+ Reply to Thread
Page 3 of 4 FirstFirst 1234 LastLast
Results 21 to 30 of 38

Thread: Quad 306 Refresh and Upgrade.

  1. #21
    Join Date: Sep 2013

    Location: North Island New Zealand

    Posts: 1,757
    I'm Chris.

    Default

    Hi Mark
    Interesting, we are actually both right, as the inclusion of R8 on your board applies to
    board M12890-6 where it is 10 ohms at the base of T9, but board 12890-4 misses out on R8 in that position altogether
    but then has availability but not fitted for what is labeled R8 where I described between TR1 collector and base.

    I have both models. I think Quad were thinking of a divider between R6 and the negative supply 6v8 with the design of
    12890-4 by providing space for R8. Its resistance value then is much higher as to not confuse the purpose of R6 - will
    report if I have success.

    R26 is the Zobel resistor which needs to be 10 ohms applying to both boards.

  2. #22
    Join Date: Sep 2013

    Location: North Island New Zealand

    Posts: 1,757
    I'm Chris.

    Default

    Hi Mark
    This is what is working exceptionally well in my own 306.
    You will see R5 previously a 3k3 is now a LM317D. I am using the 317's adjustment terminal
    which for the D type 317 delivers 10ma to both CR2 a J503 and also the base of T2 without
    any connection to the 317 output.

    Note the schematic is not a ideal representation of the 306, rather just represents what I changed
    namely R5, and D3, so see it for those changes - whilst looking at the actual 306 schematic. It should be apparent
    then just showing what I changed.

    The 6v8 zener D3 is instead a LM329, https://www.analog.com/media/en/tech...s/129329fd.pdf
    transistors are 2N5087 PNP https://www.onsemi.com/pub/Collateral/2N5087-D.PDF
    and 2N5088 NPN https://www.onsemi.com/pub/Collateral/2N5088-D.PDF
    Chris Quad 306.pdf
    Last edited by Light Dependant Resistor; 13-02-2019 at 10:23. Reason: Corrected C4 ( C2 on schematic ) to 180pf

  3. #23
    Join Date: Nov 2014

    Location: Leicestershire

    Posts: 317
    I'm Mark.

    Default

    Quote Originally Posted by Light Dependant Resistor View Post
    Hi Mark
    Interesting, we are actually both right, as the inclusion of R8 on your board applies to
    board M12890-6 where it is 10 ohms at the base of T9, but board 12890-4 misses out on R8 in that position altogether
    but then has availability but not fitted for what is labeled R8 where I described between TR1 collector and base.

    I have both models. I think Quad were thinking of a divider between R6 and the negative supply 6v8 with the design of
    12890-4 by providing space for R8. Its resistance value then is much higher as to not confuse the purpose of R6 - will
    report if I have success.

    R26 is the Zobel resistor which needs to be 10 ohms applying to both boards.
    Sorry, I meant R6 is originally 120k, changing it to 62k. R26 is indeed the 10 ohm Zobel resistor - upgraded to 1 Watt as per your recommendation!

    Sent from my G8441 using Tapatalk

  4. #24
    Join Date: Nov 2014

    Location: Leicestershire

    Posts: 317
    I'm Mark.

    Default

    Quote Originally Posted by Light Dependant Resistor View Post
    Hi Mark
    This is what is working exceptionally well in my own 306.
    You will see R5 previously a 3k3 is now a LM317D. I am using the 317's adjustment terminal
    which for the D type 317 delivers 10ma to both CR2 a J503 and also the base of T2 without
    any connection to the 317 output.

    Note the schematic is not a ideal representation of the 306, rather just represents what I changed
    namely R5, and D3, so see it for those changes - whilst looking at the actual 306 schematic. It should be apparent
    then just showing what I changed.

    The 6v8 zener D3 is instead a LM329, https://www.analog.com/media/en/tech...s/129329fd.pdf
    transistors are 2N5087 PNP https://www.onsemi.com/pub/Collateral/2N5087-D.PDF
    and 2N5088 NPN https://www.onsemi.com/pub/Collateral/2N5088-D.PDF
    Chris Quad 306.pdf
    Many thanks for all these tips Chris - I’m really enjoying this!

    Another question if I may? The Dada recommendations are to put bypass capacitors across all the zener diodes - do you recommend this?

    Cheers, Mark...


    Sent from my iPad using Tapatalk

  5. #25
    Join Date: Sep 2013

    Location: North Island New Zealand

    Posts: 1,757
    I'm Chris.

