Luxman integrated phono stage tweaks

[Ldg]

I like it. It's minimalist, and simulates well. It's based on standard component values too. There's far worse, and this looks pretty good in my book.

C104a/b look like candidates to be removed (replace with links), if one is OK with a tiny trace of cartridge dc leakage (typ 0.5uA), personally I am.

[Kei-86]

This has been suggested along with swapping the electrolytic caps out for polystyrene if i preferred to retain them. I can certainly try it out and see what its like.

[Ldg]

Yes, and if you get rid of C104a/b, there's only C103a/b to consider. The others look fine to me. And personally, I wouldn't go wildly exotic with C103a/b, type probably won't make much, if any difference. But poly film might be worth a shot there, it's still legal to try.

[Rothwellaudio]

Swapping capacitors is easy in theory and doesn't alter the design, but in practise it can be fiddly and there's always the chance of damaging tracks or pads on the board. Also, the types of capacitors that people recommend are often much bigger (physically) than the original ones, or simply don't exist - trying locating a 220uF polystyrene cap to replace an electrolytic, for example.

Fitting a socket for the IC (if you can get the old one out cleanly) would give you the option of trying a variety of luxury op-amps and might ne worthwhile.
You've just got to decide if the time/trouble/risk is worth the possible improvement in sound.

[Kei-86]

I've got a list of parts as long as my arm now so I'll have my work cut out to get it all sorted. I've noticed the size issue whilst looking for suitable replacements. C104 (RIAA input cap) and C118 (amp input cap) are being replaced with polypropylene film, all the mylar caps are being done in polystyrene where possible and all the carbon resistors are being replaced with metal film. (I may as well do everything, only one way to find out if it will actually make an audible difference. I'm a bit sceptical about it but i'm willing to spend the time to find out.)

[davidsrsb]

Scaling resistors up by x10 and capacitors down by /10 would have hardly any effect on noise for a MM source, while giving much more sensible options on non-electrolytics. It would also make the loading on the opamp far easier at 20KHz+, allowing more options on type

[Ldg]

Foolish me, but isn't it pretty good as is ?

I wouldn't be wholesale swapping passives (Rs and Cs). Metal film Rs are already fitted. Only the 22uF caps look vaguely open for improvement. C104a/b look replaceable with a piece of bent wire.......

davidsrsb has a good point though that it seems to have unnecessarily high bandwidth, and low impedance at high f. That could be fixed via a modification i suppose.

"keep it simple", is my 2p worth !

[davidsrsb]

Scaling the impedance would have no effect on impedance. I suggest doing this for anyone who wants to clone this circuit, as it would allow the electrolytics to be eliminated and prevents an issue with some opamps with click transients causing current limiting

[Kei-86]

Got some of the components through and got to work today. Sorted out a majority of the signal path resistors, the riaa op-amp, a few of the remaining electrolytic caps and some of the new film caps. The difference in sound already is actually quite surprising. The low-end has really picked up a lot. The mids and highs don't sound particularly different perhaps "slightly" more detailed but not a big difference like the LF. The riaa is another incredible difference (probably down to the op-amp) the brightness and sibilance is gone and it sounds almost perfect already. (even without the new film caps which I'm waiting for.) I found some mistakes in the service manual as well. C202a/b are 4.7uF not 47uF.


Some pictures for those interested.


PSU Filter caps


Main filter cap decoupling (EPCOS 305Vac 100nF were supposed to be those wima FKP 100v 1nF caps but they were way too small)


Transformer decoupling


RIAA, BurrBrown OPA2134 fitted via a nice socket.


Amp, New Wima FKP caps in place, the silver mica in place of the old ceramic and some of the metal film resistors. Not sure if i'm going to go the whole lot on the resistors.


Switches, All metal film resistors done and vishay MKP1837 in place. (not the neatest here due to their size)

[Kei-86]

Gave polypropylene caps a go in place of the electrolytics but found there was too small a difference to detect. I've taken them back out and put the 'lytics back in now, partly due to them damaging one of the tracks. (caused intermittent noise on the right channel. I'm keeping the "toffees" for another build as i intend to build a separate pre-power amp from scratch later this year) The PP film caps on the function switch are staying as are the ones on the tone control board. Still waiting for the rest of the film caps (styrol) from rush.





Did the new rectifiers at the same time too. (think i'm already into diminishing returns now.)

[davidsrsb]

150R in series with 10nF snubbers across the transformer secondaries is likely to be more effective and much cheaper than exotic rectifier diodes. Many Japanese makes put capacitors directly across the rectifiers with no damping resistor, causing RF ringing

[Kei-86]

Realised i never finished updating this thread. (the styrol caps from rush took a while to arrive, though the guy did apologise for the delay)

Amp, switches and tone control




RIAA


I even built a new light circuit for the front panel converting it from old fashioned light bulbs to LEDs. This also got the muting circuit working again too.


Get the feeling that the volume pot needs replacing as i've cleaned it 3 times and it still crackles when turned a bit quickly. Not a huge priority for now though. (looking at getting a ALPS

[davidsrsb]

It looks beautiful, but how does it sound now?

[Kei-86]

In a word, fantastic. I know that there are still improvements that could be made, but they would be getting a little to extreme for my tastes as i'd end up with extra components scattered about. I've still got 6 capacitors to replace on the tone control that I've not gotten around to doing. I've been distracted by a headunit for my car.