Muffsy phono stage hum problem

[skrodahl]

I'd also like to add that no safety ground can be lethal. Even if nobody dies, it could lead to other nasty stuff like fires. It's very likely that the assurance won't cover anything bad that happens.

I would first isolate all signal connections from the chassis, then connect the mains earth to the chassis. All while making sure that all chassis parts are electrically connected.

...or do away with the mains-connected transformer and use an AC wallwart, which - after all - still is a transformer.

 

[Daniel4381]

We all need a "vacation" from time to time. Mine is coming in a little over a week from now. I just hope him not being active isn't a sign of any trouble.

It is connected with the negative termina, cannot be seen in the photo. I have checked all terminal connections, and all are ok as multimeter showing continuation. I have disconnected the output grd connection ( photo attached). The spot on the board is splash if glue ( glue gun glue) and it has not damaged the cap. The main's grd and chassis is tested, that is not shorted (photo attached). The TT output cables are shielded (photo attached). There is no change in the hum or buz after this change, it is the same as it was. Just to remind, my speaker has active woofer section, it remsins dead quite when playing CD or DAC. I will change the AC input, also take out the transformer within a short time and give the update.

One mete information, when I checked the grd of DC connection (amongst the + G - connection) with chassis grd, it hss short, continuation in multimeter.

 

[skrodahl]

Excellent feedback,
The DC GND (which is also the signal GND) has been connected to the chassis, so you'd expect continuation.

Try moving the AC input when you have the time.

 

[Daniel4381]

Excellent feedback,
The DC GND (which is also the signal GND) has been connected to the chassis, so you'd expect continuation.

Try moving the AC input when you have the time.

Removed the tranformer from the chassis, connected the Secondary to PSU. Now, there is no buzzing noise, hum is still there as pronounced as it was at the left channel. By the way, I disconnected the grd from the right output as directed. I measured all the voltages as it is mentioned in the webpage, all are ok.

 

[skrodahl]

That's progress, at least.
I would try to simplify as much as possible, or remove as many sources of error as possible. The next simple test would be removing the ground connection to the chassis.

 

[Daniel4381]

That's progress, at least.
I would try to simplify as much as possible, or remove as many sources of error as possible. The next simple test would be removing the ground connection to the chassis.

Hum increases a lot when I disconnect grd from chassis.

 

[skrodahl]

You have a grounding problem, for sure.
The fact that you get less noise when you touch both the turntable and the phono pre is proof of that.

Troubleshooting remotely is really hard, especially when there are unknown factors. I suggest that you continue to simplify and remove unknowns.

A long cable connected to ground could act as an antenna, an RCA connector connected to ground and nothing else can introduce noise. You have a 5 mV input signal (at 1 kHz), that's about 1/500th of your typical DAC output. Any noise introduced at the input will be amplified several hundred times.

One other simplification is to separate the grounds on the input at output RCA connectors. You'll need to reattach that ground shield again, and try out different configurations with your chassis ground. (Yes, the grounds will meet on the PCB input/output connectors)

There's not one single silver bullet when it comes to grounding problems, so you need to keep on testing in the same manner as we've done until now.