Help! Newb here - rebuilding my first crossovers from Monitor 75T's
machine
Posts: 36
Hello all! As the title states, I am rebuilding /upgrading the crossovers in a pair of 75T's I've owned since 2013. They've only ever been driven by a Marantz SR6005, so power quality has been fairly clean. Overall, I've loved them through the years, but noticed the mids and highs have been severely lacking as of late. Turns out - the highs are barely audible and mids are pretty muffled. Went the exploratory route and removed the crossovers and performed some basic troubleshooting, just to find the common culprits are bad/going bad and the glue is a bit bubbly indicating overheating. From the first one I tested, I physically removed the ceramic resistors from the board and the 5W 7.5Ohm resistor reads about 0.9 Ohms and the 10W 5.7Ohm one reads about 6 ohms. I plan on replacing those with ones having a slightly higher power rating (8W and 12W respectively), but from what I see those exact resistor specs will be hard to come by. In addition, I will be upgrading the caps to Mills Foil film Caps (is this correct? from what I've read here, these are a good choice). That being said, my goal is to rebuild these and raise the lower Hz limit on the drivers to around 70Hz since I have a decent sub. I drew a schematic of what I believe is correct - please correct me if this is wrong.
So, my question for you audiophiles is what spec resistors and Caps should I obtain to raise the lower limit frequency to around 70Hz (or is that more of an inductor controlled thing?) and if I cant find the exact resistor Ohms, should I round up or down - and same for the farads on the caps? Id like to remain under $100 if i can, unless there are some magical specs and parts that will really make a difference in these. Thanks in advance!
So, my question for you audiophiles is what spec resistors and Caps should I obtain to raise the lower limit frequency to around 70Hz (or is that more of an inductor controlled thing?) and if I cant find the exact resistor Ohms, should I round up or down - and same for the farads on the caps? Id like to remain under $100 if i can, unless there are some magical specs and parts that will really make a difference in these. Thanks in advance!
Comments
-
Well, not trying to be negative but crossover design/redesign is definitely something for the experienced and requires the proper measurement equipment to accomplish real world because mathematical models are only approximations. Why not try using the crossover that is probably built into your sub first? Room acoustics have a huge effect upon bass response too. You may find a setting on your sub that helps your response without even needing to use any built in high pass crossover.George / NJ
Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Onkyo A-8017 integrated
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform -
Change caps and resistors, forget trying to redesign the wheel. That being said the new caps will be physically larger than stock UNLESS you are going to use the same type of caps (electrolytic). I believe that is the only way you'll stay under $100. I'd personally raise your budget and find some cheap polypropylene caps and go from there. Clarity makes some good ones, I believe they may be the PX series. I hate to recommend Dayton but in your budget that may be the only option. Yes you may need to go one way or the other close to the value. Remember the old caps may have been +/- 10% of the value so as long as you stay +/- 3-5 % you should be good. There are also much better resistors than the ceramic/sandcast garbage for a few dollars more that are tons better.
-
Unless I misread, I'm with Gardenstater on this. I don't enjoy pulling the ''Whoa there!' card, but that was my thought when I read through the first time.
I think with rebuilt crossovers to original spec with better parts, they'll mesh with your sub on the low end nicely.The Thrifty Setups in Mah House Big thrifty stereo in the basement w/ my custom SDA-1C (built with help from kind forum members) * Beautiful 1966 MCM GE console upgraded w/ Bluetooth, Dual turntable, and Paradigm speakers in family room * Swanky 1980 Realistic system and great TEAC eq with dancing colored lights in the living room * custom 5B on a system for my Dad * Ye Olde college stereo in the garage -
Gardenstater wrote: »Well, not trying to be negative but crossover design/redesign is definitely something for the experienced and requires the proper measurement equipment to accomplish real world because mathematical models are only approximations. Why not try using the crossover that is probably built into your sub first? Room acoustics have a huge effect upon bass response too. You may find a setting on your sub that helps your response without even needing to use any built in high pass crossover.
No worries, I didnt know if modifying the HPF could be easily modified by changing specs on the resistors and caps or if someone here has done it before. Im fine keeping them the same. I would rather increase sound quality if anything, so if it makes a big difference, I can spend a reasonable amount of coin upgrading the resistors and caps. I would say Id like to keep it under $80-100 for each X-over. I dont need the most expensive top of the line brands, just a decent mid-upper mid quality brands would suffice. I just dont know anything about the individual brand names.
As for the Sub - there are no outputs on it. Just a pair of RCA inputs. There is a built in Xover in the receiver though, which is fine. -
Will be interesting to see what you do for the 200uF caps.Don't take experimental gene therapies from known eugenicists.
-
-
Do the 200uf caps typically need replacing? -
I also noticed the schematics for the Monitor 70 speakers are wired the same way using similarly spec'd components, aside from the 200uf cap. the 70's use a 10uf cap. Does anyone know what using different cap would change in the 75T's?
