Au-505.. borderline bright!

[Trw]

I've replaced all of the small signal transistors with bc550c's (doesn't seem to be much love for them around here??) I find them easier to source here in the uk (higher gain than ksc1845's)
And ksa992's have replaced the Nec640's on the Amp board.
The outgoing Nec's had hfe sub 200 the 992's both circa 410.

Rebiased and it has totally transformed the sound.

I'd be curious what the hard core tinkerers made of bc550c's Vs the oft touted 1845's in these positions?

 

[olider]

Try with 1845 ? Do you have some ?
Saw somewhere bc don’t mix happily with Japanese transistors (?) ….
Restoring a ba 60 , I was really keen to use bc …same reason : high hfe .
Your experience is interesting !
(Sorry I’m not a hard core tinkerer …)

 

[Trw]

Try with 1845 ? Do you have some ?
Saw somewhere bc don’t mix happily with Japanese transistors (?) ….
Restoring a ba 60 , I was really keen to use bc …same reason : high hfe .
Your experience is interesting !
(Sorry I’m not a hard core tinkerer …)

I fitted 1845's in my Model 2000 tone board and bc550c's throughout the other boards (458 replacements) it seemed a little choked and i had a bit of hum so i decided to swap the 1845's out for 550c's and it really opened the sound up.(didn't cure the hum unfortunately)

In my 505 i felt the 640's were choking it and they most definately were i can now see where it gets it's reputation for being heavily rolled off in the treble.

I wasn't sure how the 992's (pnp) would play with the bc550's they're sold as a complimentary pair with the 1845's then i thought hold on you have the 550's working quite well with the nec640 so why shouldn't they work together??

I keep reading that in the au-505 specifically that the 1845s are 20% lower hfe than the original sc871's so that to me doesn't sound like the perfect substitute!

Nb: The Model 2000 had sc871's fitted originally as well.

 

[olider]

Yes for 871 hfe more than 350 and for 1845 hfe >200 ….( but can reach 1200 ….)
Did you check the 871 you discarded ?( even if hfe prone to drift sometimes)
Bc 550 hfe>420 for the c type
The complementary part for 550 is 560 .
Hard core tinkerers not inclined to pair npn and pnp from different manufacturers ( my feeling ).
Another point is the original 550 production is discontinued,Fairchild one doesn’t been referenced as noiseless .
Anyway you are right , the best is to try. My knowledge isn’t extending to the point to state where low/high hfe are expected . Is the highest always the best ?
For the hum, what about soldering , worn caps, ground ?
I own a 505 , never noticed an overwhelming brightness…Could be the pairing with your speakers ?
Regarding to your borderline bright title ,do you mean it was better before ( except for the choked thing ) ?

 

[stereofun]

I have 3 505's in the house. 2 of them are stock and those two have a distinctly different tweeter response. The "tweeted" up version is a late production run from Oct '74, that I only acquired a few month back. That model also has a more orangy and bright lettering on the faceplate as compared to the other two's more subtle yellow.

Normally I'd document with pics, but it's like a million degrees in my Arizona desert garage right now - BUT what absolutely intrigued me when I checked out the bright sounding October 74 model was to find that it had a slightly different main amp, can't remember if it was an extra cap in each side of the board or one less, but it was different.

That brighter sounding 505 reminded me of a 7500 I had on the bench once - also too accentuated in the tweeter, initially pleasing, but quickly tiring. This tweak in sound btw happened to many amps from the mid 70'ties on, almost like a new ideal of sound, then by late 70'ties and on, the tweeter seems to become more refined.

Not saying this is the reason for the bright 505, only that I had an unexpected experience along those lines, being quite familiar with their sonics otherwise. Cheers from still 105 degrees ;-(

 

[Trw]

Yes for 871 hfe more than 350 and for 1845 hfe >200 ….( but can reach 1200 ….)
Did you check the 871 you discarded ?( even if hfe prone to drift sometimes)
Bc 550 hfe>420 for the c type
The complementary part for 550 is 560 .
Hard core tinkerers not inclined to pair npn and pnp from different manufacturers ( my feeling ).
Another point is the original 550 production is discontinued,Fairchild one doesn’t been referenced as noiseless .
Anyway you are right , the best is to try. My knowledge isn’t extending to the point to state where low/high hfe are expected . Is the highest always the best ?
For the hum, what about soldering , worn caps, ground ?
I own a 505 , never noticed an overwhelming brightness…Could be the pairing with your speakers ?
Regarding to your borderline bright title ,do you mean it was better before ( except for the choked thing ) ?

The title was tongue in cheek,the au-505 as i interpret it has a reputation for incredible bass and rolled off highs it now has a very good top end with no detriment to the bass

 

[Sloper1940]

Goodaye all

Cut my self back to 2 AU505's, 1845's in both.
Main caps have increased capacitence as do the coupling caps.
Coupling caps are cascaded, this make the biggest difference.
One has polys in the signal path the other electros'
One has the Blaxdale mod the other doesnt.

Have to say they sound perfect the entire range, a pleasure to listen too.
One drives a a pair of modded Kef Conserto's and the other 4 TDL Super compacts.
Its a tossup which sounds better, it would take better ear than mine.
They run big hours.

