My Day improving Audio Equipment

[Light Dependant Resistor]

Hi
Today's work started last night, installing UF series diodes in my 2 Quad 306 power amps.
These diodes are very good for audio purpose making standard diodes well worthwhile replacing.
there are differences in the forward voltage specification between the 4001 - 4004 at 1v vs 4005-4007
1.7v so to replace part for part the UF 4003 is recommended.


in the 306 there are 6 x 1N4003 diodes, D5,6,7,8,9,10 on each channel, if doing this on yours
you will need some solder wick to carefully remove the existing diodes. The 306 has to be the
easiest of Quad amps to work on so is a delight. However this work needs extra care as diodes
inserted and soldered in the wrong way will result in very damaged equipment. There are nice
labels underneath the board showing you where each goes, but no labels on the top board
so you need to very carefully match position from what is seen underneath to what is on top.
taking care with D7 in particular

so 24 diodes later, the improvement in audio quality is very easy to hear.

a nice lunch later.. hmm where else can these go

8 went into my DBX 150x , another 4 into my Pioneer CD player's separate analogue
power supply.

Cheers / Chris

[Firebottle]

Good one Chris, I had only really thought of the improvement in the power supply with UF diodes.

:cool:

[Sovereign]

Fantastic Chris

[Light Dependant Resistor]

Thanks Alan and James.
The UF series diodes are a huge improvement, I prefer the UF4007 in the 306
they have a what I am hearing as better match to the bridge components.

The 2 x 22R resistors quad use are slightly out, if you want to perfect
the current dumping bridge use 27R and 30R for each channels r24 and r25
and move r35 ideally to the junction of r13 and L1 as was done in the 909
or if you are not that brave to the upper side of r13 as was done in the 606
Quad usually did the 606 mod when amps went in for service, removing
the original placement and adding the 10k resistor bridging the left and far
right leg of T3

So today I am installing a separate digital supply in a marantz CD50
yes the famous TDA1541A Dac. Here I have built up both positive
and negative regulators on a nice piece of stainless steel that serves
two purposes both as a heatsink and as a ground plane.

I trialled this with a sony PSP 5v supply changing the
SAA7310 and SAA 7220 and TDA 1541 5v+ supplies
to come from the sony and thought that's nice, so then
embarked upon doing all of the 7310 7220 and TDA 1541
digital supplies. The analogue supplies I will leave standard
for the moment, as i am researching the AD844 as an I/v

The bank of six 7805 regulators have surface mount 1206 size 0.33 caps on
input and output soldered directly to legs, and ground is the metal heatsink
pin out being vin ground and Vout left to right. i am using a T03 cased
regulator for 15v+ a 7815 and also 5v+ 7805 and 15v- 7915 and have
ordered in a 7905 as there will be some heat dissipation from the
main supply which after rectification is 18.7v+ and 18.7- the
transformer I am using came out of a unused meridian 101 ( will convert it to be
an LDR pre later )

15333

[Light Dependant Resistor]

Today I set about changing surface mount op amps in my DBX Quantum
which are placed in the analogue input and analogue output board.

SOIC op amps are often difficult not because of their size, rather because the
tracks they are soldered to are fragile. Standard there are JRC 4580
devices installed in the Quantum that are typically used in tone controls, and
a review of their data sheet finds them to be pretty average for any audio purpose,
let alone a very expensive device like this, so changing them for LM4562 also
SOIC size is very very beneficial.

A quick explanation on how I am presently using the Quantum as
it has so many features, it is a mastering processor usually used
in recording. It has what is called type 4 conversion which
utilises the top 4db of its analog to digital converter to create
an overload region in order to improve dynamic range capture.

Regular reader to the forum would be aware of how much i
praise type 1 DBX, it seems to me to be exactly what is needed
if you want to hear recordings closer to how they truly sound.
On the other hand Type 4 failed to impress me until 5 days ago
when I happened to insert it receiving the tape out of the 150x
and then through the Quantum via a digital link to my
Yamaha CDR HD1500 then back from Yamaha analogue out to the 150x
tape in and console out to ldr preamp and Quad 306's

Well its a combination that is as close as I ever heard
for getting music correct in every way. I was enthralled today
hearing Tord Gustavsen humming along like Keith Jarrett does
on one track and presentation is just so life like now.

So back to SOIC op amps, and changing them, using
solder wick can help, but can also weaken the surrounding
track, what I found was successful was to physically cut
the op amp itself not the legs, if you cut the legs this
strains the tracks, so it momentarily looks horrible
but if the op amp you are replacing is removed by cutting
the plastic frame the legs are then all intact and makes
substitution quite easy if you use a temperature controlled
iron and solder down one leg. I then usually solder the
middle two legs then the outers. If you get solder between
the legs of the SOIC device, just use solder wick to remove.

The UF diodes really prove their abilities with changes today
not forgetting D13 in the 306 a 1N4148 to be changed to a UF type.

More on the marantz CD50 to come.

Cheers / Chris

[Desmo]

...
The UF series diodes are a huge improvement, I prefer the UF4007 in the 306
they have a what I am hearing as better match to the bridge components. ...


Interesting Chris, If you prefer the UF4007 for the Quad 306, then why did you fit UF4003's? was that just what you had to hand?

[Light Dependant Resistor]

Interesting Chris, If you prefer the UF4007 for the Quad 306, then why did you fit UF4003's? was that just what you had to hand?

Hi Graeme
I fitted the UF 4007 in both 306's I listened to one channel with its standard diodes 1N4003 and
in the other channel UF 4007. That way I could assess what changes these diodes made.
what I picked up was more natural sound from the UF 4007 channel, I then changed the
other amps diodes for UF 4007.

The UF 4003 is closer in exact specification to a 1N4003 so advised to use them, however
I have had total success with the UF 4007 in positions D5, D6, D7, D8 D9, D10 and D13
in both 306 amps. I am using a 306 per channel just using the left hand channel of one amp
to drive one speaker and the right hand channel of the other amp for the other speaker
Speakers I use are either gale GS401a or Quad ESL57

Cheers / Chris

[Desmo]

Thanks Chris that clarifies things. I might try the UF4007's then.

I'm currently using a more traditional vertical bi-amping model with one 306 driving the right hand speaker (bi wired) and another doing the same for the left hand speaker. In my case the speakers are B&W P6's. Normally I'd have one of your LDR pre-amps in place, but today I confess I've got a home brew valve pre amp in service ;-)

[Desmo]

Thanks Chris for starting this thread, I've replaced all the relevant diodes on my pair of Quad 306's and you are quite right there is a noticeable improvement in sound. I think they are particularly clearer in the higher registers, but there is an overall increase in clarity. I'm going to do the same trick to my Myst G-Ohm amplifiers which use 1N4003s, and see if they also respond as well.

[Light Dependant Resistor]

Thanks Graeme, don't forget R24 and R25 in your 306's change from 2x 22R ie 44 ohms to 27R and 30R ie 57 ohms

Todays improvement was changing the rectifying diodes and 2 more near the middle of the board, all which were 1N4002
for UF 4007 in a Marantz CD52Mk2 player. Took all of about 15 minutes, and boy what a difference for the better.

My usual test piece of music is Miroslav Vitous Universal Syncopations 1 and 2 and there is now much better clarity with
what individual instruments are doing and stereo separation has improved and just much nicer, given this is a
very good sounding CD player to start with.

The only other change in this player well in fact two changes were assisting the CD clamp hinge with a coin glued to it in the middle,
Marantz also attend to the same style of thing in a CD50, and changing op amps for 2 x dual LM4562.

[Desmo]

Thanks Graeme, don't forget R24 and R25 in your 306's change from 2x 22R ie 44 ohms to 27R and 30R ie 57 ohms

Thanks Chris, I had already changed R24 and R25 on mine, but to 10R and 47R which still equals 57 ohms. This was based on the info from the Dada Electronics site.

My mods yesterday included changing 4 op amps in the Myst pre amp section from TL071CP types, and I replaced them with TLE2071CPE4 the TLE2071 are much more modern low noise, high bandwidth units. I took the opportunity to fit sockets on the board so that I can try other op amps or even go back to the originals in the future if I want.

[Colin Wonfor]

Did some fun experiment at Naim.

There most used diode was about to be obsolete, and they went changing diodes and listening this carried on for what seemed weeks.
I was called in to look at another problem and asked to listen yes there diode sounded much nicer.
After asking if they had a curve tracer Gary recalled in the past there was one but nobody had used it since Julian's time.
We drag the monster out of storage and did test on the diodes that were like and other and found on linear PSU designs soft recovery was best because the rise time are slow so no harmonic.
On fast diodes the SMPSU work best .
Next in the same diode families we tried different voltage diodes and as the curve tracer predicted the lower the voltage the better the sound, this is due to the Depletion layer capacitance at high voltage it is very much smaller, thus the diode was faster and then harmonic pop up again.
Now on some Far Eastern designs you may have noticed capacitors and capacitors with resistor across the rectifier diodes this is a Snubber to reduce spike and slow the recovery time down, and harmonic noises are reduced. Oh in a full bridge the spikes on the mains are cancelled because it is in common mode but not with and inductor. Clever devils.

