audio amplifier output transistors

Guest
I noticed that TR7 is PNP and TR9 is NPN here:
http://www.dself.dsl.pipex.com/ampins/dipa/dpafig1.gif

Then over here, TR7 is NPN and TR9 is PNP:
http://www.dself.dsl.pipex.com/ampins/dipa/dpafig33.gif

Are these correct, or in error?

Also - for building audio amps "on the cheap", would TIP41C/TIP42C do
for output transistors in these schematics?

Thanks,

Michael
 
mrdarrett@gmail.com wrote:
I noticed that TR7 is PNP and TR9 is NPN here:
http://www.dself.dsl.pipex.com/ampins/dipa/dpafig1.gif

Then over here, TR7 is NPN and TR9 is PNP:
http://www.dself.dsl.pipex.com/ampins/dipa/dpafig33.gif

Are these correct, or in error?
Click to expand...
It looks to me like the first one is using Sziklai_pairs for the output
stage, see:
http://en.wikipedia.org/wiki/Sziklai_pair

and the other is using Darlington pairs, see:
http://en.wikipedia.org/wiki/Darlington_transistor

Either of these should be suitable for audio output stages, though I
didn't study these in detail.


--
-----------------------------------------------------------------------
To reply to me directly:

Replace privacy.net with: totalise DOT co DOT uk and replace me with
gareth.harris
 
mrdarrett@gmail.com wrote:
I noticed that TR7 is PNP and TR9 is NPN here:
http://www.dself.dsl.pipex.com/ampins/dipa/dpafig1.gif

Then over here, TR7 is NPN and TR9 is PNP:
http://www.dself.dsl.pipex.com/ampins/dipa/dpafig33.gif

Are these correct, or in error?
Click to expand...
They are both right. Note that in both cases, the arrow in
the emitter points down in all cases (from positive toward
negative)

The first output is made of an inverter driving an inverter,
with 100% voltage feedback to the first emitter, so the the
pair act like a very precise follower, but with more
stability issues, because of the inversion inside the loop.

The second version has output stages made of just a follower
driving a follower, with no local voltage feedback, except
that inherent in each follower. This produces a less DC
accurate follower, but with a higher frequency response (if
the transistors are the same) and the distortion is removed
by overall amplifier feedback.

Also - for building audio amps "on the cheap", would TIP41C/TIP42C do
for output transistors in these schematics?
Click to expand...
After checking the peak voltage capability, I usually check
the gain versus current curve and pick transistors that do
not require currents much above that which forces the gain
down to half of its peak value. Then I check the safe
operating area and overall wattage rating against the
amplifier needs and heat sinks available.

The first amplifier does not specify power supply voltage
rails and I don't know your load resistance. But the second
one (with +-37 volt rails) requires transistors with at
least something like 80 volt capability.
From:
http://www.fairchildsemi.com/ds/TI%2FTIP41C.pdf
http://www.fairchildsemi.com/ds/TI%2FTIP42C.pdf
the 100 volt rating looks like a possible.

The gain falls from a typical peak of something like 55
around 0.3 amps, but falls to about 27 at 5 amps, so that is
all the peak current I would ask of these transistors. That
would limit the load resistance to about 7 ohms or more.

Checking the second breakdown (safe operating area) curves,
you might stay within the safe area with an 8 ohm load. But
I think you are risking damage with a 4 ohm load. Lowering
the supply voltages a bit helps a lot (lowers the peak
current and the peak voltage across the transistor with an
inductive speaker load that keeps the load current going a
bit as the voltage swings back through zero, so supply
voltage across the transistor while current is flowing,
briefly).

So these might serve for some loads, but will not withstand
much abuse, like paralleled speakers or speaker wiring shorts.

