Transistor/Diode Phase Shift = Ladders
Thanks again to Jurgen Haible for publishing his excellent = work. Much =20 additional research could not be carried on without his=20 generosity.
It is possible to make a variation on the Moog ladder filter =
that can =20
be used as a phase shifter. The Aries Model 329 Phase =
Shifter (
The Aries unit is a 10 stage phaser (5 notches, 20 = transistors?). The =20 Tau Systems unit is said to be 20 stages (10 notches, 40=20 transistors?) but has a lot of popcorn noise. I seem to = have lost=20 the Tau schematic, but the Aries unit is much quieter and = has more=20 features. From memory, the current drive sections are = identical,=20 but the Tau unit adds an LFO on the PCB. The Quadra phaser = has 14=20 stages (7 notches, 28 transistors). There is a practical = limit to=20 the total number of stages caused by the intrinsic voltage = drop of=20 the transistor/diode. Assuming 600mv for each diode, there = is=20 probably a practical limit of about 40 stages (20 notches) = using=20 +/-15 volt supply. It is possible noise could become a problem as = =20 the number of stages increases.
The only published information I can find on the actual ladder = topology=20 is contained in Jurgen Haible's phase shifter design = located=20 at:
As an experiment, I tried simulating a couple of sections from = Jurgens =20 design in Electronics Workbench, a SPICE program variant. = This is a=20 second set of simulations with gain set to unity. Thanks = to Don=20 Tillman for pointing out the capacitor value error in the = first=20 set. I thought Jurgen would be amused and the diode only = topology=20 is rather interesting. Opening the collectors increases = the=20 attenuation of the ladder. Connecting the collectors to = the base=20 make no difference under simulation.
The results seem to confirm differences in ladders built from=20 transistors and those from diodes only. Presumably, this = would=20 apply to lowpass topologies also.
Comments are welcomed at
Phase and frequency plots from design simulation most similar = to=20 Jurgen's original ladder, All plots are 20Hz to = 20Khz
=20
Schematic of simulation
=20
Phase Response
=20 Frequency Response
Phase and frequency plots from design simulation with = collectors=20 disconnected, All plots are 20Hz to 20Khz
=20 Schematic of simulation
=20 Phase Response
=20 Frequency Response
Phase and frequency plots, schematic rearranged to show diode = only=20 topology equivalent to open collector, All plots are 20Hz = to=20 20Khz
=20 Schematic of simulation
=20 Phase Response
=20 Frequency Response
Thanks to Mike I. for the Arp Quadra Phaser schematic and = these=20 spectral plots of the Quadra phaser frequency = response
= auxnores.gif
= =20 mainreg-a.gif
= =20 mainreg-b.gif