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

[bobgroger]

I have been enjoying my modded 555a for the summer while the tube gear gets a chance to cool off. I am very happy with the results. I have noticed though the phono preamp seems to be down 3db-ish in gain. I used KSC1845s in the preamp, 420+/- Beta and made all recommended changes. Is there a better choice here, or should I start troubleshooting?

 

[Jerry.K]

Big THANK YOU to leestereo for all your work and providing this great instructions how to restore the 555A !
i just ordered the following parts from Mouser yesterday to do this work on my untuched 555A.
it sounds good as it is today but hopefully it will get even better
i will do the work step by step and test after each board is done.
Do these parts i ordered look ok to you ? happy for any input.
Sorry about the list being in swedish but i ordered from the swedish mouser site....i will not do the phono stage right now as i use an external phono stage.

Mouser nr Tillverkare Beskrivning Ordermäng
647-LKG1K682MESCAK Nichicon Aluminumelektrolytkondensatorer - snäppfäste 6800uF 80 Volts 20% Tol. 1
647-LKG1H102MESYCK Nichicon Aluminumelektrolytkondensatorer - snäppfäste 1000uF 50 Volts 20% Tol. 2
647-LKG1H222MESBCK Nichicon Aluminumelektrolytkondensatorer - snäppfäste 2200uF 50 Volts 20% Tol. 1
625-SBYV27-200-E3 Vishay Likriktare 200 Volt 2.0A 15ns 50 Amp IFSM 2
71-CPF2-F-1K Vishay Metallfilmresistorer - genom hål 2watts 1Kohms 1% 2
71-CPF2-F-1.2K-E3 Vishay Metallfilmresistorer - genom hål 2watts 1.2Kohms 1% 1
667-ECW-F4474RHL Panasonic Filmkondensatorer 400VDC 0.47uF 3% MPP L/S=7.5mm 2
647-UEP2A100MPD1TD Nichicon Aluminumelektrolytkondensatorer - radiella med ben 10UF 100V 4
80-C330C822F1G5HA KEMET Flerskiktade keramiska kondensatorer MLCC - ledade 100V 8200pF C0G 1% LS=5.08mm 2
80-C317C202F1G5TA KEMET Flerskiktade keramiska kondensatorer MLCC - ledade 100V 2000pF C0G 1% LS=5.08mm 2
505-FKP20.033/63/2.5 WIMA Filmkondensatorer 63V .033uF 2.5% 4
505-MKS2-1/63/10A WIMA Filmkondensatorer 1uF 63 Volts 10% 2
667-ECQ-E2334JFB Panasonic Filmkondensatorer 250VDC 0.33uF 5% MPET L/S=10mm 2
647-UFG1H330MPM1TD Nichicon Aluminumelektrolytkondensatorer - radiella med ben 33uF 50 Volts 20% 1
647-UFG1V101MPM Nichicon Aluminumelektrolytkondensatorer - radiella med ben 35volts 100uF 85c 10x12.5 5LS 4
512-KSC1845FTA onsemi Bipolära transistorer - BJT NPN Epitaxial Sil 20
81-RDE5C2A100J0M1H3A Murata Flerskiktade keramiska kondensatorer MLCC - ledade 10PF 100V 5% 5.0MM 2
647-LKG1J682MESCBK Nichicon Aluminumelektrolytkondensatorer - snäppfäste 63volts 6800uF 20% 2
647-UES1C471MHM1TO Nichicon Aluminumelektrolytkondensatorer - radiella med ben 470uF 16 Volts 20% 2
667-ECW-F4105RHL Panasonic Filmkondensatorer 400VDC 1.0uF 3% MPP L/S=7.5mm 2
647-UFG1K331MHM Nichicon Aluminumelektrolytkondensatorer - radiella med ben 330uF 80 Volts 20% Tol. 1
647-UKA1V471MPD Nichicon Aluminumelektrolytkondensatorer - radiella med ben 35Volts 470uF AEC-Q200 2
667-EEU-FR1H121LB Panasonic Aluminumelektrolytkondensatorer - radiella med ben 50VDC 120uF 8x15mm LS 5.0mm 2
647-UKZ1E470MPM Nichicon Aluminumelektrolytkondensatorer - radiella med ben 25volts 47uF 85c 10X12.5 5LS 2
594-2222-368-25474 Vishay Filmkondensatorer .47uF 10% 100volts 2
647-UFG1K470MPM Nichicon Aluminumelektrolytkondensatorer - radiella med ben 47uF 80 Volts 20% Tol. 2
594-MRS25000C5601FC1 Vishay Metallfilmresistorer - genom hål 0.6W 5.6kOhm 1% 10
594-MRS16000C4701FC1 Vishay Metallfilmresistorer - genom hål .4watt 4.7Kohms 1% 10
594-MRS25000C1500FC1 Vishay Metallfilmresistorer - genom hål .6watt 150ohms 1% 12
505-MKS02-1/50/10 WIMA Filmkondensatorer 1uF 50 Volts 10% 2
72-T93YB-1K Vishay Trimresistorer - genomföringshål 3/8" SQ V/ADJ 1K 2
72-T93YB-20K Vishay Trimresistorer - genomföringshål 3/8" SQ V/ADJ 20K 2
512-KSA992FBU onsemi Bipolära transistorer - BJT PNP Epitaxial Sil 10
598-225P33491XD3 Cornell Dubilier Filmkondensatorer 100V 330nF ORANGE DROP 2
625-1N4002E-E3/53 Vishay Likriktare Vr/100V Io/1A Trim Leads 2
594-MRS25000C8250FRP Vishay Metallfilmresistorer - genom hål .6watt 825ohms 1% 2

