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Thread: Turntable RIAA tweaking

  1. #1
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    Turntable RIAA tweaking

    It will be shown how frequency response can be improved. This relates to magnetic pickups, owners of dynamic pickups are mainly on the fortunate side.
    These thoughts are only useful if you are willing to integrate the RIAA amplifier into the turntable and you must be handy with your soldering iron. May be there is no one interested, but for me it was useful.

    It is well known to care for the input impedance of the RIAA amplifier. It unevitably creates a lowpass. This relates both to the inputs capacitance and the resistance. Additionaly the inductivity of the pickup is of importance. These three parameters must fit, otherwise the result is inferior to CD playback.

    Hagerman technology offers an online calculator. With typical 680 mH (Shure V15, a formerly highly recommendated pickup) and a low capacitance value of 220 pF the upper frequency limit is 13 kHz . This is a bit compensated by a resonance between stylus mass (parts of a gram) and the elasticity of the disk , not very pleasing. Better use a stylus with low mass.
    http://www.hagtech.com/loading.html

    The solution is to keep the wire between the pickup and the circuit board as short as possible. Best to place it under the footage of the arm. If the overall capacity, mainly the wire in the arm, is not more than 50 pF it would be really good. For the above example the upper frequency limit is extended to 27 kHz.

    If you go this way one more aspect must be considered. The load resistor must be changed, otherwise the roll off is too low or you have a resonance. Use Hagermans Load Resistor Tuning (s.a.). For the example the input resistor must be 116 kOhm. This implies to go into the circuit, normally this cannot be achieved by external changes.

    When looking into a typical RIAA Phono preamp http://sound.westhost.com/project06.htm it is the resistor R1L which must be changed from 47 kOhm to 116 kOhm (or similar, not critical).

    Another aspect is the high frequency boost when cutting. It may not be done unlimited. Look here: http://www.vacuumstate.com/phono_secrets.htm ( PDF download).
    For compensating in the RIAA preamp there must be added a low value resistor. Add in series with C4L a 47 Ohm resistor. (82 nF x 47 Ohm results in 3,85 microsec).

    As a whole only minor changes but it has pleased me.

    The example preamp is only choosen for availability. A better approach with a very well explained equalisation can be found here:
    http://www.national.com/an/AN/AN-346.pdf
    Unfortunately there is no circuit layout.
    __________
    Peter
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  2. #2
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    Digitization Tweak

    A comparison between the digitized LP and CD version shows that you can come quite close.

    a)
    A comparison of the digitized LP Deep Purple "Made in Japan" and the Two-CD-Set (all concerts, EMI) shows that the frequency response of the CD version is inferior. These CDs have in fact a reduced frequency response, but it is nice to listen to.
    Generally my recorded LPs show a wider frequency response than a lot of wave files I got by ripping CDs.
    This has been documented somewhere else too:
    http://www.audioholics.com/techtips/...sCDformats.php

    b)
    Especially I compared Pink Floy "The dark Side of the Moon". The Bass (heart beat) from the CD was a bit stronger, I did not investigate this fact deeply (recording or a wrong capacitor?)

    There are some passages of the original where I have always thought that my old LP is worn out - aging with me. No, the CD shows the same effect.

    Most interested I have been in the playback of the recorded thrown coins and the bells. Yes the CD makes it better. Now I come to my tweak.

    c)
    As I judge the upper frequency limit of a magnetig pickup as problematic, I have digitized "The Dark Side ... " with half of the speed. My player does 16 1/3 rpm (some Thorens, Lenco, Braun can do). With a sound editor I have doubled the speed, the result is stunning. The bells and coins showd the same clarity as from the CD version. The recording was quite enjoyable, but it must be considered that the equalisation of the preamp was wrong. It made slightly increased lows and highs.

    When digitizing with half speed the relevant capacitors in the RIAA equalisation must be doubled. Details on demand, I fear nobody else will go this way.

    (Pickup Ortofon M15 E Super - comparable to Shure V15 /
    Soundcard Turtle Beach Santa Cruz, Crystal chip;
    look here http://www.pcavtech.com/soundcards/compare/index.htm)
    ____________
    Regards
    Peter
    Last edited by Hoerninger; 01-07-2007 at 03:09 AM. Reason: minor changes

  3. #3
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    Interesting. What brought you to try this method?

