Mackie SRM 450 replace Amp

Hi all,
Have talked about this before but still unresolved, I have 2 x mackie srm450 powered speakers with both amps blown. They are version 1 and 2.
I amp wanting a cheap way to power them efficiently, can’t seem to find a replacement plate amp so considering a separate amp and building crossover. They are both 8 ohm drivers and I’m not sure about the tweeters yet, will take apart later and check.
If anyone could help me fix these would be good to get them out on the road again.

Spencerleehorton said:

Hi all,
Have talked about this before but still unresolved, I have 2 x mackie srm450 powered speakers with both amps blown. They are version 1 and 2.
I amp wanting a cheap way to power them efficiently, can’t seem to find a replacement plate amp so considering a separate amp and building crossover. They are both 8 ohm drivers and I’m not sure about the tweeters yet, will take apart later and check.
If anyone could help me fix these would be good to get them out on the road again.

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I've messed around a bit in a version 1.  There are couple of different revisions of the circuit I believe. Here's the schematic for the one I am a tiny bit familiar with . D52 should be +15vdc ( next to transistor heat sink near transformer)....I know the ssm2164 can create problems and need replacing depending (cool audio works here if you can't find a replacement) but ,  if the thermal light is staying on and that's the issue,the 10ohm  r282 and 283 should be checked first ...they're next to the +/- 15 transistors....Q34 and Q35

Not sure how the v2 is set up though....

And , like I mentioned, there are a couple of different layouts for version 1
Good luck!

Parts list for a V1

EDIT///////////

I just read through your original thread.....

Didn't know you had already exhausted other avenues of repairs......

Those resistors I mentioned above can make the transistors appear to be bad when they are not....... Were the transistors pulled from circuit when tested??????....But, a bad vca can over heat the 15v transistors although it would take a long time to do so.....

There are a lot of components but, testing through the circuit shouldn't be impossible??????

I just tested some voltages at various points to make sure the dc was getting around like it should, then ran a sine through til I hit the problem areas..... Didn't take too long....and I don't know what I'm doing.....

These amps seem to be pretty dialed in for the drivers and cabinet....There are compression circuits and crossovers happening . Too much happening IMO....I've disabled the compression circuits by installing the jumpers and they sound like poo without them........ I'd too be curious about a separate amp/crossover for these..... They do tend to be on the bright side...

Yes my point exactly, anyone else chirp in with some alternatives ?

from what ive read in the specification for the V1 the amp is 400 watts, the horn is 100watts and the Driver is 300watts RMS.
The Horn is 8ohm and the crossover is Linkwitz-Riley 24db/oct @ 1600hz.
So if i could make a similar crossover and get a 400watt a side power amp i could power both speakers.
I don't know but assuming the driver is 8ohm as well and it is connected in series this would be driven at 4ohms right?
I can see some reasonable amps for around £100 for 960watts @ 4 ohms, if this is the case.
Ive done a bit more hunting and someone recommends using an amp 50% more powerful than your speakers can handle, so 400watts+200watts x 2 = 1200watts, the nominal impedance i think is the overall impedance needed? which in this case is 8ohm.
So am i looking for an amp which can do 8ohm 1200watt?

Spencerleehorton said:

from what ive read in the specification for the V1 the amp is 400 watts, the horn is 100watts and the Driver is 300watts RMS.
The Horn is 8ohm and the crossover is Linkwitz-Riley 24db/oct @ 1600hz.
So if i could make a similar crossover and get a 400watt a side power amp i could power both speakers.
I don't know but assuming the driver is 8ohm as well and it is connected in series this would be driven at 4ohms right?
I can see some reasonable amps for around £100 for 960watts @ 4 ohms, if this is the case.
Ive done a bit more hunting and someone recommends using an amp 50% more powerful than your speakers can handle, so 400watts+200watts x 2 = 1200watts, the nominal impedance i think is the overall impedance needed? which in this case is 8ohm.
So am i looking for an amp which can do 8ohm 1200watt?

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You seem to be thinking on the right track from my understanding......more power will keep you from having to push the amps as hard, staying safely out of the distortion range of the amp....... although I've heard 4x....

