building a small amplifier for the first time

M

Michael

Guest
I finally settled on this one:
http://www.techlib.com/electronics/audioamps.html#computer

Questions:
1. Would a 2N2222 work instead of the 2N4401? I've got a bunch of
quad-2s in my bin.

2. Would it be ok to substitute 1-ohm resistors for the 2.2 ohm
resistors on the speaker side, if I use a larger speaker? I've got a
spare 4-ohm, 10W speaker from when I upgraded the car's audio system.

3. On that note, what wattage of resistor should be chosen for the
speaker output side? 1/4W? greater?

Thanks,

Michael
 
On Oct 7, 12:00 pm, Michael <mrdarr...@gmail.com> wrote:
I finally settled on this one:http://www.techlib.com/electronics/audioamps.html#computer

Questions:
1.  Would a 2N2222 work instead of the 2N4401?  I've got a bunch of
quad-2s in my bin.

2.  Would it be ok to substitute 1-ohm resistors for the 2.2 ohm
resistors on the speaker side, if I use a larger speaker?  I've got a
spare 4-ohm, 10W speaker from when I upgraded the car's audio system.

3.  On that note, what wattage of resistor should be chosen for the
speaker output side?  1/4W?  greater?

Thanks,

Michael
Click to expand...
I imagine most any small NPN transistor can be used in place of the
4401. If you substitute 1 ohm resistors for the 2.2 ohm, the DC bias
current (through the TIP 31,32) will be higher since it will require
more current to get the same voltage and negative feedback to
stabilize the current. The diodes are used to produce a voltage just
enough to barely turn on the TIP 31,32. As they turn on, the voltage
rises between the two emitters due to the 4.4 ohm resistance. At some
point the current will be stable since the rising voltage produces
negative feedback and the transistors cannot further increase
conduction. If you short out the 2.2 resistors, the current may
runaway due to temperature rise. So, you might try the 1 ohm
resistors, but keep watch on the bias current as temp increases. It
may work on cold days and not so good on hot days.

The output peak voltage might be around 5 volts, so using an 8 ohm
speaker the resistance is 8+2.2 or 10.2 ohms, with peak current of
5/10 or 500mA. Average current would be (500mA * 0.7) / 2 = 175mA.
Power would be 175mA^2 * 2.2 = 67 milliwatts. 1/4 watt resistors
should be ok.

-Bill
 
On Oct 8, 7:21 pm, Bill Bowden <bper...@bowdenshobbycircuits.info>
wrote:
On Oct 7, 12:00 pm, Michael <mrdarr...@gmail.com> wrote:



I finally settled on this one:http://www.techlib.com/electronics/audioamps.html#computer

Questions:
1.  Would a 2N2222 work instead of the 2N4401?  I've got a bunch of
quad-2s in my bin.

2.  Would it be ok to substitute 1-ohm resistors for the 2.2 ohm
resistors on the speaker side, if I use a larger speaker?  I've got a
spare 4-ohm, 10W speaker from when I upgraded the car's audio system.

3.  On that note, what wattage of resistor should be chosen for the
speaker output side?  1/4W?  greater?

Thanks,

Michael

I imagine most any small NPN transistor can be used in place of the
4401. If you substitute 1 ohm resistors for the 2.2 ohm, the DC bias
current (through the TIP 31,32) will be higher since it will require
more current to get the same voltage and negative feedback to
stabilize the current. The diodes are used to produce a voltage just
enough to barely turn on the TIP 31,32. As they turn on, the voltage
rises between the two emitters due to the 4.4 ohm resistance. At some
point the current will be stable since the rising voltage produces
negative feedback and the transistors cannot further increase
conduction. If you short out the 2.2 resistors, the current may
runaway due to temperature rise. So, you might try the 1 ohm
resistors, but keep watch on the bias current as temp increases. It
may work on cold days and not so good on hot days.

The output peak voltage might be around  5 volts, so using an 8 ohm
speaker the resistance is 8+2.2 or 10.2 ohms, with peak current of
5/10 or 500mA. Average current would be (500mA * 0.7) / 2 = 175mA.
Power would be 175mA^2 * 2.2 = 67 milliwatts. 1/4 watt resistors
should be ok.

-Bill
Click to expand...

Wow, thanks for the explanation and power dissipation calcs! Much
appreciated.

Now I gotta go shopping...

Michael
 
On Oct 8, 7:21 pm, Bill Bowden <bper...@bowdenshobbycircuits.info>
wrote:
On Oct 7, 12:00 pm, Michael <mrdarr...@gmail.com> wrote:



I finally settled on this one:http://www.techlib.com/electronics/audioamps.html#computer

Questions:
1.  Would a 2N2222 work instead of the 2N4401?  I've got a bunch of
quad-2s in my bin.

