Ground Loop Hum

[Cyndale]

Are your amps/preamps using tube rectifiers or solid state rectifiers?

A quick test of this would be to try an interconnect cable with a higher gauge ground wire i.e one that is higher impedance & resist these return currents flowing in it rather than in the correct route to ground in the amp. It may be just one amp that needs this modification?

I checked a review of the amplifier I have and it says....
An unusual feature is a fully regulated high voltage supply that uses valve regulator elements.

I am using Van Den Hul 102MkII interconnects. I have a spare set of Audioquest Emerald interconnects which I could try on one of the amplifiers.

[jkeny]

Are your amps/preamps using tube rectifiers or solid state rectifiers?

A quick test of this would be to try an interconnect cable with a higher gauge ground wire i.e one that is higher impedance & resist these return currents flowing in it rather than in the correct route to ground in the amp. It may be just one amp that needs this modification?

I checked a review of the amplifier I have and it says....
An unusual feature is a fully regulated high voltage supply that uses valve regulator elements.

I am using Van Den Hul 102MkII interconnects. I have a spare set of Audioquest Emerald interconnects which I could try on one of the amplifiers.

What model amp is it - it could be a faulty regulator/rectifier valve? Do you have a multimeter to measure voltage difference between ground inputs & chassis -
!!don't go near the high voltage stuff!!

[Cyndale]

What model amp is it - it could be a faulty regulator/rectifier valve? Do you have a multimeter to measure voltage difference between ground inputs & chassis -
!!don't go near the high voltage stuff!!

A pair of Croft Series 4 power amplifiers, it doesn't matter which amp I disconnect the earth lead from, one or the other. As soon as I plug in the second amplifier I get hum.

[jkeny]

A pair of Croft Series 4 power amplifiers, it doesn't matter which amp I disconnect the earth lead from, one or the other. As soon as I plug in the second amplifier I get hum.

Just a quick glance at the amp here http://www.croftacoustics.co.uk/reviews/8_rev.html
I note this " high input sensitivity of typically 0.4V RMS for full power, which facilitates its use with the Croft pre-amplifiers that have unity gain auxiliary input terminals."
This is pretty high sensitivity considering around 2V (or more) RMS is the usual standard - so any small currents (ground noise) on the amp inputs will be amplified substantially which I imagine is part of the problem!

[Cyndale]

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[Cyndale]

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[Cyndale]

Well, as I mentioned in one of my earlier posts, I had actually been using the amps without the earth connected to one of them for 20 years and something I forgot to mention.. I had been using round pin plugs which didn't even have a fuse in them.


At least now I am using the modern 3-pin plugs with 5Amp fuses in them. I was always curious as to how much current the valve amplifiers were using.
Croft Series 4 - 15 valves
Croft Series 4 - 15 valves
Croft Preamp - 7 valves
Croft headamplifier 4 valves

41 valves in total!

Here is the result.

Voltage generated = 230V
Amperage generated = 2.94A
Wattage generated = 570W

[jkeny]

Well, as I mentioned in one of my earlier posts, I had actually been using the amps without the earth connected to one of them for 20 years

Yes & what I'm saying is that with the high sensitivity of the input stage of these amps, any small voltage on the input stage will be amplified so if there's a small ground voltage (due to a current loop) this will most likely result in the hum you hear. For most 'normal' input stages, this small voltage would not be a problem causing hum - so your amp is extra sensitive to these issues

Are you in US or Europe because you can get this in US but won't work on European 50Hz AC frequency, AFAIK? - Ebtech Hum X Ground Line Voltage Filter

[jkeny]

Maybe this does work in Europe as it's sold by this UK company but I would ask them first
http://www.google.co.uk/shopping/produc ... 5661229246

[Cyndale]

No, living in the ould sod here! Yeah, I saw the Ebtech all right! Thanks for all the information on ground loop!