Hello,

I have been looking around the web for a complete kit for an audio
amplifier, for a circuit that I am building that needs to have a wide,
flat as possible frequency response (0Hz - 100Khz). Need to be able to
bring 400mV up to line level. I have seen several kits based on a
LM386, but I can't find any specs that show that circuit is reliable
beyond 20hz - 20Khz. I am a beginner, so keep that in mind when
responding.

-Scott, WU2X

) writes:
Hello,

I have been looking around the web for a complete kit for an audio
amplifier, for a circuit that I am building that needs to have a wide,
flat as possible frequency response (0Hz - 100Khz). Need to be able to
bring 400mV up to line level. I have seen several kits based on a
LM386, but I can't find any specs that show that circuit is reliable
beyond 20hz - 20Khz. I am a beginner, so keep that in mind when
responding.

-Scott, WU2X

But you may be looking for the wrong thing. That's not an audio amplifier,
that's a wideband amplifier. A good op-amp is likely going to be what
you want, because line level is no more than a volt (if even that), so
a gain of about 3 is going to be enough. Of course, if you are driving
something out of the ordinary, that may require something more.

Micahel VE2BVW

This will feed a computer soundcard running at a 192Khz sampling rate
(unbalanced line level in). -Scott

On Feb 13, 12:36 pm, (Michael Black) wrote:

But you may be looking for the wrong thing. That's not an audio amplifier,
that's a wideband amplifier. A good op-amp is likely going to be what
you want, because line level is no more than a volt (if even that), so
a gain of about 3 is going to be enough. Of course, if you are driving
something out of the ordinary, that may require something more.

Micahel VE2BVW

writes:

Hello,

I have been looking around the web for a complete kit for an audio
amplifier, for a circuit that I am building that needs to have a wide,
flat as possible frequency response (0Hz - 100Khz). Need to be able to
bring 400mV up to line level. I have seen several kits based on a
LM386, but I can't find any specs that show that circuit is reliable
beyond 20hz - 20Khz. I am a beginner, so keep that in mind when
responding.

-Scott, WU2X


Who's definition of line level? For consumer audio gear, line level
is 0.1 milliwatt into 1000 ohms, or roughly 320mVrms. If your source
impeadance is sufficiently low (most gear has input impeadance in the
several-thousand ohm range), you're done.

If you need it for studio gear, then you've got to get your singal up
to 2.5 milliwatts into 600 ohms, or about 1.2 Vrms, and any of a
million op-amps can give you the gain you need to reach those levels.

The ubiquitous 741 is cheap and easy to use, but the now 40-year-old
design is kinda noisy.

I cannot imagine that a 386 would be a good match just because it's
designed for much lower output impeadance and much MUCH higher levels.

--
Lawrence Statton - m s/aba/c/g
Computer software consists of only two components: ones and
zeros, in roughly equal proportions. All that is required is to
place them into the correct order.

On 13 Feb 2007 10:29:23 -0800, wrote:

This will feed a computer soundcard running at a 192Khz sampling rate
(unbalanced line level in). -Scott

I think you'll get your best help if you ask this on
sci.electronics.design, it has a lot more traffic.

I'd definitely use a good op-amp, and definitely NOT an LM386
(single-chip audio power amp, meant to drive a small loudspeaker). The
manufacturer's page he
http://www.national.com/pf/LM/LM386.html
gives distortion as 0.2 percent, which is pretty bad by modern
standards. The soundcard and a good op-amp will surely give much
better performance.
You said in your original post you want response to DC (O Hz). All
the soundcards I've heard of are capacitively coupled, and have a
rolloff of around 5 to 10 Hz at the best, and even when this is
removed, the DC performance of such cards isn't guaranteed. It might
be better to use an "industrial" interface card such as made by
National Instruments.

On Feb 13, 12:36 pm, (Michael Black) wrote:

But you may be looking for the wrong thing. That's not an audio amplifier,
that's a wideband amplifier. A good op-amp is likely going to be what
you want, because line level is no more than a volt (if even that), so
a gain of about 3 is going to be enough. Of course, if you are driving
something out of the ordinary, that may require something more.

