RIAA and iRIAA accuraccy in the real and simmed world.

the road not taken.
Andrew
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Post by Andrew »


My suggestion is, either you do something that is right in the middle of all or you make it switchable. Think two will be enough. Anyway Hagerman that I earlier believed in, is as it looks right now a NONO as it seems to boost treble to much!
That's exactly what I did! With the Hagerman 50k point I thought, when listening the first time I ran the 1k5, that it had too much treble so reduced the value of the resistor down.

-- Andrew
izzy wizzy
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Post by izzy wizzy »

Checked your circuit and unfortunately the filter isn´t capable of driving a 600ohm RIAA. The figures you get are off. To make it work, a buffer has to be inserted. As is below shows your filters response whatever load you add.

Compare with the ideal RIAA at the bottom. No need to use your overly complicated circuit to get less accuracy.
Hi Lars,

I simmed both and get almost the same curve :? By almost, they differ at the bottom by about .008dB. So for real life, I reckon it will do :wink: unless I've done something wrong. Plus I never drive low Z with it so it doesn't bother me.

However, as you've shown, it's way more complex than I need now so I'm happy to ditch it. I remember now why I use it. I've been siming and not measuring for ages and my sim config comes from a DOS package I used to use that wasn't raw SPICE but had a "friendly" front end to, I guess, a SPICE back end.

I'm looking forward to using a better standard and seeing/hearing the results.
reVintage
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Post by reVintage »

Hi guys,
Last night I got the Neumann SAL74 Eq-card schematic. If we are to believe the schematic is right, we can forget about the Hagerman/Wright b-s alltogether.

Simmed it this morning. But might need more input as some new questions came up.

The Neumann deviates against the ideal RIAA with +0,184/-0,086dB 20-20kHz ref. to 1kHz. When comparing the Hagerman/Wright is as off as you can get. Will publish curves(but not Neumann schematic) when I get home today.
Brgds
Lars
reVintage
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Post by reVintage »

This is what happens if we trim a 600ohm RIAA to confirm to the signal from the SAB74B and use these two invRIAAs:

HW, fed by a Hagerman/AllenWright invRIAA

STD, fed by an ideal invRIAA
Attachments
74justRIAA.PNG
74justRIAA.PNG (58.2 KiB) Viewed 31038 times
Brgds
Lars
reVintage
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Post by reVintage »

This is what happens if we trim a 600ohm RIAA to confirm to an ideal RIAA and use these two invRIAAs:

HW, fed by a Hagerman/AllenWright invRIAA

74, fed by the SAB74 EQcard
Attachments
stdadjhw74.PNG
stdadjhw74.PNG (56.75 KiB) Viewed 31031 times
Brgds
Lars
reVintage
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Post by reVintage »

It looks even more grotesque if we trim to same lowend response.
Attachments
stdadjhw74bas.PNG
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Brgds
Lars
reVintage
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Post by reVintage »

And this is what happens if we adjust our RIAA according to the Hagerman/AllenWright invRIAA and feeds it with

STD, an ideal invRIAA
74, a SAB74 equalizer
Attachments
LCRHWjfrstd74.PNG
LCRHWjfrstd74.PNG (56.26 KiB) Viewed 31027 times
Brgds
Lars
Naz
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Post by Naz »

Hi Lars,

Now I'm really confused. Which RevRIAA are you suggesting is the one we should be using for Sims? And what about in the real world, where we want to do some bench testing if the Hagerman is too inaccurate?

If I include all of the variants thus far into my schematic for comparison purposes I get completely different results to the RevRIAA that you originally suggested. Any comments?

Naz
Attachments
LCR_GC_4-4-09_RevRIAAComparison.asc
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reVintage
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Post by reVintage »

Hey Naz,
Started this thread as I discovered the revRIAA, I let myself get fooled into believe in, was totally f-cked up. Ie the HW! Ie the same as I recommended you :oops: !

I thought that Hagerman and Allen Wright was right without doing a proper background check :oops: . So with a little help from Keith Howard( Thanks for the Neumann schematic, Keith!) who wrote the excellent article "Cut and Thrust" in the March Issue of Stereophile I could discover and reveal the absurd, silly thing about the "3.18mS pole" to an even greater extent than Keith himself did..

Still, about your circuit IMHO the problems isn´t about the revRIAA so I will not make any further comments.

I am at the moment working the correct invRIAA to be used.
Brgds
Lars
Jeff Davison
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Post by Jeff Davison »

Andrew
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Post by Andrew »

During a peaceful 5 minutes this morning I picked up an old copy of HiFi World Sept 2008 and re-read the article on the Emile Labs phono stage; it won their "best in year" award for 2008.

Now, I noticed looking at the measured freq response that characteristic bass lift was present. This same lift that is also very slightly present on the units I have designed mostly using the Hagerman RC-based iRIAA and only becomes apparent when tested against a perfect Spice iRIAA.

I wonder if they read the same work as I did, ie. Wright and Hagerman.

Interestingly, Noel Keywood suggested (I'm paraphrasing here) the lift might impart a full bodied sound that would ameliorate the effect of the foward/brightness found on many modern carts, I think I have read elsewhere this can be caused by generator coil capacitance?

