Since recently I use 2 MiniDSP plate amps in bridge mode for my 2 subwoofers. There is a very slight hum coming from them which I think is because of a little difference in earth voltages in my system
When I keep the 2.5 meters of interconnect in the plate amp but disconnect from the pre amp the hum disappears completely
I think a pair of input transformers will help to remove the issue by disconnecting earth at the input side. The plate amps use a 3 point (earthed) power connection
Now I have 2 questions:
1. Do you think this indeed will be the case?
2. Do you have experience with a particular model / brand (currently my options as I see are Jensen JT-112P-2HPC, Lundahl do not know which one, Sowter do not know which one)
(the plate amps are very good by the way, programmable by network cable)
When I keep the 2.5 meters of interconnect in the plate amp but disconnect from the pre amp the hum disappears completely
I think a pair of input transformers will help to remove the issue by disconnecting earth at the input side. The plate amps use a 3 point (earthed) power connection
Now I have 2 questions:
1. Do you think this indeed will be the case?
2. Do you have experience with a particular model / brand (currently my options as I see are Jensen JT-112P-2HPC, Lundahl do not know which one, Sowter do not know which one)
(the plate amps are very good by the way, programmable by network cable)
The problem is a transformer is not good at inducing with low frequencies, most are for 100Hz and more.
There should be, in the PA world that uses power from different phases off the mains, only one ground.
If the hum is at mains frequency, then there is a 'loop'.
Correct the loop, only if there is a good electrical ground to the main amplifier.
Can you supply a balanced signal to the sub amplifier? If so that will correct your issue.
There should be, in the PA world that uses power from different phases off the mains, only one ground.
If the hum is at mains frequency, then there is a 'loop'.
Correct the loop, only if there is a good electrical ground to the main amplifier.
Can you supply a balanced signal to the sub amplifier? If so that will correct your issue.
Hi,
1)Yes a transformer could help to remove ground loop. This the main reason to use them in proaudio gear ( mic preamp, compressor, eq, desks,....).
2) I've got experience with sowter 3575, cinemag cmli 15/15b2, lundahl 1540, 1545 and 7902, jensen jt11, carnhill vtb.
All are good products imho, some better in specific case but overall they are in same category ( best you could find and so not cheap as expected for top quality products).
I don't know the jensen 112p- 2hpc, but you can expect them to be quite good as jensen are amongst the better you can find.
What is out impedance of your preamp and input impedance of your plate amps?
Is your preamp single ended or balanced?
1)Yes a transformer could help to remove ground loop. This the main reason to use them in proaudio gear ( mic preamp, compressor, eq, desks,....).
2) I've got experience with sowter 3575, cinemag cmli 15/15b2, lundahl 1540, 1545 and 7902, jensen jt11, carnhill vtb.
All are good products imho, some better in specific case but overall they are in same category ( best you could find and so not cheap as expected for top quality products).
I don't know the jensen 112p- 2hpc, but you can expect them to be quite good as jensen are amongst the better you can find.
What is out impedance of your preamp and input impedance of your plate amps?
Is your preamp single ended or balanced?
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It is an Ultrapath pre-amp by Electraprint design L3500 output transformer
There is only one connection from signal to chassis ground
But I must say this a very old build for me and I want to rebuild it / build another pre amp
There may indeed be some leakage from signal to ground somewhere. That is why I am thinking about the transformer to (may be temporarily while I rebuild) remove the hum
I thought about this but I have only single ended. The pre amp opt does not support otherwise. Or I would have to convert after the pre-amp (but I would prefer a transformer)
Yes thanks I have been experimenting with the polarity and it indeed makes a difference. All in all there is still a slight hum. When the room is really quiet and I turn on the subs I get a little restless because you can slightly hear a very low sound. When the music plays it is of no difference. May be I will try trafos one day to see if this can remove the last bit of hum but this is a costly and probably in the end unneeded solution
Also I think my pre-amp is probably is the source / the reason for the ground loop. I need to build a new one
Also I think my pre-amp is probably is the source / the reason for the ground loop. I need to build a new one
DATA
I had some hum issues with one home system. On eBay, bought a few stereo Pyramid transformers (prolly meant for cars) which had all the right RCA connectors, about $8, if I recall.
Hum disappeared after installation.
REW says their output droops just a little bit below 20 Hz, as I recall. Otherwise, no HD or other shortcomings. Maybe the $120 units are better.
If I knew how to make the search function here work better, I might be able to find my previous relevant posts.
B.
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