Doepfer

Hi, this is my first post!
Anyone own a A-196? I was thinking it could be even more flexible if  
an input for the 1-pole lp/slew circuit was added, thoughts?

Yes

--- In Doepfer_a100@yahoogroups.com, Göran Sandström <vektor@...> wrote:

>
> Hi, this is my first post!
> Anyone own a A-196? I was thinking it could be even more flexible if  
> an input for the 1-pole lp/slew circuit was added, thoughts?
>

--- In Doepfer_a100@yahoogroups.com, Göran Sandström <vektor@...> wrote:
>
> Hi, this is my first post!
> Anyone own a A-196? I was thinking it could be even more flexible if  
> an input for the 1-pole lp/slew circuit was added, thoughts?
>

maybe it is a little more flexible, but i'm still not sure if
one would really want to use that simple filter circuit somewhere
else in a patch. the lp filter in the a196 is so basic and simple
that you usually want to replace it with a better one, like the
a171 vc slew. i doubt that a note cv will still make your vco
track correctly after putting it through the a196 lp filter,
so it is not that good for producing glide effects, and using it
as a filter for audio is totally unimpressive. just my 2 cents.

best wishes

ingo

I thought of it more as a means processing the CMP out signal upstream 
of the LPF, for example, coming up with an alternative cmp strategy. I 
suppose if the LPF is just a mini A-171, then one could just bypass 
the entire LPF as you suggest and use the A-171 instead.

I am still mystified as to why the LPF output leads to smooth output 
from the internal VCO, but causes jitter when going to an alternate 
VCO. It's as though the internal VCO has a built in slew or something.

--- In Doepfer_a100@yahoogroups.com, "Doug" <dougc356@...> wrote:
>
> I thought of it more as a means processing the CMP out signal upstream 
> of the LPF, for example, coming up with an alternative cmp strategy. I 
> suppose if the LPF is just a mini A-171, then one could just bypass 
> the entire LPF as you suggest and use the A-171 instead.
> 
> I am still mystified as to why the LPF output leads to smooth output 
> from the internal VCO, but causes jitter when going to an alternate 
> VCO. It's as though the internal VCO has a built in slew or something.
>

hello dough,

i find that the a196 manual explains it quite well.
the phase comparator in the a196 generates a digital
signal, which is used to drive a linear vco.
the lowpass filter is there to smooth out this
digital signal and make it less jumpy, which leads
to a more stable vco output. since other vco's are
controlled in a different way (not by a digital signal,
but a continuous analog voltage), you won't get the same
results with "normal" vco's like a110 or a111. inserting
a lowpass filter at a different position in the pll would
just compromise the function of the module.
somebody please correct me if i'm wrong here.

best wishes

ingo

I was thinking, there should be space for a jack, so why not make it  
so that the slew circuit could be used, so why not? You always need  
another slew limiter!
On Feb 24, 2009, at 13:54:18, selfoscillate wrote:

> --- In Doepfer_a100@yahoogroups.com, "Doug" <dougc356@...> wrote:
> >
> > I thought of it more as a means processing the CMP out signal  
> upstream
> > of the LPF, for example, coming up with an alternative cmp  
> strategy. I
> > suppose if the LPF is just a mini A-171, then one could just bypass
> > the entire LPF as you suggest and use the A-171 instead.
> >
> > I am still mystified as to why the LPF output leads to smooth output
> > from the internal VCO, but causes jitter when going to an alternate
> > VCO. It's as though the internal VCO has a built in slew or  
> something.
> >
>
> hello dough,
>
> i find that the a196 manual explains it quite well.
> the phase comparator in the a196 generates a digital
> signal, which is used to drive a linear vco.
> the lowpass filter is there to smooth out this
> digital signal and make it less jumpy, which leads
> to a more stable vco output. since other vco's are
> controlled in a different way (not by a digital signal,
> but a continuous analog voltage), you won't get the same
> results with "normal" vco's like a110 or a111. inserting
> a lowpass filter at a different position in the pll would
> just compromise the function of the module.
> somebody please correct me if i'm wrong here.
>
> best wishes
>
> ingo
>
>
> 



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

Hi Ingo, so the input to the VCO (the output of the LPF) is digital? 
That would certainly explain it. Not sure how I missed that in the 
manual.

