New Tube Phonopreamp Hum

[geode]

So, I just put together the Tubes4Hifi PH16 phonopre. This is the 2nd kit I have ever built. The 1st was the SP14 preamp. It came out great and sounds fantastic. The Ph16 is working great, too. Sounds fantastic. The only small issue I have is a little hum with the Sp14 gain controls maxed and the volume control at about 2:00. It doesn't interfere with the music while playing records on it. I'm thinking of trying to lower the hum as much as i can. I'm a complete newb on tube stuff. I'm thinking of redoing some of the wiring, shortening it as much as possible and rerouting it. I have already plugged everything into one outet, swapped interconnects around, and put shorting plugs into the phono input jacks. Moved the wires around gently with two chopsticks,but no change. I have some pics of the build, if there is something I should do I would appreciate the feedback.

 

[TriodeLuvr]

Have you measured the hum to determine whether it meets the factory specification?

( SNR: 76dB, A-weighted, inputs shorted )

Jack

 

[ludite]

I would suspect the hum is from the tubes. When running new 12ax7’s I always run the 12ax7lps. ( long plate spiral) I’ve had this issue on a phono preamp before. Grounds are another thing to check

 

[Lavane]

With the couple tube preamps I've built, and the one built into the preamp I bought, there was and is a slight bit of hum at max volume. My preamp is an Aikido also. With the two I built, I had a hum problem that was pretty bad at first.
It came down to grounding, re-routing wiring, and even a ground loop problem.
With the one, just flipping the power plug helped a lot. I haven't had any problems with new tubes being noisy and getting better over time needing break in though. They either were noisy to start with and stayed that way, or they were quiet. I have read several threads over at DIY concerning hum problems in Roy's preamp and phono preamp kits. Wire routing and grounding seemed to be pretty important in them. Maybe shoot Roy pictures of your build. He does sell them pre-built, so he should be able to help letting you know if anything needs changing.

 

[CohibaJoe]

With the couple tube preamps I've built, and the one built into the preamp I bought, there was and is a slight bit of hum at max volume. My preamp is an Aikido also. With the two I built, I had a hum problem that was pretty bad at first.
It came down to grounding, re-routing wiring, and even a ground loop problem.
With the one, just flipping the power plug helped a lot. I haven't had any problems with new tubes being noisy and getting better over time needing break in though. They either were noisy to start with and stayed that way, or they were quiet. I have read several threads over at DIY concerning hum problems in Roy's preamp and phono preamp kits. Wire routing and grounding seemed to be pretty important in them. Maybe shoot Roy pictures of your build. He does sell them pre-built, so he should be able to help letting you know if anything needs changing.

I had Roy Pre-Built the PH-16X 1/2022. This unit is very quiet and using Philips ECC88, Matsushita PCC88/7DJ8 tubes.

 

[TriodeLuvr]

When running new 12ax7’s I always run the 12ax7lps. ( long plate spiral)

The PCB appears to contain a DC power supply for filaments. If that's correct, spiral filaments won't be beneficial.

Jack

 

[geode]

Have you measured the hum to determine whether it meets the factory specification?

( SNR: 76dB, A-weighted, inputs shorted )

Jack

I have not measured hum. I'm not even sure how to measure it. I'm basing my opinion on the hum level being more than it should be by listening to the noise floor of other phono pres I have had. Of course, they were all solid state and installed in Integrated amps, preamps, and receivers.

 

[geode]

I would suspect the hum is from the tubes. When running new 12ax7’s I always run the 12ax7lps. ( long plate spiral) I’ve had this issue on a phono preamp before. Grounds are another thing to check

I only have the one set of tubes right now, so I can't swap tubes, yet.

 

[geode]

With the couple tube preamps I've built, and the one built into the preamp I bought, there was and is a slight bit of hum at max volume. My preamp is an Aikido also. With the two I built, I had a hum problem that was pretty bad at first.
It came down to grounding, re-routing wiring, and even a ground loop problem.
With the one, just flipping the power plug helped a lot. I haven't had any problems with new tubes being noisy and getting better over time needing break in though. They either were noisy to start with and stayed that way, or they were quiet. I have read several threads over at DIY concerning hum problems in Roy's preamp and phono preamp kits. Wire routing and grounding seemed to be pretty important in them. Maybe shoot Roy pictures of your build. He does sell them pre-built, so he should be able to help letting you know if anything needs changing.

Yeah, I read a lot of posts on hum, but most were concerning the SP14 which I really don't have much problem with. It has a very small bit of hum with gain controls maxed out and volume control almost fully engaged. It is so little I won't mess with it. I have showed pics to Roy, he says it's probably a wiring issue. I plan on rewiring the boards and try and duplicate the routing according to his pictures. My wires are tightly twisted but run close to each other. Some of the wires can be shortened. Hopefully redoing the wires isn't a pointless exercise.

