How long is too long ? cable question...

V

Voice_Coil

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Hi, im considering adding a sb to my system, but i am considering placement, would it be taking the piss if i used a 3, or even 5 metre cable to hook it up to my pre ?........That's basically it !

Many thanks in advance :^

 

surayne

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It'll be perfectly fine, I've had 5m runs with absolutely no issues. It's worth getting shielded cables as you might have a higher chance of noise otherwise.

 

NAM

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My interconnects are 7m long....years ago I 'stressed' about 10cm either way :p but it makes fuck all difference as far as I can tell :D

 

SergeAuckland

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If you think about it, studios have hundreds of metres of cables between sources and destinations, albeit balanced. Video is run over hundreds of metres at 75ohm unbalanced as is digital audio, so domestic lengths are no problem at all. At some studios, line-level balanced signals aren't even screened, just open twisted pairs with no hum or crosstalk problems.

S.

 

Valvebloke

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Which preamp is it ? Audio Synthesis say of their Passion "Due to their minimal design nearly all passive preamps exhibit an output impedance which both changes with level and is sometimes higher than a conventional active preamp's. Consequently the cable used between the passive controller and power amplifier should have a low capacitance (the shorter the cable the better) and be screened. We highly recommend SilverBlue (120pF/m terminated in WBT plugs) and SilverBlue Locap (80pF/m)" http://www.audiosynthesis.co.uk/passion.htm . I'd contact them and ask.

VB

 

June

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BBC engineers regularly ran 20m or 30m interconnects (balanced / shielded) when setting up sound rooms prior to recording.

Very short speaker cables though (less than 2.5m).

 

SergeAuckland

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Which preamp is it ? Audio Synthesis say of their Passion "Due to their minimal design nearly all passive preamps exhibit an output impedance which both changes with level and is sometimes higher than a conventional active preamp's. Consequently the cable used between the passive controller and power amplifier should have a low capacitance (the shorter the cable the better) and be screened. We highly recommend SilverBlue (120pF/m terminated in WBT plugs) and SilverBlue Locap (80pF/m)" http://www.audiosynthesis.co.uk/passion.htm . I'd contact them and ask.VB
That would be the case if the long cable was between pre and power amp, but in this case, the cable is between the SBT and the pre. The SBT has a very low output impedance, so the capacitance of the cable isn't really relevant unless ludicrously high.

S.

 

Valvebloke

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That would be the case if the long cable was between pre and power amp, but in this case, the cable is between the SBT and the pre ...
Oops :oops: . I misread sb as sub and assumed he wanted to drive a powered subwoofer from the pre. Ignore what I said ...

VB

 

Gizza

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I use an Audio Synthesis passion preamp myself and since all of the attached source components ( Dax Discrete, SBT, A/V Receiver) have their own volume control), I go from the Direct outputs on the passion pre to the power amp, thereby bypassing the pre's volume control altogether, using the pre simply as as an input switching device. You could go straight from the direct input/output on the pre to the sub in the same way, providing its an active sub with its own volume control. Presumably, the need for low capacitance/short cables would then not apply?

Hi, im considering adding a sb to my system, but i am considering placement, would it be taking the piss if i used a 3, or even 5 metre cable to hook it up to my pre ?........That's basically it ! Edit: oops, made the same mistake as the post above, thought it was a sub he was wanting to hook up!

Many thanks in advance :^
 
V

Voice_Coil

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Brilliant, thanks guys, i did kinda suspect id get told they would be ok, always better to ask :)

thanks again.

 

Muddy Funster

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If you think about it, studios have hundreds of metres of cables between sources and destinations, albeit balanced. Video is run over hundreds of metres at 75ohm unbalanced as is digital audio, so domestic lengths are no problem at all. At some studios, line-level balanced signals aren't even screened, just open twisted pairs with no hum or crosstalk problems. S.
Yes, but there's a fairly big difference between the properties of impedance matching and impedance bridging circuits. It's not a problem in this case, but an interconnect cable in a domestic audio system will begin to act as a first-order low-pass filter if it is substantially longer than about 10m (if the cable is particularly capacitive, even less than that). If your preamp is 20m from your power amp, you have a choice of either going fully balanced (or adding baluns transformers at both ends), moving the two devices a lot closer together or convincing yourself that you never liked treble anyway.

