I want to use 2- 2ch amps (Bazooka RSA 75.2 HC) in the bridged mode for mids and highs. Do the amps need to have both the right & left RCA's from the HU plugged into them, or can I use just the right channel from the HU with a Y cable for one amp, and just the left channel from the HU with a Y cable for the other amp? Does the amp need to see both right & left channel signals to develop it's full wattage in the briged mode?
Replies (12)
swez on 07/24/2007 13:54:44
In most 2 channel amps, it is best to send audio signals to both channels of a bridged amp. When bridged, the input side of the amp will automatically sum signals, (A+B Channels) to derive a stronger MONO signal that is fed to the main amplifer circuits.
If you only use one input, (Say Ch A is plugged in but Ch B has no signal line, the amp will still sum A & B, but reguires higher gain settings to achieve full amp output power to driver your speakers.
In most cases, a typical amp can achieve full output power with as little as 1/4 volt of input signal. It just depends on amp sensitivity range settings and the gain structure ratios between the amps input preamp stage and the output stages of the amp.
In a nutshell, try 1 RCA per amp and see if you can get enough power output to each amp to drive the load, (Speakers) to desired power range. (Amp gain tweaking) If not, use Y cables so that both A & B channels are getting a signal. (Tweak amp gains as needed)
Get all that?
Swez
gearhead on 07/24/2007 14:42:37
"Get all that?"
I'm cornfussed!
If there's no signal applied to 1 of the channels on a 2 channel amp, how would there be any output from the channel with no signal applied? Or in the bridged mode, how would there be any output at all since one channel isn't recieving any signal?
Ash on 07/24/2007 18:54:15
What he is saying by splitting the signal as you were wanting; you would be reducing the actual voltage in the rca's input to each amp. Essentially you would have to adjust the amp gains to compensate for the loss. I imagine it would not be much to cause a problem if your HU is putting out at least 2 volts. At the same time only using one per amp (no splitter) might accomplish the same without gain loss. Power output will still be bridged rated. Just try it and see what happens. You won't harm the amp, just the imaging if both are fed a stereo signal.
A perfect example of this, but in reverse is the JBL BP Mono series amps. Those who have run one know what I'm talking about. It has four inputs ( 2 left/ 2 right) and when fed only two, the gain has to be compensated to get the same output if all 4 were fed with a split rca. Go figure?!!!
The idea stated by Gearhead is a common one and there is nothing wrong with it as long as you understand the possible gain loss. Yes you do want all left going to one bridged amp and all right the other. Since you are bridging both amps this is the only way to keep a stereo signal. Just turn up the gain a tad more if needed.
swez on 07/24/2007 19:48:14
Good, 2 out of 3 ain't bad...
GH, it can be done as you mentioned... either/or
a. One RCA per bridged amp
b. One RCA w/ Y splitter per bridged amp
You may have to adjust the amp gains to get each amp to full power is all.
Swez
PS Yes, like the old JBL amps is exactly right Ash
Ash on 07/24/2007 20:56:09
By the way why did the BP mono series have 4 inputs? I remember the manual saying something about nonfading bass, yet I couldn't imagine a setup where you would need or waste both front and rear rca's on a mono amp. Besides most HU's that have both will still fade the same between internal amp and rca outputs???
swez on 07/24/2007 23:14:51
Yeah, that was a pretty goofy system step. I cannot imagine why they did it in that manner either. But really, it does not matter as one could still obtain full output power with only 2 channels of input. (Higher gain settings is all)
That was a pretty solid series for JBL, but they did have a fair amount or returns and refurbs when guys used them at 1 ohm loads. In reality, the BP series was a solid product line, but it was also bare bones, no frills and very low price. As I recall, this series did not even have a SSI filter.
That just kept JBL in the game until the newer amps came out with a few more features, a new look and a higher price tag. (So whatelse is new?) It was a very good low budget amp series for almost 5 years though.
