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Re: [OM] [OT] Amplifier Question

Subject: Re: [OM] [OT] Amplifier Question
From: Tim Hughes <timhughes@xxxxxxxx>
Date: Wed, 2 Jun 2010 17:16:16 -0700 (PDT)
Charles, 
                good idea to check that the DC voltage across the speaker 
terminals, is well less than 1V.  
 
But,with nothing connected to speaker terminals you might still get a voltage, 
while the output capacitors charges, even though nothing is wrong.
 
 I would connect a dc voltmeter and check that the speaker volatages are less 
than 1V with nothing connected. If there is a significant voltage I would leave 
voltmeter conected and *very briefly* connect a speaker to charge any coupling 
capacitors. If the voltages do not drop then you have a problem.  If the 
voltage is low then connect up speakers properly and play your favourite music 
, preferably piano or something with single notes whre you can here if there is 
distortion.
 
I recently tried to sell a 200W Sony Amplifier in perfect condition on 
Craigslist.  Although a consumer product, this unit has a huge industrial size 
power supply transformer and heatsinks and must weigh 30+ lbs.     
 
I had no takers even at  $30. 
 
Tim Hughes
 

--- On Wed, 6/2/10, James King <jking@xxxxxxxxxxxxxx> wrote:


From: James King <jking@xxxxxxxxxxxxxx>
Subject: Re: [OM] [OT] Amplifier Question
To: "Olympus Camera Discussion" <olympus@xxxxxxxxxxxxxxxxx>
Date: Wednesday, June 2, 2010, 4:34 PM


once you have a dummy load you prabably want to measure both DC and AC 
voltage - ac for noise and DC because its bad news. A large DC offset 
positive or negative is going to supply current to the voice coils of 
the speaker and the speaker cone will not move because only an ac 
current generates a moving magnetic field and a moving magnetic field 
moves the cone. A large DC offset can fry the voice coils in the speaker 
without you hearing anything... :-(

On 02/06/2010 21:13, Charles Geilfuss wrote:
>    Given the vast experience of this group, I'm hoping one of you can answer
> a question for me. Sunday evening I was bike riding in my neighborhood.
> Since Monday is trash day people start putting things to the road for pick
> up. I noticed a pile of stereo gear at the curb and went to investigate.
> Picked up a Technics CD player and tape deck that work fine. There was also
> a Technics SE-A50 Amplifier in mint condition. It weighs as much as a Yugo
> but I managed to get it home. Alas, someone else had already taken the
> Preamp. This brings me to the question: when I power up the unit there is a
> brief pause then a click (seems normal so far). There are two small lights
> on the front; one for each channel. The left channel light glows but the
> right does not. If only the bulb is burned out then all is well and good.
> How could I simply test the unit to see if the right channel is working? Is
> it safe to put a multimeter across the speaker terminals on the back?
>
> Thanks,
> Charlie
>    



Companies Act 2006 : http://www.londonmet.ac.uk/companyinfo


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