Doomsdelay Device

[soggybag]

What software was used to create this schematic? I like this style, it's easy to read and prints well. I also like the style of the schematics on Tim Escobedo's site, is that the same?

[DWBH]

Stupid question: we're supposed to connect all the Vr's together, right?

[DWBH]

This afternoon I worked on a pcb for this gadget.
I have some doubts:

• Are U1/U2/U3 and U4 referring to a TL072?
• What is the value of C2, in the delay section?
• All Vr's connect together?
• What does that white arrow, quite similar to the ground symbol mean? It's in the delay time pot, the expression jack and near the 78L05 also....

[Timebutt]

If somebody would make a PCB for this and verify this schematic that would be really interesting!
Go guys!

[slacker]

This afternoon I worked on a pcb for this gadget.
I have some doubts:

• Are U1/U2/U3 and U4 referring to a TL072?

Each one is an opamp, a TLO72 is 2 opamps in one chip so you could use 2 TLO72s or you could use a TLO74 which is 4 opamps in one chip.

• What is the value of C2, in the delay section?

I think it's 0.01uF, that's the value on the PT80 schematic.

• All Vr's connect together?

Yes

• What does that white arrow, quite similar to the ground symbol mean? It's in the delay time pot, the expression jack and near the 78L05 also....

It's a separate digital ground, which is used to reduce the chance of digital noise getting into the audio part of the circuit. You basically connect all those points together and then attach them to ground at one point, normally where you attach the ground wire from the battery or DC jack to the board.

[soggybag]

From what I can tell the final op-amp stage is inverting while the rest of the signal path is non-inverting. I think this last op-amp stage should be switched to a non-inverting arrangement to keep the signal path in phase with the input.

Of course this is my amateur opinion we'll an expert to make the final call.

[Ben N]

It looks to me like only the input stage is non-inverting. The mixer is inverting as a typical virtual ground mixer would be. I'm not sure why the send and return buffers are inverting. Also, I think the return buffer with the diodes would have a gain of less than 1, right? Not sure how you compensate for that, since the effective resistance of the diodes is voltage dependent. Finally, for some major craziness, how about a switchable phase inverter in one of the feedback loop buffers--or would positive feedback be uncontrollable?