Silent but audible noise (hiss) in loudspeaker and SNR

[chris256]

Hello together!

How big does the SNR have to be so that you don't hear any noise in the loudspeaker anymore - not even with the ear nearly directly on the loudspeaker membrane (2 cm)? So I'm not interested in what is audible 10 cm or more in front of it, but only the case where the ear is directly on the membrane.

Background:
I can hear very slight noise directly with the ear in the tweeter or midrange (nothing in the woofer), as long as the preamplifier (pre / power amp combo - pre including DA converter) is not muted or the volume is one stage above completely quiet (first stage of a digital managed analogue volume control - at 0 it's probably muted - because there isn't any difference any more between the mute switch). Turning the volume up (without a signal applied) does not change the volume of the noise. For the test, a digital input source is chosen (not a phono or any other analog input channel).

Logically, this can't be the noise of the DA converter, since it would have to get louder as the volume is turned up.

Therefore I assume that some stage after the DA-converter must cause the noise (which disappears when the preamplifier is muted - i.e. the output to the power amplifier is connected to ground).

That leaves only the output stage of the preamplifier or the power amplifier itself.

I tested the power amplifier (T+A A200) without input wiring and could perceive absolutely no noise (dead silence). In how far this is meaningful, I can not say of course, because I do not know if there is not still a mute even though no mute is signaled.

I can also not hear any difference, regardless of whether the connection of the pre- or power amplifier is balanced or unbalanced.

By the way, the preamp is a T+A music player balanced with an additional preamp module. To be honest - I have this in my suspicion. From my point of view it is a rather cheap solution - simply a TDA 7303. The SNR is given by T+A with 109 dB a-weighted for the music player balanced as a whole (STMicroelectronics gives 106 dB for the TDA 7303 - how there should come out 109 dB in the end, is puzzling to me) - (the power amplifier A200 is given by T+A with 113 dB).

Thanks
Chris

 

[Blumlein 88]

Sounds like you are hearing noise from the preamp if I followed your description correctly.

 

[Blumlein 88]

Looking at specs, your power amp has a gain of 26 db. So even though your preamp has 109 db SNR, that receives a boost of 26 db by the power amp. Which apparently pushes noise up enough you can hear it if close enough. Since you hear nothing with output of the preamp muted and with input of the amp disconnected, what you are hearing is prior to the power amp input and is the preamp. So if your preamp had an SNR of 135 db it would be silent (this is not really possible because of physics). It might even be silent with only a few more db quieter noise floor. BTW SNR and noise floor are not quite the same, but the only specs I have to go on.

Now I think you are being too harsh on the gear. If you have to practically put your ear on the tweeter to hear it, then you aren't going to hear it in normal use and it has no bearing on sound quality you will get. It would take almost nothing to mask that noise once music starts. And think of it this way, if you played music at a normal level and tried to listen with your ear 2 cm away, it likely is loud enough to nearly deafen you.

 

[DVDdoug]

It's not SNR when there is no "S". It's the total noise out of the amplifier, the efficiency of your speakers, how close you are to the speakers, and any acoustic noise in the room which might mask the noise from the speakers.

 

[Chrise36]

Hello together!

How big does the SNR have to be so that you don't hear any noise in the loudspeaker anymore - not even with the ear nearly directly on the loudspeaker membrane (2 cm)? So I'm not interested in what is audible 10 cm or more in front of it, but only the case where the ear is directly on the membrane.

Background:
I can hear very slight noise directly with the ear in the tweeter or midrange (nothing in the woofer), as long as the preamplifier (pre / power amp combo - pre including DA converter) is not muted or the volume is one stage above completely quiet (first stage of a digital managed analogue volume control - at 0 it's probably muted - because there isn't any difference any more between the mute switch). Turning the volume up (without a signal applied) does not change the volume of the noise. For the test, a digital input source is chosen (not a phono or any other analog input channel).

Logically, this can't be the noise of the DA converter, since it would have to get louder as the volume is turned up.

Therefore I assume that some stage after the DA-converter must cause the noise (which disappears when the preamplifier is muted - i.e. the output to the power amplifier is connected to ground).

That leaves only the output stage of the preamplifier or the power amplifier itself.

I tested the power amplifier (T+A A200) without input wiring and could perceive absolutely no noise (dead silence). In how far this is meaningful, I can not say of course, because I do not know if there is not still a mute even though no mute is signaled.

I can also not hear any difference, regardless of whether the connection of the pre- or power amplifier is balanced or unbalanced.

By the way, the preamp is a T+A music player balanced with an additional preamp module. To be honest - I have this in my suspicion. From my point of view it is a rather cheap solution - simply a TDA 7303. The SNR is given by T+A with 109 dB a-weighted for the music player balanced as a whole (STMicroelectronics gives 106 dB for the TDA 7303 - how there should come out 109 dB in the end, is puzzling to me) - (the power amplifier A200 is given by T+A with 113 dB).

