Is there any benefit of having the volume control potentiometer after an active crossover?
My thought: Usually active crossovers are fed by a preamplifier, so the signal levels of source devices are attenuated if the volume control isn´t cranked up to stop collar. In that case the active crossover handles very low signals and SNR is not ideal.
Feeding an active crossover with full signal level would increase SNR. Only drawback is that a multi-ganged potentiometer (4-ganged for 2-way stereo, 6-ganged for 3-way stereo etc.) and equivalent number of output buffers are needed.
Do I suppose right?
My thought: Usually active crossovers are fed by a preamplifier, so the signal levels of source devices are attenuated if the volume control isn´t cranked up to stop collar. In that case the active crossover handles very low signals and SNR is not ideal.
Feeding an active crossover with full signal level would increase SNR. Only drawback is that a multi-ganged potentiometer (4-ganged for 2-way stereo, 6-ganged for 3-way stereo etc.) and equivalent number of output buffers are needed.
Do I suppose right?
I used a dual track volume pot before the pair of two way active crossovers.
I was surprised at the increase in noise level at the speakers.
I redid all the R & Cs to lower impedances, but found only a small reduction in noise.
I have since reduced the gain of those power amps and the noise improved yet again but still not satisfactory.
The active crossover was all unity gain using opa275.
Unacceptable in my view.
I was surprised at the increase in noise level at the speakers.
I redid all the R & Cs to lower impedances, but found only a small reduction in noise.
I have since reduced the gain of those power amps and the noise improved yet again but still not satisfactory.
The active crossover was all unity gain using opa275.
Unacceptable in my view.
Good question SmellOfPoo,
I am using active 2way crossover to split the signal for two subwoofers and the satelites. Since I am using two different amps, solid state for subwoofers and tube for satelites, volume control on each amp after the crossover is a neccasity, since the amps have different gain and speakers different sensitivity.
I played around with volumes on amps turned lower and master volume higher up ...vs one amp all the way up, the other one lower to compensate, with master volume much lower....well, I did not found much difference in noise performance overal, since my crossover is just two buffers and passive split.
I belive the difference will be audible if only a poor active crossover is used, like for car or something.
I am using active 2way crossover to split the signal for two subwoofers and the satelites. Since I am using two different amps, solid state for subwoofers and tube for satelites, volume control on each amp after the crossover is a neccasity, since the amps have different gain and speakers different sensitivity.
I played around with volumes on amps turned lower and master volume higher up ...vs one amp all the way up, the other one lower to compensate, with master volume much lower....well, I did not found much difference in noise performance overal, since my crossover is just two buffers and passive split.
I belive the difference will be audible if only a poor active crossover is used, like for car or something.
In PA/Pro crossovers, its common to have one at the input and one at the output.
The Input is meant to adjust your gain. You would want to adjust the signal running through the crossover to be as "hot" as possible without clipping.
At the Output, it is usually a Line driving amp. It can be Unity or with modest gain. This will allow the user to control the volume out to the amplifiers.
If your amplifiers have gain controls at the inputs, you may want to do away with the output volume at the crossover. Most Hi-fi amps do not, so there's no other way but to have volume controls at the outputs of the crossovers.
Not sure I'm following you here. You only need 2-ganged pots in a stereo crossover. Doesn't matter whether its 2,3 or 4-way. Every output is 2-ganged. You don't control overall volume at the crossover. It's done either at the mixer or your Pre-amp.
Regards
Mike
Maybe I should sketch my proposal: I´m about building a sort of 'all in one monster receiver' because I dont want to have a rack full with stacks of cases any longer. Tuner, DAC, 2 3-way active crossovers and 6 mono amps combined in one enclosure, each with separate transformer and PSU. Yes, it´s gonna be huge, heavy and maybe beastly. Proper shielding and grounding maybe a challenge too.