    Default

    Using capacitors on zeners is a band aid solution, the better approach is not to use a zener at all.
    and remove the cologne of the capacitor placed -so to speak. But real world says we need a better zener or
    a alternative like a resistive divider.

    If we look at what I provided yesterday we see a different approach. R5 was a 3k3 resistor satisfying nothing more than the zener, to supply 100ma to that part of the circuit.
    The 306 delivers 39v- 40v on its positive rail, we deduct the breakdown avalanche voltage of the zener to arrive at 33.2 /3300 or in Ohms law V/R = I
    The question is, is 100ma required there, the answer is NO. The transistor base is totally saturated with such high current and acts more like a diode than
    a transistor, and the J503 feeding the emitter its output is just 0.56ma it is not needing 100ma either to function. Limiting current sufficiently and precisely, is what is needed

    With current limited by the LM317 supplying a maximum of 10ma on its adjustment terminal, we now have a dedicated current source for the base of T2 and the drain of J503
    In choosing a LM329, it is a better device , we are reducing considerably the noise of a zener diode being subsequently amplified by T2

    Where we can, as a principle, think of high impedance to separate areas, as well as supplying the current that is actually needed, Rather than just satisfying the needs of a zener diode
    and largely ignoring the components being supplied current Viewed this way we can see awful mistakes in using simple resistors and zeners

  6. #26
    Join Date: Nov 2014

    Location: Leicestershire

    Posts: 317
    I'm Mark.

    Default

    Quote Originally Posted by Light Dependant Resistor View Post
    Using capacitors on zeners is a band aid solution, the better approach is not to use a zener at all.
    and remove the cologne of the capacitor placed -so to speak. But real world says we need a better zener or
    a alternative like a resistive divider.

    If we look at what I provided yesterday we see a different approach. R5 was a 3k3 resistor satisfying nothing more than the zener, to supply 100ma to that part of the circuit.
    The 306 delivers 39v- 40v on its positive rail, we deduct the breakdown avalanche voltage of the zener to arrive at 33.2 /3300 or in Ohms law V/R = I
    The question is, is 100ma required there, the answer is NO. The transistor base is totally saturated with such high current and acts more like a diode than
    a transistor, and the J503 feeding the emitter its output is just 0.56ma it is not needing 100ma either to function. Limiting current sufficiently and precisely, is what is needed

    With current limited by the LM317 supplying a maximum of 10ma on its adjustment terminal, we now have a dedicated current source for the base of T2 and the drain of J503
    In choosing a LM329, it is a better device , we are reducing considerably the noise of a zener diode being subsequently amplified by T2

    Where we can, as a principle, think of high impedance to separate areas, as well as supplying the current that is actually needed, Rather than just satisfying the needs of a zener diode
    and largely ignoring the components being supplied current Viewed this way we can see awful mistakes in using simple resistors and zeners
    You Sir, are a knowledgeable man!
    I will be ordering the components you have recommended, can't wait to listen!!!

    Sent from my G8441 using Tapatalk

  7. #27
    Join Date: Nov 2014

    Location: Leicestershire

    Posts: 317
    I'm Mark.

    Default

    Crikey, it's been a LOOOOOOOONG time since I tinkered with this, but I'm finally on the home straight. All components bar a brace of Vishay 62k 0.6 Watt Metal Film resistors installed (Farnell were out of stock!) - even found a couple of previously used briefly Ansar Supersound 1uF caps!!!
    Looking forward to hearing this for the first time ever!

    Sent from my G8441 using Tapatalk

  8. #28
    Join Date: Apr 2012

    Location: N E Kent

    Posts: 51,624
    I'm Geoff.

    Default

    Excellent job.
    It is impossible for anything digital to sound analogue, because it isn't analogue!

  9. #29
    Join Date: Nov 2014

    Location: Leicestershire

    Posts: 317
    I'm Mark.

    Default

    Well, I've finally found half an hour and have completed the installation of the remaining four components.
    I haven't yet done the zener diode replacement mod kindly suggested by LDR - I fully intend to do it, but first I want to run it in like it is, and them make the change.
    Must admit, now I'm at this point, I'm nervous to switch it on!!!

    Sent from my G8441 using Tapatalk

  10. #30
    Join Date: Nov 2014

    Location: Leicestershire

    Posts: 317
    I'm Mark.

    Default

    Well, fart.
    Powered it up - Right Channel has about 6 millivolts DC offset, but the left has over 7.5 Volts DC offset.
    To say I'm disappointed would be something of an understatement.

    Poop.

    Sent from my G8441 using Tapatalk

+ Reply to Thread
Page 3 of 4 FirstFirst 1234 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •