| Author |
Message |
Inspar8r
Guest
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 Posted:
Wed Feb 02, 2005 5:32 am Post subject:
Preamplifier design for power amp |
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Hey guys, i have another question for a project in one of my classes.
We have to design and build a power amplifier as part o fthe final
project. Now the rquirements are really basic, in fact, so basic, i
want to do more, which is encouraged.
My question is, using the 741 as an op-amp for my pre-amp circuit, can
i just daisy chain several op-amp circuits???
I want to have the process go as follows:
mono rca input>>stg 1 pre-amp>>active filter (high low and
pass, using a three way switch)>>stg 2 pre-amp>>stg3
pre-amp>>power amplifier>>speaker.
With the setup they require, there only needs to be one pre-amp, and
using a single darlington tansistor, the output power is at a mere
.5W with the pre-amp's Vcc @10V.
When chaining them up, does the output of one pre-amp feed into the
top (-) terminal of the op-amp, and the (+) side goes to ground on
all proceeding op-amps???
On the (+) side of the op-amp, we designed 2 resistors as a voltage
divider to give us 1/2Vcc, do i need to do this for all pre-amps as
well.
Hopefully you guys can follow. I want a relatively usable amplifier.
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Karl Uppiano
Guest
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| Posted:
Wed Feb 02, 2005 2:20 pm Post subject:
Re: Preamplifier design for power amp |
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"Inspar8r" <sales@mmsport.s5-dot-com.no-spam.invalid> wrote in message
news:4200118e$1_1@127.0.0.1...
| Quote: | Hey guys, i have another question for a project in one of my classes.
We have to design and build a power amplifier as part o fthe final
project. Now the rquirements are really basic, in fact, so basic, i
want to do more, which is encouraged.
My question is, using the 741 as an op-amp for my pre-amp circuit, can
i just daisy chain several op-amp circuits???
I want to have the process go as follows:
mono rca input>>stg 1 pre-amp>>active filter (high low and
pass, using a three way switch)>>stg 2 pre-amp>>stg3
pre-amp>>power amplifier>>speaker.
With the setup they require, there only needs to be one pre-amp, and
using a single darlington tansistor, the output power is at a mere
5W with the pre-amp's Vcc @10V.
When chaining them up, does the output of one pre-amp feed into the
top (-) terminal of the op-amp, and the (+) side goes to ground on
all proceeding op-amps???
On the (+) side of the op-amp, we designed 2 resistors as a voltage
divider to give us 1/2Vcc, do i need to do this for all pre-amps as
well.
Hopefully you guys can follow. I want a relatively usable amplifier.
|
If you choose something better than a 741, you might not need to chain
op-amps. I mean, a microphone or phono preamp is frequently done in a single
op-amp. What are your requirements: Gain? Bandwidth? Noise? Distortion?
What's it going to be used for? |
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Robert Baer
Guest
|
| Posted:
Wed Feb 02, 2005 3:12 pm Post subject:
Re: Preamplifier design for power amp |
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|
Karl Uppiano wrote:
| Quote: |
"Inspar8r" <sales@mmsport.s5-dot-com.no-spam.invalid> wrote in message
news:4200118e$1_1@127.0.0.1...
Hey guys, i have another question for a project in one of my classes.
We have to design and build a power amplifier as part o fthe final
project. Now the rquirements are really basic, in fact, so basic, i
want to do more, which is encouraged.
My question is, using the 741 as an op-amp for my pre-amp circuit, can
i just daisy chain several op-amp circuits???
I want to have the process go as follows:
mono rca input>>stg 1 pre-amp>>active filter (high low and
pass, using a three way switch)>>stg 2 pre-amp>>stg3
pre-amp>>power amplifier>>speaker.
With the setup they require, there only needs to be one pre-amp, and
using a single darlington tansistor, the output power is at a mere
5W with the pre-amp's Vcc @10V.
When chaining them up, does the output of one pre-amp feed into the
top (-) terminal of the op-amp, and the (+) side goes to ground on
all proceeding op-amps???
On the (+) side of the op-amp, we designed 2 resistors as a voltage
divider to give us 1/2Vcc, do i need to do this for all pre-amps as
well.
Hopefully you guys can follow. I want a relatively usable amplifier.
