I've built a active sub and need to combine the strereo signal to mono. Trying to stay away from active filtering etc. I'm thinking of conbining my L and R signals of my gainclone in w/ 2x 33k resistors to form an attenuated sub output. Will this increase the crosstalk and if so, is there a another preferred, passive way to combine the signals?
That should work fine - the gainclones' outputs will be much lower inpedance than your resistors, so crosstalk shouldn't be affected. The resistors, together with the input impedance of your sub amp, will form an attenuator, but if you have enough gain in the sub amp then you will be ok.
Cheers
Cheers
> Will this increase the crosstalk
It will add crosstalk. Assume the GainClone speaker output is 1Ω, then crosstalk computes to 66,000/1= -96dB. That's insignificant, and the real output of most speaker amps is far lower so it will be around -120dB. If the subwoofer amp input is not infinite-Z, the crosstalk from the summer is even less. This is the least of your worries.
> 2x 33k resistors to form an attenuated sub output
Note that for a bass tone the same in both channels, if the subwoofer amp has a high-Z input, the signal at the subwoofer amp input is equal to the signal at the stereo amp speaker outputs. (For one-side bass tones, the signal is -6dB.) If the subwoofer amp has gain, this is probably too hot. Simply add a resistor from the summing junction to ground. With 33K summers, a 3K resistor to ground is a good starting point. Note also that you can add a 0.1µFd cap across that resistor to dump everything above about 500Hz before going to the subwoofer amp. That's not enough filtering for best subwoofer operation, but gives any subsequent filter less work to do.
It will add crosstalk. Assume the GainClone speaker output is 1Ω, then crosstalk computes to 66,000/1= -96dB. That's insignificant, and the real output of most speaker amps is far lower so it will be around -120dB. If the subwoofer amp input is not infinite-Z, the crosstalk from the summer is even less. This is the least of your worries.
> 2x 33k resistors to form an attenuated sub output
Note that for a bass tone the same in both channels, if the subwoofer amp has a high-Z input, the signal at the subwoofer amp input is equal to the signal at the stereo amp speaker outputs. (For one-side bass tones, the signal is -6dB.) If the subwoofer amp has gain, this is probably too hot. Simply add a resistor from the summing junction to ground. With 33K summers, a 3K resistor to ground is a good starting point. Note also that you can add a 0.1µFd cap across that resistor to dump everything above about 500Hz before going to the subwoofer amp. That's not enough filtering for best subwoofer operation, but gives any subsequent filter less work to do.
sounder said:
Hi,
This isn't such a good idea, IMHO.
Can you give more details about your sub amp? You might be able to sum up L and R signals at the line level in the sub amp input circuitry without using additional OPamps. Besides, sub amps almost always need active equalisation and filtering.
Regards
Re: Re: resistive summing network
Joe,
I'm using a line level input, planning on summing the inputs in the gainclone enclosure and running a mono line out to the sub.
My main amp is a IGC. My sub amp is a bridged gainclone ala National AN-1192 tech notes (page 5). Output is 100w with a 50K attenuating pot to ground. Signal to amp is off the wiper. You mention speaker level input, would the summing circuit I described above apply only to speaker level inputs? If so, what values would you suggest for summing resistors for a line level input? I feed the sub amp output through a passive low pass filter of approx 120hz. (a bit high really) As a matter of interest, how would one reduce the speaker level inputs to an acceptable level?
moamps,
Is there a simple active circuit you could point me to? Also, is it better to filter the input as opposed to filtering the high level output with a low pass filter? Seems like a lot of superfluous signal passing through the amp for no reason? I've been avoiding the active filters mainly because of the extra power supply I suppose. Thought of buying a active car sub filter.
Gotto keep fine tuning that race car😀
JOE DIRT® said:
Joe,
I'm using a line level input, planning on summing the inputs in the gainclone enclosure and running a mono line out to the sub.
My main amp is a IGC. My sub amp is a bridged gainclone ala National AN-1192 tech notes (page 5). Output is 100w with a 50K attenuating pot to ground. Signal to amp is off the wiper. You mention speaker level input, would the summing circuit I described above apply only to speaker level inputs? If so, what values would you suggest for summing resistors for a line level input? I feed the sub amp output through a passive low pass filter of approx 120hz. (a bit high really) As a matter of interest, how would one reduce the speaker level inputs to an acceptable level?
moamps said:
moamps,
Is there a simple active circuit you could point me to? Also, is it better to filter the input as opposed to filtering the high level output with a low pass filter? Seems like a lot of superfluous signal passing through the amp for no reason? I've been avoiding the active filters mainly because of the extra power supply I suppose. Thought of buying a active car sub filter.
Gotto keep fine tuning that race car😀
Re: Re: Re: resistive summing network
Hi,
look at
http://sound.westhost.com/project38.htm
http://sound.westhost.com/project48.htm
http://sound.westhost.com/project84.htm
You can use this circuit to get +/-15V from amp power supply +/-35V.(for preamps supply- not for auto on circuit)
Regards
sounder said:
Hi,
look at
http://sound.westhost.com/project38.htm
http://sound.westhost.com/project48.htm
http://sound.westhost.com/project84.htm
You can use this circuit to get +/-15V from amp power supply +/-35V.(for preamps supply- not for auto on circuit)
Regards
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