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My 30 Watt class A is louder than my 100 Watt Class AB?

Curious observation…

I had just done some work on my DIY Hiraga 30 Watt Class A amp, and decided I would do an A/B comparison with my Adcom GFA 545.

To my great surprise, when I switched from the Hiraga to the Adcom, leaving everything else in the set up the same, and when I turned the music back on, it needed to be turned up to play at the same volume.

Input impedance is different, and I’m wondering if this is what could be causing this counter intuitive finding? Hiraga is around 33K and the Adcom around 100K.

Wondering if anyone has any thoughts as to why this is what I’m experiencing.

Thanks

 

perkri
yogiboy's avatar
yogiboy
5,700 posts
 

It has to do with the different input sensitivity (gain) of the two amps!!

perkri OP
907 posts
 

@yogiboy 

Thanks!

That was what I thought. Wasn’t until after I had listened for a bit that it dawned on me the impedance difference was the cause.

yogiboy's avatar
yogiboy
5,700 posts
 

It’s the gain difference and input sensitivity difference of the two amps!

jjss49's avatar
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jjss49
6,612 posts
 

 

perkri OP
907 posts
 

Thanks. I re read the answers, watched the video, and it’s a bit clearer now! 

Hiraga has a gain of 26db, input sensitivity TBD.

Adcom has a gain of 27db, and an input sensitivity of 1.25V

I’m going to contact the vendor for the Hiraga PC boards I bought, and see if I can find out the input sensitivity.

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