If you choose something better than a 741, you might not need to chain
op-amps. I mean, a microphone or phono preamp is frequently done in a single
op-amp. What are your requirements: Gain? Bandwidth? Noise? Distortion?
What's it going to be used for?
|
You can (almost) double the output voltage swing to give (almost) 4
times power capability by taking driving a follower and an inverter at
the same time.
That way, when the ouput of the follower is going positive, the output
of the inverter is going negative.
Add a current amplifier (voltage follower) like the LH0002 inside the
loop of each (output of uA741 drives the current amp and output of
current amp goes to load and feedback).
The load connects between the outputs of the two (composite) op-amps.
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SteveB
Guest
|
| Posted:
Thu Feb 03, 2005 1:21 am Post subject:
Re: Preamplifier design for power amp |
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You could use the circuit at http://www.elexp.com/t_audio.htm as a pre-amp
building block, AC coupled for no biasing problems, set the gain with R2/R1.
"Inspar8r" <sales@mmsport.s5-dot-com.no-spam.invalid> wrote in message
news:4200118e$1_1@127.0.0.1...
| Quote: | Hey guys, i have another question for a project in one of my classes.
We have to design and build a power amplifier as part o fthe final
project. Now the rquirements are really basic, in fact, so basic, i
want to do more, which is encouraged.
My question is, using the 741 as an op-amp for my pre-amp circuit, can
i just daisy chain several op-amp circuits???
I want to have the process go as follows:
mono rca input>>stg 1 pre-amp>>active filter (high low and
pass, using a three way switch)>>stg 2 pre-amp>>stg3
pre-amp>>power amplifier>>speaker.
With the setup they require, there only needs to be one pre-amp, and
using a single darlington tansistor, the output power is at a mere
5W with the pre-amp's Vcc @10V.
When chaining them up, does the output of one pre-amp feed into the
top (-) terminal of the op-amp, and the (+) side goes to ground on
all proceeding op-amps???
On the (+) side of the op-amp, we designed 2 resistors as a voltage
divider to give us 1/2Vcc, do i need to do this for all pre-amps as
well.
Hopefully you guys can follow. I want a relatively usable amplifier.
*---------------------------------*
Posted at: http://www.GroupSrv.com
*---------------------------------*
Posted Via Usenet.com Premium Usenet Newsgroup Services
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Inspar8r
Guest
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| Posted:
Thu Feb 03, 2005 2:31 am Post subject:
Re: Preamplifier design for power amp |
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| Quote: | Karl Uppianowrote:
If you choose something better than a 741, you might not need to |
chain
| Quote: | op-amps. I mean, a microphone or phono preamp is frequently done in
a single
op-amp. What are your requirements: Gain? Bandwidth? Noise?
Distortion?
What's it going to be used for?
|
IT's for a audio amplifier that we are building, but it's only to
learn the aspects of the amplifier design. I'm a bit advanced in the
class, so instead of just meeting the basics, i want to build and
amplifier that has USABLE power, not .5W, but has a similar circuitry
to the requirements.
The basic requirements is a regulated Power supply that has 10V
output, a power amplifier that utilizes a Darlington TIP120
transistor, and a pre-amp that uses a 741 inverting op-amp...
I found a op-amp IC that has 4 op-amps in one chip (LM148/248/348),
and my plan was to have 3 stages of pre-amplification.
1st stage- Pre-amp
2nd stage- pass-through/active high pass filter/active low pass
filter
determined by a 3 way switch
3rd stage- Pre-amp
I have the circuit drawn out that i have planned, if you want me to
scan it. The filters are first order active filters.
Thanks for the help guys.
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Dope mcSmoke
Guest
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| Posted:
Thu Feb 03, 2005 4:57 am Post subject:
Re: Preamplifier design for power amp |
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| Quote: |
I have the circuit drawn out that i have planned, if you want me to
scan it. The filters are first order active filters.
|
Active filters are at least 2nd order. |
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Inspar8r
Guest
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| Posted:
Fri Feb 04, 2005 12:28 pm Post subject:
Re: Preamplifier design for power amp |
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| Quote: | Dope mcSmokewrote:
[quote:e998840fcd]
I have the circuit drawn out that i have planned, if you want me to
scan it. The filters are first order active filters.
