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Old 11th August 2011, 04:14 AM   #1
ttan98 is offline ttan98  Australia
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Default Class A Buffer Op amp

Hi,

I need a buffer amplifier that can drive a least 2 sources, Power amp and Subwoofer amp, I have a few options one is using tubes and the other using solid state discrete/op amp.

I am asking those who have some experience in using Class A the solid state op amp, namely:

BUF634
LME49600


I remember using an old LT series unity gain op amp. I cannot remember the number. Would any recommend the above op amp and why?

Thanks.
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Old 11th August 2011, 04:57 AM   #2
kevinkr is offline kevinkr  United States
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Please do not post duplicate threads to multiple forums. Most forum participants here are active across multiple forums and if your question has any merit at all it will get answered.
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Old 11th August 2011, 05:21 AM   #3
ttan98 is offline ttan98  Australia
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The main reason for multiple thread is that similar question was ask here however I could not get my answer from reading the responses.

Anyway point taken.
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Old 11th August 2011, 05:46 AM   #4
jcx is online now jcx  United States
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most audio power amplifiers will have very high input impedance, dominated by any volume pot at the input - 50K is a common value

A output stage is Class A for a range of loads, output V for a given bias condition

to drive 2 parallel 50 K loads to 2 Vrms requires ~110 uA - many "audio" op amps will do that without external bias or buffers

for somewhat higher I requirement op amp ouputs may be biased into SE Class A by pulling on the output with a ccs or resistor to a PS rail
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Old 11th August 2011, 06:22 AM   #5
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Quote:
Originally Posted by ttan98 View Post

I remember using an old LT series unity gain op amp. I cannot remember the number.
Quite possibly LT1010. As jcx handily points out, quite unnecessary if you're just driving two normal inputs.
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Old 11th August 2011, 11:56 AM   #6
AndrewT is offline AndrewT  Scotland
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What capacitance will the source have to drive?
Cable capacitance and input filter capacitance. How big?

The capacitances are likely to require more current from the source driver than the resistive parallel Rin.
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Old 11th August 2011, 12:26 PM   #7
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Hi.My friend built a preamp by using opa627 and LME49600 in front of the F5 amplifier.And he said that he had the best preamp (he is 25 year experienced about audio and fixed thousands of preamplifiers and amplifiers)
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Old 11th August 2011, 03:54 PM   #8
jcx is online now jcx  United States
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there are reasons engineers use numbers, if you want to drive 50' of typical cable C in Class A with audio signals then you may want a few mA of bias - still easily within monolithic op amp capability with just a single bias R to a power supply

if you wwere bulding a professional distribution amp for a large studio or stage you might need 10's of mA and separate buffers become more attractive
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Old 12th August 2011, 07:50 PM   #9
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So, if I understand your question, you want to make a dual output Class A Pre-amp?
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