Swez
gearhead on 07/25/2007 00:48:09
My HU has 2.2v preouts, and the amps have a low input level spec of 200mv-6v. So, if I use a Y cable that should give me 1v per channel, which "should" be enough to get full power, correct?
swez on 07/25/2007 07:42:00
That should work out OK.
Just don't be too surpirsed if you find your amp gain settings are closer to 1 volt to get the amp(s) up to full power though. That would be normal and not unexpected.
Swez
gearhead on 07/27/2007 21:11:40
OK,new question. My amps have RCA outputs to enable daisy chaining to another amp. If I run an RCA from the HU R output to the amps R input, then run an RCA from the amp R output to the same amps L input, would that give me 2.2v on both inputs?
swez on 07/27/2007 23:30:54
I think I would use a Y splitter to feed both amp input channels before trying your alternate method.
It, (Your idea) probably will work as most daisy chain outputs are just parallel wired to the input jacks too. If you try it, do it at very low power and test amp performance w/ and w/o the jumper RCA line.
If you note a hum or other noise issues, use the Y splitter method.
FYI: Avoid connect/disconnecting RCA lines when the amp is powered up. Before the grounding claw grabs and connects, we don't have a ground and that often leads to a nasty and loud hum. (Bad for speakers)
Swez
gearhead on 08/12/2007 13:28:04
A 2ch amplifier is 1ohm stable in stereo and has the following ratings:
300w x 2 @1ohm (stereo)
150w x 2 @2ohm (stereo)
75w x 2 @4ohm (stereo)
Question: If 4- 75w/4ohm speakers (wired in parallel = 1ohm) were connected to 1 channel, and 2- 75w/4ohm speakers (wired in parallel = 2ohm) were connected to the other channel, would all speaker recieve approximately equal power? (The gain setting on the amp sets both channels)
swez on 08/12/2007 13:47:41
I feel like I have regressed back to a math class of what 5th grade... all these story probelms... hehe GH, you sure keep me on my toes... CLAP (That was 40 years ago dude) Dang... am getting old huh?
4//4 = 1 Ohm or 300 Wrms/4 = 75 watts/speaker
4/2 = 2 Ohms or 150/2 = 75 watts/speaker
Looks pretty good to me, how 'bout you?
Swez
Replies (12)
swez on 07/24/2007 13:54:44
In most 2 channel amps, it is best to send audio signals to both channels of a bridged amp. When bridged, the input side of the amp will automatically sum signals, (A+B Channels) to derive a stronger MONO signal that is fed to the main amplifer circuits.
If you only use one input, (Say Ch A is plugged in but Ch B has no signal line, the amp will still sum A & B, but reguires higher gain settings to achieve full amp output power to driver your speakers.
In most cases, a typical amp can achieve full output power with as little as 1/4 volt of input signal. It just depends on amp sensitivity range settings and the gain structure ratios between the amps input preamp stage and the output stages of the amp.
In a nutshell, try 1 RCA per amp and see if you can get enough power output to each amp to drive the load, (Speakers) to desired power range. (Amp gain tweaking) If not, use Y cables so that both A & B channels are getting a signal. (Tweak amp gains as needed)
Get all that?
Swez
gearhead on 07/24/2007 14:42:37
"Get all that?"
I'm cornfussed!
If there's no signal applied to 1 of the channels on a 2 channel amp, how would there be any output from the channel with no signal applied? Or in the bridged mode, how would there be any output at all since one channel isn't recieving any signal?
Ash on 07/24/2007 18:54:15
What he is saying by splitting the signal as you were wanting; you would be reducing the actual voltage in the rca's input to each amp. Essentially you would have to adjust the amp gains to compensate for the loss. I imagine it would not be much to cause a problem if your HU is putting out at least 2 volts. At the same time only using one per amp (no splitter) might accomplish the same without gain loss. Power output will still be bridged rated. Just try it and see what happens. You won't harm the amp, just the imaging if both are fed a stereo signal.