  4. #4
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    Quote Originally Posted by Titanium Dome View Post
    ... What brought you to try this method?
    In short: It is hobby and I wanted to transform some of my LPs into CDs. But I was never satisfied.

    Lengthy: I was not satisfied with my first DIY RIAA preamp somewhere in the seventies. Although at that time it was the best I had ever heard something was wrong (not meaning distortion). It made me to create a programm for calculating the frequency response (good ol' HP 41 - pre PC time). I saw the deviation but at that time I did not know how to make it better not meaning by try and error. Later I have learned how to do it. After a lot of reading in the WWW I tweaked my latest RIAA preamp with help of the programm Electronics Workbench.

    Changing of stylus and soundcard made significant improvements.
    Washing discs, no level adjusting or declickering by programm (only diminishing severe cracks by hand) gave best results.

    The last step with reduced speed is still under investigation, the right capacitors must be build in. It is only a minor step because it has been at hand with my gear. I use IBMs "OS/2 WARP" and their older soundeditor makes the job.

    Modern soundeditors (Mac or Windows) are much more sophisticated, but the above way must already be seen as foretime. For a short time I do own a DVD player and this shows me the way for listening to recorded music.

    I have read your remark "Stunning" on Beatles LOVE in several aspects , and I really do agree (not yet tried multichannel).
    http://audioheritage.org/vbulletin/s...6&postcount=34
    ___________
    Peter

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    Hi, Peter,

    Your half-speed technique is interesting, and I intend to try it sometime. One could simplify the EQ mod by substituting a multiple pole switch for the speed control, using the added pole(s) to shunt an alternate set of (parallelled, equal value) caps when appropriate. Alternately, you could bypass the initial EQ and add it back with software when doubling the speed, though whether it would be any easier or better would depend on the program.

    As you noted, soundcard quality is tantamount in digitizing LPs. I splurged on an external Firewire unit with extensive I/O to aid in acoustic measurements (Edirol FA-66), and an added benefit is the abilty to record at 24 bit/192kHz. Best toy/tech aid I've bought since my first DMM!

    (Add/edit) One should be aware that any DC offset present at a soundcard's input will be recorded right along with the program material, assuming the level is low enough to not blow the card.

    If you've not yet tried it, check out the RightMark Audio Analyzer, a free and very useful program that automatically runs several tests on your soundcard in a loopback configuration. Once your card parameters are known, you can insert virtually any device it can handle in the loop and test it as well, by subtracting your soundcard baseline from the results. I use it for initial testing of amps I've repaired or restored, and if any problems are noted, I then verify and solve them the old-fashioned way. A real time saver as long as your soundcard performance exceeds that of the device you're testing.

    RMAA is at;

    http://audio.rightmark.org/products/rmaa.shtml

  6. #6
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    Hi Moldyoldy,

    good news, thank you.
    Edirol FA-66...
    ... I did not know, it fascinates me. There are coming up some questions :dont-know besides some dreams [*]:
    - Can four channels be simultaniously recorded and afterwards played back with with 96 kHz?
    - Which software will do it?
    - Is it possible to make any sort of audio DVD, which can be played at any DVD player with four tracks? (There is no need for Dolby.)
    (A Pioneer DVD-575A and follow ups can be "updated" to 92 kHz and more as Freerider (dyndns) points out.)
    ... since my first DMM!

    If you've not yet tried it, check out the RightMark Audio Analyzer ...
    Did not know. Good tool, seems to "loosen some breaks".
    (Add/edit) One should be aware that any DC offset present at a soundcard's input will be recorded right along with the program material, assuming the level is low enough to not blow the card.
    I do not see the context so far, in my audio paths there are always capacitors.
    ... a multiple pole switch for the speed control ...,
    ... and add it back with software when doubling the speed ...
    Good suggestions, but I will choose neither. I have several TT. (Don't ask why, I 'm no collector. ). One extra external half speed preamp will do it.
    ___________
    Peter

    [*]
    Once I was preparing a school project about miking - but it will never happen, pupils wanted horns as mentioned.
    Some interesting facts and listening demos can be found here:
    http://hauptmikrofon.de/
    Highly recommended:
    http://www.irt.de/wittek/hauptmikrofon/theile/Multich_Recording_30.Oct.2001_.PDF
    Some AES papers:
    http://hauptmikrofon.de/wittek.htm
    (o.K. totally OT, normally we are discussion the other edge of the audio chain.)

