The Ultimate Monitor 70 Active Crossover Multi-Amp Project

Cybershaman

Greetings, True Believers! After pretty thoroughly hashing the ins and outs of bi-amping the Monitor 70 speaker in another thread (here), I was left with the feeling that after doing all of the work I was proposing, not much of any improvement would result. However, I suddenly hit upon an idea that while again it might not make much of a difference sound-wise would at least be aesthetically pleasing and show that all of my hard work wasn't for naught.

In a nutshell...I would like to tri-amp my Monitor 70's! The uber-cool (at least in my opinion) aspect of this project is that the high frequency/tweeter amp will be a small tube model which will sit/mount on top of each speaker! How cool would THAT be!


Here are the key points of this project:

- I will be using two active crossovers which are built into two different vintage AudioControl components (a Phase Coupled Activator and a Richter Scale). These are 24db per octave Linkwitz-Riley XOs (XO = "Crossover". It's getting to hard to type that out all of the time.) which I will be making my own custom plug in XO modules; one set at 2600 KHz and the other as yet to be determined for the low range woofers. If anyone has any advice on where to get good quality 1/4 watt 1% tolerance resistors, that would be great.

- The mid/low and low/low drivers will be powered by two Carver TFM-15 amps each rated at 100 wpc.

- The high range drivers (tweeters) will be driven by two as yet to be determined low wattage mono amps. This is probably the one item I'm going to need the most input and advice on. I would like to be able to mount/set each amp on top of its respective speaker. I think that that would be not only asthetically pleasing (imagine the soft gentle glow of the tubes) but also quite the conversation starter. I also visualize there being some sort of cage around the tubes in order to protect them from things like...cat noses. Any suggestions as far as wattage and make/model is welcomed. I would even like to perhaps build my own if anyone knows of a good kit out there. Price is a factor here as well. I know that this area of audio is usually the domain of the higher end of the high end HiFi guys so price could easily get out of hand. As a purely arbitrary price point, let's throw out a figure of 200 bucks for both amps to start. Of course, I can go higher if need be. This is just a "real world grounding" figure so things don't get way out of hand...

- I will need new binding post plates as well. EndersShadow helpfully gave me a link to this thread (here and mentioned that VR3 might be able to help in this department.


I think that about covers it. So! What do you guys think? :twisted:


(I am going to post mrviper100's very helpful diagram of the internal passive crossover of the Monitor 70s again here. I just need to figure out how to compute what the lowpass XO point is for the mids/woofers and woofers and I'll be all set...)

tonyb

Looks cool and all, but personally I wouldn't waste my time on it. Not to rain on anyones parade here, but since you are seemingly skilled at computer building, wouldn't it make more sense to build a few 'puters and sell them to make more coin for better gear ? Just asking is all, I know you have time on your hands, why not turn your time and talents into something that would put some coin in your pockets ?

EndersShadow

Interesting concept, but why not go DIY using stuff from Parts Express so you can make this build as cool as you want? That way your not stuck with having to stick to the Monitor 70's configuration?

Cybershaman

Well, tony, you bring up a perfectly valid point that I will try to explain again. It's not so much the destination as it is the journey. I have no allusions to the results of my project resulting in an astounding leap in performance or quality. If I have to really think of the "why" then I would have to say that not only do I learn something about what I'm working on but at the same time discover things about myself. Who knows. Maybe while working on this I will discover a subject or field of study that I enjoy which I might not have ever found otherwise. Not to mention meeting and conversing with new people who might also lead me to new and wonderful things. Also, as far as making money goes, there is a lot more involved than just making stuff and selling it. I actually seriously considered doing custom computer work but after talking with a few people in the business decided that in the end I could actually end up turning something I loved into something not so fun. What I can do and the product I could offer really isn't special and I could easily end up losing more money than I put into any venture of that sort. Don't get me wrong, the entrepreneurial spirit is definitely strong in me but I would have to be absolutely certain to feel the 110% passion and the life long drive to make a business work. So right now, I will continue to tinker here and there and maybe someday I will hit on the right idea or meet the right people. I'm afraid that if I began to constantly start thinking about money that I would quickly lose the magic that is at the core of my endeavors. And if I were to move on to any sort of business, that magic would always have to be there or, at least to me, it would seem empty and hollow. I should also point out that we never really know what is truly going on in another person's life. So to others, it would seem that someone like me has, disability aside, an idyllic lifestyle. However, there are things about my life that I have chosen not to reveal which might help you understand that it's not all it's cracked up to be.

I think that's enough for now. I hope that answers your question...

