Phono preamp headroom - why?

[Multicore]

Amir often gives extra points to phono preamps that can cleanly and linearly pass big input spikes from pops on the disk as big output spikes. It's been a while but I recall one of them could output 20 V spikes. And I thought: Why is clipping in a subsequent stage in the system better then clipping in the phono preamp? Or is the goal to pass these spikes with all the dynamic range they represent over the music all the way to the speakers or headphones?

Related question: is there a signal processing technique that can reduce those spikes that's preferable to simple clipping that could be tailored for use in a phono preamp?

 

[MaxwellsEq]

And I thought: Why is clipping in a subsequent stage in the system better then clipping in the phono preamp?

Excellent question. I think it's because the input circuitry is frequently not end-user adjustable. Later stages allow the user to turn the gain down to suit. This means if the front-end gain stage does not have enough headroom, dynamic swings can unsettle the amplifier for several cycles. Bear in mind this is not just about clicks, but actually because some disks are cut very very hot. There was a chart on here a while ago showing how much output some LPs have.

Related question: is there a signal processing technique that can reduce those spikes that's preferable to simple clipping that could be tailored for use in a phono preamp

Progressive compression and limiting would do it, but as above it would also compress hot cut LPs.

 

[Multicore]

Progressive compression and limiting would do it, but as above it would also compress hot cut LPs.

So a phono stage with a nice clean preamp into a 24 bit ADC (should be enough for any vinyl) followed by a carefully crafted anti-pop filter could handle that with user-adjustable parameters and the filter/limiter/compressor could benefit from look-ahead to guess if it sounds like a dirt/scratch pop or music. Sounds like a DIY project.

 

[DVDdoug]

I've wondered about that too. I would have thought that an higher amplitude click or pop would sound worse than a clipped/limited one. But I trust Amir.

If you are de-clicking a digitized record, a loud "unlimited" defect is obviously easier to identify/find and that usually makes it easer to fix. But realistically, it's going to stand-out either way.

Personally, I don't play records. I only occasionally digitize one so headroom for extra-loud clicks (that I'm going to attempt to remove) isn't an issue.

followed by a carefully crafted anti-pop filter could handle that with user-adjustable parameters and the filter/limiter/compressor could benefit from look-ahead to guess if it sounds like a dirt/scratch pop or music. Sounds like a DIY project.

There's software for that but usually it doesn't run in real-time. I have Wave Repair ($30 USD) which is manual so it only "touches" the audio where you identify a defect (and it's super time-consuming), and Wave Corrector (FREE) which is fully automatic.

 

[LTig]

Amir often gives extra points to phono preamps that can cleanly and linearly pass big input spikes from pops on the disk as big output spikes. It's been a while but I recall one of them could output 20 V spikes. And I thought: Why is clipping in a subsequent stage in the system better then clipping in the phono preamp?

It is not.

Or is the goal to pass these spikes with all the dynamic range they represent over the music all the way to the speakers or headphones?

My saying - this is not a good idea.

Related question: is there a signal processing technique that can reduce those spikes that's preferable to simple clipping that could be tailored for use in a phono preamp?

Make sure the phono preamp has a very short recovery time so ticks are not lenghened. Then apply a limiter to clip their amplitude.

 

[levimax]

I am starting to think the 20 dB headroom requirement is a myth. Looking at the worst of the worst of my second hand records it is rare to see a click or pop louder than the music peaks and in a few instances I have seen it is more like 2 to 3 dB above peak music and these are extremly damaged records. I think the issue is more complicated, see a plausable explanation from a member https://www.audiosciencereview.com/...lain-the-vinyl-renaissance.32420/post-1332275

 

[MaxwellsEq]

This article is to a good summary on maximum recorded velocities (output is a function of velocity). As I stated in post 2, it's not just clicks, but hot cuts.

 

[sergeauckland]

I have a pair of Type 1 PPMs on the output of my sources, which I've calibrated such that 5cm/sec recorded velocity is 0dBu output. (I know, I'm a nerd!)
Most of my LPs peak at around +12 to +15dBu, which is pretty much in line with the cluster of actually measured recorded velocities above. I haven't seen any that actually get to +20dB, but have no reason to think that some won't. Consequently, headroom of 20dB above 5cm/sec recorded velocity is sensible as a practical minimum to ensure that LPs don't clip the phono stage. Of course, what headroom is available in a home system depends on the phono stage, but also on the particular cartridge output. A cartridge with 3mV output will allow 6dB greater headroom than one that outputs 6mV at 5cm/sec recorded velocity for the same gain of phono stage.

As to why clipping the phono stage is better or worse than clipping downstream, it isn't! Clipping anywhere is bad, but hopefully the pre-amp stage of the amplifier will have greater than 20dB headroom before the volume control, and after the volume control it doesn't matter. Amplifiers need to have their input headroom verified, as most amplifiers have excessive gain for marketing reasons (This amp's so powerful, I can blow the windows out with the volume control only at 9 o'clock) so if the amplifier's front-end clips on the output of a hot LP or other source, that's just as bad.

The ideal phono stage will have adjustable gain so it can be matched to the cartridge output to balance S/N ratio with overload margin, but that risks confusing users, so is seldom done except for MM/MC gain switching.

