Sansui QRX-777 Restoration

[xoaphexox]

Tonight I finished restoring my 3rd Sansui QRX-777, the Euro version of the QRX-7001.

Usually as I move through I pitch the old parts in the trash and keep moving. I read an old exchange on AK between QuadBob and Echowars and it made me think this time I decided I was going to keep the parts I swapped out to get an idea of how much work and replacement parts was actually involved.

There were a total of 209 electrolytic capacitors to replace!

The amp was pretty straightforward because it was working before I decided to restore it.

I replaced the relay, ripple filter caps, fuses, tantalum caps, electrolytic caps, lights, fusing resistors, thermal paste, and mica insulators.

I added vishay roedersteins across the ripple filter caps (trick I learned from Dr*Audio).

Then I gave it a thorough cleaning, adjusted bias, offset, and preamp supply voltage to spec.

Then I used the information contained on this site http://hometown.aol.com/matrixquad/sansui.htm to dial in the QS synthesizer boards to spec.

If only I had the proper equipment I could align the FM as well, but this unit was pulling in stereo FM stations from my basement where I can barely get cell phone reception, let alone FM, so I think the tuner is good to go!

Here is a pic of the parts replaced:

Listening to a Warren Zevon album (Excitable Boy) and it sounds fabulous!

 

[zenith2134]

Excitable boy is one of my favorite LPs too.

WOAH. You have a great deal of patience and skill since this is a LOT of work to dig into! Awesome job. :thmbsp:

Just curious--why did you feel that the fuses needed replacing? Do they 'wear out' and degrade the sonics in your opinion? :scratch2:

 

[xoaphexox]

Just curious--why did you feel that the fuses needed replacing? Do they 'wear out' and degrade the sonics in your opinion? :scratch2:

Well, if I held the fuses up under a light, the thin strand of metal that runs from cap to cap was visually oxidized in parts, in a marbled dark-and-light metal appearance.

It appeared to me that they had been stressed in the past and fuses are cheap and readily available so I figured I would "reset" them to the way they were when they came off the assembly line.

Their replacement was more for longevity than sonic characteristics.

Thanks!

 

[fvoelling]

Wow, nice job! Just wondering, how many hours do you think you spent on this?

 

[xoaphexox]

Wow, nice job! Just wondering, how many hours do you think you spent on this?

I did not keep track but if I had to guess I would say about 16-20 hours

 

[xoaphexox]

I put the amp back on the bench today to do some frivolous 'upgrades'. I replaced the differential pairs with matched Zetex 694B transistors, replaced the power amp diodes with fast 1n4004 diodes, replaced the two VD-1212 diodes on the driver boards with series 1n4148's, replaced the signal path resistors with PRP 1% metal film audio resistors.

A few months ago I replaced all the mylar caps and signal path electrolytics with polypropylene caps. I also replaced the bulbs with LEDs and all the trimmers with new Bournes 25 turn sealed units.

I have the unit playing right now and I think it sounds absolutely fabulous. I am taking it in to the office tomorrow to replace my Luxman L-80V because I can't stop listening to it!

 

[Sir.Byrd]

Nice work!

 

[xoaphexox]

Nice work!

Thanks, I, like yourself, got really hooked on the recapping thing and it just took off from there - thanks to AK & OCD - can't leave well enough alone! As long as you keep the old parts I see no harm in trying new things out to see where it takes you :scratch2:

 

[Sir.Byrd]

What kind of caps did you use?

 

[xoaphexox]

Well, for signal path I used WIMA, for mylars I used Panasonic ECQ-P(Z), for power supply I used Panasonic FC, for ripple filters I used Panasonic T-SHA (maybe it was T-HA).

My first iteration had Panasonic FC as the signal path and I thought that was OK. Then I tried Nichicon FG and thought it sounded a bit sweeter. Now that I use the poly caps I think things sound, well, 'alive'.

If things sounded worse I was going to try the Elna Silmic II - I use those in my other restorations most frequently but this amp has special sentimental value to me so I wanted to really squeeze everything I could out of it as I plan to pass it on to my children as my father did to me.

 

[Sir.Byrd]

I've been using Nichicon exclusively but maybe I'll try some Panasonic FC later on.

 

[xoaphexox]

Try the Elna Silmic II if you get the chance - they can be had at Digikey, just search for 'RFS'. They are a bit physically bigger than their FC/FM or FW/KW/FG/KZ counterparts but I think they sound really good.

What Nichicons do you prefer?

 

[newguy1]

Hey xoaphexox, you are probably the person that I want to ask this question to. Not sure if I should post here, start a new thread or PM.

