I'm thinking of building an active subwoofer using this amplifier http://www.advanceae.com.au/car/prod426.htm. however i'm not sure how i'm going to control the volume of the sub if i use the low level input (RCA). I'm going to have a go at building my own stereo amp for the mains (hopefully a gainclone) and i want to put a set of pre-outs or a mono preout on it that can feed the subwoofer amp which has a built in crossover. I want the preouts to be controlled by the main volume control on the amp. however i thought the idea of a pre-out was that it wasn't volume controlled at all yet i see home theatre recievers with subwoofer outputs so i assume there is a way to do it. thanks for any help.
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You may be thinking of tape monitor outputs, which run at full volume all the time. Pre-outs are affected by the main volume control - look at any component preamp, or for that matter a car stereo head unit, both of which are examples of devices made to connect to a power amplifier (which likely has no volume control of its own).amoeba86 said:
So yes, if you're planning on building your gainclone with a volume knob (in other words a preamp stage) and pre-outs, the pre-outs should be post-volume control. And that's how it's normally done, so no worries.
JasonL is correct that you could simply run speaker wires to that sub amp and daisy-chain them along to your speakers, but down-converting a speaker level signal to drive your sub amp may add a bit of noise and distortion. It might not even be audible, but something to consider. You'll have to work out whether it's worth the extra trouble of adding pre-outs to your main amp for the possible sonic benefits and flexibility down the line of having extra connectors for additional/different amplifiers.
ok thanks, i think i wasn't fully understanding how the pre-outs worked, i know this isn't the chip amp forum but could someone possibly show me how i would integrate a set of preouts that are controled by the main volume control, i don't have to worry about summing or anything since the plate amp does that.
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Joined 2002
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Joined 2002
i have one of those amp plates. what were u thinking of driving from it? they are quite good, and i think you'll be happy with it, but they do get quite hot if u drive them hard, so have a think about that. i've put a 80mm fan attached to the heatsink, and even at low speed it's all that is needed (this is in north queensland, so if you're down south you'll be fine)
if u make a stereo amp, just go from the rca inputs -> volume control (be it a dual log pot or otherwise)
then split it from there to the audio inputs of the amps and to the rca outputs. the plate amp has stereo line level inputs, so you don't need a mono output.
with this, you'll be running the stereo amps at full range, and having the sub playing bass (adjustable crossover from 100hz down).
if u want to use the sub plates line level crossover, you'll have to go input -> volume -> plate amp -> stereo amp. i should also make u aware that although the plate amp has an adjustable crossover, the line level outputs are always high passed at 100hz - it can't be adjusted.
if u make a stereo amp, just go from the rca inputs -> volume control (be it a dual log pot or otherwise)
then split it from there to the audio inputs of the amps and to the rca outputs. the plate amp has stereo line level inputs, so you don't need a mono output.
with this, you'll be running the stereo amps at full range, and having the sub playing bass (adjustable crossover from 100hz down).
if u want to use the sub plates line level crossover, you'll have to go input -> volume -> plate amp -> stereo amp. i should also make u aware that although the plate amp has an adjustable crossover, the line level outputs are always high passed at 100hz - it can't be adjusted.
no, that's the best price i know of sorry. jaycar don't sell those ones anymore i don't think, they do sell the ones of higher power ratings tho. i run a 12" jbl car sub off mine and it is plenty of power
i have read and tested once a 'simple line mixer' circuit i found on google. it says to just combine the gounds of the inputs and output, and then put a 10k resistor in series with each input, then just combine them to the output. hope that makes sense.
i've read of other examples using different value resistors. i guess with the higher resistance, the better stereo imaging you'll keep but the more attenuation you'll get. i found that 10k resistors kept acceptable stereo imaging and the attenuation was no problem, but i don't use this circuit, just tested it.
it's also good that u can VERY easily put this in the middle of a cable and put tape around it, and it's barely noticable. i suggest trying it. i will probably induce a little noise too.
i have read and tested once a 'simple line mixer' circuit i found on google. it says to just combine the gounds of the inputs and output, and then put a 10k resistor in series with each input, then just combine them to the output. hope that makes sense.
i've read of other examples using different value resistors. i guess with the higher resistance, the better stereo imaging you'll keep but the more attenuation you'll get. i found that 10k resistors kept acceptable stereo imaging and the attenuation was no problem, but i don't use this circuit, just tested it.
it's also good that u can VERY easily put this in the middle of a cable and put tape around it, and it's barely noticable. i suggest trying it. i will probably induce a little noise too.
thought u might be interested, www.altronics.com.au also have a relatively cheap 150wrms plate amp
my guess would be that they are all the exact same design. the one from jaycar and advanceca are identical looking.
personally i'd buy a kit if i already had a line level crossover, as they can work out much cheaper. jaycar have a nice amp that would require a xo, but puts out some neat figures:
115wrms@8ohms, 175wrms@4ohms, 0.002%thd@155w@1khz, 0.004%thd@175w@1khz. s/n 112db@115w 20hz-20khz
it is a silicon chip design. it's $95, but requires a toroidal, bridge rectifier, filter caps and heatsink. altronics also have some good amps like this.
the advantage of such amps is that if u later decide to use it to power a full range speaker, you can - and with exellent power.
i very recently put together two SC480 (KC-5345 at jaycar) kits with fantastic results. i guess it all comes down to financial and soldering ability restrictions - oh, and risk.
my guess would be that they are all the exact same design. the one from jaycar and advanceca are identical looking.
personally i'd buy a kit if i already had a line level crossover, as they can work out much cheaper. jaycar have a nice amp that would require a xo, but puts out some neat figures:
115wrms@8ohms, 175wrms@4ohms, 0.002%thd@155w@1khz, 0.004%thd@175w@1khz. s/n 112db@115w 20hz-20khz
it is a silicon chip design. it's $95, but requires a toroidal, bridge rectifier, filter caps and heatsink. altronics also have some good amps like this.
the advantage of such amps is that if u later decide to use it to power a full range speaker, you can - and with exellent power.
i very recently put together two SC480 (KC-5345 at jaycar) kits with fantastic results. i guess it all comes down to financial and soldering ability restrictions - oh, and risk.
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