(Resolved) Low hum/buzz even when DAC is not connected.

[elgringo81]

Ok first off, testing for noise with out shorting plugs or DAC plugged in, or the tube removed, is not really going help moving forward. However if you still have noise with the amp turned off that means that the amp is not generating the noise. If you suspect your mains, take the amp and shorting plugs somewhere else, to work or something and have a listen

The next thing I can think of is to remove the choke and replace the resistor...John

Once I discovered the shorting plugs, I have been using them to test this hizz issue I have ever since.
You can see it earlier in this threat that I made some and did the test with them plugged in.

I am basically not interested at this point how the amp sounds with empty RCA inputs.


I will need to wait for a good time to roll back the choke, I will most likely test that here over the weekend.

Here are my thoughts at the current moment.

I would say that if I dont use the Clear tops, both my HD800S and HD650 are silent at all volume levels.
If there is hiss, its even hard for me to notice it. But I can notice a small hizz like I have descripted earlier with my DT-1770-Pro closed headphones (Impedance: 250 Ohm, SPL: 102 dB) They seem to be more sensitive or that its more noticeable because of the closed back design.

I am starting to wonder if this hizz is basically normal because HD800S and HD650 don't seem to be picking it up anymore.

If that (Tired) conclusion is correct. Then I only have one small issue remaining.

That is the 50Hz buzz interference when my hand gets close to the Pre tubes.
Could it be because if ground issues in the apartment I am living in?
I have tried different sockets in the kitchen but its does not seem to matter.

I will report back with results from (rolling back) the choke upgrade.

 

[elgringo81]

I have ordered 1x Mullars 12au7 and 2x Clear tops.
I should be getting these tubes next week.

it will be interesting to see how that goes.

 

[elgringo81]

Just wanted to update this threat.

I could not wait so I have now rolled back the choke upgrade. (So far I cannot hear much difference in SQ, I will spend some more time with it like it is)

the Hizz remains the same and maybe as expected,
the 50Hz buzz is still there when I come close to the 12au7 tubes.
I have re-flowed the pre socket 2x times and re-flowed the TRS socket and pot.

I am starting to give this new TKD pot a bad eye..

 

[Paul Birkeland]

If you have hum that appears when your hand gets close to the 12AU7, then the Crack is still not properly grounded.  I would recommend checking to see if the electrical outlets where you are using your Crack are grounded.  This isn't all that uncommon in older structures, and it is a nice upgrade to add a grounding rod and provide a solid ground path for your electronics.

 

[elgringo81]

@Paul.

Thanks Paul.

You were right. The amplifier was not grounded, but that has been sorted now.

I have now connected it to a second outlet which I have opened and verified it has a ground wire in place.
The 50Hz interference is now gone for good. I will check the old socket for faults later.

I am going to stop worrying about the low hizz when I use the DT 1770 Pro headphones. I believe its just because they are more sensitive than the HD800S and HD650.

I bought them because they got great reviews and they are 250 Ohm for my Crack. I really like them,
but it seems that they would need lower gain then the Sennheisers, the crack was build around.

I have no complains about the TKD pot now, it works fine and the Crack sounds great.

Thank you for all the information and help.

 

[Paul Birkeland]

I'm glad you got it sorted.  It's certainly worth checking all your outlets to be sure they are grounded.

-PB