Tau Pipe Phaser build. I need a stereo camera....

[Ronan]

Utterly fascinating, I've emailed bridechamber re a pcb and parts kit.

It would be interesting to put an expression pedal on the pitch control, which just happens to be 100k, same as a wah pot.

So it works OK with clean guitar, the input impedance is OK? From the schematic it looks like 100k input impedance give or take a bit, to my untrained eye, which should be OK.

Thanks so much for posting this one Dino.

[digi2t]

Utterly fascinating, I've emailed bridechamber re a pcb and parts kit.

It would be interesting to put an expression pedal on the pitch control, which just happens to be 100k, same as a wah pot.

So it works OK with clean guitar, the input impedance is OK? From the schematic it looks like 100k input impedance give or take a bit, to my untrained eye, which should be OK.

Thanks so much for posting this one Dino.

I`m no genius when it comes to impedance, but one thing that threw me during the build was this document;

http://www.google.ca/url?sa=t&rct=j&q=tau+pipe+phaser+impedance&source=web&cd=3&cad=rja&ved=0CDcQFjAC&url=http%3A%2F%2Fwww.musicsynthesizer.com%2FDiode%2520Phaser%2FInstructions_All.pdf&ei=iJtoULaPKeKQyQGLp4CYDg&usg=AFQjCNH3T4V5y_9GZnEr611JqsEnb1qAeA

Specifcally the «Guitar Input» section. I tried the 2M resistor in the R3 slot, but it oscillated badly. I went back to 100K. It sounds fine with my guitars. If it is 100K, then 10K to 15K going into 100K should be fine, right?

I realize the two circuits are not quite the same, but I figured from the input side of things I would try the 2M, as per the document.

I`m still such a noob when it comes to the finer details of impedance...

[Ronan]

It sounds fine with my guitars. If it is 100K, then 10K to 15K going into 100K should be fine, right?

Yep, should be fine, and your ears are a good judge. Maybe on the borderline for modern guitar pedal practice,  but if it works well then best to leave it alone.

Specifcally the «Guitar Input» section. I tried the 2M resistor in the R3 slot, but it oscillated badly. I went back to 100K.

I realize the two circuits are not quite the same, but I figured from the input side of things I would try the 2M, as per the document.

I see, yes, the JH pcb is slightly different to the original unit on the input stage, so a 910K (instead of 2M) in slot R3 would probably carry out the same intent of the original document, maybe 470K would be safer. The advantage would be higher signal to noise ratio. I don't know if you'd hear the difference or not. It would also boost the output levels 4.7 times if you use a 470K, 9 times if you use a 910K. The document mentioned a resistor on the output to drop the signal level for (say) a guitar amp, but I'm guessing you have pots on the main and aux outputs. The values of R31 and R33 on the outputs, and the values of the output pots themselves could be altered to get the levels right. There could be other hidden traps as well, since there are many parts of the circuit I don't understand. I'll play around with it when I get mine built (assuming I can get a pcb).

All looks good, hope there are still some pcb's in stock.

[jimbeaux]

The two black plastic "blocks" are the two rectangles labeled "PD-10" on the TAU 1190 schematic. They're transistor/diode phase shift ladders and are similar to Jurgen's schematic.

http://www.jhaible.de/tau/jh_tau_sch_page2_allpass.pdf

I'm not sure why they're encapsulated in plastic. Each block had 10 stages of phase shift. The Aries Phase Shifter had one & the Tau "Pipe" had two.



Here's a link with an explanation on transistor/diode phase shift ladders.

http://www.musicsynthesizer.com/Diode%20Phaser/Diode%20Phaser.html

I'm almost through soldering all the parts onto my new board - all I lack is finishing it up  

(Thanks for posting & video - gives me inspiration to get it going!)

[digi2t]

but I'm guessing you have pots on the main and aux outputs. The values of R31 and R33 on the outputs, and the values of the output pots themselves could be altered to get the levels right

By golly Ian, that's right, I do. Input pot as well. I did the "DELUXE" version. Pots on input, and both outputs. I forgot to mention that. 

Damn! You're a Sharpie!

@jimbeaux

Get'er done man! It's a great unit. I've never heard any phaser like it. Thanks for the comparison pic as well! Super cool!

[Ronan]

It might sound even better if you disconnect the input pot completely. It would have no purpose except to attenuate line level signals. If you plan to use line level signals, maybe put a switch on it to disable it for guitar use. A 100K input pot would drop the input impedance to 50K, getting real borderline there.

