Anyone built a (cheap) passive pre-amp kit?

[rabski]

Don't forget that the power supply can introduce its own noise and resulting distortion. As it's powering an active device stright in the signal path, I personally wouldn't use the circuit shown in the article, as LT1085/1033 are not particluarly 'quiet' and the smoothing there won't give a flat DC waveform. Good enough, but certainly not 'very low noise'.

 

[Bogart]

The 'stepped' bits are good for big holes if you don't have a pillar drill (or if you do, for that matter). The 'punch' type ones are fine for sheet metal, but no good for aluminium casework. Normal metal drill bits are easy for phono socket holes and the like.

Hole punches are fine in aluminium uo to 2mm

 

[Bogart]

Don't forget that the power supply can introduce its own noise and resulting distortion. As it's powering an active device stright in the signal path, I personally wouldn't use the circuit shown in the article, as LT1085/1033 are not particluarly 'quiet' and the smoothing there won't give a flat DC waveform. Good enough, but certainly not 'very low noise'.

Taking a large step forward will reduce the noise to damn all if using a TPS7A4700 or similar
but the circuitry gets more complicated. I reckon the 1033 and 1085 are not bad for what they offer

 

[Bogart]

Am 75% of they way with my purely passive ' attenuator '. Looks a bit of the proverbial dog's dinner
just lashed together temporarily to ascertain what resisitor values I need for my setup. Getting a nice looking case is not as easy as I would have thought.

 

[Bogart]

Have one of these on its way
https://www.takachi-enclosure.com/products/MXB
MXB 4-10-14 Will be a tight squeeze but think is doable.
Worth a punt as they are offereing a sample for free.

 

[George 47]

Great article and really descriptive, I fear it might be a little above my head though!

You don't have to make it in the attic!!

 

[Psilonaught]

Don't forget that the power supply can introduce its own noise and resulting distortion. As it's powering an active device stright in the signal path, I personally wouldn't use the circuit shown in the article, as LT1085/1033 are not particluarly 'quiet' and the smoothing there won't give a flat DC waveform. Good enough, but certainly not 'very low noise'.

What solution do you consider 'very low noise' for flat, ripple free DC then?

Been trying to find a suitable 12v board but it's a minefield out there!

Currently have this on order but I can do better no doubt.

Ideally something with terminal screws so I don't have to both with soldering!

 

[rabski]

What solution do you consider 'very low noise' for flat, ripple free DC then?

Been trying to find a suitable 12v board but it's a minefield out there!

Currently have this on order but I can do better no doubt.

Ideally something with terminal screws so I don't have to both with soldering!

That one should do nicely. They're also available from Audiophonics and you will find a couple of them in my own build DAC power supply. They are indeed very low noise and have a nice, flat waveform output.

Possibly you can find better, but as you don't need big current delivery, that should do the job fine.

 

[Psilonaught]

I also bought

https://a.aliexpress.com/_EugFm6L


AC filters that I'll run in series after a fused IEC inlet filter and before that regulated power supply board. Double power filtration

Once all my parts arrive I'll start a build thread.

 

[halx00]

Hi
I've built lots of passive preamps and the best sounding to me and others was the Zfoil pre I built for a Mr I Walker.
Not a cheap build but worth it.

Happy Days
Duncan

https://photos.app.goo.gl/9Cg4huCivjSRED5S9

 

[Bogart]

Very nice looking. I like how you have the selection switch set back to reduce length of wires.

 

[halx00]

Yes, using pure silver wire it helps with costs, though the Charcoft Z-Foil Resistors start at £16.60 to £36.42 each and there's 42 of them.

Happy Days

 

[pmcuk]

The 'stepped' bits are good for big holes if you don't have a pillar drill (or if you do, for that matter). The 'punch' type ones are fine for sheet metal, but no good for aluminium casework. Normal metal drill bits are easy for phono socket holes and the like.

I have quite a collection of hole saws. Pride of the collection is a bunch of Hilti hole saws which just pull on and off. Absolutely beautiful tools but not cheap. My son briefly worked for Hilti and they were a present.

https://www.hilti.co.uk/c/CLS_POWER_TOOL_INSERT_7126/CLS_HOLE_SAWS_7126/r7067

 

[Bogart]

Will get around to doing mine shortly when last bit, remote control, arrives from China. Decided on
using TKD motorised pot so I can have remote control over it.