Monitor 11 Upgrade/Restoration
Livinloud
Posts: 43
I have jumped into an upgrade/restoration of a pair of Monitor 11’s. Not the early 80’s RTA 11 variant. The late 80’s Monitor 11’s that I am working with essentially came with the same crossover as the Monitor 10b. I have yet to be able to confirm the inductor values but the capacitor and resistor values appear the same. The mw drivers on this model are the 6510’s.
The first step I took in the midst of getting to know these speakers was to epoxy the magnets on the mid drivers. This is a know issue with tons of information so I will refrain from getting into it here.
While originally staying up late, reading and listening to music I heard the highs on the speakers degrade over a few hours. Playing soft piano tunes with lots of space for notes and reverb to decay gave the ability to hear distortion on the high end with certain frequencies. I was running from a Pioneer SA-8500 integrated amp that has yet to have the tone board serviced with quieter transistors and addressing potentially bad caps. Thinking the distortion could be a source issue I hooked up to my Denon receiver and had the same result so I ruled out the source.
Because I believe I perceived it getting worse I was inclined to think it may be crossover issues. Hard for me to tell. Parts were ordered to upgrade the crossovers!
At this point I was speculating they sounded very similar to 10’s but I have never heard a 10 to compare. The low end was not as present as I would think which may be a cap issue as well? It was there, but was not at all boomy and some have described the lows on the 10b. It just could’ve been more from my subjective evaluation. Eventually I moved the speakers closer to the wall which brought some of the lows out. It may be that I am just more accustomed to the accentuated lows from closer wall proximity. The mids are nice. Overall I liked the sound at this point and speculated it could improve from here.
Cap Upgrade:
I order capacitors and when they showed I had the opportunity to open one up on my lunch break and recap it. That was fun! One down, one to go. Only got to listen to it for about 5 minutes. I bypassed the poly switch. I knew I could add a low value resistor if the details were too bright. From my short listen, I did not hear the breakup I had previously heard from the sl2000 on the recapped side. I do think the majority of the distortion I was hearing was the poly switch because I no longer heard it to the same extent. I did hear the harshness of the 13k spike though and this was the range that still seemed to break up a bit. I also had previously perceived the speaker had a noticeable volume drop previously and that was definitely gone.
Some more details on the recap. I used Sonicap and Audyn Q4 caps and a Dayton Precision Resistor on the High Shunt with Mills Resistors on the rest but more on that in a bit.
Listened some more. And compared the recapped speaker to the original crossover. I quickly ordered the Rd-0194’s, the tweeter’s were just not quite right. I shortly jumped into the recap of the second crossover.
Poly Switch:
During this process I wanted to hear the speaker with the Poly Switch bypassed without any adjustments to evaluate the differences. With no Poly Switch and no additional value changes I was hearing sibilance that was forward in the mix. It was not off putting but some of the sibilance I was hearing very well may have been from the extra brightness of not increasing the resistance.
Resistor Upgrade:
Ultimately I decided I wanted to tame the highs a bit. I was faced with the decision to up the value of the 2ohm cap bypass resistor or simply install a .5Ohm resistor in its place to compensate for the resulting resistance decrease in the circuit. I decided to add the .5ohm resistor and use a mills 2ohm value to keep the contour original.
Resistors were then installed… was pretty quick and easy at about 10 minutes per speaker. At this point highs just sat back into the mix a hair better. It was not a drastic difference at all, just a slightly smoother sound. I couldn’t wait for the new tweets as the slight distorted sound of the sl2000’s at certain frequencies was hard to ignore.
New tweeters installed… they do not seat perfectly in the routed cavity. They are about 1/32 of an inch taller than the cavity. Considering my options…
On the sound front, the speakers are beautifully balanced! Very easy listening with no fatigue!
The first step I took in the midst of getting to know these speakers was to epoxy the magnets on the mid drivers. This is a know issue with tons of information so I will refrain from getting into it here.
While originally staying up late, reading and listening to music I heard the highs on the speakers degrade over a few hours. Playing soft piano tunes with lots of space for notes and reverb to decay gave the ability to hear distortion on the high end with certain frequencies. I was running from a Pioneer SA-8500 integrated amp that has yet to have the tone board serviced with quieter transistors and addressing potentially bad caps. Thinking the distortion could be a source issue I hooked up to my Denon receiver and had the same result so I ruled out the source.
Because I believe I perceived it getting worse I was inclined to think it may be crossover issues. Hard for me to tell. Parts were ordered to upgrade the crossovers!
