• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

New Tube Phonopreamp Hum

Lavane said:
If it were mine, I would still be curious if unsoldering the ground wire from the IEC socket would further lower the hum in the phono preamp. I get a slight hum through my phono stage if I turn the volume up to around 5:00 also though.
Its kind of expected with a tube phono stage. But disconnecting the earth ground in a stand alone EAR clone I gave to my son lowered the slight hum even further. It probably had a ground loop being connected to the preamp I gave him also?
Click to expand...

I may very well do that in the future. Right now the hum is very small, in fact I can't be certain the hum I do hear isn't the preamp. It has a very small hum when volume control is at about 5 o'clock. Right now, though :rockon:
 
A metal chassis (if it isn't double insulated) containing mains voltage should be connected to mains earth for safety. Signal 0V doesn't have to be connected to mains earth but the chassis has to be for safety.
 
Lavane said:
If it were mine, I would still be curious if unsoldering the ground wire from the IEC socket would further lower the hum in the phono preamp. I get a slight hum through my phono stage if I turn the volume up to around 5:00 also though.
Its kind of expected with a tube phono stage. But disconnecting the earth ground in a stand alone EAR clone I gave to my son lowered the slight hum even further. It probably had a ground loop being connected to the preamp I gave him also?
Click to expand...

Well, I finally decided to look at the hum issue again. So, I noticed the chassis ground readings I was getting from the screws holding the PCBs were wonky. Turns out the screws were really loose. After tightening them up, I got good readings from all of them. I also removed the IEC filter and reinstalled it. With the earth ground removed from the PCB I did continuity tests on all the RCA jacks. No continuity between the chassis and the jacks. Resoldered earth back to IEC filter. Now I get continuity between jacks for earth or chassis ground. This seems normal since the chassis and earth are connected via the filter. The phonopre is very quiet with tiny hum at full volume. This newbie learned that screws need to be tight along with the transformer to chassis. My preamp started a mechanical hum that was solved by tightening everything up.
 
geode said:
Well, I finally decided to look at the hum issue again. So, I noticed the chassis ground readings I was getting from the screws holding the PCBs were wonky. Turns out the screws were really loose. After tightening them up, I got good readings from all of them. I also removed the IEC filter and reinstalled it. With the earth ground removed from the PCB I did continuity tests on all the RCA jacks. No continuity between the chassis and the jacks. Resoldered earth back to IEC filter. Now I get continuity between jacks for earth or chassis ground. This seems normal since the chassis and earth are connected via the filter. The phonopre is very quiet with tiny hum at full volume. This newbie learned that screws need to be tight along with the transformer to chassis. My preamp started a mechanical hum that was solved by tightening everything up.
Click to expand...
Good the hear it was something simple. Even the two tube phono preamps I bought and one built have a tiny bit of hum at full volume. But that's with the volume all the way up. It's nothing I worry about.
 
Lavane said:
Good the hear it was something simple. Even the two tube phono preamps I bought and one built have a tiny bit of hum at full volume. But that's with the volume all the way up. It's nothing I worry about.
Click to expand...

:thumbsup:
 
geode said:
Well, I finally decided to look at the hum issue again. So, I noticed the chassis ground readings I was getting from the screws holding the PCBs were wonky. Turns out the screws were really loose. After tightening them up, I got good readings from all of them. I also removed the IEC filter and reinstalled it. With the earth ground removed from the PCB I did continuity tests on all the RCA jacks. No continuity between the chassis and the jacks. Resoldered earth back to IEC filter. Now I get continuity between jacks for earth or chassis ground. This seems normal since the chassis and earth are connected via the filter. The phonopre is very quiet with tiny hum at full volume. This newbie learned that screws need to be tight along with the transformer to chassis. My preamp started a mechanical hum that was solved by tightening everything up.
Click to expand...

Good detective work.
 
You must log in or register to reply here.
Back
Top Bottom