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Thread: DIY phonostage.

  1. #511
    Join Date: Mar 2010

    Location: Sheffield

    Posts: 2,898
    I'm Simon.

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    new traffo's 24v giving me a healthy 27.5v that i can trim back to my preferred 26v with 20r resistor in the CLCRC on the rectifier smoother boards.
    Kuzma Stabi/S 12", (LP12-bastard) DC motor and optical tacho psu, Benz LP, Paradise (phonostage). MB-Pro, Brooklyn dac and psu, Bruno Putzeys balanced pre, mod86p dual mono amps, Yamaha NS1000m

  2. #512
    Join Date: Jan 2016

    Location: Shenfield

    Posts: 573
    I'm Slav.

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    Finally I had short listening session , many thanks to Simon for matched transistors , it sounds bit thin and harsh and it occurred to me that Paradise gain is too much for my carts(both Benz carts and Zyx are ~ 0.7mV@5cm/sec). Looks like I need to drop gain by roughly 6dB , it means halving RIAA resistors and doubling caps value , any other way to achieve this?
    I looked at through hole SIL sockets so I could easily change gain in the future but cannot find 1-way ones , anyone makes them?
    As to the grounding , done it as simple as possible , mains to the chassis star in the PSU , tonearm connected to the star with 100R and it proves to be silent at max volume level.
    On reflection , thin sounding is not correct description , I'd say balance shifted towards highs , first impression was "dynamic" but after a while it becomes tiring , it reminded my of my Whest when by mistake I left gain @65dB , dropped to 55dB and it was it , well balanced .
    Next step , changing gain, run it for a bit , test freq. response of phono/cartridge , pull scope out of the cupboard and do some proper probing, but it will be another couple of weeks till I get to it.
    Last edited by mac72; 22-10-2017 at 10:36.

  3. #513
    Join Date: Mar 2017

    Location: Liverpool

    Posts: 766
    I'm Sandro.

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    I would let it run for a few days to form the capacitors then try loading the cartridge for my Elitte the recommended is 100 R but it works quite well whit 10 R and a generous 1nF (will need listening to get it right)
    There are alternative RIAA values on the Guide as the original curve was described a lively
    Riccardo= 11nF 32.1nF 9.9k 73.7K
    Sallas = 12nF 34.7nF 9.1K 67.8K
    Best way would be to use the like of LT spice

    I was thinking about this but my electronics is limited my thinking is as the current in the mirrors halves must be equal maybe a small change in the like of R4 and R8 would change the gain
    Last edited by Bksabath; 22-10-2017 at 11:59.

  4. #514
    Join Date: Jan 2016

    Location: Shenfield

    Posts: 573
    I'm Slav.

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    Definitely I have too much gain so I start with dropping few dB , I might try different RIAA curves at some point if original one is too "lively" .
    Any advice on one way SIL sockets ?
    I might try to simulate circuit with Spice to check f there is an easier way to change gain , as to loading I normally stick to 8-10x cartridge impedance , I tested freq. response in the past and slight loading variations don't make much difference .
    I still have ~1V on OPA I hope running for few days should help it , output +/-30mV without lid and thermal coupling , shame I won't be home for another 2 weeks.

  5. #515
    Join Date: Mar 2010

    Location: Sheffield

    Posts: 2,898
    I'm Simon.

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    From new it'll need 50 hours to form the caps, DC won't settle until they form fully. 30mV with the case off will be 1/10 of that with lid on, so you're almost there.

    0.7mV is a touch high, but the paradise has plenty of input margin, do you're actually not driving it close to clipping. Also your cart is only actually about 0.5mV at 3.5cm sec, which is the more usual measure of cart output level. I've used it with similar output Lyras with no issue, no hint of clipping when scoped.

    The native input impedance is about 1.2K so adjust your loading resistor accordingly. Use a parallel resistor calculator to get the value spot on, it'll be higher than uou expect.

    Leave it on for a week, then redo input bias with new loading values and trim the Calvins out one last time.

    I finished my psu last night and rebuilt my Calvins. Picture to follow.
    Kuzma Stabi/S 12", (LP12-bastard) DC motor and optical tacho psu, Benz LP, Paradise (phonostage). MB-Pro, Brooklyn dac and psu, Bruno Putzeys balanced pre, mod86p dual mono amps, Yamaha NS1000m

  6. #516
    Join Date: Jan 2016

    Location: Shenfield

    Posts: 573
    I'm Slav.

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    Quote Originally Posted by sq225917 View Post
    The native input impedance is about 1.2K so adjust your loading resistor accordingly. Use a parallel resistor calculator to get the value spot on, it'll be higher than uou expect.
    Sorry , you got me confused , Paradise input impedance looks to be around 10k
    Have you ever used push in connectors in RIAA section ?

  7. #517
    Join Date: Mar 2010

    Location: Sheffield

    Posts: 2,898
    I'm Simon.

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    I use them for input loading on my own unit and have built two units with push in riaa. They're fine.
    Kuzma Stabi/S 12", (LP12-bastard) DC motor and optical tacho psu, Benz LP, Paradise (phonostage). MB-Pro, Brooklyn dac and psu, Bruno Putzeys balanced pre, mod86p dual mono amps, Yamaha NS1000m

  8. #518
    Join Date: Jan 2016

    Location: Shenfield

    Posts: 573
    I'm Slav.

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    Where did you buy one way SIL connectors , I have ordered 2way and try to split them.
    As to the gain my main concern is the signal level reaching my preamplifier , I don't want the amp to reach full power from the nominal output level of the cartridge.If cartridge has a nominal level of 0.7V RMS at 5cm/s I want the maximum level of a typical LP to put about 2V RMS output from the phono preamp. So, if the nominal level is 0.7mV, and the maximum recorded level on the LP is 20dB above that, that is 10X the 0.7mV level, or 7mV. 2000mV/7mV =285 gain, or only 49dB gain add a few dB for good measure and I get something like 55dB of gain.

  9. #519
    Join Date: Mar 2017

    Location: Liverpool

    Posts: 766
    I'm Sandro.

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    WP_20171024_15_18_40_Pro.jpgWP_20171024_15_18_51_Pro.jpgWP_20171024_15_18_59_Pro.jpgWP_20171024_15_21_04_Pro.jpg
    First of all
    Once again Big tanks to Simon for the Jfet's
    I got one of the Calvin buffers working as I like



    The square wave is at 100 KHz



    I found much easier to adjust the offset by placing a trimmer on the 75R R2this way it can be pretty low and the current trough the 6r8 can be kept aroundthe ball park 200mV

  10. #520
    Join Date: Mar 2010

    Location: Sheffield

    Posts: 2,898
    I'm Simon.

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    I just push them out of 2.54mm header strips
    Kuzma Stabi/S 12", (LP12-bastard) DC motor and optical tacho psu, Benz LP, Paradise (phonostage). MB-Pro, Brooklyn dac and psu, Bruno Putzeys balanced pre, mod86p dual mono amps, Yamaha NS1000m

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