Death of My Polk Audio RT 1000 P's?

[velorush]

Compared to a lot of the high-end home audio that gets discussed here, I'm sure my speakers are a pretty humble affair, but I've really enjoyed these and for a really long time. My Polk Audio RT1000P's look like this:

each with a powered 6.5" downward firing subwoofer. About a month ago, the right speaker started humming (120 Hz). I unplugged it and the humming stopped - something obviously to do with the sub amp. This past weekend the same thing happened with the left speaker. Now I'm without subs and, having been used to that kick for more than ten years, the difference is really bad.

So, experts, is this fixable? Or should I just suck it up, throw them out and buy a new set? I really like these as they 1. sound good playing music (at least to me), 2. work great as the forward L/R surround speakers in the home theater system. FWIW, the non-powered part of the speakers still sound fine.

If this is relevant: I do not have a bi-amped system (if that's the correct terminology). The frequency cutoff is handled by the speakers, themselves.

The answer may be to contact Polk Audio, with whom I have been very impressed - I contacted them years ago about a cracked base plate and they had a new one in the mail to me within days, no questions asked.

[mathman]

It is possible to buy a replacement amplifier. The amount you want to spend will determine what to get. I've been looking to replace my plate amplifier in my Samson powered sub that died. I've found two companies that make replacement amps. I don't know what the amp looks like on these but look around at parts express and search for Yung and Dayton plate amplifiers or subwoofer amplifiers.

I'm looking at this and this. They also have other amplifiers that may replace what you have at parts express.

I heard good things about the Dayton amps.

[LordOfTheThighs]

[JohnnyB]

Polk plate amp repair service on eBay; $75 per.

If you're uncomfortable with that (the vendor has 100% rating on 214 transactions), you could call around to your local repair shops and see what you turn up. It sounds like you really like your speakers. If you can repair the pair for about $172 including shipping, that's way cheaper than what it would cost for viable replacements. Aftermarket replacement plate amps would cost more, probably use a different size cutout hole, and may not be a match for gain or EQ, both of which are engineered and factory-matched on the originals.

Given that you're about 145 miles from either Memphis or Nashville, mailing them to the eBay guy is probably your most economical way to do this. However, you could call electronics repair shops in those two towns to see if anybody sounds like they'd know what they're doing. Even in that case, it would be more economical to pull the amps yourself and mail them to the repair shop. Otherwise you're looking at a total of 8+ hours driving time and 600 miles cumulative distance.

And here's another Polk plate amp repair service on eBay.

[velorush]

I saw that eBay repair service when searching for options. I'll definitely check it out. The replacement amps Mathman suggested look great, but like JohnnyB pointed out, what are the chances they would actually fit in the speakers without modification?

I did, in the interim, email and hear back from Polk Audio:

Good-afternoon Mr. Frush,
The Amp Assembly we have available for the RT1000p is the Export Model (RF0385-1) that has a Switch that goes from 110 t0 220 and they are $200.00 each + S&H.
You can order with a Credit Card or Money Order.
Please contact us at the address listed below. Most States require that you pay Sales Taxes.

Mr. Frush... $200 each seems steep to fix speakers this old. I'm not sure how long an audio speaker is supposed to last, but it probably isn't long enough to get another $400 in use out of the pair.

If I can get some time tomorrow or this weekend, I'll see if I can yank the amps out. What are the chances the problem is something I could fix? I'm pretty handy with an iron. If not, the repair service seems (so far) the best way to go.

As for really liking the speakers, I'll point out again: I'm less than fifteen miles from Skullbone Store. These speakers didn't come from WalMart which means they, despite being more than ten years old and likely not the most highly regarded speakers even when new, are likely the highest-end audio speakers in the area [excepting, of course the probability of some Yuppie's kid having a set of Klipsch in his dorm at the University in Martin].

In other words, what do I know of speakers? But yeah, they're a'ight for me!

[mathman]

Sounds like the ebay repair may be the best idea. I tried to get my subwoofer repaired locally. He wanted nearly $225.00 to repair it. They were only 270 new. The good thing is Yung has either flat or eq'ed amps so I can get a flat eq amp to closer match what I had.

