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 Post subject: Phono Preamp humming
PostPosted: Wed Sep 26, 2018 5:32 pm 
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Joined: Mon Jan 25, 2016 7:19 am
Posts: 104
Location: Toronto, ON, CA
Hi All. After a good deal of troubleshooting it appears that my phono preamp (Audio Research PH6) has began humming after it's been on a while. It sounds over the system as a grounding issue might, but what essentially is happening is that if the pre-amp is turned on it begins to hum somewhere toward the center of the unit (ie it doesn't sound like it's coming from the tubes located on the far right of the amp). The humming seems to get louder the longer the unit is on, but goes away once it been allowed to cool. I'm assuming this will require service, but before I take it in I'm curious as if anything else might be amiss.

Around the same time I started noticing this, I had upgraded the tubes in my integrated rogue amp to kt-120s, using socket savers to make them fit. The phono preamp is a completely separate component located earlier than the amp in the circuit, so am I correct to assume this wouldn't be affected by the amplifier? The other thing is that I changed the power cable on my power conditioner to another one I bought on Amazon, which is very well made and received great reviews. I swapped them back and forth and it didn't make a difference. Is it at all possible this could have somehow compromised the circuitry of the phone pre?

I imagine a capacitor or something needs to be replaced, but I figured I'd ask for input first as I'm not at all technically endowed. Thanks!

Edit: I should note that the hum appears evening in the unit is muted. It then becomes amplified when injured, but it's there regardless.


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 Post subject: Re: Phono Preamp humming
PostPosted: Wed Sep 26, 2018 6:34 pm 
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Joined: Wed Mar 18, 2009 3:59 pm
Posts: 311
Location: Ottawa, ON, CA
I assume you have checked the TT ground to the preamp and that your cartridge clips are secure? It's a process of elimination before pointing to the preamp.


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 Post subject: Re: Phono Preamp humming
PostPosted: Thu Sep 27, 2018 2:41 am 
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Posts: 219
Location: Ottawa, ON, CA
Hum can come from all sorts of weird things, so be patient. Have you tried:

moving the pre-amp to see if it hums in a different location?
disconnecting the cables coming into the pre-amp to see if it still hums?
disconnecting the cable coming out of the pre-amp?
swapping tubes in the pre-amp?

additionally, do you know what else is on that electrical circuit? Have you added anything on that circuit recently?

Have you bought any new equipment or appliances in your house? A/C units, fridges, freezers, lighting, anything?

Once the hum starts, if you leave it on, does the hum ever stop?

I strongly doubt that changing tubes on your amp would have any affect on this, unless the new tubes are throwing off spurious rf noise somehow. Have you replaced the original tubes and does it still hum? Same thing for the new power cord, unless it's so badly made that it's somehow spewing noise (not even sure how that could be).

Can you give the pre-amp a lyric sheet to see if it stops humming? ;)

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 Post subject: Re: Phono Preamp humming
PostPosted: Thu Sep 27, 2018 4:16 am 
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Joined: Thu Jan 13, 2011 11:29 am
Posts: 800
Location: St.Catharines, ON, CA
Transformer hum? Does the unit vibrate also?
Try snugging up the transformer bolts.
Try with no power conditioner.

G


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 Post subject: Re: Phono Preamp humming
PostPosted: Thu Sep 27, 2018 3:14 pm 
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Joined: Mon Jan 25, 2016 7:19 am
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Location: Toronto, ON, CA
Hi all. So I'll elaborate, and thank you.

There are two ground cables connection my turntable to my amp. Don't ask me why, but I've always needed two to get proper grounding. I've double and triple checked the connections, and swapped cables etc...I've been through this before. After taking everything apart and losing hair over a weekend, I eventually found that one of the two ground wires got severed somehow.

There is nothing added other than the new tubes and the power cord, and I've otherwise used this setup successfully for a long time.

