Alesis Monitor Ones Crossover Cap Replacement

[effitall]

Monitor Ones are cool...Although the top end is kinda nasty. I still have a pair that I've kept around since the late 90's.

I don't think I'd expect too much from a cap upgrade on these, but I would look for polypropylene caps. Try here:

http://www.parts-express.com/wizards...omo=&srchAttr=

Those aren't the end-all be-all of caps...But any polypropylene will kill an electrolytic. Besides...Is it really worth spending much money on these?

If you really want to make a significant upgrade to these...I would look at a replacement tweeter. Look to something from Vifa.

Something like this:

Vifa XT25SC90-04 1" Dual Ring Radiator Tweeter 264-1014

That could be a significant upgrade from the dome tweeter that's in the Monitor Ones.

These are things I've thought about for my own Monitor Ones.

[andybot]

Thx effitall, appreciatte it. I think i bought these new in 98 and im going to hang onto them even if im not using them as reference monitors.

I think ill do the cap replacement and see what i think from their but ive been looking at a monitor and amp upgrade and for me im just going in blind not having much experience with any other monitors or amps for that matter.

Im not really sure what to think about swapping out a tweeter or if putting in a better tweeter would improve the system as a whole though the vifa page just loaded and $25 bucks is less than i expected.Might be worth an experiment.

Thx

[effitall]

I hadn't really listened to my Monitor Ones in awhile. I had them loaned to a buddy of mine with my modded RA-100 amp and was over at his place checking out some mixes he had been working on. I was struck by two things...

One...The bottom end was surprisingly good. Better than I remembered.

Two...The top end was ragged and edgey. Not smooth at all.

What do I remember about my mixes on those things? Boomy bottom and subdued top. Why? Probably because all that spit and distortion from the high-end of the monitors was making me turn it down.

That said...I don't think the crossover mod alone will get you to where you need to be. I've heard a similar Vifa tweeter to the one I linked and thought it sounded really good. Both Blue Sky and Lipinski have used a version of it in their monitors so it's in good company.

Look here and see if there's anything in here that makes sense:

Zaph|Audio

One thing to keep in mind...The tweeter, woofer and crossover work together as a system...Change out one component for another and the whole system behaves differently.

I have no doubt that replacing the electrolytics in the crossover will make things sound better. Maybe that will be enough for you. But to go further down the rabbit hole with a new tweeter will require some math.

There's quite a bit of learning to be had from that Zaph site. You'll pick up alot by just thumbing through it.

Keep us posted on what you do and your impressions. I might just join you on the journey.

[illacov]

I had the opposite experience on my Monitor 1s but I have the passives are you referring to the Actives?

I'm going to recap mine with film caps but also install film bypass caps (.01 uf).

I've always suspected that my top end on the Monitor 1s was a little dull and not as bright as other monitors. The tweeter upgrade is interesting but I don't have complaints about the high end on mine.

With the passive monitors, your amp is going to determine how they perform as well. I'd definitely have something like at least 300 or 500 watts available.

My buddy has a 1000 watt power amp for his Tannoys and he's loving it
PS Just to add here's a website where a guy did do this upgrade and he posted his findings.

http://minirig.org.au/2010/01/26/min...itor-speakers/

Peace
Illumination

[andybot]

Thx fitall for getting back. In all honesty i dont really know where im going with this but i have been looking at a change to my mixing set up as its been the same for 14 years. Ive been looking at monitor kits and amps that may be
worth buying.

I have had a problem in the high end that follows a particular crossover and i stumbled across a thread where the caps were replaced with higher quality
ones with reported pleasing results. Its not like im unhappy with the speakers
as i tend to audition on other systems and use some large older advents as references to and i like the results and im familiar with the systems.

My main problem is that i just try to get the most out of what i have and when im done i forget to think about what may be more suited to what i do.

I will keep you updated as i go along.

Thx

[andybot]

Sorry Illacov, we were posting at the same time. I dont think you were askingh me but im talking about the passives and the link you posted was the same page i found the got me interested in trying this.

If you do do the mod could you post the parts that you use.

Thx

[effitall]

Hey Illacov,

I'm talking about the passives as well.

One thing I always like to say is the only piece of gear you ever actually hear are your speakers. So it's worth it to spend some money here.

To my ears, there's a distortion in the top end of the Monitor Ones that makes them edge-y. I don't think they're "bright" per se...I think they're trashy on the top. It's an odd combination of things....A lack of high-end extension but an aggressive, spitty, high end that seems imbalanced to the rest of the speaker.

In other speakers, I've replaced electrolytics in crossovers which cleaned up the top end. That said I still think the tweeter in the Monitor Ones is a little lacking compared to woofer.

See what the crossover mod does for you.

[andybot]

I was checking through some caps on digi-key and noticed that some caps are rated for both ac and dc and some are rated for ac or dc only....what does this mean?

Also while im here the caps in the crossover are rated at 50v im assuming that this is an ac voltage but i have been wrong before.

Thx

[LeeYoo]

Hi andybot.
Use crossover caps.
They are made to handle the currents in a crossover.
IMHO, only the 5uF tweeter cap has to be replaced.
4.7uF is a standard value.
e.g. Dayton Audio DMPC-4.7 4.7uF 250V Polypropylene Capacitor 027-422
If you are worried about having exactly 5uF in there, put a 270n film cap over the 4.7uF.
I wouldn't bother, because the electrolytic cap that's in there now has most likely a 20% tolerance.
If you replace the tweeter, make sure you get one with the same impedance and sensitivity, otherwise you will change level and crossover point.
Leo..

edit: The woofer side of the crossover is a standard 4ohm/1750herz Butterworth crossover point. (16.071uF+0.5145mH+Zobel)
http://ccs.exl.info/calc_cr.html#second
The tweeter side doesn't make sense. Maybe that's why there is a nasty peak around the crossover frequency.

edit: Is there a MkII crossover with different parts?
HELP! Alesis Monitor One MK2 NO HIGH FREQ

[andybot]

Thx LY,
im wondering why you believe only the 5uF cap need replacement?
Thx for your iunput

[LeeYoo]

Hi andybot.
I will try to explain in simple terms.
The 5uF cap is in series with the tweeter.
All the current for the tweeter passes through this cap.
I would'n use an electrolytic cap here, because of the high frequencies involved.
The other two caps in the woofer circuit are not as important.
They are basically shorting mid/high frequencies to ground.