Now go and play and have fun.:)

[Light Dependant Resistor]

Todays work involved building a few stereo coffee power supplies, and sorting out obvious distortion
on a Marantz CD7300. The Marantz is now fixed and sounding great. a very simple cure disconnecting
the headphone line running to the main board.

A study of the Marantz schematic shows LM4556 op amps and a pot all being driven off the
existing outputs. The marantz is now producing some beautiful music. A later job is to
build a better headphone interface possibly doing this with its own D/A convertor

Cheers / Chris

[r100]

Hi Chris, I just discovered this thread with the tip on the diode swapping for the 306 ;-) thanks for sharing !

what about the PS for the stereoCoffe attenuator ?

[Light Dependant Resistor]

Hi Chris, I just discovered this thread with the tip on the diode swapping for the 306 ;-) thanks for sharing !

what about the PS for the stereoCoffe attenuator ?

Hi Rupert
Yes power supply is very nice indeed. I am presently doing these on a hobby board, with everything fitting well
I will send you a standard one and Richard one tailored to his 12v battery supply, will be a few weeks though
as I am a bit behind at the moment... Also latest control board that partners with the
power supply.

You will need an AC supply of at least 12v and 15v is about max to use.

Cheers / Chris

[Light Dependant Resistor]

Here is a diagram showing how balanced audio can be provided to 2 balanced outputs.

Cheers / Chris

15720

[Light Dependant Resistor]

Todays improving was a repair to a lovely Sony minidisc Recorder/ Player, a MDS Je470
that would not eject its minidisc. No fun not being able to change minidiscs.... at all.

I found on the right hand side a tiny hole in the front metal hinge, just sufficient room to fit a spring.
It is as though Sony had thought about this themselves as it is strange to have a small tab of
metal with a hole in it, but no spring.

What I did was find a biro spring that was fairly long and threaded it into the tab hole
then upward to a further bracket, and back to the tab, so doing a full circle.

Then finely adjusting the way the spring creates a small tension, enables the
minidisc to eject, and seems to act in a downward way as well, so to improve
the tray locating the disc to play and record.

The MDS JE470 is now working really well, and the biro had failed,so an excellent bit of
recycling. A very satisfying repair.

Cheers / Chris

[LozR]

I have recently acquired two Quad 306 amps and have replaced the electrolytic capacitors and also added caps across the zener diodes.
I think I will have a go at replacing these other diodes too, could someone tell me a good reliable place to buy?

Also one of my 306's has a 1K resistor soldered between R14 and R16 on the non component side of the pcb on each channel - any ideas what that is about? To my ears both amps sound the same......

Thanks

[Light Dependant Resistor]

Hi
Quite a few sellers on ebay have the UF 4007, all that I have purchased ( approx 600 ) arrived.

The placement of a 1k is interesting, have you an image ? Is it between the bases of
T4 and T7 ?

Cheers / Chris

[Light Dependant Resistor]

Hi
Some really nice modifications to Quad 306
TR1 is now a 2N5087 PNP and TR3 a 2N5088
both Fairchild brand low noise transistors. Note
these transistors are complementary - well as
complementary as transistors can be as NPN and PNP pairs :)

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.

R17 and R18 the 560R replaced with 5 watt metal film round types ( not wirewound )
I finished one of my 306's tonight, the other I have scheduled later in the coming week.

I normally use one 306 per channel, well the one I have just done sounds as good
if not quite a bit better than using both amps, I am extremely happy with audio it is now producing.

Cheers / Chris

[Light Dependant Resistor]

Concerning the Quad 306
With CR2 now a LM317, op amp controlling offset ( although not in audio path )
can be substituted for one with better specification such as LME49710
To my ears, a marked improvement over the TLC271. From one amp alone
( I usually use one 306 per channel ) I immediately noticed improved stereo separation
and better sound stage, similar to when a 303 is used instead of a 405.

The bugbear of all other attempts at improving the TLC271 namely turn on turn off issues
has now been solved. The cause being insufficient current delivery by the standard CR2
a J503

Cheers / Chris