If a "commercial" tube amp has 84 dB SNR, be glad and enjoy it....
With commonly used tubes, and power supplies it is really hard to get over that value. To go higher you'll need noise selected high quality input tubes, DC heater, and very well filtered HV supply lines. Assuming a very quiet listening environment (30 dB background noise) and 110 dB
eek max listening level, the mentioned 84 dB should be more than satisfying in most cases.
With commonly used tubes, and power supplies it is really hard to get over that value. To go higher you'll need noise selected high quality input tubes, DC heater, and very well filtered HV supply lines. Assuming a very quiet listening environment (30 dB background noise) and 110 dB
eek max listening level, the mentioned 84 dB should be more than satisfying in most cases.
Is it a problem at –84 dB?
Let me think of ways by which it could be. Hmm… if one has an amplifier (plus either integrated, or separate preamp) “turned to 10”, and is feeding it with a source (such as an iPad, computer, Alexa box, BOSE whatever, or low-output turntable) that has its own regulation of 'volume', … then when playing not-very-loud music levels, the –84 dB SNR … with a –50 dB source material is only –34 dB SNR of “headroom”. Something that with headphones on, you'd definitely hear. And would be annoying.
But just imagining that case, the “solution” also becomes obvious. Drive the darn amplifier higher, and use its attenuation to drop the background noise to imperceptible. Yah-know-what-I-mean?
Anyway, maybe “obvious”, but seems … obvious.
Just saying,
GoatGuy ✓
Use resistors with less noise.
Keep audio input screened.
Decouple well each power supply stage.
Keep audio input away from transformers and HVAC.
Keep valves away from transformers and HVAC.
Some people recommend DC heater supply but in my experience any hum I have had has been for a different reason.
Keep audio input screened.
Decouple well each power supply stage.
Keep audio input away from transformers and HVAC.
Keep valves away from transformers and HVAC.
Some people recommend DC heater supply but in my experience any hum I have had has been for a different reason.
Yes, how did you measure it?
Preferably you have made a spectrum plot with a soundcard, as that will show us the noise floor (possibly just of your soundcard and measurement setup) and all the residuals coming up from the noise floor. Then the query will be whether any of the residuals are hum due to your test setup, and what bandwidth you are making a noise measurement over.
Preferably you have made a spectrum plot with a soundcard, as that will show us the noise floor (possibly just of your soundcard and measurement setup) and all the residuals coming up from the noise floor. Then the query will be whether any of the residuals are hum due to your test setup, and what bandwidth you are making a noise measurement over.
Hi Guys,
Thanks for the response. It's just a curious question. I assume if one can improve SNR you could hear more details from the speakers. Yes if speakers are hi efficiency type could even hear hiss or even hum. So the question is would there be any SQ benefit if we are able to improve SNR say from 84 - 90db ?
Thanks
Thanks for the response. It's just a curious question. I assume if one can improve SNR you could hear more details from the speakers. Yes if speakers are hi efficiency type could even hear hiss or even hum. So the question is would there be any SQ benefit if we are able to improve SNR say from 84 - 90db ?
Thanks
Yes DF 96 you brought out a very good point. I post thread on why a pre amp is needed when an amp only needs slightly more then 1 volt for full power.
Im wondering too why there's a number of PP amps using 12AX7 tubes as input tube.
This tube has a Mu of 100, is this really necessary ?
Thanks
Im wondering too why there's a number of PP amps using 12AX7 tubes as input tube.
This tube has a Mu of 100, is this really necessary ?
Thanks
I suspect it's a matter of "That's the way they did it in the 50's".
A 12AX7 can drive a pair of 6V6 tubes in PP with only 2 stages (VA/PI as one stage, power as the other), and it was cheap to implement while still having enough gain to run a feedback loop.
More powerful amplifiers (Williamson at least) used 6SN7 instead and added a driver stage between the VA/PI and the power tubes.
Personally, I use the pentode of a 6F12P as a triode (mu ~70) to feed the triode section used as a concertina/cathodyne PI which drives a 6SN7 which then drives the output tubes (connected as triodes, of course). My -3db is well over 50kHz...
I'm not an engineer, but I assume it's because I am running the 6F12P sections much hotter than a 12AX7 would allow (6F12P is almost like 10 12AX7 in parallel) and that current can drive the Miller capacitance.
With a modest gNFB loop 1V in produces 11V out.
A 12AX7 can drive a pair of 6V6 tubes in PP with only 2 stages (VA/PI as one stage, power as the other), and it was cheap to implement while still having enough gain to run a feedback loop.
More powerful amplifiers (Williamson at least) used 6SN7 instead and added a driver stage between the VA/PI and the power tubes.
Personally, I use the pentode of a 6F12P as a triode (mu ~70) to feed the triode section used as a concertina/cathodyne PI which drives a 6SN7 which then drives the output tubes (connected as triodes, of course
). My -3db is well over 50kHz... I'm not an engineer, but I assume it's because I am running the 6F12P sections much hotter than a 12AX7 would allow (6F12P is almost like 10 12AX7 in parallel
) and that current can drive the Miller capacitance.With a modest gNFB loop 1V in produces 11V out.
The 12AX7/ECC83 is a very linear valve when used properly. It has high gain, so this gain can then be used to provide loop gain for significant feedback to linearise the output stage. That is why you will see it used as an input tube in hi-fi applications. Guitar amps use it for quite different reasons.
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