Cybershaman

Something like this link to eBay item seems like it would be perfect. It's an APPJ EL84+12AX7 mini tube amp ( Original miniwatt N3 ) which is a mono 3.5 wpc tube amp which is running for around 200 bucks for a set (minus tubes, it looks like). But at least it gives a good idea as far as the styling I'm looking for...

I'm curious what the rating is on the Polk tweeters and while I know that I don't need much juice for them, I'm going to guess that 3.5 watts might be on the lean side...

Cybershaman

Do you mean, build my own speakers, Enders? Keep in mind I'm in a wheelchair. I about killed myself unpacking the 70s and paid for it with a few days of more pain than I usually have. Yeah, that was pretty dumb of me to do that. Ouch!

Rest assured, I would totally build my own if I could. I think I even still have all of my old books on design back at my parents house! I was geeked about building speakers back in the day. I had several planned out but sadly never got around to building them before life took me in a different direction. (I think that's when I took off to Japan. Not sure. Man, that seems like so long ago. Getting old. Hehehe...)

EndersShadow

Cybershaman wrote: »

Do you mean, build my own speakers, Enders? Keep in mind I'm in a wheelchair. I about killed myself unpacking the 70s and paid for it with a few days of more pain than I usually have. Yeah, that was pretty dumb of me to do that. Ouch!

Rest assured, I would totally build my own if I could. I think I even still have all of my old books on design back at my parents house! I was geeked about building speakers back in the day. I had several planned out but sadly never got around to building them before life took me in a different direction. (I think that's when I took off to Japan. Not sure. Man, that seems like so long ago. Getting old. Hehehe...)

I am aware you are in a wheelchair, however you could build your speakers in two cabinets (one for tweets and midrange) and another for the subs. Then just fashion a way for them to stack on each other. I only mention it as Parts Express not only sells the parts, crossover boards, ect, they also sell enclosures for speakers.

It was more of a passing thought since you have the mental skills to do the research and whatnot.

I think FACE on this board built a set of really nifty looking speakers similar. Also here is an example build from the Parts Express website that gave me this idea for you.

Here is a link to the list of all of them just as an FYI

Even if you dont have the woodworking skills or tools, I bet there are more than enough folks that are capable of making speaker cabinets for you custom (though not sure how pricey that would be).

cnh

I find myself in agreement with tonyb and I own a set of these. However, it seems like this is "fun" for you, so whatever floats your boat. There are definite limitations of the M-70s and, personally, I feel (and there are some people on the Polk side who agree with me) that M-70s are one speaker that Polk got fairly right--no need to mess with them and messing with them won't do much, but it will if this is a "hobby" for you. DIY is not something I like to do...takes time away from listening! lol

But I'm sure that all the wonderful diagrams above are candy for all of our DIY-ers! So have fun.

cnh

tonyb

Thats cool man, whatever floats your boat. However you did ask what we thought, and I just expressed mine. The thing that still stumps me, is you yourself aren't expecting any real sound improvements so that journey has little payout at the end. For me anyway, it's always nicer when a journey has some benefits at the end. If tinkering is your deal then tinker away my good fellow, won't hurt anything.

Cybershaman

It's all cool, my brothers! And, yes, I'm thinking that what I'm feeling is the re-awakening of that old desire to build speakers! It's just that's it's all happening right after I got the 70's so we'll see how things go. I super appreciate the feedback. Even if it causes me to go into a self examining existential revere. I like that too! I'm a weird one...

Cybershaman

How's this for an interesting experiment and would lead to actually getting a base bass...heh...enclosure/transducers to try:

Since my M50's have been relegated to side surround duties, thus replacing the M30s that were there, how about a little experiment to use the M50's for the bass with the M30s on top for mids/highs? I wonder how easy it is to take off the black piano lacquer looking top of the M50's as I would probably like to couple the M30's to the top via some spikes. That might keep me busy for a while!

Cybershaman

Good morning (I'm you in this quadrant), True Believers!

I have taken the next step in my little experiment. I just plugged in a 2.6KHz 18db/Octave phase-coherent XO (crossover) module into my AudioControl Phase Coupled Activator's active XO circuit, hooked up the hi/low output to 2 Carver TFM-15 (100 watts per channel) amps each bi-wired to the proper binding posts, set my system to pure stereo (no processing), popped in some music and sat back. And I...was...floored...

First off, just a few things... This might be grade school level audiophile knowledge, but I really noticed that the Monitor 70's benefited from a generous break-in period. I've seriously been putting these things through their paces; constant casual to moderate volume music listening and several movies at near theater level volume. This seemed to "loosen up" the woofers which is the best way I can think of to put it. I've also been running them with the two aforementioned amps in the bi-amp configuration. All in all, I've been very happy with them and they have encouraged me to revisit many albums in my music collection that I haven't listened to in a long time. But then, I implemented the active XO and this happened...

