Class A--B amps

[Orion Man 10+ year member]

Hey guys, I am doing a system in my new Subaru and I have been searching amps. Would using a class A/B on the mids/highs make a total difference in SQ? I'm guess yes, but I thought I'd ask. The only company I have found that makes 1 is SoundStream. Any others?

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[squeak9798 5,000+ posts]

The only company I have found that makes 1 is SoundStream. Any others?

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95%+ of multi-channel amplifiers on the market are class A/B

 

[revrider1 5,000+ posts]

Almost all 2 channel and 4 channel are class A/B amps...

 

[Orion Man 10+ year member]

Ahhh, IC. Alright sorry for a stupid question. Just wasn't sure.

 

[OldSchoolBass-G 10+ year member]

Are you saying Class A Because soundstream did make a Pure Class A Amp back in tha Day.And they are excellent for SQ. IMO

 

[its_bacon12 10+ year member]

alot of companies made purely class A amps. those are pretty much purely SQ nowadays. most a/b amps today run in the B stage for the most part. the part A stage only operates up to about 1 watt because of inefficiency and noise created by the high idling current required

 

[JimJ 5,000+ posts]

Solid state Class A's are just as quiet as any other properly-built solid state topology //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Inefficient as all hell, yes...

 

[desertheat 10+ year member]

I thought monolithic was the only company to produce a proven true class A for car audio..? Mabey I am mistaken.

 

[OldSchoolBass-G 10+ year member]

nah i seem to remember a class A soundstream.Real ineffecient but real nice sound.could be wrong but ... Meh.

 

[its_bacon12 10+ year member]

Solid state Class A's are just as quiet as any other properly-built solid state topology //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
Inefficient as all hell, yes...

hmm i was moreso thinking of home audio when i posted. my bad.

 

[helotaxi 5,000+ posts]

I'm pretty sure that there were very few actual Class A amps ever made for the car. Class A driver and input stages, but the actual output stage is almost always Class A/B for the reasons of efficiency.

 

[squeak9798 5,000+ posts]

nah i seem to remember a class A soundstream.Real ineffecient but real nice sound.could be wrong but ... Meh.

They had some that were labeled "class A", but it was simply a class A/B amplifier. For example, the 50 II is labeled in their literature as being a "pure class A".....but it's idle current draw is only 1.5A. On 14.4V with that current draw, and assuming the maximum efficiency class A operation can have of 25%....that means it's limited to a maximum [under ideal conditions] "class A" power output of 5.4w (total, so 2.7w per channel). Anything above and beyond that (it's rated 25w x 2 @ 4ohm) is class B.

To my knowledge, the ONLY pure class A amplifier for car audio is the HSS Fidelity tube amplifier. Only a class A output stage.

Every other car audio amplifier labeled as "class A" has been a class A/B amplifier, some with a higher bias (such as the Tru A class amplifier).....but all of them at a certain power level will switch to class "B" operation. Monolithics included.

 

[Grinder1989 5,000+ posts]

They had some that were labeled "class A", but it was simply a class A/B amplifier. For example, the 50 II is labeled in their literature as being a "pure class A".....but it's idle current draw is only 1.5A. On 14.4V with that current draw, and assuming the maximum efficiency class A operation can have of 25%....that means it's limited to a maximum [under ideal conditions] "class A" power output of 5.4w (total, so 2.7w per channel). Anything above and beyond that (it's rated 25w x 2 @ 4ohm) is class B.
To my knowledge, the ONLY pure class A amplifier for car audio is the HSS Fidelity tube amplifier. Only a class A output stage.

Every other car audio amplifier labeled as "class A" has been a class A/B amplifier, some with a higher bias (such as the Tru A class amplifier).....but all of them at a certain power level will switch to class "B" operation. Monolithics included.

Would this explain the Helix amp that puts out 790 watts @ 2 ohms bridged? it says class A amplifier. Ampguts isn't loading up so I don't know the model number off hand.

EDIT: Helix a2 competition http://ampguts.realmofexcursion.com/Helix_A2_Competition/

 

[bonesninja 5,000+ posts]

i was under the impression that probably 99% of people couldn't tell the difference between a class d amp and a class a/b amp in a blind sound comparison in a car audio enviroment. i think i read about such a test before and the results were very inconclusive.

 

[squeak9798 5,000+ posts]

Would this explain the Helix amp that puts out 790 watts @ 2 ohms bridged? it says class A amplifier. Ampguts isn't loading up so I don't know the model number off hand.
EDIT: Helix a2 competition http://ampguts.realmofexcursion.com/Helix_A2_Competition/

I can't get the page to load, but it's definitely not a pure class A amplifier. I don't believe it's even "high biased" at all either. Just a run of the mill class A/B.

One thing to keep in mind is that in class A operation, the outputs are always on. So they will draw full current even at idle with no input signal (which is why it's easy to tell how much "class A" power an amplifier will have by looking at the idle current). Class A operation also has a maximum efficiency of 25%. So under perfect conditions (14.4V & 25% efficiency) a 790w class A amplifier would draw a constant 220A. Good luck with that electrical system //content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif