Monitor 10 Crossover Rebuild Question

wald0

This is some helpful info that, sadly, i neglected to take into consideration. I am looking at the Adcom GFA-555 (I don't know if you are familiar with them. They seem like a good option for me within my price range without having to spend thousands on a BAT or McIntosh setup.

Am I understanding it right though, that with more clean power, I will be able to power more louder bass because not only will the amp be able to push the driver out, but also be able to stop it from over-extending? Is that what you mean by control the drivers? Right now I think the bass is kind of sloppy. Honestly though I have never heard a very high-end set up besides at a concert or dance, but then I obviously was not analyzing things and measuring, lol. Thanks for the help. I love this forum! =D

ben62670

The GFA-555 is a great bang for the buck amp. You should be very pleased with it.

wald0

ben62670 wrote: »

The GFA-555 is a great bang for the buck amp. You should be very pleased with it.

Heh... I sent you a PM concerning possibly building me some wires >_<

Systems

wald0 wrote: »

Am I understanding it right though, that with more clean power, I will be able to power more louder bass because not only will the amp be able to push the driver out, but also be able to stop it from over-extending?Is that what you mean by control the drivers?

You might not be able to play it louder but the quality of the bass should improve with a better amplifier.The extra power should impart a greater sense of control and ease to the bass reproduction making it sound tighter and more detailed(less sloppy).

woodsman10b

ben62670 wrote: »

Hey Arron there is a lot of info here on the forum about modding the old Polk's. I use Sonicaps on the highs, and Dayton's on the lows for most of my mods. Mills resistors are used to replace the stock ones. You need to pull the XO to find the exact values of the caps, and R's. There are a lot of variations in the vintage Polk's.
Ben

Ben, or anyone with input, ive been considering this upgrade also, what Im wondering is, if I do it, do I also need to upgrade the sl1000 tweeters to notice any difference? Can you give me and idea what the differeces will be with each upgrade? If it will be a substancial difference I will upgrade the tweets as well. Any help will be appreciated.

thanx tom

F1nut

The SL1000 is a terrible tweeter. You will get a lot of mileage upgrading from it. You will get even more improvements from upgrading the crossovers.

wald0

I was also considering improving the crossovers (though it would be my first attempt). Basically my concern is if you play any kind of low frequency bass (10-30hz) it doesn't sound healthy. I know the designer purposely didn't put a high pass filter on these, but shouldn't he have at least put maybe a 12db one at around 35hz? I was running test tones from my audio editor through them to see what would happen, and I have to tell ya it's not comforting running a 20hz tone. What if I bought a sub? Would I have to put my own HPF on the 10's?

-Mike

F1nut

Unless you are playing organ music, you'll never hit anywhere close to 20Hz.

Get a better amp.

ben62670

wald0 wrote: »

I was also considering improving the crossovers (though it would be my first attempt). Basically my concern is if you play any kind of low frequency bass (10-30hz) it doesn't sound healthy. I know the designer purposely didn't put a high pass filter on these, but shouldn't he have at least put maybe a 12db one at around 35hz? I was running test tones from my audio editor through them to see what would happen, and I have to tell ya it's not comforting running a 20hz tone. What if I bought a sub? Would I have to put my own HPF on the 10's?

-Mike

You can't even hear 20hz. It is pretty much just SPL. Most people would be lucky to actually start hearing 30hz. Like F1 said you aren't going to have nearly any music under 40hz. Most subs if they listed low bass performance you would see that they start to roll off pretty hard a 35hz.
Ben

Systems

wald0 wrote: »

but shouldn't he have at least put maybe a 12db one at around 35hz?

No, because they would want to try and get the maximum bass extension they could from the design.Why would they then turn around and throw some of it away?

test tones from my audio editor through them to see what would happen, and I have to tell ya it's not comforting running a 20hz tone.

