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Alrighty, threw this together with some 2N5458, and a 5.1v zener. As is, I'm getting distorted noise with no phasing.....

The LFO is working and I can hear the ticking in the background, changing with the speed pot.

My FETs are matched within .002v with Rob Strand's FET matcher. Pretty sure I've got the pinout right and in the right holes on the pcb. But if I reverse them I get the same sound, so who knows......

Any ideas where to look? IC's have power....I can follow the signal all the way through the circuit with an audio probe...

Thanks,
Michael

Just look where it distorts with your probe. then look around that part for any errors you may have made, or maybe you need to replace something...

Fets socketed?
Which ICs?
Vr is correct?
Diode polarity?
Which schem?

Regards

RDV

Could someone give some IC voltages? So I can compare.....

IC's are TL072s....

Thanks, Michael

Michael, doesn't that use a 4.7 Zener? I don't know if that would matter. Nothing happening when you adjust the trimpot? If you remember RDV's build, discovered the tranny pinout was backward.

Yeah FP's says to use a 4.1V zener, but another says to use a 5.1v. I had a 5.1v so i figured it would be ok.

I can't seem to get a steady voltage to any of the pins except the power pins. Is this normal? On my Small Stone and Phaseur Fluer, I can read steady voltages, but not on this one.....

The voltage that goes to the opamps, the rail that the zener is connected to measeures ~1.5v. Is this about right? I thought it should be about half the voltage of the battery?

I'm pretty sure of the pinouts.....As it is now though, I get the same sounds no matter which way the FET is orientated.....

Also, the trimpot I made a chassis mount pot, and near as I can tell it does absolutley nothing...

So it's still just distorted sounds so far...

Thanks Michael

Quote from: Michael Allen
Also, the trimpot I made a chassis mount pot, and near as I can tell it does absolutley nothing...

That's definately not right. The trimpot adjusts the bias of the FET's. Normally, it has only a small range where it phases (inside that is the sweet spot), and the rest of the range obliterates the phasing. Maybe your particular FET's need a lower value zener. Sounds like a biasing problem.

Alright I'm making progress. Sorta....

I was tracing this through with the audio probe and took out the second IC. I get good signal off of pin 1 so I plug back in the second IC. HOLY COW! Wild siren screeching! The speed pot obviously affects the speed, and the bias is now working. It affects the pitch of this screech. So now i shut off the battery and then plug it back in. And it goes back to the same distorted signal, with no phase.....

So by plugging the battery on and off, and taking the second ic out and in, I occasionally get this wild siren noise and the Vr will be ~4v.

This is the only noise that i get, the signal passes through but without any phase. Only the siren, which i can hear even on the power rail.

I'm pretty certain now that the FETs are orientated right. With one FET in I get a steady screech, and with both FETs in it turns into an oscillating siren.

Man, I'm baffeled..... But the bias is working....

Thanks all,
Michael

QuoteThe voltage that goes to the opamps, the rail that the zener is connected to measeures ~1.5v. Is this about right?

The rail that the Zener (-) is connected to should sit virtually at the Zener voltage (5.1V) since it has a much smaller bias resister (10k) than anything else hanging off that rail.  Is the diode connected the right way around??

good luck

Yeah, the Zener is in the right way....

Still have no idea what to do...

Thanks again,
Michael

Quote from: Michael AllenYeah, the Zener is in the right way....
Still have no idea what to do...

What PCB is this? Did you do your own layout, or is it Tonepad's. You have a layout, or wiring problem or both.

Regards

RDV

I'm confused, earlier, you mentioned that you chassis mounted the trimpot. Later, when I asked about it not having an effect when you adjusted it, you mentioned the speedpot. They are not the same. Without the bias properly set by the trimpot, the speed control is useless. If it doesnt turn out to be a connection or solder trace problem, it sounds like a bias problem.

Nope nope, the bias has an affect the whole rotation.  The siren phasing continues no matter where the bias is at. The only thing the bias does is to change the pitch from really high, to a deep growl. I switched out the TL072's for some 4558's and the bias had a more pronounced control. As it was turned it sounded like the sound was being squeezed down. So I'm pretty sure the pot is working correctly.

The LFO is working and changes the speed of the siren. The speed and bias pots work all the time, regardless of the position of the other.

Getting closer here.....

anyone?

You never said which layout, or schematic. There's a good chance if you did the layout yourself that you made a mistake. The Tonepad layout has the op-amps little cutout facing each other.

Regards

RDV

This is FP's layout, stock with no mods....

This is FP's layout, stock with no mods....

Can anyone measure some voltages for me?

I just built that one. I'll do it for you. I'll try to get to it within the next couple of hours.

Regards

RDV

Okay, here goes:

IC1:
1. 3.52v
2. 3.52v
3. 3.52v
4. 0.1mv(ground)
5. 3.37v
6. 3.52v
7. 3.52v
8. 9.73v

IC2:
1. 3.53v
2. 4.6 to 5.35v(oscillating)
3. 4.32 to 5.41v(oscillating)
4. 0.1mv(ground)
5. 3.52v
6. 3.53v
7. 3.53v
8. 9.73v

Q1. D 3.52v
     S 3.52v
     G 3.52v

Q2 D 1.35v
    S 3.52v
    G 3.52v

Zener Cathode(striped) end: 3.52v
         Anode end: 0v

Hope this helps

RDV

Ok. I'm pretty sure you guys are right about the bias. My voltages are similar to yours but about 2v lower. My bias voltage is messed up. The Zener I used was a quick fix from Radio Shack. I'll try the other one (pack of 2) but can I replace it with a resistor in order to bring it to the right voltage? If so, what value will do? THanks a lot....

Michael

No subbing. A zener is a diode, not a resistor. Should be 4.7v, not 4.1 or 5.1.  Stock build off of tonepad? That means you have a 500k pot (speed) mounted on the outside of the box, and a little 250k trimmer pot soldered directly on the circuit board, correct?

Yes, I know what the zener is, but I see that the purpose is to bring the bias down to a certain voltage...correct? This is possible with resistors so I wondered if it could be done....

Yes I have a 500k speed pot. And no it is not a trimmer. I didn't have a trimmer so I used a regular 250k potentiometer.

Ok, I no longer think the bias is the problem. When I take the second IC out the bias and voltages of the first IC pins are at acceptable values. But here's where it gets crazy..... When I test for continuity between the IC pins, Pins 6 and 7 have continuity with pin 8, not with each other and pin 7 has continuity with pin 1. When I unplug the battery there is no longer continuity between any pins. AHH? EH? No entiendo.....

Any ideas?

Thanks a lot for all the help!!
Michael

Where are you setting the 250k when you take your measurements? Middle is about good.

I think your second IC is in backwards. When in, they should face each other head on. Little Dot to Little Dot.

Regards

RDV

yeah......

I realize that I sound a bit forlorn here, but just to clarify I'm not exactly a beginner. I realize you guys are trying to help (and God knows I appreciate it! :) ) but when it comes down to the basics, I've got it covered.... I do make mistakes however!

I think I've got a fuzzed out problem somewhere along the line. Also my PCB was pretty scraggly and i might have some itermittent traces. I think i'll start over with a new board...

Thanks,
Michael

I said about the Ic being backwards cause you said you got better voltage on one when you pulled the other out. Let us know how it goes when you make another PCB. I think it will work with the 5.1v zener, but I'd like to know if it doesn't also. I did it the easy way by ordering the PCB.

Regards

RDV