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Adcom GFA-565 Slight Thump

Hello,

I recently acquired a pair of Adcom GFA-565 monoblock amplifiers which I'm using to power my Kef XQ5's. They sound really great, but there is a slight bump from the speakers (midrange) when I turn them on. Is this normal? I've read about the standard repair for a loud thump (I assume from the woofers), but I don't think I have this problem yet. Think it's time for me to perform the repair? Can I test this with a multimeter?

Thanks,
Chris
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6 responses Add your response
rcprince
3,070 posts
 
I don't know if it is normal, but the Adcom 555s that I got for my son years ago both exhibited the same behavior. Didn't seem to hurt the speakers.
tpreaves's avatar
tpreaves
2,686 posts
 
My GFA-535 Adcoms also did this on shutdown.Make sure to keep the volume low when you power down(I don't know if this helps,but it sure can't hurt!!).I think it's capacitors discharging that causes this.I might be wrong,have been before!!I asked Adcom about this thru their website but never got an answer.I guess they don't care about people with older equipment.
cdface
12 posts
 
Yep, a normal thump at turn-on (not anywhere near dangerous levels), and also usually a little pop at shutdown. Mine have had the common capacitor repair done, so it's nothing that I worry about. If I remember, I might check the DC offset later just for S&G.
hifitime
715 posts
 
I've had them do this it during shutdown on other model Adcom amps I own.I don't remember if this was supposed to be the normal,but mine sure did it.They are in a closet somewhere.I just found it on a Adcom site,and they say the same as Tpreaves said.I thought it may be the caps too but wasn't sure until now.Adcom>>[http://www.adcom.com/faqs.aspx#faq10]
pops
2,273 posts
 
Yep, what they said - mine did the same thing, no problem
jdoris
972 posts
 
Another former ADCOMer (GFA 555II) who experienced apparently harmless thumpimg. Weird glitch, tho. John
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