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Thread: DIY phonostage.

  1. #501
    Join Date: Mar 2017

    Location: Liverpool

    Posts: 766
    I'm Sandro.

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    WP_20171015_13_12_49_Pro.jpg
    Yes I was talking about the one on Calvins

    I got my R3 working and pretty well it is still out of the box for now and need work on the Calvins
    Imo much better than the R2 I have selecting the transistors for close Hfe make a big difference on staging
    But more of this later ...
    PS.
    Sorry about state of rug It has been cleaned a few time since I moved in but is still in a pretty poor state as it was left from previous owner At 9 x 12 ft it will need much big washing machine

  2. #502
    Join Date: Mar 2017

    Location: Liverpool

    Posts: 766
    I'm Sandro.

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    WP_20171016_12_01_06_Pro.jpgWP_20171016_12_01_28_Pro.jpgWP_20171016_12_01_43_Pro.jpg
    Just got a batch of PF5102

    I am trying to match them as in the drawing
    Where the voltage drop across the resistor give me the Idss
    V/r=a
    I am using a 100 homes resistor
    I am using a variable resistor to set the voltage to thegate as on guide
    This is set at -1 v
    Most of the Jfet do not conduct and only one or 2 give me avolt drop of 0.03 V
    0.03 / 100 = 0.0003 or 0.3mA
    Either:
    1) I am doing something wrong
    2) Fakes
    I have tried to use the DCA PRO the graph Id/VDS show aboutthe same results and the Jfet start conducting whit Vgs of -0.8 Volts

    Help please
    PS Looking at the data sheet Vgs of is stated as -0.7 to -1.5 volts so maybe is just a bad batch ?
    Last edited by Bksabath; 16-10-2017 at 12:39.

  3. #503
    Join Date: Mar 2010

    Location: Sheffield

    Posts: 2,898
    I'm Simon.

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    I've just set up Herman's Calvins. One board came up at a few mV +/- and dialled straight in to 0v offset. The other dropped the current source LEDS on the - rail and took the rail down to only 13.3v. I had to dial this one right across on the trim pot on the Calvins. But then magically as it got close the rail voltage came up, the LEDS lit up, the voltage climbed to 17v and then when I dialled in the trim pot for the current source to 18v I found that the Calvins were within a few mV which dialled straight out.

    There is definitely a situation where the Calvins sink so much current on one rail that the supply voltage drops out and throws everything off. It worth persevering with, I got the voltage across the 2.2r at 133mV on both sides of each board with zero offset, so it's all dialled in.
    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

  4. #504
    Join Date: Jan 2016

    Location: Shenfield

    Posts: 573
    I'm Slav.

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    Exactly same problem as I have with one of the calvins but I couldn't go any lower than 30mV to achieve 0V I had to increase the range of the pot by soldering another 220R .
    board was drawing more than 60mA on a single rail , which I thought was bit too much as PSU supplies 140mA , so I changed 6R8 resistor to something around 2.2R and I have approx. 30mA going through the branch .
    Whats the voltage drop on 2R2 on the other board?

  5. #505
    Join Date: Jan 2016

    Location: Shenfield

    Posts: 573
    I'm Slav.

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    Quote Originally Posted by Bksabath View Post
    WP_20171016_12_01_06_Pro.jpgWP_20171016_12_01_28_Pro.jpgWP_20171016_12_01_43_Pro.jpg
    Just got a batch of PF5102

    I am trying to match them as in the drawing
    Where the voltage drop across the resistor give me the Idss
    V/r=a
    I am using a 100 homes resistor
    I am using a variable resistor to set the voltage to thegate as on guide
    This is set at -1 v
    Most of the Jfet do not conduct and only one or 2 give me avolt drop of 0.03 V
    0.03 / 100 = 0.0003 or 0.3mA
    Either:
    1) I am doing something wrong
    2) Fakes
    I have tried to use the DCA PRO the graph Id/VDS show aboutthe same results and the Jfet start conducting whit Vgs of -0.8 Volts

    Help please
    PS Looking at the data sheet Vgs of is stated as -0.7 to -1.5 volts so maybe is just a bad batch ?
    Idss is the current which flows in the drain-source channel when Vgs= zero ,you need to match transistors so they draw 6mA when Vgs=0V, you won't pull much if anything at all when Vgs=-1V ,
    Vgs is a cut off voltage you need to match them to have similar cut-off point .

