[labusas]

Hello fellow AKSA fans,
I'll go right to the point: My kids shorted speaker cables, pulled them out, while AKSA 100 was playing. I could smell something burning and I turned it off withing 10 seconds.  Now, I can clearly see all four 7A fuses are gone and all 100R R25, R26 resistors are burned also.  What else could be damaged?  Is it possible to diagnose the extent of the damage by the fact that speaker wires shorted?
Could output transistors T1 and T2 be damaged also? How do I proceed to solve this problem? Change fuses and four R25 R26 resistors and see what happens or...?
Thanks

[AKSA]

Hi Labusas,

Tsk, tsk!  Those naughty children!!  

You will need to replace:

1.  All output devices T7/8 and T9/10.
2.  The 7A5 fuses
3.  The fuse resistors, R25 and R26, each 100R
4.  T1/T2, the input pair, which MAY be damaged also.

That's it.

Now, it is possible that some or even all of the outputs are OK.

Best way to check this is to insert new fuses, switch on, and check the bias in the output stage with DMM probes across the emitters of the outer output devices.  If it is more than about 200mV, Houston, we have a problem.........

Let me know by private email how it's going.  I'll naturally assist in whatever way I can.

Cheers,

Hugh

[labusas]

Thanks Hugh for your valuable input,
Transistors are all OK!  All I had to do is change 100R resistors and fuses. Then I checked voltage at base + emitter got .5V on all devices. Hooked everything up and my AKSA came back to live.

The lesson learned - try to avoid all metal banana plugs or insulate them like, like I did now, if you have curious 3. 5 years running around the house.

[Jens]

Thanks Hugh for your valuable input,
Transistors are all OK!  All I had to do is change 100R resistors and fuses. Then I checked voltage at base + emitter got .5V on all devices. Hooked everything up and my AKSA came back to live.

The lesson learned - try to avoid all metal banana plugs or insulate them like, like I did now, if you have curious 3. 5 years running around the house.

Hi labusas,

You might want to use Speakons instead (see other thread on speaker binding posts). Even your kids will have trouble making a mayhem with those.

Cheers,

Jens

[Carlman]

Speakons on your amp are great if you're going to:
Make your own custom speaker cables w/ Speakon connectors.. AND
You don't want to experiment with any other cable or speaker with that amp.

Other than that, I'm sure they're great.

[PSP]

A less secure (but still reasonablly secure) alternative is the Cardas CPBA binding post ( see http://welbornelabs.com/speakerstuff.htm and scroll down to the Cardas CPBA).  These binding posts take 1/4 inch spades (only) and are very difficult to short.  They also have a very short signal path.

Peter

[Lost81]

A less secure (but still reasonablly secure) alternative is the Cardas CPBA binding post ( see http://welbornelabs.com/speakerstuff.htm and scroll down to the Cardas CPBA).  These binding posts take 1/4 inch spades (only) and are very difficult to short.  They also have a very short signal path.

Peter

Have you tried using them, Peter?

I was looking at them earlier.
One end of my speaker cables have 1/4" spades, while the other has 5/16." It is too expensive and troublesome to get the 1/4" reterminated. That is why I was looking at the Cardas CPBA binding posts.

How do they install though?
It loks like the CPBA need 3 holes instead of the usual 2.


Cheers,
-Lost81

[AKSA]

Labusas,

You've been incredibly lucky.  Your children clearly have quite a touch with amplifiers;  be sure to offer them a job in assembly of AKSAs at Aspen when you are through telling them how naughty they have been!

I'd guess it was playing quietly;  there would have been tears with Black Sabbath, I assure you.......

Guys, this is a good test.  If an amp can withstand this sort of treatment, it's pretty hardy.

Cheers,

Hugh

[Carlman]

1.  All output devices T7/8 and T9/10.
2.  The 7A5 fuses
3.  The fuse resistors, R25 and R26, each 100R
4.  T1/T2, the input pair, which MAY be damaged also.
 ...

Just out of curiosity, how do you know the wattage of resistors?  I get the bands, colors, etc., but I wouldn't know which wattage value to get.  1 watt, 1/2 watt, 1/4 watt?  

I even looked in the manual and couldn't find any wattage/resistor relationship for the fuse resistors.  

Just thought adding this tidbit to this discussion might be helpful.

-C

[AKSA]

Carl,

Measure the voltage across the resistor at idle (no music), square it, divide it by the resistance in ohms, this gives you the steady state dissipation, which for audio is all we need.

Then multiply this dissipation by three times, and select the nearest preferred rating.

For example, the 3K3 1W resistor on the AKSA 100W has about 28 volts across it.  Square it to get 784, divide this by 3,300 ohms, and we get 0.237 watts.  Multiply this by three and we come up with 0.712 watts.  This is clearly over our standard 0.6 watt rating, so we move up to 1W.

Something very similar is done with transistor selection, to indicate what size device we need.  My factor of three is extremely conservative, and reflects my design aim of constant commercial service in Death Valley.....

Cheers,

Hugh