# JL Audio HD amps - inputs w/bridging configuration?



## jhsellers (Jan 7, 2012)

I'm a bit puzzled with how my inputs need to be connected if using HD amplifiers with outputs in bridged mode. 

I have both HD600/4 and HD900/5 amplifiers. Will be using these in separate vehicles, but am planning to run both units with some of the outputs bridged to speaker loads. 

Both vehicles will have 2-way passive component front stage, and a single subwoofer. 

The owner's manual says that mono inputs are needed when bridging channels (using y-cables if needed). Both amps have input mode selector switches, so that I can choose 2/4 channel inputs on the HD600/4, and 2/4/6 channel inputs on the HD900/5 amp. I have multiple outputs available on head units, but thought it simpler to use just one stereo pair of RCA cables for each amp. (no rear stage speakers...) 

For the 4-ch amp, this seems almost straightforward - I can use the single L/R stereo pair, and switch the amp for 2-ch input. But, with the rear channels bridged for a subwoofer, this won't present a mono input for the two bridged rear channels. I don't have a mono output available for use with any head unit; so will use of either just the left signal (or just the right) make an appreciable difference? Will output be compromised if the input for this bridged channel pair is stereo? Do I need to use the 4-channel input mode? 

With the 5-ch amp, I had planned to bridge front and rear channels, and use these bridged outputs for my L/R front stage components. The 5th channel will remain for the subwoofer. The manual for this amp also states that monaural input is required for the bridged channels. I can use y-cables for this, but what mode do I use for the Input Mode Switch? 4-channel? If this mode, what inputs are summed for the subwoofer channel? If I use the 6-ch input mode, I'll still be left with a lack of mono input for the subwoofer channel? 

This seems to be related concern for both amps, but with a little bit of difference in specifics since I'm bridging different channels. Can anyone help? Isn't there a JL Audio person here on the forum? 

Thanks for indulging the extended read,
John


----------



## minbari (Mar 3, 2011)

I have never owned the JL specifically, but if the 4ch have a 2ch/4ch switch. then switch it to 2ch and wire the speaker outputs to the "bridged" config and connect your single 2ch RCA to the amplifier on the 2ch input. it will feed all 4ch with signal.

for the 5ch, if there is no 2/4/5 channel input switch, then you will need y-adpaters.


----------



## jhsellers (Jan 7, 2012)

minbari said:


> I have never owned the JL specifically, but if the 4ch have a 2ch/4ch switch. then switch it to 2ch and wire the speaker outputs to the "bridged" config and connect your single 2ch RCA to the amplifier on the 2ch input. it will feed all 4ch with signal.


Yes, but this won't give the bridged channels a monaural input, correct? Will the "minor" difference between L/R channel signals matter a lot? 




minbari said:


> for the 5ch, if there is no 2/4/5 channel input switch, then you will need y-adpaters.


I think I will need the y-cables for this amp in any case. This amp does have the input switch, but it's 2/4/6-ch selection. And, use of the y-cables will give the mono signal. But, for this amp, the question is where should the input mode selector be set? Is this still a 2-ch mode? 

Thanks for the help, minbari. 
John


----------



## minbari (Mar 3, 2011)

jhsellers said:


> Yes, but this won't give the bridged channels a monaural input, correct? Will the "minor" difference between L/R channel signals matter a lot?


depends on how it is bridged. does it bridge front/back or left/right? if it bridges both left channel together and both right channels together, then it wont matter. if it bridges both front(left/right) and both rear (left/right) then I would use a y-adpater, as they suggest.

most of the time if wont make enough difference to hear. but might as well do it right 


> I think I will need the y-cables for this amp in any case. This amp does have the input switch, but it's 2/4/6-ch selection. And, use of the y-cables will give the mono signal. But, for this amp, the question is where should the input mode selector be set? Is this still a 2-ch mode?
> 
> Thanks for the help, minbari.
> John


again, it will depend on how it bridges. (see above) my guess is you will need y-adapters and then just set it to 4ch or 6ch.


----------



## jhsellers (Jan 7, 2012)

minbari said:


> depends on how it is bridged. does it bridge front/back or left/right? if it bridges both left channel together and both right channels together, then it wont matter. if it bridges both front(left/right) and both rear (left/right) then I would use a y-adpater, as they suggest.


