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Boban 1st March 2003 03:30 AM

Pearl - internal wires and grounding question
my Pearls are progressing well. Boards are more or less done and I am collecting all the necessary parts for the power supply. The aluminum box will arrive next week (Mouser).

Just for fun I tried some wire I have at home and realized that the hole on the board is not big enough. It seems to me that internal wire have to be in 20 -22 gauge range. What are you using for the internal wire?

Second, grounding options. I did search the archives and still don't have clear picture how to connect everything. Where to connect the ground wire from the turntable? Should two metal boxes be ground connected or not? Can anyone elaborate?


Ren 1st March 2003 12:16 PM


Yes, the two chassis do need to be grounded in some fashion for safety.

I'm sure there are other ways to accomplish this, but the following worked for me. I suggest that both chassis be connected directly to "earth ground" (i.e. AC third wire). Then connect the PS "ground" to the chassis through a power NTC thermistor (a.k.a. inrush limiter) like Digikey KC011L-ND. This keeps the PS ground (which gets connected to signal ground near the input & output RCA connectors) isolated from earth ground by a few ohms under normal conditions. The use of a thermistor in this fashion has been employed in several Pass DIY projects. You'll find several discussions in this forum on that topic.

You may or may not need to connect your turntable's ground to the phono pre's ground. If you do, I suggest an insulated binding post near the RCA connectors (isolated from the chassis ground) connected to the PS / signal ground.



Boban 1st March 2003 05:12 PM

Thanks Ren,
what about internal wire?

Ren 2nd March 2003 04:03 PM

I used multi-stranded 22 guage hookup wire internally, and double runs of the same wire for the DC umbilical cord... but that is mainly because I had several spools of it around.

I could not find the good explanation someone posted maybe 2 -3 weeks ago on this forum regarding current carrying capacities of various wire gauges. If my memory is correct (possible, but no guarantees), 22 gauge should be good for up to 1 A continuous current in free air.

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