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2litre 11th February 2006 11:03 PM

Sub amp question
Hi All,

I was wondering about dedicated amps for subwoofers vs plate amps. I don't think I have the ability to add another amp to my system so, rather than rebuy a whole system, I was looking at getting 2 120w plate amps from PE

(because of the 6db bass boost at 30Hz) and using one each to drive larger woofers (bass augmentors) in open baffle.

Does this hurt the amp? Only using one high level input I mean.

How far off base is this thought? The filters, gain control and hardware is already there, right?



rabbitz 12th February 2006 01:02 PM

IMO building sub amps can be a pain and a lot of work. Power amp, several power supplies, gain, filters, inverters, buffers, relays.... phooey, who needs it. I just finished a P3A, P101 and an aborted LM4780 (parallel) as sub amps only because I had the bits and a learning exercise. Just bought another plate amp and much easier, more flexible and a few minutes it's done and sounds great.

PE have a resistor chart in the instructions where you can change the boost and they also tell you to use the red (right) input if using a single input due to the way the resistors are set up for the mixing of stereo channels to mono. No harm to the amp at all using a single input.

All the PE plate amps I've had have been good and great value.

2litre 12th February 2006 04:07 PM

Cool. I must have missed the inferance that there would be no harm done when I read the users guide .PDF's. Since I have little in the way of an electronics background some things must be specifically addressed. I did notice the instructions for changing the boost values and also noticed that the value is across a 5Hz range. So the +6db@30Hz setting affects 30-35Hz.

It appeared to me that plate amps were a good value for the money. Easy to integrate into the system and all. I've choosen +6db @ 30Hz because I plan to have 'them' driving a 10+ inch driver in OB. The company that markets the Servo-Sub (escapes me ATM) seems to have similar 120W amps for sale. They can also (or have the DIY guide) put a low frequency cut off filter on them for you at purchase. I only do stereo music and have little interest in the ELF of HT. Now while the amp offers a 6 dB high pass filter (125 Hz, 8 ohm) output for satellite speakers, I've read in other posts that this might not be the best way to wire up the sats.
Any experience there?

Thank you for the help.



rabbitz 12th February 2006 10:21 PM

It's best not to wire the satellites through the sub amp as that requires the inputs to the plate amp to be speaker level and the odds of the HP filter being suitable match is minimal.

Wire the satellites normally and use low level inputs on the sub amp, then blend the bass using the crossover and gain on the plate amp.

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