The tweeter is 8ohms ..... I do think there are two separate amps in the plate amp circuit so that sounds right.... ....That would mean 8ohms for each driver.......

My concern would be how these cabinets and drivers sound without the compression as I mentioned before, they really sound pretty rough for some reason without the compression circuit to my ears....Could be the circuit though and going the route you are taking may be better.....

Didn't they make a passive version of these SRM cabinets? Maybe there are some forums that talk about what people were using to power them?????

What did you do with the plate amps????

I still have the plate amps, the v1 has had surgery and keeps blowing two fets, the v2 two big resistors have blown and I fear it’s taken out lots on the pcb!

Spencerleehorton said:

I still have the plate amps, the v1 has had surgery and keeps blowing two fets, the v2 two big resistors have blown and I fear it’s taken out lots on the pcb!

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Well, like I mentioned on the V1, the resistors next to the +&-15v transistors can make any number of the other fets "appear" blown in circuit so, hopefully that is not happening....... and the caps next to those same resistors being bad can blow the the resistors.... not sure why, but it happened to me....

And the ssm2164 vca is notorious for blowing with the slightest problem with it's rails..... and that vca going creates all kinds of weird stuff.....
I think I remember it was r114 where I saw the sine voltage get whacky which pointed to a bad ssm2164 in mine..... and it was overheating my 15v transistors.....they shouldn't be really that hot......

There's one guy on youtube in the UK that seems to know his way around these.....I actually followed his advice on those resistors I mentioned and it was great advice on two different occasions...... He also pointed out that the later model transformers on the V1 could be prone to broken windings......

But yeah.....can they squeeze more tiny components in there????? and they're not the tiny tiny ones.....



I'm not sure how different the v2 circuit  is aside from the power supply......

But, I'm still interested in an alternative option for getting a good sound from the drivers and cabinets.....There has to be some kind of combo that will work .....

Or just sell what you have and invest in something else.......


Let me know if you ever want some voltages or something tested from a working V1...... if you ever decide to waste any more time on your amps....... I'd be happy to help...... My wife, not so much...... but she does leave to go shopping.... ;D

Well as far as I can see I need to get hold of a 2 x 600 watt power amp and an active crossover.
If I run the 8ohm tweeter and 8 ohm speaker in parallel it would run in 4 ohms.
The crossover seems to be at 1600hz 24db per octave so really need to find something about this?
I have a small amp I could test everything at low level but waiting on a 1200watt that I can borrow from a friend.

Spencerleehorton said:

Well as far as I can see I need to get hold of a 2 x 600 watt power amp and an active crossover.
If I run the 8ohm tweeter and 8 ohm speaker in parallel it would run in 4 ohms.
The crossover seems to be at 1600hz 24db per octave so really need to find something about this?
I have a small amp I could test everything at low level but waiting on a 1200watt that I can borrow from a friend.

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I'm not certain on the ohms....I think the Mackie is two different amps in one......, each at 8ohms????? damping probably better for woofer...but probably no big deal.....

and an external crossover would need to feed two different amps wouldn't it???? Unless you are speaking of a passive one for the cabinet

Spencerleehorton said:

from what ive read in the specification for the V1 the amp is 400 watts, the horn is 100watts and the Driver is 300watts RMS.
The Horn is 8ohm and the crossover is Linkwitz-Riley 24db/oct @ 1600hz.
So if i could make a similar crossover and get a 400watt a side power amp i could power both speakers.
I don't know but assuming the driver is 8ohm as well and it is connected in series this would be driven at 4ohms right?
I can see some reasonable amps for around £100 for 960watts @ 4 ohms, if this is the case.
Ive done a bit more hunting and someone recommends using an amp 50% more powerful than your speakers can handle, so 400watts+200watts x 2 = 1200watts, the nominal impedance i think is the overall impedance needed? which in this case is 8ohm.
So am i looking for an amp which can do 8ohm 1200watt?

Click to expand...