Everything is connected to a power conditioner designed for audio - has amp inputs etc..., So everything is on that circuit through the conditioner. This may seem odd to say, but my house is tiny and putting the unit anywhere else is not any option. I think transformer hum might be a possibility. I'm concerned its the unit itself because of how it develops as it is left on. Then if I turn the unit on and off it remains, but if the unit is left off for a while there are no issues until it warms up again. I just turned it on and can't here it at all, but in a few hours it will show up and get worse the longer it's left on. I think the unit may indeed vibrate too, I'm going to pay more attention to that tonight.

I'm mean, is there any danger of something blowing? Or does that seem unlikely? It's a newish unit and looks pristine.


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 Post subject: Re: Phono Preamp humming
PostPosted: Thu Sep 27, 2018 3:27 pm 
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Joined: Fri May 18, 2018 6:35 am
Posts: 822
Location: Toronto, ON, CA
Does the preamp hum/buzz when only it is powered up? As in, no cables other than power connected to it?

This is a symptom of DC offset affecting the transformer inside the unit. Given that it appears to have an EI type (which are more resistant to DC offset than toroidal) it would indicate that you have a serious problem. Certainly you should check the mounting screws for it are tight but if they are and there is noise...Well, you need to get rid of the DC offset. My vote is for Emotiva CMX-2 although you may need something even stronger.

https://www.kempelektroniksshop.nl/line ... ocker.html

Note: even if you have some AC "purifier" already you should be aware that most do not deal with DC offset.


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 Post subject: Re: Phono Preamp humming
PostPosted: Thu Sep 27, 2018 6:23 pm 
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Location: Toronto, ON, CA
Thanks, but why would this develop? I've been using the same rig for a year or so with no problem. Cant they just replace something that's needs to be replaced? I'm going to try your suggestion now.

Actually before I do this, is it not a bad idea to run a tube amp with no load? I would have to leave it on for a few hours. Thanks.


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 Post subject: Re: Phono Preamp humming
PostPosted: Thu Sep 27, 2018 7:50 pm 
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Joined: Sun Jul 05, 2009 3:15 pm
Posts: 39
Location: gatineau, QC, CA
Toi should first try to determine the frequency of the hum. Download an app on your phone such as spectroid and put your phone on the preamp. If the frequency of the hum is a multiple or fraction of 60hz, my quess is that the transformer is vibrating. If that's the problem (as someone else mentioned) tighten the transfo down to the casing. Good luck.


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 Post subject: Re: Phono Preamp humming
PostPosted: Fri Sep 28, 2018 8:07 am 
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Location: Markham, ON, CA
OK, the system starts a hum now. This is after you have made some changes. simple. Go back and undo the changes you made. One thing at a time. If the hum goes away, you have identified the culprit.

If the hum stays, then you will need to be systematic and scientific about sourcing the problem. Typically, the hum is ground-related. So make sure you run a ground wire from everything to the amp. Here is one for you; I had a hum in my turntable. I checked everything. Still the hum....then I noticed that the hum got louder when I moved my hand closer to the tonearm....voila....it tuns out the green cartridge wire was kinked (I bought the arm used) and the previous owner (or me) had damaged that wire....a simple re-location of the offending wire (slightly further away from the other three wires) was all it took. And the tonearm IS separately grounded.....sometimes we do things (moving a cable as an example) that is just enough to cause a hum in the system

Go back and (one at a time) re-trace your recent changes...and reverse the changes. Also check each cable....moving and-or re-connnecting each RCA connection, move each cable with the amp or and see if the sound changes....you will eventually find the issue.

No, there should be no problem leaving your phono amp on etc....I do that with both my tube pre-amps. No issues


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 Post subject: Re: Phono Preamp humming
PostPosted: Fri Sep 28, 2018 3:13 pm 
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Joined: Mon Jan 25, 2016 7:19 am
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Location: Toronto, ON, CA
I appreciate the responses, but what's not accounted for is the fact that the hum develops as the unit is on, over an hour or so. That's not a normal grounding issue (I do. Have some experience here and have done what's been suggested). I'm going to try the app thing. I do think the transformer explanation makes sense.

Ps, Brownline, you leave tube equipment with no load (is no cables or speakers) left turn on? I've heard that's a major no no.


