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Leestereo's Restoration/Upgrade of a Sansui AU-555A

I rebuilt a 1060 6 weeks ago, using leestereo approved updates and modifications. Have a AU555a, that also has leestereo mods. My impression of both amps is the exact opposite of yours. The 555a seems to sound flat, bass is not as heavy and sound stage vague. Differences while slight, I much prefer the 1060.
 
Dom123 said:
I was curios to know what aspect of the restoration makes this amp ever so slightly too bright,
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If the difference is 'ever so slightly', why not use your tone controls? Quite often a restore will increase the feeling of 'presence' (i.e. upper-mid range frequencies), the treble tone control is meant for controlling exactly this range. :idea: Personally I like the added 'sparkle' that the enhanced presence gives to the listening experience. :)
 
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My 1060 is very pleasant, but quite bland & inoffensive, and to be honest really underpowered despite massively uppping the power supply & coupling caps.
My AU-555a is the polar opposite - very up-front and strident, but almost too much. Voices are increadible and the background is so dark, but it's not lush like my AU-7900.

Never use tone controls, it's something that seems unnatural to me, but hell yes why not.
Tomorrow I'm going to do an apple to apple comparison with my un-restored AU-555a as a reference.....
 
My 1060 pushed 40 watts per channel, the au555a did 25. Volume knob on the 1060 is turned to 12:00 ++ more than any of my other amps, so it has less gain.
 
Thanks Scott Muni,

On my 1060 I have the volume at 12:00 to get a decent volume whereas on other amps it's usually between 9 to 10. If it's just a gain issue maybe I should just turn it up more ! To be fair, the sound is very very smooth and it only has 2 hours running since recapping. I kept all the original transistors for the moment as nothing is noisy.

But hey, completely different experience to you. My AU-555A has a very lively sound with very deep bass.

My restored AU-555a seems plenty powerful enough. Just opened up my "new" AU-555a and noticed it uses an earlier version of the main amp board with the flying saucer transistors.
 
I kept the flying saucers on mine when restored. They are quiet, but have modern replacements in stock just in case. I do enjoy the sound quality, it's just different than the 1060, and it has all new outputs and drivers.
 
I have restored many 555a and 1060 with numerous cap brands and cap upgrades and replicated restorations with same specs to original I find any combination recap really freshens up the sound with more resolution and most likely gives you a closer to the original sound… old caps sound flatter as they are at their end of life and I doubt they sounded like that new - old signal transistors adding the background hiss can darken the sound a bit too I suspect. You could try restoring your newly acquired 555a with all exact components to compare for yourself and then add the mods later if you feel you need it
 
Yes on my "new" 555a, I'm thinking of upgrading the power supply identical to this restoration thread, and my other 555a, but then keep all other electrolytics standard, apart from upping the output caps capacitance a couple of notches.

Will leave the original fim caps in initially, and then eventually add the power amp board improvements (baxandall/Vbe) after an extensive listening test.

That leaves the question of the flying saucer transistors. Change them or leave them in ?
 
I would leave them in I used to change them without question haven’t seen one fail in 10 years not to say can’t happen maybe I been lucky but I reckon 2sa726 and 2sc871 are much less reliable
 
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JRH99 said:
Seems the signal generator on this scope only puts out a 2.5V peak to peak signal in sine wave mode, with not way to adjust. I will have to look in to getting a proper signal generator.
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Get an excellent Signal Generator JDS6600 from AliExpress.
 
olegau said:
Get an excellent Signal Generator JDS6600 from AliExpress.
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That one is certainly rich with features, but I feel with its 'function generator' features it is more suited to digital work than purely audio work. For the money I would have thought there might be more suitable choices. :idea:
 
quadmatrix82 said:
I would leave them in I used to change them without question haven’t seen one fail in 10 years not to say can’t happen maybe I been lucky but I reckon 2sa726 and 2sc871 are much less reliable
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Thanks for the great advice.
Actually just hooked up the my new AU-555a, 100% original, 50 year old capacitors & all. I did reset the centre voltage and bias beforehand. I was expecting it to be a bit of a dud , but no ! Sounds absolutely great, again very detailed and fairly bright sounding, but with good bass. Has the same basic sonic characteric as my restored amp, just a bit "less". Superb airy 3D sound. I really didn't see that coming.

My other AU-555a was very tired and dull before restoration.

I like the sound, so want a recapping to preserve this sound.
20230806_135024.jpg
 
Hello
I did this restoration without the Baxandall diode. (I haven't dared yet but it's something pending that I'm going to do shortly).
The 555A sounds great all day long without listening fatigue, at least for me.
I even used slightly larger capacitors than indicated in this thread for the current source.
I am really very surprised for a simple source equipment and I will surely do the same restoration to another G2000 that I bought recently.
Thank you.
Dom123 said:
Hi everyone,

Just wondering if anyone had made any comparisons of the AU-555a restoration, following this thead, with & without the power amplification modification (baxandall & Vbe modification) ?

