Just constructed an Aikido linestage - connected the output to a Jensen 4:1 stepdown output transformer, via cap. Output winding floating. Hey - it hums, even turned off and unplugged! All l have to do is connect my Citation 12 and it's LOUD! What could be going on?
If there's hum/buzz from the power amp without the preamp on, then it's obviously the interface to the power amp that's the problem. With the power amp on, but with nothing connected to it, does you get noise from the speakers?
Joel
Joel
It's an odd situation. The old amp is silent with nothing connected, buzzes like nuts with the preamp connected but turned off, quiets right down when the pre is powered up, and now has developed a new problem - an intermittent short in one channel (the power amp - not the pre). I'm forced to conclude that the power amp is on it's last legs and needs repair or replacement - but still - I've never seen any combination act like that. Bill.
Bill*B said:
Hi Bill,
I think you got two separate issues here. The preamp thing is known - with the secondary of the output transformer floating, and not driven, it picks up any stray fields that are around. And there are a lot around with all those apparatus in a modern home. Switch it on and the driver stage low impedance reflects to the secondary and absorbs the stray fields. Nothing special here, and there really isn't a problem, except the stray pickup. Try to ground the secondary terminal that ultimately connects to the screen of the interconnect, to the ground of the preamp, that'll fix it I think.
The power amp thing is a separate thing - over to you 😉
Jan Didden
Hi Bill,
I tried that same situation last night with my transformer-coupled preamp, and the same thing happens to me. My secondary is floating, and if I turn off the preamp but leave the power amp on, the noise level gets loud.
I think this is the problem with using a balanced driver into an unbalanced receiver? The obvious fix is to create a "fully balanced transmission line" by making the power amp input balanced as well, and using a twisted pair, or star quad interconnect. This is the solution I prefer.
Joel
My preamp is at http://www.joeltunnah.com
I tried that same situation last night with my transformer-coupled preamp, and the same thing happens to me. My secondary is floating, and if I turn off the preamp but leave the power amp on, the noise level gets loud.
I think this is the problem with using a balanced driver into an unbalanced receiver? The obvious fix is to create a "fully balanced transmission line" by making the power amp input balanced as well, and using a twisted pair, or star quad interconnect. This is the solution I prefer.
Joel
My preamp is at http://www.joeltunnah.com
I have a transformer output line stage preamp in my system with the output floated, and it is silent when it is powered off and the amplifier is on. The schematic is in figure 3 here.
http://www.raleighaudio.com/active_output.htm
Before this I had another transformer output line stage preamp in my system and it also was silent when it was powered off and the amplifier was on. The schematic is here.
http://www.raleighaudio.com/figure_12.htm
So, in some cases the situation causes a problem and in other cases it doesn’t. Something interesting is going on here. I wonder what it is?
Dave
http://www.raleighaudio.com/active_output.htm
Before this I had another transformer output line stage preamp in my system and it also was silent when it was powered off and the amplifier was on. The schematic is here.
http://www.raleighaudio.com/figure_12.htm
So, in some cases the situation causes a problem and in other cases it doesn’t. Something interesting is going on here. I wonder what it is?
Dave
By the way, my amplifier has an unbalanced single ended input. There is no transformer on its input.
Dave
Dave
David Davenport said:
I told you guys what it is above. With the amp off, his transfo turns into a magnetic field probe connected to an audio amp.😉 .
Termination will fix that, either at the primary or at the secondary.
Jan Didden
"Something interesting is going on here. I wonder what it is?"
Ground problems can occur for dozens of reasons, and unfortunately it's usually not possible to simply implement "A" and have a noise-free system.
Not all single-ended, unbalanced input stages are equivalent, when it comes to noise. I also have tube amps that can be left on with the preamp off, and don't make noise. Others buzz like crazy. The gain of the first stage makes a big difference.
There is absolutely no reason to defeat the balanced output of the preamp by grounding one side. You lose many of the benefits of using the transformer in the first place, IMO. I would try to attack this problem from different angles, or at least don't run the amp with the preamp off...
Joel
Ground problems can occur for dozens of reasons, and unfortunately it's usually not possible to simply implement "A" and have a noise-free system.
Not all single-ended, unbalanced input stages are equivalent, when it comes to noise. I also have tube amps that can be left on with the preamp off, and don't make noise. Others buzz like crazy. The gain of the first stage makes a big difference.
There is absolutely no reason to defeat the balanced output of the preamp by grounding one side. You lose many of the benefits of using the transformer in the first place, IMO. I would try to attack this problem from different angles, or at least don't run the amp with the preamp off...
Joel
This discussion has been very helpful. I'll play with it some more, and post my findings in a few weeks. Bill.
Why not just have the preamp on when the power amp is? Then there is no need to re invent the wheel.
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