Regarding compromising the function of the PLL, of course I want to 
compromise the function of the PLL! The poor thing is always the 
object of abuse, isn't it?

Doug

> 
> i find that the a196 manual explains it quite well.
> the phase comparator in the a196 generates a digital
> signal, which is used to drive a linear vco.
> the lowpass filter is there to smooth out this
> digital signal and make it less jumpy, which leads
> to a more stable vco output. since other vco's are
> controlled in a different way (not by a digital signal,
> but a continuous analog voltage), you won't get the same
> results with "normal" vco's like a110 or a111. inserting
> a lowpass filter at a different position in the pll would
> just compromise the function of the module.
> somebody please correct me if i'm wrong here.
> 
> best wishes
> 
> ingo
>

> I was thinking, there should be space for a jack, so why not make it
> so that the slew circuit could be used, so why not? You always need
> another slew limiter!

The "low pass" in the A-196 is not a standard passive low pass
(resistor+capacitor) but a "low pass with offset" as recommended in the
74HC4046 data sheet for this application. It does not behave like a standard
6dB low pass or slew limiter. For details please refer to the 74HC4046 data
sheet (e.g. www.nxp.com/acrobat_download/datasheets/74HC_HCT4046A_CNV_2.pdf
page 6 and 27)

Best wishes
Dieter Doepfer

> Regarding compromising the function of the PLL, of course I want to 
> compromise the function of the PLL! The poor thing is always the 
> object of abuse, isn't it?

and in this case the poor thing won't be harmed even by abuse,
so i fully agree  :-)


best wishes

ingo

I don't have the 196, but I did build my own PLL's (discrete but not for musical purposes).
I think the output of the phase comparator is digital, in the sense that it is a square wave generated by digital logic. If the output is of the same frequency as the VCO free running freq (the one set by the offset) then the comparator out is of 50% duty cycle. If the output is higher, the duty cycle is higher (always assuming in lock). If you then lowpass filter this square wave, you'll get a DC voltage (with maybe a little ripple remaining). This voltage is fed back into the VCO.

You can build a PLL in a a100 without an a196. Use a VCO, a ring mod as a phase comparator and slew limiter as LPF. The LPF should be DC coupled, and the cut off frequency much below the normal LPF's. It does not work super good though. I think one of the problems is the slew limiter. A slew limiter is not an LPF, and an LPF should work better for an PLL. 

So I agree with Göran. An input for the LPF would enable the use of the LPF for filtering CV's and it would enable to replace the a196's phase comparator with another (ring mod, for instance). But then, maybe it does not add so much in practise. 

Christophe

--- On Wed, 2/25/09, Doug <dougc356@yahoo.com> wrote:

From: Doug <dougc356@yahoo.com>
Subject: [Doepfer_a100] Re: A-196 lowpass in mod?
To: Doepfer_a100@yahoogroups.com
Date: Wednesday, February 25, 2009, 12:32 AM











    
            Hi Ingo, so the input to the VCO (the output of the LPF) is digital? 

That would certainly explain it. Not sure how I missed that in the 

manual.



Regarding compromising the function of the PLL, of course I want to 

compromise the function of the PLL! The poor thing is always the 

object of abuse, isn't it?



Doug



> 

> i find that the a196 manual explains it quite well.

> the phase comparator in the a196 generates a digital

> signal, which is used to drive a linear vco.

> the lowpass filter is there to smooth out this

> digital signal and make it less jumpy, which leads

> to a more stable vco output. since other vco's are

> controlled in a different way (not by a digital signal,

> but a continuous analog voltage), you won't get the same

> results with "normal" vco's like a110 or a111. inserting

> a lowpass filter at a different position in the pll would

> just compromise the function of the module.

> somebody please correct me if i'm wrong here.

> 

> best wishes

> 

> ingo

>




 

      

    
    
	
	 
	
	








	


	
	


      

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