Quad 306 Upgrade-parts? [Archive] - The Art of Sound Forum

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Bonky

19-07-2016, 18:14

DSJR

19-07-2016, 19:09

Ask on the dada website, as I think they possibly know more about this product, how it ages and what *really* needs doing. I'd respectfully suggest that even Quad service may not know too much about such things as you want to do, as their job is to fix faults, rather than tweak the design.

My choice, but I tend to get more specialised electrolytics from Hifi Collective. Nichicon FG's are cheap enough and have suited the gear I've tinkered with. HFC also have a great range of film caps, from fairly expensive to outrageous :)

Wakefield Turntables

19-07-2016, 19:10

NET Audio are quite good as well.

DSJR

19-07-2016, 19:16

On the 306? I had suspicions with one of their 303 mods, to the power supply, which apparently ignored the careful design tweaks made by Peter Baxendall in the original design - can't remember the details sadly. The 306 is a far later amp of course...

agk

19-07-2016, 20:59

Where have you found this mod? I'd be interested to have a read before passing judgement.

That said, as Quad is a decent quality brand I personally would want to push the boat out a bit further and spend a bit more.

Bonky

19-07-2016, 21:45

Andrew, are you referring to my OP or that from NET Audio?

BW

Richard.

Light Dependant Resistor

19-07-2016, 23:08

I have just bought a Quad 306 which has been serviced 'with all capacitors replaced'. However it comes without the PS mods (caps across the diodes etc). Knowing virtually nothing about the various quality of capacitors etc I'm a little concerned that Maplins' components may not be 'audiophile' quality.

I'm thinking of the following:

4x 22uF for D1, D2 Maplin code DT58 (22uf 100v) stock level 2 @54p each
4x 2u2F for D3, D4 Tants Maplin code N78KF (2.2uf 100v)stock level 2@59p each
2 x 100n SMR for C2 Maplin code N42CN (1250v) stock level 1 at 2.49 each
2 x 100nF MKT 63v for C7 Maplin code N24CN (50v) stock level 2 at 89p each

Would anyone with expertise at this kind of mod care to cast their eye over the list and tell me if they are suitable?

many thanks,

Richard.

Hi Richard
These mods are not good,
D1 and D2 are zener diodes for the bias offset opamp
D3 is in the current source for J503 and D4 in the collector of T1
C2 is a coupling capacitor for the input
and C7 is a bootstrap capacitor.

The choice Quad made of J503 is where improvements can be made
basically there is insufficient current for the base of T3 and the emitter of T1
hence their use of a difficult type of opamp for iC1 is the only choice not
to cause turn on and turn off difficulty.

The changes to make are replacing Cr2 with a LM317 to supply current
just from that devices adjustment terminal ie 1.3ma vs Cr2 .05ma
using a Dpak device soldered under the board. Make T1 a 2N5087 and
TR3 a 2N5088 which are complementary low noise transistors.

You are then free to make IC1 a better type of opamp like a LME49710
- although this opamp is not directly in the audio path it has influence on
what is possible to achieve.

I have covered some of this already in "My day improving audio equipment"
and can revisit to add a bit more detail for you.

As for capacitors around zeners, zeners are OK when placed on bases of transistors
so to maintain steady voltage and capacitors in parallel on the base in such an
arrangement form a capacitive multiplier which is C x hfe of transistor
so a good circuit. So the short answer is you need transistors relative to
the circuits polarity controlling the former 6V8 devices, in which case use 7V5 due
to transistor semiconductor voltage drop.

If you are still reading then you would have worked out it is not just a matter of
splashing a capacitor here and there.

Cheers / Chris

Bonky

20-07-2016, 08:33

Thanks Chris (and all others).
Chris, your reply filled me with foreboding as I was basing my mods on the DADA mods - which have been well received.

