What could I do to cut my the power that my Audiobahn amp puts out in half (right now it's wired so it puts out 110wRMS x 2 @ 3ohms Audiobahn says it puts 100x2 @ 4 ohms and 140x 2 @ 2 ohms). I need to get, like 55wRMS x 2 @ 3 ohms (I think). Can I use a passive - in-line 3 ohm resistor or something, and where could I find such an item?
Thanks
Replies (10)
Swez on 08/18/2003 05:35:04
The amp gains usually control that. But if you have a HU that puts out close to that 4.0 volts mentioned before, dialing up the gains to 4.0 may not be enough.
What you need are a pair of inline attenuators for this amp that drop the output power of the HU to more usable levels to the amp. These are much better than passive resistors at the output as a 4 ohm, 100 watt resistor is much more expensive. (big, bulky and generate heat)
Look here:
http://www.thezeb.com/caraudio/harrision_labs.html
"Attenuators reduce the voltage of signal to the amplifier so that the input level or Gain control can be easily adjusted. Just put 'em in-line with your RCA Interconnect cables before your amplifier. These can be stacked and mixed for more attenuation. Comes in pairs: 1 for the left channel, and one for the right.
Sample Application: If the signal from your stereo headunit (or line driver) is 8 volts, and your amplifier has a signal input range of up to 2 volts, the Gain Knob would have to be all the way up. A 12dB attenuator will allow you to adjust the amp to about half-way."
I would say the -3/-6dB attenuator is adequate if you do not use a line driver presently. If you have a line driver over 6 volts, than the
-12dB version will work well here.
900087 12dB Attenuator (pair) $ 28.99
900086 6dB Attenuator (pair) $ 28.99
900085 3dB Attenuator (pair) $ 28.99
Do you know the output voltage range of your HU out of the RCA's?
Also, what is the gain range on the input side of your amp?
Do you have any line drivers or active EQ devices between HU & amp? If yes, what kind? (brand & model)
Depending on your answers, I can suggest the best version attenuator for low noise, adequate signal gain ratios.
Swez
Swez on 08/19/2003 21:56:36
So Big J Man, what's the status on this one?
Swez
ckoscin2 on 08/27/2003 04:11:16
could you explain this more i dont get what u mean but i think i may have this kind of problem ?
ckoscin2 on 08/27/2003 04:12:42
i have a Eclipse CD 8052 with 8 volt output going to my Crossfire CFA-1000D, with it being a older amp i am guessing that the input level would be low ? i cant get on the crossfire site to see what the input is ?
also would the newer 1000d's be more efficent then my old white CFA series, like the BMF or VR (same thing just newer model) ?
Swez on 08/27/2003 09:13:17
Here's the web site for Crossfire products. The data you need in probably in the Tech section of the site in a .pdf file which I cannot open for some reason. Flash site and adobe DL is very slow. (modem connection here)
Worst case, call or write Tech service to find out what the input sensitivity section allows.
OK, it finally loaded... input sensitivity is 1/2 volts - 4.0 volts. I you have too much gain from the HU, going into your amp, it can overdrive the amp inputs and give high distortion levels, even if you gain settings are set to 4.0 volts.
If you are sure the HU is 8 volts to RCA's, then antennuators will; help bring the 8 volt signal down to a more usable voltage to the amp. Here, a -3 or -6 dB attenuator between the amp and HU are a good choice.
Here's the .pdf you want to review and print:
http://crossfirecaraudio.com/frameset.asp
In Tech Info section, click on Class A/B amplifers, the search for your series (CFA) and get a drop down box with all amps in that series. Click on CFA-1000d and allow the .pdf file to load. This a long file (16 pages) and may take a while to load.
Print it out for future references.
Swez
Swez
ckoscin2 on 08/28/2003 09:51:57
my eclipse cd player sayes 8 volt pre out right on the HU itself .
C.K.
Swez on 08/28/2003 16:22:42
Good... you definitely need to attenuate the HU signals as they will clip and overdrive the preamps on your Crossfire amp. The -3dB unit will cut your HU voltage by 50% (~4.0 volts) The -6dB unit will cut input signal to 2.0 volts.
In your case, I would think the -3 dB device will be fine for your Crossfire amp.
Swez
ckoscin2 on 08/29/2003 03:00:38
also another question i know it kinda sound funny but i hear the word "clip" alot i know its bad but i really dont know what it is ? i always though it was just another word for distortion ? its like i kinda know and i kinda dont know what it is ? thanks, C.K.
audionewb on 08/29/2003 08:25:13
From what I've gained from reading things, let's say you have your 2 subs set on low pass filter on ur amp. Now lets say you have an 4 volt pre out coming from your deck. Now lets also say you set the gain on your amp for 5 volts. Now what your making the amp do is amplify the frequencies at a higher voltage then what the amp can handle and the amp starts cutting off the top and bottom of the frequency curves. Not only that the amp will also start amplifying the higher range frequencies, the ones your low pass filter was suppose to cut out, and send them into the sub. Very bad for the sub.
Swez on 08/29/2003 08:25:11
Clipping is a form of distortion. It is when the natural sound waves of an audio signal are driven beyond the limits of the amplifer to manage and instead of a nice, snooth grouping of sinusodial waves, we get flat spots at the upper and lower peaks of the vave form.
Most folks cannot hear distortion levels below ~2%. But as the distortion levels (clipping) rise above that range, excess voltage turns to distortion that looks like a DC signal to the speakers. A DC signal is very hard on speakers and whe clipping doe begins to happen, voltage spikes often exceed the speakers ability to take it and they fail.