 

[mr_macgee]

Big THANK YOU to leestereo for all your work and providing this great instructions how to restore the 555A !
i just ordered the following parts to do this work on my untuched 555A.
it sounds good as it is today but hopefully it will get even better
i will do the work step by step and test after each board is done.

Awesome, we look forward to your build and seeing pics of your progress. Please do us a favor and currently give a good listen to your 555A while still untouched and then let us know how it sounds and its characteristics after you have completed the rebuild? Curious to find out.

skål!

 

[Jerry.K]

So ,i got some work done this weekend. Mounted some binding post (KLEI Harmony Classic) ,only using speaker A.
replaced the internal wires from speaker switch to binding post with copper OCC wires.
mounted Soundcare superspike feet to bottom plate.
ac inlet socket mounted.

Measured voltages before i started changing parts.
at C001 58v ,AC balance at C819 31.20v C820 31.22v , idle bias R843 6.08mv R844 2.42mv
Changed all the parts for the Power Supply ,see list above... (all Nichicon caps)
Power up and adjusted AC Balance to 27v and idle bias to 10mv.
Did a test session for an hour with some reference tracks i know well.
sounded good ,not a huge difference ,but good

next step was the Main amplifier block.
changed all parts as suggested by Leestereo (also a matched pair of KSA992 for TR801 & TR802)
measured and adjusted voltages again.
Test session again.
First impression , more base, "tighter base" , as others also has written.
such a big difference that i backed off the base from +2 to 0.
overall i am very pleased so far ,sounds great.
looking forward to do the tone control block next and finally the mods.

 

[Jerry.K]

Did the Tone control and the mods this weekend and had a listening session.
i think the tone control board and the mods (Baxandall diode and Vbe multiplier by-pass cap's) made the biggest change/improvement !
vocals and acoustic music sounds amazing ,very clear ,and a nice improvement in base as i wrote before.
Muddy Waters album "Folk Singer" sounds even more amazing now than before as does all my reference tracks !

it also feels like the overall volume level has increased a bit ...had to turn it down a notch to get to the same listening level as before ... or is it just my imagination ?

just got the parts to do the phono stage next
will compare it to my external ifi audio phono amp.

super happy so far !

 

[dapbmw]

6800µF/42V.

Why 42V only? the rails are 60v or 30v on the amp board? ,
unless it's a typo error, Lee?

 

[Leestereo]

Why 42V only? the rails are 60v or 30v on the amp board? ,
unless it's a typo error, Lee?

Yes, you are correct, the rail voltage is ~60VDC, but since the 555A does not use a split/dual power supply, an output coupling capacitor is necessary to protect the speaker from DC voltage. The output coupling capacitor is only subjected to approximately half the B+ voltage, in the 555A that would be ~30VDC and hence the 42VDC rating of the 6800uF output capacitor is appropriate.

