Overspill?

[estregan]

I read about this problem/feature over at Synthex's thread. I'm taking a step at posting a new topic for this.

I have also built a new board according to Synthex's build (using MAX4558CPE) and am also encountering this overspill when I hit my pad dead center on the piezo. But the thing is, this doesn't happen with my previous build of separate digital and analog boards (original build using 4051 ICs).

I know it was suggested that pots be used as a solution but one of the features I liked with this project is the absence of the pots as compared to Admir's edrum.

I would like to create another video showcasing Megadrums capabilities but I can't seem to move on because of this phenomenon. Can someone add light to this please?

[dmitri]

There is no possible magic with hot pads. If they're too hot, i.e. produce too strong signal even on a low impedance inputs, the only way around this is to use a voltage divider, e.g. a trimpot, or an inline resistor of 1k-20k value. I don't know for sure but it is possible that MAX4558CPE is more susceptible to "overspill" effect than 4051, but even with 4051's if you don't experience the "overspill" effect, you still lose dynamic range with too hot pads.
If I had too hot pads I would rather place trimpot or an inline resistor in a pad, or better yet use a cable with a built-in trimpot or an inline resistor. Please note if you choose to use inline resistors built into a MegaDrum PCB on all Edge/Rim input channels, you will lose possibility to use Piezo/Switch dual pads on them (same thing with trimpots if they're not set to max)

[Synthex]

Yes, with hot pads, you lose dynamic range !
The better way is to use a trimpot or a simple resistor directly soldered on the output jack of the pad.

[estregan]

Hmmm... How do I determine if I have hot pads or not? Any way of measuring that? If there is a way...can you please post your measurements so I can compare my diy pads to everybody else's?

[Synthex]

Hmmm... How do I determine if I have hot pads or not? Any way of measuring that? If there is a way...can you please post your measurements so I can compare my diy pads to everybody else's?

Precisely, if you have overspilling, you have hot pads.

[Synthex]

I have done more testing with the 74HC4851 and the MAX4558.

With the 74HC4851, there is no overspilling even if the signal is too strong.
74HC4851 appears to be better if you have hot pads ...
But, with hot pads, you lose dynamic range !
The better way is to use a trimpot directly soldered on the output jack of the pad.

[estregan]

I have done more testing with the 74HC4851 and the MAX4558.

With the 74HC4851, there is no overspilling even if the signal is too strong.
74HC4851 appears to be better if you have hot pads ...
But, with hot pads, you lose dynamic range !
The better way is to use a trimpot directly soldered on the output jack of the pad.

Fine, I'll try to acquire 74hc4851s so I can try them. I'll also observe the dynamic range. Thanks.

[jerzy]

With the 74HC4851, there is no overspilling even if the signal is too strong.

Although I can't find definition of "injection current", it seems that it is key here. But my HC4851 looks like dead... At what temperature have you soldered yours?

[Synthex]

my HC4851 looks like dead... At what temperature have you soldered yours?

I did not soldered them, I use support ...

[jerzy]

So you have DIP-16 package version? Where did you bought it?