[digi2t]

It might sound even better if you disconnect the input pot completely. It would have no purpose except to attenuate line level signals. If you plan to use line level signals, maybe put a switch on it to disable it for guitar use. A 100K input pot would drop the input impedance to 50K, getting real borderline there.

I'll try that Ian, and report back.

Thanks dude!

[jimbeaux]

There are a couple of posts at electro-music.com about using a guitar with the Pipe.

http://electro-music.com/forum/topic-18396-275.html

8th & 9th posts.

(for what it's worth - I used a simple preamp (741) ahead of my old unit & didn't have any problems)

[Strategy]

A secret neat thing about Tau with guitar is that it sounds great as a vibrato, its tempting to do the super deep phase on 100% all the time, but you can use the mild pitch shift effect and less depth on LFO to get an almost Roger Mayer Voodoo Vibe sounding effect. Pretty much as close as I've come to a Leslie simulator as I've gotten. Use it on guitar, farfisa and yamaha organs, and fender rhodes as a killer vibe pedal.

strategy

[Ronan]

Thanks for the link jimbeaux! Now I understand, the junction of R2/R3/R4 is a summing node, if R3 is increased the resonance will also be amplified more, unless R4 is also increased, (which could have caused the oscillation you noticed Dino). R4 is already largish, so it becomes a bit of a juggling act. JH suggested using a discrete FET stage. It seems though that the phaser also works fine for guitar just as it is.

[digi2t]

You know guys, I find the vibrato a bit weak for guitar. So, I`m kind of game to try and mess with the input side a bit. This is what I lifted off the electro forum;

In short: If you increase the feedback resistor, you must also increase the resistor that comes from the resonance pot to the same opamp accordingly.
And decrease the 33p capacitor in the feedback loop to something like 10pF.

And don't use a 10k log input level pot with guitars.

OK, ditch the 10K pot? Or maybe up it to 100K or 500K? How about I replace the 1M (R1) with a pot for input volume (just trying to save the pot that`s already there  )? Insofar as resistors are concerned, if I lower the cap to 10p, what would be a decent combo of resistors here?

[Ronan]

I'm not real cluey with electronics, but if it were mine, and I had to keep the input pot, I would change it to 500K (like a guitar volume pot) and run it fully clockwise for guitar.

From what JH said, to get say a x2.2 gain from U1A, double R3 to 220K and double R4 to 470K.

Definitely the 10K input pot will not be helping your guitar sound, your guitar pickups are seeing a 10K input impedance, that is, when you have the guitar directly plugged into the phaser.

Its possible your dirt box has no problem driving the 10K input impedance of the current 10K pot. Also, most pedals without true bypass could also (more than likely) drive the 10K input impedance.

[digi2t]

I'm not real cluey with electronics, but if it were mine, and I had to keep the input pot, I would change it to 500K (like a guitar volume pot) and run it fully clockwise for guitar.

From what JH said, to get say a x2.2 gain from U1A, double R3 to 220K and double R4 to 470K.

Definitely the 10K input pot will not be helping your guitar sound, your guitar pickups are seeing a 10K input impedance, that is, when you have the guitar directly plugged into the phaser.

Its possible your dirt box has no problem driving the 10K input impedance of the current 10K pot. Also, most pedals without true bypass could also (more than likely) drive the 10K input impedance.

Alright Ian, I`ll try that tomorrow, and report back. 

[digi2t]

Well guys, I think Ian was pretty spot on insofar as his guesstimation is concerned. 

Changed R3 to 220K, R4 to 470K, switched C2 to 10pF, and replaced my 10K input pot with a 1M (didn't have a 500K).

Overall, the effect sounds even better now, especially where the vibrato is concerned. It was pretty dull before, but now, while still subtle, cuts through much nicer. If anyone is going to be using this with guitar, then I recommend the mods. Or, for maximum flexibility, take a page out of the Ludwig Phase II, and install two input jacks. One Hi-Z, and and one Lo-Z. I suppose one could use a 9 pin switching jack to do this, and run wires to the board. I'm just thinking out loud here.

Good call Ian. Thanks again!

[Ronan]

Just glad it worked out OK Dino. Will do the same when/if I can get hold of a pcb.

[digi2t]

Just glad it worked out OK Dino. Will do the same when/if I can get hold of a pcb.

I think I'll post the schematics in my Gallery, with notes for guitar use. Make it a bit easier to find.