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Checking the DC offset on Adcom 545 mkII

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Posted on October 12, 2016 at 15:11:33
gonzo
Audiophile

Posts: 2512
Location: new england
Joined: November 28, 2002
 I know I can safely turn on a solid state amp without speakers hooked up With a simple amp can you test for the DC offset with nothing plugged into it, or do you need to have a pre amp connected even though you would be testing to a non used source at the lowest volume possible. I guess I am asking, is there any kind of circuit change that occurs in the amp when the pre amp is plugged in, or can I just plug in the amp and check the speaker terminals. Norm
PS - if anyone has the owners manual for the adcom 545 mkII, I would sure love a copy. Thanks

 

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RE: Checking the DC offset on Adcom 545 mkII, posted on October 12, 2016 at 20:17:11
fredtr
Audiophile

Posts: 1987
Location: Phoenix
Joined: January 4, 2005
 Yes it is ok, you do not need anything connected to the input.

 

RE: Checking the DC offset on Adcom 545 mkII, posted on October 13, 2016 at 06:31:38
geezerrocket
 PM me with your email and I will send you the service manual.

Or, click on the link and download the top one (II).


 

RE: Checking the DC offset on Adcom 545 mkII, posted on October 13, 2016 at 07:46:22
airtime
Audiophile

Posts: 11287
Location: Arizona
Joined: February 4, 2003
 go over to hifi engine and login. A wealth of manuals and schematics for free. Sometimes it's fun to cross reference a stereo mentioned

 

Thanks guys, I checked them out, posted on October 13, 2016 at 09:59:10
gonzo
Audiophile

Posts: 2512
Location: new england
Joined: November 28, 2002
 I got 0.41 mv on one channel and 1.21 mv on the other, so I am good to go. Norm

 

RE: Thanks guys, I checked them out, posted on October 13, 2016 at 11:17:02
airtime
Audiophile

Posts: 11287
Location: Arizona
Joined: February 4, 2003
 shouldn't it be zero?

 

I think in a perfect world zero would be ideal, , posted on October 13, 2016 at 13:09:11
gonzo
Audiophile

Posts: 2512
Location: new england
Joined: November 28, 2002
 but I am guessing that these are really very good especially when you work out the formula for power the speakers see. I don't remember it now, but maybe others can chime in. There is a long thread on AK in the solid state forum , DC offset and you. Norm

 

RE: I think in a perfect world zero would be ideal, , posted on October 13, 2016 at 16:54:15
fredtr
Audiophile

Posts: 1987
Location: Phoenix
Joined: January 4, 2005
 Those readings are fine.

 

RE: I think in a perfect world zero would be ideal, , posted on October 14, 2016 at 04:56:46
JonM
Audiophile

Posts: 292
Joined: December 29, 2000
 At DC:

(P = watts, V = volts, R = ohms)

P = V^2 / R
R = 8 (typical)
V = 1.2 * 10^-3
V^2 = 1.44 * 10^-6
P = V^2 / R = 1.44 * 10^-6 / 8 = 0.18 * 10^-6 = about 1/5 of a microwatt

That will cause negligible voice coil heating and virtually zero deflection of the voice coil in the gap. Nothing to worry about.

 

We do not live in a perfect world., posted on October 14, 2016 at 15:11:03
briggs
Audiophile

Posts: 1674
Location: Connecticut
Joined: April 16, 2002
 In engineering schools there was a classic anecdote about "close enough". I think these measurements qualify.

 

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