Passive preamp cabling

[mgoode180566]

I am looking to rebuild my passive preamp and would like to know opinions on the best cable to wire it up with ......

[V-bro]

I've used this stuff to great satisfaction:
http://www.bscav.com/prod_foto/P01.jpg

http://www.bscav.com/?id=6&more=598

------X-max. can be several meters on any driver, too bad it can be done only once...------

[abelma]

Look for shielded cable, and the lower capacitance per meter (Usually in Pf/meter). Then you have expensive cables with silver and gold to lower the resistance, but the capacitance is the important value to look for signal cables. Normally the teflon type cables have low capacitance. A good value is for example lower than 60Pf/meter.
I've used those ones with good results:
http://www.bluejeanscable.co.uk/pages/technicaldocs/1694tech.htm
The twisted pair and shielded as Vbro is showing I believe is very good also.

[V-bro]

Capacitance is only important when the source has VERY high output impedance like passive guitars with gigantic inductance from the pickups. On active circuits (so in 999 per 1000 cases) the capacitance can be completely neglected...

Resistance is also only to be worried about on LOOOOOOONG cables...

I do like the strands to be tin plated as this makes them more corrosion resistant....

------X-max. can be several meters on any driver, too bad it can be done only once...------

[abelma]

I am agree 100%. I understand that in the case of a passive preamp with potentiometer, the amplifier is looking an high impedance as it is the potentiometer as a source?

[V-bro]

No, it's just passive circuitry between active circuitry, so the impedance seen by the amplifier input is low...

The cable quality is really not so important here... You just need basic shielded cable...

------X-max. can be several meters on any driver, too bad it can be done only once...------

[mgoode180566]

Could i use cat5 twisted pair ?

[krilli]

mgoode180566: Lots of people do it at least! I think I've seen lots of discussion of Cat on head-fi.org among other places ...

[abelma]

Ok Vbro. Because reading in the past before my buy of a Dact attenuator, I was looking for tech explanations about the passive preamps.
If you have time, please take a look of this tech note that it says the contrary.
http://www.dact.com/html/passive_preamp.html

[V-bro]

Oh sure it is more important than with an active pre, but not as bad as with a guitar or some microphones...



------X-max. can be several meters on any driver, too bad it can be done only once...------

[tuo]

Well, it is a passive pre"amplifier", it does not amplify anything. Somehow this term has found its way to common use. Probably because preamplifiers usually have two purposes: to select the source and to adjust the volume and a passive preamplifier does this with the most simplest way. So a passive preamplifier is a switch to select the source and a potentiometer to adjust the volume.

[Scratchy]

Everybody seems to take it for granted, but not me: what is a -passive- preamp?!?! It does amplify, or not? (is it just a volume pot?!)
A more accurate term might be Pre-Attenuator or Pre-Att.



And cabling: I use coax, only the cores for the signal , the shield I ground (to where it CAN be grounded (Agnd/Pgnd/Earth/Chassis), always works. I use thin (0.1mm to thick (3mm). For inputs and outputs.

I'm not sure what you mean by "CAN", but the sheilding should always be connected to chassis - earth, and only on one end.

[V-bro]

I'm not sure what you mean by "CAN", but the sheilding should always be connected to chassis - earth, and only on one end.

Eventually the AGND and PGND meet on one point, with ground lift switch it is even possible that the chassis is connected to PGND, also ONLY on one point. Shielding however indeed should be done to earth, even though it may give good results to shield to ground...