Hi everyone, I need some help for my UcD700 build. I’ve noticed a couple of months after having finished my amp, a weak noise, like a sort of crackling hiss, coming from one channel with the amp powered on and disconnected from any source. The weird thing is that if I connect the preamp and turn it on, the noise disappearrs. Some kind of ground issue? Bad solderings? If I unmount the UcD modules and swap them from one channel to the other, the noise has a channel swap too. So I think there is a problem on one of the two modules. What can it be? Does someone of you have an idea?
Thanks in advance,
Gaetano.
Thanks in advance,
Gaetano.
This is a popular misconception:
For case 2: if that "~20khz" offset in switching frequency is not an exact amount of switching periods then sub-harmonics as well as harmonics are generated. Even for a 40khz offset it is not possible to remove intermodulation products from noise floor at <20khz completely.
To make it worse, the audio signal modulates the offset in switching frequency, moving it closer or further to a fixed amount of periods, so a very complicated, variable, mixture of harmonics and subharmonics appears at the noise floor, as music signal is played.
btw: UCD700 are single channel modules. Separating the modules buries the interference in noise floor. I doubt the original poster was experiencing intermodulation issues, but maybe intermittent contact of mains line noise pickup.
For case 2: if that "~20khz" offset in switching frequency is not an exact amount of switching periods then sub-harmonics as well as harmonics are generated. Even for a 40khz offset it is not possible to remove intermodulation products from noise floor at <20khz completely.
To make it worse, the audio signal modulates the offset in switching frequency, moving it closer or further to a fixed amount of periods, so a very complicated, variable, mixture of harmonics and subharmonics appears at the noise floor, as music signal is played.
btw: UCD700 are single channel modules. Separating the modules buries the interference in noise floor. I doubt the original poster was experiencing intermodulation issues, but maybe intermittent contact of mains line noise pickup.
I don’t know why, but I think that you are right. Could it be that the module is catching in some way RF? If yes, how could I check and eventually fix it? In the end it is a little shortcoming which (weird thing) even disappears when I connect and turn on the preamp. My fear is that it can affect the overall performance of the amp. Any suggestion?
Many thanks!
Gaetano.
How long are the cables between the preamp and the amp? Wouldn't be the first time a long floating cable on a high impedance input acted as an antenna and picked up RF noise.
As Eva said, the dual mono approach (although more costly) is the best way to eliminate any noise issues between two modules.
As Eva said, the dual mono approach (although more costly) is the best way to eliminate any noise issues between two modules.
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I have many experiences with this case.
Single channel separation sometimes not help. But most cases are solved with this approach.
A 20kHz at least both channel switching speed difference sometimes also not help because in UcD design with common parts available on market, each channel switching speed will keep changing and hence still can resonate each other if the switching speed almost meet. But if stable enough this will help. Intermodulation and harmonic always there but if not amplified at next ordes then will not audible. We are talking a DIY way.
In this case, only good parts and good layout will help. also using closed type inductor. This is the reason why hypex use only closed inductor.
First of all thanks everyone for the kind replies!
The problem here is that I hear this weak noise (which seems like a sort of RF) when the power amp is turned on and phisically disconnected from preamp. When I make this connection this disturb is still present, but it completely disappears when I turn on the preamp, so from the loudspeaker I can hear only silence. And if I try to swap the two ucd700 from one channel to the other, the noise has this swap too.
Gaetano.
The problem here is that I hear this weak noise (which seems like a sort of RF) when the power amp is turned on and phisically disconnected from preamp. When I make this connection this disturb is still present, but it completely disappears when I turn on the preamp, so from the loudspeaker I can hear only silence. And if I try to swap the two ucd700 from one channel to the other, the noise has this swap too.
Gaetano.
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