> > and above
> > 
> > The allpass does not change the level, but still changes the phase.
> > 
> > You could use e.g. a Lowpass also for a phaser, but since there is also 
> > this level-thing, the phaser effect would stop soon above the center 
> > frequency: one ocatve above the center frequency there is nothing to mix 
> > with the input signal anymore - it is filtered away already. Same for 
> > all other types of filters. With exception of the allpass: The allpass 
> > provides the wonderful phase shift, wothout spoiling the game by muting 
> > the shifted frequencies.
> > 
> > A phaser works only with an allpass - nothing else. But the other way 
> > around: a phaser never can be used as a filter.
> > 
> > Florian
> >
>