You got a lot of your maths wrong. Supposing the speakers are in series is utterly wrong. The speakers are powered by two dedicated amps, one that can delever about 400W to the woofer and the other about 100 to the HF driver. You can't connect a woofer and a tweeter together without a x-over network, either passive (one amp which output is separated to the speakers) or active (electronic separation to two amps).
Increasing power by 50% does not mean doubling, it means 1.5 times.
You are unfortunately facing a situation where actually repairing these would be quite costly, either paying an experienced tech or buying from the manufacturer new amps.
Supposing the drivers are OK, you could indeed use an electronic x-over and 4 channels of amplification, 2 of about 400W and 2 of about 100. You can probably find that second-hand at dirt-cheap price.

Ah ok, so your saying I need an amp per speaker to the rating.
I had watched something which said add 50% again so I did 300 + 100 + 200 to get 600 Watts per channel. But yes this would have been in series at 16 ohm I think which is not what is needed.
I can see now that each driver needs an amp, could a 4 channel plate amp do like the ones that fit in cars? Or 2 x 2 channel ones?

Spencerleehorton said:

Ah ok, so your saying I need an amp per speaker to the rating.
I had watched something which said add 50% again so I did 300 + 100 + 200 to get 600 Watts per channel. But yes this would have been in series at 16 ohm I think which is not what is needed.
I can see now that each driver needs an amp, could a 4 channel plate amp do like the ones that fit in cars? Or 2 x 2 channel ones?

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I don't think you could find automotive amps with a genuine rating of 400W into 8 ohms. Beware they are typically rated at "instantaneous peak power", which is generally measured by the mktg department. Inst peak power is typically 4x the real "rms" power.

Spencerleehorton said:

Ah ok, so your saying I need an amp per speaker to the rating.
I had watched something which said add 50% again so I did 300 + 100 + 200 to get 600 Watts per channel. But yes this would have been in series at 16 ohm I think which is not what is needed.
I can see now that each driver needs an amp, could a 4 channel plate amp do like the ones that fit in cars? Or 2 x 2 channel ones?

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I've used car amps before but, not for something like these.....I used an old computer supply for the 12v......

Yes, so you need an amp for the highs and an amp for the lows.......

Too bad.......those Mackie amps, although Mackie crazy design, sound quite ok in this set up..... They have put in many ambitious processes to fine tune these cabs...... and are pretty reliable if nothing else from my experience.....

I am surprised that they are destroyed but, I don't know too much....I've shorted things in them (tiny parts and coffee)and had to hunt down a couple of things, but it was always there to find ... I've even accidentally ran the +15v to the wrong circuit when I disabled the muting switch and, it just blew a diode and one tiny transistor .....

Even replacing the vca was a nightmare for me and had to jump some traces around but everything worked great.....

Yes it took me a week off and on when I could find time and parts but was worth it..... I have to start somewhere.... Might have had an easier time with a hammer....

Good Luck!

And some amps today like the Crown xls have dsp and crossovers built in.....  Hopefully any amp you get will not break down....

Stupid Murphy...

Well all I can think of doing is building a 400 watt 8 ohm amp and a 100 watt 8 ohm amp building a cross over and put them in each cab!
Or repairing them, there doesn’t seem to be any other way to actually get these working easily!
Pretty annoying really!!!!!

Spencerleehorton said:

Well all I can think of doing is building a 400 watt 8 ohm amp and a 100 watt 8 ohm amp building a cross over and put them in each cab!
Or repairing them, there doesn’t seem to be any other way to actually get these working easily!
Pretty annoying really!!!!!

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Yeah.....Frustrating.....

Well you could list the Mackie amps and fund your new direction......

............ like I mentioned earlier, if you need any readings from a working V1 amp , let me know.....
Good luck!

I have a pair of the srm350's they only ever get light usage ,but worked faultlessly for me .
I think the srm's use class d switching amps, Id imagine the limiters play a role in keeping these things sounding sweet ,class d clipping is gonna rip your head off . One option could be to fit your speakers with four pole speakons and you could try something like Behringer I nuke dsp series,they come in a range of outputs powers and have all the nessesary functions in the dsp to do crossover and limiting ,there also very light weight and competitively priced.

Tubetec said:

I think the srm's use class d switching amps,

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No, the schemo is clear, the HF amp is a conventioanl Class AB design with +/-45V rails, the LF amp is class H with additional +/-80V rails.

is there a DIY design that could be used to do something functional for these?

or shall i just bite the bullet and ebay them?