Vintage Mic Transformer for MC step-up - gain-phase and impedance measurements

[Brian Roth]

Paul, we're on the same "planet" here! <g>

I merely used the standard recording tape operating levels (and mentioned MRL tapes) as a comparison because I suspect that is more familiar to the readers of this list compared to vinyl cutting operation/setup/calibration levels.

Best,

Bri

 

[Gold]

Paul, we're on the same "planet" here! <g>

I merely used the standard recording tape operating levels (and mentioned MRL tapes) as a comparison because I suspect that is more familiar to the readers of this list compared to vinyl cutting operation/setup/calibration levels.

Best,

Bri

Absolutely. For those following along I think this thread provides what you need to know to measure the noise floor of your phono reproduction system.

Those dealing with records in a professional capacity should understand how to calibrate a turntable. A calibrated turntable should be used in a studio environment. Some have no clue such a thing exists.

 

[Brian Roth]

Being a Newbie (only the past 5+ years) in the Lacquer World...

I see more than a few vinyl calibration discs on the shelf here. What would be the Gold <g> Standard disc in year 2023? IE comparable to MRL tapes?

Also, it would be interesting to exchange test tone lacquers which SHOULD be cut at the correct levels for comparisons. PM or email me......

Best!

Bri

 

[abbey road d enfer]

But now terminate the phono input with a resistor the value of the cartridge and see what happens to those numbers.

Inductive or capacitive sources don't lend themselves to noise evaluation by substituting resistors.
The actual impedance of a MM phono cartridge varies from about 1kohm at LF (<200Hz) to 30kohm at 20kHz, with about 10kohm in the critical 3-4kHz region.
A MC cartridge usually has less variation, but still a resistor does not results in proper noise stimulation.

 

[Gold]

Inductive or capacitive sources don't lend themselves to noise evaluation by substituting resistors.
The actual impedance of a MM phono cartridge varies from about 1kohm at LF (<200Hz) to 30kohm at 20kHz, with about 10kohm in the critical 3-4kHz region.
A MC cartridge usually has less variation, but still a resistor does not results in proper noise stimulation.

Yet phono pre designers insist on quoting noise figures that way. They certainly don’t say you’ll never be able to do better than -55dBu despite the vanishingly small noise figure they quote.

 

[Gold]

Being a Newbie (only the past 5+ years) in the Lacquer World...

I see more than a few vinyl calibration discs on the shelf here. What would be the Gold <g> Standard disc in year 2023? IE comparable to MRL tapes?

Also, it would be interesting to exchange test tone lacquers which SHOULD be cut at the correct levels for comparisons. PM or email me......

Best!

Bri

I use the original blue NAB record. I collect test records. They are all close. Any one is better than none.

 

[abbey road d enfer]

Yet phono pre designers insist on quoting noise figures that way. They certainly don’t say you’ll never be able to do better than -55dBu despite the vanishingly small noise figure they quote.

Of course. A 47k resistor has an intrinsic noise of ca. -107dBu, which results in ca. 52dB S/N referenced to 5mV.
It only gives a coarse indication of the noise performance of the phono preamp.

 

[Gold]

Of course. A 47k resistor has an intrinsic noise of ca. -107dBu, which results in ca. 52dB S/N referenced to 5mV.
It only gives a coarse indication of the noise performance of the phono preamp.

With a microphone preamp you can generally expect to see the stated noise figure in the real world. Not so with an unbalanced phono input.

 

[Cqwet Dbdfte]

Measuring system noise of the electronics to include the surface noise of a test record is of course a practical and valid dynamic range test, however, the test records noise swamps the noise of amplifiers, and would be useless in determining their noise.
As I'm also interested in finding a number for the dynamic range, I used a peak-holding AC RMS DMM to get a rough number with various non-test records, not absolute but a rough number, and I got like 2200:1 signal to noise, or 67dB, measured at the speaker terminals.

My first reported measurement of -55dBu was calibrated against 2.2V p-p, or 0dBu, at 1KHz, included the gain of about 48dB from the RIAA stage, and a 27dB transformer, so subtracting the gain from the noise measurement would indicate a noise source voltage -127dBu from the MC cartridge.
This includes nearby electronics, motors, controller, and amplifiers contribution, if any.

 

[Gold]

Stop making an ass of yourself. Read the Audio Cyclopedia. Or read the thread again. The necessary information is here. You haven’t grasped it yet.

 

[abbey road d enfer]

With a microphone preamp you can generally expect to see the stated noise figure in the real world. Not so with an unbalanced phono input.

