Vintage HiFi Audio Forum
Repair / Help Forum => Repair / Help => Topic started by: Jim Pittsburgh on November 06, 2013, 08:40:50 AM
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THe SDA 2A speakers require an amp with a common ground... does anyone know if a HT receiver uses a common ground?
I am using a Sony STR SH520 for the garage system.... I do not believe that HT receivers use a common ground? is there anyway to make this work?
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I have the repair manual now for the Sony STR dh520 http://elektrotanya.com/sony_str-dh520.pdf/download.html (http://elektrotanya.com/sony_str-dh520.pdf/download.html)
if someone can read them better than I can I'd appreciate it or I'd be happy to email them, if you could please take a look. It was suggested that jumping the main speakers negative terminals would work? I'm dubious and don't want to destroy either the receiver or the speakers help? thoughts?
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Look on page 17 of the service manual.
On the right hand side of the page is the schematic for the audio signal output (to loudspeakers) section.
Observe that all speaker grounds are tied to the common chassis and are not isolated from one another.
You're good to go.
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Pulled from the Polk forum...
Test it with an ohmmeter. < 1 ohm between negative terminals of opposite channels = good.
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According to this schematic, you should have an open signal between negative terminals.
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OK I borrowed a better meter... testing the ground between the two main speakers, with the dial set at 200 the reading was .8 set at 2K it read .001
am I reading it correctly? so it is a common????
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According to the schematic all negative speaker terminals are tied to chassis ground....your ohm check seems to confirm
this as well. You could try one more check. Put one lead on a NEG terminal and the other meter lead on a bare metal
spot on the receiver. This should show a <1 ohm as well. Any NEG terminal to any NEG terminal to chassis should be less
than 1 ohm.
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OK I borrowed a better meter... testing the ground between the two main speakers, with the dial set at 200 the reading was .8 set at 2K it read .001
am I reading it correctly? so it is a common????
Use the meter to test the resistance at the two negative outputs on the amp. if your reading around 1 ohm, you have a common ground amp. Most receivers are common ground.
A word of advice from a long time SDA owner, that receiver won't do those speakers justice. I would use a separate preamp/amp combo. You'll need more than 100 wpc to make them sound their best. Those speakers are around 5 to 6 ohms, most receivers don't do well with a speaker less than 8 ohms. If you have a set of preouts on your receiver, run those into a separate amp. Those Polks will sound much better.
Placement is also very important. They should be set up in an equilateral triangle, no toe in. Each speaker should be two or more feet from the side wall to sound best. The speakers should be around 6 - 10" from the wall directly behind them.
Set them up right and give them some good clean power and they will amaze you!
Good luck!
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There isn't a receiver made that isn't common ground.
As Carl indicated, those speakers are actually 4 ohm nominal and will kill that receiver given any volume.
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thanks all... your thoughts and expertise are very much appreciated..... both the education and search continue lol
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This remids me I need to add Polk SDAs to the bucket list. O0