2.  Would it be ok to substitute 1-ohm resistors for the 2.2 ohm
resistors on the speaker side, if I use a larger speaker?  I've got a
spare 4-ohm, 10W speaker from when I upgraded the car's audio system.

3.  On that note, what wattage of resistor should be chosen for the
speaker output side?  1/4W?  greater?

Thanks,

Michael

I imagine most any small NPN transistor can be used in place of the
4401. If you substitute 1 ohm resistors for the 2.2 ohm, the DC bias
current (through the TIP 31,32) will be higher since it will require
more current to get the same voltage and negative feedback to
stabilize the current. The diodes are used to produce a voltage just
enough to barely turn on the TIP 31,32. As they turn on, the voltage
rises between the two emitters due to the 4.4 ohm resistance. At some
point the current will be stable since the rising voltage produces
negative feedback and the transistors cannot further increase
conduction. If you short out the 2.2 resistors, the current may
runaway due to temperature rise. So, you might try the 1 ohm
resistors, but keep watch on the bias current as temp increases. It
may work on cold days and not so good on hot days.

The output peak voltage might be around  5 volts, so using an 8 ohm
speaker the resistance is 8+2.2 or 10.2 ohms, with peak current of
5/10 or 500mA. Average current would be (500mA * 0.7) / 2 = 175mA.
Power would be 175mA^2 * 2.2 = 67 milliwatts. 1/4 watt resistors
should be ok.

-Bill
Click to expand...

Say... if I use a 4 ohm speaker, are these calcs correct?

peak current I = V/R = (5V) / (4 + 2.2 ohm) = 830 mA
avg current = 830 mA * 0.707 / 2 = 293 mA
P = I^2 R = 0.19W, 1/4W resistors still ok ?

What's the reason for dividing by 2 in the second equation?

Thanks again!

Michael
 
On Oct 7, 12:00 pm, Michael <mrdarr...@gmail.com> wrote:
I finally settled on this one:http://www.techlib.com/electronics/audioamps.html#computer

Questions:
1.  Would a 2N2222 work instead of the 2N4401?  I've got a bunch of
quad-2s in my bin.
Click to expand...
Undoubtedly yes. The National Semiconductor 2N2222 and 2N4401
are both the exact same silicon chip (process 19), just in different
packages.
 
On Sat, 09 Oct 2010 10:31:54 -0700, whit3rd wrote:
On Oct 7, 12:00 pm, Michael <mrdarr...@gmail.com> wrote:

I finally settled on this
one:http://www.techlib.com/electronics/audioamps.html#computer

Questions:
1.  Would a 2N2222 work instead of the 2N4401?  I've got a bunch of
quad-2s in my bin.

Undoubtedly yes. The National Semiconductor 2N2222 and 2N4401 are both
the exact same silicon chip (process 19), just in different packages.
Click to expand...
I never knew this. For some reason, I had always thought the '4401 was
somehow more "robust" than the '2222, maybe a difference in Icmax, or
power dissipation, albeit the dissipation could be accounted for by
the package.

Now I'll go and look up both data sheets and em-bare-ass myself. ;-)

Ah! The 1N3904 is the wimpy one. :)

Thanks!
Rich
 
On Oct 8, 7:58 pm, Michael <mrdarr...@gmail.com> wrote:
On Oct 8, 7:21 pm, Bill Bowden <bper...@bowdenshobbycircuits.info
wrote:



On Oct 7, 12:00 pm, Michael <mrdarr...@gmail.com> wrote:

I finally settled on this one:http://www.techlib.com/electronics/audioamps.html#computer

Questions:
1.  Would a 2N2222 work instead of the 2N4401?  I've got a bunch of
quad-2s in my bin.

2.  Would it be ok to substitute 1-ohm resistors for the 2.2 ohm
resistors on the speaker side, if I use a larger speaker?  I've got a
spare 4-ohm, 10W speaker from when I upgraded the car's audio system.

3.  On that note, what wattage of resistor should be chosen for the
speaker output side?  1/4W?  greater?

Thanks,

Michael

I imagine most any small NPN transistor can be used in place of the
4401. If you substitute 1 ohm resistors for the 2.2 ohm, the DC bias
current (through the TIP 31,32) will be higher since it will require
more current to get the same voltage and negative feedback to
stabilize the current. The diodes are used to produce a voltage just
enough to barely turn on the TIP 31,32. As they turn on, the voltage
rises between the two emitters due to the 4.4 ohm resistance. At some
point the current will be stable since the rising voltage produces
negative feedback and the transistors cannot further increase
conduction. If you short out the 2.2 resistors, the current may
runaway due to temperature rise. So, you might try the 1 ohm
resistors, but keep watch on the bias current as temp increases. It
may work on cold days and not so good on hot days.

