Audio Amp Power Supply?

G

gene ohara

Guest
I have seen audio amps with expensive repairs due to power surges. As
a result, I would like to build an audio amp designed to blow only the
fuse(s) if a power surge occurs.

Would appreciate any suggestions or links to information on how to do
this.

Thanks,

Gene
 
"gene ohara" <genosmm@yahoo.com> wrote in message
news:9361bb67.0307071217.50232eeb@posting.google.com...
I have seen audio amps with expensive repairs due to power surges. As
a result, I would like to build an audio amp designed to blow only the
fuse(s) if a power surge occurs.

Would appreciate any suggestions or links to information on how to do
this.
Click to expand...
No offense, but you're not the first person to think of that. It's actually
quite a difficult problem to solve in the general case, because devices have
a variety of failure modes. In general, one approach is to simply massively
overrate the output devices. That is, get a 100W amp and run it at 10W.
But if you want more efficiency than that, you need to build some pretty
tricky circuitry to detect the operating conditions and shut down or reduce
power accordingly. The protection circuitry can easily be more complex than
the entire rest of the amp. What protection circuitry is appropriate
depends in part on what kind of output devices you're using (BJTs, MOSFETs,
....) and on what kind of loads and environments you anticipate (are you
talking about home hifi or are you talking about touring sound
reinforcement).

Books on power amps will tell you more. Check out books by Douglas Self
and/or Ben Duncan.

A fuse will *not* ever be able to do what you need. Fuses are inaccurate
and much, much too slow. A fuse should be seen as a device to help avoid
short-circuit-related fire hazard, not as a device to protect circuitry.

-walter harley
http://www.cafewalter.com
 
"Walter Harley"

Thanks for your comments and tips!

Seems more difficult than I first expected. I would like to build a
very simple inexpensive audio amp for home hifi to drive cone
loudspeakers. For these reasons am Guessing I will be using BJTs.

I have looked at a number of audio amp design books but do not have
the expertise to know what is Good and Bad(which is why I posted my
question here). I will definately check out the 2 books you
mentioned.

To start this project I am trying to research what can be done to
protect the amp before even deciding on a circuit design so would
appreciate your thoughts as to what is most cost effective and simple,
based on your experience. Am wondering if it might be best to
seperate the 2? Have an excellent surge protection device before the
audio amp? But am a believer in Murphies Law so would also like an
audio amp design that would protect the expensive components!

Question: Is one type of output semiconductor less volunerable to
damage?

Gene

PS thanks for the link to your website really enjoyed it!



<walterh@cafewalter.com> wrote in message news:<vgm419l74i7l86@corp.supernews.com>...
"gene ohara" <genosmm@yahoo.com> wrote in message
news:9361bb67.0307071217.50232eeb@posting.google.com...
I have seen audio amps with expensive repairs due to power surges. As
a result, I would like to build an audio amp designed to blow only the
fuse(s) if a power surge occurs.

Would appreciate any suggestions or links to information on how to do
this.

No offense, but you're not the first person to think of that. It's actually
quite a difficult problem to solve in the general case, because devices have
a variety of failure modes. In general, one approach is to simply massively
overrate the output devices. That is, get a 100W amp and run it at 10W.
But if you want more efficiency than that, you need to build some pretty
tricky circuitry to detect the operating conditions and shut down or reduce
power accordingly. The protection circuitry can easily be more complex than
the entire rest of the amp. What protection circuitry is appropriate
depends in part on what kind of output devices you're using (BJTs, MOSFETs,
...) and on what kind of loads and environments you anticipate (are you
talking about home hifi or are you talking about touring sound
reinforcement).

Books on power amps will tell you more. Check out books by Douglas Self
and/or Ben Duncan.

A fuse will *not* ever be able to do what you need. Fuses are inaccurate
and much, much too slow. A fuse should be seen as a device to help avoid
short-circuit-related fire hazard, not as a device to protect circuitry.

-walter harley
http://www.cafewalter.com
Click to expand...
 
