robbie010

Amplifier Hum - Whats realistic?

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Super Wammer

I’ve recently switched amplifiers, the latter, which were 300B monoblocks had a physical hum issue with the toroidal transformer... not the end of the world but enough for me to notice in a quiet room. 

My new amp, a Trilogy VTI (EL34) valve amp has no physical noise but has a very feint background hum through the speakers. Now, with a pair or old Wharfedale XP2’s (86db) it was pretty much inaudible. However, with the la scala’s (105db) It is audible when silent or during very quiet passages when listening. 

I’m beginning to obsess over it but am I being unrealistic when it comes to hums or vibrations?

Are EL34 valves particularly noisy?

Could it simply an issue with speaker sensitivity?

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Super Wammer
13 minutes ago, robbie010 said:

I’ve recently switched amplifiers, the latter, which were 300B monoblocks had a physical hum issue with the toroidal transformer... not the end of the world but enough for me to notice in a quiet room. 

My new amp, a Trilogy VTI (EL34) valve amp has no physical noise but has a very feint background hum through the speakers. Now, with a pair or old Wharfedale XP2’s (86db) it was pretty much inaudible. However, with the la scala’s (105db) It is audible when silent or during very quiet passages when listening. 

I’m beginning to obsess over it but am I being unrealistic when it comes to hums or vibrations?

Are EL34 valves particularly noisy?

Could it simply an issue with speaker sensitivity?

It is a fact of life that as transformers age the laminations lose compression and they hum - my oldest Hafler hums along nicely .. but of course as soon as you put on the music you cannot hear it.   If the hum becomes intrusive on listening then I will consider fitting a new transformer (perhaps - it is currently held in reserve in case one of my other two packs up).  

You may be able to reduce the hum by checking the bolts holding the transformer to the chassis are nice and tight .. also isolating the amp (the vibrations can be amplified by the chassis or the furniture it is on vibrating in sympathy) and with solid state amps provided you do not impede air flow sometimes placing a solid  weighty item on the amp can help reduce the noise (I visited one bloke had a brick on his amp) #.

So if it is not intrusive on listening to music do not worry about it .. if it is worrying you then work out the specification and get a new transformer to replace the old one.

As to noisy valves you can get vibration rings to put around valves to stop noise I think -  (I could be wrong Rab will put me right if I am, the sound is nothing like transformer hum and can be microphonic and make its way to the output signal so will increase and decrease as you change the volume on the amp.  Transformer hum is a single frequency buzz and should not find its way into the audio signal).

I am no expert - least of all with valves so I hope all I have said here is correct (it is my understanding) and I hope other wammers will point out if I have got anything wrong here (not least for my education) 

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Super Wammer
Posted (edited)

I notice the manufacturer does not quote a figure for Signal to Noise. I would expect not to hear any hum from the speaker. You could try re-locating the amp away from other products. My Luxman is -105dB which is a very good figure (KT88 Valves).

Edited by Radioham

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Super Wammer
Posted (edited)
16 minutes ago, Radioham said:

I notice the manufacturer does not quote a figure for Signal to Noise. I would expect not to hear any hum from the speaker. You could try re-locating the amp away from other products. 

No way I can do that, unfortunately. 

My assumption was that it was just the background noise floor being exasperated by the overly sensitive speakers. I don’t think it is anything to do with the power or a ground loop, as I have a shielded mains cable plugged in to a DC blocker, which in turn has a tachima 6 way power strip plugged in to it supplying all my equipment from a single socket. So no DC and there should be no ground loop. 

just to add, I did a little testing by unplugging the speakers and could hear nothing, so the amp is physically silent. I then plugged in the low frequency and high frequency connections separately (bi-wire) and could only hear the hum from the low frequency driver, even with my ear next to the mid and tweeter it was silent, so it is definitely only a low frequency hum. 

Edited by robbie010

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I think 105db speakers would be asking a lot from many amps. I've never had speakers above 94db and heard a bit of low level hum/noise here !.Tried a dc blocker, that didn't help. It's the late night, noodly music when I notice it most, oh not to get hung up on stuff.