Very low frequency test tones are a brutal test and are not a realistic representation of what 98% of all music signals would demand of a speaker.

ben62670 wrote: »

Many subs if they listed low bass performance you would see that they start to roll off pretty hard a 35hz.
Ben

A slight correction:DI know of several and have some examples in my own living room that are flat into the low 20's.(but I guess DIY does'nt count).

gdb

For anyone interested in squeezing all the bass out of their 10's etc.,here's an oldie but goodie thread about bedding the drivers to effect the best seal and coupling with the baffles. Try it, you'll like it!!;)

Courtesy of Darque Knight:
http://www.polkaudio.com/forums/showthread.php?t=74524&highlight=mortite

juanbanzai

Hi All. After 8 months I'm finally getting around to rebuilding the XO in my Monitor 10s. Ben, you had replied to a post saying that I should use the Dayton DMPC-12 12uF 250V Polypropylene Capacitor from Parts-Express. I was getting ready to order these caps this morning when I noticed that the schematic calls for a 12uf electrolytic and a 12uf mylar. MY logical way of thinking put the brakes on and figured I'd better ask about that. These Dayton caps are acceptable subs for both of the original caps? Any electrolytic I've used in the past for jukebox amps have had positive and negative terminals on it. In fact, electrolytics are what's in the original XO... but according to the schematic, they are coming off the + side of the XO. I'm confused.
Thanks for taking the time to respond.

Face

Yes, that cap would work for both locations. I would avoid the use of electrolytic caps in speaker crossovers, especially the tweeter circuit.

Systems

juanbanzai wrote: »

Any electrolytic I've used in the past for jukebox amps have had positive and negative terminals on it. In fact, electrolytics are what's in the original XO... but according to the schematic, they are coming off the + side of the XO.

Electrolytic's are available in both polarized and non polarized(bi polar) varieties .The bi polar types are what are used in speaker crossovers.As Face mentioned film caps should be used in the tweeter circuit. IMO Electroltyics are OK to use in the shunt section of the low pass filter when large values are needed and space and budget are factors.

juanbanzai

Perfect! Thanks so much.

juanbanzai

Argh. I'm so darn disappointed and frustrated. I just rebuilt the crossover using Dayton and Jantzen caps, and Mills resistors. I even replaced one of the original drivers with a new one from Polk. I was shocked when I powered everything up and found that the speaker didn't sound any different! The bass still sounds flat, and at a higher volume, the speaker still clips while the original unmodified left speaker is booming away like crazy. It's almost as if the XO is being completely bypassed...but then, having never purposely bypassed an XO before, I wouldn't know for sure what that would sound like. Was I expected too much from the upgrade?

I checked and double-checked the tightness of the PR and the drivers using the "push-in on the PR" test. The cabinet is more air-tight than it ever was based on the amount of time it took the drivers to return to their "at rest" position.

Is there anything else I should be checking on the XO to try and solve this issue? I had read about bypassing the safety guard, but that won't do anything for the sound quality, will it?

Thanks again.

ben62670

What are you driving them with? What is your whole system?

juanbanzai

Hi Ben. I have a Sansui G-8000 receiver, a Technics SL-3300 turntable, an ancient Garrard turntable for playing 78s, an Audio Source EQ-8 II EQ, and an iPod with a dock. I also have a Yamaha KX-530 cassette deck and a Technics SL-P1300 CD player. The main source for ALL music played through the system is the iPod and the turntable. I play vinyl more than anything else. It doesn't matter what the source is, the results on the speaker are the same. Whether the EQ is switched out or not doesn't make a difference. With the EQ in line, I can tweak the bass response on the bad speaker using the EQ, but it just clips much sooner at higher volume and never really achieves the bass that the other speaker does. I can switch the EQ out, and run the receiver flat and that give me more room before the speaker clips. I can turn the loudness control on or off with pretty much the same results...the speaker just clips sooner rather than later.

I tried several different amps... a Sansui 9090, and Pioneer 980 and 1080 receivers. Same thing... the one Monitor 10 sounds flat and clips and a higher volume. During all of this testing, the left 10 is flawless.

The bad speaker has two brand new 6503 drivers and is really air tight. New gaskets all the way around. I'm at a loss.

What do you think? A mess?

ben62670

Where are you?

F1nut

I had read about bypassing the safety guard, but that won't do anything for the sound quality, will it?

If the polyswitch is bad, your speaker will sound lifeless. Remove the poly and replace with a jumper. Report back.

an Audio Source EQ-8 II EQ, and an iPod with a dock.

