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Thread: Quad 306 Refresh and Upgrade.

  1. #11
    Join Date: Nov 2014

    Location: Leicestershire

    Posts: 317
    I'm Mark.

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    Quote Originally Posted by fatmarley View Post
    I replaced all the small carbon resistors for Vishay mrs25 metal film. It gave more bite to the treble but it was a little bit ott. I then replaced the polystyrene caps for copper foil polystyrene and that balanced out the sound.

    Just like matching hifi separates, there's a synergy in replacing components. I learned that from years of messing with the Naim preamp circuit.
    All the faults I found were open circuit resistors, so I'm replacing them all, both channels. Lots of capacitors are getting swapped for polypropylene or polystyrene too...

    Sent from my G8441 using Tapatalk

  2. #12
    Join Date: Nov 2014

    Location: Leicestershire

    Posts: 317
    I'm Mark.

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    Play Time!
    Out come all the old carbon resistors!
    Found a resistor (R8) not shown on the schematic or Quad's parts list - drew where it goes!

    Sent from my G8441 using Tapatalk

  3. #13
    Join Date: Nov 2014

    Location: Leicestershire

    Posts: 317
    I'm Mark.

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    Now with all the resistors and capacitors I'm changing removed, and all output transistors removed to clean up the heatsink. Got some new insulators with better thermal properties to fit.

    Sent from my G8441 using Tapatalk

  4. #14
    Join Date: Apr 2012

    Location: N E Kent

    Posts: 51,624
    I'm Geoff.

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    You're doing a grand Job Mark. I must bung a meter across the innards of mine some time.
    It is impossible for anything digital to sound analogue, because it isn't analogue!

  5. #15
    Join Date: Apr 2011

    Location: cheltenham

    Posts: 746
    I'm matt.

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    Just remembered - In the service manual supplied ba Dada R11 is 47R but mine measured 120R.

  6. #16
    Join Date: Nov 2014

    Location: Leicestershire

    Posts: 317
    I'm Mark.

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    Quote Originally Posted by walpurgis View Post
    You're doing a grand Job Mark. I must bung a meter across the innards of mine some time.
    Thank you!

    Sent from my G8441 using Tapatalk

  7. #17
    Join Date: Nov 2014

    Location: Leicestershire

    Posts: 317
    I'm Mark.

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    Quote Originally Posted by fatmarley View Post
    Just remembered - In the service manual supplied ba Dada R11 is 47R but mine measured 120R.
    Mine too - a few differences actually.
    The schematic is for a Revision 3, my board is a Revision 6...

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  8. #18
    Join Date: Apr 2011

    Location: cheltenham

    Posts: 746
    I'm matt.

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    Ahh, that explains it. I'll have to see what revision my board is...

  9. #19
    Join Date: Sep 2013

    Location: North Island New Zealand

    Posts: 1,757
    I'm Chris.

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    Hi Mark
    Concerning R8 resistor , it is placed on the pcb layout drawings between the collector and base of TR1.
    rather than as you show hand drawn as 10 ohms heading toward the base of T9.

    If placed it solves the traditional method of biasing a PNP , however what is interesting is that the PNP works happily anyway without it.
    and it would appear the value of R6 at 120k creates ability for TR1 to be turned on just enough with tiny contribution by C4
    These components are coming from different points to bias TR1 , so maybe R8 was excessive - it suggests a high value of resistance
    if it was going to be used - maybe 68k

    I changed TR1 to a 2N5087 and TR2 to 2N5088 in mine. I am willing to give R8 a go so will report back.

    Cheers / Chris
    .

  10. #20
    Join Date: Nov 2014

    Location: Leicestershire

    Posts: 317
    I'm Mark.

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    Hi Chris,
    I believe that I have drawn the position of R8 correctly, as it is fitted on my PCB.
    The value I'm changing R26 to is 62k.
    Please do correct me if I'm being stupid!!!

    Sent from my G8441 using Tapatalk

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