My idea is that tuner, DAC and 3 miscellaneous input signals pass a selector switch, go into a buffer, then into 3-way crossover, followed by 6-ganged attenuator (3*2 channels), 6 (3*2) buffers and finally into the amps. Possible gain differences between the amps (SymAsym for low and mid, LM3875 GainClone for high) are equalized by simple voltage dividers on the amps inputs.
So the signals would run on full level all the way until the attenuator.
Will I achieve that in the way I described? Forgive me if my exposure isn´t clear, I´m no native english speaker.
My idea is that tuner, DAC and 3 miscellaneous input signals pass a selector switch, go into a buffer, then into 3-way crossover, followed by 6-ganged attenuator (3*2 channels), 6 (3*2) buffers and finally into the amps. Possible gain differences between the amps (SymAsym for low and mid, LM3875 GainClone for high) are equalized by simple voltage dividers on the amps inputs.
So the signals would run on full level all the way until the attenuator.
Will I achieve that in the way I described? Forgive me if my exposure isn´t clear, I´m no native english speaker.
agreed a bit strange. I didn't expect using 100nF and 10k to cause a noise problem with +34dB amp and 86dB speakers. But it does. 200nF & 5k into +28dB amp and 86dB speakers is better but still not acceptable.Michael Chua said:
I haven't tried my 90dB or 94dB speakers in this arrangement.
I have not tried using discrete buffers either side of the crossovers/pots.
Dual track pots before the crossovers is much more convenient than 4 or 6track pots after the crossover. That convenience has a consequence.
Here are some pictures of one of the best installations in France.
http://www.cinetson.org/phpBB3/haut-rendement-f3/photo-salle-audiophile-t9877.html
All to have an extremly high overall definition.
His owner, THXRD, has compared both solutions for the attenuator :
N/A converter of the digital source --> two channels attenuator --> A/N converter of the speaker processor --> N/A converter of the speaker processor --> power amplifiers
and
N of digital source --> N of the digital processor --> N/A converter of the digital processor --> six channels attenuator --> power amplifiers
He did'nt notice any change despite the more many stages included in the first scheme.
I did the same and did not agree until I got a much better N/A for the digital source. My speaker processor is a BSS366. The volume control before it is much more handy.
My 6 ways / 6 positions stepped attenuator (-10 to -60 dB) is still in the circuit at the -10 dB position. A -14 dB attenuation would be preferable I think, the voltage gain of the power amplifiers being about 30 dB.
http://www.cinetson.org/phpBB3/haut-rendement-f3/photo-salle-audiophile-t9877.html
All to have an extremly high overall definition.
His owner, THXRD, has compared both solutions for the attenuator :
N/A converter of the digital source --> two channels attenuator --> A/N converter of the speaker processor --> N/A converter of the speaker processor --> power amplifiers
and
N of digital source --> N of the digital processor --> N/A converter of the digital processor --> six channels attenuator --> power amplifiers
He did'nt notice any change despite the more many stages included in the first scheme.
I did the same and did not agree until I got a much better N/A for the digital source. My speaker processor is a BSS366. The volume control before it is much more handy.
My 6 ways / 6 positions stepped attenuator (-10 to -60 dB) is still in the circuit at the -10 dB position. A -14 dB attenuation would be preferable I think, the voltage gain of the power amplifiers being about 30 dB.
noise performance
and that with an amp @ +16dB, the attenuator could perform just as well before the crossover?
If so, this corresponds with my findings, but I did not go that far since none of my amps are likely to be stable if the gain is reduced that low.
are you saying that volume control after the crossovers is better if the amp gain is >+16dB?forr said:
and that with an amp @ +16dB, the attenuator could perform just as well before the crossover?
If so, this corresponds with my findings, but I did not go that far since none of my amps are likely to be stable if the gain is reduced that low.
Hi Andrew,
The signal is better handled through a digital processor if quite high, so its output is also quite high. I did not want to modify the closed loop gain of my various power amplifiers, so I left a 10 dB passive attenuator ahead of them. I think 14 dB would be slightly better, so the level could be at a somewhat higher level in the processor.
Volume controls of the power amplifers are by-passed, just replaced by
a two resistors divider at their unbalanced input.
The signal is better handled through a digital processor if quite high, so its output is also quite high. I did not want to modify the closed loop gain of my various power amplifiers, so I left a 10 dB passive attenuator ahead of them. I think 14 dB would be slightly better, so the level could be at a somewhat higher level in the processor.
Volume controls of the power amplifers are by-passed, just replaced by
a two resistors divider at their unbalanced input.
Maximize bits
The active crossover (if it is using DSP, eg Behringer etc) has a A-D conversion. The bits are assigned according to the signal (voltage). If the signal is not hot enough then you are giving up bits. This will increase your quantization error.
Back in the days of PCM (before sigma delta mod was popular), we worried about this. With the newer converters (sigma delta), the problem/consequence is not as severe or audible. However it is still there. BTW, the signal can also be too hot for the ADC and you will get clipping.
So you really need to examine the gain structure, dynamic range you are expecting, and the ADC of your crossover (if it is DSP). It really is about maximizing bits. That is why the attenuator is best located after the crossover's DAC. It is more fool-proof that way.
The active crossover (if it is using DSP, eg Behringer etc) has a A-D conversion. The bits are assigned according to the signal (voltage). If the signal is not hot enough then you are giving up bits. This will increase your quantization error.
Back in the days of PCM (before sigma delta mod was popular), we worried about this. With the newer converters (sigma delta), the problem/consequence is not as severe or audible. However it is still there. BTW, the signal can also be too hot for the ADC and you will get clipping.
So you really need to examine the gain structure, dynamic range you are expecting, and the ADC of your crossover (if it is DSP). It really is about maximizing bits. That is why the attenuator is best located after the crossover's DAC. It is more fool-proof that way.
Hi SmellOfPoo
I see what you are trying to do. You will then need to have a way to control all 6 outputs at once. Here are a few options.
1) Pots
This is probably the most cost effective method. ALPS have a 6-ganged motorized pot
http://cgi.ebay.com/ALPS-6-gang-mot...58164QQcmdZViewItemQQ_trksidZp1742.m153.l1262
I don't own one of these but on paper, it seems quite fine.
2) VCA
Using VCAs will give you better tracking between channels. Analog Devices SSM2164 is very affordable. With one IC, you can control 4 outputs. Only $6 each at Digikey. Use 2 and you have control up to 8 outputs.
3) Digital Volume Control
These ICs generally need to be programmed. Usually PIC or I2C. A well known part is PGA2310.
4) Stepped Attenuators
Costly but the best performance. Below are some of my ALPS and stepped attentuators. The 6-ganged DACT on the right is pretty long.
An externally hosted image should be here but it was not working when we last tested it.
Regards
Mike
Hi Andrew
It could be noise from Grounding. I'm not referring to system Ground but Grounding within the crossover, especially the de-coupling caps for the ICs.
Electronic crossovers are very sensitive to this. I get a nice hum and hiss from my vintage Peavey V4X. For PA its not too bad but I won't recommend it for Hi-Fi.
Have you measured the output of your High Pass network wiith a scope?
Regards
Mike
SmellOfPoo said:Is there any benefit of having the volume control potentiometer after an active crossover?.
Feeding an active crossover with full signal level would increase SNR. Only drawback is that a multi-ganged potentiometer (4-ganged for 2-way stereo, 6-ganged for 3-way stereo etc.) and equivalent number of output buffers are needed.
Do I suppose right?
Yes, definitely.
But in most cases it works out fine with the pot before the x-over. Just choose lownoise precision opamps, and you'll have good sound without clearly detectable added noise.
reagards from a happy analog active X-over owner ( I use OPA2134 opamps)
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