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Subwoofer problem with low level connections. But high level seems to work. Low vs high?

citysoundman

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I've got a Definitive Tech PF15 sub, purchased in 1995. It has both low level RCA and high level speaker connections. I've always used the RCA connections from my Rotel preamp. I also have a Rotel power amp, which gets a separate feed from the preamp.

Yesterday after changing some stuff in my rack and disconnecting and reconnecting cables, the sub doesn't work - no audio is coming through but I hear a steady tone (60Hz?) that changes in volume as I adjust the volume pot. The tone is constant. But it goes away when nothing is connected to the RCA inputs. FYI I don't believe the subs RCA outs ever worked - I remember trying to send the signal through the sub to my amp input to try and use the sub crossover and never got an output signal so I guess there has been an issue here.

After feeling kinda dejected with the lovely thought of needing to get this beast serviced I tried the high level speaker connections and it seems to be working. That's a relief!

So I'm interested to see if anyone can help diagnose what the problem might be. Perhaps I can try and fix it if it seems doable.

And also, what's the consensus on using low-level vs high level connections? Is one preferred over the other?
 

tvrgeek

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Bad cable or bad output from the preamp. Not the sub.
Low level will likely be lower distortion, but that does not matter much on subs.
 
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citysoundman

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Bad cable or bad output from the preamp. Not the sub.
Low level will likely be lower distortion, but that does not matter much on subs.
Thanks for the reply. I tried different cables, also tried a different source (iPhone lightning headphone adapter jack, stereo mini to RCA cable, it was the most convenient thing I had) and no change in the problem.
Why do you think it isn't the sub?
 
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citysoundman

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Then a bad ground in the sub. Broke loose from boutique too tight cable maybe.
Bad ground sounds like it. If I pull the amp out do you think it's something I can probably see? like a ground cable that's loose or disconnected?
 

Slayer

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I've got a Definitive Tech PF15 sub, purchased in 1995. It has both low level RCA and high level speaker connections. I've always used the RCA connections from my Rotel preamp. I also have a Rotel power amp, which gets a separate feed from the preamp.

Yesterday after changing some stuff in my rack and disconnecting and reconnecting cables, the sub doesn't work - no audio is coming through but I hear a steady tone (60Hz?) that changes in volume as I adjust the volume pot. The tone is constant. But it goes away when nothing is connected to the RCA inputs. FYI I don't believe the subs RCA outs ever worked - I remember trying to send the signal through the sub to my amp input to try and use the sub crossover and never got an output signal so I guess there has been an issue here.

After feeling kinda dejected with the lovely thought of needing to get this beast serviced I tried the high level speaker connections and it seems to be working. That's a relief!

So I'm interested to see if anyone can help diagnose what the problem might be. Perhaps I can try and fix it if it seems doable.

And also, what's the consensus on using low-level vs high level connections? Is one preferred over the other?
Had this exact sub and your post gave me flashbacks. I had the same problems you are experiencing. Turns out it was the control board itself, they are cheap and start to crack. I replaced the entire board and within a year or so, same issues again. Also the RCA low-level inputs on that thing sucked, the input gain sensitivity was just well sh...

I ended up using the speaker high-level inputs that you are thinking about doing, and it worked ok. Although it never produced the output a 15'' should produce. Needless to say I ended up giving it away to one of my boys. He bypassed the internal amp and ran a pro amp on it.
I have some 10's today that make that one look like a useless product.
Probably not going to be the news you wanted to hear, but I wanted to be honest. By the way, the board I replaced was around 2002 or so, and it was $200 back then. So, if you're going to keep it, save your money and just use the speaker level inputs.
 
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citysoundman

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Had this exact sub and your post gave me flashbacks. I had the same problems you are experiencing. Turns out it was the control board itself, they are cheap and start to crack. I replaced the entire board and within a year or so, same issues again. Also the RCA low-level inputs on that thing sucked, the input gain sensitivity was just well sh...

I ended up using the speaker high-level inputs that you are thinking about doing, and it worked ok. Although it never produced the output a 15'' should produce. Needless to say I ended up giving it away to one of my boys. He bypassed the internal amp and ran a pro amp on it.
I have some 10's today that make that one look like a useless product.
Probably not going to be the news you wanted to hear, but I wanted to be honest. By the way, the board I replaced was around 2002 or so, and it was $200 back then. So, if you're going to keep it, save your money and just use the speaker level inputs.
Thanks very much Slayer, so deja vu huh? :D
I might end up pulling the amp out, now I'm curious to see what it looks like.
But at least the high level connections are OK.
 

raindance

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I've heard those subs do the same thing. A hum and no other audio. It's not uncommon. It's had a pretty good innings though...
 
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