  7. #7
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    Wow, Peter, I haven't been asked so many questions since my ex-wife vanished...

    I should explain that I'm an aspiring musician in addition to my audio interests, and I selected the FA-66 to meet those needs as well as acoustic measurement, LP ripping, amp testing, etc., and I forget that my posts may sometimes be confusing to those thinking audio-only. Rather than chance a wrong answer, I'll include the FA-66 specs below. There is no bundled software except the driver, the FA-66 just allows your own software to access the world beyond your hard drive and disk drives in high quality real-time and most common formats and levels. I got mine for $275 USD, which seemed a lot at the time, but I now feel was money well spent.

    For recording software, I've been using the free Kristal engine, available at;

    http://www.kreatives.org/kristal/

    So far it's done all I need, and best of all it's free. Most other recording engines are compatible too, including ASIO.

    To burn audio DVDs from your computer, you'd need a DVD burner and software for it. If you have an independant real-time DVD burner, I'm sure the FA-66 is compatible, with either optical or analog I/O.

    DMM= digital multimeter

    My note on DC offset only applies to automated amp testing and the like where DC might exist.

    The preamp switching suggestion was a brain fart. I was just thinking how I might apply it on my own turntable.

    Sorry to get so far OT, but didn't think you'd mind.

    I'll check out your links, always looking for reliable resources. Thank you.


    Edirol (Roland) FA-66 specifications

    Number of Audio Record/Playback Channels
    <44.1/48/96 kHz>
    Record: 6 channels
    Playback: 6 channels
    (Full duplex)
    <192 kHz>
    Record: 4 channels
    Playback: 4 channels
    (Full duplex)
    * Depending on the computer you are using, you may be unable to obtain sufficient
    performance.

    Signal Processing
    PC interface:24 bits
    AD/DA Conversion:24 bits (linear)

    Sampling Frequency
    Digital output:44.1/48/96 kHz
    Digital input:44.1/48/96 kHz
    AD/DA Conversion:44.1/48/96/192 kHz

    Frequency Response
    96.0 kHz: 20 Hz to 40 kHz (+0/-2 dB)
    48.0 kHz: 20 Hz to 22 kHz (+0/-2 dB)
    44.1 kHz: 20 Hz to 20 kHz (+0/-2 dB)

    Nominal Input Level
    Input Jack 1–2 (XLR type):-50 to -10 dBu
    Input Jack 1–2 (1/4 inch TRS phone type):-35 to +4 dBu
    Input Jack 3–4: -10 dBu to +13 dBu (balanced)

    Nominal Output Level
    Output Jack 1–4: +4 dBu (balanced)

    Residual Noise Level
    (input terminated with 1 k ohms, MAIN VOLUME: 0 dB, INPUT SENS: +4 dBu,
    DIRECT MONITOR VOLUME: OUT1/2 position, IHF-A typ., Balanced)
    Output Jack 1–2: -95 dBu

    S/N RATIO (Typical)
    OUTPUT: 105 dB (typ.)
    INPUT: 102 dB (typ.)

    Interface
    Firewire (IEEE1394)
    Digital input/output
    Optical type (conforms to IEC60958)
    MIDI IN/OUT

    Connectors
    <Front Panel>
    Input Jack 1–2 (XLR type / 1/4 inch TRS phone type)
    XLR type (balanced / phantom power +48 V)
    1/4 inch TRS phone type (balanced)
    * Input jack 2 supports high impedance
    Headphones Jack (Stereo 1/4 inch phone type)
    <Rear Panel>
    Input Jack 3–4 (RCA pin type)
    Output Jack 1–4 (1/4 inch TRS phone type (balanced))
    Digital In Connector (Optical type)
    Digital Out Connector (Optical type)
    MIDI Connectors (In, Out)
    FireWire Connectors (6 pins type, 4 pins type)

    Power Supply
    DC 9 V (AC adaptor)
    * FireWire Bus Power

    Current Draw
    650 mA

    Dimensions
    164 (W) x 148 (D) x 44 (H) mm
    6-1/2 (W) x 5-7/8 (D) x 1-3/4 (H) inches

    Weight
    0.65 kg / 1 lb 7 oz

    Accessories
    Owner’s Manual
    CD-ROM
    AC Adaptor
    FireWire cable (6 pins to 6 pins, 6 pins to 4 pins)
    (0 dBu = 0.775 V rms)
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