Measuring noise and SINAD of MM phono preamps properly

[morillon]

I ask a simple question I believe. What is the highest dynamic range vinyl carries? I’ve heard of a sample “somewhere” of about 70 db.

At what point does noise become a diminishing factor?

This noise is added to the noise of the LP... it's all the more unfortunate...

 

[StevenSGT98]

It is a demonstration of the audible influence of the input current noise of the bipolar opamp (LT1028 here), which is in no way revealed in a usual test with the low impedance generator. With the low impedance generator, the noise (and thus SINAD) is lower with the bipolar LT1028 opamp, just the opposite of the real world scenario with the MM cartridge. This is the reason why tests with low impedance generator (as in the reviews here) are pointless and do not reflect the real world operating conditions.

Does this invalidate the other measurements, such as linearity and overhead clipping?

 

[StevenSGT98]

This noise is added to the noise of the LP... it's all the more unfortunate...

Please explain. I would assume the surface noise would be above the thermal noise. If the maximum dynamic range is - say 70 db - won’t that sit on top of the thermal noise?

 

[MaxwellsEq]

Please explain. I would assume the surface noise would be above the thermal noise. If the maximum dynamic range is - say 70 db - won’t that sit on top of the thermal noise?

Noise in this case will be incoherent, so one doesn't act like a concrete floor for the other. In other words, we can detect things below a noise floor.

 

[narshorn]

(excuse the off-topic..what analyzer fft are you using?) ;-) )

I was myself a little off-topic ... ; ) It is the built-in Wavelab FFT function.

Regards,

n.

 

[StevenSGT98]

Noise in this case will be incoherent, so one doesn't act like a concrete floor for the other. In other words, we can detect things below a noise floor.

Perhaps this has been answered somewhere else, but I haven’t run across it. How far below a noise floor can a person hear?

It begs another question.

Is what is beneath a noise floor worth hearing? The maximum dynamic range I’ve personally experienced from vinyl is 53 db on a Mofi pressing of the Cincinnati Orchestra. I’ve heard rumors of 70 db, though have never heard if that was a commercial pressing. If someone knows what recording this is, I would be interested to know.

My turntable has a published spec of 78db snr. So, let’s say if the noise on a preamp matches this, then theoretically rumble from the table and noise from the preamp will match. Ok. Again this is a published spec. (Denon Dp-45f) Denons best tables spec’d out at 82.

According to Recording Technology Inc.

On SVS Forum.

“Although the blog gives vinyl dynamic range as 70 dB, that's optimistic. A more realistic value for a very good pressing would probably be more like 60 dB, and then only at mid-band. High-frequency, and especially low-frequency, dynamic range will be substantially less. …. And, indeed, most recorded music has a dynamic range of 40 dB or less--often much less in pop music.”

I tend to agree.

So, a valid question is, if a preamp does generate slightly more noise, but the design leads to other desirable qualities, such as higher overhead, is the tradeoff ok?

 

[Skeeter]

Perhaps this has been answered somewhere else, but I haven’t run across it. How far below a noise floor can a person hear?

It begs another question.

Is what is beneath a noise floor worth hearing? The maximum dynamic range I’ve personally experienced from vinyl is 53 db on a Mofi pressing of the Cincinnati Orchestra. I’ve heard rumors of 70 db, though have never heard if that was a commercial pressing. If someone knows what recording this is, I would be interested to know.

My turntable has a published spec of 78db snr. So, let’s say if the noise on a preamp matches this, then theoretically rumble from the table and noise from the preamp will match. Ok. Again this is a published spec. (Denon Dp-45f) Denons best tables spec’d out at 82.

According to Recording Technology Inc.

View attachment 436969

On SVS Forum.

“Although the blog gives vinyl dynamic range as 70 dB, that's optimistic. A more realistic value for a very good pressing would probably be more like 60 dB, and then only at mid-band. High-frequency, and especially low-frequency, dynamic range will be substantially less. …. And, indeed, most recorded music has a dynamic range of 40 dB or less--often much less in pop music.”

I tend to agree.

So, a valid question is, if a preamp does generate slightly more noise, but the design leads to other desirable qualities, such as higher overhead, is the tradeoff ok?

No. You can have low noise AND high overload. They are not mutually exclusive and if one is traded off for another, it’s a flawed design period.

On a separate note, any phono preamplifier that has hum components above the thermal noise floor with a real-world cartridge attached would be an instant fail in my book. On measurement setups, you may get a 50/60 Hz spike from external mag fields coupling into the input wiring but nothing more than that.

 

[Skeeter]

I ask a simple question I believe. What is the highest dynamic range vinyl carries? I’ve heard of a sample “somewhere” of about 70 db.

At what point does noise become a diminishing factor?

We can ask exactly the same question about distortion. Below what point is absolute distortion level of no consequence? Research says a highly trained ear may be able to detect 0.05% if the harmonic content is high order odds (ie > 3rd). So if your amp produces no more than 0.01% at all power levels and frequencies across the audio band and it’s low order harmonic distortion, you’re good to go.

For a phono preamp, you want at least 6 dB better than the surface noise of a record during play. But, such a preamp will have clearly audible hiss at nominal listening levels in the normal seating position when the needle is up. For this reason, you really want to be above about 72dB ref 5mV. Anything above this is a bonus and reflects good engineering.

 

[Nick_Sukhov]

Are there any drawbacks to building input stage of a MM amplifier based on JFE2140?

Yes, see here https://www.diyaudio.com/community/...high-pass-included.413649/page-6#post-7965752

 

[Nick_Sukhov]

cartridge is from the thermal self-noise of the generator itself - it is a resistor with complications, but a resistor, the mandated 47kOhm load

Wrong. Mandated is >= 47kOhm.

 

[Heinrich]

Wrong. Mandated is >= 47kOhm.

Right in case if your special equalizer is used.

 

[AnalogSteph]

You're in a very luxurious position if you can afford to go all the way up to 150k, probably with a preamp (or at least a buffer) inside the turntable. Higher-end AT cartridges used to be notorious for their treble peaking with typical cable lengths and input capacitances, and people would go down to 36-39k to combat this on a fairly regular basis. But yes, from a noise and bandwidth POV a higher input resistance would absolutely be preferred.

I have thought about what it would take to integrate buffer circuitry pretty much directly at the cartridge or headshell interface (today's small-fry SMD electronics weigh next to nothing after all), but it's not entirely trivial, not to mention that you'd have to choose between MM or MC.

 

[Nick_Sukhov]

I have thought about what it would take to integrate buffer circuitry pretty much directly at the cartridge or headshell interface (today's small-fry SMD electronics weigh next to nothing after all), but it's not entirely trivial

see my version attached or more detailed here https://www.patreon.com/posts/otsenite-tekst-90783025