Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on March 11, 2018, 04:00:43 pm

Title: Speaker jacks, isolated or not
Post by: dude on March 11, 2018, 04:00:43 pm

6V6 Plexi build using "Fender speaker jacks", main and extension speaker, so do they need to be isolated? Using standard 18 watt OT, 7K with three sec, 4,8,16


Some amps I've build I had to isolate, the speaker jack, some not. Couldn't find much info on this subject.


I'm drilling an AO43 chassis for spk jacks and if I need an isolating washer hole size is different.


al

Title: Re: Speaker jacks, isolated or not
Post by: Colas LeGrippa on March 11, 2018, 04:19:27 pm

Hi !  The speaker ground is a common ground, it doesn't need to be isolated. The gnd is only a reference. In all of my builds, I hooked up the 4,8, and 16 ohm to the tip of the  female 1/4 jacks, and the gnd, usually a black lead,  to the gnd terminal of the 1/4 female jack.  The gnd is the same for filter caps, center taps, 115V gnd and so on.

Colas

Title: Re: Speaker jacks, isolated or not
Post by: pdf64 on March 12, 2018, 07:51:52 am

Quote from: dude on March 11, 2018, 04:00:43 pm

6V6 Plexi build using "Fender speaker jacks", main and extension speaker, so do they need to be isolated? Using standard 18 watt OT, 7K with three sec, 4,8,16


Some amps I've build I had to isolate, the speaker jack, some not. Couldn't find much info on this subject.


I'm drilling an AO43 chassis for spk jacks and if I need an isolating washer hole size is different.


al

If it's a proven layout, and you build it exactly, then you should be ok.
But good practice with global negative feedback loops is to reference the speaker 0V to the power amp input 0V, ie the 0V return of the LTP.
Merlin explains it all very clearly http://www.valvewizard.co.uk/Grounding.pdf

Title: Re: Speaker jacks, isolated or not
Post by: jjasilli on March 12, 2018, 09:56:46 am

Google: "bogen loudspeaker installation" and download the PDF booklet.  See pp 9 - 10 which explains the use of floating / balanced vs. grounded / unbalanced speaker outputs.  (The speaker output can be both grounded and balanced, if the OT secondary uses a center tap, which has largely fallen into disuse.)


For safety reasons it seems like a good idea to use a grounded speaker out.  See:  http://www.aikenamps.com/index.php/grounding
If an isolated speaker-out jack is used, then it can be grounded at the point of your selection.  This can improve both safety & any noise issues.

Title: Re: Speaker jacks, isolated or not
Post by: dude on March 12, 2018, 05:08:41 pm

Thanks, good reading