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SOMA 84
#1
Why is the input jack not insulated from the chassis? 

What is the 270R from the OPT 16 Ohm tap to ground on the schematic, is it on the wiring layout?  Gathering parts for this.
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#2
I now see the 470R on many of the schematics.
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#3
Hi Sinusoids

What makes you think the input jack is not insulated from the chassis? Every TUT3 and TUT5 project has ONLY insulated jacks.

The back view of the jack looks as if it is not, and these are Switchcraft long bushing types where you add the shoulder bushing on the inside face of the chassis and insulating plastic washer under the outside metal washer and nut.

The R across the output in every TUT3 and TUT5 project limits how open the load can be.

have fun
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#4
You have "non insulated jack" written on the wiring layout. Under the input jack. I was wondering. Good to know about the 470R. I know you recommend 3/8" internal lock washer under the shoulder as well so I have those. I'll insulate the jacks as usual.

Thanks!
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#5
hey

Soma-84 is the exception that makes the rule Smile

I designed this for a friend who then built it using transformers I supplied. He chose to ground the circuit at the input jack and it was quiet so he left it that way. It is not how I would do it as witnessed by all the other projects.

You can get away with certain things like this in low-gain amps, but were you to modify the amp later it would be wise to insulate the input jack and take the ground tie from the middle of the circuit.

All those old projects use Switchcraft jacks which are good and bad. The large contacts make the jacks robust but the weak part is the crimp holding the whole thing together. If you over-tighten the jack, the crimp loosens and the wafers and layers of the jack rotate out of alignment and do not stay tight any more. It is a good reason to switch to plastic jacks which are already self-insulating. With plastic jacks, Switchcraft becomes a poor choice as theirs always seem to have smaller contacts than the competition.
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#6
Any recommendations on plastic jacks? They seem to break if a straight plug bets bumped.
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#7
Hi

Neutrik is pretty good, or Cliff - depends if you need PCB mount or solder lugs.

If bumping into straight quarter-inch plug ends that are inserted into jacks is a habit you can't break - or maybe it's a hobby? - get some 90-degree cable ends. "Expensive yes, but I like it too"

Have fun
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