The first circuit does not detail the Vbias part of the
circuit between the two output half drivers, but that bias
has to see the transistor temperature, so it can compensate
for the changes in base emitter drop of the hot output
transistors. the second schematic shows one way to make
such a bias generator, and TR13 should be thermally coupled
to the output heat sink.
--
Regards,

John Popelish
 
mrdarrett@gmail.com wrote:

And here I thought that with +/- 37V, with each transistor only seeing
|37| V, the 40V one would be fine...
Click to expand...
When one transistor is fully on, the other has the sum of
both supplies across it. If the load is not pure resistance
(part inductance or capacitance), there is also some current
through the load as it passes through zero volts, instead of
the current being instantaneously proportional to the
voltage across the load. This means that it is possible
that there will be almost the full sum of the two supplies
across a transistor and it will still have to be conducting
some current.

I'll have to research in detail what "safe operating area" for
transistors means. (I'm still new at this.)
Click to expand...
The two dimensions of the safe area are voltage and
simultaneous current (instantaneous power). The higher the
voltage across the transistor, the smaller part of the total
die conducts that current, so the power gets concentrated in
small hot spots. The die cannot heat sink those hot spots
(and keep them below the peak allowed temperature) as well
as it can spread the heat of full die heat production, so
the power capability goes down and the duration of peak
power goes down. Very short duration heat pulses can be
soaked up by the die, itself, but cannot get out to the
package fast enough. This is why the safe area chart
contains several lines representing voltage and current
combinations of various durations.

--
Regards,

John Popelish
 
On Wed, 15 Oct 2008 20:37:13 -0400, John Popelish <jpopelish@rica.net>
wrote:

mrdarrett@gmail.com wrote:

And here I thought that with +/- 37V, with each transistor only seeing
|37| V, the 40V one would be fine...

When one transistor is fully on, the other has the sum of
both supplies across it. If the load is not pure resistance
(part inductance or capacitance), there is also some current
through the load as it passes through zero volts, instead of
the current being instantaneously proportional to the
voltage across the load. This means that it is possible
that there will be almost the full sum of the two supplies
across a transistor and it will still have to be conducting
some current.

I'll have to research in detail what "safe operating area" for
transistors means. (I'm still new at this.)

The two dimensions of the safe area are voltage and
simultaneous current (instantaneous power). The higher the
voltage across the transistor, the smaller part of the total
die conducts that current, so the power gets concentrated in
small hot spots. The die cannot heat sink those hot spots
(and keep them below the peak allowed temperature) as well
as it can spread the heat of full die heat production, so
the power capability goes down and the duration of peak
power goes down. Very short duration heat pulses can be
soaked up by the die, itself, but cannot get out to the
package fast enough. This is why the safe area chart
contains several lines representing voltage and current
combinations of various durations.
Click to expand...
---
Beautiful.

JF
 
On Oct 15, 3:13 pm, John Popelish <jpopel...@rica.net> wrote:
mrdarr...@gmail.com wrote:
I noticed that TR7 is PNP and TR9 is NPN here:
http://www.dself.dsl.pipex.com/ampins/dipa/dpafig1.gif

Then over here, TR7 is NPN and TR9 is PNP:
http://www.dself.dsl.pipex.com/ampins/dipa/dpafig33.gif

Are these correct, or in error?

They are both right. Note that in both cases, the arrow in
the emitter points down in all cases (from positive toward
negative)

The first output is made of an inverter driving an inverter,
with 100% voltage feedback to the first emitter, so the the
pair act like a very precise follower, but with more
stability issues, because of the inversion inside the loop.

The second version has output stages made of just a follower
driving a follower, with no local voltage feedback, except
that inherent in each follower. This produces a less DC
accurate follower, but with a higher frequency response (if
the transistors are the same) and the distortion is removed
by overall amplifier feedback.

Also - for building audio amps "on the cheap", would TIP41C/TIP42C do
for output transistors in these schematics?

After checking the peak voltage capability, I usually check
the gain versus current curve and pick transistors that do
not require currents much above that which forces the gain
down to half of its peak value. Then I check the safe
operating area and overall wattage rating against the
amplifier needs and heat sinks available.

The first amplifier does not specify power supply voltage
rails and I don't know your load resistance. But the second
one (with +-37 volt rails) requires transistors with at
least something like 80 volt capability.
From:http://www.fairchildsemi.com/ds/TI%2FTIP41C.pdfhttp://www.fairchildsemi.com/ds/TI%2FTIP42C.pdf
the 100 volt rating looks like a possible.

