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Mackie MR10Smk3 - inside pics, personal thoughts

trl

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I purchased this subwoofer immediately after I got the two MR6mk3 studio monitors. I felt like I need more punch in the bass, so I said to myself that I deserve it, hence here it is: MR10Smk3 subwoofer.

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Front view with cover

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Front view without cover


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Rear view with controls



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Inside view - DMOS transistors heatsink and the big transformer



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Inside view - mains EMI/RFI filter on the left, inputs and tone control on the right, also transformer and amplifier on top

Based on Mackie's documentation manual http://mackie.com/sites/default/files/PRODUCT RESOURCES/MANUALS/Owners_Manuals/MR10Smk3_OM.pdf, the MR10Smk3 subwoofer is powered by a 120W RMS (240W peak) Class A/B monolithic integrated circuit amplifier with DMOS power stage, exactly like in MR6mk3 active monitors. If inside the active monitors there's indeed a Class A/B monolithic IC, inside the MR10Smk3 there is actually a Class D amplifier instead! Fine with me, but I was expecting the specs and datasheet to state that in the first place...although, I'm sure I wouldn't purchase it anymore if I knew it's class D, but I'll call myself too subjective.

For example, inside the MR6mk3 there are two reputable low-noise 100-Watts TDA7294 Class A/B amplifier chips, so I thought that inside the MR10Smk3 would be something similar, instead I found one IRS2092S Class D chip followed by three TO-220 transistors soldered on the back of the PCB and mounted to a big heatsink. Two of them are probably IRF6645 or similar, based on the datasheet and recommended schematic. Also, on main PCB is written Class-D v1.0 amplifier, so I don't know why the specs from their website says otherwise. Also IRF datasheet here: http://www.irf.com/product-info/fact_sheet/audio-irs2092.pdf.

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The IRS2092S Class D chip

However, probably amplifier's schematic is similar with the one found on pag. 2 of https://www.infineon.com/dgdl/an-1138.pdf?fileId=5546d462533600a40153559a077610d1 and the two MOSFETs are the ones already mounted on the big heatsink; also, the coil could be seen in the pictures. As per chip's specs, there are no Turn-ON and -OFF audible click noise, so when powering ON I need to check the LED if it's lighten or not, yes that quiet, which is great actually.

Class-D_schematic.png


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The two MOSFET transistors on top

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The two MOSFET transistors on top


I wrote Mackie a message about this, through their website, over 1 year ago, but no reply yet, although their website got updated to reflect the reality and correct their initial "mistake":

Screen Shot 2018-09-01 at 22.06.51.png


Too bad the PDF datasheet and all vendor are still using the AB class wording. :(

The internal mixer and analogue controls is getting power from the internal EI transformer (2x15V/0.5A), then is regulated through a small rectifier bridge and ST L7815CV/L7915CV 3-pin LDO chips. The power amplifier gets the power from the same EI transformer (2x32V/1.8A) that is regulated via a big rectifier bridge and two big 6800uF/80V @105C CapTop capacitors. The opamps used are JRC 4558, similar with the ones found in MR6mk3: ST 4558.

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The two linear regulators powering the internal mixer and analogue controls



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Top view of the class-D amplifier

Despite the JRC4558 opamps and the thread from here, my MR6mk3 speakers sound very good connected through this subwoofer. Basically, the sound coming from the DAC enters the subwoofer where is getting mixed with the subwoofer's amplifiers, so JRC4558 opamps are there as additional output buffers that act as a sound mixer/preamplifier circuit. However, there's no additional noise injected into the two MR6mk3 studio monitors connected to this sub and clarity and details are really good, definitely above average. Also, retrieval of details and audio quality is not affected in any way by the mixer from inside this subwoofer.

JRC4558.png

I found the gain/amplification for the subwoofer as being too high. Even if I'm feeding it with a normal 2V RMS DAC, via single ended TRS plugs, I keep the LEVEL knob to about -25dB to match monitors volume, which is very low. This is not something bad, but I was hoping the LEVEL should be somewhere around 0dB.