Have noted that when the AU70 (Tube) is running how similar the AU505 sounds.

l use KSC1845 because l have heaps of Fairchild ones sitting here.

regards Bruce

 

[Trw]

Goodaye all

Cut my self back to 2 AU505's, 1845's in both.
Main caps have increased capacitence as do the coupling caps.
Coupling caps are cascaded, this make the biggest difference.
One has polys in the signal path the other electros'
One has the Blaxdale mod the other doesnt.

Have to say they sound perfect the entire range, a pleasure to listen too.
One drives a a pair of modded Kef Conserto's and the other 4 TDL Super compacts.
Its a tossup which sounds better, it would take better ear than mine.
They run big hours.

Have noted that when the AU70 (Tube) is running how similar the AU505 sounds.

l use KSC1845 because l have heaps of Fairchild ones sitting here.

regards Bruce

My Au-505 was all original until very recently i will recap and perform other mods eventually i'm just weighing up which way to go,there's no urgency it sounds excellent as is.

To be fair i ran out of 1845's a while ago they're not that easy to come by here (UK) So most of my decisions are based on what i have kicking about,i had the 992's left over so i took a punt because it was easier than ordering the BC complimentary pnp.
Listening as i type i've got the radio on really quiet as everyone's asleep it still sounds open and authoritative.

 

[olider]

Good news ! Bc550 doing a good job in your unit ! I’ll recall that for mine !

I have 3 505's in the house. 2 of them are stock and those two have a distinctly different tweeter response. The "tweeted" up version is a late production run from Oct '74, that I only acquired a few month back. That model also has a more orangy and bright lettering on the faceplate as compared to the other two's more subtle yellow.

Normally I'd document with pics, but it's like a million degrees in my Arizona desert garage right now - BUT what absolutely intrigued me when I checked out the bright sounding October 74 model was to find that it had a slightly different main amp, can't remember if it was an extra cap in each side of the board or one less, but it was different.

That brighter sounding 505 reminded me of a 7500 I had on the bench once - also too accentuated in the tweeter, initially pleasing, but quickly tiring. This tweak in sound btw happened to many amps from the mid 70'ties on, almost like a new ideal of sound, then by late 70'ties and on, the tweeter seems to become more refined.

Not saying this is the reason for the bright 505, only that I had an unexpected experience along those lines, being quite familiar with their sonics otherwise. Cheers from still 105 degrees ;-(

Yes that’s right ,mine is missing 2 decoupling caps on the main board , see the joined pic , c815 and c816 not here on mine .
Maybe worth the try to add two there and check what happens to the brightness.

 

[Trw]

August 72

 

[stereofun]

Another little hack is to add a 1uf Wima -(polyprop best) to the back of shunt leg feedback caps C809/810. This will improve tone across the board imo.

 

[Leestereo]

...Yes that’s right ,mine is missing 2 decoupling caps on the main board , see the joined pic , c815 and c816 not here on mine .
Maybe worth the try to add two there and check what happens to the brightness.
View attachment 2337501

Nice pic ;-) This F-1266-1 board is actually from an AU-555A
C815 and C816 are not decoupling capacitors, they're emitter by-pass capacitors that allow the signal to by-pass the emitter feedback and avoids any effect of the signal level on the TR803/TR804 bias.

 

[olider]

Hi leestereo and thanks so much for your great job on the 505/555a main board !

Nice pic ;-) This F-1266-1 board is actually from an AU-555A
C815 and C816 are not decoupling capacitors, they're emitter by-pass capacitors that allow the signal to by-pass the emitter feedback and avoids any effect of the signal level on the TR803/TR804 bias.

Ok ,my mistake. Some boards are missing these caps , why ?

 

[stereofun]

@Leestereo curious too. Have you noticed 505/555a's missing these caps from factory ? Could of course be a coincidence when the "new" 505 sounded not just brighter but as the entire sound was tweaked differently than the two older 505's

I went out to my garage early am before another 104 degree (40c) day and pulled the lid.

Sansui 505 serial 833060566 - June 1973




Sansui 505 serial 834100464 - October 1974




@LBPete (added to in base)

I've earlier proposed some tweaks to get the 505's top end a bit more enhanced.......well, it might depend on the year. What I hear from the late production run is more tweeter than I care for, while the two older 73 models, are more muted in the tweeter and imo needs some top detail that I find missing compared to the 555a.

 

[Leestereo]

The omission of C815/C816 in late production AU-505s may just be an economic decision; as an entry-level product, the profit margin on the 505 is lower than its more expensive siblings.

 

[playittwice]

The omission of C815/C816 in late production AU-505s may just be an economic decision; as an entry-level product, the profit margin on the 505 is lower than its more expensive siblings.

To add to this “economic decision”, I wish they would have at least used the same metal knobs on the 505, as the 555. As beautiful sounding as this amp is, they could have @ a minimum, used the same knobs one would have thought, especially in that era. But I guess a buck is a buck, doesn’t matter how ya get it.
The plastic knobs give it a cheesy feel, compared to all my other Sansui’s. Oh well, it’s still my favorite SS amp BTW mine is a ‘72 model and no bright top-end here.