On Sat, 22 Apr 2017 18:56:51 -0700, Jeff Liebermann <
je...@cruzio.com>
wrote:
>On Sat, 22 Apr 2017 08:21:01 -0500, Foxs Mercantile <
jda...@att.net>
>wrote:
>
>>On 4/22/2017 1:54 AM, Phil Allison wrote:
>>> The amp uses bridge mode output - right ?
>>> So both speaker terminals are amp outputs.
>
>>I'm going to go with this as the correct answer.
>>The audio output of a Motorola Spectra is like this, and
>>there are warnings repeatedly through the service manual
>>NOT to ground either side of the audio.
>>
>>This has nothing to do with "hot chassis" or floating
>>grounds.
>
>I just hate to agree with you, but y're right. Nobody builds AC-DC
>transformerless radios and audio amps these daze.
>
>It's probably a bridge amp:
><
https://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers>
>That looks like this:
><
https://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers#/media/File:Bridge_amp.GIF>
>Notice that neither speaker wire is grounded.
>
>If you want to look at the output of a bridge amp with a scope, you
>need to have a scope with an A-B (that's channel A minus channel B)
>input. Connect one probe each from each scope channel to each speaker
>lead. Connect both scope ground leads to ground.
You're right. First off, it has a power transformer.
Secondly it is an amp made to be bridged. After reading the user manual
a second time, I determined that this floating ground is only needed in
Bridge mode.
I have never had an amp that was bridgable (that I know of anyhow). I
dont think this is possible with the old tube amps, but I could be
wrong. This amp is a solid state, with power transistors (not chips for
the output). 16 power transistors to be exact.
Although I like tube amps, I could not pass this amp up for the price he
wanted. It's rated at 300W per channel using 4ohm speaker load, or 200W
per channel using 8 ohm speakers. Or it's brigable to be a 600W mono
amp. I'm gonna have fun with this thing....
It's a Altec Lansing 9444A power amp. It appears it was made around 1988
to 1990.
And Altec Lansing is top of the line equipment.
This is a commercial amp, with balanced XLR inputs, so I will have to
buy or make some adaptors so I can connect 1/4" or RCA jacks to it for
home use. But I know that my speakers wont handle that full power
either, but I suppose I dont have to run it wide open either....