Trying to get my amps as clean as possible I seem to run into the same noise floor issue every time. On 2 channel amps that share the same power supply I get an increase of the noise floor by 5-15dB when I connect both channels to the amp. I have tried all the groundloop fixes I have found on here and it have helped significantly but the issue is still there. I also have a few dual mono amps that don't have this issue and I am starting to think this might be unavoidable given a shared PS.
I've attached a REW dump to illustrate the issue and looking to understand if its as good as it gets with shared power supplies or of I should keep chasing a fix?
It's the same with multiple amps and sources so not just one amp or source.
I've attached a REW dump to illustrate the issue and looking to understand if its as good as it gets with shared power supplies or of I should keep chasing a fix?
It's the same with multiple amps and sources so not just one amp or source.
Maybe I figured it out, when I route the signal cables from the preamp tightly together the issue mostly disappear. The current cables are double shielded Albedo MKII Sommer cables so should be ok and even though I have read and was aware keeping the cable "loop" as tight as possible I never would have thought it would have this much of an impact. Great if anyone has any experience or thoughts on this.
Will try a few other cables to see if it gets less sensitive.
Will try a few other cables to see if it gets less sensitive.
Large magnetic loops pick up a lot, and act as a high pass filter too which is why you get so many mains harmonics visible - induced voltage is proportional to rate of change of flux times loop area. A lot of commercial stereo signal leads miss a trick by not using twisted configuration for the two screened leads which would cancel loop area out better than side-by-side screened cable does.
here is a nice write-up by member djoffe
https://www.updatemydynaco.com/documents/GroundingProblemsRev1p4.pdf
https://www.updatemydynaco.com/documents/GroundingProblemsRev1p4.pdf
To test whether this is a cross-channel ground loop or not, try the following debug procedure:-
1. Short the inputs (connect signal hot to signal ground right at the input on each channel.
2. If you still have serious noise as in your plot above, there is a good chance the problem is a common impedance coupling problem around your power supply wiring
3. If you have no noise or very low noise, then the next step is to check if it is a cross-channel ground loop
4. To do this, take a single cable and connect the right channel to the left channel
5. If your noise shoots up like it is on your plot, then you probably have a cross-channel ground loop.
This presentation can offer some useful insights https://hifisonix.com/wp-content/uploads/2019/02/Ground-Loops.pdf
Here are DIYAudio member ilimzn's posts which offer some excellent insight https://hifisonix.com/wp-content/uploads/2019/04/ilimzns-Excellent-Posts-on-Ground-Loops.pdf
Finally, some additional guidance for layout etc https://hifisonix.com/wp-content/uploads/2023/11/More-Notes-On-Amplifier-Hum-Problems.pdf
(NB - for debugging, it's probably easier to work in dBV while you try to get the noise problems resolved. This will give an absolute reference as to the noise floor.)
1. Short the inputs (connect signal hot to signal ground right at the input on each channel.
2. If you still have serious noise as in your plot above, there is a good chance the problem is a common impedance coupling problem around your power supply wiring
3. If you have no noise or very low noise, then the next step is to check if it is a cross-channel ground loop
4. To do this, take a single cable and connect the right channel to the left channel
5. If your noise shoots up like it is on your plot, then you probably have a cross-channel ground loop.
This presentation can offer some useful insights https://hifisonix.com/wp-content/uploads/2019/02/Ground-Loops.pdf
Here are DIYAudio member ilimzn's posts which offer some excellent insight https://hifisonix.com/wp-content/uploads/2019/04/ilimzns-Excellent-Posts-on-Ground-Loops.pdf
Finally, some additional guidance for layout etc https://hifisonix.com/wp-content/uploads/2023/11/More-Notes-On-Amplifier-Hum-Problems.pdf
(NB - for debugging, it's probably easier to work in dBV while you try to get the noise problems resolved. This will give an absolute reference as to the noise floor.)
Outstanding content Bonsai, thanks. I had already found your page though and downloaded all the relevant content. My issue on this amp was indeed a cross channel groundloop and even though I thought I had broken the loop fully there was still a pcb trace "hiding" between both channels signal grounds.