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Earth loops.

Geoff WILTON

Geoff WILTON

Member
I am posting here in the hope that I will get some expert advice from the DIY guys. I have a system, (one of three) incorporating a Harman Kardon Citation 16 (my avatar), euro version,240 V, twincore plus earth lead. connected to a Citation 17 preamp, U.S. version 110V running off a transformer through US twincore lead.
Moderately annoying hum and buzz until I disconnect the ground connection in the 16 power amp plug. Blissfully silent! The question is...is it safe to carry on using it like this? I really want to but not at the risk of electrocution.
 
Geoff WILTON said:
I am posting here in the hope that I will get some expert advice from the DIY guys. I have a system, (one of three) incorporating a Harman Kardon Citation 16 (my avatar), euro version,240 V, twincore plus earth lead. connected to a Citation 17 preamp, U.S. version 110V running off a transformer through US twincore lead.
Moderately annoying hum and buzz until I disconnect the ground connection in the 16 power amp plug. Blissfully silent! The question is...is it safe to carry on using it like this? I really want to but not at the risk of electrocution.
Click to expand...

No, in a word, it doesn't sound like it. Try connecting the two chassis together.
 
You don't say what *source* components you have connected.

It would help if you had/have a cheap multimeter. Given that you could disconnect everything from mains (for safety) and then check if the earth pin of the mains plug(s) are all connected to the outers of signal sockets, or not. The 'ideal' tends to vary but either all units have their own ground via their mains lead or just one unit does, and the others all go via the signal lead grounds from unit to unit. if the units were designed to act in the latter way, having all their power leads connect to earth will cause a loop. But beyond that this is a 'depends' sort of situation. Units need an earth via some means, depending on the design.
 
Geoff WILTON said:
I am posting here in the hope that I will get some expert advice from the DIY guys. I have a system, (one of three) incorporating a Harman Kardon Citation 16 (my avatar), euro version,240 V, twincore plus earth lead. connected to a Citation 17 preamp, U.S. version 110V running off a transformer through US twincore lead.
Moderately annoying hum and buzz until I disconnect the ground connection in the 16 power amp plug. Blissfully silent! The question is...is it safe to carry on using it like this? I really want to but not at the risk of electrocution.
Click to expand...

A quick google of images HK Citation 17s shows two things that may be helpful to you, if applicable:

1. The image I found of the back of a 17 shows a fixed lead with multiple input voltages printed above it: 100/120/220/240V

2. A series of US power output sockets, rated up to 300W - which I would assume are intended to allow you to attach other HK kit - up to and including a matching Citation 16.

harman-kardon-citation-seventeen-s-17.jpg


If yours is similar, I would get yourself onto something like a US-based HK-themed forum, or DIYaudio, and check with experienced owners and see if the voltage of the pre-amp is internally switchable - I imagine that it is, in which case you can (unplug first!) switch to 120VAC operation - you can (and must!) then run the pre-amp from your stepdown transformer - next you bung a US two-pin plug on the power amp's lead, and then plug the power amp into the 300W output socket on the pre.

One other small job, if you're running a nominally 240VAC unit at 120VAC, you'll need to change any internal fuses to roughly double their existing current rating, e.g. 1.25A will need uprating to 2.5A, or the fuses' life expectancy will be much reduced.

You'll no longer have any connection to Mains Earth, but these units were evidently designed to be safe (for their time!) working without it.

If you do this, I would suggest you don't make any additional connections between amps, as at best it'll do nothing, and at worst may introduce hum loops or even dangerous currents.
 
Notwithstanding the serious and sensible posts by others above, which I agree with - a late thought on a simple thing to try -
Geoff WILTON said:
...
connected to a Citation 17 preamp, U.S. version 110V running off a transformer through US twincore lead.
...
Click to expand...


.. a lot of such simple voltage converters are actually autotransformers, and often not necessarily of any, let-alone great kwality (in several dimensions..)

Have you simply tried reversing (rotate 180 degrees) the US 2pin plug feeding the pre from the the stepdown unit? Depending on how things are arranged, one orientation over the other might provide a lower leakage current, leading to diminished hum just as things stand.
 
Last edited:
earlofsodbury said:
A quick google of images HK Citation 17s shows two things that may be helpful to you, if applicable:

1. The image I found of the back of a 17 shows a fixed lead with multiple input voltages printed above it: 100/120/220/240V

2. A series of US power output sockets, rated up to 300W - which I would assume are intended to allow you to attach other HK kit - up to and including a matching Citation 16.

harman-kardon-citation-seventeen-s-17.jpg


If yours is similar, I would get yourself onto something like a US-based HK-themed forum, or DIYaudio, and check with experienced owners and see if the voltage of the pre-amp is internally switchable - I imagine that it is, in which case you can (unplug first!) switch to 120VAC operation - you can (and must!) then run the pre-amp from your stepdown transformer - next you bung a US two-pin plug on the power amp's lead, and then plug the power amp into the 300W output socket on the pre.

One other small job, if you're running a nominally 240VAC unit at 120VAC, you'll need to change any internal fuses to roughly double their existing current rating, e.g. 1.25A will need uprating to 2.5A, or the fuses' life expectancy will be much reduced.

You'll no longer have any connection to Mains Earth, but these units were evidently designed to be safe (for their time!) working without it.

If you do this, I would suggest you don't make any additional connections between amps, as at best it'll do nothing, and at worst may introduce hum loops or even dangerous currents.
Click to expand...
Thank you for your input. Yes, my 17 looks just like that except it was a home market only and does not have a switchable transformer. I know that HK made export models that were switchable. I have owned a 19 power amp that had jumper plugs inside. I will open up my 16 again and see if can be switched back to 120V operation then run it off the preamp.
 
martin clark said:
Notwithstanding the serious and sensible posts by others above, which I agree with - a late thought on a simple thing to try -



.. a lot of such simple voltage converters are actually autotransformers, and often not necessarily of any, let-alone great kwality (in several dimensions..)

Have you simply tried reversing (rotate 180 degrees) the US 2pin plug feeding the pre from the the stepdown unit? Depending on how things are arranged, one orientation over the other might provide a lower leakage current, leading to diminished hum just as things stand.
Click to expand...
Great idea Martin. I hadn't thought of that. I'll try it
 
For everyone who 'chipped in' with much appreciated suggestions, here is the update. The noise was coming from a Lexicon RT-20 that i use for playing audio discs. For some reason it disagrees with the 'old' H/K gear. I bought a ground loop blocker to interrupt the hum which worked but there was still a higher pitched tone that was in the signal (video noise?) and increased with use of volume control.
The solution was to connect up an old Rotel CD only player and all is now quiet . The Lexicon is banished to my A/V setup where it works fine.
'Go figure' as our American friends would say!
 
Geoff - glad you have a complete fix; and thank you very much for updating your thread with the resolution.
Doing so really helps anyone who might search for similar problems in the future.

ATB - and enjoy your classic amps!
 
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