I've recently come into an AU-888 and want to update/upgrade it. I can find the exact match as far as values go, but have no idea what to upgrade to as far as what to replace with poly, electrolytic, etc, as well as is it worth it to replace the resistors, etc.

Most people say do only the electrolytic caps. Does it make a noticable difference replacing the resistors?

I've got no problem doing the work, but it is the knowledge of what make/brand to replace things with.

The next question is who would know what upgrades to the amp can be completed such as the vishay roedersteins that you stated in the first post, or adding to the filter cap values.

 

[Sir.Byrd]

Try the Elna Silmic II if you get the chance - they can be had at Digikey, just search for 'RFS'. They are a bit physically bigger than their FC/FM or FW/KW/FG/KZ counterparts but I think they sound really good.

What Nichicons do you prefer?

I order from Mouser. I was thinking of using Cerafine caps.
I use KZ and FG mostly.

 

[laatsch55]

Say there xoaphexox, fixed a QX 4500 a couple months ago and was very impressed with it. It had a "warmer" sound than my Pioneer stuff and I'm looking forward to comparing after I recap the 3 Spec 1's I have. Just finding the time now.....

 

[xoaphexox]

I order from Mouser. I was thinking of using Cerafine caps.
I use KZ and FG mostly.

Ahh, I didn't realize that Mouser had Cerafine - the only place I found them was Handmade Electronics and they were very pricey and the selection was not comprehensive enough for an entire signal path. I will have to check that out, thanks!

 

[xoaphexox]

Most people say do only the electrolytic caps. Does it make a noticable difference replacing the resistors?

Replacing the electrolytic caps is the best place to start. That will 'reset the clock' so to speak; you could reasonably view each electrolytic as a 'ticking time bomb'.

I used the word frivolous to describe the extravagant parts replacement regiment on this amplifier because I have no empirical way to measure if an increase in quality actually happened. You just have to use your ears. As in the case with (some) speaker wire, power cables, and binding posts - some of it may be psychological as well - but if your brain is telling you the sound is more pleasing then that is what matters.

With regards to longevity, replacing the caps is a must. Maybe replace the fuses to prevent any of them from being old and frail and blowing for no good reason, maybe replace the trimmers if they are oxidized and it is hard to dial in the offset and bias. You may want to replace the bulbs with LEDs to lower power consumption and heat. You may also want to replace the relay instead of removing and cleaning it because they are easy enough to be found and not terribly expensive (around $7).

The reason I replace the signal path resistors and mylars is to decrease the tolerance from +/- 20% to +/- 1%. People say this improves concepts like realism, soundstage and imaging - but once again, I have no proof of this. It is time consuming and expensive to do these last two things because the resistors are $0.40 each and the capacitors range from $0.33 to $5 each (and you could use upwards of 100 of each in a quad unit!)

So you can see why you don't want to go all out for every one of your pieces of gear unless you are retired and have Bill Gate's pension. I typically don't replace all the mylars and resistors in a unit unless it is a unit that I think is very special and I plan to cherish. I have only done this with my QRX-777 and Kenwood 700M/C combo.

The next question is who would know what upgrades to the amp can be completed such as the vishay roedersteins that you stated in the first post, or adding to the filter cap values.

It seems that step was omitted from the mid to low units until the late 70's from what I have seen in schematics. Some units have this already (the Sansui AU-11000a comes to mind). I doubt the AU-888 does. It is a trick I learned from fellow AKer (Dr*Audio - who is a *real* tech - not a 'parts replacer/quasi tech in training' like myself). I also add these caps using a value of 1/10,000 of the cap I am bypassing them with.

I get my parts from Mouser, Digikey, B&D Enterprises (or MCM) (when I foul something up and it needs NOS replacement parts), or Handmade Electronics. I like to try out different brands/lines of parts. I am very happy with Elna Silmic II for capacitors, Panasonic ECQ-P(Z) for poly caps, Bourns 25 turn trimmers, and PRP for resistors.

Overall, it is the law of diminishing returns. Replacing (electrolytic) caps is the best investment. The rest is just for fun unless the amp actually has a problem.

Good luck - start a thread with pics if you feel like!

 

[xoaphexox]

Say there xoaphexox, fixed a QX 4500 a couple months ago and was very impressed with it. It had a "warmer" sound than my Pioneer stuff and I'm looking forward to comparing after I recap the 3 Spec 1's I have. Just finding the time now.....

I really do like the warm sound of these old Sansui's - even the middle of the road ones like this QRX-777 sound great. You may find it interesting that the QRX-777 (QRX-7001) shares the same driver boards as the 881 and the 9090 - and they all sound very similar to my ears.