help needed in troubleshooting a faint hissing sound from speakers!!

aKnyght

aKnyght

Active member
Joined
Jan 18, 2018
Messages
1,052
Location
saṃsāra
as some here have almost certainly experienced and worked on this type issue, i wanted to see if they can help me identify the source and to suggest possible remedies…

the issue i am experiencing is a faint hissing / white-noise sound coming from both speakers. increasing system volume at the pre-amp increases the volume of the hissing. at somewhat higher than normal listening levels, the hissing can be heard up to about 3 feet away from each speaker and is inaudible from the listening position ~15 feet away.

my system has never sounded better and i am exceedingly happy with it; however, i feel that solving this small issue will only improve an already great listening experience.

system architecture is:

roon ROCK server > USB cable > DAC > I/C > pre-amp > I/C > amp > S/C > speakers

the single-ended I/C cables are shielded with one floating end. currently, i am using stock power cables which are all plugged into a single serge protector.

in an attempt to troubleshoot and identify the source of the hissing, i have done the following tests (in isolation):

1. disconnected the I/C cables from the pre-amp to the amp …result: hissing stops and the speakers are dead quiet.

2. disconnected the I/C cables from the DAC to the pre-amp …result: hissing still present.

3. connected the DAC directly to the amp …result: hissing stops and the speakers are dead quiet.

4. cycled through the pre-amp input selector …result: hissing still present on every input regardless of whether or not there is an I/C cable connected to that input.

5. increased / decreased the volume at the preamp …volume of hissing noise increases / decreases with pre-amp volume

6. reversed direction of I/C cables from pre-amp to amp to have the non-floating end connected to the amp …result: hissing still present.

7. swapped out I/C cables from pre-amp to amp with 3 others, all shielded …result: hissing still present.

8. installed different tubes (2) in the pre-amp …result: hissing still present.

9. installed different signal and rectifier tubes (5) in the power-amp …result: hissing still present.

10. plugged the pre-amp directly into the wall outlet rather than the surge protector …result: hissing still present.

11. activated the mute on the pre-amp ...result: hissing stops and the speakers are dead quiet.​

it is almost certain the noise is attributable to the pre-amp itself (perhaps caused by a less than ideal power source?). however, at this point, i have tried everything i can think of to pin down the source of the noise but have exceeded my knowledge / experience in this area.

given the above, does anyone have any thoughts on the source, other tests and/or remedies? ...or, seems unlikely but maybe this is just how the pre-amp is?

any and all help is greatly appreciated — thanks !!!


______________________________________

notes:

other than the takatsuki 300B output tubes, all the normally installed tubes for both the pre-amp and amp are sourced from VTS and are specified for ultra-low microphonics.

the pre-amp has an internal MM phono amp. i did not replace the associated three tubes. while this phono-amp is not in the signal chain described above, it is conceivable these tube could be involved.

the ATC-5 is a pretty high gain pre-amp at 18 dB.
 
Based on the results of your thorough diagnostic testing the source of the hiss is clearly the preamp itself. Hiss is generally caused from the gain circuitry in active devices and is often more prevalent in tube amplification. Since you've tried replacing the tubes without reducing the level of hiss it may just be inherent in the preamp's circuit although depending upon its age may be able to be reduced by having it serviced. Cables and their shielding can affect hum levels but not typically hiss. I doubt that the phono stage tubes would affect the hiss you're hearing on non-phono inputs, think you'd be best focusing on the preamp's line level and power supply tubes. Tubes with low microphonics won't necessarily help lower hiss levels, rather you should be trying to find tubes which are specifically selected for low noise levels. Since the level of hiss is inaudible at the listening position at normal volumes it may just be something you may decide to live with. Trying a different preamp would be another step you could take if you wish to pursue the issue. Good luck and hope I was able to be of some assistance!
 