Thanks
ChrisView attachment 262269

It depends on the sensitivity of your speakers also

 

[Blumlein 88]

It's not SNR when there is no "S". It's the total noise out of the amplifier, the efficiency of your speakers, how close you are to the speakers, and any acoustic noise in the room which might mask the noise from the speakers.

I agree, but noise out of the amp is sure to be at least as high as SNR would indicate, and might be lower. Again, I couldn't find specs for the noise floor.

 

[chris256]

Now I think you are being too harsh on the gear.

Yes, that's right. It's not really a problem to me - it's just out of curiosity.

Looking at specs, your power amp has a gain of 26 db.

Your explanation via the gain (btw. where did you found it) sounds plausible to me.

Meanwhile I did now one more test: I connected my headphone amplifier via unbalanced fixed and variable (= preamplifier module) output and couldn't hear any noise in the headphone (gain of the headphone amplifier (Sennheiser HDVD 800) was quite low - but enough to get the same volume compared to the digital input) - even using max volume on the preamp side (and headphone amplifier side).

 

[chris256]

It depends on the sensitivity of your speakers also

85 dB / 1 W / 1 m

 

[Blumlein 88]

Yes, that's right. It's not really a problem to me - it's just out of curiosity.


Your explanation via the gain (btw. where did you found it) sounds plausible to me.

Meanwhile I did now one more test: I connected my headphone amplifier via unbalanced fixed and variable (= preamplifier module) output and couldn't hear any noise in the headphone (gain of the headphone amplifier (Sennheiser HDVD 800) was quite low - but enough to get the same volume compared to the digital input) - even using max volume on the preamp side (and headphone amplifier side).

I calculated it. They gave sensitivity of input and max power. So it is close to 32 volts max on the power amp (32 volts over 4 ohms is 256 watts). So the ratio of input voltage for max power to output voltage at max power was real close to 26 db.

Yes the headphone probably has not very much voltage gain. You also have some difference in sensitivity of headphones with headphone amp and speakers with power amp. So that isn't really surprising. 109 db SNR or so isn't a bad spec.

 

[Chrise36]

85 dB / 1 W / 1 m

Not that high. Usually preamps are cleaner than amps. I am guessing it is the amp unless there is any smps near the amps that is causing noise.

 

[Blumlein 88]

Not that high. Usually preamps are cleaner than amps. I am guessing it is the amp unless there is any smps near the amps that is causing noise.

He stated with preamp muted or with no connections to the amp input there is no noise. Not from the amp. Even if preamps are cleaner, the signal gets amplified by the power amp which pushes the noise level upwards.

 

[Chrise36]

He stated with preamp muted or with no connections to the amp input there is no noise. Not from the amp. Even if preamps are cleaner, the signal gets amplified by the power amp which pushes the noise level upwards.

This is suspicious for ground loop noise not sure it is the preamp alone. He can try with a battery powered source laptop or phone.

 

[chris256]

So the ratio of input voltage for max power to output voltage at max power was real close to 26 db.

Just found the gain given by T+A - they say it would be even ~ 37 dB.

 

[Chrise36]

Just found the gain given by T+A - they say it would be even ~ 37 dB.

Can you try with your phone only connected to the amp?

 

[Blumlein 88]

Just found the gain given by T+A - they say it would be even ~ 37 dB.

Well they are getting numbers 6 db different, but I'll take their word for it. Makes it even more likely you are hearing the preamp noise floor because of amp gain.

 

[chris256]

Can you try with your phone only connected to the amp?

Good idea - but the amp doesn't have a headphone connector.
I'm thinking about a battery driven source - but do not have any idea at the moment. It should be a device with low noise floor I think.

 

[Chrise36]

Good idea - but the amp doesn't have a headphone connector.
I'm thinking about a battery driven source - but do not have any idea at the moment. It should be a device with low noise floor I think.

Any macbook around?

 

[chris256]

no

 

[Chrise36]

Ok from a quick look on company site a polish magazine measured the S/N of the amp at 84 db

 

[chris256]

Well, those S/N values measured by different magazines and T+A itself differ extremely (some give a reference point - others not):

T+A:
113 dB

Audio Poland:
S/N 84 dB (Dynamic: 105 dB - what is dynamic exactly?)

Stereo:
S/N at 50mW/5W 67/63 dB 87/85 db (8 Ohm / 4 Ohm)

Stereoplay:
XLR (2,83 V at 8 Ω) 93 dB
XLR (10 V at 8 Ω) 104 dB

All those completely different values are confusing. Why isn't there a standard?