# Connect passive sub to 2.0 receiver using plate amp



## bobdebouwer (Oct 21, 2014)

Hi,

I'm looking at building a DIY sub (lilwrecker) and not sure if I would take a plate amp (quite expensive and not a good option as I will need to build an external box for it anyway) or a PA amp (Behringer EP4000 or Crown XLS)

I only don't really see how to connect the PA amp to my receiver with a classic A and B channel exit but no subwoofer exit.

Plate amp looks quite simple, connect wires to amp, and connect them again from amp to speakers, done.

Have been looking at the connections at the back of the behringer and googling but still not clear how to connect...

thanks in advance!


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## Wayne A. Pflughaupt (Apr 13, 2006)

If I understand, you have a basic stereo receiver, with no subwoofer output jacks? You’ll need to go with a plate amp that has speaker-level inputs.




bobdebouwer said:


> Plate amp looks quite simple, connect wires to amp, and connect them again from amp to speakers, done.


That will certainly work but if you have really nice gear I wouldn’t recommend it, because it adds a passive crossover between your receiver and main speakers. If the receiver has “Speaker B” terminals, use them to get a signal to the sub. This means your main speaker will be running full range, so you’ll have to set the sub’s plate amp’s crossover for whatever frequency the main speakers’ low end rolls out naturally.

Regards, 
Wayne


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## bobdebouwer (Oct 21, 2014)

Thanks for the info. This means there is no way to add 'something' between my pre amp and end amp so I can split the low hz signal and send it to a pa end amp connected to a sub?

Reason why i ask this anyway is because I want to build a lilwrecker tapped horn but a 1000 w plate amp with dsp would be 70% of the total project cost. A 2nd hand pa amp can be had for half

Thanks!


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## Kal Rubinson (Aug 3, 2006)

bobdebouwer said:


> Thanks for the info. This means there is no way to add 'something' between my pre amp and end amp so I can split the low hz signal and send it to a pa end amp connected to a sub?


Oh. You have separates? Then, you can insert a subwoofer crossover between preamp and power amp.


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## bobdebouwer (Oct 21, 2014)

Indeed I have separates, pre amp and 2x200w end amp. Do you have a link to a good crossover? Do I really need a pa amp with dsp or not? There are a lot 2nd hand pa amps for sale but few with dsp. 

I could build the crossover and pa amp in a nice box with a silent fan to get the waf factor up


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## Wayne A. Pflughaupt (Apr 13, 2006)

If all you’re interested in is dividing out the lows to the sub, then all you need to do is split the pre-amp outputs and send them to the plate amp. Just makes sure you get a plate amp that has built-in crossover.

Now, if you also want to high-pass the mains, then that will indeed require a separate electronic crossover.

Regards, 
Wayne


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## Kal Rubinson (Aug 3, 2006)

Wayne A. Pflughaupt said:


> If all you’re interested in is dividing out the lows to the sub, then all you need to do is split the pre-amp outputs and send them to the plate amp. Just makes sure you get a plate amp that has built-in crossover.
> 
> Now, if you also want to high-pass the mains, then that will indeed require a separate electronic crossover.
> 
> ...


Indeed and, imho, building and using a subwoofer today should include DSP/EQ for it.


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## bobdebouwer (Oct 21, 2014)

So if I got it right, I need to split the out signal from my pre amp, I have 2 exits on my pre amp so I can leave one going to the end amp and one going to the subwoofer. The sub I could power with a 1000 W dayton audio plate amp, they are not that expensive, around 400 EUR. Still more expensive than a PA Crown or Behringer amp, going around 300 EUR (and more Watt)

The signal going to my end amp (and to my speakers) I indeed would need to high pass...

Still the question remains why I should bother with a (expensive, per Watt) plate amp. If I can get the active high/low pass, can I not split one 'out' to the 'hifi' end amp (powering my speakers) and one 'out' to another end amp (PA as it's cheaper) powering my subwoofer?

Or am I missing something? The sub would be a 'lilwrecker', which requires at least 500W RMS (preferably, 1000)


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## bobdebouwer (Oct 21, 2014)

As I do not have enough posts I cannot post a link, but I would need:

pre amp
out 1 => low pass filter, "80 Hz Low Pass 8 Ohm Crossover" (from Ebay) => PA Amp => subwoofer
out 2 => high pass filter "80 Hz High Pass 8 Ohm Crossover 266-458" (also Ebay) => hifi Amp => 2 speakers

The low and high pass would be +/- 40 USD together, a PA amp used +/- 200 USD, and maybe I should put an equalizer in between, they can be had easily for +/- 40-50 USD.

In total this would thus be +/- 300 USD (but I won't have the fancy DSP and it will need to be put completely out of sight for being too ugly...)


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## Kal Rubinson (Aug 3, 2006)

bobdebouwer said:


> As I do not have enough posts I cannot post a link, but I would need:
> 
> pre amp
> out 1 => low pass filter, "80 Hz Low Pass 8 Ohm Crossover" (from Ebay) => PA Amp => subwoofer
> out 2 => high pass filter "80 Hz High Pass 8 Ohm Crossover 266-458" (also Ebay) => hifi Amp => 2 speakers


Neither of these will work. Placing the filters between the preamp and amp puts them in a higher impedance situation. You need line-level filters and, preferably, tunable/adjustable ones since textbook/off-the-shelf solutions are usually far from optimal in practice. See here: http://www.marchandelec.com/


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## dgmartin (Oct 29, 2011)

If you can solder, you have 2 options:
The first option is a passive line-level XO (see attached). This will not yield a perfect response but even a textbook response will be multiplied by than the mains/sub's own rolloff and the room response at these frequencies. Also it is limited to 2nd order. Note that I did not bother to optimize since it needs to be optimized to your preamp's output impedance and power amp's input impedance. I just took typical values of 1k for output and 100k for input. This was done using LTspice (free). The circuit illustrate why you cannot use a 8 Ohms crossover (As Kal mentioned )

The second option is to build an active line-level crossover (like Kal was proposing). This one will have buffers between each stage and yield text book response at the power amp input, so you are free to use a plate amp or PA amp. A good example can be found here at http://sound.westhost.com/project09.htm (a 4th order is also available from there).


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## dgmartin (Oct 29, 2011)

I realize the flow of the thread set me in DIY-mode. You can simply used a MiniDSP b/w pre- and power-amp if you do not want to bother... you GET the EQ as a bonus!


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## bobdebouwer (Oct 21, 2014)

Ok, thanks again! 

I'm not really that hugely experienced in soldering, I do if I need to but try to limit it to 'repairing' my amp by replacing stuff if it's broken. (as I will need to replace my 4050v modules...)

So if I understand it correctly, this 

http://www.amazon.com/Hifonics-HFEQ...18&keywords=active+electronic+crossover+2-way

I could simply put between my pre amp and amp for the sub and the other amp for the normal speakers. it's for cars but I guess a modified laptop power supply would do the trick? If I take an Inuke PA Amp, I have DSP there. Or can I get a crossover with DSP in it?

It would help if you could post some links or the product name of stuff I need. I know I need to have a crossover to do the high/low filtering, it should have 1 input and 2 outputs (or 2 inputs and 2 outputs) but i'm really getting confused:huh::huh:

This is why I added below a diagram of what I think based on this information would be the setup. Help in finding the right side (passive sub) would be appreciated. I put all the boxes I need information on in Red.

Thanks!


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## bobdebouwer (Oct 21, 2014)

actually I think I simply need a minidsp 2x4 and can connect any PA amp of my liking to it to power my subs...maybe I was over complicating things...only downside is that the minidsp is quite expensive, 160 euro.

Is there a cheap(er) alternative to the miniDSP? Except maybe for 'freeDSP', an open source initiative. Pity I live in Europe...

this for example:

http://www.ebay.com/itm/2-Channel-2...e-assembled-/121382782553?hash=item1c42fa4659


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## dgmartin (Oct 29, 2011)

bobdebouwer said:


> actually I think I simply need a minidsp 2x4 and can connect any PA amp of my liking to it to power my subs...maybe I was over complicating things...only downside is that the minidsp is quite expensive, 160 euro.
> 
> Is there a cheap(er) alternative to the miniDSP? Except maybe for 'freeDSP', an open source initiative. Pity I live in Europe...
> 
> ...


This seems like what you want in therms of XO but doesn't come with a case at 75CAD. He is using quality op-amps but there is more to it.
The thing you linked on amazon is about 125CAD. 
The MiniDSP 2x4 "in a box" is 105USD (see http://www.minidsp.com/products/minidsp-in-a-box/minidsp-2x4). It has all the XO + EQ/DSP you need and you can switch from one setup to another as the music is playing. It has my vote!


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## bobdebouwer (Oct 21, 2014)

Yeah, I have to say I totally agree with you! 

I was a bit worried to buy a minidsp as I need to pay a lot of customs and VAT etc. when I buy this from hong kong, about 50 EUR extra. 
There was a webshop in holland (100km away from me) selling it for 160 EUR (!!), one in germany for 120 (EUR) but strangely enough, I have actually found a French webshop, 'Audiophony.fr' where I can buy it for only 95 EUR! At this price it's an absolute no-brainer. 

http://www.audiophonics.fr/fr/appar...o-usb-2-vers-4-canaux-asymetrique-p-8270.html

I have been looking the web for a second hand amp, there are plenty of amps for sale which have +/- 500-1000W RMS for +/- 150 euro.

This would mean I can get a 1000W RMS system with the best DSP on the market for only 250 EUR. I can build the passive lilwrecker subwoofer (if I use the cheapest driver) for about 300 EUR which means 550 EUR for a 500W RMS sub extending to 18Hz -3db...


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