I would investigate the MkII version of the filter.
I see an aircore inductor for the tweeter and different cap values.
Maybe someone has a diagram/part values.
Try to PM the poster of the picture..
The "problems" could have been fixed in the MkII version.
Also look at the phase of the tweeter. That could be reversed in the MkII.
Leo..

[andybot]

Thx Leo...

[LeeYoo]

Goooooooogle
Alesis Monitor One MKII ( Monitor One MK2 ) Spare Parts

[effitall]

I dunno...That mkII crossover looks pretty different. Besides...Without knowing the performance of drivers...It's all just guesswork.

I would do this...

You need to know how these drivers perform. Sooo...You need to measure and listen and measure some more.

You'll need a good space to test the speaker (controlled room or open air), a measurement microphone, an RTA, an amp, a digital speaker processor, and a noise generator. (Room EQ wizard, a Behringer ECM8000, and something like a DBX DriveRack is a good place to start.)

Bypass the internal crossover and wire an amp straight to the woofer. Run some pink noise through it and look at the RTA. (One note...If might be a good idea to use the digital crossover/speaker processor to keep the really high stuff out of the woofer but still let it pass signal up to about 10k or so).

Looking at the RTA you should see some nastiness in the upper mids, some ragged response and a drop off in the highs. You'll probably hear the nastiness too. This is where the above mentioned speaker processor is handy. Dial in some parametric notches and smooth out the response in the mids. You'll want to take note of those curves as you'll want to duplicate these in the analog crossover (if you choose to rebuild it...You might prefer to just use the digital crossover).

Once you've got the response smooth on the woofer...You'll want to see where it rolls off...How fast it rolls off and think about how you want to integrate the tweeter into the mix.

Getting the tweeter to work together with the woofer is the "magic" in a crossover design. For now...Start with a 12db/oct high-pass at about 2k on the processor, and hook that into a second amp channel...Hook that amp up straight to the tweeter.

You can do a couple of things now...You can listen to the woofer by itself...The tweeter by itself...The system together...And you can play around with different crossover styles, crossover points, and any additional filters/notches that need to be applied to the system to smooth out the response.

I'd suggest firing up the tweeter by itself and listen to it (with the pink noise still). Any harshness? Anything weird showing up on the analyzer? Add in the woofer. Pay attention to the frequencies at the crossover point. Any weirdness there? Phasiness? You should be able to see anything really bad in the analyzer. Your ear should be able to confirm the good/bad stuff. Tune around and see what you can find.

Now...You should have a good idea about how the woofer performs...How the tweeter integrates with it...What crossover points are needed...What notch filters are needed...Etc. Now you can decide. Do you want to try to do that in the analog domain? Or maybe you just want to use the digital crossover box to do what you want.

That's alot more work...But I'm sure the pay-offs are well worth it. Instead of just "guessing" and randomly swapping parts...You'll be able to really optimize the speaker.

Happy tweaking.

[andybot]

I ended up replacing the 5uF cap with a Solen PB-MKP-FC 5.2uF 400v dc +/- 5%. It improved the bass and mid clarifty, the signal sounds more like the original live signal that i recorded which is what im going for . Im very glad i did it.
Thx

[speiris]

Originally Posted by LeeYoo

edit: The woofer side of the crossover is a standard 4ohm/1750herz Butterworth crossover point. (16.071uF+0.5145mH+Zobel)
Crossover Design Calculators
The tweeter side doesn't make sense. Maybe that's why there is a nasty peak around the crossover frequency.

edit: Is there a MkII crossover with different parts?
HELP! Alesis Monitor One MK2 NO HIGH FREQ

The tweeter side crossover seems to be an 8ohm/1750Hz Linkwitz-Riley (5.686uF + 1.455mH). Is it common to mix crossover types like this?
Or when it was being designed did one person favour Butterworth and another prefer Linkwitz-Riley and both too stubborn to yield. lol. Or did someone use the wrong crossover calculator for one of the drivers? Maybe neither.

I changed all components on one of my Monitor One (Mk1) crossover boards. Air-core inductors and Jantzen Crosscaps. Resistors as well. Was a real effort to get it all to fit. Those 400V caps are quite big. One had to be off-board. I used a 2.5KHz Butterworth crossover. Layout not ideal since it's so crammed and inductor relative positions are bad.

That monitor sounds much nicer than the stock. I might try a Linkwitz-Riley configuration and compare. Didn't know at the time about the 3db peak at the crossover frequency with the Butterworth. Only after doing the mod did I read up on "crossover theory".

When I first did a sound test the crossover assembly was hanging out of the speaker cabinet. I'm pretty sure it didn't sound as good after I screwed it all back in. Could it be that the proximity of the magnets of the drivers are affecting things? It could just be in my head. But no doubt a real nice improvement.

I'm currently on holiday in Sri Lanka. Before I left I bloody blew one of my tweeters! Oh well. It served me well since 1999. Might replace both tweeters with "scan-speak" tweeters. Prob not worth it but I'm attached to them. My first set of monitors. Got them with an RA-100 amp. Paid close to a thousand dollars for the amp and almost another thousand for the monitors!!