So, as it happened, the first thing I listened to was "Random Album Title" by Deadmau5. It's techno house/trance and really pushes the limits of bass without treading into rap territory. Like I said, I popped it in...and my jaw hit the floor. I'm really not exaggerating. The bass was tight, defined, more detailed and just a tad deeper. The soundstage just opened right up. Overall, the detail in the music was just amazing. I was like "Oh, so THAT'S what that is supposed to sound like!" I then popped in Jeff Buckley "Grace"...and sat with my eyes closed through the whole album. As I shook myself back to reality, I threw in a recording of Holst "The Planets" and tried to really focus on the music and think about what was happening...

The only thing that I can think of is that the 18db/Octave active XO plus the 12db passive one built into the 70's really complement each other. If my understanding is correct, between the two XOs, the resulting roll-off comes to 30db/Octave, right? Now, I think it's safe to say that speaker manufacturers take that into account when they design and test their speakers. But aren't steeper roll-off XOs more desirable? And isn't the primary reason to use a 12db roll-off in a passive design is that an 18 or 24db/Octave passive XO is prohibitively expensive due to the greater complexity?

At any rate, there you have it. The great experiment continues! In other news, I ordered a couple of monoblock tube amp kits (http://www.tubesandmore.com/products/K-501)and I'm excited to not only build them but try them out on the high end. Since the meter needles are barely moving, even at high volume, on the "high range" Carver amp, I'm encouraged that 8 wpc should be sufficient, at least for casual listening. In the mean time, I'm going to do some more switching back and forth to further test things out. Thanks again for all of the feedback and caveats, guys. Rock on!

PS: I also just completed the much touted "Carver Meter Bulb LED Mod" and I must say the results were more than worth the effort. Here is a, sadly, over saturated pic to ooo and aww over.

cnh

Sexy Blue meters are always cool! Very nice! I have to find out whatever you're on. Because you have enough enthusiasm for both of us. When I wake up in the morning it literally takes me almost two hours to say: "Yeah, I think I'm here, at least I don't seem to be dreaming anymore and the tiredness of waking up is gone!".

Keep us updated, you're excitement is like a strong cup of coffee!

cnh

Cybershaman

I'm not sure what it is. Things have changed recently in my life and I find myself sometimes hauling myself out of bed at night to work on some crazy project or idea or write something. I'm trying to make sure and check myself so that I don't end up heading for manic burn out. But so far...things seem to be pretty steady! I actually have one or two other things to post. Nothing as epic as this but maybe something useful for someone out there... Laterz!

Cybershaman

This is sort of related to my project in a weird sort of way. If you don't like nostalgic reflection stories, move along right now!

So, I just found out from my bio-dad (yeah, I have two dads. long story.) that his dad designed and built his own tube pre-amp, amps and speakers. He remembers his dad measuring and cutting the tubing for the bass reflex ports which he put into some antique cabinets. Then he acquired some horn tweeters and made it so you could aim them toward the listening position. And THEN he built a fricken 15 inch subwoofer to put behind the sofa "because he said bass frequencies were hard to localize". Oh, and he built all of the crossovers too. No word on whether the crossovers were active or passive though. Hehehehe... I then asked him what sort of high fidelity media was available at the time and he said that they listened to music on a phonograph and reel to reel tape. Pretty crazy, huh? I guess the fruit really doesn't fall too far from the tree...

Cybershaman

Update: My baby tube amp kits arrived! I will be slowly assembling them over this next week. I say slowly because I'm still deciding on some of the cosmetic factors that I want to incorporate.

For the curious: These are, uhttp://www.tubesandmore.com/products/K-501

They are actually made by this company: http://www.s5electronics.com/thome.html and what I have is an older model which has been replaced by the K-8LM. Still, these kits are half the price of the 8LM so if things don't work out it will be less of a sting. But I have a good feeling and can't wait to fire them up!

Will keep you posted!

cnh

Those kits look cool! Should probably consider one for my KLH 17s! I know John (jstas) put an 8 watt x 2 together that sounded phenomenal with the pair he demoed at Lou's Polkfest!

Of course, I have a lot more "thumbs" than you do for such a task! lol

Have fun!

cnh

Cybershaman

cnh wrote: »

Those kits look cool!cnh

Did you check out some of the l33t ("elite". this isn't a gaming forum, cyber...) mods at the S5 site? http://www.s5electronics.com/gcust.html Some wicked "cases" there. Man... And here I am painting a pine board and, oooooooo!, ordering brass screws and spacer sleeves! Wow. Way to walk on the edge there... heh...

