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Old 10-02-2015, 03:19 AM   #121
Togu
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

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What did you replace those capacitors with?
I replaced all twice
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Old 10-02-2015, 06:06 AM   #122
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

That's not exactly what i asked I was asking what brand / series the "new" capacitors are (not if, or how many times you replaced them)
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Old 10-02-2015, 09:32 AM   #123
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Ok ;-) 2x390uF 200v SAMWAH HK 105c(m) , 1uF 85c, 330uF 35v 105c Chengx
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Old 10-02-2015, 09:46 AM   #124
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

The big primary caps don't fail too often, but i REALLY WOULDN'T trust those other two caps...

I don't suppose you have something like an ESR-meter, do you?
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Old 10-02-2015, 10:08 AM   #125
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

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The big primary caps don't fail too often, but i REALLY WOULDN'T trust those other two caps...

I don't suppose you have something like an ESR-meter, do you?
I have not got ESR :/

This is a very curious situation

Because the first I replaced 330uF 35V -power supply does not work, next 1uF power supply work 1 day, next replaced 2x 390uF - power supply work 1 day
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Old 10-02-2015, 10:10 AM   #126
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I changed two times 1uF and 330uF
R5 i D5 - damaged. Tomorrow Replacing and check

Last edited by Togu; 10-02-2015 at 10:30 AM..
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Old 04-09-2016, 08:21 AM   #127
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

hi, i sorted the psu issue, but seem to have no low/woofer output. drivers measure ok, any ideas from any of your genius'?
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Old 04-09-2016, 07:00 PM   #128
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Are the DC rails measuring (roughly) as they should?
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Old 05-15-2016, 12:27 PM   #129
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Smile Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I'm curious if recapping the crossover circuit in addition would improve the quality of the sound. ( bass response ). It seems high quality caps should bring the relation between the pair of monitors closer in response. At least bring it closer to the ideal that the engineers were trying to achieve.

What caps would have the most effect on quality of sound?

I understand some of the bass roll off was due to damping for a more even (flat) response causing a tendency to roll off below 50 Hz. Could the response below 50 be improved by recapping.

The other question of course, is should it in a small room near field monitor.
For me the answer is yes as these are my only monitors.

I purchased a new amp circuit leaving me able to experiment with the fried one, But the cross over remains the same. I need to open up the other monitor to move , and replace the caps on that supply. Seems like a good time to recap any thing else that might improve performance on both monitors.
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Old 05-17-2016, 04:40 PM   #130
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

The only electrolytics on the "signal" board are on the supply rails, and realistically, you won't gain much (if any) benefit from changing those. The caps in the actual crossover circuit itself are film caps, which you shouldn't need to worry about.

I can promise you, you'll get (and hear) the most benefit from actually treating your room
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Old 05-18-2016, 08:08 AM   #131
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

That is what I thought. I read on some other forum of a guy recapping another brand monitor with poly caps, and claiming it improved them a great deal. It did not sound right, but I felt it couldn't hurt to ask. Thanks

Improvement on bass response would seem to require a larger woofer. Someday I will buy some KRK Rokit 8's and use the Alesis as cross reference.

100 percent agreement about the room.
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Old 05-18-2016, 11:05 AM   #132
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Improvement in bass response is affected in a great degree by 1) the placement of the speakers in the room, and 2) your listening position within the room.

http://www.harman.com/sites/default/...ndRoomsPt3.pdf
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Old 05-18-2016, 05:15 PM   #133
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

45Hz isn't particularly low which is what the Alesis M1 go down too.
Get a proper sub if you want decent bass, something that does the 20-40Hz range.
Leave those monitors to do middle and treble.
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Old 05-21-2016, 06:39 AM   #134
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

That is what I am referring to. I found the roll off spec in my m1 mk2 manual says 50 hz.

A better sub response would as you say be 20 - 40hz .

I do take into account the room placement and treatments to reduce boominess and muddy bass.
Near field monitors also help to reduce room problems.
There is a lot of sub base in modern mixing and it is real easy to over do it when your monitor rolls off at 50hz. An 8 inch cone would have a greater effect.

I was having wishful thinking about higher quality caps improving quality because of a different forums post. Krohn knows his stuff about these monitors I felt there is no better place to ask.

I will swap the caps that might blow and leave it at that.

I recieved the new revised board. I have not scrutinized the traces to closely, but it seems all they did was swap c8 with c33 and beef up the high voltage trace that fries near the offending cap. I plan on using Krohns method with c33 on the back side. I believe he is correct about the distance being further away then desirable. Who would think the engineers would get this wrong

I will still repair the blown PSU when I have time, but with the new board, I am up and running now.