Active filters are at least 2nd order.[/quote:e998840fcd] |
Maybe an ideal design, yes, but not in general... The order depends on
the number of reactive elements in the circuit.
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Dope mcSmoke
Guest
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| Posted:
Mon Feb 07, 2005 5:39 am Post subject:
Re: Preamplifier design for power amp |
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|
"Inspar8r" <sales@mmsport.s5-dot-com.no-spam.invalid> skrev i meddelandet
news:42031615$1_1@127.0.0.1...
| Quote: | Dope mcSmokewrote:
[quote:e998840fcd]
I have the circuit drawn out that i have planned, if you want me to
scan it. The filters are first order active filters.
Active filters are at least 2nd order.[/quote:e998840fcd]
Maybe an ideal design, yes, but not in general... The order depends on
the number of reactive elements in the circuit.
|
Yes, but If you only have 1 reactive component i would call it a passive
filter and an amplifier.. |
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Dope mcSmoke
Guest
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| Posted:
Wed Feb 09, 2005 6:27 pm Post subject:
Re: Preamplifier design for power amp |
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To make myelf clear. With a first order filter, what you mean is a plain R-C
link, either lowpass or highpass. IF you build a filter wih an OP-amp you
can build either a first order Bandpass filter or a second order
Low-/Highpass, What you describe seems to me like a RC-filter and an
amplifier, so if it is, check out Sallen-Key and if it isn't, sorry for
misunderstanding..
/Johan
"Dope mcSmoke" <dope@mc.smoke> skrev i meddelandet
news:TUxNd.16651$d5.135453@newsb.telia.net...
| Quote: |
"Inspar8r" <sales@mmsport.s5-dot-com.no-spam.invalid> skrev i meddelandet
news:42031615$1_1@127.0.0.1...
Dope mcSmokewrote:
[quote:e998840fcd]
I have the circuit drawn out that i have planned, if you want me to
scan it. The filters are first order active filters.
Active filters are at least 2nd order.[/quote:e998840fcd]
Maybe an ideal design, yes, but not in general... The order depends on
the number of reactive elements in the circuit.
Yes, but If you only have 1 reactive component i would call it a passive
filter and an amplifier..
|
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Inspar8r
Guest
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| Posted:
Fri Feb 11, 2005 5:40 am Post subject:
re:Preamplifier design for power amp |
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Well,
I'm going to dump the filters, because I am having a hard time giving
the filters (the lowpass in particular) initial bias without
affecting the cutoff point.
So I'm dumping them.
My problem now is, my 2 stage pre-amp is not working. I have a gain of
10 on the first pre-amp, with a 200mV input, and the second stage
isn't giving any gain. I have the Feedback resistor on the second
stage as a potentiometer for volume control, and the waves are all
messed up.
Keep in mind the op-amps are in single supply config as well.
Isn't daising chaining pre-amps the best way to get a decent ouput on
a power amplifier???
My power amp is just a simple class AB push pull config with a couple
darlingtons.
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Dope mcSmoke
Guest
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| Posted:
Fri Feb 11, 2005 5:53 am Post subject:
Re: re:Preamplifier design for power amp |
|
|
"Inspar8r" <sales@mmsport.s5-dot-com.no-spam.invalid> skrev i meddelandet
news:420bf0d3$1_2@127.0.0.1...
| Quote: | Well,
I'm going to dump the filters, because I am having a hard time giving
the filters (the lowpass in particular) initial bias without
affecting the cutoff point.
So I'm dumping them.
|
What kind of filter are you using? it wouldn't be too hard to give them a
bias voltage from half V+ through a large resistor. Anyway, you can always
use passive filters and boost the signal later (earlier?) in the chain.
| Quote: |
My problem now is, my 2 stage pre-amp is not working. I have a gain of
10 on the first pre-amp, with a 200mV input, and the second stage
isn't giving any gain. I have the Feedback resistor on the second
stage as a potentiometer for volume control, and the waves are all
messed up.
Keep in mind the op-amps are in single supply config as well.
Isn't daising chaining pre-amps the best way to get a decent ouput on
a power amplifier???
|
If you post a schematic someone can probably find what's wrong. What voltage
are you driving the power transistors with?
/Johan |
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