Mackie SRM350 crossover bodge

[cedd]

Hi all

As the title suggests, I've had a dodgy SRM350 for some time now. The PCB that holds the gain pot and input XLR's is duff and the gain changes randomly and sometimes quite painfully. I've exhausted most avenues in getting the thing repaired. I've replaced the pot and as the fault seemed to only occur when the pot was moved, I've currently got a pair of fixed resistors in place so the pot can't be adjusted (the idea being nobody can disturb the pcb by moving the knob). None of these have worked for long!

 

I've also tried getting hold of an input pcb, but can't source one (if anybody knows of a source I'd be greatful!).

 

For the time being, I can't afford to give any more time or much money to this, but need the cabinet. I have spare amplifiers so am now thinking I could just remove the amplifier module, keep it on a shelf somewhere for another day, and put in my own crossover and a speakon socket on a back panel that would fit where the amp used to be. Dirty fix, but would sort it out!

 

So, I need a crossover. Thing is, most of my usual suppliers and any googling I've done, come back with quite cheapo modules that aren't up to the power needed. What makes do people use?

I need 24dB Linkwitz riley at 2.4kHz. The amp spec from the original module is 165W LF and 30W HF, so at least 200W power handling to be up to the previous spec.

 

Or... if anybody has the pinout for the ribbon connector that goes between the input PCB and the amp module, I could ignore the mackie input boart completely and build my own!

[Brian]

I need 24dB Linkwitz riley at 2.4kHz.

You're not going to get such a beast as a passive crossover.

 

Go active.

[cedd]

You're not going to get such a beast as a passive crossover.

Go active.

Very true, thought had escaped me for a second there. That's the spec of the original crossover within the amp. That said, I'd ideally like to be able to use a jack cable or speakon, but ideally one amp channel would be needed only.

With that in mind, I'd perhaps be happy to settle for a different type of crossover. The cabinet is only really on foldback duties, and not particularly high end jobs either. I just want some noise out of the box!

[boswell]

Can't you reverse engineer the input PCB in the manner of some of the cheaper makers of amps ;)

[Brian]

The steep cut-off will be used to limit the amount of power into the HF unit. If you go with a simpler filter you'll need to increase the frequency to limit the LF energy going to the tweeter.

 

TBH, I'd not bother filtering the feed to the LF unit and I'd just stick something in the line to the HF. Just watch the amount of LF you feed the box.

[cedd]

That sounds like a pretty sensible idea, thanks. It's only 10" driver, so I do need to watch the bottom end. Where do people buy their crossovers from? Any makes I should look out for?

[Jivemaster]

http://www.bkelec.com/HiFi/ClassD/ClassD.htm

 

http://www.terralec.co.uk/loudspeaker_part..._/10136_0c.html

 

Are the drivers 4, 8, or other impedance? The crossover frequency is a function of the driver impedance so it matters with passive crossovers, but doesn't matter with active crossovers. 24dB crossovers don't happen in passives unless you cascade two 12dB ones and then would it be L-Riley curve and what would the insertion loss be???? and the phase shift????

 

BK in Southend (first link) used to have a range of boards ready to fit to a passive cab to go active.

 

Totally different approach would be to look for a second hand mackie unit on ebay and the like and do a mix and match.

[Matt Riley]

Hey,

 

Are you aware of the Mackie C200? This is the passive version of the 350. This means that there is a passive xover assembly which bolts in the place of the current active assembly, so my advice would be to try and get the part from a mackie dealer.

 

Alternatively, here's the specs for the c200 which would provide a better indication of the kind of things to look for in a passive xover than the active settings of the c350:

 

Frequency response: 89Hz-20kHz

Frequency range: 59Hz-22khz

Max SPL: 118 dB

LF crossover type: 6 dB/oct time corrected

HF xover type: 12 dB/octave

Xover frequency 1800 Hz