audio.bill said:
Based on the results of your thorough diagnostic testing the source of the hiss is clearly the preamp itself. Hiss is generally caused from the gain circuitry in active devices and is often more prevalent in tube amplification. Since you've tried replacing the tubes without reducing the level of hiss it may just be inherent in the preamp's circuit although depending upon its age may be able to be reduced by having it serviced. Cables and their shielding can affect hum levels but not typically hiss. I doubt that the phono stage tubes would affect the hiss you're hearing on non-phono inputs, think you'd be best focusing on the preamp's line level and power supply tubes. Tubes with low microphonics won't necessarily help lower hiss levels, rather you should be trying to find tubes which are specifically selected for low noise levels. Since the level of hiss is inaudible at the listening position at normal volumes it may just be something you may decide to live with. Trying a different preamp would be another step you could take if you wish to pursue the issue. Good luck and hope I was able to be of some assistance!
Click to expand...

thanks for this thoughtful and detailed post which is of great help. given the testing i had done, it is hard to think of a conclusion other than the one you suggest.

the pre-amp does not have tube rectification and i am pretty sure the line-level tubes are low noise as well as low microphonics, but it is definitely worth circling back with VTS on the issue.

the SQ might be a notch better if the hissing could be made to go away, but as you mention the design may preclude that. given the current (phenomenal) SQ of my system, the issue is certainly not anywhere near a level that would cause me to change pre-amps.

i chose this pre-amp for it's synergy with the power amp and for the phono stage which would allow me to add a "side-car" analog source if i ever decide to go there. however, if i choose to stay with only a digital source then it might be worth investigating another pre-amp at some point in the future.

thanks again!!
 
audio.bill said:
Based on the results of your thorough diagnostic testing the source of the hiss is clearly the preamp itself. Hiss is generally caused from the gain circuitry in active devices and is often more prevalent in tube amplification. Since you've tried replacing the tubes without reducing the level of hiss it may just be inherent in the preamp's circuit although depending upon its age may be able to be reduced by having it serviced. Cables and their shielding can affect hum levels but not typically hiss. I doubt that the phono stage tubes would affect the hiss you're hearing on non-phono inputs, think you'd be best focusing on the preamp's line level and power supply tubes. Tubes with low microphonics won't necessarily help lower hiss levels, rather you should be trying to find tubes which are specifically selected for low noise levels. Since the level of hiss is inaudible at the listening position at normal volumes it may just be something you may decide to live with. Trying a different preamp would be another step you could take if you wish to pursue the issue. Good luck and hope I was able to be of some assistance!
Click to expand...

Very good assessment. I agree that the troubleshooting points the finger to the preamp.
 
Moreover… Tube preamps are inherently noisy (at least that was my experience).
Is it possible that the noise was always there and only now you are hearing it?

If replacing all tubes did not make any difference, then you should contact the manufacturer and see what they recommend.

And of course, since you can’t hear it when sitting 15 feet away, you always have the option of not worrying about it and keep enjoying the music.
 
nicoff said:
Moreover… Tube preamps are inherently noisy (at least that was my experience).
Is it possible that the noise was always there and only now you are hearing it?

If replacing all tubes did not make any difference, then you should contact the manufacturer and see what they recommend.

And of course, since you can’t hear it when sitting 15 feet away, you always have the option of not worrying about it and keep enjoying the music.
Click to expand...

the pre-amp was bought new about 2 months ago. the hiss is not something one would normally notice unless looking for it. it has probably always been there but i never noticed it until a few days ago when i installed the NOS tubes from VTS and then stuck my ear up against the speakers.

just on the off chance it is a faulty unit, i plan to run the issue by my dealer to see if he can put the question to the manufacturer via the importer to see what they have to say. it is interesting to note that with my almarro integrated tube amp the speakers are dead quiet.

i am certainly happy to keep enjoying the music but just tinkering and trying to make things perfect ...that's how we do, right?

;)
 
Why don't you take the pre with you to the dealer and hook it up there and see if the noise is present on his system.
And, as has been suggested, put a different pre in your system to see if the noise might ,by some chance, be coming from a different component
 
stereogeek said:
I see you did install different tubes in the preamp, were they the stock ones?
Click to expand...

i have two sets of pre-amp tubes: one is the set of stock tubes and the other is a set of valvo/telefunken NOS tubes from VTS. i observe the hissing with both sets.
 
jadedavid said:
Why don't you take the pre with you to the dealer and hook it up there and see if the noise is present on his system.
And, as has been suggested, put a different pre in your system to see if the noise might ,by some chance, be coming from a different component
Click to expand...

i only have this one pre-amp as i was using an integrated previously. also, the dealer is a 5+ hour drive. in any event, the various tests i ran pretty much confirm the noise is coming from the pre- amp.
 
