Marshall Ministack great with stock speaks rubbish with anything else! Why?

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My buddy bought this setup used (not SWIM thank you)
Marshall MG Series MG15CFXMS 15W Guitar Mini Stack Carbon Fiber | Musician's Friend

He is a shredder sort of guy and it sounds... ok... let's be nice :( it sounds like very heavy distortion. MegaDeath, RamStein, etc.

So we hooked the head to some of my speakers thinkin it would sound AWESOME!
NOT!
2x12" 25w ceramic guitar speakers :dead:
2x12" alnico (FANTASTIC) guitar speakers :ill:
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EVM12L music PA speaker (my go-to) :h_ache:
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2x10" alnico (SCREAMING) music speakers :ashamed:
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2x6" alnicos (what like 3w each?) meh... ok....:(

Original speakers? :hypno2:

My speakers aren't junk, maybe not top $$$ but we've run a variety of amps through them with good results. Sometimes amazing results. :eek:
How does his amp sound SOOOOOO bad with all but the stock 10"s ???

Have you seen this before?

EDIT don't know what all that "click to see fullsize image" is about. I only put smileys, no other images. Can't edit them out either.... hmmm.
 
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That's a good suggestion. We did try them on another amp and they sounded pretty decent.

To more directly address your post, I'd forgotten to mention how his head sounded on other speakers.
Thin and hissy. More than hissy, static like. Like we'd plugged in a full stack of tweeters.
Completely lacking bass even on a [email protected] speaker (there is some roll off around 100hz but it sounds quite nice with another 15w amp)

I wonder if there is some passive crossover in the boxes?
I just don't get it....
 

Gnobuddy

Member
2016-03-01 4:10 pm
Thin and hissy. More than hissy, static like. Like we'd plugged in a full stack of tweeters.
Completely lacking bass even on a [email protected] speaker
<snip>
Are you plugging your speakers into the same speaker jack that normally drives the stock speaker cabinets?

I'm wondering if you were using a different speaker-out jack, and it was actually defective, causing the symptoms you described. "Thin and hissy" is what you'd get if you have a too-small capacitor in series with the speaker, and turn up the amp gain and volume in the attempt to compensate.

(Since this is a solid-state amp, a capacitor in series with the speaker is a real possibility. If someone soldered in the wrong value cap in series with the output jack, that might cause the symptoms you're hearing.)

I once got "thin and hissy" out of a singer/songwriters guitar. The problem was a bad guitar cable.

-Gnobuddy
 

Gnobuddy

Member
2016-03-01 4:10 pm
single supply solid state amps were common 40 years ago, but not now.
I agree, but I have seen stranger things in commercially manufactured products. And the symptoms the OP described could be caused by a series cap.

A lot of the lower-power stuff today seems to use a single supply rail (rather than split bipolar rails), two power amps on one chip per audio channel, and a bridge-mode connection to the speaker.

I guess they're trying to use lower supply rail voltages and get away with a simpler power supply. It's probably an additional bonus if you can make the thing work on the single 12V (nominal) battery voltage in an automobile, as that opens up another market for the product.

-Gnobuddy
 
The combo amp appears to use the same board into a single 8 ohm vs 2x 16 ohms parallel.
Sorry for the lack of components and crappy pics, it took a while to even find this.

[IMGDEAD]http://images.postadsuk.com/2015/06/10/postadsuk.com-marshall-mg15-parts-for-spares-or-repairs.JPG[/IMGDEAD]
[IMGDEAD]http://images6.postadsuk.com/2015/06/10/postadsuk.com-1-marshall-mg15-parts-for-spares-or-repairs.JPG[/IMGDEAD]​


I'm going to see if he'll bring it back by so we can have a little peeky inside.
 
No surprise your amp does not work very well ... lazy bench worker left out a few parts ... some 275 of them ... Friday afternoon job? ;)


seriously now: that amp is as generic as can be, you can clearly see the 5 hole cluster where a typical chipamp should be: TDA2030/2050/LM1875 (all 3 equivalent by the way in a 15W practice amp).

And they run on split ~+/-18V supplies .

2 details:
1) if designers do their homework, and specially knowing they *will* be used as a whole set (if anything, because of the fake "carbon fiber" look), they will equakize the h*ll out of them so they sound better than they cost ... kudos to them for that.
2) even without knowing which speaker will they be used with, many late model Marshall amps add what they call "FDD" , in ad copy "full/fat/warm Marshall Sound), in practice a strong Bass boost around 90 or 100Hz.

Might have a special button for that or simply solder it solid if it matches *those* speakers ... with others it's anybody's guess.

Here's Marshall FDD in all its glory, here pulled from the 30W one, where it's switchable.
If somebody cares to simulate it and post curves, he's most welcome ;)
J6zB6C0.gif
 
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