Throw that crap in the trash. Seriously.

juanbanzai

The speaker actually does sound lifeless. Completely flat. I'll try and get that out and report back later this evening. Unfortunately, the iPod has become a part of my arm. If I throw it away, I'm handicapped for life.

Ben, I'm in Buffalo, NY. Too bad...another Polk guru near by would be perfect in a case like this. It's hard to describe a "sound" problem in a forum.

ben62670

Pull the tweeters and read how many ohms they are with an ohm meter. If you are clipping you are pushing your amp to hard. Don't use the loudness control, or any tone controls. They should be set to flat.

juanbanzai

I pulled out the PolySwitch. The speaker may sound a little better, but it still doesn't have half of the "booming" bass... or better yet..."fuller" bass that the other speaker has. I don't run the EQ normally...only for listening to 78s or old vinyl from the 50s or early 60s. Most of the time, the loudness control is out and all three of the tone control are flat.

This is the thing that drives me crazy, Ben. At first I thought it was the amp that was clipping...but this same speaker sounds like crap no mater which receiver/amp I use. I tried it on 4 different ones. I know it's not safe to do this, but I can crank any one of those amps up to ear bleed levels and the left speaker will not distort or clip at all. The one I'm currently working on sounds like it's banging....like the cones are being extended way to far.

Now the dangerous extension and the clipping I understand. It's the lack of bass I don't understand. Don't get me wrong...there IS bass, but if you were to put the two speakers side by side...you'd hear all of the bass from the one speaker while the other one mostly fills in the mids and highs.

I'll pull the tweeters and measure. But I should say the the tweeter on the speaker that isn't performing well is VERY loud. In fact, that's one of the reasons I use the EQ....I keep all of the settings flat but roll off the high end because the tweeter is so obnoxious.

kcoc321

Couple of ideas:
1. What are the "other" MW's in speaker #2?
2. Did you try hooking up only one of the MW, in the "bad speaker"?
IF that doesn't show anything....
3. Since you say the "bad speaker has 2 brand new MW6503's, try swapping them out for the MW65xx's you have in the other speaker...does the issue change with the MW's or stay with the updated X-over?
4. What reading do the new MW's have? The MW6503's should read around 8ohm (from what I saw from other posters)

Just saw your post while I was posting...
Have you verified that the wiring is "in phase" I know it probably a stupid question, and I mean no disrespect, but some of the symptoms seem like "out of phase" symptoms....just a nother thought.

Good luck....sorry man

juanbanzai

Messing with the other speaker is the one thing I really don't want to do since it's performing flawlessly. I'm afraid that if I remove one of the 6503 drivers, then the air-tight characteristics of the good speaker will be lost. What I DID do was swap the new 6503s with the original ones that came with the speaker. In fact, that's what started this whole thing. I called Polk and complained about lack of bass and clipping out of this speaker...they recommended that I replace the drivers...so I did. No change. The XO update was next.

I thought about the out of phase issue too. I triple checked that. Purposely wiring them out of phase and back again. No change.

I'm still going to pull the tweeter and measure as per the last suggestion...but not until tomorrow. Thanks for all the help guys. Oh! I got a lead on another set of Monitor 10s WITH matching stands. May be picking those up tomorrow. Who knows what these ones will sound like. I still don't want to give up on this one problematic speaker though. It wouldn't be fair.

kcoc321

I can emphasize with not wanting to mess with a 'good' speaker, however it would also be a good chance to do the mortite upgrade....and just pulling out a MW is a pretty safe operation....http://www.polkaudio.com/forums/showthread.php?t=74524&highlight=mortite

IDK a better way to trouble shoot your issue without eliminating probably issues...

F1nut

At this point I think you should be looking for a bad/wrong connection on the large inductor.

Compare the known good crossover with the questionable one.

juanbanzai

I found a box of Mortite in the shop. I must have used it at one point for a jukebox restoration at some point so I'll make that modification later this afternoon. One thing I did notice is that the soldering connection to the XO board for the large inductor looked a little chaulky....as in a cold solder joint. I'm going to trace that entire thing out and see if that is indeed the case.

One thing I'm REALLY curious about now is what I mentioned earlier. What exactly would the speaker sound like if the entire XO was indeed bypassed for some bizarre reason?