The output peak voltage might be around  5 volts, so using an 8 ohm
speaker the resistance is 8+2.2 or 10.2 ohms, with peak current of
5/10 or 500mA. Average current would be (500mA * 0.7) / 2 = 175mA.
Power would be 175mA^2 * 2.2 = 67 milliwatts. 1/4 watt resistors
should be ok.

-Bill

Say... if I use a 4 ohm speaker, are these calcs correct?

peak current I = V/R = (5V) / (4 + 2.2 ohm) = 830 mA
avg current = 830 mA * 0.707 / 2 = 293 mA
P = I^2 R = 0.19W, 1/4W resistors still ok ?

What's the reason for dividing by 2 in the second equation?

Thanks again!

Michael
Click to expand...
Probably ok at normal volume level. The figures are worst case and
assume the amp is driven at max output with a continuous tone. With a
4 ohm speaker at 293mA and 6 volts, the heat from the TIP 31,32 will
be .293 * 6 = 1.76 watts, so you may need small heat sinks on the
transistors if you crank the thing up for too long. But should be ok
at normal low volume. You divide by 2 since only one transistor and
resistor are conducting at the same time. They take turns on the
positive and negative half cycles, so that each is on 50% of the time.

-Bill
 
On 8/10/2010 5:00 AM, Michael wrote:
I finally settled on this one:
http://www.techlib.com/electronics/audioamps.html#computer

Questions:
1. Would a 2N2222 work instead of the 2N4401? I've got a bunch of
quad-2s in my bin.

2. Would it be ok to substitute 1-ohm resistors for the 2.2 ohm
resistors on the speaker side, if I use a larger speaker?
Click to expand...
No it will not be OK. The resistors provide thermal stability for the
output transistors. I just roughed it out, but with 1 ohm resistors, if
you pump out any decent sound you have a good chance of the whole thing
going "splat". Use the 2.2 ohm resistors AND a small heatsink for the
TIP31/TIP32

I've got a
spare 4-ohm, 10W speaker from when I upgraded the car's audio system.

3. On that note, what wattage of resistor should be chosen for the
speaker output side? 1/4W? greater?

Thanks,

Michael
Click to expand...
 
On Sat, 09 Oct 2010 13:31:52 -0700, Rich Grise <richgrise@example.net> wrote:

:On Sat, 09 Oct 2010 10:31:54 -0700, whit3rd wrote:
:> On Oct 7, 12:00 pm, Michael <mrdarr...@gmail.com> wrote:
:
:>> I finally settled on this
:>> one:http://www.techlib.com/electronics/audioamps.html#computer
:>>
:>> Questions:
:>> 1.  Would a 2N2222 work instead of the 2N4401?  I've got a bunch of
:>> quad-2s in my bin.
:>
:> Undoubtedly yes. The National Semiconductor 2N2222 and 2N4401 are both
:> the exact same silicon chip (process 19), just in different packages.
:
:I never knew this. For some reason, I had always thought the '4401 was
:somehow more "robust" than the '2222, maybe a difference in Icmax, or
:power dissipation, albeit the dissipation could be accounted for by
:the package.
:
:Now I'll go and look up both data sheets and em-bare-ass myself. ;-)
:
:Ah! The 1N3904 is the wimpy one. :)
:
:Thanks!
:Rich


.... 2N3904 perhaps...
 
On Tue, 12 Oct 2010 16:51:14 +0800, Ross Herbert wrote:
On Sat, 09 Oct 2010 13:31:52 -0700, Rich Grise <richgrise@example.net
:On Sat, 09 Oct 2010 10:31:54 -0700, whit3rd wrote:
:> On Oct 7, 12:00 pm, Michael <mrdarr...@gmail.com> wrote:
:
:>> I finally settled on this
:>> one:http://www.techlib.com/electronics/audioamps.html#computer
:
:>> Questions:
:>> 1.  Would a 2N2222 work instead of the 2N4401?  I've got a bunch of
:>> quad-2s in my bin.
:
:> Undoubtedly yes. The National Semiconductor 2N2222 and 2N4401 are
:> both the exact same silicon chip (process 19), just in different
:> packages.
:
:I never knew this. For some reason, I had always thought the '4401 was
:somehow more "robust" than the '2222, maybe a difference in Icmax, or
:power dissipation, albeit the dissipation could be accounted for by the
:package.
:
:Now I'll go and look up both data sheets and em-bare-ass myself. ;-)
:
:Ah! The 1N3904 is the wimpy one. :)

... 2N3904 perhaps...
Click to expand...
Gack! I normally proofread - guess I was in a hurry or something. :)

Thanks,
Rich
 
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