Just an interesting note, really...and demonstrates the level to which the work by Wright and Hagerman (and no disrespect to them) has become a standard in itself.

Lars, how's progress on the new iRIAA? I am about to embark on the boxing up of my LCR breadboard and this is the perfect time to put your excellent work to the test.

best regards,

-- Andrew
TonyB
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Post by TonyB »

Hi Lars,

Any news on the iRIAA? I would LOVE to see the Neumann circuit.

Regards,

TonyB
Naz
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Post by Naz »

Hi Lars, sorry we are all bugging you about this but could you confirm that this is the ideal Spice iRIAA we should be using please?

Regards,
Naz
Attachments
Ideal RevRIAA_22-4-09.asc
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reVintage
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Post by reVintage »

Hi Naz,
DO NOT USE THAT ONE! As I have told you before this is the f-cked up Wright/Hagerman curve. Change R4 to 1ohm and you will be at the theoretical correct/ideal RIAA-curve. Adjust the last "e" to get the same out as in voltage.

IRL I still have no solution as there probably isn´t such a thing as an ideal curve. You will need a two pole switch to compensate for Neumann, Ortofon, Westrex etc. That is if you know what cutting equipment and EQ is used on the specific records you play.
Brgds
Lars
Naz
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Post by Naz »

Thanks Lars,

For the record this is the one that you recommend.

Care to share an opinion on a "reasonable compromise" for the 4th pole or do you think we should just forget about it?

I realized that I was unclear on this aspect of the "ideal RIAA". I was referring to one that included the 4th pole and you are (rightly) referring to a classic RIAA.

Rgds,
Naz
Attachments
Ideal RevRIAA_Lars 23-4-09.asc
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reVintage
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Post by reVintage »

Naz wrote:I was referring to one that included the 4th pole

Rgds,
Naz
You where referring to what Hagerman/Wright thought was a 4th pole compensation. But they where totally wrong as there is not such a thing like a 4th pole 1st order filter. Please read the Keiths article again. Also check my previous sims of what happens, they are very clear!

Will not comment this anymore. Still working on a solution.
Brgds
Lars
Naz
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Post by Naz »

Hi Lars,

I re read Keith's article and your previous posts and I think I get it now :oops: Should have taken the time to read everything properly but time is my enemy at the moment ... never an excuse!

Anyway, I understand that the 4th Pole is a misnomer but Keith's article does refer to the SAB74 equalizer having a 2nd order filter with a corner frequency of 49.9kHz. However we can ignore this since it has a minimal 0.1db effect at 20kHz.

Apart from the obvious AW JH error, of greater significance (to me) is the circa 0.5db deviation of the SAB74 equalizer from Std throughout much of the audio band according to your Sims. But I guess with all of the other potential sources of errors throughout the entire recording / playback chain we should not too hung up on all of this. Problem is it's difficult to ignore when you are part purist at heart and when you know how audible these errors can be.

I think I can approximate an appropriate compensation for now. But I have to say that for years I have incorporated some degree of adjustment of RIAA components in my Phono stage, mainly to compensate for bad recordings or ones that just don't sound right. Although this is akin to painting a moustache on the Mona Lisa by many in audio circles I feel better in knowing that it has some basis of fact.

Sorry for upsetting you and thanks for your efforts and your help, much appreciated :)

Cheers,
Naz
reVintage
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Post by reVintage »

Anyway, I understand that the 4th Pole is a misnomer but Keith's article does refer to the SAB74 equalizer having a 2nd order filter with a corner frequency of 49.9kHz. However we can ignore this since it has a minimal 0.1db effect at 20kHz.
Just a small note: Unfortunately SAB74 introduces almost 0,3dB error at ca 5kHz with reference to the original RIAA :( . That is even worse.......
Needs more investigation!
Brgds
Lars
Andrew
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Post by Andrew »

OK, Lars here's a thought (I'm holding off my boxing up while this research plays out), but would it make sense to use the inverse of the most common cutter machine as the defacto standard iRIAA? Other than that a switch-able RIAA to accommodate standard and SAL74 settings?

-- Andrew
reVintage
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Post by reVintage »

Andrew wrote:OK, Lars here's a thought (I'm holding off my boxing up while this research plays out), but would it make sense to use the inverse of the most common cutter machine as the defacto standard iRIAA? Other than that a switch-able RIAA to accommodate standard and SAL74 settings?

-- Andrew
Hi Andrew,

I have come to the conclusion that this is an unsolveable problem :( .


I do not the think the most common cutter is relevant. IMHO many of the best recordings where made before SAL74(most common?) .

To use the SAL74 as iRIAA is the worst idea.

Do you by the way know what cutters the different recording companies used as I have no clue? I know Decca used Neumann. SX66 might have been used when they did their best recordings.

Now to my ideas whatever bad or good cutters have been used:

We must assume the recording engineers at their best tried to trim their machines to comply with the RIAA curve on the endproduct: the vinylrecord. We must also assume that they, when installing the machines, also did testrecordings to check that the endproduct was OK against the standard RIAA. Otherwise they must have been totally stupid!

