My Day improving Audio Equipment

[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

4 Control Board 1 balanced input and 2 output.pdf

[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