Micahel VE2BVW

Also, don't forget that the sampling rate of the sound card doesn't have
anything to do with the preamlifier stage that you are trying to build. A
stage that is limited to the audio range will be fine. Any of the higher end
op-amps will be fine.
The Analog Devices OP275 is a good choice, because of its fast settling
time.

Pete

"Lawrence Statton XE2/N1GAK" wrote in message
...
writes:

Hello,

I have been looking around the web for a complete kit for an audio
amplifier, for a circuit that I am building that needs to have a wide,
flat as possible frequency response (0Hz - 100Khz). Need to be able to
bring 400mV up to line level. I have seen several kits based on a
LM386, but I can't find any specs that show that circuit is reliable
beyond 20hz - 20Khz. I am a beginner, so keep that in mind when
responding.

-Scott, WU2X


Who's definition of line level? For consumer audio gear, line level
is 0.1 milliwatt into 1000 ohms, or roughly 320mVrms. If your source
impeadance is sufficiently low (most gear has input impeadance in the
several-thousand ohm range), you're done.

If you need it for studio gear, then you've got to get your singal up
to 2.5 milliwatts into 600 ohms, or about 1.2 Vrms, and any of a
million op-amps can give you the gain you need to reach those levels.

The ubiquitous 741 is cheap and easy to use, but the now 40-year-old
design is kinda noisy.

I cannot imagine that a 386 would be a good match just because it's
designed for much lower output impeadance and much MUCH higher levels.

--
Lawrence Statton - m s/aba/c/g
Computer software consists of only two components: ones and
zeros, in roughly equal proportions. All that is required is to
place them into the correct order.

wrote:
I have been looking around the web for a complete kit for an audio
amplifier, for a circuit that I am building that needs to have a wide,
flat as possible frequency response (0Hz - 100Khz). Need to be able to
bring 400mV up to line level. I have seen several kits based on a
LM386, but I can't find any specs that show that circuit is reliable
beyond 20hz - 20Khz. I am a beginner, so keep that in mind when
responding.

What exactly are you trying to do?

400mV isn't that far from line level going into a computer soundcard.
Is there a gain, volume, or full-scale adjustment you can make in
software that'll pull up the signal?

If you do need the gain, as others say a standard op-amp circuit will do
the trick. I've found the NE5534 to be a decent low-noise choice. Stay
away from the LM386; it's great if you need a bit of audio fast and
cheap, but that's about all it's good at.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

On Feb 19, 10:48 am, Doug Smith W9WI wrote:
wrote:
I have been looking around the web for a complete kit for an audio
amplifier, for a circuit that I am building that needs to have a wide,
flat as possible frequency response (0Hz - 100Khz). Need to be able to
bring 400mV up to line level. I have seen several kits based on a
LM386, but I can't find any specs that show that circuit is reliable
beyond 20hz - 20Khz. I am a beginner, so keep that in mind when
responding.

What exactly are you trying to do?

400mV isn't that far from line level going into a computer soundcard.
Is there a gain, volume, or full-scale adjustment you can make in
software that'll pull up the signal?

If you do need the gain, as others say a standard op-amp circuit will do
the trick. I've found the NE5534 to be a decent low-noise choice. Stay
away from the LM386; it's great if you need a bit of audio fast and
cheap, but that's about all it's good at.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66http://www.w9wi.com

100Khz band width seems like a lot of overkill to me to be feeding a
sound card. Several years ago I built something like is beig asked
about using and instumentation grade op amp with a bipolar emiter
follower circuit . Negative feedback to the opamp was taken at the
output of the amp. Specs on this thing was unbelievable. DC to
500khz(limit of the test equipment) with about 1.5 mv of noise. How I
dream of the days of having a bench stock like that to select parts
from again. Made a great headphone amp.

BTW, initally used a 741 in the circuit and it had about 5mv of noise.
If this OK it could still do the job for you.