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Measuring phono stage RIAA accuracy with a computer
Measuring phono stage RIAA accuracy with a computer
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Old 13th March 2018, 11:20 AM   #71
luckythedog is offline luckythedog  United Kingdom
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Quote:
Originally Posted by billshurv View Post
So as to not pollute this thread any more as it has useful info and a still good SNR I will open a new thread to discuss cartridge non-linearities where data can be presented and ideas discussed.
I think that's a good idea, Bill.

At any given playback level, a cartridge's overall 'f-response' comprises a composite of several separate component parts. Electromagnetic generator (typically hf loss/roll-off), a mechanical 'top' resonant system (centred 8kHz-30kHz) that sometimes props up generator hf roll-off, an electrical resonant LCR impedance system (10-20kHz) that also sometimes props up generator roll-off system in MM/MI carts, and a lf spring-mass elastomer system. There's also a contribution from geometric thd and mistracing distortion that can influence f-response somewhat. And other contributing elements besides.

When combined, the well-known f response curve results: lf peak, mid-dip, resonant peak and hf roll-off. Nominally +3dB/-1dB at normal test levels. However, each of the component parts has losses and non-linearities which are level sensitive, and many of them slew-rate sensitive as to losses. It's slew-rate, rather than 'frequency' per se, which is mostly at issue.

I first encountered significant level-sensitive parameters about 6 years ago in collaboration with David Laloum trying to 'perfectly' terminate MM carts, where cartridge inductive behaviour, and hence the generator (not least LCR resonant f and Q), apparently changed significantly dependant upon test level for some cartridges. Especially for very small signals. I still have the charts from that work, and stand by that it is very probably real and a part of vinyl sound.

Exploration of theoretical loss mechanisms in each of the contributing elements to f-response reveals many and various level-sensitive non-linearities. Some are slew-rate specific, or displacement specific. Some increase with level, some decrease.

One might surmise the overall result is probably a level-dependent series of contours of f-response, typically within a bracket of +/- 3dB at the mid-dip, over the decades of normal playback level range where the most audible effects happen. AFAIK there is no single test record to confirm.

IMO the audible result is probably then a big part of vinyl sound - certainly something one doesn't get from digital sources, and only to an extent from tape.

LD

Last edited by luckythedog; 13th March 2018 at 11:31 AM.
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Old 13th March 2018, 11:43 AM   #72
Hans Polak is offline Hans Polak  Netherlands
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@Bill

I look forward to seeing the first results of your new thread, perfect idea to isolate this topic.

Hans
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Old 13th March 2018, 03:10 PM   #73
scott wurcer is online now scott wurcer  United States
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Quote:
Originally Posted by luckythedog View Post

I first encountered significant level-sensitive parameters about 6 years ago in collaboration with David Laloum trying to 'perfectly' terminate MM carts, where cartridge inductive behaviour, and hence the generator (not least LCR resonant f and Q), apparently changed significantly dependant upon test level for some cartridges. Especially for very small signals. I still have the charts from that work, and stand by that it is very probably real and a part of vinyl sound.
LCR equalizers can do the same thing. One wonders how many engineers put that into their bag of tricks?
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Old 13th March 2018, 05:43 PM   #74
MarcelvdG is offline MarcelvdG  Netherlands
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Originally Posted by billshurv View Post
Many cartridges have a +3/-1dB FR specification into the specified load. Pointless as it may be, I might want better, but to get better you need to understand what is going on. Outside the scope of this thread yes, but important in terms of driving home the point that 0.1dB RIAA accuracy is only of use if you cartridge can deliver to the same order of magnitude. A point I think we are all in violent agreement on.
Well, I don't agree with that. As it is relatively easy to make an amplifier with good RIAA accuracy and apparently much more difficult to make cartridges with a flat response, I would want the amplifier's inaccuracy to be negligibly small compared to the cartridge's response errors, so the accuracy of the combination is set by the cartridge. 0.1 dB seems like a perfectly reasonable target to me when the cartridge does +3 dB/-1 dB.

Similarly, I like the distortion of my power amplifier to be at least a decade below the distortion of the loudspeakers, so not of the same order of magnitude.

Last edited by MarcelvdG; 13th March 2018 at 05:46 PM.
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Old 13th March 2018, 05:52 PM   #75
scott wurcer is online now scott wurcer  United States
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Quote:
Originally Posted by MarcelvdG View Post

Similarly, I like the distortion of my power amplifier to be at least a decade below the distortion of the loudspeakers, so not of the same order of magnitude.
This is all very reasonable, why would anyone want it another way?
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Old 13th March 2018, 06:30 PM   #76
PMA is offline PMA  Europe
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Measuring phono stage RIAA accuracy with a computer
Quote:
Originally Posted by MarcelvdG View Post
when the cartridge does +3 dB/-1 dB.

Similarly, I like the distortion of my power amplifier to be at least a decade below the distortion of the loudspeakers, so not of the same order of magnitude.
Only a decade ? I would say no problem to make it 2 - 4 decades lower, including high order harmonics.
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Old 14th March 2018, 05:40 AM   #77
PRR is offline PRR  United States
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Originally Posted by luckythedog View Post
I think that's a good idea, Bill. <snip!>
And yet this thread *continues* to be flooded with hobby-horses which avoid the root question "Measuring phono stage RIAA accuracy".

(I omit "using a computer" because I submit you use whatever tool works best, which is NOT always a computer, and any calibrated-stick numbers can always be entered into a (computer?) spread-sheet for graphing.)
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Old 14th March 2018, 06:34 AM   #78
MarcelvdG is offline MarcelvdG  Netherlands
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My method is in post #38. It requires the measuring device to be able to accurately handle +/-20 dB level differences. If that's a problem, you could change the fixed 40 dB attenuator in one with a few settings. The attenuator is just a home-made resistive voltage divider; 0.1 % accurate resistors are readily available nowadays.
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Old 14th March 2018, 07:12 AM   #79
sottomano is offline sottomano
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Originally Posted by PMA View Post
Only a decade ? I would say no problem to make it 2 - 4 decades lower, including high order harmonics.
Yet no one can hear a difference in a blind test, wasn't it you who showed us that we cannot even hear rather beefy crossover distortion?
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Old 14th March 2018, 07:14 AM   #80
sottomano is offline sottomano
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Back to the question of the first post.

Was ARTA mentioned?

Quote:
You can define .MIC compensation files for other purposes. I.e. Peter de Jong has contibuted .MIC files (RIAA_MIC.ZIP) to compensate for phone RIAA response.
here: ARTA Faqs
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