A perfect example of this, but in reverse is the JBL BP Mono series amps. Those who have run one know what I'm talking about. It has four inputs ( 2 left/ 2 right) and when fed only two, the gain has to be compensated to get the same output if all 4 were fed with a split rca. Go figure?!!!
The idea stated by Gearhead is a common one and there is nothing wrong with it as long as you understand the possible gain loss. Yes you do want all left going to one bridged amp and all right the other. Since you are bridging both amps this is the only way to keep a stereo signal. Just turn up the gain a tad more if needed.
swez on 07/24/2007 19:48:14
Good, 2 out of 3 ain't bad...
GH, it can be done as you mentioned... either/or
a. One RCA per bridged amp
b. One RCA w/ Y splitter per bridged amp
You may have to adjust the amp gains to get each amp to full power is all.
Swez
PS Yes, like the old JBL amps is exactly right Ash
Ash on 07/24/2007 20:56:09
By the way why did the BP mono series have 4 inputs? I remember the manual saying something about nonfading bass, yet I couldn't imagine a setup where you would need or waste both front and rear rca's on a mono amp. Besides most HU's that have both will still fade the same between internal amp and rca outputs???
swez on 07/24/2007 23:14:51
Yeah, that was a pretty goofy system step. I cannot imagine why they did it in that manner either. But really, it does not matter as one could still obtain full output power with only 2 channels of input. (Higher gain settings is all)
That was a pretty solid series for JBL, but they did have a fair amount or returns and refurbs when guys used them at 1 ohm loads. In reality, the BP series was a solid product line, but it was also bare bones, no frills and very low price. As I recall, this series did not even have a SSI filter.
That just kept JBL in the game until the newer amps came out with a few more features, a new look and a higher price tag. (So whatelse is new?) It was a very good low budget amp series for almost 5 years though.
Swez
gearhead on 07/25/2007 00:48:09
My HU has 2.2v preouts, and the amps have a low input level spec of 200mv-6v. So, if I use a Y cable that should give me 1v per channel, which "should" be enough to get full power, correct?
swez on 07/25/2007 07:42:00
That should work out OK.
Just don't be too surpirsed if you find your amp gain settings are closer to 1 volt to get the amp(s) up to full power though. That would be normal and not unexpected.
Swez
gearhead on 07/27/2007 21:11:40
OK,new question. My amps have RCA outputs to enable daisy chaining to another amp. If I run an RCA from the HU R output to the amps R input, then run an RCA from the amp R output to the same amps L input, would that give me 2.2v on both inputs?
swez on 07/27/2007 23:30:54
I think I would use a Y splitter to feed both amp input channels before trying your alternate method.
It, (Your idea) probably will work as most daisy chain outputs are just parallel wired to the input jacks too. If you try it, do it at very low power and test amp performance w/ and w/o the jumper RCA line.
If you note a hum or other noise issues, use the Y splitter method.
FYI: Avoid connect/disconnecting RCA lines when the amp is powered up. Before the grounding claw grabs and connects, we don't have a ground and that often leads to a nasty and loud hum. (Bad for speakers)
Swez
gearhead on 08/12/2007 13:28:04
A 2ch amplifier is 1ohm stable in stereo and has the following ratings:
300w x 2 @1ohm (stereo)
150w x 2 @2ohm (stereo)
75w x 2 @4ohm (stereo)
Question: If 4- 75w/4ohm speakers (wired in parallel = 1ohm) were connected to 1 channel, and 2- 75w/4ohm speakers (wired in parallel = 2ohm) were connected to the other channel, would all speaker recieve approximately equal power? (The gain setting on the amp sets both channels)
swez on 08/12/2007 13:47:41
I feel like I have regressed back to a math class of what 5th grade... all these story probelms... hehe GH, you sure keep me on my toes... CLAP (That was 40 years ago dude) Dang... am getting old huh?
4//4 = 1 Ohm or 300 Wrms/4 = 75 watts/speaker
4/2 = 2 Ohms or 150/2 = 75 watts/speaker
Looks pretty good to me, how 'bout you?
Swez
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