"gene ohara" <genosmm@yahoo.com> wrote in message
news:9361bb67.0307081328.999a882@posting.google.com...
To start this project I am trying to research what can be done to
protect the amp before even deciding on a circuit design so would
appreciate your thoughts as to what is most cost effective and simple,
based on your experience. Am wondering if it might be best to
seperate the 2? Have an excellent surge protection device before the
audio amp? But am a believer in Murphies Law so would also like an
audio amp design that would protect the expensive components!

Question: Is one type of output semiconductor less volunerable to
damage?
Click to expand...
I just realized from your posts on other groups that you're talking about
vulnerability to surges on the AC mains, rather than vulnerability to
output-related factors (such as playing the music too loud and frying the
output stages, or short-circuiting the speaker leads). Sorry for any
confusion - although, it's still the case that fuses will be useless,
they're much too slow.

For mains surge protection, I'd have to say that the other suggestions are
just fine: MOV's, and/or plugging the thing into a decent surge protector.
Personally, I have not seen that many amps damaged by power line spikes,
although I have seen techs blame things on power line spikes without any
real evidence. My experience may or may not be a good guide for you; my
background is more to do with pro audio, less home hifi.
 
Walter Harley wrote:
"gene ohara" <genosmm@yahoo.com> wrote in message
news:9361bb67.0307071217.50232eeb@posting.google.com...

I have seen audio amps with expensive repairs due to power surges. As
a result, I would like to build an audio amp designed to blow only the
fuse(s) if a power surge occurs.

Would appreciate any suggestions or links to information on how to do
this.


No offense, but you're not the first person to think of that. It's actually
quite a difficult problem to solve in the general case, because devices have
a variety of failure modes. In general, one approach is to simply massively
overrate the output devices. That is, get a 100W amp and run it at 10W.
But if you want more efficiency than that, you need to build some pretty
tricky circuitry to detect the operating conditions and shut down or reduce
power accordingly. The protection circuitry can easily be more complex than
the entire rest of the amp. What protection circuitry is appropriate
depends in part on what kind of output devices you're using (BJTs, MOSFETs,
...) and on what kind of loads and environments you anticipate (are you
talking about home hifi or are you talking about touring sound
reinforcement).

Books on power amps will tell you more. Check out books by Douglas Self
and/or Ben Duncan.

A fuse will *not* ever be able to do what you need. Fuses are inaccurate
and much, much too slow. A fuse should be seen as a device to help avoid
short-circuit-related fire hazard, not as a device to protect circuitry.
Click to expand...
That's very well said. Like they say, the transistor will blow, to
protect the fuse! But if you want decent surge protection, do _not_
depend on those surge power strips. They don't do the job.


-walter harley
http://www.cafewalter.com
Click to expand...


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I design audio power amps for a living. Actually its not a very common
problem but its one very difficult to solve. Remember the fuses are not
there to protect the amp. They are there to prevent a fire if the amp
fails.

The only amps out there that are pretty well immune to surges are tube
amps.

--
Dan Fraser

From Costa Mesa in sunny California

Check out my electronic schematics site at:
http://www.schematicsforfree.com
If you are into cars check out www.roadsters.com
 
For very good protection, I would have a very good amplifier, and run
it on a high quality true UPS. This is a bit expensive, but is very
good for protection. Since the amp is running from a high quality
inverter that is on batteries, any surges on the AC line that is
driving the charger for the batteries, will not have much effect on
the amplifier. Infact an added feature is that any AC noise
characterists from the AC mains will most likely be reduced.

Jerry Greenberg
http://www.zoom-one.com

--



Dan Fraser <dmfraser@sbcglobal.net> wrote in message news:<3F333D4C.8F88FC71@sbcglobal.net>...
I design audio power amps for a living. Actually its not a very common
problem but its one very difficult to solve. Remember the fuses are not
there to protect the amp. They are there to prevent a fire if the amp
fails.

The only amps out there that are pretty well immune to surges are tube
amps.
Click to expand...
 
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