 

SergeAuckland

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Yes, but there's a fairly big difference between the properties of impedance matching and impedance bridging circuits. It's not a problem in this case, but an interconnect cable in a domestic audio system will begin to act as a first-order low-pass filter if it is substantially longer than about 10m (if the cable is particularly capacitive, even less than that). If your preamp is 20m from your power amp, you have a choice of either going fully balanced (or adding baluns transformers at both ends), moving the two devices a lot closer together or convincing yourself that you never liked treble anyway.
Not quite right, in that whether balanced or unbalanced, what matters is the output impedance of the source and the capacitance of the cable. Modern sources send from a low output impedance into a high input impedance so even 100m of decent cable will not affect treble. Impedance matching, i.e. 600 ohms in and out haven't been used for certainly the 40+ years I've been in audio with the exception of analogue telephony.

S

 

Muddy Funster

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Not quite right, in that whether balanced or unbalanced, what matters is the output impedance of the source and the capacitance of the cable. Modern sources send from a low output impedance into a high input impedance so even 100m of decent cable will not affect treble. Impedance matching, i.e. 600 ohms in and out haven't been used for certainly the 40+ years I've been in audio with the exception of analogue telephony. S
I suspect we're sort of playing both ends against the middle here. You are right, but domestic audio's propensity to have a liberal interpretation of what represents a low output impedance and a high input impedance and then adding something close to insult to injury by using twisted pair interconnects as an accidental gimmick capacitor means most of us have a reluctance to recommend cables much longer than about 10m. If the audio gods are smiling, you could massively increase the distance between devices with no signal loss. OTOH, I know of a couple of cable brands I wouldn't recommend out of principle and certainly not recommend beyond about 2m, because they are less of a cable, more of a capacitor in a witness protection program.

 

SergeAuckland

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I suspect we're sort of playing both ends against the middle here. You are right, but domestic audio's propensity to have a liberal interpretation of what represents a low output impedance and a high input impedance and then adding something close to insult to injury by using twisted pair interconnects as an accidental gimmick capacitor means most of us have a reluctance to recommend cables much longer than about 10m. If the audio gods are smiling, you could massively increase the distance between devices with no signal loss. OTOH, I know of a couple of cable brands I wouldn't recommend out of principle and certainly not recommend beyond about 2m, because they are less of a cable, more of a capacitor in a witness protection program.
You're right in that I find myself in disbelief at the technical stupidity of what passes for audio engineering amongst some of the more "boutique" brands. Being different seems more important than being technically right, probably on the basis that different=better in the minds of the gullible.

Ho-hum....

S.

 

tuga

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Which preamp is it ? Audio Synthesis say of their Passion "Due to their minimal design nearly all passive preamps exhibit an output impedance which both changes with level and is sometimes higher than a conventional active preamp's. Consequently the cable used between the passive controller and power amplifier should have a low capacitance (the shorter the cable the better) and be screened. We highly recommend SilverBlue (120pF/m terminated in WBT plugs) and SilverBlue Locap (80pF/m)" http://www.audiosynthesis.co.uk/passion.htm . I'd contact them and ask.VB
80pF/m is not that low...

Blue Jeans Cable makes a low capacitance screened cable, the LC-1 (40pF/m) that is adequately priced : http://www.bluejeanscable.co.uk/store/audio/index.htm

R

 
S

stereo70

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I have always found 1 meter at 25 quid a meter to be 1 meter too long.

 

SergeAuckland

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I have always found 1 meter at 25 quid a meter to be 1 meter too long.
For unbalanced cable, RG59 at around £0.30/m is what I would pay, for line-level balanced cable about the same, perhaps 50p/m for Starquad.

S.

 
S

stereo70

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For unbalanced cable, RG59 at around £0.30/m is what I would pay, for line-level balanced cable about the same, perhaps 50p/m for Starquad.S.
I'm afraid I learned the hard way Serge, they do look nice, though.

 

tuga

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I have always found 1 meter at 25 quid a meter to be 1 meter too long.
Sure, you can buy a length of cable for peanuts but you'd have to make the cable yourself and buy the plugs.

Besides, would you have to find an equally low capacitance coaxial (such as the BJC LC-1)...it's possible but it may prove to be a bit dificult.

And I think that low capacitance is a bonus with long ICs.

R

 

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