[sdiy] Aries modular schematics detail

[houshu at dsp.cl.nec.co.jp]

Hello JH and List,

I was wrong.  JH is right.  Transistor ladder in Quadra phaser is an
almost perfect all pass filter.

I checked my note and analyzed again in the weekend.

First of all, my memory was wrong. What I analyzed was not phaser, but
low pass filter using Quadra style transistor ladder.

Anyway, my analysis results are:

 * LPF based on EMS style diode ladder (EDL) has different transfer
   function (frequency response) from LPF based on Moog style
   transistor ladder (MTL). (Very famous as Grant mentioned.)
 * Quadra style transistor ladder (QTL) can be an all pass filter
   (APF).
 * EDL can not be an all pass filter (APF).
 * MTL can not be an APF.  At least very difficult.
 * (QTL based LPF, which I imagined from Quadra, does not have the
   same transfer function as MTL based LPF nor EDL based LPF.)

I had a very interesting weekend.  Thank you so much.

> Date:    Fri, 18 May 2001 11:32:54 JST
> From:    jhaible at t-online.de (jh.)
> 
> > > I don't think the use of transistors is essential to the design, such as
> the
> > > difference between the Moog transistor ladder and the EMS diode ladder.
> >
> > I agree with you here.  I analyzed the transistor ladder phase shift
> > network using a simple transistor model (voltage controlled current
> > source), and found that it is equivalent to a diode ladder.
> 
> I think I did the same analysis some years ago, but came to different
> results.
> But that's all I remember - I must look it up again.
> 
> 
> > Actually, I suspect that the transistor/diode ladder networks (not
> > Moog complementary transistor ladder for high pass filter) can not be
> > exact phase shifter (all pass filter), because each stage is not
> > isolated.
> 
> If memory serves, *that* was the difference between using diodes and emitter
> followers. Single stage would be the same, but transistors prevent loading
> effects. But as I said, memory is very cloudy here, I must look again.
> 
> Transistor ladder is still no perfect all pass filter, though. That's why
> this
> phaser sounds much better with resonance than without I guess.
> 
> JH.
- -- ---- ----------- --- --- - ----- -- --- --- - - ------ - - - --
 Osamu HOSHUYAMA                    NEC Corporation  Kawasaki JAPAN
--------------------------------------------------------------------