Correct. That's because in most cases, the actual output impedance of microphones does not vary much with frequency.
Dynamic and ribbon mics have a rise of impedance at their resonance but it's generally happening in the low-mids, where the noise contribution is minor.

 

[JohnRoberts]

We could try being a little kinder...

====

It seems to me that the surface noise of a record would be significantly higher than electronic preamp noise floor.

Back last century when I designed my last few phono preamps I/we used appropriate passive input terminations for noise measurements.

JR

 

[Gold]

We could try being a little kinder...

====

It seems to me that the surface noise of a record would be significantly higher than electronic preamp noise floor.

Back last century when I designed my last few phono preamps I/we used appropriate passive input terminations for noise measurements.

JR

That’s correct. That’s why I said it’s used to establish a Standard Reference Level. Using a test record as a noise measurement is idiotic.

 

[Gold]

Back last century when I designed my last few phono preamps I/we used appropriate passive input terminations for noise measurements.

JR

Did you ever measure the actual real world noise with a cartridge attached?

 

[JohnRoberts]

Did you ever measure the actual real world noise with a cartridge attached?

No, but there were some more sophisticated loads with inductance...
==
My better, later preamps used JFET input devices so exhibited extremely low input noise current.

JR

 

[Gold]

No, but there were some more sophisticated loads with inductance...
==
My better, later preamps used JFET input devices so exhibited extremely low input noise current.

JR

Ignorance is bliss. Do you really think quoting unrealistic simulated noise figures helps anything besides the designers ego? The reason no one does the actual real test is that it would be a giant failure every time. The noise problem is the unbalanced interface. Until that is fixed none of the noise numbers mean much because even the worst noisiest phono pre will beat the real world noise floor.

 

[JohnRoberts]

Ignorance is bliss. Do you really think quoting unrealistic simulated noise figures helps anything besides the designers ego? The reason no one does the actual real test is that it would be a giant failure every time. The noise problem is the unbalanced interface. Until that is fixed none of the noise numbers mean much because even the worst noisiest phono pre will beat the real world noise floor.

Over the decades I had many opportunities to drop the needle on a record with the turntable motor turned off. The noise increase after the motor was turned on was significant and very obvious.

I don't consider myself ignorant about phono preamp design. I do consider phono preamp design a more than mature topic at this point. Back some 45 years ago there was much room for improvement in the electronic path, nowadays there are numerous off the shelf op amps that spank former premium discrete designs (including mine).

If there was a "reference" phono cartridge to use for specification measurements, I would have used one.

JR

 

[Gold]

Over the decades I had many opportunities to drop the needle on a record with the turntable motor turned off. The noise increase after the motor was turned on was significant and very obvious.

I don't consider myself ignorant about phono preamp design. I do consider phono preamp design a more than mature topic at this point. Back some 45 years ago there was much room for improvement in the electronic path, nowadays there are numerous off the shelf op amps that spank former premium discrete designs (including mine).

If there was a "reference" phono cartridge to use for specification measurements, I would have used one.

JR

Oh, come on. Improvement in the electric path doesn't mean anything because you will never do much better noise wise than -55dBu in the actual world. Who cares if you shave a dB off the fake noise figure. It's totally meaningless except to publish specs that no one will ever be able to realize. Reference Phono Cartridge? Use any one you wish. It's the cable that's the problem. Don't include the cable in the measurement and everything looks great. Endless masturbatory fun.

 

[JohnRoberts]

Oh, come on. Improvement in the electric path doesn't mean anything because you will never do much better noise wise than -55dBu in the actual world. Who cares if you shave a dB off the fake noise figure. It's totally meaningless except to publish specs that no one will ever be able to realize. Reference Phono Cartridge? Use any one you wish. It's the cable that's the problem. Don't include the cable in the measurement and everything looks great. Endless masturbatory fun.

That can be fun too....

if -55dBu is the "actual world" noise floor, they could have stopped digital development at 10 bits.

I stopped thinking about phono preamps in the 1980s so I will tap out of this scrum and defer to your superiority.

JR

 

[Gold]

That can be fun too....

if -55dBu is the "actual world" noise floor, they could have stopped digital development at 10 bits.

I stopped thinking about phono preamps in the 1980s so I will tap out

Phono preamp designers weren’t thinking too much about it back then either. You might think a designer would be interested in the actual performance of the device. Apparently not. It appears to be news that the real world performance of a phono system has a noise floor of about -55dBu dominated by dirty nasty hash.