This site will help explain this scenario in very good detail...
http://www.eatel.net/~amptech/elecdisc/2ltlpwr.htm
Swez
Thanks
Replies (10)
Swez on 08/18/2003 05:35:04
The amp gains usually control that. But if you have a HU that puts out close to that 4.0 volts mentioned before, dialing up the gains to 4.0 may not be enough.
What you need are a pair of inline attenuators for this amp that drop the output power of the HU to more usable levels to the amp. These are much better than passive resistors at the output as a 4 ohm, 100 watt resistor is much more expensive. (big, bulky and generate heat)
Look here:
http://www.thezeb.com/caraudio/harrision_labs.html
"Attenuators reduce the voltage of signal to the amplifier so that the input level or Gain control can be easily adjusted. Just put 'em in-line with your RCA Interconnect cables before your amplifier. These can be stacked and mixed for more attenuation. Comes in pairs: 1 for the left channel, and one for the right.
Sample Application: If the signal from your stereo headunit (or line driver) is 8 volts, and your amplifier has a signal input range of up to 2 volts, the Gain Knob would have to be all the way up. A 12dB attenuator will allow you to adjust the amp to about half-way."
I would say the -3/-6dB attenuator is adequate if you do not use a line driver presently. If you have a line driver over 6 volts, than the
-12dB version will work well here.
900087 12dB Attenuator (pair) $ 28.99
900086 6dB Attenuator (pair) $ 28.99
900085 3dB Attenuator (pair) $ 28.99
Do you know the output voltage range of your HU out of the RCA's?
Also, what is the gain range on the input side of your amp?
Do you have any line drivers or active EQ devices between HU & amp? If yes, what kind? (brand & model)
Depending on your answers, I can suggest the best version attenuator for low noise, adequate signal gain ratios.
Swez
Swez on 08/19/2003 21:56:36
So Big J Man, what's the status on this one?
Swez
ckoscin2 on 08/27/2003 04:11:16
could you explain this more i dont get what u mean but i think i may have this kind of problem ?
ckoscin2 on 08/27/2003 04:12:42
i have a Eclipse CD 8052 with 8 volt output going to my Crossfire CFA-1000D, with it being a older amp i am guessing that the input level would be low ? i cant get on the crossfire site to see what the input is ?
also would the newer 1000d's be more efficent then my old white CFA series, like the BMF or VR (same thing just newer model) ?
Swez on 08/27/2003 09:13:17
Here's the web site for Crossfire products. The data you need in probably in the Tech section of the site in a .pdf file which I cannot open for some reason. Flash site and adobe DL is very slow. (modem connection here)
Worst case, call or write Tech service to find out what the input sensitivity section allows.
OK, it finally loaded... input sensitivity is 1/2 volts - 4.0 volts. I you have too much gain from the HU, going into your amp, it can overdrive the amp inputs and give high distortion levels, even if you gain settings are set to 4.0 volts.
If you are sure the HU is 8 volts to RCA's, then antennuators will; help bring the 8 volt signal down to a more usable voltage to the amp. Here, a -3 or -6 dB attenuator between the amp and HU are a good choice.
Here's the .pdf you want to review and print:
http://crossfirecaraudio.com/frameset.asp
In Tech Info section, click on Class A/B amplifers, the search for your series (CFA) and get a drop down box with all amps in that series. Click on CFA-1000d and allow the .pdf file to load. This a long file (16 pages) and may take a while to load.
Print it out for future references.
Swez
Swez
ckoscin2 on 08/28/2003 09:51:57
my eclipse cd player sayes 8 volt pre out right on the HU itself .
C.K.
Swez on 08/28/2003 16:22:42
Good... you definitely need to attenuate the HU signals as they will clip and overdrive the preamps on your Crossfire amp. The -3dB unit will cut your HU voltage by 50% (~4.0 volts) The -6dB unit will cut input signal to 2.0 volts.
In your case, I would think the -3 dB device will be fine for your Crossfire amp.
Swez
ckoscin2 on 08/29/2003 03:00:38
also another question i know it kinda sound funny but i hear the word "clip" alot i know its bad but i really dont know what it is ? i always though it was just another word for distortion ? its like i kinda know and i kinda dont know what it is ? thanks, C.K.
audionewb on 08/29/2003 08:25:13
From what I've gained from reading things, let's say you have your 2 subs set on low pass filter on ur amp. Now lets say you have an 4 volt pre out coming from your deck. Now lets also say you set the gain on your amp for 5 volts. Now what your making the amp do is amplify the frequencies at a higher voltage then what the amp can handle and the amp starts cutting off the top and bottom of the frequency curves. Not only that the amp will also start amplifying the higher range frequencies, the ones your low pass filter was suppose to cut out, and send them into the sub. Very bad for the sub.
Swez on 08/29/2003 08:25:11
Clipping is a form of distortion. It is when the natural sound waves of an audio signal are driven beyond the limits of the amplifer to manage and instead of a nice, snooth grouping of sinusodial waves, we get flat spots at the upper and lower peaks of the vave form.
Most folks cannot hear distortion levels below ~2%. But as the distortion levels (clipping) rise above that range, excess voltage turns to distortion that looks like a DC signal to the speakers. A DC signal is very hard on speakers and whe clipping doe begins to happen, voltage spikes often exceed the speakers ability to take it and they fail.
This site will help explain this scenario in very good detail...
http://www.eatel.net/~amptech/elecdisc/2ltlpwr.htm
Swez
Copyright ClubKnowledge 2009 * All Rights Reserved