At this point I was speculating they sounded very similar to 10’s but I have never heard a 10 to compare. The low end was not as present as I would think which may be a cap issue as well? It was there, but was not at all boomy and some have described the lows on the 10b. It just could’ve been more from my subjective evaluation. Eventually I moved the speakers closer to the wall which brought some of the lows out. It may be that I am just more accustomed to the accentuated lows from closer wall proximity. The mids are nice. Overall I liked the sound at this point and speculated it could improve from here.
Cap Upgrade:
I order capacitors and when they showed I had the opportunity to open one up on my lunch break and recap it. That was fun! One down, one to go. Only got to listen to it for about 5 minutes. I bypassed the poly switch. I knew I could add a low value resistor if the details were too bright. From my short listen, I did not hear the breakup I had previously heard from the sl2000 on the recapped side. I do think the majority of the distortion I was hearing was the poly switch because I no longer heard it to the same extent. I did hear the harshness of the 13k spike though and this was the range that still seemed to break up a bit. I also had previously perceived the speaker had a noticeable volume drop previously and that was definitely gone.
Some more details on the recap. I used Sonicap and Audyn Q4 caps and a Dayton Precision Resistor on the High Shunt with Mills Resistors on the rest but more on that in a bit.
Listened some more. And compared the recapped speaker to the original crossover. I quickly ordered the Rd-0194’s, the tweeter’s were just not quite right. I shortly jumped into the recap of the second crossover.
Poly Switch:
During this process I wanted to hear the speaker with the Poly Switch bypassed without any adjustments to evaluate the differences. With no Poly Switch and no additional value changes I was hearing sibilance that was forward in the mix. It was not off putting but some of the sibilance I was hearing very well may have been from the extra brightness of not increasing the resistance.
Resistor Upgrade:
Ultimately I decided I wanted to tame the highs a bit. I was faced with the decision to up the value of the 2ohm cap bypass resistor or simply install a .5Ohm resistor in its place to compensate for the resulting resistance decrease in the circuit. I decided to add the .5ohm resistor and use a mills 2ohm value to keep the contour original.
Resistors were then installed… was pretty quick and easy at about 10 minutes per speaker. At this point highs just sat back into the mix a hair better. It was not a drastic difference at all, just a slightly smoother sound. I couldn’t wait for the new tweets as the slight distorted sound of the sl2000’s at certain frequencies was hard to ignore.
New tweeters installed… they do not seat perfectly in the routed cavity. They are about 1/32 of an inch taller than the cavity. Considering my options…
On the sound front, the speakers are beautifully balanced! Very easy listening with no fatigue!
Comments
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Can't wait until this is the only Uber Modded Monitor 11 on the planet
. Any way to get the inductors measured? Maybe a local audio tech/ repair shop? 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 -
I have a small electronics repair shop down the street. I will try to drop by and ask if he can measure them for me. Maybe that can happen next week.
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A bit of work and the tweets seat!
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Great write-up. Looking forward to more thoughts as they break in .
Excellent work.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 -
Tonight I am kicking back with a drink and enjoying a listen to a variety of relaxing tunes. Some guitar finger style, piano jazz, and chill ambient music. The past few days I have had the speakers playing quite a lot. This is my first relaxing listen though.
I have been plagued with hearing the slightest crackle. There have been many steps to addressing this as there have been many contributing factors.
The first thing that helped some was reworking the crossovers. The poly switches were definitely giving some noise. I have no doubt. Then went the sl2000. Better yet but not right still. I changed my source to my Denon AVR. That finally cleared up what I was hearing but the Denon did not sound anywhere as good as my Pioneer SA-8500. The Denon was sterile and thin compared to the Pioneer.
I dug into it the Pioneer and replaced the remaining suspect transistors. Just got it buttoned up and plugged in! Wow! Full, detailed, deep soundstage, no more slight distortion. I couldn’t ignore that sound. Particularly on soft piano parts. The strike of the keys was breaking up. Originally the poly caps and sl2000’s were accentuating the problem and adding distortion of their own.
It’s been a good day!
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What transistors were the problem, dumbing it down for a non EE type such as myself. Did you replace all the output transistors? How did you determine which ones?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 -
I was going off of recommendations from Audio Karma regarding transistors that were known to start to distort or fail. I had already replaced the transistors on the power amp assembly, the equalizer board and half of the switch board. The tone control board and a few stragglers on the switch board were the ones I got to in the past few days.
I worked through them without testing simply from a preventative maintenance perspective. Yes, that can be debated but it is the approach I chose. Some of the transistors considered “bad” ended in 725, 726, 1312, 1313, and 945. I took the recommendations and went with it and I am pleased with the results! -
I still haven’t been able to connect with the electronics shop. They have been closed every time I have been by. Does anyone have a good instructional source for measuring induction with a multimeter? The stuff I have looked at indicates it is possible but the process has not been clarified in my mind yet.
