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Please help. Why would higher power amp require gain? Marantz/Adcom

Hi,

This is my first post.

I recently connected my Adcom GFA-555 to the front preouts of my Marantz SR5015. I recently had the Adcom evaluated at a reputable repair business as I’ve owned it for 30 plus years. The Adcom had a clean bill of health.
I prefer to setup my speaker gains manually with a sound meter manually with slow C weighting at 75db. I set the Front Left speaker at 0db then turn the volume up to obtain 75db.
The Marantz receiver volume required was 84 where as with the Adcom it was 88. As a result the remaining 5 speakers required a reduction in db to balance out.
Hope this makes sense.....I was expecting a lower volume number on the Marantz to obtain the same 75db, as the Adcom is rated MUCH higher wattage.

Please explain.

Newbie
volfan72
213runnin
914 posts
 
One other thing.  Any amplifier requires a certain voltage to achieve unity power.  The 555 can do 200 wpc, but it requires around 1.7 volts on its input rca jacks to do this.  At least the current 555SE needs 1.7 volts, perhaps the old 555 needs a different spec.

So the question is, what is the max voltage of the pre outs on the Marantz?  Most mid level AVR's do 1 volt max, which will not let the Adcom get to 200 wpc.  

I believe that many multi channel amp manufacturers take this into account and achieve unity power at 1 volt, not sure about the GFA 7500.
volfan72 OP
3 posts
 
Thank you for the response.

How difficult is it to determine the Marantz SR5015 Pre-Out voltage?

Also, the required voltage for my GFA-555 and GFA-7500?
213runnin
914 posts
 
I found an old review of the 555 II.  It needed 1.75 volts at the inputs to achieve full power.

Another old review of the 7500 says it needed 1.14 volts to hit 150 wpc, so that should be fine for the Marantz.

http://www.users.interport.net/a/d/adcom/gfa7500.html

https://www.kenrockwell.com/audio/adcom/gfa-555-ii.htm

The pertinent information is buried in these links, hope this helps.


volfan72 OP
3 posts
 
I now have the GFA-555 running my LR Fronts and the GFA-7500 running my Center, SLR, and SBLR.
I ran Audyssey again and then adjusted with a sound meter. Look at the gain difference between the Adcom amps. I’m thinking of moving the GFA-555 to the Surround Back LRs.
My Fronts and Center are identical NHT M7s. The Center is set at +2.0 db and the Front LRs are +7.5 db.

Maybe I’m just OCD and this is not an issue?

Thoughts?

Thanks to everyone responding!!!
213runnin
914 posts
 
My knowledge on this is by no way exhaustive, but it’s a little concerning to me that Audyssey is having to run the left and right so hot to compensate for the input sensitivity of the 555.

it might be better to have the 555 on the rear channels where less demand will be put on the marantz preout section.  Others may have additional thoughts.
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