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Phil Allison[_4_] Phil Allison[_4_] is offline
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Default Crosstalk in snake cable that include speaker cables and mic cables

Trevor wrote:




Are we talking Doug Self's book here?
If so, you should buy the printed edition instead of bootlegging it, because
Self is a good fellow and deserves your support.


As I said, I already have a printed copy. Just wanted to see what may
have been added in a newer edition. Certainly no real need for me to buy
a new printed copy these days, not doing that design work any more. I
have far too many copies of the same books in various editions as it is.



** In the section on speaker protection, Doug discuses the use of speaker relays and mentions only in passing that there can be an issue with a relay's ability to break DC current. This is important if an amp develops a large DC offset or blows an output device.

Bench testing reveals that typical 10A or even 20A, 250VAC rated relays break into a continuous arc if asked to switch off 50VDC with an 8 ohm resistor.

This is sailing way too close to the wind for most and there is a simple fix - wire the speaker line to the moving arm of the relay and ground the rest position contact. The amp output connects to the third contact and if an arc develops upon opening, it is immediately shorted to ground so protecting the speaker from DC.

Note: The amplifier should have DC rail fuses installed and it is a nice idea to use plug-in relays.


..... Phil