Amplifier died after working for a while!!!!

[Himlam8484]

Hi people,

I made a amplifier following the Project 3A ( link is
http://sound.westhost.com/project3a.htm). I make some chnages such as
replace current source to a mirror current source, and added some big
capacitor at the power supply.

When it worked, it is really nice, but last about one hour and it
died. I replace some died power transistor, and test again. I try to
increase the quiesent current by adjusting the pot VR1, and it broken
again.

Can someone explain for me? What did it do like that?

I am looking forward hearing from people soon!!!

Van Hau

 

[Eeyore]

Hi people,

I made a amplifier following the Project 3A ( link is
http://sound.westhost.com/project3a.htm). I make some chnages such as
replace current source to a mirror current source, and added some big
capacitor at the power supply.

When it worked, it is really nice, but last about one hour and it
died. I replace some died power transistor, and test again. I try to
increase the quiesent current by adjusting the pot VR1, and it broken
again.

Well there are many possibilities but the first thing I'd like to know is how
you heatsinked the power transistors. They are easily killed by excessive
temperature rise.

" If the temperature continues to increase, the heatsink is too small. This
condition will (not might - will) lead to the destruction of the amp. Remove
power, and get a bigger heatsink before continuing. Note also that although the
power transistors are mounted to the board, never operate the amp without a
heatsink - even for testing, even for a short period. The output transistors
will overheat and will be damaged. "

A short circuit on the output would kill that design too.

I would use MJE15035 rather than BD140 for that design too.

Graham

 

[Tam/WB2TT]

Hi people,

I made a amplifier following the Project 3A ( link is
http://sound.westhost.com/project3a.htm). I make some chnages such as
replace current source to a mirror current source, and added some big
capacitor at the power supply.

When it worked, it is really nice, but last about one hour and it
died. I replace some died power transistor, and test again. I try to
increase the quiesent current by adjusting the pot VR1, and it broken
again.

Can someone explain for me? What did it do like that?

I am looking forward hearing from people soon!!!

Van Hau

I would start by measuring the quiescent current in the output and driver
transistors. Also, see if there is any DC current flowing to the speaker.

Tam

 

[nospam]

I made a amplifier following the Project 3A ( link is
http://sound.westhost.com/project3a.htm). I make some chnages such as
replace current source to a mirror current source, and added some big
capacitor at the power supply.

When it worked, it is really nice, but last about one hour and it
died. I replace some died power transistor, and test again. I try to
increase the quiesent current by adjusting the pot VR1, and it broken
again.

Can someone explain for me? What did it do like that?

Sounds like thermal runaway. Did you thermally couple Q9 to Q5 and Q6?

Q9 is supposed to do thermal compensation of the output quiescent current.

--

 

[Jamie]

Hi people,

I made a amplifier following the Project 3A ( link is
http://sound.westhost.com/project3a.htm). I make some chnages such as
replace current source to a mirror current source, and added some big
capacitor at the power supply.

When it worked, it is really nice, but last about one hour and it
died. I replace some died power transistor, and test again. I try to
increase the quiesent current by adjusting the pot VR1, and it broken
again.

Can someone explain for me? What did it do like that?

I am looking forward hearing from people soon!!!

Van Hau

for one thing, the VR1 is there to reduce the current to it's minimum
and most likely used to balance the output to 0 volts with no signal on
the input while making adjustments.

You don't show how you have mounted your power transistors?, I do
hope you are using heatsinks?
And I hope you are monitoring the heat level ..

 

[Eeyore]

for one thing, the VR1 is there to reduce the current to it's minimum

It's there to *adjust it* to the recommended value.

and most likely used to balance the output to 0 volts with no signal on
the input while making adjustments.

Absolutely not in any way at all.

You do talk absolute crap.

Graham

 

[neon]

One solution HEAT

 

[Fred Bloggs]

I made a amplifier following the Project 3A ( link is
http://sound.westhost.com/project3a.htm). I make some chnages such as
replace current source to a mirror current source, and added some big
capacitor at the power supply.

When it worked, it is really nice, but last about one hour and it
died. I replace some died power transistor, and test again. I try to
increase the quiesent current by adjusting the pot VR1, and it broken
again.

Can someone explain for me? What did it do like that?

I am looking forward hearing from people soon!!!

It most likely burned up with excessive bias through the output
transistors... This is not a good design, there is no necessity for
bootstrapping the output stage in a modern circuit...

 

[Eeyore]

It most likely burned up with excessive bias through the output
transistors... This is not a good design, there is no necessity for
bootstrapping the output stage in a modern circuit...

The bootstrapping amused me slightly.

Without it, the performance would suffer (not that it's anything special
anyway). I'd use (I DO use) an active load myself of course.