You identified the problem yourself earlier in the thread when you said the preamp has 18db of gain. The amp has a very low input sensitivity of 290mv so with those two pieces in front of speakers with a sensitivity rating of 97db what you are hearing is the base noise floor of that complete system. Not likely that continuing to change tubes is going to lower it any further and as you have to get 12 feet closer to the speakers than your NSP it's really not causing you a problem and you yourself didn't even notice it until you were close enough when changing the preamp tubes. With lower efficiency speakers the distance before hearing the tube hiss would be smaller and with higher efficiency ones larger.
 
both the ATM 300R and Almaro a318B have attenuators and high input sensitivities. If your line source outputs 2v you shouldn't need an active line stage, it will compound the noise issues. Bottom line, what you're hearing is the self-noise of the electronics, add to that 300Bs which from my experience are nosier still.
 
This may be things you know already but I found this information on Air Tight. You might try a wood platform under the preamp if not already on wood. That's a fairly expensive preamp and the care taken in design it's hard to accept the hiss is normal. But, maybe, due to circumstance as Jack mentioned.

I didn't know much about AR and found this interesting myself. After reading this again I can't tell if the writer is referring to the power amps or all AR components in regards to wood isolation, it's worth a try though if not already that way.
The company´s name is A&M LTD - Air Tight is the brand name.
A&M LTD has also a second brand - acoustic masterpiece, which is moderate priced and not made in Japan in the Air Tight factory.
Th founder of Air Tight is Miura San, who worked more than 30 years for Luxman and designed most of their legendary tube amps.
The company is really small, Miura and his partner, and 6 other people are working there.
Everything is handmade.

All Air Tight components have some things in common:

1. All chassis are made of steel - not aluminium.
This philosophy shares Air Tight with Shindo and also Kondo.
The reason for using steel is, that those companies do not use screened cables throughout their topology, to get proper shielding, the amplifiers has to be build in a certain style, were every section has his own compartment.
If you ever see a Shindo, Kondo or Air Tight open, you see the amazing amount of metal work.
The stele is also not screwed together, it is made of one pice, only the top plate and the bottom plate is screwed on.

Most of the bottom plates (every power amp...) are made of copper!
And some of the internal parts, which needs extra shielding and decoupling are also made out of copper - this technique shars Air Tight with Kondo.

The whole chassis is made in a style, that it is not recommended to use moern rack systems, as Finite Elements or HRX base systems.
It is ment to be put on simple plywood - this is exactly the same philosophy Shindo San employed in his amplifiers.
With air tight you should use a Box Furniture system or Norbert Gütte´s Bench.
The amplifiers bring everything, which is needed to decouple them from the platform, were they stand - if you do not follow that rule, they will sound slow, muddy and lifeless....
 
thanks for this info. air tight internal design and build quality are indeed quite impressive.

both the pre-amp and amp are on a core audio design wooden rack -- which is made of a plywood material (apple ply) and similar to the gutte bench and box furniture racks mentioned.

i plan on following up with the importer / manufacturer just to see what they have to say.
 
Mr Peabody said:
This may be things you know already but I found this information on Air Tight. You might try a wood platform under the preamp if not already on wood. That's a fairly expensive preamp and the care taken in design it's hard to accept the hiss is normal. But, maybe, due to circumstance as Jack mentioned.

I didn't know much about AR and found this interesting myself. After reading this again I can't tell if the writer is referring to the power amps or all AR components in regards to wood isolation, it's worth a try though if not already that way.
The company´s name is A&M LTD - Air Tight is the brand name.
A&M LTD has also a second brand - acoustic masterpiece, which is moderate priced and not made in Japan in the Air Tight factory.
Th founder of Air Tight is Miura San, who worked more than 30 years for Luxman and designed most of their legendary tube amps.
The company is really small, Miura and his partner, and 6 other people are working there.
Everything is handmade.

