Author Topic: Signal Traces under PT2399?  (Read 2263 times)

dpresley58

Signal Traces under PT2399?
« on: January 03, 2013, 08:34:09 AM »
Anyone have any ideas about whether or not running signal traces under the Princeton PT2399 chip is okay?
The signals in question are from the input side of the stompswitch.
I'm routing a board for a delay unit and it hit me that maybe I should ask before pulling the trigger on the board order...
Thanks.
Little time to do it right. Always time to do it over.

R.G.

Re: Signal Traces under PT2399?
« Reply #1 on: January 03, 2013, 11:31:36 AM »
Anyone have any ideas about whether or not running signal traces under the Princeton PT2399 chip is okay?
The signals in question are from the input side of the stompswitch.
I'm routing a board for a delay unit and it hit me that maybe I should ask before pulling the trigger on the board order...
In general, it's a bad idea to run high impedance analog signals under digital logic of any kind. A signal coming in from a stompswitch will probably have a high impedance termination (i.e. the standard 1M input impedance for most stomp boxes) and so the impedance on the wire at low frequencies is the impedance of the signal source; at high frequencies it's the impedance of the trace itself. So this may act differently with a guitar driving it and another stompbox, but it has the possibility to pick up digital noise. That noise may or may not be audible in the audio later.

If you can, sidestep this issue by not doing that. No reason to fight noise later if you can avoid it now.
R.G.

Quick IQ Test: If anyone in a governmental position suspected that YOU had top-secret information on YOUR computer, how many minutes would you remain outside a jail cell?

dpresley58

Re: Signal Traces under PT2399?
« Reply #2 on: January 03, 2013, 11:55:58 AM »
Thank you... I thought that was a no-no, but wasn't sure. Something was nagging at the back of my mind this morning (pre-1st cup) and since I couldn't recall exactly what the rule of thumb was on the matter, I thought I'd ask.
I appreciate the explanation, and hope you're year is starting well.
Little time to do it right. Always time to do it over.

MoltenVoltage

Re: Signal Traces under PT2399?
« Reply #3 on: January 03, 2013, 12:20:23 PM »
Generally keep the analog and digital circuits/traces as physically isolated as possible and connect the separate grounds at a common point at the power jack.

Since you have both signals in the PT2399, use the separate analog and digital ground connections as shown in the datasheet.

http://www.datasheetcatalog.org/datasheet/PrincetonTechnologyCorporation/mXyzsyzt.pdf

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