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Old 11th July 2005, 09:52 AM   #1
miksin is offline miksin  Finland
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Default active AD/DA xover as RIAA-amp?

Has someone ever tried to use active x-over as RIAA equalizer?
I use one such,( running active two-way system) namely Alto Maxidrive , and of course there is out plenty of them, all Behringers and DBX's and so on, but the question is: most such devices has easily enough EQ power to make RIAA curve. One could possibly need line pre or step-up tran between a xover and a cartridge, but is there some window to aim, to make A/D converter to work in 16-bit or perhaps even 24bit and not yet saturating ADchips with RIAA.s uncorrected tr3eble emphasis? complicated, ehe? Yes , I think so but I also think that could be something to at least to try, namely, if you already has one such device (Active xover, that is if you are usin active multiway system with such device) so why not to try to skip separate RIAA preamp with it, if possible., or replace it with just line pre. Help with maths please? How much one could boost carts signal before ad-chip begins to clip, and does it seems possibe to achieve reasonable line level takinf into account chips sample rate and dynamics? ...


Mika
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Old 11th July 2005, 10:34 AM   #2
CLS is offline CLS  Taiwan
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That might be an excellent idea!

Here is some useful info about the curve.

And I guess a digital EQ maybe up to the job

Say, a cheap Behringer DEQ2496 has PEQ for + 15dB range & GEQ for another +15. That should be enough to make up the curve of +20 low to -20 high.
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Old 11th July 2005, 11:27 AM   #3
EC8010 is offline EC8010  United Kingdom
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I'm sorry to rain on your parade, but RIAA is best done analogue. If you do it digitally, you immediately use up 40dB of digital dynamic range. Given that the A/D chips have only about 106db of dynamic range (and that's a weighted figure), that only leaves 65dB. Further, by applying an unequalised signal to the A/D, you are stressing it just where it's weakest - its HF performance. And what about leaving some overload margin etc?
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Old 11th July 2005, 12:03 PM   #4
miksin is offline miksin  Finland
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So it does not matter whether the xover is fed with -60 or +6 dbU, the converter anyway uses its entire dynamic range to input signal, right?
And all eq-ing-lets say for example -12 db automatically reduces dynamic range with same number?
If you feel like I dont really know what I am talking about you propably just are right! Sorry if askin stupid questions, that is only because I liked to learn some more :-) And thanks for "raining on my parade", that was exactly what I was askin for!
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Old 11th July 2005, 03:06 PM   #5
EC8010 is offline EC8010  United Kingdom
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Quote:
Originally posted by miksin
So it does not matter whether the xover is fed with -60 or +6 dbU, the converter anyway uses its entire dynamic range to input signal, right?
It does matter. I'm afraid I was assuming very best case. An A/D needs to be fed with a signal large enough to almost overload it, but no more. That's why many people who use digital crossovers use stepped attenuators on the output of the crossover to feed their valve amplifiers etc. That way, the crossover always sees a large signal.
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Old 11th July 2005, 04:35 PM   #6
PRR is offline PRR  United States
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If you must do it the hard way:

1) Put about 10:1 of gain in front. That will put the hot 5KHz-20KHz tones around the A/D's nominal input level.

or

2) Use an integrator in front. The main slope in the RIAA curve is really due to the differentiator action of the dynamic (velocity) pick-up. If you used a displacement pickup, the RIAA curve would be nearly flat, a 6dB shelf from 500Hz to 2KHz. Integrator with gain of about 100 at 1KHz would be about right.

Note that the standard integrator has low input impedance and excess voltage noise. You need to complicate it. Pretty soon it is more complex than a standard analog RIAA amp.

Since all the slopes in a phono recording and pickup are simple analog effects, and well standardized, I'm not sure what you'd gain with exotic digital EQ. While a phono needle could have a few degrees excess phase at 20KHz, they do not have the huge internal resonances of cone speakers, and don't need nearly as much EQ complexity.

I could picture using digi-EQ in 78 transcription where every company used a different EQ. Still I suspect it would be best to start with a semi-universal analog preamp, and then use the digi-EQ to give the variations between different recording curves. But good 78 transcription is such an Art, that each person finds his/her own preferred techniques.
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Old 11th July 2005, 05:57 PM   #7
miksin is offline miksin  Finland
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I could picture using digi-EQ in 78 transcription where every company used a different EQ.

that's exactly one of the things I had in my mind too.. I am spinning an TD124 :-)

Since all the slopes in a phono recording and pickup are simple analog effects, and well standardized, I'm not sure what you'd gain with exotic digital EQ.

Well, if I already have one such device in my setupp with with one possibly could make a riaa-correction, why couldnt I at least to think or try it? you see, it took me a while to accept use of such device -digi-xo- in my place. I used to listen for four or five years only fullrange drivers and I felt almost as a sinner, you know:-) So I could see some beauty in a idea to avoid one amplification\equalization device with use of another one, namely that XO, I am sure you understand that idea. Unfortunately it seems to be not a good idea.
Still, I have some RCA-6,3mm-plug adapters and because that XO accepts both xlr- and 6,3-mm inputs I will try it as soon as I next time swap carts, now I am running a DL103 and I think that is perhaps too long shot but I also occasionaly use a Benz MC Silver and high output mc could perhaps be more realistic :-)
Perhaps I will report conclusions, that is if you are interested.

I am just thinkin, 65 db of dynamics is still quite respectable amount. There are quite a few recordings with larger dynamics and perhaps even less domestic systems capable producing 50-60db (lowest levels in a recording in normal listening eniviroments background noise, I think? add there 65db, you'll end around 115-120?
I think I will at least try, to see how much microdynamics and details suffers. Perhaps it sucks, but at least, I tried it :-)
That 10:1 stepup tran to cart could be nice idea:-) perhaps with treble equalization:-)
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Old 11th July 2005, 07:08 PM   #8
PRR is offline PRR  United States
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> couldnt I at least to think or try it?

Of course you can.
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Old 11th July 2005, 07:31 PM   #9
miksin is offline miksin  Finland
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-perhaps it was just one more silly idea :-)

Thank you for your thoughts and interest!
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Old 11th July 2005, 09:58 PM   #10
miksin is offline miksin  Finland
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-Just got to write this more:
I tried, with DL103 putting out whoooppin 0,3mV, directly in that Alto Maxidrive 3,4.
Needless to say, I listened very quiet, -70 db compared what my RIAA (Musical Fidelity x-lps v3, that is the newest edition) gives. Also, time here is 00.40 am, but I often listen in the middle of the night at very low levels and that was exactly right level for my night listenings.
I made _very_ rude correction with input eq, putting -15db in 12khz and and +15db in 70 hz, peak width set wit ears and a handful of familiar recordings.
Unfortunately difference in to favor of that Alto was not subtle. Except that output level there was not a single thing that my RIAA makes better, and again, difference was not subtle.
Perhaps I really should set up one pre-pre with perhaps Lundahl LL9206 step up for Denon and transformer coupled e55l or somethin, perhaps intentionally miscalculating output iron to achieve some treble attenuating:-)
Or perhaps it is just that Musical fidelity which sucks.
Really, has some one ever tried something similar? how do you know how does it sounds if you not try?
Perhaps propellerhead is my middle name :-)
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