Pre Amp wire

[daxtojeiro]

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]

Originally Posted by daxtojeiro

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]

... 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]

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]

Here's one with shunt pot,

[Ali Tait]

I think you'd get more bang for the buck swapping out the Alps for something better.

[Chris]

Really nice work Richard..

Chris

[bob orbell]

I like the chocolate bar in the bottom Richard . Bob

[Greg.]

Originally Posted by Ali Tait

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]

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