If I subtract the already-changed caps, I am left with:

* 2 x R 18R 1% for R13b (brown-grey-black-gold-brown) (*)  
*  *2 x R 27R 1% for R13c (red-violet-black-gold-brown) (*)   (These are to change the input sensitivity)
* 10 x C 100nF MKT x

* 2 x R 62K 1% for R6 (blue-red-black-red-brown)
*
* 2 x C 330nF MKT for C2  
*  *2 x C 1μF MKT for C3  
* 2 x C 100μF 63V for C7
*
* or, according to another website (Les W on PinkFish I think):
*
*
*
* "The TLC271 is not strictly in the signal path per se but acts merely as a DC servo to keep the offset at the output to a low level. Crucially though, this IC adds a signature to the output, not because of intrinsic weaknesses but because it is supplied by the crudest power supply imaginable. Series dropper resistors R3, R4 (3K3) supply 6V8 Zener diodes D1 & D2 respectively from the main voltage rails. There are no decoupling capacitors around the Zeners and adding a 22uF across each diode improves the sound by an order of magnitude.
* Decoupling D3 & D4 similarly but with 2u2F tants (larger values create switch on thumps), will pay dividends. Replacing the 100n input cap C2 by a 470n SMR also reaps rewards."

Needless to say I am a little confused! The amp sounds fine at present (I am still burning-in), although the input sensitivity is too high, and there is a slight mains hum.

I would welcome peoples' views/feedback!

Thanks,
Richard.

agk

20-07-2016, 08:43

Andrew, are you referring to my OP or that from NET Audio?

BW

Richard.

I was replying to your post Richard. I would take the advice offered by Chris (LDR) and get to work, he knows his sh1t. As an alternative you could just enjoy the Quad for a while and then buy a better amp. As nice as the 303, 306 and 405 can sound there are better amps available for less cash.

Bonky

20-07-2016, 13:28

I was replying to your post Richard. I would take the advice offered by Chris (LDR) and get to work, he knows his sh1t. As an alternative you could just enjoy the Quad for a while and then buy a better amp. As nice as the 303, 306 and 405 can sound there are better amps available for less cash.

...apologies if this comes up twice ...BT BroadBand problems.

Which other amps have you in mind Andrew?

Chris' helpful and detailed comments have left me in a quandary.There are sites such as DADA etc that advocate something almost completely different from that which Chris advances. I will certainly alter the input sensitivity, but am now wondering, apart from that, if it's better left alone. I can solder etc but although I have a multimeter, don't really feel confident in making too many changes.

I also have a Rega Brio R and Sugden a21a, so it will be interesting to compare them all when I get the time.

Comments welcome!

Thanks,

Richard

Bonky

20-07-2016, 16:35

Chris,

I have tried to collate all your various bits of advice on the Quad 306 so far. Am I right in my summary (below). There is also a question...

Thanks,

Richard.

Quad 306 Mods.

Replace 6 x 1N4003 diodes, D5,6,7,8,9,10 on each channel with UF4007. Also D13.

2. Replace R24 and R25 from 2x 22R ie 44 ohms, to 27R and 30R ie 57 ohms

3. Replace TR1 with a 2N5087 PNP and TR3 a 2N5088 - both Fairchild brand low noise transistors.

4. CR2 normally a j503 is replaced by a ON brand LM317 D2T its adj terminal delivering 2.85ma on its own without any assistance from the output - ie output left unconnected,( A 317 appears to be much better than the miserable 0.56ma from a J503 as the current source for above transistors.
The 317 substitutes perfectly, with no turn on or turn off issues.)

5. Replace R17 and R18 - 560R with 5 watt metal film round types ( not wirewound ) .

No Caps over the zenner diodes!

No Cap changes.

Is the LM317D2T just a simple like-for-like replacement for the J503 but the middle pin disconnected?

I don’t understand this: “ The changes to make are replacing Cr2 with a LM317 to supply current
just from that devices adjustment terminal ie 1.3ma vs Cr2 .05ma
using a Dpak device soldered under the board.”

What is a Dpak device (Google is of little use - some form of packaging?).

