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Input impedance for Adcom GFA 555?

I’ve owned a pair of these amps since I bought them in the late 80s and now I’m adding a Vandersteen 2WQ subwoofer and to set the crossover I need to know the input impedance of the power amps. A couple Google searches lead me to an impass because I see both 100K ohms and 22K ohms listed. Note this is the original GFA555. Can anyone out there help me confirm the actual value? Thank you.

cantarkus
erik_squires
16,146 posts
 

For most solid state 50k to 25k is more common.

Try the low impedance setting. If you hear no change at all when using the crossover use the higher value.

Also, what are your main speakers?  If they are ported it may help to plug the port before configuring the sub.

joenies's avatar
joenies
258 posts
 

Greetings 

Per a Stereophile review of the GFA-555 they list it at 22K. 
Not sure if Adcom is still in business. It would be best to call them.

Joe Nies

cantarkus OP
7 posts
 

Thanks guys! Adcom is definitely still in business so that is a sound recommendation. As far as main speakers, I have Vandersteen 3A’s.

erik_squires
16,146 posts
 

OP: Ok, sealed then!

You might also want to look at the AM Acoustics room mode simulator.  Try to keep your speakers, subs and listening location out of the way of the bottom most room modes.

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