Tonepad Phase 90 Build Troubleshooting

[guitarplayer83]

Ok so I built a tonepad phase 90.  I etched the board myself.  I am not getting any phasing but can make it phase if I move the trim pot.  Its not a phase but fixed filter sound.  Also when the pedal is turned on a very noticeable drop in volume happens to the point I have to turn the amp up to hear anything.  I have double check the board and the soldering 3 times and used a magnifier glass to make sure there were no bridges, cold solder joints etc.  I'm lost.  Here are the specs of what I have measured with my dmm.  Its wired up with true bypass and no led. The bypass signal is fine.   If anything else is needed let me know.  

The only difference is I used .047uf instead of the .05uf and 10uf instead of the 15uf caps.  Also the 500kc pot does nothing when I adjust it.

Power:  9.6 Volt 200ma Wall Wart with correct polarity.

Tl072
IC1                              IC2                            IC3
Pin                              Pin                             Pin
1- 4.9   5-1.4               1-4.9     5 4.8              1-4.9    5-4.8
2-4.9    6-1.2               2-4.9     6-4.9             2-5.1     6-4.9
3-4.9    7-1.4               3-4.8     7-4.9             3-4.8     7-4.9
4-0       8-9.5               4-0        8-9.5             4-0       8-9.5

5.1 Zener Diode=  4.9
1N914 = 9.6

Matched 2N5952
Pin = all 4
1  1.2
2  4.9
3  4.8

2N4125
C-1.0
B-3.5
E-5.0

[guitarplayer83]

anyone?

[Tony Forestiere]

I am no genius, but pins 6 and 7 should "wiggling". Someone correct me.

[R.G.]

I am no genius, but pins 6 and 7 should "wiggling". Someone correct me.

No correction needed. You're right, they should be wiggling.

Also, the voltage on the 2N4125 indicate a problem. the base should be no more than 0.7V more negative than the emitter. This shows 1.5V. Either the measurement is in error, or there is something wrong that will not let these two work properly. This, all by itself can account for not hearing audio in the output.

[guitarplayer83]

What could be the cause of that though.  Im lost I have rechecked everything with the dmm and still come up with the same values. 

[R.G.]

What could be the cause of that though.  Im lost I have rechecked everything with the dmm and still come up with the same values. 

That was a good thing to do - always verify funny looking readings because there is a good chance of measurement errors. At least there is when *I'm* running the meter. 

In general, a bad solder joint, wrong resistor value, incorrect wire, part in the wrong way - the usual suspects.

Could you put in a link to the schematic? The reason I asked for that in "what to do when it doesn't work" is that it make things so much faster and error free for someone who's trying to debug remotely to know they have the actual schematic the builder used, and aren't finding the wrong one by doing their own search.

[guitarplayer83]

here is a link to the pdf from tonepad http://www.tonepad.com/getFile.asp?id=42

[R.G.]

That helps.

From the schematic, the emitter is held at the same voltage as the sources of the JFETs. You report 4.9V on all the sources, but 5.0V on the emitter of the 4125. Using your meter as an ohmmeter, with the power off, what is the resistance between the emitter of the 4125 and the source of each of the JFETs? It should bez zero ohms as nearly as your meter can measure that. The base of the 4125 should be at 4.9V - 0.6V, roughly. It measures 3.5V. Something is pulling it lower than it ought to go if your measurement is correct. The base only connects to three other places: pin 1 of IC1, pin 7 of IC2, and the collector. All of these are through 150K resistors.

The pins of the ICs are at 4.9V. So they are not dragging the base down. They would pull it to a higher voltage. It must be the collector. The collector of the 2N4125 measures 1V, so it could be pulling the base lower.

On the other hand, pulling the base lower should cause the amplification of the 4125 to allow more current into the collector and raise the collector voltage so it does not pull the base so low.

That tells me that the 4125 is not amplifying correctly. It is possible that it's inserted backwards, or that there are bad connections, wrong part values, bad soldering, etc. on this part.

Have you checked the pinout of the 2N4125 you're using against the datasheet and against the board layout for which pin goes into which hole?

[guitarplayer83]

Well i measured the base and source and its not zero ohms.  my dmm gave me a reading of 164.6 using the 200k ohm setting.  I don't know whats going on.  I will try to get a picture of the board and post it in a little bit when I have somemore time.  Thanks

[Govmnt_Lacky]

Well i measured the base and source and its not zero ohms.  my dmm gave me a reading of 164.6 using the 200k ohm setting.  I don't know whats going on.  I will try to get a picture of the board and post it in a little bit when I have somemore time.  Thanks

Are you SURE that you didn't mistake one of your 150K resistors with a 150 ohm resistor. You should double check ALL of your component values and placements.

Good Luck 

[guitarplayer83]

I got it working.  After checking everything again and going through the color codes on the resistors.  I found that Tayda Electronics sent me 470 instead of 470k,  they lable them correct but sent the wrong ones.  So after a trip to radioshack and some 470k resistors in place it fires up. I have to get a new 4125 one of the legs broke so I threw in a 2n3904 just to fire the pedal, and it works. Thanks for the help.

[R.G.]

Hey! Great! It had to be something like that.

What people have a hard time understanding is that electronics is deterministic. If you hook up the right value parts in the right connections, and feed it the right power, it **will** work. Mother Nature is incredibly picky that everything has to be right, but after that She forces it to work. That's so consistent that if it doesn't work, there *is* something that's either out of spec or hooked up wrong.

Good work.

[rockguitar77]

  Hi,
When I turn on the guitar pedal the Diode 1n914 burns and glows. And when I press the on switch it picks it radio signal. But when I switch it again it have guitar sound. But no phase. Please help. also the doide was smoking. i was confused about the wiring. i used http://www.tonepad.com/getFile.asp?id=76 digram 5.
on the input is the diagram properly lableled with the postion on the 3 metal parts on the diagram matchign the input jack?

[CurtisWCole]

My original post sucked...never mind.

[PRR]

> When I turn on the guitar pedal the Diode 1n914 burns and glows

Polarity is backward. Either your battery (power supply) or this diode.

You need to replace the smoked diode. Use 1N4007. It is typically the same price and much more rugged.

Get the diode pointing the right way. If you are using the TonePad Phase 90 PCB, the stripe goes toward the center of the board.