I'm using a high powered crown amp on the high frequency channels of my actively crossed tri-amped speakers. Specifically it's an B&C DE10 compression driver (8 ohm) crossed at 7.2Khz.
The crown amp causes the compression driver to buzz. I'd like to use a cap across the speaker (or amp) terminals to filter this out. Filtering everything below 1-2 Khz should do the trick. How do I calculate the capacitance? Also which type of capacitor? I assume a 10 volt cap is OK since this is for home use and the driver isn't going to see more than 10watts max.
The crown amp causes the compression driver to buzz. I'd like to use a cap across the speaker (or amp) terminals to filter this out. Filtering everything below 1-2 Khz should do the trick. How do I calculate the capacitance? Also which type of capacitor? I assume a 10 volt cap is OK since this is for home use and the driver isn't going to see more than 10watts max.
Well to answer my own question...
This is just a simple high pass filter
http://en.wikipedia.org/wiki/High-pass_filter
f (-3db point) = 1/(2pi*rc)
c = 1/(2pi*r*f) = 1/(2*3.14*8*1000)
so I'll need a 20uF cap which will go (in series) between the amp's +'ve terminal and the speakers +'ve terminal for a 1Khz hpf or a 10uF cap for a 2khz hpf
In my initial post I stated that the cap goes between the speakers/amp +'ve and -'ve terminals. THIS IS INCORRECT.
This is just a simple high pass filter
http://en.wikipedia.org/wiki/High-pass_filter
f (-3db point) = 1/(2pi*rc)
c = 1/(2pi*r*f) = 1/(2*3.14*8*1000)
so I'll need a 20uF cap which will go (in series) between the amp's +'ve terminal and the speakers +'ve terminal for a 1Khz hpf or a 10uF cap for a 2khz hpf
In my initial post I stated that the cap goes between the speakers/amp +'ve and -'ve terminals. THIS IS INCORRECT.
Yes, that's a good point and I should really put a cap on my midrange compression drivers for the same reason.
.... anyway the 10uf cap did reduce the buzz about 10db, which is still not enough. I really should buy a more suitable amp, but I'd rather work with what I have for now.
I might try a different cap which filters a little higher and see if that helps.
.... anyway the 10uf cap did reduce the buzz about 10db, which is still not enough. I really should buy a more suitable amp, but I'd rather work with what I have for now.
I might try a different cap which filters a little higher and see if that helps.
This is a 20W driver. What do you need the Crown amp for?
What kind of horn is it driving?
Something is seriously out of whack if you can hear anything low enough to be called a 'buzz' coming out of this unit. I'm surprised it hasn't self-destructed. I'd be very cautious about running it in these circumstances at all. Does it work normally otherwise?
w
What kind of horn is it driving?
Something is seriously out of whack if you can hear anything low enough to be called a 'buzz' coming out of this unit. I'm surprised it hasn't self-destructed. I'd be very cautious about running it in these circumstances at all. Does it work normally otherwise?
w
wakibaki said:
I need the crown amp because my preamp goes to 11!
But seriously, I have a bunch of crowns lying around (xls 402Ds). The buzz is really only annoying when I'm sitting at my PC which is about 1.5 meters from the B&C DE10 (on an ME10 horn to answer your question). When I'm at the normal listening position (approx 3 meters) it's not much of an issue.
And yes, it functions as normal - crossed at 7.2Khz. I should sell the crown and get a t-amp.
Unfortunately, I think you're going to have to use another amp. Any noise that can be accurately described as a "buzz" contains high-frequency harmonics -- otherwise, it would be just a hum. These HF components are right in the operating range of the tweeter, so you can't filter them out without losing the highs in your program material.
Your filter's corner frequency (1-2 kHz) is right in the range of notes you can whistle. Most of the energy in the buzz that you are hearing is probably above 10 kHz.
Gary Dahl
Your filter's corner frequency (1-2 kHz) is right in the range of notes you can whistle. Most of the energy in the buzz that you are hearing is probably above 10 kHz.
Gary Dahl
Hmmm... I would say there is definitely something wrong here. But I have part of my system bi or tri-amped also and I sometimes have a problem like this (especially when running tv sound through amps). I just threw a resistor between the positive and negative and a 2200uF bipolar capacitor on the last line to the speakers (tweeters only I would recommend). Much better sound in my opinion.
g3dahl said:
Good point re the harmonics.
wakibaki said:
Yeah a Fizz or Buzz would describe the sound depending on your accent lol.
I have t-amp (TA-10.1) driving the Altec 288's on MR64 horns and I'd agree - no complains. It would be nice to try a SET amp one day or a class A amp, but that's probably not going to yeild a huge improvement for the cost.
For now I'm going to do some searching and see what people think of these
http://cgi.ebay.com/215-watt-4ohm-t...ssPageNameZRSS:B:SRCH:US:101#ebayphotohosting
Steve,
If the buzz (normally associated with 50/60 HZ and it’s harmonics) goes away when the input of the amp is disconnected, it is caused by a ground loop.
Eliminating the ground loop requires different approaches depending on the components you use, and whether your system is balanced or unbalanced.
If the buzz (or fizz, which is a symptom of too much gain) does not go away when you remove the amp input, you simply need to turn the amp down, and the crossover output up to maximize signal to noise.
Your best s/n will be when your pre amp is running at it's maximum before clipping, the crossover maximum before clipping, and amps turned up as little as needed to achieve the volume you desire. If you are moving between near and far listening positions, and don't want to adjust six amp inputs, you need to strike a balance between the two.
Moving from 3 meters to 1.5 meters the speakers are going appear 6 dB louder in the near position, to be “apples to apples” from a signal to noise standpoint, all your amps should be turned down 6 dB when you are that close.
If the noise persists with the amp inputs at zero, and no input, it is possible that the amp is defective.
If the amp has no volume controls, attenuation pads can be made from resistors.
If the buzz (normally associated with 50/60 HZ and it’s harmonics) goes away when the input of the amp is disconnected, it is caused by a ground loop.
Eliminating the ground loop requires different approaches depending on the components you use, and whether your system is balanced or unbalanced.
If the buzz (or fizz, which is a symptom of too much gain) does not go away when you remove the amp input, you simply need to turn the amp down, and the crossover output up to maximize signal to noise.
Your best s/n will be when your pre amp is running at it's maximum before clipping, the crossover maximum before clipping, and amps turned up as little as needed to achieve the volume you desire. If you are moving between near and far listening positions, and don't want to adjust six amp inputs, you need to strike a balance between the two.
Moving from 3 meters to 1.5 meters the speakers are going appear 6 dB louder in the near position, to be “apples to apples” from a signal to noise standpoint, all your amps should be turned down 6 dB when you are that close.
If the noise persists with the amp inputs at zero, and no input, it is possible that the amp is defective.
If the amp has no volume controls, attenuation pads can be made from resistors.
Thanks for the response Weltersys. The buzz is still still present with the inputs unplugged. I also tried a cheater plug to lift the ground and even wired up the pre-amp, x-over and crown chassis together.
Basically I've tried everything including a new amp. With the crown plugged into 90db/w/m speakers the buzz is all but inaudible.
I think the lesson here is that inexpensive 300w/ch amps and high sensitivity low power compression drivers are not a match made in heaven.
BTW I still use my preamp for volume control, but I've padded down the output from my digital xover so that I still have a pretty good gain structure. A multi channel volume control after the x-over would be ideal at some point, but since this is a home theater setup things could get pretty silly.
Basically I've tried everything including a new amp. With the crown plugged into 90db/w/m speakers the buzz is all but inaudible.
I think the lesson here is that inexpensive 300w/ch amps and high sensitivity low power compression drivers are not a match made in heaven.
BTW I still use my preamp for volume control, but I've padded down the output from my digital xover so that I still have a pretty good gain structure. A multi channel volume control after the x-over would be ideal at some point, but since this is a home theater setup things could get pretty silly.
BTW: What model Crown, age?
If the amp is inserted in another system with other speakers, other power source - Does it still have the noise?
If the "noise" travel with the amp, it's the amp.
Otherwise it could be an uneven ground potential
If the amps bad I'd get it fixed - guessing bad cap if it's old.
Sometimes a through cleaning and attention to loosen and dirty/marginal connection can help.
Crown repair is usually exemplary.
If the amp is inserted in another system with other speakers, other power source - Does it still have the noise?
If the "noise" travel with the amp, it's the amp.
Otherwise it could be an uneven ground potential
If the amps bad I'd get it fixed - guessing bad cap if it's old.
Sometimes a through cleaning and attention to loosen and dirty/marginal connection can help.
Crown repair is usually exemplary.
Steve,
You said you padded down the output from my digital xover so that "I still have a pretty good gain structure".
If you padded the xover output, and still have the amp gain turned wide open, that will not maximise your signal to noise ratio. You want the pre amp and the crossover running near maximum before clipping, it's full output sent to the amp, then the amps turned up/down to the listening level you want, which very likely might be -20 dB or less on the input gain pots.
Still curious, is the amp noisy with the input levels turned down?
If it is, as you say, just noisy cheap amps designed for noisy club use where no one would notice.
In which case you could make 10 or 15 dB resistive output pads (speaker level) for the tweeters, since you have power to spare. That would drop your efficiency down to the point where you could use the amp in its normal output level range.
You said you padded down the output from my digital xover so that "I still have a pretty good gain structure".
If you padded the xover output, and still have the amp gain turned wide open, that will not maximise your signal to noise ratio. You want the pre amp and the crossover running near maximum before clipping, it's full output sent to the amp, then the amps turned up/down to the listening level you want, which very likely might be -20 dB or less on the input gain pots.
Still curious, is the amp noisy with the input levels turned down?
If it is, as you say, just noisy cheap amps designed for noisy club use where no one would notice.
In which case you could make 10 or 15 dB resistive output pads (speaker level) for the tweeters, since you have power to spare. That would drop your efficiency down to the point where you could use the amp in its normal output level range.
weltersys said:
The amps gains are turned down to the minimum. But even then I had to pad down the output of my crossover in order to get enough gain going into the crossovers A/D converters.
Yes, with the input disconnected the gain controls have no effect on the level of the buzz. With the gain controls at maximum there is a little bit of hiss though. I have also tired a cheater plug to lift the ground but it didn't improve things.
Funny you should mention that as I was just thinking about that last night. In the end though I think I'll just sell the crown while it still has a year of transferable no fault warranty left and put together a little 20 watt class D amp from a pre assembled board.
Honestly the Crown's are really nice sounding amps, they're just a little to noisy for 110db/w/m HF horns. I have a tapped horn (16-80hz) and a midbass horn (80-400hz @ 110db/w/m) both using the same crown amps and they work great in that application.
BTW thanks a bunch for all the help guys!
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