I rotate all my amps every week, and just coming back to my restored AU-555a after completing a Marantz 1060 restoration. Haven't listened to it for a few months. My AU-555a is increadibly detailed across the whole spectrum, really deep bass, cristal clear mid range, and excellant highs. You hear absoultely everything. Voices are really clear. However this translate to quite a bright sounding amp, and to be honest it's a little fatiguing compared to my recapped 517, 5900, 7900 or 771. My other Sansuis have a beautiful sound too, but can be listened to all day long. I do tend to listen to music at failry high volumes

I was curios to know what aspect of the restoration makes this amp ever so slightly too bright, and whether the power amp modification is a contributory factor ? Don't get me wrong, the amp is technically brilliant sounding, trully impressive.

Actually I just picked up another AU-555a in 100% original conditions. One owner & still workig fine. I'm going to recap it also, but would like to have a slightly more vintage sound. Any advice ? Maybe leave the original film caps in ?
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Just finished recapping my 2nd AU-555A. Trying to set the bias before testing it, but are struggling a bit.

I am measuring the mA across the fuse holders, and there is no problem to adjust it with the trimmers. The issue is that it just keeps rising continually for 20-25 minutes before settling down. There is approximately a 10mA delta between initial switch on and a stable value a long time later. The output transisitors remain cold to the touch but I guess under load it coud be a different story. . The target value according to the SM should be 20mA.

If I hold the metal holder of the bias transistors attached to the heatsink, the bias stops rising after after a few seconds, and then starts dropping rapidly, so these are working fine.

How should I set the bias ? Just wait 20-30 minutes before setting to 20mA or alternatively try to measure the mV across the output emitter resistors ?

The amp sound absoulutely fine
 
Dom123 said:
Just finished recapping my 2nd AU-555A. Trying to set the bias before testing it, but are struggling a bit.

I am measuring the mA across the fuse holders, and there is no problem to adjust it with the trimmers. The issue is that it just keeps rising continually for 20-25 minutes before settling down. There is approximately a 10mA delta between initial switch on and a stable value a long time later. The output transisitors remain cold to the touch but I guess under load it coud be a different story. . The target value according to the SM should be 20mA.

If I hold the metal holder of the bias transistors attached to the heatsink, the bias stops rising after after a few seconds, and then starts dropping rapidly, so these are working fine.

How should I set the bias ? Just wait 20-30 minutes before setting to 20mA or alternatively try to measure the mV across the output emitter resistors ?

The amp sound absoulutely fine
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My 555 acted that way too. I gave it 30 minutes to warm up and then after adjusting the bias, monitored it for about 5 more minutes to make sure it actually settled where I set it. Mine drifts around a bit - within a couple mA. I don't think it's much of anything to worry about.
 
This is a good observation you could try testing mv over the emitter resistor just to see if it takes the same amount of time to settle and adjust there also
 
zeste said:
I apologize, I made a mistake numbering the transistors. Also the voltage jumper was set at 250V, I set it to 240V so B1 is around 52V



I have made some test yesterday evening and with the speaker connected, I can push the volume more than 5 with music and the 100W bulb doesn't light.

But as soon as I connect resistance load on each channel (I tried 8ohm, 16ohm and 4ohm) with a sinusoidal signal in input, the 100W bulb light when I turn the volume knob around 2 or 3.
It's a weird behavior of the amp. It is the same with all the transistor I tested. It is the first time that I have this issues for this operation with the resistance.

I finally perform the setting by measuring the voltage at (+) of C819. I set it as the other channel #22.9V where I was able to set the clipping of the sinus wave with the oscilloscope.
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Hello,

I reply to myself, because I found the problem of the right channel of my Sansui. Since the restoring of my AU555A, I have listened it and a couple week ago, the right channel start to be fuzzy.

Today, I have the time to investigate. The transistor TR802 was not Ok (the voltage on each pin was not the TR801), And with osciloscope, the signal after the TR802 was ugly.
I replace it but it was still the same problem. I check the resistors and all have almost the same value as the other channel. So I check the schematic once again, and the only capacitor I haven't tested was the C812 (47pF). I checked it onboard with the DMM, the value it measure was changing whereas on the left channel I measured a fixed value. So I changed it with what I have on my hand, I put a 150pF. It works !!!

This time I achieve to perform the main-amp section output adjustment without blowing the fuse. Hope it can help some else !

@Leestereo : do you know if the value of this capacitor is important ? Is it acting as filter cap ?
 
I'm curious as to whether bumping up Capacitance and performing mods increases the output power
 
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