All Air Tight components have some things in common:

1. All chassis are made of steel - not aluminium.
This philosophy shares Air Tight with Shindo and also Kondo.
The reason for using steel is, that those companies do not use screened cables throughout their topology, to get proper shielding, the amplifiers has to be build in a certain style, were every section has his own compartment.
If you ever see a Shindo, Kondo or Air Tight open, you see the amazing amount of metal work.
The stele is also not screwed together, it is made of one pice, only the top plate and the bottom plate is screwed on.

Most of the bottom plates (every power amp...) are made of copper!
And some of the internal parts, which needs extra shielding and decoupling are also made out of copper - this technique shars Air Tight with Kondo.

The whole chassis is made in a style, that it is not recommended to use moern rack systems, as Finite Elements or HRX base systems.
It is ment to be put on simple plywood - this is exactly the same philosophy Shindo San employed in his amplifiers.
With air tight you should use a Box Furniture system or Norbert Gütte´s Bench.
The amplifiers bring everything, which is needed to decouple them from the platform, were they stand - if you do not follow that rule, they will sound slow, muddy and lifeless....
Click to expand...

So… a simple wood platform can fix the hiss issue? I Would love to hear back from the OP after he tries that.
 
Jack said:
You identified the problem yourself earlier in the thread when you said the preamp has 18db of gain. The amp has a very low input sensitivity of 290mv so with those two pieces in front of speakers with a sensitivity rating of 97db what you are hearing is the base noise floor of that complete system. Not likely that continuing to change tubes is going to lower it any further and as you have to get 12 feet closer to the speakers than your NSP it's really not causing you a problem and you yourself didn't even notice it until you were close enough when changing the preamp tubes. With lower efficiency speakers the distance before hearing the tube hiss would be smaller and with higher efficiency ones larger.
Click to expand...

thanks so much for this post. it has taken me a while to research, learn more about and test to confirm the diagnosis you describe.

further tests:

1. i put my pass ACA 8 wpc SS power amp into the system. this amp has a much lower input sensitivity (higher mV). the hissing noise could only be very faintly heard with my ear right at the speaker. as soon as moving a few inches away it was no longer possible to hear the hissing.

2. i hooked up my 91 dB jm-Labs speakers. as expected the hissing noise was reduced significantly although by not quite as much as with test #1

3. taking the pre-amp out of the system in both tests #1 and #2 caused the speakers to become dead quiet.

i think your diagnosis is almost certainly the answer ... with the pre-amp being the source of the noise and the high sensitivity power-amp and speakers doing a great job of exposing it.

however, the question still remains as to whether my specific pre-amp is exhibiting normal behavior in this regard.

i have put the question to the dealer and asked him to have the importer confirm with the manufacturer.

thanks again!
 
to close the loop for those following along at home...

i spoke directly with the importer / distributor who could not have been nicer or more helpful. after describing the noise, he said it sounded like normal tube rush which is made more noticeable by my 97 dB speakers, but he said he would speak with the manufacturer to confirm and get their thoughts. a few days later he called to report the manufacturer confirmed this is quite normal for the pre-amp and suggested turning down the attenuators on the power amp a notch or two in order to compensate for the high sensitivity speakers.

so... great to know the pre-amp is functioning normally and not something else!!

given the noise is really quite faint and can only be heard when putting an ear right in front of the speakers, it is a total non-issue and, perhaps, just my being a perfectionist rather than anything else ...which is quite reassuring as my system sounds so much better with the pre-amp in the chain -- fuller, richer, more textured and 3-D

thanks to all here for the help!!
 
It sounds like a quite fantastic pre-amp with really good support. I know how a little noise can drive you crazy. I have had a couple tube pre-amps with similar miniscule noise. Luckily my Hattor is dead quite, but it only has two tubes.

Congrats on such a fine piece!
 
If the hiss varies with volume a lot depends on the topology of the preamp. Obviously decreasing the input sensitivity of the amps/speakers is a fix.

But- this particular symptom is one I've seen many times. It can happen if there is no stopping resistor between the volume control and the first stage of gain- the hiss will vary with the volume control setting until you get quite high on the control at which point it might settle down again. I don't know the internal design of the preamp, but with most (competent) line stages the volume control is placed prior to any amplification so as to prevent the input signal from overloading the input stage.

I have been surprised by how many times I've seen stopping resistors omitted from 'high end audio' circuits...

Good Luck!
 
You must log in or register to reply here.
Back
Top