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Biasing op amps in class A does it worth it?

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hentai

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Hi!
I've been reading about some experiments with op amps having their final stage working in class A by adding a current load from the negative supply rail to output, thus forcing the output stage to run single ended. From what i've seen most belive its a great tweak for the sound but what about the op amp is this safe? Did any of u tried it?
Thx
 
I seem to recall this been used years back on a specific opamp?, I'm SURE Audiguru will remember exactly which one? :D

Considering almost everything you play, CD's etc. will usually already have been through hundreds of opamps without any such mod it seems a total waste of time!.
 
This eliminates the cross-over distortion, but has some drawbacks. When choosing the current you must consider the characteristics of the op amp: maximum output current, maximum power dissipation and the voltage levels of the signal. Also.. the load impedance will depend on the output impedance of the current source (FET?).
I would look for low distortion op amps, but this is just my opinion.
 
hmm mb ur right but still couldn't this be used in low level preamps (like phono stages, mic preamps...) or little headphone amps? Most ppl who tried it said it brings an improvement to the sound... or its just placebo effect? :D
 
hentai said:
hmm mb ur right but still couldn't this be used in low level preamps (like phono stages, mic preamps...) or little headphone amps? Most ppl who tried it said it brings an improvement to the sound... or its just placebo effect? :D

Probably so - the only way to test it is by blind testing, which would probably show no difference.
 
The old LM324 and LM358 opamps have a high amount of crossover distortion. National Semi who invented them recommend biasing the output in class-A to eliminate the crossover distortion. A Japanese company copies them and shows curves of the amount of crossover distortion. BUZZZ!

Some audiophiles must have seen it and tried it with opamps that have only 0.00008% distortion. They think that biasing the output in class-A makes their excellent opamps have even less distortion. Ridiculous.
 

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audioguru said:
The old LM324 and LM358 opamps have a high amount of crossover distortion. National Semi who invented them recommend biasing the output in class-A to eliminate the crossover distortion. A Japanese company copies them and shows curves of the amount of crossover distortion. BUZZZ!

Some audiophiles must have seen it and tried it with opamps that have only 0.00008% distortion. They think that biasing the output in class-A makes their excellent opamps have even less distortion. Ridiculous.

Told you AudioGuru would remember the number! :D
 
Some audiophiles must have seen it and tried it with opamps that have only 0.00008% distortion. They think that biasing the output in class-A makes their excellent opamps have even less distortion. Ridiculous.
hahaha i guess ur right
 
I though low distortion op-amps always had class ! outputs anyway.
 
The old LM324 and LM358 were the first low power opamps. They made them use less current by biasing the ouput transistors in class-B. BUZZZ!

All other opamps, even newer "low power" ones bias their output transistors properly in class-AB so there is hardly any crossover distortion.
 
Keep in mind, people that love tube amps think that the distortion they impart on the signal is an improvement in sound. Acoustical perception is a very relative thing, and a very expensive industry.
 
I said low distortion not low powe and my above post did contain a typographical error. Am I right in saying that most low distortion op-amps have class A output stages?
 
Opamps don't use class-A output stages because they would melt and would have a high output impedance if they did.
They all use low impedance class-AB except for the old LM324 and LM358.
 
I know that's not true, the rail rail CMOS omps like the CA3130 have class-A output stages.
 
I forgot about the old CA3130 opamp with a Cmos class-A output stage.
With its max supply voltage of only 15V its supply current is a very high 10ma when its output is linear.
Its output has very high distortion when it drives a load and a load reduces its voltage gain.
Its output impedance is about 500 ohms.
 
cadstarsucks said:
Actually most amps you run into today in all your battery operated toys are class D.
I don't believe that. I have never seen a class D amplifier in piece of consumer electronic equipment before.
 
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