This leads to the conclusion that the iRIAA should fully comply with the RIAA-standard.

Whats wrong with fine tuning your RIAAs against lets say two test records: One European and one American?? One would then have a chance to adjust for imperfections in the electromechanical gear, player, arm , cables and pickup.
Brgds
Lars
Andrew
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Post by Andrew »

OK, so it seams the best approach is to use the Spice one on the Hagerman paper?

-- Andrew
reVintage
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Post by reVintage »

Andrew,
First of all Jim did a mathematical error in the spicemodel. Second the model he made is built on a misunderstanding of the Neumann cutteramp function. Stay away from that one!!!!!

You can change it to standard RIAA by substituting the last resistor before the second "e" to 1ohm. Also change the gain of "e" to get the same output as input voltage.

I explained this in my last answer to Naz, so check just a few posts up.
Brgds
Lars
Andrew
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Post by Andrew »

Thanks Lars, good stuff as ever....I shall have to clip lead out the 4th pole on my LCR and see what I think. I shall report back.....

Back to inverse RIAA.....

For the avoidance of doubt, is this what you mean?

much appreciated,

-- Andrew
Attachments
Ideal RevRIAA.asc
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Last edited by Andrew on Mon Apr 27, 2009 9:22 am, edited 1 time in total.
reVintage
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Post by reVintage »

Hello Andrew,
Right on spot :) ! But you will need to adjust e2 to 1515 to get the same output- as input-level.
Brgds
Lars
Naz
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Post by Naz »

Hi Lars, that's the one I'm using now (same as my last post) and the curve seems very accurate compared to the standard RIAA curve. Do you consider that the phase is also completely accurate?

Rgds,
Naz
reVintage
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Post by reVintage »

Naz wrote: the curve seems very accurate compared to the standard RIAA curve.

Rgds,
Naz
Hi Naz,
This IS the standard RIAA, but inverted! It is totally impossible to get any closer. OK, there is a minor error it has a 4th pole at 15MHz or so. If in doubt read between the lines in Hagermans pdf and use your slideruler to check the timeconstants :wink: .
Brgds
Lars
Naz
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Post by Naz »

>>This IS the standard RIAA, but inverted!<<

Yes I Agree. I should be more succinct. My point was really in relation to Phase angle. There is a huge discrepancy between the Std iRIAA and Hagerman's (& Wright et al) at 20kHz. It would seem to me then, that many designs will contain the same error. A few degrees should not be audible but I wonder at what point it becomes noticeable?

Rgds,
Naz
Naz
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Post by Naz »

Travelling is one of the few opportunities I have to read these days and in a recent OS trip I re-read "Cut & Thrust" in March Stereophile where I've gained a better understanding of the "thrust" of the article (pun intended). I also read Michael Fremer's article "Ripping LPs with Channel D Pure Vinyl" where he eluded to the software incorporating about 50 EQ curves other than RIAA. I was surprised that so many existed and wonder (a) where they got the information and (b) whether it's easily obtainable. Do any of you guys have any detail of other curves?

Also, I'm happy to report that my 6C45P LCR Phono utilising Dave's inductors (impedance around 7.5K) worked almost exactly as Simmed and preliminary results are fantastic without any tweaking!

FWIW, I modified my Hagerman RevRiaa to match the ideal Curve in order to test RIAA accuracy, the only downside being that attenuation is approx -75dB. You will note from the accompanying files that after correcting for input signal differences both amplitude and phase curves are perfectly aligned and appear as one when superimposed. The mods were simple and apart from one resistor, are easily achieved by paralleling components.

Naz
Attachments
Hagerman RevRIAA corrected for ideal curve.
Hagerman RevRIAA corrected for ideal curve.
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Corrected Haggerman Ideal RevRIAA.asc
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reVintage
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Post by reVintage »

Naz wrote: FWIW, I modified my Hagerman RevRiaa to match the ideal Curve in order to test RIAA accuracy, the only downside being that attenuation is approx -75dB. You will note from the accompanying files that after correcting for input signal differences both amplitude and phase curves are perfectly aligned and appear as one when superimposed. The mods were simple and apart from one resistor, are easily achieved by paralleling components.

Naz
Be sure your generator has 0 ohm Zout otherwise it will not work IRL :wink: :.
Brgds
Lars
Naz
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Post by Naz »

Good point, it was .001R as a leftover from a copy paste which was low enough not to be at all significant. It's now zero. :)

Incidentally, upon re-reading "Cut & Thrust" many times it makes me wonder just how much total phase shift really exists from recording to playback in the real world and since we have no way of knowing, from an engineering perspective it both frustrates and for me, puts all argument about the need for close phase accuracy out the window. :(

Also, for the believers in Ultrasonics having an effect within the audible range one would have to think it would be a good idea to compensate to some extent for the appreciable roll off that must exist beyond 20KHz. I'm not sure I fall into this camp but I probably lean this way a little, the caveat being again that we have no way of knowing how much to apply or at what point and we must be careful not to affect the top end of the audible range. But, is something better than nothing :?:

Naz
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