Also I would like to thank Krohn for the schematic.

It has been thirty years since I worked as a tech it is slowly coming back. I am seeing these monitors for $100 a pair on ebay they are likely blown. Ten bucks in parts and thirty minutes of repair seems like a good deal. When I bought mine they were $350 street price.

Last edited by gpj1136; 05-21-2016 at 07:07 AM..
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Old 05-21-2016, 07:15 PM   #135
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

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Get a proper sub if you want decent bass, something that does the 20-40Hz range.
Leave those monitors to do middle and treble.
I agree.

Generally, 6.5" inch woofers are simply too small to be able to provide the air displacement needed for anything less than 30 Hz without significant loss in SPL - unless you run them in a really small room, of course. If the drivers in these Alesis M1 speakers are capable of frequencies down to 25-30 Hz without significant roll-off, you can try lowering the tuned frequency of the speaker boxes by extending the ports. Of course, your mid and high-end bass response will decrease too. But that kind of trade-off is expected with any speaker really. However, I have a feeling that the cabinets/boxes for these speakers were designed with those particular drivers in mind (which likely do have a steep roll-off past 40-50 Hz). So it's quite possible that even if you extend the port, you may still not get much improvement in the low-end bass response. But it's worth a try since it is easy to do. Just roll a piece of paper and stick it in the port so it extends 1-2 inches more. *OR* since these speakers have two ports, you can try plugging up one of them to lower the tuning of the box.

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An 8 inch cone would have a greater effect.
If the speaker motor for the 8 inch cone is sized accordingly, then yes.

But bigger cone size does not automatically guarantee better bass response. I say this, because cheap speakers may sometimes use a small and shallow motor to drive a large cone. And if the speaker cone is heavy (paper cones on vintage speakers, anyone? ), the bass response is guaranteed not to be good. What if you add a huge cone on a very small motor? - Disastrous bass response

Last edited by momaka; 05-21-2016 at 07:27 PM..
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Old 05-25-2016, 12:58 AM   #136
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

[QUOTE=momaka;659054]I agree.


If the speaker motor for the 8 inch cone is sized accordingly, then yes.

The KRK rockit series arn't to shabby for the price.
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Old 05-28-2016, 12:12 PM   #137
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

While waiting for my parts the other monitor decided to pop a few cap also.
Both of mine burned c6 also. This one did not burn the traces though on both L1 got real hot. Seems to be a hard size to find. If they heated up enough to discolor the but are still intact I'm thinking they are OK. I do not have much experience with inductors. Any thoughts?

I'm thinking of buying a few more amps from Ebay and maybe building a set of monitors with 8" cones since I'm going to have extra parts.
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Old 05-28-2016, 02:16 PM   #138
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

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This one did not burn the traces though on both L1 got real hot. Seems to be a hard size to find. If they heated up enough to discolor the but are still intact I'm thinking they are OK. I do not have much experience with inductors. Any thoughts?
L1 and L2 are common-mode chokes for the power line. Check the for short-circuit between Live and Neutral. Also measure the resistance for each coil. Should be showing you near zero Ohms or whatever is the lowest resistance that your meter can measure.

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I'm thinking of buying a few more amps from Ebay and maybe building a set of monitors with 8" cones since I'm going to have extra parts.
That would sure be interesting to see. Let us know how that goes if you do it.
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Old 05-28-2016, 02:48 PM   #139
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

When I wrote the post I did not have the schematic in front of. The correct part was L4 which heated enough to discolor the glipt or what it is they globbed onto the parts.
I do not have a lot of time for this right now. I can get two full amps complete with crossover, basically the whole panel with all connectors intact. One working, one not for $89 US, or purchase a power supply replacement for $94 free shipping. If I went the ebay route I'd have all I need to build the monitors after repairing the supplies when I get all the parts.

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Old 05-29-2016, 07:17 PM   #140
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

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When I wrote the post I did not have the schematic in front of. The correct part was L4 which heated enough to discolor the glipt or what it is they globbed onto the parts.
They used glue. However, that glue does turn conductive when heated over time. So it is advised to remove as much of it as possible.

As for the L4 inductor, check the if the wire coating is still intact. If it's flaking and/or you can measure resistance between the wire strands, then that inductor is gone - or at least the wire is. In such case, you'd have to either rewind it with new wire of find the same replacement inductor (25 uH, 3A according to service manual)

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I do not have a lot of time for this right now. I can get two full amps complete with crossover, basically the whole panel with all connectors intact.
Okay, well keep us posted what you do.
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