Other related to thread stuff: The amp, while "only" rated at 8wpc is said in several posts I found to be plenty "loud". I hear this is unique to tube amps? They can really push the juice or something. And even though I plan on dropping the high crossover point down a little from 2.6KHz, these amps should be more than plenty to run the M70's tweeters.

In other news, EndersShadow would be happy to know that he's totally turned on the speaker builder bug in me back on. This project is really turning out to be a precursor to ordering my own cabinets and drivers. So...thanks Ender! You've made a bored guy very happy!

EndersShadow

Wow, thats a great price for that kit. They even have a slightly more powerful kit for 200. Thats pretty friggin awesome!

Eventually I would like a very small wattage tube amp for my setup at the home office.

Cybershaman

EndersShadow wrote: »

Wow, thats a great price for that kit.

Yup. I can't wait to hear how they sound!

For what it's worth, the kits come with everything you need. If I were to find any fault so far with them, it's that I don't really like the cheap power switch which is one of those snap-on-the-power-cord jobs. I've had those on a couple of lamps and they both eventually wore out and died with a nice pop with a flash and smoke. heh, heh. So I think I'm just going to plug them into a surge protector and turn them on that way.

And just for fun I ordered some metal film 2% tolerance resistors from Radio Shack to use instead of the carbons that came with the kit. I decided not to mess with the capacitors but I'm sure they're fine. They seem to be well constructed. I also ordered some silver solder (http://www.amazon.com/gp/product/B00099EDSC/) again, for fun. I figured why not.

Will keep ya posted!

Cybershaman

Welp, tube amps are done! And they are going to have to burn in for a bit. They've already smoothed out a bit with some intense listening but they've got a ways to go. That and one of them has a significant 60Hz buzz that, while you can only hear it if you put your ear up to the tweeter, needs to be fixed. The other one has it if you listen really hard. I was checking out some mod posts that addressed this very problem. All in all, though, I think I lucked out. Very little experience and I'm lucky the damn things didn't just go POOF as soon as I fired them up.

I'm pretty much ready to go for pure tri-amp/bypassing the passive XOs just as soon as I get my wicked new binding post plates from VR3 (http://www.vr3mods.com/). VERY cool guy and what he does makes my project look like I'm banging rocks together. His work is high art. Thanks for the tip, EndersShadow!

That's it for now. Stay tuned, True Believers!

Excelsior!

Cybershaman

Sitting atop my M70's! Aesthetics aren't done yet. The are going to be painted black, sitting on spiked feet and I'm still figuring out a cage...

Fired up. The digital camera is trying to compensate for the light. Longer exposure adds camera shake too! Doesn't do the "glowing tubey goodness" enough credit!

EndersShadow

Cybershaman wrote: »

I'm pretty much ready to go for pure tri-amp/bypassing the passive XOs just as soon as I get my wicked new binding post plates from VR3 (http://www.vr3mods.com/). VERY cool guy and what he does makes my project look like I'm banging rocks together. His work is high art. Thanks for the tip, EndersShadow!

No worries mate, glad to help make some connections for folks!

Dan

P.S. since your going down the rabbit hole on these babies, might I suggest purchasing some mid grade interconnects, power cords, and speaker cables for your amps and for the setup? I suggest looking at Signal Cable, yet another great company that gives us Polkies discounts. More suggestions would be Audioquest, Blue Jeans Cable, and I am sure I am missing others :biggrin:

Cybershaman

Greetings, True Believers! Your friendly neighborhood Cybershaman here! And, lo, after many days, after the venerable VR3 created some custom binding post plates, the tri-amp project is complete and now running! And it is everything I hoped and more! Now...I approached this project from the standpoint of a Tinker. I was just doing it for the pleasure of the doing; creating in a Rube Goldberg-ian fashion something that my speakers were already doing. That's what makes the outcome all the better...

To try and reiterate what it was I was trying to do in as quick a fashion as Mr. Verbose is capable of: I wanted to remove the passive crossovers from my Polk Monitor 70 speakers, split the audio signal with two active crossovers (one built into an AudioControl Phase Coupled Activator and the other built into an AudioControl Richter Scale half octave "bass" equalizer) before the amplifiers (two 100 watt per channel Carver TFM-15s and two 10 watt S-5 K-501 kit built monoblock tube amps) and then send the results to the naked transducers.