The gain falls from a typical peak of something like 55
around 0.3 amps, but falls to about 27 at 5 amps, so that is
all the peak current I would ask of these transistors. That
would limit the load resistance to about 7 ohms or more.

Checking the second breakdown (safe operating area) curves,
you might stay within the safe area with an 8 ohm load. But
I think you are risking damage with a 4 ohm load. Lowering
the supply voltages a bit helps a lot (lowers the peak
current and the peak voltage across the transistor with an
inductive speaker load that keeps the load current going a
bit as the voltage swings back through zero, so supply
voltage across the transistor while current is flowing,
briefly).

So these might serve for some loads, but will not withstand
much abuse, like paralleled speakers or speaker wiring shorts.

The first circuit does not detail the Vbias part of the
circuit between the two output half drivers, but that bias
has to see the transistor temperature, so it can compensate
for the changes in base emitter drop of the hot output
transistors. the second schematic shows one way to make
such a bias generator, and TR13 should be thermally coupled
to the output heat sink.
--
Regards,

John Popelish
Click to expand...


And here I thought that with +/- 37V, with each transistor only seeing
|37| V, the 40V one would be fine...

I'll have to research in detail what "safe operating area" for
transistors means. (I'm still new at this.)

Thanks!

Michael
 
<mrdarrett@gmail.com

I noticed that TR7 is PNP and TR9 is NPN here:
http://www.dself.dsl.pipex.com/ampins/dipa/dpafig1.gif

Then over here, TR7 is NPN and TR9 is PNP:
http://www.dself.dsl.pipex.com/ampins/dipa/dpafig33.gif

Are these correct, or in error?

Also - for building audio amps "on the cheap", would TIP41C/TIP42C do
for output transistors in these schematics?
Click to expand...

** No.

Piss off - you utter dickhead.



...... Phil
 
On Oct 15, 5:37 pm, John Popelish <jpopel...@rica.net> wrote:
mrdarr...@gmail.com wrote:
And here I thought that with +/- 37V, with each transistor only seeing
|37| V, the 40V one would be fine...

When one transistor is fully on, the other has the sum of
both supplies across it. If the load is not pure resistance
(part inductance or capacitance), there is also some current
through the load as it passes through zero volts, instead of
the current being instantaneously proportional to the
voltage across the load. This means that it is possible
that there will be almost the full sum of the two supplies
across a transistor and it will still have to be conducting
some current.

I'll have to research in detail what "safe operating area" for
transistors means. (I'm still new at this.)

The two dimensions of the safe area are voltage and
simultaneous current (instantaneous power). The higher the
voltage across the transistor, the smaller part of the total
die conducts that current, so the power gets concentrated in
small hot spots. The die cannot heat sink those hot spots
(and keep them below the peak allowed temperature) as well
as it can spread the heat of full die heat production, so
the power capability goes down and the duration of peak
power goes down. Very short duration heat pulses can be
soaked up by the die, itself, but cannot get out to the
package fast enough. This is why the safe area chart
contains several lines representing voltage and current
combinations of various durations.

--
Regards,

John Popelish
Click to expand...

Thank you for taking the time to explain this to me.

I appreciate it.

Michael
 
mrdarrett@gmail.com wrote:

I noticed that TR7 is PNP and TR9 is NPN here:
http://www.dself.dsl.pipex.com/ampins/dipa/dpafig1.gif

Then over here, TR7 is NPN and TR9 is PNP:
http://www.dself.dsl.pipex.com/ampins/dipa/dpafig33.gif

Are these correct, or in error?

Also - for building audio amps "on the cheap", would TIP41C/TIP42C do
for output transistors in these schematics?
Click to expand...
Since the original devices aren't mentioned, it's anyone's guess. Do you
know what fT means ? And why it's important for an amplifier output
stage.

TIPs are generally fairly shitty for audio IME.

Graham
 
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