Simple Tails mod for delays.

[madbean]

As I mentioned before, the mechanical noise of the 3PDT is at fault here. If using an SPDT just for the tails, I found no switching noise at all. For the tails/TB mod, this pop may not be able to be removed.

One possible idea is to place a huge resistor between 9v and the "Tails" lug on the 3PDT. Like 10 or 20 meg. Can't say for sure

[midwayfair]

....
bugger.

I know how to do the tails so that it won't pop (and doesn't use the FET), but it won't light the LED at the same time. Not enough lugs.

[madbean]

Yeah, you could probably do just an SPST in place of the decoupling cap if you don't care about the LED.

Hmm--maybe the SPDT with some kind of millenium bypass?

[midwayfair]

You need to reference the delay side to Vb to avoid DC offset (the delay is 2.4v, the op amp is 4.5v) when simply shunting the connection to the decoupling cap. Otherwise it'll still pop. I actually suspect that's part of what's going on here, rather than mechanical noise. The voltage to the delay line is jumping pretty suddenly.

Maybe there's some solution there I'm not thinking of. Do we have enough poles between a SPDT and 3PDT (toggle) to go between millenium and tails? I can't wrap my head around it.

A 4PDT stomp would have enough poles to do the simple tails bypass + LED ... Tayda has them.

[madbean]

Yes, I see you point. Perhaps a 1M resistor from the source to VB would be the way to go? That way both sides of the transistor are referenced to the same voltage, then it's decoupled and referenced to the bias output of the PT2399. Or, do you think it should be after the decoupling cap and then the bias point of the PT input would just be higher. I don't know what effect that has since it is awfully close to the supply voltage in value.

[matropiero]

I found the problem: led popping. Without led works perfect.

Sorry...thats not the problem 

[Vince_B]

Has anyone found a solution yet? I would like to have tails on my Zero Point SDX

[midwayfair]

On the Zero Point, this works just fine for tails:
Remove R8
solder in two wires where R8 used to be.
Solder a 10K to one of the wires. (This is R8, which we still need.)
Solder the termini of the 10K and the other side of "R8" to lugs 1 and 2 of a foot switch.
Add the LED as normal.

On mine, there's no popping and no need to reference Vb as in the Multiplex. I assume it's because it's decoupled from the audio path, unlike the set up in the Multiplex. It's still in the testing rig, but I've tried a couple different switches and it's not popping. Fingers crossed.

If something changes, I'll let everyone know in my build report.

[timbo_93631]

dredging up an old post here but has anyone successfully implemented tails on the Zeropoint SDX or the Multiplex?

[midwayfair]

dredging up an old post here but has anyone successfully implemented tails on the Zeropoint SDX or the Multiplex?

I used the shunt bypass I talked about in my ZPSDX.

http://www.madbeanpedals.com/forum/index.php?topic=9314.0

[timbo_93631]

Jon, can you go over again?  There is nothing in the link that I could see explaining it, and I'd like to know specifically how to implement it in a Multiplex.

[midwayfair]

Jon, can you go over again?  There is nothing in the link that I could see explaining it, and I'd like to know specifically how to implement it in a Multiplex.

You have to cut a trace to do it in the Multiplex. Check the schematic and find the connection to pin 1 to the rotary. Then use two lugs to make the connection and the third 'off' lug should be connected to Vb to prevent DC offset into the delay line.

[ilearn]

Thanks for the great mod.
I added this mod to my Deep Blue Delay and works really good.
But this mod introduced white noise which the pedal didn't have before the mod.
Can anyone give me some advice?

Thanks in advance.

[timbo_93631]

I am not sure I understand.  If you get a minute can you make a diagram/snippet of schematic?  Thanks.

[midwayfair]

I am not sure I understand.  If you get a minute can you make a diagram/snippet of schematic?  Thanks.

Foot switch:

1 4
2 5
3 6

4 = LED
5 = Ground
3 = VB

The VB connection is necessary because the Multiplex doesn't have a coupling cap at the PT2399 input and there's significant DC offset (~2v)

1 = IC1 pin 1
2 = Rotary A

6 is either not used, or you could use a 2-color LED to flip between bypass and delay

Cut the trace between IC1 pin 1 and rotary A. I'm pretty sure the trace is under the PCB.

In designs where there is a coupling cap before the PT2399s, you can use the simple shunt bypass I used in the Hamlet if you don't want to use Merlin's bypass scheme. That's what I did in my ZPSDX.