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daxtojeiro 28th January 2020 11:05 PM

Pre Amp wire
 
Hi all.
I have a passive pre-amp that I built years ago. It's basically an ALPs pot, a selector switch and some quality phono cable. (screened)
Looking at it, its a mess inside and I'm thinking about re-wiring it. I have seen pictures using un-screened cable and what looks like resistors in line with the switches.

I've also grounded the chassis, connecting the input / output grounds via a 100R / 0.1uF capacitor in parallel.

Is this grounding method OK, or should I totally insulate it and only allow the grounds of the inputs / outputs to connect at the main amp?

Is there a good quality, but thin cable I should be using for the cabling inside, as my thick old cable with shielding has made it a bit of a mess inside.

I have seen selector switches with resistors on them, what are they used for, I have nothing on mine, its simply wires, switches and a pot,
thanks for your hep
Phil

snowman_al 29th January 2020 09:10 AM

Re: Pre Amp wire
 
Quote:

Originally Posted by daxtojeiro (Post 90324)
Hi all.
I have a passive pre-amp that I built years ago. It's basically an ALPs pot, a selector switch and some quality phono cable. (screened)
Looking at it, its a mess inside and I'm thinking about re-wiring it. I have seen pictures using un-screened cable and what looks like resistors in line with the switches.

I've also grounded the chassis, connecting the input / output grounds via a 100R / 0.1uF capacitor in parallel.

Is this grounding method OK, or should I totally insulate it and only allow the grounds of the inputs / outputs to connect at the main amp?

Is there a good quality, but thin cable I should be using for the cabling inside, as my thick old cable with shielding has made it a bit of a mess inside.

I have seen selector switches with resistors on them, what are they used for, I have nothing on mine, its simply wires, switches and a pot,
thanks for your hep
Phil

The switch with resistors on is likely to be a 'stepped attenuator' or stepped volume control. Basically the alps pot, but with 23 or 41 or so positions instead of the constant variable track of the pot. It can give better channel balance as the resistors can be matched accurately. Posh one use posh types of resistor too...

Thin wire ummm. CAT5 or 6 network cable stripped and made into twisted pairs is fine and well liked. All the way to silver wire and Teflon insulation. Like the stepped control, price is the only constraint!

If the enclosure is metal best to have it earthed to mains earth, just in case.
Ground lifting the signal ground (the 100R/0.1uF) is fine, it is to stop earth or ground loop mum.

A Stuart 29th January 2020 10:44 AM

Re: Pre Amp wire
 
... or else resistors were put in to compensate for different outputs from different sources?
... or the "shunt modification" in FAQs>Upgrades and tweaks. http://www.world-designs.co.uk/forum...ead.php?t=5795

Richard 29th January 2020 11:57 AM

Re: Pre Amp wire
 
2 Attachment(s)
Yes I've done a few, with and without the shunt pot resistors, and use enamelled copper wire. I use isolated phonos, an ally box for overall screening, and earth the box and pot (for safety and to stop hums) to the phono screens.

Richard 29th January 2020 12:07 PM

Re: Pre Amp wire
 
2 Attachment(s)
Here's one with shunt pot,

Ali Tait 29th January 2020 12:32 PM

Re: Pre Amp wire
 
I think you'd get more bang for the buck swapping out the Alps for something better.

Chris 29th January 2020 01:56 PM

Re: Pre Amp wire
 
Really nice work Richard..

Chris

bob orbell 29th January 2020 04:42 PM

Re: Pre Amp wire
 
I like the chocolate bar in the bottom Richard :D. Bob

Greg. 29th January 2020 08:21 PM

Re: Pre Amp wire
 
Quote:

Originally Posted by Ali Tait (Post 90329)
I think you'd get more bang for the buck swapping out the Alps for something better.

Maybe Ali, but I suspect when used with the shunt pot mod, it makes little difference because the wiper is not passing signal.

Ali Tait 29th January 2020 10:48 PM

Re: Pre Amp wire
 
Yeah that'll get you most of the way there, guess it depends how far you want to go.


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