AU 555 - small noise right channel

[pasgal]

Sorry for my bad English, I'm Italian.

Dear friends, all the capacitors have been changed, except the 4 large on the left and 4 small ones in the selector module (aux1 / Phono etc). The old little noise, on the left channel, very small but can be heard at night, has not gone away. My AU555 is wonderful as a sound, but with my Klipschorns (105 db) I hear this little noise.

 

[pasgal]

Many thanks, no low frequency noise, but higt in the tweeter.

 

[Peter lye]

if this was my amp, I would 1st pull the jumper at the back , connect to an external source ,maybe music from your phone using aux cable to the Main input RCA. you also can connect your pre output to another amp. this would narrow down where the problem is.
if the noise is present when using the main input> F-1058 main amp > check TR807/805/803

if in the pre output> F-1060 and F-1064 > all the 2SC458 transistor have to go

Peter

 

[pasgal]

OK, I have a NAD3020 and also Quad 303 final to do the tests you said.
Are the 2SC458 on small potentiometer boards?

if this was my amp, I would 1st pull the jumper at the back , connect to an external source ,maybe music from your phone using aux cable to the Main input RCA. you also can connect your pre output to another amp. this would narrow down where the problem is.
if the noise is present when using the main input> F-1058 main amp > check TR807/805/803

if in the pre output> F-1060 and F-1064 > all the 2SC458 transistor have to go

Peter

 

[Peter lye]

OK, I have a NAD3020 and also Quad 303 final to do the tests you said.
Are the 2SC458 on small potentiometer boards?

there are total 7 2sc458 on both pcb
https://www.hifiengine.com/manual_library/sansui/au-555.shtml

 

[pasgal]

Grazie mille Peter, ho un altoparlante ad altissima efficienza, Klipschhorn, in quanto in insieme del 2sc458 che mi suggerisci, non voglio guadagnare di potenza, l'AU555 ha già troppa voce anche prima di raggiungere 1/3 del volume del piatto .
Quali transistor si acquista in negozio per sostituire
2sc458?

ci sono un totale di 7 2sc458 su entrambi i pcb
https://www.hifiengine.com/manual_library/sansui/au-555.shtml

 

[Peter lye]

https://audiokarma.org/forums/index.php?threads/sansui-au-555-—-hiss.936067/#post-14250971

The AU-555 preamplifier stage uses 6 x 2SA458LG transistors; these are known to age poorly. As they fail they exhibit the symptoms you describe: increased hiss noise/crackling. The 2SA458LG can be replaced with KSA1815 transistors.

As above

 

[pasgal]

https://audiokarma.org/forums/index.php?threads/sansui-au-555-—-hiss.936067/#post-14250971

As above

 

[pasgal]

Do I have to fit these, do they have reversed feet? I have to put them in the AU555, thanks.

PXL_20220225_080231983

• pasgal
• Feb 25, 2022

 

[Peter lye]

Do I have to fit these, do they have reversed feet? I have to put them in the AU555, thanks.

PXL_20220225_080231983

• pasgal
• Feb 25, 2022

cannot see your picture

 

[pasgal]

Many thanks, it was a private album, but I didn't know that.
The question is: how do i understand in which direction i have to mount the new ones (bce / ecb)?

cannot see your picture

 

[Peter lye]

the 2sc458 is ECB so is KSC1815
if you took out the 2sc458 flat side facing you, you must install the ksc 1815 flat side facing you too

 

[Peter lye]

you can double check the old/new transistor pinout with transistor tester.

 

[pasgal]

you can double check the old/new transistor pinout with transistor tester.

Many many thanks.

What do I set on the tester, signal continuity?
Collector connected to base, no beeps?

 

[Peter lye]

you can't use a multimeter tester to test, unless it have that function built in it.

just use post #12 has guide

 

[pasgal]

non puoi usare un tester multimetro per testare, a meno che non abbia quella funzione incorporata.

usa solo il post n. 12 ha una guida

Yes! Many thanks!