Graham

 

[Eeyore]

It most likely burned up with excessive bias through the output
transistors..

It's possible he doesn't have good thermal coupling to the bias setting circuit
too.

The thermal coupling should only be between Q5, 6 and 9 of course NOT Q7 and 8.
I see the text makes no mention of this and suggests that no coupling is
required.

Admittedly there's only 3mA through Q5 and 6 at idle but if they're not
heatsinked (as the text suggests) they'll get rather hotter with some signal.

An 'un-heatsinked' TO-220 can only dissipate ~ 2 watts without exceeding Tj max.
At 35 volts that's only 57mA ! I would definitely heatsink Q5 and 6.

A poor design throughout.

Graham

 

[Phil Allison]

"Fred Bloggs

It most likely burned up with excessive bias through the output
transistors...

** Bollocks.

This is not a good design, there is no necessity for bootstrapping the
output stage in a modern circuit...

** ROTFLMAO !!!!!!!!!!!!!!

Slaves to audiophool, voodoo inspired fashion are asinine fuckwits indeed
!!!!!!!!!!!!!!!!!!!!!!!!!!!


The Bloggs congenital, autistic, MORON regularly obliges, on cue - as
usual .......


Bowel cancer is too good.






....... Phil

 

[John B]

Hi people,

I made a amplifier following the Project 3A ( link is
http://sound.westhost.com/project3a.htm). I make some chnages such as
replace current source to a mirror current source, and added some big
capacitor at the power supply.

Perhaps you would have been better to have built and tested the design
as given before trying to improve it with your own modifications.

..
..
..

 

[Himlam8484]

I would start by measuring the quiescent current in the output and driver
transistors. Also, see if there is any DC current flowing to the speaker.

Tam

when i did not connect a speaker, i can not measure the voltage drop
across power resistor.

 

[Eeyore]

when i did not connect a speaker, i can not measure the voltage drop
across power resistor.

Why not ? What are you measuring ? I'm doubtful that you're measuring the right
thing.

You need to measure the voltage across R13 or R14 *with no load*. The voltage
should be about 25 mV.

Alternatively measure the current in either the positive or negative supply. It
should be about 80mA.

Graham

 

[Jamie]

Jamie wrote:




It's there to *adjust it* to the recommended value.





Absolutely not in any way at all.

You do talk absolute crap.

Graham

Look again.

this isn't my first rodeo .

That circuit design is so common and old it isn't funny.


Gexxxxzzxc
I don't know why I waste my time.

 

[Eeyore]

Look again.

I've looked at it in some detail. There is for starters, no way whatever that
the bias adjustment affects the DC offset as you suggested.

this isn't my first rodeo .

I have no idea what you mean by that.

That circuit design is so common and old it isn't funny.

It's certainly 'basic'.

Gexxxxzzxc
I don't know why I waste my time.

You certainly shouldn't waste it talking nonsense.

Graham

 

[Jamie]

Jamie wrote:




I've looked at it in some detail. There is for starters, no way whatever that
the bias adjustment affects the DC offset as you suggested.





I have no idea what you mean by that.





It's certainly 'basic'.





You certainly shouldn't waste it talking nonsense.

Graham

Like I said, waste of space that surrounds you.
please do others a favor and give them your air, it's being
wasted on you.

 

[Eeyore]

Like I said, waste of space that surrounds you.
please do others a favor and give them your air, it's being
wasted on you.

Whatever your personal opinion of me, I can totally wipe the floor with you when
talking about audio for sure.

I'm pretty damn bloody expert on high power and high performance audio
amplification btw. It's a little speciality of mine. It might have something to do
with taking a particular interest in the subject from age ~ 16. There are several
hundred thousand professional amplifiers of 200 - 1000 W/ch rating out there in
the big wide world of my design.

I'm not impressed by a gesturing clown like yourself who mistakes a bias pot for an
offset adjust.

Graham

 

[Jamie]

Jamie wrote:




Whatever your personal opinion of me, I can totally wipe the floor with you when
talking about audio for sure.

I'm pretty damn bloody expert on high power and high performance audio
amplification btw. It's a little speciality of mine. It might have something to do
with taking a particular interest in the subject from age ~ 16. There are several
hundred thousand professional amplifiers of 200 - 1000 W/ch rating out there in
the big wide world of my design.

I'm not impressed by a gesturing clown like yourself who mistakes a bias pot for an
offset adjust.

Graham

yeah sure, what ever you say expert.

You can stop digging any time now and save your energy.

 

[Meat Plow]

yeah sure, what ever you say expert.

He is an expert and it shows when ignorant twits like you make mistakes
then don't own up to them. I too am very impatient with twits like you not
so much in electronics but in computer hardware/networking/intra-internet.

You can stop digging any time now and save your energy.

Take your own advice.