The Smoked 400

[laatsch55]

THD & N , left channel

 

[laatsch55]

At 206 watts out , into 8 ohms, at 20khz, both channels loaded and driven, smoked R78 on the right channel, took out the minus rail fuse and other things I havent found yet..

 

[laatsch55]

Q7 on the right channel is toast..

 

[laatsch55]

Now THAT would make a fun youtube video! No highs.....No lows................BOOM No Bose!

Yeppers...

 

[oldphaser]

At 206 watts out , into 8 ohms, at 20khz, both channels loaded and driven, smoked R78 on the right channel, took out the minus rail fuse and other things I havent found yet..

Ouch!

I wouldn't expect that into 8 ohms both channels driven.

I might expect it into a 4 ohm load. Particularly if the Zobel network resistors are to low a wattage.

If the amp is a 400 series 1 with 5 amp B+ and B- fuses you might consider going from 5 amps to 8 amps like they did on the 400 series 2's.
Likewise, if the amplifier is a series 1 with 8 amp line supply fuses it should be replaced with a 10 amp fuse just like the series 2 amps had.

If you ever drive a 4 ohm load both channels driven at 20KHz to rated output you may need to increase them even still further.

Also with a 700 series amp that is driving both channels into 4 ohms at 20KHz at rated output the 10 amp line supply fuse should be increased from 10 amps to 15 amps and the B+/B- fuses increased to 10 amp fuses.

Ed

 

[laatsch55]

Yep, I didn't expect that either...

 

[oldphaser]

Lee

Is this a Rev D board? If so, is R78 a 44.2 ohm 1/4 watt resistor?

Ed

 

[Wheel-right]

Now THAT would make a fun youtube video! No highs.....No lows................BOOM No Bose!

Is there a doctor in the house? Calling Dr.Bose, we have a problem!

 

[oldphaser]

Is there a doctor in the house? Calling Dr.Bose, we have a problem!

Amar Bose died in 2013

 

[oldphaser]

Lee,

With amplifiers that have blown, I have found the "Octopus Tester" (a.k.a. "component tester") to be a handy device to find/locate leaky semiconductors quickly.

It is particularly useful when 1 channel is good and the other is bad. Simply going back and forth between channels and looking at Lissajous patterns on a oscilloscope. The component tester would be hooked up to 2 channel scope set up in X/Y mode.

It may be time to use the one I sent you.

Ed

 

[laatsch55]

I still haven't built it Ed.

It was Q7 on the left channel and the left backplane pico fuse. It was R78 on the right channel.
1/2 watt R78 on the left channel, 1/4 watt R78 on the right. Should have been 1/4 watt in both. More collateral damage on the 1/2 watt side.

It's all good now...relay click, good offset, good bias. And I used my last 5AGX....gotta make a Mouser order tonight...

 

[laatsch55]

Lee

Is this a Rev D board? If so, is R78 a 44.2 ohm 1/4 watt resistor?

Ed

It used to be two 44 ohm, one in R78, one in R79. Now it is 22 ohm in either position..but I noticee in the latest BOM Joe sent on the D board it is now showing a 10 ohm..

 

[oldphaser]

It used to be two 44 ohm, one in R78, one in R79. Now it is 22 ohm in either position..but I noticee in the latest BOM Joe sent on the D board it is now showing a 10 ohm..

I only took a quick look at the documentation I have for the Rev D before I typed my previous posting.
What resistor size is for a quasi-comp and which was used for a fully comp?
I thought the 10 ohm was quasi and the 44 was for fully-comp?
Where did the 22 ohms come in? So is it that the (2) 44 ohm resistors are in parallel with R78 and R79 for an effective 22 ohms?
Is there a latter revision to the Rev D I am missing?

Ed

 

[oldphaser]

I still haven't built it Ed.

It was Q7 on the left channel and the left backplane pico fuse. It was R78 on the right channel.
1/2 watt R78 on the left channel, 1/4 watt R78 on the right. Should have been 1/4 watt in both. More collateral damage on the 1/2 watt side.

It's all good now...relay click, good offset, good bias. And I used my last 5AGX....gotta make a Mouser order tonight...

Lee,

As a side note: Larger wattage resistors are less noisy than smaller wattage resistors.

Ed

 

[laatsch55]

I only took a quick look at the documentation I have for the Rev D before I typed my previous posting.
What resistor size is for a quasi-comp and which was used for a fully comp?
I thought the 10 ohm was quasi and the 44 was for fully-comp?
Where did the 22 ohms come in? So is it that the (2) 44 ohm resistors are in parallel with R78 and R79 for an effective 22 ohms?
Is there a latter revision to the Rev D I am missing?

Ed

I don't know Ed. I think you are correct on the quasi/full comp resistor values. The 22 was in place of the 2--44 in parallel.

 

[laatsch55]

Yep, 10 ohms on the Quasi, 22 ohms on the full comp..

 

[laatsch55]

The little lovely is back on the horns..

 

[derek92994]

Yeah, the sub hand that was over the other day picked up a couple pairs of 901's that he wants to light up. So the 400 will go back on the horns and the Perry 700 will go on a seek and destroy on some Bose...

Shouldnt be a problem, the bose have infinity power rating

 

[mlucitt]

Shouldnt be a problem, the bose have infinity power rating

Do they have a DBT inside?

 

[derek92994]

Do they have a DBT inside?

Yeah, but it works different. You get a brief flash of light when they explode