Aurex SB-150

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Hi!

Anyone have info on this integrated amp? The only thing I can manage to get from the web is that Aurex is (was?) Toshiba's high-end line.

A friend gave me the unit, the left and right channels "drift", sounding horribly underbiased or clipped, then later ok, then later clipped again. I have not confirmed if the problem happens to both channels at the same time.

Any info / data appreciated...


Cheers!

Clem
 
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Hi Clem,
The information you got is correct. Aurex was Toshiba's higher end audio line.

Wait until you here distortion and look at the output with a 'scope. Measure the bias current with speakers disconnected.

I don't have a diagram, sorry.

-Chris
 
Hi Chris,

Funny thing about it is it doesn't follow the usual crossover distortion sound pattern (i.e. as volume increases the distortion gets to be less audible). When it acts up, the distortion sounds about the same regardless of power level, leading me to think its more like an assymetric signal (thus some kind of saturation or cutoff problem). The output remains essentially DC-free though, the offset is around 4mV, pretty good!

Popped the lid off and gave it a cleaning. Its got a single-package diff-amp input and complementary outputs... promising but no exotic parts... I'll put a 'scope onto it sometime this week...

Cheers,

Clem
 
Re: !

viktor1986 said:
I had once Toshiba Aurex A-50 amplifier.it's not powerfull amplifier,only 2*30W 8ohm!


Hi Victor1986,

Yes, you're right, the trafo is very small; in fact the output transistors are TO-220, although the rails are +-35 volts. So I'd guess this SB-150 is rated even less, perhaps 20W/ch. If I manage to get it working I might use it in a small room, so I think the low power isn't an issue...

Cheers,

Clem
 
SB-150 - pics

Well, have a look at it, nice 1980s (?) integrated amp!

Cheers!
 

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Hi Clem,
Bring on the nasty sine wave. It may have clues.

Man, I have fixed so many of those amps over the years. Whatever the model number is at the time, the amp stage remains the same.

Are you sure it's not in the preamp stage or a switch contact?

-Chris
 
Hi Chris,

Nothing eliminated yet, I agree that the problem could be in the preamp, was going to 'scope the line drive to the amp as well. The switches - seem to be ok. Only one is a bit flakey, that's the loudness.

I'll see if I can get to scope it tonight.. :)

Cheers!


Clem
 
Re: Re: !

clem_o said:



Hi Victor1986,

Yes, you're right, the trafo is very small; in fact the output transistors are TO-220, although the rails are +-35 volts. So I'd guess this SB-150 is rated even less, perhaps 20W/ch. If I manage to get it working I might use it in a small room, so I think the low power isn't an issue...

Cheers,

Clem

Your amplifier it's very similiar with SB-A50.I am not sure that this is high-end!Electrolit capacitor's are only 6800uF 45V,only TWO for stereo!It's realy bad for high-end!Ouput ransistor' are 2N249C&250C.Original's was 2SB and 2SD.
I had and VU-METER.Power suplly is 285W or 295W.
 
Updates

Hi Chris,

Sorry, no 'scope traces. I fired up the thing, and there was ONE small little instance of distorted sound. Then it was gone. Had it playing all afternoon and evening, and it was clean. AAARGH.

I'll have to wait until it plays up again.... if...

This definitely ain't no hi-end amp.. Basically, the output amplifier stage provides the whole system gain. Passive bass and treble controls are placed in the feedback path of the power amp (OMG!!). Ah well, there's two other gain stages - one for the mic input and the other for the MM phono in - the latter provided by a JRC-4558 op-amp...

I'll probably pass it on to my daughter when she grow old enough... hehehe...


Cheers!

Clem
 
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Hi Clem,
Many receivers place the tone controls in the feedback loop. Still, it works. Really easy to defeat if you want to :devilr: !

I am using one (JVC R-1X) for computer sound. Why not? It's slim and looks okay. MP3 files sound rough anyway. I even have a sub on it (yeah, I'm a sick puppy).

So I surmise you have no active stages before the amplifier stage? In that case it cuts down your problem area to switches and the amp. A purist would love this - it has a built in passive preamp!

Look for cracked solders around the tone controls and around the heavier components (heatsink, etc). Operate the switches very slowly to see if the fault occurs as well.

-Chris
 
anatech said:

A purist would love this - it has a built in passive preamp!
-Chris


Hi,

Speaking for the purists - passive pre-amps are great,
and tone controls in the feedback loop are terrible.

This is because implementing treble cut means the power amplifier
has to be compensated to be stable at lower gains (more feedback).
The extra compensation slows the amplifier down and increases
distortion at high frequencies because of the reduced open loop gain.

:)/sreten.
 
Hi all,

Thanks for the great inputs:

Chris - defeating the tone controls is definitely something I was considering last night. I can't judge the quality of the amp just yet, as I was evaluating it on a 'sacrificable' pair of speakers (sadly, a pair of KEF C55s - the tweeters died on their own, grrr!). You're right about the switches - the only instance the amp glitched was when slowly moving the loudness switch. Probably another thing to defeat... :)

sreten - absolutely agree, the slowdown capacitors look aggressive, and they have to be given the tone controls! The designers put in very mild boost/cut levels though...

mikeks - ditto. One of the reasons why I can't understand the number of iPod users!!! Car dealerships here have started making an iPod connector a 'feature' of the vehicle. Ouch.

Cheers,

Clem
 
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