20 output distribution amp

I'm trying to build an audio distribution amp to split a 4v line level audio signal from a car cd player into about 20 outputs- I work in a store selling car audio equipment and need the distribution amp to demo power amps. I remember seeing a schematic here recently with 4 outputs- pretty simple opamp circuit. Would something simple work for as much as 20 outputs?

Thanks.

Brian.
 

millwood

Disabled Account
2003-04-22 2:21 am
US
biff584 said:
I'm trying to build an audio distribution amp to split a 4v line level audio signal from a car cd player into about 20 outputs- I work in a store selling car audio equipment and need the distribution amp to demo power amps. I remember seeing a schematic here recently with 4 outputs- pretty simple opamp circuit. Would something simple work for as much as 20 outputs?

Thanks.

Brian.


yes it would. I think either TI or National has a schematic about a distribution amp. Just make sure that you get a stable op amp at unity gain.
 

millwood

Disabled Account
2003-04-22 2:21 am
US
my understanding is that distribution amps are NOT power amps. their job is to essentially split input into many outputs, drive the signal over a reasonably long distance and terminal at a power amp (thus the name).

so you aren't going to use power amps for this.
 
Millwood, You Thought Wrong.

Typical DA's provide a means of driving multiple device inputs from one signal source.
One metod is to provide say, 20 opamps each driving an individual output, another method is to to resistively split the output of one amplifier stage that is capable of driving said 20 loads.
Resistively splitting the output from one amplifier provides guaranteed uniformity of the signal, and the resistors ensure that if one output is short circuited the remaining 19 signals are unaffected.
Normal broadcast and PA usage is one amplifier with resistive splitting.
Using an integrated power amplifier provides economical and appropriate output voltage and current capability in one package.

Eric.
 

millwood

Disabled Account
2003-04-22 2:21 am
US
biff584 said:
Thanks for the replies everyone. Can someone direct me to one of the schematics from TI, national, or some other schematic showing a resistive splitter distrubtion amp?

Thanks again.

Brian.


I am not sure exactly what "resistively" mean. I guess it is simply putting a large resistor in serial with the load and hang it to the output of an amp in parallel with other loads.

I would you will find this types of distribution amps from TI or National as it discourages the sales of their products.
 

millwood

Disabled Account
2003-04-22 2:21 am
US
Re: Millwood, You Thought Wrong.

mrfeedback said:
Typical DA's provide a means of driving multiple device inputs from one signal source.
One metod is to provide say, 20 opamps each driving an individual output, another method is to to resistively split the output of one amplifier stage that is capable of driving said 20 loads.
Resistively splitting the output from one amplifier provides guaranteed uniformity of the signal, and the resistors ensure that if one output is short circuited the remaining 19 signals are unaffected.
Normal broadcast and PA usage is one amplifier with resistive splitting.
Using an integrated power amplifier provides economical and appropriate output voltage and current capability in one package.

Eric.


Eric, I am sure that a professional audio engineer can make a DA out of a power amp if s/he had to.

But I am not sure how good that kind of a DA is.

First of all, in a typical design, the signal out of a DA is to be power amplified remotely before going into a speaker/speaker array. so what a self-respecting audio engineer wants to power amplify an attenuated signal from another power amp?

plus, it is quite difficult to find a power amp that's unity stable - I don't know one.

and if you work out the math, it is quite tough to design a resistor network that will work (reasonably well) for a large number of outputs.

BTW, no resistor network by itself will assure you of unaffected performance in case of a short in one or more channels: a amp with low / no output impedance will do that.

for the incredible price/performance ratios of op amps, it makes little sense to use one power amps vs. multiple op amps for distribution amps.

I hope DA manufacturers think the same way. But what does a dumb bank know about electronics, right? :)
 
biff584 said:
Thanks for the replies everyone. Can someone direct me to one of the schematics from TI, national, or some other schematic showing a resistive splitter distrubtion amp?


"some other schematic"
On each output place R=100-150R
 

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Re: Re: Millwood, You Thought Wrong.

millwood said:
But I am not sure how good that kind of a DA is.
[/B]

Noise figure is poor.

for the incredible price/performance ratios of op amps, it makes little sense to use one power amps vs. multiple op amps for distribution amps.[/B]

Correct. Also, DA have mostly balanced outputs, and tracking between + and - output must be very good.

I hope DA manufacturers think the same way.

True.

Regards
 

millwood

Disabled Account
2003-04-22 2:21 am
US
Re: Millwood, You Thought Wrong.

mrfeedback said:
One metod is to provide say, 20 opamps each driving an individual output, another method is to to resistively split the output of one amplifier stage that is capable of driving said 20 loads.

Eric.


Eric, I was going through another thread (the mic preamp one) where somemone mentioned Rane. Playing around their site, I found the following schematic:

http://www.lashen.com/vendors/Rane/da-26.asp

It is down towards the bottom. to my untrained eyes, it shows 6 channels each driven by its own op-amps.

Granted, I am not a sound engineer and haven't seen a distribution amp in person and you seem to be in this profession. but do you know of actual distribution amps using power amp (chip or otherwise) to resistively split the signal? I would love to know.