 

[Lavane]

Phono preamps tend to be more sensitive. Again, I would shoot Roy some pictures of your build to see if he would do anything different. Try plugging the phono preamp into another circuit. An outlet outlet not on the same circuit as the preamp.

 

[geode]

The PCB appears to contain a DC power supply for filaments. If that's correct, spiral filaments won't be beneficial.

Jack

View attachment 2713898

It is DC. So, they are tightly twisted. Is that a problem? I think Roy's pictures show them twisted, too.

Phono preamps tend to be more sensitive. Again, I would shoot Roy some pictures of your build to see if he would do anything different. Try plugging the phono preamp into another circuit. An outlet outlet not on the same circuit as the preamp.

I did send Roy pictures, his response was

"make sure all your equipment is plugged into the same outlet strip, so all the grounds are common at the same place.

Make sure all AC wiring is as short as possible and as far away from gain stages as possible.

Make sure you have no internal ground loops, and that every is grounded."

 

[Lavane]

I wonder if a ground buss would help? I've started using ground busses now instead of star grounds. I put busses in several guitar amp builds and they reduced hum dramatically compared to the star grounds shown in the scnematics. I've used them in several preamp builds now too.

 

[geode]

Just thought of something. The SP14 preamp has a grounding lug on it next to the phono inputs. The PH16 also has a grounding lug next to its input. I connected the TT to the PH16 input and the TT ground wire is connected here. Should I try and run a ground wire from the PH16 ground to the SP14 ground? Doesn't seem necessary, though.

 

[geode]

I wonder if a ground buss would help? I've started using ground busses now instead of star grounds. I put busses in several guitar amp builds and they reduced hum dramatically compared to the star grounds shown in the scnematics. I've used them in several preamp builds now too.

I'm not certain my limited knowledge would allow me to do that. My level of expertise is I can solder, follow directions and pictures but circuit analysis and electronic theory, not so much.

 

[geode]

I'm in the process of buying another set of tubes from Jim McShane, including new rectifier. I need another set anyway. This will allow me to rule out the tubes.

 

[theflattire]

My grain of salt take: tube phono stages are going to have some hum because of the amount of gain. I suppose you pay for blackness in higher end stages.
In my main amp and phono stage, I never bothered to check for hum, I just assume that it's there and I never push the volume way up or hold my ear to the speaker anyway. If I could hear it during playback it would bother me, but I can't so it doesn't.
Not saying not to worry about it, but unless its indicative of an error in the build or defect in design, and again, you can't hear it at normal listening levels, I just give it a pass. As long as nothing is smoking or glowing or making popping sounds...
BTW, I've put together three tube amp kits, one pre and two main.
YMMV

 

[Lavane]

Have you tried lifting the earth ground? I had an EAR phono pre clone I gave to my son that had a switch to disconnect the earth ground. It was quieter with the earth ground disconnected.

 

[TriodeLuvr]

It is DC. So, they are tightly twisted. Is that a problem? I think Roy's pictures show them twisted, too.

"Spiral filaments" refers to construction inside the 12AX7. It's a technique for reducing hum when the filaments are AC powered. Not the case here, so it's irrelevant. About your filament wiring, It will make no difference whether it's twisted or how tightly. That's only an issue for AC heating.

Can you tell whether the hum is 60Hz or 120Hz? Also, what is the third wire ground from the power inlet connected to?

Jack

 

[geode]

My grain of salt take: tube phono stages are going to have some hum because of the amount of gain. I suppose you pay for blackness in higher end stages.
In my main amp and phono stage, I never bothered to check for hum, I just assume that it's there and I never push the volume way up or hold my ear to the speaker anyway. If I could hear it during playback it would bother me, but I can't so it doesn't.
Not saying not to worry about it, but unless its indicative of an error in the build or defect in design, and again, you can't hear it at normal listening levels, I just give it a pass. As long as nothing is smoking or glowing or making popping sounds...
BTW, I've put together three tube amp kits, one pre and two main.
YMMV

I agree with that. But there are quite a few folks that claim their PH16 is dead silent. Roy says there should be no hum. I just think mine has more than it should, so I want to try and quiet it down some if I can. It's perfectly playable right now and sounds good.

 

[geode]

Have you tried lifting the earth ground? I had an EAR phono pre clone I gave to my son that had a switch to disconnect the earth ground. It was quieter with the earth ground disconnected.

No switch on this phonopre.