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I would appreciate your help..

63.142.209.123
Posted on May 15, 2017 at 21:39:51
cloudwalker
Audiophile

Posts: 634
Location: central wa
Joined: September 27, 2012
 I will be as open as possible. I understand that many do not bother with things like this, but I still have a couple questions. I have an extra receiver (A Yamaha RX V800) which works well, and I was going to try to sell it along with some speakers I had. (I will try not to mention names where it does not matter.) I was at a thrift store and saw a JBL PSW1200 sub that looked good and the red LED indicated that it powered on, so I bought it for $40. It looks very nice, but I cannot make it work with different input methods, or the phase reversed. The driver works, but I think the amp is bad and the only fuse I could find is intact. The power supply warms appropriately when left on. I doubt that paying JBL to fix it would be worth it. You know the feeling you get with some brands when the deeper you look, the worse things look? From the outside, this thing looks good. I suspect this is one of their better products, but I am really disappointed....I was really fooled. This receiver is 5.1, and I would like to try using one of it's other amps to power the sub. Since I plan on using it with 2 speakers anyway, to keep things simple, I will try to power it with the B speaker terminals. I would like to use low pass capacitors to limit frequencies the speaker sees and need to know just what I need? And the driver only has 2 terminals, so it only has 1 voice coil. Will the volume likely be enough to help?

 

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RE: I would appreciate your help.., posted on May 15, 2017 at 22:50:21
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
 Easier said than done since that receiver does not have its own sub amp. Not sure if you can run it off the center output, it might have a high pass filter.

All capacitors are high pass, coils are low pass. You can't use them because they are likely to cause DC instability in the amp, which will cancel out and you might be totally unaware of it eating the outputs. Maybe a couple of like three ohm resistors. That makes for some power loss but should treat the amp OK. Then a cap to common, like maybe a 100 uF or something.

Or you could just connect it to one channel. I know it is not really Kosher but it beats nothing, either that or just sell it with the two speakers. Later you might be able to find a lone monoblock and power it with that. I assume you don't want to go out and get one and include it, that raises the price and one thing about private sales, the higher the price for most items, the longer they take to sell. Like we used to flip cars. Fix them and sell them, and in no case did we want anything we would have to charge more than a grand for. Today that figure would be higher, but there is still a limit. I don't need to have the thing in the drive for six months after putting a bunch of money on it. We don't do that anymore because of too many problems with the newer cars. I can handle most of them but the parts are going through the roof, and on some of them you can't even change the computer. In fact some of them you have to go to the dealer to get a new key. Too much hassle.

So you might be best off just selling it with two speakers. The sub, well maybe one of these days. If you sold a monoblock and the sub together, with something that would sum the channels if the amp doesn't have a sub out, that might sell on its own, leaving you more money.

Actually the thing seems like it would make a half decent garage stereo, provided of course that you have a real garage.

 

RE: I would appreciate your help.., posted on May 18, 2017 at 08:32:46
fredtr
Audiophile

Posts: 1987
Location: Phoenix
Joined: January 4, 2005
 Just curious, didn't understand your DC imbalance concern. I thought your suggestion of 100uF cap across the sub and running it from an unused channel would work fine. The amplifier will have volume levels for each channel so he can set the volume for the sub in relation to the mains.

 

RE: I would appreciate your help.., posted on May 19, 2017 at 16:00:18
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
 " I thought your suggestion of 100uF cap across the sub and running it from an unused channel would work fine."

That's not what I said and you can't just do that. It is a twp channel amp, and even if it did have separate amps for the B speakers you still can't do that. The cap will blow up if there is nothing to limit the current through it. Through a resistor is a different story.

Whether AC or DC, amp outputs should not be paralleled unless they are specifically designed for it, and some are but most are commercial. On a regular amp, the DC offset is controlled by feedback. If you attach what maight be a DC source or sink to the output that prevents that feedback from working, the amps work against each other leading to high dissipation in the outputs. And you might not even hear it.

 

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