Phono preamp headroom - why?

[TriodeLuvr]

As to your output level of 2 or 3v, I don't know where you get those numbers from

That's the maximum that can be accepted by many power amps without overloading their input stage (and likely clipping the output of the preamp itself as well). Specifying headroom on the basis of output above this level is just as meaningless as attempting to characterize it with a single number.

Jack

 

[sergeauckland]

That's the maximum that can be accepted by many power amps without overloading their input stage (and likely clipping the output of the preamp itself as well). Specifying headroom on the basis of output above this level is just as meaningless as attempting to characterize it with a single number.

Jack

Nonsense. Any half decent preamp can handle 8v from the phono amp and pass only 1-2 v to the power amp. That's what a volume control does.

S

 

[atmasphere]

Ticks and pops results from used and dirty records. They are only amplified by the phono preamp, not generated.

I've found this to not be correct. Sure, you can have dirty or damaged LPs.

I'm not talking about that.

I've seen cases where the LP was just fine but still the ticks and pops, caused by ultrasonic noise overloading the phono section. I first encountered this about 35 years ago. Change the preamp and the ticks and pops were gone- nice, silent grooves. Didn't take all that long to sort out what was going on.

I ran an LP mastering operation for 20 years. Producers have to sign off on a pressing (using a 'test') and one of the things they listen for is ticks and pops. So when you buy a new LP it should be fine. All that I've bought in the last 30 years or so have been with one or two exceptions.

 

[LTig]

I've seen cases where the LP was just fine but still the ticks and pops, caused by ultrasonic noise overloading the phono section. I first encountered this about 35 years ago. Change the preamp and the ticks and pops were gone- nice, silent grooves. Didn't take all that long to sort out what was going on.

Interesting, never heard of that before. Where does this ultrasonic noise come from? What's the frequency range, and how high must be its level to clip a phono preamp?

 

[LTig]

Nonsense. Any half decent preamp can handle 8v from the phono amp and pass only 1-2 v to the power amp. That's what a volume control does.

What if you listen loud, with volume set high? Surely a spike 20 dB higher would then clip the power amp.

 

[sergeauckland]

What if you listen loud, with volume set high? Surely a spike 20 dB higher would then clip the power amp.

Of course.

S

 

[LTig]

Of course.

Hence in my opinion one should not look for very high headroom but rather for good limiters which reduce the voltage of the spikes, and also prevents clipping if done correctly..

 

[0bs3rv3r]

so the 2nd stage with a linear gain of 20 dB may end up with a noise penalty of up to 20dB compared to the active RIAA EQ shown above. You don't want that either.

With the usual high level of background surface noise, SNR of 60db?, even from good vinyl, is this really a concern?

 

[0bs3rv3r]

Hence in my opinion one should not look for very high headroom but rather for good limiters which reduce the voltage of the spikes, and also prevents clipping if done correctly..

What would be a good way to implement limiting ahead of a phono preamp? This is something I woud liketo try.

 

[atmasphere]

Interesting, never heard of that before. Where does this ultrasonic noise come from? What's the frequency range, and how high must be its level to clip a phono preamp?

I'm guessing you've not read all the way through this thread. I described the mechanism just a few pages back.

 

[TriodeLuvr]

Nonsense. Any half decent preamp can handle 8v from the phono amp and pass only 1-2 v to the power amp. That's what a volume control does.

It clearly depends on the topology of the preamp and the exact location of the volume control. In any event, this isn't the crux of the argument.

Jack

 

[atmasphere]

With the usual high level of background surface noise, SNR of 60db?, even from good vinyl, is this really a concern?

Yes. Really good vinyl can have a noise floor so low the phono section is the noise floor. IOW in the area of -80dB. Only one plant we've encountered (QRP) is capable of that.

 

[LTig]

I'm guessing you've not read all the way through this thread. I described the mechanism just a few pages back.

I did but I thought this is prevented by proper loading.

 

[TriodeLuvr]

Really good vinyl can have a noise floor so low the phono section is the noise floor.

Sadly, after you play your favorite LP about 30 times, its floor begins to intrude a little.

 

[atmasphere]

I did but I thought this is prevented by proper loading.

It can, which is why its so important to properly load a high output MM cartridge. Its important even if the phono section has good overload character, since the peak causes phase shift in the audio band.

That IMO is the main weaknesses of analog- so much more setup required and it really has to be right, something most people simply do not accomplish.

 

[JP]

Sadly, after you play your favorite LP about 30 times, its floor begins to intrude a little.

I've some 500 QRP pressings here and I've never ran across one where the vinyl noise wasn't audible, let alone some 80dB down. I find that claim to extraordinarily far-fetched.

 

[atmasphere]

I've some 500 QRP pressings here and I've never ran across one where the vinyl noise wasn't audible, let alone some 80dB down. I find that claim to extraordinarily far-fetched.

A lot depends on the title.

I ran an LP mastering operation for about 20 years. What most people don't know is that a lacquer cut, if the cutter stylus is properly set up (correct angle, which varies from stylus to stylus, cutter depth, stylus temperature and so on) properly, it can cut a groove that is essentially dead silent. Play it, and literally you will wonder if the system is turned on or not until the music plays.

We did a few projects thru QRP. They found that by damping the pressing machines so they were more still while the vinyl was cooling caused a much lower surface noise. I had to talk to Chad Kassem directly (I"ve known him for over 30 years) to allow us to do our customer's limited run of 500 copies. The tests we got back were so quiet that just like the lacquers the surfaces were so quiet I was wondering if the system was on the right input when the music started.

Our source for the project was a digital file. You're not going to see those noise floors on larger runs with old analog sources.

 

[Thomas_A]

Does anyone have a lacquer or a mastercut record? I've also heard that they are very silent but never heard one. They are possible to buy but too expensive for me.

 

[JP]

Does anyone have a lacquer or a mastercut record? I've also heard that they are very silent but never heard one. They are possible to buy but too expensive for me.

I've a couple dozen lacquers including eight of the Supersense Mastercuts. Unfortunately the only samples I could share are from the Mastecuts but those are shit. More than half went very noisy unplayed in their boxes. They kind of offered to replace them but the process was so burdensome and my time so short that I decided to walk away. I was after the uniqueness of the purported flat cuts from master, so all I really wanted was to be able to do one clean layback to digital. I managed that on only one of them.

I've some tests teed up with some local (NYC) mastering engineers and with those I'll include some content that can be shared. It's an "as time permits" thing, so I don't really know when we'll all get to it.

 

[atmasphere]

A good lacquer cut is expensive and the lacquer only lasts a few plays, plus they degrade quickly over time.

I've seen 'dub cuts' recently but they are not the same thing!