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Class A bias, speaker sensitivity, watts...?

Hello

Please help me understand the relationship between Class A bias and wattage output. I recently bought a used Vincent Audio SV236MK used for a great price. The specs state 150 watts into 8 ohms, 250 into 4 ohms, and the first 10 watts being Class A @ 8 ohms.

My speakers are Sonus Faber Lumina II which are rated as 4 Ohm with 86db sensitivity. Everything is set up in my small cube shaped office. I used a DB meter on my iPhone and found that when I turn the volume up to what I consider to be "loud" the peak measurement I get is 80db and under.

 

Given the specs above, am I hearing mostly/all Class A watts while listening?

craigvmn
tomcy6's avatar
tomcy6
2,608 posts
 

@richardbrand

Yes it would be interesting to hear from some high bias Class A/B amp builders whether their amps switch over to Class B power sooner as speaker impedance drops. Maybe I just misunderstood.

richardbrand's avatar
richardbrand
301 posts
 

@tomcy6

I've been trying to think of the physics that may be responsible.  When an AB amplifier is in Class A. the bias voltage is sufficient to accommodate the signal swings.  If the impedance of the speaker drops, more current is needed to keep the output voltage at the right level, but the current also tends to make the voltage drop.  I'll surmise that if the amplifier cannot keep up with the current demand, the bias voltage could drop sufficiently to actually reduce the Class A power.

According to Stereophile, the OP's Vincent Audio SV236MK measured 150-Watts into 8-Ohms and 231 in 4-Ohms.  It is specified at 10-Watts Class A into 8-Ohms but not specified into 4-Ohms.  Pity!

tomcy6's avatar
tomcy6
2,608 posts
 

@richardbrand

There is only one number given for Class A watts that I’ve seen, which is why it stuck with me when the guy said they dropped into 4 ohms. It’s nothing to spend your time on, If someone who knows for sure comes across this thread maybe we’ll find out, but until then, forget I mentioned it.

richardbrand's avatar
richardbrand
301 posts
 

@tomcy6 

What was it you mentioned?

invalid
1,250 posts
 

Most solid state amplifiers can double the output power when impedance is halved if well under the max power spec. Not one amplifier I have seen measured by a third party has the ability to double max power when impedance is halved (not even the big Krell amps) the 8ohm spec is usually underrated to give this illusion. 

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