davethebassman Posted July 22, 2012 Share Posted July 22, 2012 Hi All First of all many apologies if this query has been posted before, but my particular set up probably hasn't and I am betting that anyone who is trying to sort out a cheap PA system may benefit from this thread. First of all let me say that I am an electronic engineer, who used (20 year ago) to specialise in audio. So please, no thread comments about blowing myself up LOL I am in the process of trying to sort out a PA system of the following specification: Behringer mixing desk, which is used for the inputs (Banjo, Acoustic Guitar, Bass, Backing tracks, Electric guitar etc...) Sub outputs from the mixing desk going to 2X Velleman 200W power amp modules used for the monitors (full range monitor cabs) Main outputs from the mixing desk going to 4X velleman 200W power amp modules used for the main speakers (facing audience) This may become more high powered if need be (probably 400W per amp) The main speakers I am envisaging to be a 15" bass speaker cab for the low end (200W per cab), and then a 12/10" speaker with tweeter for the high end cabinet (200W per cab). My question is this. Has anyone got any ideas about an active crossover component which can enable the main speaker system to work as I envisage? I am worried about dead spots in the frequency response. I would design my own, but I have forgot all the calculus needed to work out the op amp frequency response stuff. I would prefer a kit module, ie velleman et al but I am not adverse to buying the right equipment if need be. Oh forgot to mention, this is for a band project playing predominatly Irish / acoustic / rockabilly material. (Don't know if this is relevant for the question but thought I would mention it. Hope this question is detailed enough to warrant some sensible suggestions, and I would like to thank everyone who responds for your thoughts. As a newbie to performing live, I respect everyones opinion. Cheers folks Dave PS Cost of amp kits are £14.99 per unit + about £25 for the transformer + £15 for heatsink which makes a total cost of £55 + case for a 200W power amp. Hope this helps someone. My disclaimer, don't even think about making this amp if you are not competant in electronic / electrical matters, high power sh*t is involved, be safe, don't blow yourselves up. Quote Link to comment Share on other sites More sharing options...
icastle Posted July 22, 2012 Share Posted July 22, 2012 An active crossover is a little OTT given your selection of base equipment. If you're going to use a pair of cabs per side then why not place a passive x-over in the bass cab and then run a loop up to the mid/top cab... Quote Link to comment Share on other sites More sharing options...
bertbass Posted July 22, 2012 Share Posted July 22, 2012 Those 200w are music power watts. RMS watts are 100w into 4 ohms and 70w into 8ohms. Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted July 22, 2012 Share Posted July 22, 2012 When you get into serious PA design, should definitely head towards working in voltage swing rather than watt ratings, at the very least RMS watts with known impedance and passband. How big a venues are you hoping to work with with it? Quote Link to comment Share on other sites More sharing options...
davethebassman Posted July 23, 2012 Author Share Posted July 23, 2012 The venues will be small(ish) pubs, where 100W per side will be ample. Quote Link to comment Share on other sites More sharing options...
Jack Posted July 24, 2012 Share Posted July 24, 2012 [quote name='davethebassman' timestamp='1343081755' post='1745109'] The venues will be small(ish) pubs,[/quote] Cool. [quote name='davethebassman' timestamp='1343081755' post='1745109'] where 100W per side will be ample.[/quote] Really? Is this your first foray into this kind of stuff? I don't mean to sound condescending, it's an honest question. Do you know that 100W a side is enough? If you do because it's replacing your current system for example then fair enough. Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted July 25, 2012 Share Posted July 25, 2012 Hi Dave, I used to build this sort of thing and still have some of my old power amps but it doesn't make sense economically any more. You could buy a 100W RMS a side amp for around the £100 mark which is cheaper than the components. For £224 you could buy the Thomann t-amp which is 4x500W to run FOH and the monitors or tops and bass bins with a crossover. Again you can buy a ready made electronic crossover for less than £100. It bugs me to say it but the days of home building to save money are gone except for building high end speaker cabs. If you are home building for fun then go for it, of course. Quote Link to comment Share on other sites More sharing options...
Pbassred Posted July 29, 2012 Share Posted July 29, 2012 [quote]It bugs me to say it but the days of home building to save money are gone except for building high end speaker cabs. If you are home building for fun then go for it, of course. [/quote] +1 You have to remember what your core activity is. If its playing bass, do that. If its running a PA system, do that. If electronics is your thing, do that. If you are a bass player who needs a 100W per Chan PA, get a mixer amp, and plug 2 speakers into it. Anything else is distracting you. I speak as someone with [b]30[/b] years of playing and building his own sh*t with an unused 1.5 K PA in the garage. Why unused? Because I dont spend enough time playing. When I HAVE used it it I get anoyed because I need to move it and set it up myself! I just threw out 2 old Mosfet amps because I realised thar they wouldn't be reliable. Go practice scales instead. Quote Link to comment Share on other sites More sharing options...
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