I really like the EMI/RFI filter from mains, just before the transformer. I wasn't expecting for such a filter on a not so pricey subwoofer.

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All the internal components were very well soldered and also glued on the backplate: caps, bigger resistors, cables were mostly wrapped together, so no strange noises could be created inside the speaker. Even the big heatsink was very well glued on the backplate as well. All holes, all PCB and backplate screws and input/output plugs/connections were sealed too with incolor or with black sealing glue, so all air movement is done correctly only from the front bass port.

I'm not a fan of CapTop capacitors, but at least all of them are rated to 105C; hope they'll last enough years to please my ears. :)

The padding/stuffing from the internal cabinet was above average glued and size, so I needed to glue again some part of the padding, just to be sure the air will not move the padding inside. Also, the black vinyl coating was getting unglued when I was moving the sub with my hand, probably I was not paying too much attention to the edges, so a bit of glue fixed it instantly. I will be treat it with good care after. :)

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External coating pealing off from corners

Case is 15 mm thick on all sides and the 4 corners and sides are reinforced with small pieces of wood of 20-25 mm thickness. Under the case there are 4 generous rubber feet that minimise bass vibrations and make the subwoofer's case very steady on the floor.

Speaker itself has exactly 3.5 ohms of internal resistance and is connected to the power amplifier through about one feet of 20 AWG cables. Kinda thin cables I'd say, but should probably sustain the max. 5-6 ampers that feed the 3.5 ohms speaker for average-to-high listening levels. After all, this subwoofer is not a house-shaker, but it has plenty of power for my 15 m2 bedroom and also for my 25 m2 living room when I test it recently (actually 40 m2 open space, but plenty of bass for entire space). The main issue is the furniture I'm using that is shaking and gets "noisy", not the sub itself. :)

I'm not using the Auto Power "feature" because either is not working as expected in my setup, either it has some flaws. I'm keeping it ON for 100% of time, this is the only way I can get the Green-light and to hear the music.

Power consumption written on the back of the subwoofer, 250W, seems unrealistically high for a 120W RMS Class-D amplifier, but to be honest I wasn't testing how much power it drains from the outlet. This amplifier should have a power efficiency of 90%, so I estimate that power consumption is somewhere lower than 200W

PRO:
- bass sounds very good, well extended
- great punch (though, could sound a bit relaxed with some tracks)
- crossover freq goes down to 40Hz, that should help out in paring with lot of monitors

CON:
- no RCA in/out (some could still use non-balanced cables)
- no XLR out (though, there is XLR in)
- gain is just too high, I use volume level knob at 9 o'clock (half volume is at 12 o'clock, max. volume is at 5 o'clock)

PDF datasheet attached to this post as well.
 

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trl

trl

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Found some pics, editing now. They did modified their website meanwhile, but the PDF and website that sells this sub are still showing it as class AB...well, not all of them, thomann.de shows this: "MACKIE MR10S MK3 IS NO LONGER AVAILABLE, UNFORTUNATELY.

Product I purchased was https://www.thomann.de/ro/prod_AR_318984.html, indeed not being available now.

From my inbox:
1x Mackie MR10S Mk3
Mackie MR10S Mk3 Active Subwoofer, 10" (254 mm) glass aramid composite woofer, 120 watts (240 peak) Class A/B amplification. Stereo balanced XLR and TRS line inputs. Stereo balanced TRS line outputs. Adjustable 40Hz to 180Hz crossover. Polarity switch. Frequency Response: 28Hz - 220Hz. Max Peak SPL: 113dB. Dimensions: 381mm x 320mm x 381mm (HxWxD), 12,4 kg
Nr. articol: 318984

L.E.: That's how the product was advertised by the manufacturer when I bought it (April, 2017 - thanks to https://web.archive.org/web/20170429180843/https://mackie.com/products/mrmk3-series):

