Phase 90 Build

[ny_racer_xxx]

 I did some testing last night.....

4.2 volts on the Zener, that seems a little low for a 1n5231B  5.1 volt....  I swapped that with another from the same batch, same reading.....

I checked the voltage on the gates, seems to get about a 150 millivolt rise and fall...

I did spend some time f'ing with the bias, and it does sound better.  I left the jack off so I can hear the static (Ghetto Signal Gen) it made it easier to tune the bias.  It sounded the best around 2.00 volts.

I was looking at some info on electrosmash page, if I can see both notches on the scope, then I'm getting full range...

CR

[Seljer]

You can let more current into the zener to get a higher reference voltage. Make the resistor thats between the zener's cathode and the positive supply rail smaller. It'll draw slightly more current but thats not that much of an issue if you're not running it from the battery.

[ny_racer_xxx]

 Looks like a 10k from the original schem, I'll look at that in the AM, thanks....

CR

PS
Maybe drop another 10k across that one and see what I get....

[duck_arse]

you can stick a red led in series with the low-reading zener to jack the voltage by 1V6, as well. but, if you are getting phase with 2V bias ......

[ny_racer_xxx]

 Well, I messed around with the power supply resistor, fried the zener!!!  Put a spare in, back in business.  I didn't mess with it long enough, I must have dropped a short across the resistor, but I did see about 4.4v before it fried...

I started messing with some audio type oscilloscopes, but the one I tried earlier was junk...  I downloaded that visual analyzer, that looks like the shizle!!!  I have to try that one tomorrow.....

CR

[ny_racer_xxx]

 Messed around with that visual analyzer, cool stuff!!!!  It has a nice sine waver generator, and you can also set it to sweep, really bugs the crap out the neighbors!!!!  Didn't get me any closer to a solution though!!!!  I'm having a hard time stabilizing the trace so I can study it, I'll have to come back to it....

In doing some more reading I might have figured out a few things.....  I have TL072's in there and the original were TL062's....  Well the TL062's draw 200 micro amps, and the TL072 draw 1.4 MILLI amps each amp!!!  So 1.4 times 2 equals 2.8 milli amps which equals 2800 micro amps!!!!  14 times what it was designed for.... So maybe that's why he voltage is low at the zener?

I was going to order a selection of Zeners, so maybe I'll toss in some 062's also....

CR

[Seljer]

If you can adjust the bias trimmer to get a phasing sound and the setting that works is not right at the edge of its travel it means it's not the zener diode. I once built a phaser with some jfets that had a very high Vp, combined with a low zener voltage (I had a high power 4.7V zener that was only giving me 3.87V) meant I couldn't bias them at all into a usable area.

The zener diode is used so the circuit holds a constant bias no matter what the supply voltage is (so you don't have to mess with the trimmer as your battery discharges). It's used only for biasing stuff so theres barely and current draw on it.

The low current opamps are mainly good for the LFO where the lower current draw prevents 'ticking' in the audio sections of the circuit )though certain opamps may not want to oscillate). You can go all out high end and use fancier opamps for the phase stages if you wished (e.g. a NE5532 which draws 10mA!)


Build yourself an audio probe http://www.diystompboxes.com/pedals/debug.html and poke through the line of the phasing stages to make sure each one is adding to the total phase shift


Also, make sure you didn't put the PNP transistor in backwards, that'll make you lose a lot of volume (you can verify by measuring the voltages)

[ny_racer_xxx]

 I should be able to scope each stage?  How do I tell if the that stage is going through a phase shift?

CR

[ny_racer_xxx]

I did the audio probe, and I found the 2nd stage sounded much different than the rest (U3 pin7).  It was a lot louder and had some clipping or noise on it.  Checked all the traces around that IC (U3), all looked good, check the resistor for that op amp, that was correct, so a swapped the jfet associated with that stage (Q3), same thing...  Last resort, I swapped the IC, noise went away, volume seems the same as the others.

Definitely sounds better, I still don't think it's giving me a full sweep.  I guess the only way to tell if each stage is adding to the signal, is to socket the jfets as was suggested previously, and pop them out one at a time?

CR