Echo Base - a new PT2399 delay

[waheng19]

cant find a 47k linear pot at my local electronic store. any replacement suggestions

[jacobyjd]

50k linear?

Or you could use a 100k pot w/ a 100k resistor across it. That would give you a slightly reverse-log 50k pot.

[WhenBoredomPeaks]

cant find a 47k linear pot at my local electronic store. any replacement suggestions

Who the hell specified a 47k pot? That must be a joke.

[slacker]

Who the hell specified a 47k pot? That must be a joke.

I did  it's a standard pot value, or it is my part of the world anyway. I can't help it if you crazy foreigners insist on using 50k instead.

[waheng19]

we'll thanks for the info guys 

[slacker]

Sorry A 50k linear pot will work fine.

[Valoosj]

Ian, is it normal that with a standard echo base with the extra time mod, that you have to set the delay to longer delays when plugging in the power?
If I do not set it to long delays when plugging it in, I get no delay sound whatsoever. I have this problem with both echo bases that I have built.

[Taylor]

Did you put a second 2399 to get extra time, or just a bigger time pot? I did the latter and mine acts very strangely. My stock one is fine, though.

[Valoosj]

I added the extra PT2399. The mod is somewhere around page ten in this thread, with the extra litte pcb.

[slacker]

I don't think you should have to set it before plugging in the power. I haven't looked at that mod schematic for a while though, I'll double check it later just in case there's an error somewhere.

[WhenBoredomPeaks]

Who the hell specified a 47k pot? That must be a joke.

I did  it's a standard pot value, or it is my part of the world anyway. I can't help it if you crazy foreigners insist on using 50k instead.

England and their crazy imperial system.

(j/k )

[Naz Nomad]

England and their crazy imperial system.
(j/k )

That we're no longer allowed to use in public ... 

[slacker]

If I do not set it to long delays when plugging it in, I get no delay sound whatsoever. I have this problem with both echo bases that I have built.

I've had a look at the schematic and the only thing I can think of is that for some reason the 100R on pin 6 is too small a resistance and does something strange to the chip when it's powered on. I take it switching between short and long works once you've powered it up in long mode.
I'd try increasing the 100R to 1k and see if that solves the problem.
I can't help any more than that I'm afraid, I never built it, I think you're the only person who did

[mth5044]

SemiOT, but is it possible to to keep the entire Rebote 2.5 intact, including the 1k resistor, and just flip the time pot from ground to the one end of the 39k resistor and at the same time, just connect the other end of the 39k from pin 4? Then flip the switch that cuts the time put from the 39k to ground, then disconnects pin 4 from the other end of the 39k?

And probably make it 38k?

The reason I ask is I have a project with two seperate pt2399 and would like to have one mod circuit switched between the two of them, and an off position. This would be done on a rotary of course. Is this viable?

[slacker]

Yeah that would work, you can do it even simpler than that though. You can leave the 39k and the emitter of the transistor connected to pin 4 of one of the PT2399s, and just switch the time pot between ground and the other end of the 39k.

[mth5044]

Thanks Slacker, you are fantastic.

[JKowalski]

I have a question.

I am making an echobase-type pedal (not the same design), and I am wanting to add tails but without the digital switching mechanism. However, as soon as I disconnect the path between the buffer and the first PT2399 chip, the repeats go to maximum and clip. I can't seem to figure out why this is happening, and I am just wondering if you experienced the same situation while designing the echo base and have discovered a way to fix this.

It's got rebote 2.5 style filtering, if that helps you visualize it a little better.

[slacker]

I never noticed anything like that, but I designed mine with the switching in place pretty much from the start.
Using the Rebote 2.5 as an exmaple, I think the problem is probably caused by the fact that the 12k and 1uF cap after the buffer are connected to audio ground at pin 7 of the opamp. So the 12k resistor and "red" feedback resistor form a voltage divider, lowering the the volume of the repeats signal. If you just cut the connection, between the buffer and PT2399 you're removing the voltage divider effect which might cause the problem.

I'm not sure how you're doing the switching but if you're breaking the connection between the opamp and the 1uF cap, try putting a pulldown resistor before the cap. That way the resistance to ground will be constant, whether or not the buffer is connected. That will hopefully solve the problem. 

[JKowalski]

I never noticed anything like that, but I designed mine with the switching in place pretty much from the start.
Using the Rebote 2.5 as an exmaple, I think the problem is probably caused by the fact that the 12k and 1uF cap after the buffer are connected to audio ground at pin 7 of the opamp. So the 12k resistor and "red" feedback resistor form a voltage divider, lowering the the volume of the repeats signal. If you just cut the connection, between the buffer and PT2399 you're removing the voltage divider effect which might cause the problem.

I'm not sure how you're doing the switching but if you're breaking the connection between the opamp and the 1uF cap, try putting a pulldown resistor before the cap. That way the resistance to ground will be constant, whether or not the buffer is connected. That will hopefully solve the problem. 

It's just a mechanical switch. Nothing fancy.

I feel like that (grounding the cap) was the first thing I tried when troubleshooting it (This thing has been on my breadboard for a long time, and I just haven't worked on it in a long time... can't remember too well what I did)

Well, no harm trying it again. Maybe I really haven't done it yet.

Regardless, thanks a ton for the reply.

[Valoosj]

If I do not set it to long delays when plugging it in, I get no delay sound whatsoever. I have this problem with both echo bases that I have built.

I've had a look at the schematic and the only thing I can think of is that for some reason the 100R on pin 6 is too small a resistance and does something strange to the chip when it's powered on. I take it switching between short and long works once you've powered it up in long mode.
I'd try increasing the 100R to 1k and see if that solves the problem.
I can't help any more than that I'm afraid, I never built it, I think you're the only person who did

Thanks Ian, it works just fine now.