[JohnnyB]

I saw that eBay repair service when searching for options. I'll definitely check it out. The replacement amps Mathman suggested look great, but like JohnnyB pointed out, what are the chances they would actually fit in the speakers without modification?

It's more than just a physical fit to the size. Some of these plate amplifiers are mono; some are stereo with the assumption that the subwoofer has two voice coils to handle both L and R channels. The Polk would have no such need as there is a single mono sub amp in each tower. Look at the difference in the Polk amp plate vs. a Parts Express Dayton:

Notice that the controls and I/Os are not the same. The Polk plate is bespoke for the crossover point, gain, and configuration of your towers' internal subwoofers. The one on the right is a general purpose one for the DIYer making his own sub to handle a stereo input signal.

If I can get some time tomorrow or this weekend, I'll see if I can yank the amps out. What are the chances the problem is something I could fix? I'm pretty handy with an iron. If not, the repair service seems (so far) the best way to go.

The problem with DIY is that you have to factor in a learning curve of unknown length. The learning curve doesn't just include the procedures for troubleshooting the amp and replacing the bad parts, it also involves finding out where you can get these replacement parts. They may not be that easy to find. This eBay guy can do it for $75 because he totally knows the routine and has parts sources. Besides, as it is, you're saving an hour or two of labor charges by removing and re-installing the plate amps yourself. I think that's enough to learn the first time out. While we're on the subject, make sure you label the ends of all the wires you disconnect so you know how to re-connect them when you get the amps back. Take pictures of the wires in place before you disconnect them.

[LordOfTheThighs]

I have an old (late '90s) JBL sub-woofer, that I got at Best Buy. Long story short ... I had to have it "repaired" (under Best Buy warranty) a few times, and it never worked right after being "fixed".

I came home from work one day, and the sub sounded like a loud arc welder, and the amp HOT as hell. Its fortunate it didn't catch on fire. The amp on it is shot, as far as I can tell.

So its been sitting in my basement, awaiting a miracle. I've looked at the Parts Express Dayton amps, but never pulled the trigger on one, for fear of buying something

that isn't exactly what I need. I replaced that JBL turd with a Velodyne sub, that has performed flawlessly, for the past dozen or so years. I'm not knocking JBL, because the rest

of my home theater speakers are JBLs, and I've been more than satisfied with them. But after researching the JBL model sub I have, the problem mine has is well documented.

[velorush]

I found the RT1000P schematics and guess what op amp it uses?

That photo isn't the RT1000P amp, it's a gut shot of my 80's TS-10 Tube Screamer. Yes, the RT1000P uses the JRC4558 op amp.

Haven't cracked open the RT1000P to see if they use the TGP-endorsed "D" variation (JRC4558D) as does the TS-10.

Interesting stuff!

Edited to add (cause I keep forgetting): great Photoshopping there, LOTT!

[HAMERMAN]

You can find a schematic here:

http://elektrotanya.com/polk_rt-1000-p_amplifier_1997_sm.pdf/download.html

If it were mine I would at least pull the amp modules and take a look at C18-C21.

[velorush]

You can find a schematic here:

http://elektrotanya.com/polk_rt-1000-p_amplifier_1997_sm.pdf/download.html

If it were mine I would at least pull the amp modules and take a look at C18-C21.

Thanks! I have the schematic PDFs at home. IIRC, they came from the Polk web site via a Polk message board (can't remember where exactly as it was a long and Googled trail...). I'll compare with the one you linked.

That's exactly what I'm thinking: I have to pull them anyway; it won't hurt for me to have a look around. Meant to do that this weekend but the son had a ball tournament.

I'm no electrical engineer. Do C18 through C21 represent some sort of area of vulnerability?

Thanks, again.

[HAMERMAN]

"Do C18 through C21 represent some sort of area of vulnerability?"

They are the (electryolytic) capacitors that are doing the bulk of the work in the power supplies. Electrolytic capacitors can dry out especially when near a heat source like C18 and C19 probably are.

[velorush]

^^^ Great insight! Thanks!

Hopefully I'll pull at least one of the amps this weekend.