Screen Shot 2018-09-01 at 23.23.32.png
 
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trl

trl

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The MR10S Mk3 was replaced by the new MR series which is advertised as Class AB as well, per https://www.thomann.de/ro/mackie_mrs10.htm#bewertung:

Active Studio Subwoofer
  • Equipped with: 10" (254 mm) woofer
  • Power: 120 Watts
  • Class A/B
  • Frequency range: 28 - 180 Hz
  • Bass reflex system
  • Crossover adjustable from 40 to 180 Hz
  • Phase reverse switch: 0°/180 °
  • Vibration absorbing rubber feet
  • 2x XLR and 6.3 mm jack input
  • 2x XLR and 6.3 mm jack output
  • Dimensions: 339 x 320 x 386 mm
  • Weight: 15 kg
  • Incl. foot switch for bypass function
Even amazon.com is presenting it as being class-AB here: https://www.amazon.com/Mackie-MRS10-10-Powered-Studio-Subwoofer/dp/B073V7SGGH: "Designed for responsive and accurate low frequency reproduction. 120 watts of Class A/B amplification. 10″ glass aramid composite woofer" and seller is Mackie.

I assume the new MRS10 subwoofer appeared initially on the papers as class-AB and later got modified to class-D...not sure, just assuming.

However, on their website this sub is presented as Class D:
Screen Shot 2018-09-01 at 22.59.42.png


Same Class D appears on the datasheet attached: "Monolithic IC, Class D with DMOS power stage".
 
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trl

trl

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Forgot to say: the 10" woofer is connected to the Class-D amplifier via an approx. 40 cm (1.2 ft.) 2-wire long cable having a thickness of 20AWG (0.5mm2) and made of 100% aluminium (brand Zelongkang).

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Based on https://www.sab-cable.com/fileadmin/user_upload/pdf/catalog_gb/kapitel_N/N_en_26-27.pdf and https://www.rapidtables.com/calc/wire/wire-gauge-chart.html 20AWG = 0.5mm2 diameter, for multi conductor copper cables @30C this means a nominal current of 5A, but AFAIK 20AWG for aluminium should be similar with AWG24 for copper: 3.5A nominal current. Also, 2 ft. of 20AWG aluminium cable is around 0.033 Ohms, probably the same as internal resistance of the amplifier itself, so it has a direct impact on the final damping factor.

Given the fact that this speaker is handling about 120W of RMS power, about 21V and 6A (speaker has a DC-resistance of 3.5 Ohms), I had replaced this cheap 2-wire cable with a decent 2-wire 15AWG (1.5mm2) speakers cable, made of 100% copper. This has a nominal current handling of about 12.5A and 2 ft. of 15AWG copper cable has an internal resistance of 0.0063 Ohms, so 5 times lower resistance and 3.5 times more current handling capacity.

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20AWG aluminium vs. 15AWG copper

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20AWG aluminium vs. 15AWG copper

I don't want to be a troll here, I own this sub and I like its sound (besides the very low rattling sound the rear port does, it sounds pretty good), but I wonder how much money does manufacturer saves by using very cheap 20AWG aluminium cables instead of regular 15AWG copper ones? I guess is less than 1 USD/feet when you purchase wholesale. :)
 
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pozz

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Can't believe I missed these before...

Added a new "Speaker" section to the master review thread.
 

Trdat

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These sub reviews are very enlightening. Appreciate your effort.
 

Citizen

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Nice, have the older Mackie/Tapco 10" sub, have had it from new so 18-20 years old, very nice warm sounding sub with 10" dual voice coil sub and a dual 60w amp, XLR and phono inputs/outputs and left and right channel linkwitz riley filters, only thing that went wrong was the volume pot stopped working in the notched position but just moved it a fraction higher for a while and the problem went away, not contact cleaner or anything.

Have had it apart and it seems decent enough.

Thanks for the teardown, it is super interesting.
 
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