Quad 306 Refresh and Upgrade.

[M6NTL]

Having found the fault causing a 20V DC Offset on one channel of the 306 I bought broken, I've started to tweak and refresh/upgrade some components.
I've started by changing the main reservoir capacitors from 4,700uF to 6,800uF Nichicon Gold Tune, and the other 2 electrolytics to Nichicon too. Replaced the four marginal rated 560 ohm 4 Watt resistors to 5 Watt ultra low inductance wire wound, and the two 10 ohm 1 Watt resistors in the Zobel Network to 2 Watt 1% precision metal film (both tips very gratefully received from Light Dependent Resistor!).
More to follow!!!https://uploads.tapatalk-cdn.com/20190203/68f5aac0eaf84d492f80fc145a2e057b.jpghttps://uploads.tapatalk-cdn.com/20190203/13d170360d66c5eca971d84f9ed1ac6f.jpghttps://uploads.tapatalk-cdn.com/20190203/53ff48aed9c11614df0c4ea8dcaf3640.jpghttps://uploads.tapatalk-cdn.com/20190203/e36f2d108a6295ead0bf9d1f17bc2d22.jpg

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[walpurgis]

Interesting. Keep us posted. :)

[Pepperamip]

Ive got an upgraded 306 but have never opened it up to see whats been done. I might have a look tonight if i get the chance

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[Clive]

Keep the updates coming please! I've done the Dada updates to my 306. The resistor updates you've made look very sensible. I'll be interested in more inspiration for what to improve.

[M6NTL]

Keep the updates coming please! I've done the Dada updates to my 306. The resistor updates you've made look very sensible. I'll be interested in more inspiration for what to improve.Have you fitted the capacitors across the zener diodes? If so, do you think that improved the sound?
I'm replacing every other resistor in the amp, with 1% metal film, and as I took out the power transistors to test them out of circuit, I will replace the thermal insulators with higher efficiency items...

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[Clive]

Have you fitted the capacitors across the zener diodes? If so, do you think that improved the sound?
I'm replacing every other resistor in the amp, with 1% metal film, and as I took out the power transistors to test them out of circuit, I will replace the thermal insulators with higher efficiency items...

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I have fitted caps across the zeners but I can't comment about whether they improve the sound as I fitted the whole Dada kit in one go. :-(

[M6NTL]

I have fitted caps across the zeners but I can't comment about whether they improve the sound as I fitted the whole Dada kit in one go. :-(What did you set the input sensitivity to?

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[Clive]

I think it was 500mV.

[M6NTL]

I think it was 500mV.Cheers.
I'm changing mine to 1V...

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[fatmarley]

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.

[M6NTL]

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...

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[M6NTL]

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! https://uploads.tapatalk-cdn.com/20190209/d58e5325be30e207a5b9b06c7db6f569.jpghttps://uploads.tapatalk-cdn.com/20190209/7c7830d6717a48b210d66b73dfa47f37.jpghttps://uploads.tapatalk-cdn.com/20190209/bd767980886a979941b227cbb96d5a81.jpghttps://uploads.tapatalk-cdn.com/20190209/6d103620c98197739c24a3dd769272bf.jpg

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[M6NTL]

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. https://uploads.tapatalk-cdn.com/20190210/d880f135d98c8e84b13434589486db3d.jpghttps://uploads.tapatalk-cdn.com/20190210/cdc115eea2047bcdb271551cbe1e8ef6.jpg

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[walpurgis]

You're doing a grand Job Mark. I must bung a meter across the innards of mine some time.

[fatmarley]

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

[M6NTL]

You're doing a grand Job Mark. I must bung a meter across the innards of mine some time.Thank you!

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[M6NTL]

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...https://uploads.tapatalk-cdn.com/20190210/b3bf37c58d03233692f3f84b0944f43b.jpghttps://uploads.tapatalk-cdn.com/20190210/8490bc69f6673c3492a78864ef945e8d.jpg

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[fatmarley]

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

[Light Dependant Resistor]

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
.