-
If you can find them, Erse makes a PulseX 100uf propylene cap that you could double-up on and then like Pittdogg said, Clarity PX in the tweeter circuit.Don't take experimental gene therapies from known eugenicists.
-
Change caps and resistors, forget trying to redesign the wheel. That being said the new caps will be physically larger than stock UNLESS you are going to use the same type of caps (electrolytic). I believe that is the only way you'll stay under $100. I'd personally raise your budget and find some cheap polypropylene caps and go from there. Clarity makes some good ones, I believe they may be the PX series. I hate to recommend Dayton but in your budget that may be the only option. Yes you may need to go one way or the other close to the value. Remember the old caps may have been +/- 10% of the value so as long as you stay +/- 3-5 % you should be good. There are also much better resistors than the ceramic/sandcast garbage for a few dollars more that are tons better.
Okay, I'll look into Clarity caps. Thanks for the advice!
-
Sonic Craft has a 7.5 ohm 10 watt Mills, a 5.6 ohm 10 watt Mills.
Solen offers a 200uF 400V cap. It's a big cap. I generally don't suggest this, but you could replace with an electrolytic to save money and for space.
That "small cap?" on your schematic is likely a bypass cap. Is it dark brown?Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Sonic Craft has a 7.5 ohm 10 watt Mills, a 5.6 ohm 10 watt Mills.
Solen offers a 200uF 400V cap. It's a big cap. I generally don't suggest this, but you could replace with an electrolytic to save money and for space.
That "small cap?" on your schematic is likely a bypass cap. Is it dark brown?
Yes, its a bypass cap. I was advised to remove it and just use 1 good 9.1 film cap in its place. As for the Large cap, I may run 2 100uf film caps in parallel if I can find them for a reasonable price.
Right now I am looking at replacing the one 200uf cap with 2 SuperTech MDT 100uf film caps depending if they can be ordered with longer leads or not. -
Sonic Craft has a 7.5 ohm 10 watt Mills, a 5.6 ohm 10 watt Mills.
Solen offers a 200uF 400V cap. It's a big cap. I generally don't suggest this, but you could replace with an electrolytic to save money and for space.
That "small cap?" on your schematic is likely a bypass cap. Is it dark brown?
Yes, its a bypass cap. I was advised to remove it and just use 1 good 9.1 film cap in its place. As for the Large cap, I may run 2 100uf film caps in parallel if I can find them for a reasonable price.
Right now I am looking at replacing the one 200uf cap with 2 SuperTech MDT 100uf film caps depending if they can be ordered with longer leads or not.
Is the original cap a 9.1uF or a 9? I suspect it is a 9 as 9.1 is not a common value. If someone told you to use a 9.1 to make up for removing the bypass cap, ignore that advice.
You can add a piece of copper wire (solid) to any cap lead. Make a dog leg joint and solder the joint.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Sonic Craft has a 7.5 ohm 10 watt Mills, a 5.6 ohm 10 watt Mills.
Solen offers a 200uF 400V cap. It's a big cap. I generally don't suggest this, but you could replace with an electrolytic to save money and for space.
That "small cap?" on your schematic is likely a bypass cap. Is it dark brown?
Yes, its a bypass cap. I was advised to remove it and just use 1 good 9.1 film cap in its place. As for the Large cap, I may run 2 100uf film caps in parallel if I can find them for a reasonable price.
Right now I am looking at replacing the one 200uf cap with 2 SuperTech MDT 100uf film caps depending if they can be ordered with longer leads or not.
Is the original cap a 9.1uF or a 9? I suspect it is a 9 as 9.1 is not a common value. If someone told you to use a 9.1 to make up for removing the bypass cap, ignore that advice.
You can add a piece of copper wire (solid) to any cap lead. Make a dog leg joint and solder the joint.
Yes, its 100% a 9.1uf, and i've actually come across a few of them. Odd. -
Odd indeed. Good luck finding a film cap of the value. Just use a 9uF with a tight tolerance. Your original is likely +/- 10%, but +/- 20% isn't uncommon.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Researching what you guys have suggested, I will be going with a CSA-9.1 Film cap for the tweets, and a high-end Electrolytic for the lows, I'm thinking a Mundorf 220uF 450Vdc MLytic® HV. As for a resistors I will go with mundorfs as well. Anyone have any opinion regards Mundorf components?
-
I see that Parts Connexion doesn't carry a CSA 9.1uF, but Madisound does...odd.
I wouldn't use Mundorf resistors.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
So far, I ordered Dayton Audio wirewound resistors and a 9.1uF Solen Film cap for the highs. For now, I am using a higher end electrolytic cap for the LPF, and I plan to toss the small ceramic bypass cap on the HPF. I would imagine this setup at least or as good as OEM. With that said, I will eventually order a 200uF Solen film cap for the LPF and install it in one speaker and see if I notice any difference. Ill post my findings after everything is installed, and maybe create a DIY write up since I'm sure I'm not the only one that has experienced this and couldnt find much of anything related to a crossover upgrade for the 75T's.
