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Thread: LCR phono stages - opinion

  1. #41
    Join Date: Nov 2015

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    I'm Oliver.

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    Quote Originally Posted by Marra View Post
    Waiting on a quote from Cinemag.
    You going for the DIY? I am sorely tempted but I'm going to re-box the Phonostage I'm using and separate the power supply from the main case instead.
    Analogue: Technics SP10 MK2 > Phonomac AT-1010 tonearm > Ortofon Kontrapunkt b > Wizard Jfet MC Valve Phonostage (Telefunken Valves)
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  2. #42
    Join Date: Dec 2010

    Location: North Lincs

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    I'm Keith.

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    I am just pricing things up at the moment. Had this book marked for a couple of years but as I have four diy phonostages already I keep asking myself do I really need another; but am curious as to how an LCR version would sound.

  3. #43
    Join Date: Oct 2016

    Location: Bolton, England

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    I'm Andrew.

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    Quote Originally Posted by Marra View Post
    There is a diy version but have no idea how it sounds.

    http://www.pmillett.com/LR_phono.html
    Actually, that isn't an LCR phonostage, it's an LR phonostage. To me, that makes more sense - if you want to eliminate capacitors and use inductors instead, why go only half way? CR equalisation is commonplace and LR equalisation makes sense if you want to do away with capacitors, so what's the point of LCR equalisation? Combining inductors and capacitors does allow you get steeper roll-offs, but you don't need steeper roll-offs for RIAA equalisation, so the design in the link makes more sense than LCR equalisation.

  4. #44
    Join Date: Dec 2010

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    I'm Keith.

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    My error Andrew I stand corrected.

  5. #45
    Join Date: Oct 2016

    Location: Bolton, England

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    I'm Andrew.

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    No problem.
    BTW, I had a snoop around his site and found this quote relating to a microphone preamp:

    "The power supply is, uh, unconventional. What? Who? Me? Yup. A switching supply, generating 6.3V filament voltage and +200V B+ from a 48VDC input. The beauty of switching supplies is that the noise they generate - and yes, they do generate some noise - is at high enough frequency that it's easy to filter, and above the audible range. For a low-level preamp like this I'd rather have a few millivolts of 100kHz than a few millivolts of 60Hz!"

    I agree entirely Hi frequency noise/ripple is easier to deal with than low frequency noise/ripple. I don't know why switching power supplies get so much stick in audiophile circles.

  6. #46
    Join Date: Jan 2009

    Location: Essex

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    Quote Originally Posted by RothwellAudio View Post
    No problem.
    BTW, I had a snoop around his site and found this quote relating to a microphone preamp:

    "The power supply is, uh, unconventional. What? Who? Me? Yup. A switching supply, generating 6.3V filament voltage and +200V B+ from a 48VDC input. The beauty of switching supplies is that the noise they generate - and yes, they do generate some noise - is at high enough frequency that it's easy to filter, and above the audible range. For a low-level preamp like this I'd rather have a few millivolts of 100kHz than a few millivolts of 60Hz!"

    I agree entirely Hi frequency noise/ripple is easier to deal with than low frequency noise/ripple. I don't know why switching power supplies get so much stick in audiophile circles.
    I think it's because of the 'crap' they put back out into the mains supply and hence back into other audio components.

    But you are right - high frequency power supplies were developed for aeronatical use as they would only need smaller and lighter capacitors for filtering. And in the aircraft industry weight is everything.
    Have you listened to this month's choice in the Album Club?

    Barry

  7. #47
    Join Date: Jan 2014

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    I'm Martin.

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    Quote Originally Posted by Marra View Post
    There is a diy version but have no idea how it sounds.

    http://www.pmillett.com/LR_phono.html
    I built one of these last year. I had to wait for the inductors to be wound by Cinemag, took about two weeks so not too bad.

    If you build this you need to order a few more of the AD797 opamps than you need. This is because itís DC coupled and the opamps have high gain. You need to swap them around in order to get the adjustment for zero DC volts on the output. With some combinations itís impossible to zero the DC on the outputs.

    Itís a nice sounding phono stage, but in the end I found I preferred my valve phono.


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  8. #48
    Join Date: Oct 2016

    Location: Bolton, England

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    Quote Originally Posted by Barry View Post
    high frequency power supplies were developed for aeronatical use as they would only need smaller and lighter capacitors for filtering. And in the aircraft industry weight is everything.
    Yes, I used to work at British Aerospace in a section whose job was designing switch mode power supplies. Actually, the main weight reduction benefit comes from smaller inductors/transformers required at high frequency operation.

    Quote Originally Posted by disarmamant View Post
    If you build this you need to order a few more of the AD797 opamps than you need. This is because itís DC coupled and the opamps have high gain. You need to swap them around in order to get the adjustment for zero DC volts on the output. With some combinations itís impossible to zero the DC on the outputs.

    Itís a nice sounding phono stage, but in the end I found I preferred my valve phono.
    The circuit diagram has offset trim adjustment. Doesn't it work properly?

  9. #49
    Join Date: Jan 2014

    Location: Northants

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    I'm Martin.

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    Quote Originally Posted by RothwellAudio View Post
    The circuit diagram has offset trim adjustment. Doesn't it work properly?
    Yes, it does work and you can null the DC offset to near zero, but there is something with the AD797 which in certain combinations the DC offset cannot be nulled. Swapping the Opamps fixes the problem. Its a known problem apparently, hence I ordered a couple of spareís as advised. I needed to use them.

    I think itís due to the DC coupling and the high gain of the circuit.

    There is some discussion about it on the DIY Audio forum.


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  10. #50
    Join Date: Oct 2016

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    Quote Originally Posted by disarmamant View Post
    I think it’s due to the DC coupling and the high gain of the circuit.
    The first gain stage has a gain of about 21dB and the second has a gain of about 41dB. Making the gain about 31dB in both stages would help and using the offset trim facility of the second stage would help too. One other thing I don't like the look of is that at low frequencies the first stage is seeing a load of only 143 ohms, assuming L1 has negligible resistance. That seems a rather low figure for maintaining low distortion.

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