The sorbothane domes are inexpensive and can help with the mechanical side of vibrations. I don't expect el34 amps to be more prone to noise than other valve types. Maybe silent ss amps are easier to build ? What amps were popular with the klipsch systems of the past ?

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With 105dB speakers you need a couple of watts or so, 6 max. In such amps hum is critical since most listening is with the amp delivering 1-20mW power, or up to a quarter of a volt at the speaker. It's not a valve thing, it's a circuit topology issue. If you have an amp that puts out 25W a channel then for most people that equates to 83-90dB 'average sensitivity' speakers and a few mV hum it will dissappear. At the sensitivity you have it will be a problem.

So it's the amp. Get a smaller one with quieter PSU and enjoy your lovely speakers. Yamamoto or Tom Evans come to mind, or a nice T-amp?

Sent from my BLA-L09 using Tapatalk

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Not sure if running the amp with no speakers is wise, even for a short time, unless you put a dummy load resistor on the terminals ?

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Super Wammer

I think you are asking a lot, for an amp to be totally silent into 106 Db speakers. Most of the good class D amps are near silent, in my system, but again would they be into your speakers. Every speaker has its compromises.

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My kt88 tubes also used to hum through the speakers when no music was playing. I could actually hear small church bells ring through the tweeters when I place my ear next to them. But it is a muffled hum from the mid range and bass drivers. But no issues once I started playing. 

 After trying several different things including the kitchen sink, I found that changing my interconnects solved the issue. My previous interconnects from Hifidelity though stupidly expensive were some how picking up noise. My muxh cheaper transparent music links are quiet. So may be something you can try sir.

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My t amp and bantam amp run silent..t amps are cheap on ebay..worth a thought? Need sensitive speakers though..

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It sound like a grounding issue inside the amp. Look inside and check the heater circuit it may have a hum pot if your lucky, but there should be a connection to the ground somewhere, if your not sure post a good pic of the internals. 

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Super Wammer
1 hour ago, steve 57 said:

It sound like a grounding issue inside the amp. Look inside and check the heater circuit it may have a hum pot if your lucky, but there should be a connection to the ground somewhere, if your not sure post a good pic of the internals. 

I can’t see any pots in there....

D7A57D15-C0E4-485B-86EB-06EA8CAD31BE.jpeg

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E0489EFF-1110-4E59-AD91-BBDA192F60A4.jpeg

0617E3E3-8374-4CD4-8EB8-8B515455482F.jpeg

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Super Wammer
5 hours ago, newlash09 said:

My kt88 tubes also used to hum through the speakers when no music was playing. I could actually hear small church bells ring through the tweeters when I place my ear next to them. But it is a muffled hum from the mid range and bass drivers. But no issues once I started playing. 

 After trying several different things including the kitchen sink, I found that changing my interconnects solved the issue. My previous interconnects from Hifidelity though stupidly expensive were some how picking up noise. My muxh cheaper transparent music links are quiet. So may be something you can try sir.

Thanks for the tip, I’ll try playing around with the cables. 

I’ve also got another set of EL34 valves I could try switching out. 

I already tried using a lower gain 5751 tubes, in place of the high gain ECC83s in the pre-stage and I’m not sure it made much difference, if any. 

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It's worth first off swapping the valves for your others, just in case they've sub standard CH insulation, but really, you'll need to get it on a scope to trace where the hum is coming from. There's a lot of socking great transformers in quite close proximity to the signal valves, and the relay trafo right next to the '34s. It's a nice looking layout, but not a quiet looking one!

Sent from my BLA-L09 using Tapatalk

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Thanks for the pics. They don't show too much detail. 

1st. ensure the ribbon input cable is well down on the chassis it needs to be away from the valves. 

2nd. do you have a multimeter? if so check if there is a connection between the ground  (outside of the phono sockets? ) to the heater circuit.. you may need to trace these. Check with no power to the amp! The heater circuit should be grounded 

I can't find a circuit for the amp but the heaters and the basic layout will be similar (not the same) as a mullard 5/20. Looking at that circuit will help your understanding. 

Be careful and check with the amp unplugged

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