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 Post subject: Re: Phono Preamp humming
PostPosted: Fri Sep 28, 2018 4:38 pm 
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Location: Toronto, ON, CA
JasonGR wrote:
I appreciate the responses, but what's not accounted for is the fact that the hum develops as the unit is on, over an hour or so. That's not a normal grounding issue (I do. Have some experience here and have done what's been suggested). I'm going to try the app thing. I do think the transformer explanation makes sense.

Ps, Brownline, you leave tube equipment with no load (is no cables or speakers) left turn on? I've heard that's a major no no.


If you plug in some piece of gear - particularly with no other connections - and it starts making a humming/buzzing sound then there is a problem with the main transformer in the unit.

There are two possible causes, not necessarily separate...

First is that the transformer has windings that are now not physically fixed - usually by potting. Note: the transformer itself could be loose but I would still say windings are no longer fixed which caused mounting screws to also back out...

The second is DC offset...DC offset is becoming very common in urban areas due to so many crap devices now on the grid. These can range from Tesla charging units, solar invertors and way too many cheap (as in: all) wall-warts and LED light bulbs...

Now, from what you say it could be either or both...Because excess heat can cause windings to loosen up. And DC offset will definitely cause transformers to heat up beyond normal operating conditions...


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 Post subject: Re: Phono Preamp humming
PostPosted: Fri Sep 28, 2018 5:13 pm 
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Joined: Sat Sep 01, 2012 5:08 am
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Location: Montréal, QC, CA
The problem is likely a supply capacitor that's leaking...

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 Post subject: Re: Phono Preamp humming
PostPosted: Fri Sep 28, 2018 8:10 pm 
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Location: Toronto, ON, CA
Well. It's definitely 60 cycle hum. That app recommend is great. I've never used one that allows you to zero in on frequency like that. So at least I know nothing will be exploding...or could that still be a capacitor?

I tightened the transformer, and it wasnt that. I unplugged the phono preamp and bypassed the power conditioner - that didn't work. I swapped all of the cables, replaced the power cables back to the original, swapped out the rca cables and changed the inputs, adjusted the height of the shelf in case the unit wasn't getting enough air. It's definitely the phono preamp itself making the noise and I think it is the transformer, but its not loose. I'm curious if it is something there previously that's being amplified now by the larger tubes. I may swap the tubes tomorrow and compare - but then again if that's the case it won't fix anything. Im not picking anything up on my other phono pre-amp, but it's of much poorer quality. My only other guess is that the rca connection to my current turntable may be loose? It's hard to trouble shoot that as it's wired into the table. It also doesn't really would like it.


Can I ask, assume this is a line issue and not a preamp issue, is there a way to provide additional grounding? I already have two ground wires going from the turntable to the amp. The preamp has a connection for a ground wire, but I wasn't able to achieve any improvement by using it. Any "audiophile ground cables" on the market? :)

Luckily I'll have another turntable soon that is more heavy duty. I could get lucky.

Fifth business I will look more into this DC offset stuff. I've never heard of it and not sure what it is..,so thanks.

On the upside I had the chance to experiment without the rubber tube dampers that were on when I got the unit. They make a massive difference. Sounded like garbage without them. Food for thought.


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 Post subject: Re: Phono Preamp humming
PostPosted: Sat Sep 29, 2018 2:37 am 
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Joined: Sun Jul 05, 2009 3:15 pm
Posts: 39
Location: gatineau, QC, CA
Is the 60hz humm coming out of your speakers?
My understanding from prior posts was that the noise was the actual preamp humming but it wasn't transmitted throught to the output. If that's the case them your problem is NOT caused by your turntable or ground or RCA interconnects or power câbles.

If it's actually being heard via the speakers, it would be important to know if the humm increases proportionally to the volume setting.


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 Post subject: Re: Phono Preamp humming
PostPosted: Sat Sep 29, 2018 4:07 am 
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Joined: Thu Jan 13, 2011 11:29 am
Posts: 800
Location: St.Catharines, ON, CA
Article on transformer noise.

http://www.briangladstone.com/wp-conten ... ormers.pdf

Considering it takes an hour or so to develop the hum makes transformer/power supply component suspect.
Flexing components with a chopstick might reveal the issue.

G


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