 

[djkcb]

Hello! Great update of this amplifier @Leestereo . Thanks so much! It used to sound muddy and boring. Now the bass sounds much tighter and the top airy and pleasant. The midrange is clear and prominent, in a good way.

For those of you who plan to do this upgrade, I want to inform you to mount the bipolar transistors in the correct direction, not the same direction as the circuit board shows but the other way around. Another thing not to miss is to make measurements in DC and not AC when adjusting CAPs C819 & C820. to the correct volts and idle bias.

Given this update what would you compare it to for another amp, what price range?

PS I ordered the exact same components as Jerry.K

 

[Trw]

I have a modded au-555a i can't shift a slight hum (presumed Transformer hum) it's not a big issue just annoying because i'm aware of it.. any ideas/tips on what i could try?

 

[olegau]

If it is transformer, try to tight the transformer nuts. If it the circuit hum, check power supply capacitors and signal path transistors.

 

[pete_mac]

I have a modded au-555a i can't shift a slight hum (presumed Transformer hum) it's not a big issue just annoying because i'm aware of it.. any ideas/tips on what i could try?

I'm assuming you're listening/testing with the internal metal shields installed? If not, these amps can hum.

 

[djkcb]

Hello! Please can someone please help me. I have just completed the phono stage and now there is hardly any sound. I can hear a low sound but nothing more. Can someone help me what could be wrong, could it be the C632A transistors?

(i had stacked film types but i thought that they might be faulty so i replaced them with regular polyester films, alså had higher grade bipolar capasitors but i replaced them aswell just to check..)

replacement caps are 100uf 16v ad 22uf 35v.
What am i missing here? Thanks for any help!

UPDATE:
I got it working it seemes the Tape switch was a bit glitchy. Some contactcleaner and it came back to life.

 

[samsag]

Hi,
to me it looks like you've soldered the contacts of the capacitors on the uppser side of the pictures to the same track, e.g. to the outer hole of C611 and innermost hole of C617.

 

[djkcb]

Hi,
to me it looks like you've soldered the contacts of the capacitors on the uppser side of the pictures to the same track, e.g. to the outer hole of C611 and innermost hole of C617.

Hi! Thanks. They are not on same track, just looks liket maby. They are little to big

 

[Aircooled]

Good day fellow AKers, I just finished my 3rd attempt of a 555A restoration Leestereo style (thank you @Leestereo ) and made an interesting observation, thought it might be worth sharing here.

I used mainly Nichicon KG 6800uf capacitors for the power supply filter and output capacitors in my first 2 amps, and I was satisfied with the sound.

This time however, I used general purpose Chemicon SMH capacitors in all 3 areas of the amplifier and the sound quality is truly astounding. All other capacitors remained the same as the first 2 amps but I can really hear a positive difference in the sound quality in this 3rd unit. It seems odd that these general purpose capacitors perform better (in my amplifier) compared to the nichicon KGs, perhaps someone with more experience might be able to provide further insights

 

[winch]

Bumping this as it really is a thread for the ages. I've been studying page 1 for hours...

What's really instructive is how much Leestereo leaves alone. There's carbon resistors and disc ceramic caps all over the place, and much of the original silicon.

I'm completely revising my upgrade plans.

 

[JimEGR]

May this thread never rest!

 

[ChevyS]

New member here. My dad's very fist amp was a Sansui AU 555A. I've known this amp as long as I've known myself. He's had it stored away for the better part of the last two decades. He gave it to me this weekend and I'm very excited to restore it and have it setup in my own living room.

This thread is incredible. I'm going to study it in detail before touching a thing. I'll be sure to post pictures of my progress.

 

[ChevyS]

Started a little work on my 555A today. Just wanted to do an initial inspection and see what I'm dealing with.

All the boards look good, they just need some cleaning up. But I was surprised to see the chassis in such poor condition.

I was initially just going to do a recap but now I think I'll strip her down and send out the chassis to be zinc coated as well.

 

[Kolner]

Question re the Baxandall diode and Vbe bypass cap mods, which are seemingly in universal opinion that these make the largest difference…

Are these suitable mods for the AU-555 also?

Second, what about Sansui receivers? Any receivers use the same circuit as the 555 and 555A?