S.

 

[Multicore]

The ideal phono stage will have adjustable gain so it can be matched to the cartridge output to balance S/N ratio with overload margin,

ART Precision Phono Pre Review

This is a review and detailed measurements of the ART Precision Phono Pre. It was kindly drop shipped to me by a member and costs US $81. The look reminds of Radio Shack equipment of 1970s! So outdated but I guess it keeps their costs down. You get variable gain which is handy together with a...

www.audiosciencereview.com

 

[Verig]

My experience is like Levimax's. I don't even play records in condition where this would matter much.
My iFi Zen Phono works absolutely wonderfully even though it's rated mediocre for headroom here and I have a pretty hot cart at 6mV.
This is not to say I disagree with the measurements, I just don't value that part of the review as much as some may.

A vinyl record is a physical media that gets a little bit worse each time you play it. I don't see much reason to hop all the loops for some minor defects.

Very good point on the freely adjustable gain though. That would be nice. And there are plenty of reasons to play records that are in very bad shape so this is interesting topic.

 

[pogo]

Sounds like a DIY project.

... or a Waxwing Phono DSP

 

[Multicore]

... or a Waxwing Phono DSP

It was reading the Waxwing measurements that got me started thinking about it.

 

[pogo]

I am already one step further

 

[WDeranged]

I was entirely sceptical that headroom could reduce the effect of pops and crackles. I'd previously tried a Rega Fono Mini, Schiit Mani and a Zen Phono and I never heard any change in surface noise. I decided it was time to buy a preamp known to have high headroom and I ended up with a Spartan 15.

The majority of surface crackle sounds the same, but most of the really nasty ones had been softened tremendously. I guess those particular pops were splatting into the gain ceiling and being distorted. Quite a few records in my 'must replace' pile were made completely listenable.

 

[audio_tony]

I regard Douglas Self as an authority on phono preamps, and he advocates a lot of headroom.

His reasoning is that if enough headroom is maintained, when there is a high amplitude 'pop' the preamp doesn't clip and the sound remains cleaner and the pop is not as pronounced.

Some years ago (80's) I built a 'high end' phono preamp (ETI if I remember correctly) and that handled surface noise better than the built in phono preamp I was using previously. I don't remember if high headroom was the aim with this preamp though.

I'm also aware of a Technics phono preamp design (SU-9600) which used +/- 24v rails and a single third rail at 136v rails to improve the dynamic range and headroom.
The maximum input was rated at 900mV...

 

[antcollinet]

So a phono stage with a nice clean preamp into a 24 bit ADC (should be enough for any vinyl) followed by a carefully crafted anti-pop filter could handle that with user-adjustable parameters and the filter/limiter/compressor could benefit from look-ahead to guess if it sounds like a dirt/scratch pop or music. Sounds like a DIY project.

Sounds exactly like a waxwing. Or is that what you had in mind?

 

[levimax]

While headroom is good 20 dB is just so extreme compared to anything I have ever seen on a real record (or anything that could be handled correctly downstream) that I have my doubts this is being looked at correctly.

I previously linked to a post by @atmasphere but here is the text from the link in case you missed it. I am thinking that 20 dB of headroom "seems" necessary due to this effect. In his opinion much of what people think is "LP noise" is actually "self generated" by the interaction between the phono preamp and electrical resonances. I have no doubt experienced some phono preamps having less surface noise than others, it "could" be more headroom but if @atmasphere is correct it is more complicated than "20 dB of headroom".

FWIW, ticks and pops are often the result of the phono section overloading at high frequencies due poor high frequency overload margins and an electrical resonance set into excitation by the action of the cartridge. The inductance of the cartridge and the tonearm cable capacitance are the source of the resonance. FWIW I designed and manufactured the first fully differential balanced phono section ever made so this isn't coming from some sort of anecdote.

 

[Salt]

A RME ADI 2/4 pro would give headroom in all circumstances for MM systems, but that was not the question, not?

 

[Multicore]

Sounds exactly like a waxwing. Or is that what you had in mind?

Well, in a roundabout way, partly. Once I wrote it out it sounded like maybe the waxwing could do it but I really don't know enough about it to know of it actually offers this kind of processing. The question I asked in the OP has been on my mind from time to time for a couple of years. Then the recent waxwing measurements prompted me to finally ask it. So waxwing turned up at the beginning and end.

 

[antcollinet]

Well, in a roundabout way, partly. Once I wrote it out it sounded like maybe the waxwing could do it but I really don't know enough about it to know of it actually offers this kind of processing. The question I asked in the OP has been on my mind from time to time for a couple of years. Then the recent waxwing measurements prompted me to finally ask it. So waxwing turned up at the beginning and end.

Well the functionality you described is almost exactly what the Waxwing does plus a whole load more. Riia (Plus a whole bunch of alternative EQ) is done digitally, there are various frequency response modifiers (tone controls), Adjustable gain down to 0dB, Ultra and subsonic filters with adjustable corner frequencies.... and so on. I'm not going to list it all, it's all here:

https://parksaudiollc.com/waxwingmanual.html