Thanks,

Richard

Light Dependant Resistor

21-07-2016, 10:49

Hi Richard
The changes you outline from my thread " my day improving audio equipment"
mirror pretty well exactly what I have done to my own 306's
I have also changed the TLC271 to be a LME49710 and added a
mosfet across the LM317 -see below

The TO92 package LM317Z is going to be much easier to fit with just 2 of its
pins. I have just done some tests on a LM317LZ TO92 device @ 6.9v and it delivers
1.53 ma. I will do some tests on the other packages and see if current changes.
I am using ON brand LM317D2T in my own 306's. Will try and post results tomorrow
for other packages,

You need to carefully follow the different pinouts relative to where they
replace what was originally there, referring to TR1 and TR3

Another nice change is to add a SMD 2N7002 mosfet across the LM317
here using that surface mount device, its drain connects to LM317 input
and gate and source both to adjustment, current then lowers slightly to
1.46ma., and current delivery appears even more stable.

A TO92 LM317Z with the flat side facing you, legs down is Adj in the left
and In on the Right

The use of just using the adjustment pin is not covered very well by
Texas Instruments, as they describe that pins current much lower at 100ua
being returned to the output, But measurements I have taken show current
available is very stable, being effectively the inverted input of the regulator
when viewed as an op amp. It would appear current from the output internally
assists the adjustment pin when the output is floated.

A look and see would be to connect a LED in a test circuit to observe the
adjustment pin happily delivering sufficient current to illuminate that device
so V+ say 12v to LM317 In , adj to LED anode and LED cathode to gnd

I have all of these parts in drawers here, send me a PM as I can post them to you
if that would help.

Cheers / Chris

Bonky

21-07-2016, 11:57

Thanks Chris very much indeed.

PM sent.

BW

Richard

PS I got this error:

Light Dependant Resistor has exceeded their stored private messages quota and cannot accept further messages until they clear some space.

Light Dependant Resistor

21-07-2016, 16:33

Hi Richard
Space cleared

Cheers / Chris

Qwin

03-08-2016, 09:42

Bonky

03-08-2016, 12:32

Hi Richard,
Thread here on 306 mods may be of use: http://www.pinkfishmedia.net/forum/showthread.php?t=4983

There are a few companies offering upgrade parts kits, Dado already mentioned: http://www.dadaelectronics.eu/

There is one in Doncaster which is not far from you http://www.redhillaudio.co.uk/
Ooops, I see they have moved to Chesterfield since I last visited, still close though.

Hope that's some help

Thanks; I ordered the DADA kit yesterday and posted a question on their forum about altering the zeners to faster ones. (Answer - don't bother).

I'll look at the RedHill site as well.

Thanks,

Richard.

Qwin

03-08-2016, 13:38

I was considering going the 306 route a while back, so I had look at the upgrade options available at the time.

One thing I don't like, is putting large binding posts on the back as replacements for the original banana sockets, so I use these whenever I need to renew that type:

http://www.jkwynn.co.uk/Project_Images/Yam/yam_20.jpg

They are "Hirschmann" brand, are solid Brass (no through hole so sealed for speaker use), Gold plated and rated at 32Amp. RS do them at £2.04 each with free delivery.
RS #787-2350 Red
RS #787-2357 Black

Arkless Electronics

03-08-2016, 13:43

I'll not comment further than this but IMO there are no worthwhile upgrades to the 306 other than fitting bigger smoothing caps.

Bonky

03-08-2016, 17:29

Thanks Ken and Jez; understood.
BW

Richard.

I'll report back when/if I do all the upgrades!

Qwin

03-08-2016, 17:38

Upgrade is probably the wrong description, its more like a refresh.
The Dada kit has larger value smoothing caps as you mention Jez and replaces some of the other ageing electrolytics with same value. It upgrades a few of the parts to a slightly higher spec to match what Quad did themselves for the 606mkII 707 and 909. The speaker output sockets were not high quality and with age/use don't always give a good connection, I've seen examples that barely stopped the banana plugs falling out, so new parts help there.
So nothing major in what's done, for the most part its just bringing things back to as new performance.