Help! I want to Build A Maestro Phase Shifter...where to get the parts...?

[charlesdbruce]

I want to building a Maestro MPS-2 but can't seem to locate some of the components because they're not manufactured any longer.  Specifically...
Operational Amplifier with part number SN72741
Transistor with a part number 2N4303
Transistor with a part number TIS97

How do I find substitutions for these?

Thanks in advance for any help you can provide.

[nickbungus]

Can you please provide a schematic?

[Aph]

Welcome, Charles.



SN72741 = 741 opamp. Could use dual or quad opamps, too (RC4558, TL072, TL062, TL074,  TL064)
2N4303 = N-channel FET transistor (J201, 2N5457, etc)
TIS97 = NPN transistor (2N3904, etc)

Parts:

https://diystompboxes.com/zencart/
http://www.smallbear-electronics.mybigcommerce.com/

[thermionix]

The bigger challenge will be scoring enough JFETs to match four of them.

This method has worked well for me:

http://www.geofex.com/article_folders/fetmatch/fetmatch.htm

[Aph]

The bigger challenge will be scoring enough JFETs to match four of them.

This method has worked well for me:

http://www.geofex.com/article_folders/fetmatch/fetmatch.htm

Just curious, have you tried runoffgroove's tester? Just uses 2 resistors and a switch.

[charlesdbruce]

Thanks for the help!  I'm now a little apprehensive though... with all this discussion about matching components.  I don't have *any* background in electronics (I took Circuits 1&2 in college for my ME degree - all is long forgotten).  I was hoping I could just make the circuit on a bread board with the various components, test it, then muddle my way through some free software to make a PCB and go from there.  I was going to start with this phase shifter but I was ultimately going to try to make a Maestro PS-1b later.

You guys have scared me a little... :-)

[Aph]

You could always breadboard it and try different combinations of FET's.
Small Bear sells matched FET's. http://www.smallbear-electronics.mybigcommerce.com/transistors-fets-mosfets-1/
Or, you could make a phaser that does not need matched parts: http://www.runoffgroove.com/tri-vibe.html
No reason to be apprehensive 

[charlesdbruce]

Thanks... I think I'll try that... I'll post my progress over the forthcoming months (it will be months... as this will just be a little side activity).

Cheers!

[Aph]

  Great!

[nickbungus]

J112s for the fets are really cheap and I've had success using them in phasers.

I use this to match

[thermionix]

The bigger challenge will be scoring enough JFETs to match four of them.

This method has worked well for me:

http://www.geofex.com/article_folders/fetmatch/fetmatch.htm

Just curious, have you tried runoffgroove's tester? Just uses 2 resistors and a switch.

I've built it, but haven't used it for matching anything yet.  Very limited knowledge on such things here, but I think the Geofex method was developed for phaser circuits specifically.  And I don't understand how Vp and Idss relate to VgsOFF.  All I know is my Phase 90 sounds perfect!  It's one of very few pedals that I haven't changed at all since building.  I haven't even dared to touch the trimpot since the initial quick setting.

[thermionix]

I've built it

Actually, scratch that.  I built the "Greatly Improved JFET Matcher II" from nickbungus' link.  Two resistors, a cap, and a switch.  Two switches on mine, I guess I added battery on/off (it's been a while).

[PRR]

> I don't understand how Vp and Idss relate to VgsOFF.

"Vp" and "Vgs(OFF)" are about the same thing. How much Gate voltage is needed to turn (approximately) OFF.

Idss is the other end of the working zone. When Vgs is zero, how much current flows?

My dogs attack you. Idss is how big a chunk of you each can pass through the throat: Corgi a finger, Pyr a hand. Vp or Vgs(off)  is how hard you have to choke them to allow 'none of you' to go through throat: 5 pounds for Corgi, 20lbs for Pyr. In a given species the two values may be somewhat related: big throats pass bigger food and are harder to choke. However a critter could be re-designed with a large weak throat (sea anemone) or small strong throat (snake).

Stephen King‏ writes:
Molly {Corgi}, aka the Thing of Evil, turns four. As a special treat, we gave her a postman for dinner.

[thermionix]

Thanks Paul.  So, for a Phase 90 type circuit, is there any need to match Idss?  Should both Idss and Vp be matched?  Would matching only Vp yield the same results as matching only VgsOFF?

[PRR]

You want both. You want 4 or 8 dogs with similar throat-size and choke-force.

I may have to walk-back that bit about VP. Someone will clarify my fog.

[Tony Forestiere]

My dogs attack you. Idss is how big a chunk of you each can pass through the throat: Corgi a finger, Pyr a hand. Vp or Vgs(off)  is how hard you have to choke them to allow 'none of you' to go through throat: 5 pounds for Corgi, 20lbs for Pyr. In a given species the two values may be somewhat related: big throats pass bigger food and are harder to choke. However a critter could be re-designed with a large weak throat (sea anemone) or small strong throat (snake).

Paul's analogies continue to fascinate me. Dogs as FETs. Wow.  The Gate is the throat. Not liking the doggie teeth aspect for the Source.

[smallbearelec]

I would not have suggested a four-stage phaser as a first project...too many components, and therefore too many ways to screw up and get frustrated. However, you seem interested and determined, so a suggestion:

Rather than mess with a schem that requires a lot of obsolete parts, take a look at the schem for the Phase 90 at Tonepad.com. It's also a four-stage op-amp- and JFET-based phaser, but all of the parts are still more-or-less current and in stock at my store and others. Also, the Tonepad PCB is available if you want a ready-to-solder board.

The 2N5952 that Tonepad suggests is a good number for matching. It usually takes eight or 10 raw parts to yield a quartet, or you can order matched.

Happy Construction!
SD

[Tony Forestiere]

However a critter could be re-designed with a large weak throat (sea anemone) or small strong throat (snake).

I completely missed this gem! "Critter" is the FET, and the design of the surrounding circuitry controls , Ummmm...control?

[pinkjimiphoton]

i've had one of these suckers on my bench for a while now. lfo seems to work, as i get voltage sweeps. passes audio. i can't tell if its on or off tho, i cannot get it to phase. maddening. i replaced all the electros on the board with fresh ones, the only thing i can think of is the pot or switch. all 4 stages read the same <last i checked, anyways> so assume they are working.

any ideas? would be appreciated

[diffeq]

any ideas? would be appreciated

My line of thinking: phasing occurs when you mix input signal with shifted signal, so if it sounds clean, shifting stage output is not getting through (busted S1 switch, or a short somewhere between IC4 and S1). Maybe probing from 2.2K/43K output junction both ways would show where the problems is. Maybe one of the stages is clogging up.