OK so headroom is measured relative to the "nominal cart output", I never would have thought that is how it was measured as "nominal output" is more a marketing number and not really a very accurate but close enough I guess. I always assumed the 20 dB headroom was "above the peak music signal". Glad to learn something new today. In this case then I think the 20 dB headroom above nominal cart output and the 6 dB above peak music signal (which is higher than the loudest pop I have ever measured) are pretty much the same thing.
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Phono preamp headroom - why?
- Thread starter Multicore
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Nominal output is specific to the individual cartridge. It is the output at 1kHz at 5cm/sec recorded velocity, so not a marketing number. 5cm/sec was chosen as the 'nominal' number as it represents more or less the 'average' recorded velocity. LPs don't have a fixed maximum level on them, unlike digital which is limited to 0dBFS. It's however much the cutting engineer can get on the LP, balancing noise against distortion, running time against level as higher levels need wider track spacing, and making the LP trackable by the sort of cartridges used in 'record players', not just Shure V15s.
20dB above nominal cartridge output depends on the cartridge, whereas 20dB above 5mV input is a specific number, which will apply to all cartridges. If one understands what that means, and what one's specific cartridge outputs, then one can calculate what the headroom will be in one's own specific case.
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Multicore
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Just for example, does the frequency dependence of the headroom of the Pro-Ject that Amir just reviewed suggest anything to be concerned about?
While music power decrease with frequency, some cartridges can have quite large peaks around 10-20 kHz. Pops and clicks are broadband, but I have not looked at the spectral content. So I would guess, it depends.
I have a recording of a "loud pop" in a medium quiet part of a song. I tried to zoom in and do a Spectrum analysis and it does indeed show more HF content for the "zoomed in pop" as compared to the zoomed out spectrum. It was captured at 48Khz so there may be more HF than this shows. I think a safe assumption is pops do have relatively large amount of HF content compared to music and HF headroom is an issue to be concerned with.
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FWIW dept.: LP mastering equipment is extremely low distortion often with a 30dB feedback loop around the cutter head and cutter amplifier. Its impossible to overload with normal signals since the amps are capable of frying the cutter head well before they reach 25% of full power. Any LP mastering system can cut undistorted grooves that no playback system has a prayer of tracking. So the 'distortion' to which you refer is really 99% in playback mode, which is why its important to use a competently designed tone arm and a phono section of equal competence. Put another way the engineer's job is to cut a playable groove. I might be considered splitting hairs here but I felt it important to point out that the media isn't the distortion problem- playback is. Most of the studies of 'LP distortion' are bad science since the people doing the study took none of this into account.
IMO, Yes.
Is the frequency dependence of many of these stages a function of the topology? That is, is this the result of RIAA in the feedback loop, or RIAA between two gain states, or something else entirely?
This sort of dependence seems to be a recurring theme among many stages tested here.
This sort of dependence seems to be a recurring theme among many stages tested here.
Some interesting discussion regarding this question can be found here:
Pro-Ject Phono Box DS3 B Review
I don’t get it, $800 for a phono stage! Is it really that much better? The reason I gravitated to this site is because they call this stuff out. It seems like balanced is the reason for the cost. I guess if you have the budget for a balanced turntable this isn't that expensive. I'm sticking...
www.audiosciencereview.com
There seem to be significant difference in headroom performance between preamps with passive vs. active RIAA implementation.
How do we measure if a phono preamp has good overload behavior? My LXV-OT10 does a fine job for reproducing vinyl (with the op amp upgrades). The tube adds so much harmonics that there really isn’t a clear bend in the curve.
This is what I measure with 52 dB of gain.
This is what I measure with 52 dB of gain.
KSTR
Major Contributor
You overload it with a pulse of known shape and look at the clipping and its recovery, at the actual waveform, because that's what's really important.
One pre with a higher clipping threshold may sound much worse than another one with a lower threshold because the clipping behavior is nasty and extending the time needed to recover, even with some extensive ringing until it settles again. OpAmp feedback going open loop with large capacitors involved (that then charge up to wrong voltages) is one way for bad clipping behavior.
What we really want is a *fast* and nice clipping and recovery, and preferably with a soft clipping characteristic. For opamp stages this means they must never go open-loop, rather the feedback must be properly clamped so that the output is stopped from going higher and the feedback remains closed at all times.
So just plotting the clipping threshold only tells half of the story. You have to look at it right in the time domain.
Or
Dropbox
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Convert with reverse RIAA? For music. A click/pop should not be RIAA engraved.
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I did not manage to do that yet. Spectral analysis tool in Audacity is not working for the very brief pops.
Maybe someone else can advise?
I can also share the Audacity project file if that helps.
Edit: find attached some spectra of flat recorded music (several seconds), not specifically filtered to isolate ticks and pops.
Attachments
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Some interesting discussion regarding this question can be found here:
Pro-Ject Phono Box DS3 B Review
I don’t get it, $800 for a phono stage! Is it really that much better? The reason I gravitated to this site is because they call this stuff out. It seems like balanced is the reason for the cost. I guess if you have the budget for a balanced turntable this isn't that expensive. I'm sticking...
There seem to be significant difference in headroom performance between preamps with passive vs. active RIAA implementation.
Thank you.
Are there any reviews @ this site which show frequency-dependent headroom for MM phono stages performing RIAA in the feedback loop?
Maybe this one?
Edit: There is also a MM version available.
www.audiosciencereview.com
Edit: There is also a MM version available.
Classic Audio MC Pro Phonostage Review
This is a review and measurements of the Classic Audio MC Pro by Michael Fidler. It was sent to me by the company and costs US $850 (£650/€750). As non-fancy enclosures go, this is pretty nice looking and with some unusual features such as low frequency blending to reduce noise, mono switch and...
www.audiosciencereview.com
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