The mod was accomplished with the help of VR3, who not only provided the custom, and I might add extremely high quality, binding post plates but also listened, and responded!, to many a random thought, babbled idea and seriously newbie question. I also used the Dayton Audio OmniMic V2 Precision Measurement System (http://www.parts-express.com/pe/showdetl.cfm?partnumber=390-792) to take my pre-mod measurements of the speakers. I haven't done the post-mod test yet because I was just too excited. But I have given these things a good listening to...

Right now, a Best Of Queen disk is in... The bass is clean and tight. Mids are not hollow at all; just "there" as they should be. Highs are crystal without "piercing". Next to the quality of the bass, and I'm not sure how to describe this but, things like finger snaps, fingers on guitar strings, rim shots, claps, "clacking/clonking" (!) percussion instruments...all sound as real as I've ever heard coming out of a speaker system. I noticed it because, well, I never noticed it before on the Monitor 70s! Particularly when I was getting over the post-mod quality shock and I heard, even when every other instrument/voice was loud, the clicking percussion of a...I think it's a small wood block or something? Whatever it is, I had to listen to the track "Killer Queen" about three times because I never noticed it before! That's one reason why I love HiFi so much. Whenever you get a new piece of equipment or mod something, it's like your whole music collection is brand new...

At any rate, I have some measurements to take now. Here are a few pics...

Stock cup/crossover vs. super cool plate from VR3...

Installed! And looking sweet! Again, VR3 rocks! He's on the forum here and on Facebook. Check out his site here: http://www.vr3mods.com/

Testing with the Dayton Audio OmniMic V2 Precision Measurement System. Note: Ubiquitous cat...

This is one of the tube amps I built...

I also built this...

My other passion...

I'll be sure to post some graphs of frequency sweeps. I'm not sure how entirely helpful they will be but at least I'll have them. I'm sure that the tonal results are too subtle to see in a graph but we'll see. Until then...Excelsior! :cool:

VR3

That's turned out great!

Very cool project you have done!

Good job broski!

Cybershaman

Why, thank you, sire! I was going to say that I still have yet to install all of my wire tracks/sleaving so they won't be all "hangin' out" like that. But that wont happen until I finish a little project called Operation CS2...which is a subject for another post and also happens to involve a certain VR3...

That and I still have yet to solder up the new fuse holders on the tube amps so that stupid power wire isn't hanging off to the side like that. So many projects...so little time... heh...

Now...I still have to do those short sine sweeps...

cnh

Nice work. Love the amps above the speakers. And VR3s plates are always "classy"!

Who would've "thunk" that one could do that to a set of M-70s. So whatja gonna do to the CS2s?

cnh

Cybershaman

Yeah, cnh, the whole idea seriously came to me in a dream. Seriously. And it turned out pretty darn cool! And it always gets comments when people come over which then leads to tech talk which is exactly what I had intended!

Yes. My 70s do tricks.

As far as the CS2 goes...

http://www.polkaudio.com/forums/showthread.php?138709-Just-completed-VR3-quot-Fortress-quot-crossover-mod-on-Polk-CS2-center-channel!-)

EndersShadow

Cybershaman wrote: »

Yeah, cnh, the whole idea seriously came to me in a dream. Seriously. And it turned out pretty darn cool! And it always gets comments when people come over which then leads to tech talk which is exactly what I had intended!

Yes. My 70s do tricks.

As far as the CS2 goes...

http://www.polkaudio.com/forums/showthread.php?138709-Just-completed-VR3-quot-Fortress-quot-crossover-mod-on-Polk-CS2-center-channel!-)

I expect to see FR sweeps soon :biggrin:

Cybershaman

Oh, yeah! I almost forgot!

Sort of half-way, pre-mod. At this point, I was bi-amping with the tube amps and one Carver. I had one active XO set up but the passives were still in place...

Here we are post-mod. I really need to figure out some sort of anechoic solution. Nothing fancy; just something to maybe tighten up the results a bit. In this snapshot, you can see a bump up in the 20s which, seriously, I think was a truck going by. Also, the swift roll-off before 20k is curious. Then again, I did a Google image search and it seems that that is about par for the course.

These were taken with the mic pointed straight at the tweeter from a distance of 1.5 feet. I also think I need to pump up the volume a bit. I had my receiver set at -30db for each snap. At any rate, it looks a bit flatter to me!

Of course, comments/suggestions from guys with actual experience is GREATLY appreciated! I am using the OmniMic V2 Precision Measurement System.

Cybershaman

And the active crossovers are 18db/oct...

Tweeters: 2.4k high-pass
top 2 woofers: 2.4k low-pass
lower 2 woofers: 800 low-pass