[M6NTL]

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!!! https://uploads.tapatalk-cdn.com/20190212/a9f49aa108f7f8d39cba6b0c903c8b52.jpghttps://uploads.tapatalk-cdn.com/20190212/678e18fa5be1588443785a4945da7d7d.jpg

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[Light Dependant Resistor]

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.

[Light Dependant Resistor]

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/technical-documentation/data-sheets/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
25301

[M6NTL]

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!

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[M6NTL]

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/technical-documentation/data-sheets/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
25301

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...


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[Light Dependant Resistor]

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

[M6NTL]

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 zenersYou Sir, are a knowledgeable man!
I will be ordering the components you have recommended, can't wait to listen!!!

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[M6NTL]

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! https://uploads.tapatalk-cdn.com/20190705/b83ea38572bde998e3252b2ce23e4cca.jpghttps://uploads.tapatalk-cdn.com/20190705/64b63fee06a0991ac8144215fe4b09de.jpghttps://uploads.tapatalk-cdn.com/20190705/fcd000d85f96e51de1f80995000577e7.jpg

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[walpurgis]

Excellent job. :)

[M6NTL]

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!!! https://uploads.tapatalk-cdn.com/20190906/aa4c755b67b14c99d243ed4aae42f242.jpg

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[M6NTL]

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. [emoji26]https://uploads.tapatalk-cdn.com/20190928/6b53ef26d63e9bfa3cbb4aa6fd587b86.jpghttps://uploads.tapatalk-cdn.com/20190928/b60b58118ae576c8531e8353eae0fb7e.jpg

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[Light Dependant Resistor]

Setting about solving for you, offsets have a defined reason that are always fun to solve, the good thing it is running.

[M6NTL]

Setting about solving for you, offsets have a defined reason that are always fun to solve, the good thing it is running.Well, since I've replaced every passive component in there, and tested the 'big' transistors out of circuit, it must be a small signal transistor or the Op Amp that's the culprit!!!

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[Light Dependant Resistor]

Hi Mark
You have omitted r6 a 120k resistor on the channel which has positive offset, this would appear why
solder a 120k in and see how that goes. Cheers / Chris

[M6NTL]

Hi Mark
You have omitted r6 a 120k resistor on the channel which has positive offset, this would appear why
solder a 120k in and see how that goes. Cheers / ChrisR6 is there Chris - replaced with 62K as per Dada upgrade recommendations... https://uploads.tapatalk-cdn.com/20190928/ce8d44b02a591f3a0f8d1e1218a03e55.jpg

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[Light Dependant Resistor]

Hi Mark
Sorry i was looking at a earlier image where r6 had not been placed in. R13 though should be 9R1 as raising the resistance to 27R as your image shows will make the sensitivity way too high
Try 9R1 at R13 which is on the emitter of TR3, and follows would raise the voltage at TR3 emitter which i think might solve if it was 9R1 - its a fussy part of the circuit.

[M6NTL]

Thanks Chris.
I changed this from 9R1 to 27R to reduce the input sensitivity to 1V - at least that's what Dada detailed. Have they/I got this backwards?

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[Light Dependant Resistor]

Thanks Chris.
I changed this from 9R1 to 27R to reduce the input sensitivity to 1V - at least that's what Dada detailed. Have they/I got this backwards?

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If we refer to a Quad 909 which has 7R5 and as I recall 775mv sensitivity, lowering the value of R13 changes the sensitivity upward
the opposite of the 27R value , If it was me I would restore R6 to 120k and r13 to 9R1 and measure for offset. But it would suggest approx 6R8 would
give you 1v sensitivity.

The R6 change to 62k hmmm it places the TLC271 op amp to have more influence, but R13 at 27R is too high in value and needs to be ideally 9R1
but 6R8 will work

[M6NTL]

Thanks again Chris...

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