-
Solens in that high pass, OUCH!
Solen in the low end is fine Solen in the high pass is very hard on the ears.
I fail to understand thisI would imagine this setup at least or as good as OEM.
The whole point of doing XO work is to better the speaker. The company had already made huge concessions in cost to bring it to market to begin with. Better XO components can and do "elevate" a mediocre speaker to a much more pleasent speaker to listen to, better bass, midrange and pin point highs where you can now discern each individual cymble instead of every cymble sounding the same.
Honestly if you wanted "JUST" as good then you sould have just bought the same that was in it to begin with.
I just have to shake my head at times. Many new members come here to ask advice, we have many members here who have done many many crossovers and know what works very good at each price point. Some can and do throw out the board and do point to point XO's instead of board work on the original board.
90% of the time the original OP will then go nope THIS is what I'm going to do!
Honestly it gets frustrating.
How much difference in cost was there between the Clarity PX and the Solen ? It may actually been the same price and the 400V rating it will be very large (verses 200v) and may be hard to accommodate on the board.
Post edited by pitdogg2 on -
Never use a Solen in the high pass and never use a bypass when upgrading to film caps.
Finally, never ignore the advice given by experienced people.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Sorry, I didnt know that Solens where a definitive no on the HPF. Let me clarify a little about the bypass cap - I am tossing it - as in not using it. I will get a Clarity Film for the HPF then. Just curious, whats the issue with Solens in the HPF?Solens in that high pass, OUCH!
Solen in the low end is fine Solen in the high pass is very hard on the ears.
I fail to understand thisI would imagine this setup at least or as good as OEM.
The whole point of doing XO work is to better the speaker. The company had already made huge concessions in cost to bring it to market to begin with. Better XO components can and do "elevate" a mediocre speaker to a much more pleasent speaker to listen to, better bass, midrange and pin point highs where you can now discern each individual cymble instead of every cymble sounding the same.
Honestly if you wanted "JUST" as good then you sould have just bought the same that was in it to begin with.
I just have to shake my head at times. Many new members come here to ask advice, we have many members here who have done many many crossovers and know what works very good at each price point. Some can and do throw out the board and do point to point XO's instead of board work on the original board.
90% of the time the original OP will then go nope THIS is what I'm going to do!
Honestly it gets frustrating.
How much difference in cost was there between the Clarity PX and the Solen ? It may actually been the same price and the 400V rating it will be very large (verses 200v) and may be hard to accommodate on the board.
I am planning on making a complete new boards with high end components eventually, but for now I am in the learning and research phase. The speakers are torn apart right now and I just need to get them going again ASAP until I can make new crossovers. I drew up the schematic and now my intent is to build some complete new boards with all the better components. What are the better caps for use in the HPF? The ClarityCap CSA CopperConnect Poly Caps or the Clarity PX line? I saw the PX line was half the price. -
CSA is definitely better than the PX. It is the most recent line afaik. The CSA is only about $20 more for the pair, vs the Solens and will be smaller being 250V vs 400V.
Point to Point will let you do pretty much whatever you want in the future. You could go with $10K Duelunds lol.George / NJ
Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Onkyo A-8017 integrated
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform -
Solen in high pass is fingernails on a chalkboard.
-
Solen in high pass is fingernails on a chalkboard.
Thank you for pointing out that red flag. Didn’t realize that even with the exact same spec, they would sound much different. Clarity CSA it is!
So, that being said, does anyone have a schematic of a homemade Xover that would really make these 75T’s wake up? Or should I just follow the same OEM schematic? I can spend around $150ea on my first home built ones if that can be done.
Thanks for your input and guidance everyone! -
Stick with the original topology.
Honestly, you would be wasting money investing in high end components for those speakers. My advice would be save your money and put it towards speakers that are better from the start. That's not to say those better speakers from the start wouldn't benefit from better crossover components, they would, but you can only squeeze so much out of a budget speaker such as the 75T.
Edit: I'm not saying you shouldn't do what you are currently planning, by all means go for it, but leave it at that.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Well, figured out that both tweeters are shot, open loop between both terminals. Any recommendations on a decent replacement? Even if these are available, Id rather use an upgraded one if possible.
-
Time to buy new speakers. Look at the Reserve series, way better than yours ever could be.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Nah, not an option right now. These belong to the 2nd 7.1 system in the house. Id rather spend a few hours routing out a different hole and making a new tweeter fit. We a buying a new house in a couple years, then the R700's will be the new ones. just need something until then.
-
You can't just slap in a different tweeter. They all have different parameters and without knowing those of the original you are shooting in the dark.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk
