[sdiy] Aries modular schematics detail

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

Hello Grant,

> Date:    Mon, 14 May 2001 16:06:22 JST
> From:    Grant Richter <grichter at asapnet.net>
> > The ladder topology is the same as that used in the
> > ARP Quadra 14-stage phaser, where it is implemented with transistor
> > array IC's instead of discrete transistors.
> 
> OK, WHERE is that Arp Quadra schematic link again?
> 
> I'm rummaging through all my stuff and can't find it.

Quadra phaser clone is available at JH's schematics page.

http://home.debitel.net/user/jhaible/additional_schemos.html

> 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 the sound differences should be in the I/O structures and not the
> semiconductor? 

I guess type of distortion could be different, because mutual
influence between phase shift stages is opposite.  But, the difference
in distortion may be cancelled out in diff amp.  Nonlinear analysis is
not easy for me.

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. Frequency range where approximation is sufficiently close is
limited, and amount of phase shift in each stage is small. I guess
that's the reason so many phase shift stages (10 to 14) are used in
this type of phasers.   (Maybe I'm wrong.)

I hope you understand my English.

> The EMS Hi-Fli used a phase shifter made from diodes parallel
> connected with capacitors. And is the Hi-Fli schematic anywhere on the web?
> 
> Would anyone be willing to comment on differences between a diode and
> transistor used as a current variable AC impedance?
> 
> About a year ago, I started a web page about this phaser topology, I have
> the AR-329 schematic scanned in, and am looking for the Tau Systems
> schematic (I had it around here somewhere), Hi-Fli schematic and Quadra
> schematic (or links to already posted schematics). This is just for fun and
> has no connection with Wiard. Perhaps as many as 5 people on this list would
> find it interesting to compare the different implementations.

It'll be very interesting for me.  If I were good at English.... ;-)

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 Osamu HOSHUYAMA                    NEC Corporation  Kawasaki JAPAN
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