  6. #506
    Join Date: Jan 2016

    Location: Shenfield

    Posts: 573
    I'm Slav.

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    Quote Originally Posted by sq225917 View Post
    I've just set up Herman's Calvins. One board came up at a few mV +/- and dialled straight in to 0v offset. The other dropped the current source LEDS on the - rail and took the rail down to only 13.3v. I had to dial this one right across on the trim pot on the Calvins. But then magically as it got close the rail voltage came up, the LEDS lit up, the voltage climbed to 17v and then when I dialled in the trim pot for the current source to 18v I found that the Calvins were within a few mV which dialled straight out.

    There is definitely a situation where the Calvins sink so much current on one rail that the supply voltage drops out and throws everything off. It worth persevering with, I got the voltage across the 2.2r at 133mV on both sides of each board with zero offset, so it's all dialled in.
    Can you check 8R2 resistor voltage drop ,

  7. #507
    Join Date: Mar 2017

    Location: Liverpool

    Posts: 766
    I'm Sandro.

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    Quote Originally Posted by mac72 View Post
    Idss is the current which flows in the drain-source channel when Vgs= zero ,you need to match transistors so they draw 6mA when Vgs=0V, you won't pull much if anything at all when Vgs=-1V ,
    Vgs is a cut off voltage you need to match them to have similar cut-off point .
    Yes I understand but is not what guide sez
    Still got the paradise running whit 2SK170 matched at 8.5 mA whit the gate connected to the source
    And I have similar situation whit one board Led camming up slowly I am using 7.5 R on the supply instead of the 8.2 and oversized heat sinks

  8. #508
    Join Date: Mar 2010

    Location: Sheffield

    Posts: 2,898
    I'm Simon.

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    What's your incoming psu voltage to your Paradise 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

  9. #509
    Join Date: Mar 2010

    Location: Sheffield

    Posts: 2,898
    I'm Simon.

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    Transistors sent out. You're not going to like the J107, they were awful, I bought 50, only two sets of four, well matched but only -2.5 to -2.6v, nowhere near 3. I didn't even get a set for myself. We can count those from Farnell as dead.
    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

  10. #510
    Join Date: Mar 2017

    Location: Liverpool

    Posts: 766
    I'm Sandro.

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    WP_20171018_18_02_56_Pro.jpgWP_20171018_18_02_42_Pro.jpg
    Hi Simon
    The voltage to the boards is Low at 24.5 V I am getting 2 20 V transformers to take it up to 26 but I am using the old R2 rectifiers boards (CRC whit R of 3R3 ) and the new ones whit CRCRC where R are 4R7 and 4R7

    the v drop across the 7R5 is Right board neg 1.264 and pos 1.241 on the left 1.249 and 1.238 I have not fitted the x resistors to balance the current on the shunts

    The 2 buffers have different output transistors but I have set the V drop on the 6R8 at 200 mV ~ 30mA
    it is very much work in progress but I must say it sound better than the old R2 and focus / staging is much improved no doubt due to matching the transistors so closely

    I had If I die I die virgin prunes and the 1979 1983 Bauhaus on the spinner and whit the XP10 set at 75 = 0dB (not to loud maybe 8 V peak at speakers terminals ) I was taken back years to the Live gigs

    As I said is not there but punch and attack are second to none
    Another track that I have been listening to is Fairport convention The Bunny bunch of roses

    Quite simple and mellow tune ... NOTTTTTTTTTTTTT!

    BTW no need of a box I can ear a bit of noise but only whit ears 2 inches away from the speakers

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