Are phono stages properly designed?

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I don't think so. First the cheaper ones have at most 2 opamps, the input is a linear amp with gain adjustable, followed by a passive low pass (RIAA) , a passive high pass ( rumble filter) and then the RIAA "bass enhancing" active RIAA filter and output.
Venyl records are defined 0 dB= 22 millimeters / sec displacement at 1 khz.
That yields about 5 mV output voltage of a moving magnet system.
At 10 kHz 0 dB is already about 25 mV.
Before the introduction of microgroove, old LP came with +15 dB to +20 dB.
Thus just those old Blue Note LPs recorded treasures in Jazz can easily overdrive the first stage linear Opamp. And old records have damages which come as loud cracks...has any one measured the output voltage for hefty cracks?
These can drive the first stage into saturation and the recovery time is audible.

For real world valuable LPs the usual design of phono stages is highly off topic.
 
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In his Small Signal Audio Design book, Douglas Self mentions several records with higher than 22 mm/s displacement. I seem to recall the highest he was aware of was about 100-110 mm/s. He also has a survey of available cartridges. Many of them give higher output than the 5 mV you mention. He goes on to conclude that to have sufficient margin in a system operating on ±17 V rails, the gain should be no higher than 30 dB at 1 kHz.

You're probably right that some RIAA stages aren't well designed. That's the case for a lot of systems and circuits, actually.

Tom
 
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You might enjoy studying the "archival" phono preamplifier design published in Linear Audio magazine, volume 5. (web link)
An Archival Phono Preamplifier is a phono preamplifier designed for playback of vintage recordings long-playing, 45- and 78-rpm records made before the RIAA curve was universally adopted by the recording industry ... ... Although there are some (expensive) commercial preamps available with customizable replay characteristics, Gary Galo found them wanting and has over the years developed a phono preamp designed to replay all these different formats and recording curves. That design is described in this article.
There is a photo of the device on the magazine cover, see below.

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You might enjoy studying the "archival" phono preamplifier design published in Linear Audio magazine, volume 5. (web link)
An Archival Phono Preamplifier is a phono preamplifier designed for playback of vintage recordings long-playing, 45- and 78-rpm records made before the RIAA curve was universally adopted by the recording industry ... ... Although there are some (expensive) commercial preamps available with customizable replay characteristics, Gary Galo found them wanting and has over the years developed a phono preamp designed to replay all these different formats and recording curves. That design is described in this article.
There is a photo of the device on the magazine cover, see below.

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Hi Mark, is this an OPAmp?
 
You might enjoy studying the "archival" phono preamplifier design published in Linear Audio magazine, volume 5. (web link)
An Archival Phono Preamplifier is a phono preamplifier designed for playback of vintage recordings long-playing, 45- and 78-rpm records made before the RIAA curve was universally adopted by the recording industry ... ... Although there are some (expensive) commercial preamps available with customizable replay characteristics, Gary Galo found them wanting and has over the years developed a phono preamp designed to replay all these different formats and recording curves. That design is described in this article.
There is a photo of the device on the magazine cover, see below.

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Neat trick that Mr. Galo used...
 
He goes on to conclude that to have sufficient margin in a system operating on ±17 V rails, the gain should be no higher than 30 dB at 1 kHz.

Tom

As 30dB (@ 1KHz) is too low - then obviously one needs to use 24v rails. :)

You're probably right that some RIAA stages aren't well designed. That's the case for a lot of systems and circuits, actually.

Absolutely!


Regards,

Andy
 
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I think 30dB gain max at +-17V rails is taking it a bit too far.

If you use all active feedback on +-17V rails, you have between 35 to 40dB OLM ref 3~5mV input and a gain of 30 to 36 dB.

Your power amp is clipping long before this.

If of course you are using passive EQ with opamps, then OLM will be traded off at HF.

Passive EQ is best suited to tube stages IMV - you have enormous head room because of the supply voltages involved.
 
Many moons ago I added this to my notes:-
Having serviced a wide range of solid state Hi-Fi amplifiers from Quad to NAD, I was always disappointed in the way their respective phono amplifier stages operated. They all seemed to run out of steam at the low frequency end when a +20dB boost was required. All seemed to run out of steam around 200Hz when the gain stopped increasing much above +10 dB though some actually made +15dB. On each occasion the sine wave output was seen to flatten off, both on positive and negative excursions. Researching various manufacturers circuit diagrams it became clear to me that all of their later circuits had their phono stage supply rails lifted from the usual +/-12V to +/-15V, some even going higher to +/-18V supplies. This necessitated a change in their design whereupon all that the manufacturers did was to choose a type of operational amplifier capable of working with higher supplies and going for something like +/- 20V. Was this the answer to the poor bottom end performance? Well it seemed to be as it gave sufficient headroom for the lower RIAA specification to be achieved without limiting provided the input was kept below 100mV. This seemed to be the key as without the higher supply the amplifiers bottomed out with an input, in some instances, of just a few mV!

OK so 100mV seems a bit unrealistic but it is surprising what a MC can deliver if you try playing a test record with a maximum possible output test track.
 
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