Maestro - PS-1A Phase Shifter (197x)

Post by **modman** » 01 Jan 2008, 23:07

Here's some background info, don't know about accuracy though:

http://www.wingspreadrecords.com/maestro_ps1_page.html

Discofreq links to a schemo :
http://filters.muziq.be/model/maestro/ps1a

oberheim_ps-1.pdf: (16.65 KiB) Downloaded 165 times

BJF · Post by **BJF** » 03 Jan 2008, 02:25

modman wrote:Here's some background info, don't know about accuracy though:

http://www.wingspreadrecords.com/maestro_ps1_page.html

Discofreq links to a schemo :
http://filters.muziq.be/model/maestro/ps1a

Hi

The schematic is correct. I have serviced one of those.

A good pedal more for keyboard players than guitarists

Have fun
BJ

vanessa · Post by **vanessa** » 03 Jan 2008, 03:29

BJF wrote: Hi

The schematic is correct. I have serviced one of those.

A good pedal more for keyboard players than guitarists

Have fun
BJ

With stomp switches it's up there as one of the best phase shifters for guitar I've come across. You are right though with the rocker switches it's not that accessible for guitarists.

Mayniac · Post by **Mayniac** » 03 Jan 2008, 03:42

modman wrote:Here's some background info, don't know about accuracy though:

http://www.wingspreadrecords.com/maestro_ps1_page.html

Discofreq links to a schemo :
http://filters.muziq.be/model/maestro/ps1a

Based on the drawing style, the schematic appears to be drawn by R.G. Keen. Hence, I think it's pretty safe to say that's it's accurate...

analogguru · Post by **analogguru** » 03 Jan 2008, 07:57

I believe the original factory schematic could be inside this fle:
http://hammer.ampage.org/files/Maestroworld.zip

analogguru

pandadandan · Post by **pandadandan** » 03 Sep 2008, 15:59

Are there any layouts or pcbs for this? It seems like a fun project!

nelson · Post by **nelson** » 03 Sep 2008, 17:13

vanessa wrote:
BJF wrote: Hi

The schematic is correct. I have serviced one of those.

A good pedal more for keyboard players than guitarists

Have fun
BJ
With stomp switches it's up there as one of the best phase shifters for guitar I've come across. You are right though with the rocker switches it's not that accessible for guitarists.

This is probably due to the higher headroom +/- 15v supply and the Voltage controlled sine wave LFO.

Other than that it might as well be a phase 90.

This could probably be built rather stomp friendly by replacing the Bipolar 15v power supply with an LT1054 charge pumped +30v supply with a buffered voltage divider virtual ground. I would also replace the fast and slow phase switches with a single 1M pot and make the osc amplitude trim an external depth control.

Professor SourTone · Post by **Professor SourTone** » 04 Sep 2008, 10:11

There's a company that makes a replacement for the original 3-way Maestro footswitch. I ordered one and it works fine.

Bernardduur · Post by **Bernardduur** » 13 Jan 2009, 13:33

Hey all!

Just got one in for repair as it doesn't do anything....... turned out to be the FET switching the phaser on and off. When I A/B'ed it with the schematic I already had I noticed some small differences between the schematic and mine

Factory schematic

My unit

I replaced some values as they were not readable on the factory schematic but the biggest differences:
- no 100k parallel to the FET to ground
- no output offset but a 2.4M resistor to -12V

(the traces are there, just not filled)

Would the unit benefit from these missing components?

Photo's follow!

tictac · Post by **tictac** » 13 Jan 2009, 15:32

The biggest improvement you can make is to replace those trimmers with some 10 turn trimpots. It really helps to dial your tone and waveform in. The 2M resistor can be replaced with a 2 Meg pot. I think it is a manual speed control for the fastest phase setting. The preset settings seem to be the most useful tones but it's nice to have that adjustment and easy to do.

TT

Bernardduur · Post by **Bernardduur** » 14 Jan 2009, 11:17

Pic 1
Pic 2
Pic 3
Pic 4

Better follow

What should be a good replacement for Q8 (2N4303)??? I tried several N channel FET's but all fail to switch

@ Tictac; thanks! Only I talk about another 2M resistor that is on the output of the phase circuit, not the one on the schematic in the LFO as there is no 2M on that place in my unit.

analogguru · Post by **analogguru** » 14 Jan 2009, 11:55

Bernardduur wrote: What should be a good replacement for Q8 (2N4303)??? I tried several N channel FET's but all fail to switch

Did you try 2N5952 or 2N5458 ?

analogguru

Bernardduur · Post by **Bernardduur** » 14 Jan 2009, 12:12

Yes! I tried both and no switching.

I measure -4.07V when the switch is off, 1.72V when it is on

analogguru · Post by **analogguru** » 14 Jan 2009, 12:24

What are the voltages at:
the emitter of Q7
the source of Q8
the gate of Q8

analogguru

Bernardduur · Post by **Bernardduur** » 14 Jan 2009, 14:14

analogguru wrote:What are the voltages at:
the emitter of Q7
the source of Q8
the gate of Q8

analogguru

Emitter Q7 = -0.16V

source Q8 = 5.36V -> 5.55V (during phase cycle)
drain Q8 = 0.51V

All voltages with a BF245A in the FET's place

Bernardduur · Post by **Bernardduur** » 09 Feb 2009, 22:34

Any idea's??? I'm running out of FET's to test

theehman · Post by **theehman** » 10 Feb 2009, 19:27

http://www.synthfool.com/store/product_ ... c2b8706ceb

Bernardduur · Post by **Bernardduur** » 10 Feb 2009, 22:18

Thanks man!!!!!!!!!

Today I found an old MPF102 under the couch; popped it in and it works...........

as you can see; best things can be found under your couch!

Bernardduur · Post by **Bernardduur** » 11 Feb 2009, 12:27

Hmmm, tried to tweak her and she sounds ok.......... not great. The phase sound is far away, not really thick. Turning the trimpots do something but the right settings gives loud pops......

I guess I'll change the ELCO's in the unit and add some new trimpots (they look really old).

Bernardduur · Post by **Bernardduur** » 24 Feb 2009, 20:03

Small update:

The FET did not do the trick completely. It makes the pedal works for 20% or so..... that's why it sounded so bad. ELCO change made the unit sound a lot better btw...........

Talked to the owner and I'm gonna make her TB with a relais that is switched by the first switch; this also cures the huge tone suck this pedal has when it is off