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So what can you do to mitigate the lobing, since Polk didn't bother on this model?Don't take experimental gene therapies from known eugenicists.
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So what can you do to mitigate the lobing, since Polk didn't bother on this model?
I think that's a tough one there, short of re-designing the crossover network in the vein of the original Model 11 (RTA 11), or doing an SDA mod of some sort.
I wonder about the flagship Legend speaker with the 2 drivers at a different angle on the baffle. Do they receive the same signal or is that a dimensional signal to one and stereo to the other? But regardless, what would it do to do something like that in this speaker?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 -
Ha! Set the speakers on their side?
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Ha! Set the speakers on their side?
I was going to say that but then I thought that it would probably adversely effect the imaging/soundstage since so much of that is the tweeter.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 -
Yep. Though if Monitor 10’s can have such a good reputation among people who an enjoy them, I see no reason why these can’t fall into the same category. Combing aside. These speakers sound another level compared to the budget ELAC B6 speakers I use with my HT setup. Granted, the purchase and refurb cost was a bit more. Even so, worth every penny.
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I am interested in BH5. It may be an interesting comparison to BH5 one mw of one side vs both mw’s of the other to see what the effect is on combing. Has anyone done that on a 10?
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ELAC B6 looks like a TSi100, albeit with a heftier price point.I am interested in BH5. It may be an interesting comparison to BH5 one mw of one side vs both mw’s of the other to see what the effect is on combing. Has anyone done that on a 10?
I would try that and foam-frame all the MWsDon't take experimental gene therapies from known eugenicists. -
I am interested in BH5. It may be an interesting comparison to BH5 one mw of one side vs both mw’s of the other to see what the effect is on combing. Has anyone done that on a 10?
Jazzhead used extra internal damping material in the form of a box with open bottom behind one of his original RTA 12 MW drivers to help with that and felt that it was successful. He also went to the later crossover if I'm not remembering incorrectly.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 -
I didn't do anything with the crossover (except upgrades), but with my RTA-12's (1980), hyperdamping the outer drivers (a westmassguy mod) did the trick for mitigating lobing. I haven't heard the 11's, but stock first-generation RTA-12's also have a shouty midrange. Damping the outer drivers largely eliminated the lobing, and also balanced the midrange (to my ears). I now have dramatically better imaging and soundstage. Before doing this, if I played FM hash I could actually hear a "blip" or "dead area" in the listening sweet spot - sort of a resistance of the stereo image to "merge". Damping one driver also helps my speakers maintain composure at loud volumes (my ears cry uncle first). YMMV with a different model, but I would definitely experiment with BH5 behind (or around) the outer drivers, as you can easily undo if you don't like it. Interestingly, the more extreme I got with the outer driver damping, the better sound I achieved. Do one mod at a time, so you don't introduce more than one variable into you listening experiment:
https://forum.polkaudio.com/discussion/173834/westmassguys-idea-employing-damping-to-mitigate-comb-filtering-and-lobing/p1 -
Cool! More fun stuff to read and research. This has been a welcome rabbit hole. It’s nice to set life aside for a bit and explore an interesting subject. Not to mention that listening to something that sounds great is fun!
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@Jazzhead the mod you did takes the idea I was considering to another level! Any regrets? I was thinking of keeping all mods reversible but this one has me thinking…
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No regrets. The only thing not easily reversible is the extended brace (referenced in the link posted above), but that brace has other benefits. I had noticeable baffle vibration at the intersection of the two midwoofers and the PR. The extended brace (which creates the "box" housing the damping material) stops that vibration. Also, to be clear, the goal here is to damp the outer drivers (absorbing the higher frequencies produced) and mimic what the crossover does in more advanced models where the outer driver is rolled off (you end up with a right/left, mirror-imaged set of speakers). You want to maximize the difference in frequencies produced by the dual drivers. Therefore, minimize the damping material behind the inner driver (4x4, 3x3 piece etc). Try to keep all the dacron batting in place behind the drivers, but don't compress it, and allow soundwaves and air to move to the lower PR area. I had so much dacron in my speakers to start with that I couldn't fit it all behind the midwoofers (I tried and killed the life). Some of it had to go, but I now have good, realistic bass reproduction. Remember however, that your speakers aren't the same model and if you feel that you don't have some midrange output to sacrifice it may not work as well. I lucked out. Do you sense your speakers have a diffuse, shouty, "in your face" midrange quality at high-ish volumes? If so, this mod may work out well for you.
