I have been using my SSE for quite a few months and really enjoy it. The challenge is when connected to the rest of my system -- another pre-amp / tube amp, subwoofer pre-amp / power amp, and a third amp the drives music to remote speakers, I get a subtle ground hum.
I have tried many solutions such as insuring all (but one, more on this later) components are plugged into the same power strip and are solidly grounded. Have used diode pairs on the amps ground connection. Tried using the resistor in parallel with a small capacitor on the way to ground solution. By isolating components it has become clear that both the sub amp and the other preamp each add a bit of hum. Haven't had much luck curing this.
So the question is this, what is a good, sonically transparent ground isolating transformer that I can wire in-line to the RCA jacks on the amp? I have a cheap isolation transformer that absolutely cures the hum, but due to it's cheapness, I'm wondering how much sound quality is being lost.
Also if I may ask, what is the proper impedance for the transformer?
Thank you in advance for any and all advice!
-- Pete
I have tried many solutions such as insuring all (but one, more on this later) components are plugged into the same power strip and are solidly grounded. Have used diode pairs on the amps ground connection. Tried using the resistor in parallel with a small capacitor on the way to ground solution. By isolating components it has become clear that both the sub amp and the other preamp each add a bit of hum. Haven't had much luck curing this.
So the question is this, what is a good, sonically transparent ground isolating transformer that I can wire in-line to the RCA jacks on the amp? I have a cheap isolation transformer that absolutely cures the hum, but due to it's cheapness, I'm wondering how much sound quality is being lost.
Also if I may ask, what is the proper impedance for the transformer?
Thank you in advance for any and all advice!
-- Pete
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I have some Hammond 850G transformers that have excellent specs, but I haven't used them in a project.
One trick that sometimes works (assuming this is happening from a ground return problem) is to insert a small 3 to 10 ohm resistor in series with the input tube's cathode network, at the bottom where it connects to ground. Then disconnect all the "ground" connections to the left of that point (the ones to the level control, input connector, and grid return resistor) and connect them instead to the ungrounded end of the added resistor. Do the same for both channels, essentially making the input ground return references of the two channels slightly different from each other and from the chassis ground, loop currents will change.
I've had very good luck with this on some circuits. Not very hard to try, and easy to remove if it doesn't help (just jumper across the added resistor).
Good luck!
I've had very good luck with this on some circuits. Not very hard to try, and easy to remove if it doesn't help (just jumper across the added resistor).
Good luck!
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2 pictures are worth 2000 words...
Thought the previous post might not be clear, so some illustrations.
I strongly recommend you try this before investing in expensive transformers and inserting them unnecessarily into your amp! From what you describe, I am pretty confident that this will fix the issue. It won't change circuit gain or DC idle currents, but can decrease ground current induced noises by large amounts. In the last circuit (very similar input topolotgy) I used it in, it made the difference between very annoying hum and an inaudible background.
Thought the previous post might not be clear, so some illustrations.
I strongly recommend you try this before investing in expensive transformers and inserting them unnecessarily into your amp! From what you describe, I am pretty confident that this will fix the issue. It won't change circuit gain or DC idle currents, but can decrease ground current induced noises by large amounts. In the last circuit (very similar input topolotgy) I used it in, it made the difference between very annoying hum and an inaudible background.
An externally hosted image should be here but it was not working when we last tested it.
Thank you all very much for the information. Hopefully tomorrow I'll get the chance to try your idea Bwaslo... The pictures are very helpful!
If the noise is too stubborn to be cured by that, it will be on to the isolation transformers.
If you get a chance, would you advise me on proper impedance for line level isolation transformers?
Thanks,
Pete
If the noise is too stubborn to be cured by that, it will be on to the isolation transformers.
If you get a chance, would you advise me on proper impedance for line level isolation transformers?
Thanks,
Pete
I would recommend a 10K:10K in your application. Though I haven't tried it the Hammond 140UEX specs as an excellent candidate as do Cinemag or Jensen:
Hammond Mfg. - Studio Grade - Impedance Matching - Audio Transformers - (140 "EX" Series)
Hammond Mfg. - Studio Grade - Impedance Matching - Audio Transformers - (140 "EX" Series)
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