Balanced connections

[old_school]

I'm having a problem of hum/noise pickup with single-ended ICs between my pre and monoblock amps. There is no hum at all with shorting plugs in place. I reduced some that was likely an earth loop by reconnecting the amps to the same mains as the sources. Then an effort in dressing the cables reduced it more, but finally I moved the pre closer and reduced the length of the cables. The result was what I consider an acceptable level of hum, but puts my pre in an unacceptable location (including an earth loop issue, though I can possibly resolve that with a longer mains cable).

The pre is capable of fully balanced operation, on inputs and outputs, but the amps are only SE input. I was wondering if I would get some or a lot of benefit by running either a) balanced to SE cables, or b) balanced cables to a balanced/SE converter close to each amp with a short SE run. Most of what I've read indicates the maximum benefit is from fully balanced circuitry from end to end, but clearly I can't manage that without an amp change that I'm not quite ready to do at this time. I'd appreciate a little advice before I splash out on some new cables and/or converters. Also appreciate any suggestions I haven't mentioned.

The equipment in question is:

Pre: Aesthetix Calypso

Amps: Leak TL12+

Sources: CD/DAC Cambridge 840C (balanced out), Phono: Aesthetix Rhea (balanced out), Tuner ReVox B260 (SE out), and various RtR tape with a mix of balanced and SE ins and outs.

 

[SergeAuckland]

If you want to try a balanced input on your amplifier, the easiest is to use a pair of transformers to isolate inpur from output. There are some very cheap ones on eBay sold as hum isolators. They're not very good, but for a few pounds will tell you whether balancing is right for your installation. If so, then you can get a pair of decent transformers, at around £50 each.

I can lend you a box I made up to go from XLR-phono and back using four top quality Sowter transformers, but the cost of postage will probably be more than buying a couple of cheapies to try.

That's the best suggestion I can make. It should be possible to avoid hum even without using the transformers, but sometimes depending on the details of the installation, it's the simplest way.

S

 

[Tenson]

I second that suggestion. Transformers will allow good cancellation of hum on the line even when one end is connected to an RCA and they also isolate the two bits of kit so ground loops don't crop up.

At any rate try to find the cause of the hum pickup. If the shorter interconnect helped the issue I presume it is due to the cable going past a transformer or similar. Maplin do some tipple shielded phono cable - two layers of braid plus a metal film. http://www.maplin.co.uk/shark-audio-twin-screened-two-core-131

 

[clap]

I had a similar problem of hum. My pre is single ended only, the power accepts balanced. A specially made RCA to balanced cable totally cured the problem.

 

[old_school]

Thanks. A couple of things to try, and the cheapie transformers can be had for under a fiver, so I'll give them a shot before I spend too much.

 

[Tenson]

Just to make things easy these look like the cheapest suitable transformers on eBay -

http://www.ebay.co.uk/itm/2-Channel-Isolation-Transformer-for-MP3-Laptop-PC-to-Audio-Amp-Stop-buzzes-/380496814425?pt=UK_AudioTVElectronics_HomeAudioHiFi_Amplifiers&hash=item589760a159

http://www.ebay.co.uk/itm/TY-145P-Triad-Magnetics-Transformer-Audio-0-1W-/140941927971?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item20d0cb2623

I doubt they will sound great but will tell you if the hum is gone.

If you want something better, I can recommend these - http://www.ebay.co.uk/itm/A262A7E-OEP-Oxford-Electrical-Products-Transformer-Audio-1-1-1-1-/360676553844?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item53f9ff7474

 

[vacdac]

Just to make things easy these look like the cheapest suitable transformers on eBay - http://www.ebay.co.uk/itm/2-Channel-Isolation-Transformer-for-MP3-Laptop-PC-to-Audio-Amp-Stop-buzzes-/380496814425?pt=UK_AudioTVElectronics_HomeAudioHiFi_Amplifiers&hash=item589760a159

http://www.ebay.co.uk/itm/TY-145P-Triad-Magnetics-Transformer-Audio-0-1W-/140941927971?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item20d0cb2623

I doubt they will sound great but will tell you if the hum is gone.

If you want something better, I can recommend these - http://www.ebay.co.uk/itm/A262A7E-OEP-Oxford-Electrical-Products-Transformer-Audio-1-1-1-1-/360676553844?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item53f9ff7474

hi Tenson re the better Traffo's in your second link they aren't stated as flat down to 0 hz.

Is this likely to be a real world issue for anyone who fancies trying these?

>>>

Primary Impedance:	600ohm
Secondary Impedance:	600ohm
Transformer Mounting:	Through Hole
DC Secondary Resistance:	58R+58R
External Depth:	23mm
External Length / Height:	22mm
External Width:	28mm
Frequency Max:	35kHz
Frequency Min:	30Hz
Mounting Type:	PCB
Power Rating:	100mW
Primary DC resistance:	42R+42R
Transformer Type:

Cheers.

Chris.

 

[Tenson]

They go lower of course, it's probably just a case of the other specs not holding true below that such as 100mW power rating.

 

[vacdac]

Churz:^