Both amps bridge either front channels, or rear channels (or both). With the 4-ch amp, I plan to bridge the rear channels for the sub. Use of the y-cable will still limit the input to this bridged pair to either left or right HU signal. So, technically, there might be some "missing" bass? 



minbari said:


> again, it will depend on how it bridges. (see above) my guess is you will need y-adapters and then just set it to 4ch or 6ch.


For the 5-channel amp, with both front and rear channels bridged, I can use y-cables from L/R HU signals to give each bridged channel pair the mono signal. But now, my question is - what sort of input is summed for the subwoofer channel? Wording of the owner's manual speaks of the Input Mode selector as if you're using the amp with all channels independantly. And, I'm not sure what mode setting this configuration needs - is it still a 2-channel mode? If that's the case, then the subwoofer will still only get a "left" signal input (since that's the signal inputted to the Front pair of channels). I think the same situation will apply if the mode selector is set to 4-channel. If I use the 6-channel mode, then I'm still needing a monaural signal to y-connect to the two RCA jacks for the sub channel input - will have to use either left or right. 

Seems that all explanations still leave some uncertainty - no? 



minbari said:


> most of the time if wont make enough difference to hear. but might as well do it right


Exactly - do it right the first time, or regret it later. (and, we'll always know there's something "wrong", whether we can hear it or not....) 

Thanks again,
John


----------



## minbari (Mar 3, 2011)

jhsellers said:


> Both amps bridge either front channels, or rear channels (or both). With the 4-ch amp, I plan to bridge the rear channels for the sub. Use of the y-cable will still limit the input to this bridged pair to either left or right HU signal. So, technically, there might be some "missing" bass?


for this application I would set it to 2ch input. here is why. you are going to use the front channels in stereo for full range speakers (coax, comps, whatever) then the rear channels bridged for a sub. since a single sub on a bridged channel will be mono no matter what, it wont matter. like you said, you dont want to miss anything, so using both left and right material on the bridged channel will sum it mono. the front channels will be used normally and get stereo as well.

what they want when they say you need a mono input for each side would be if you were to use this amplifier with both channels bridged for left and right input to full range speakers. (2ch mode) then you would want to use 4ch input and y-adapters.

hopefully that was clear as mudd?


> For the 5-channel amp, with both front and rear channels bridged, I can use y-cables from L/R HU signals to give each bridged channel pair the mono signal. But now, my question is - what sort of input is summed for the subwoofer channel? Wording of the owner's manual speaks of the Input Mode selector as if you're using the amp with all channels independantly. And, I'm not sure what mode setting this configuration needs - is it still a 2-channel mode? If that's the case, then the subwoofer will still only get a "left" signal input (since that's the signal inputted to the Front pair of channels). I think the same situation will apply if the mode selector is set to 4-channel. If I use the 6-channel mode, then I'm still needing a monaural signal to y-connect to the two RCA jacks for the sub channel input - will have to use either left or right.
> 
> Seems that all explanations still leave some uncertainty - no?


for that config I would do it 6ch. y-adapters so both front inputs get left and both rear get right and then input left and right into the 5,6 ch input.


> Exactly - do it right the first time, or regret it later. (and, we'll always know there's something "wrong", whether we can hear it or not....)
> 
> Thanks again,
> John


----------



## jhsellers (Jan 7, 2012)

minbari said:


> for this application I would set it to 2ch input. here is why. you are going to use the front channels in stereo for full range speakers (coax, comps, whatever) then the rear channels bridged for a sub. since a single sub on a bridged channel will be mono no matter what, it wont matter. like you said, you dont want to miss anything, so using both left and right material on the bridged channel will sum it mono. the front channels will be used normally and get stereo as well.
> 
> what they want when they say you need a mono input for each side would be if you were to use this amplifier with both channels bridged for left and right input to full range speakers. (2ch mode) then you would want to use 4ch input and y-adapters.
> 
> ...


Your suggestion seems plausible/practical - reinforces my own opinion mostly - so I'll hope for the best performance. 

I'm tempted to send JL Audio a communication - their manuals seem to imply that only mono inputs are suitable (and must be y-connected to both inputs) when bridging the channels. Common sense would suggest that a stereo signal can be summed without much difference. 

Thanks for the discussion, 
John


----------



## minbari (Mar 3, 2011)

yup, all depends on the application.


----------



## mcintoshi (Feb 22, 2011)

Go back and re read the manual for the 900/5. You only need y connectors if you run the amp in* 6 channel input mode*. This is because the amp is only a 5 channel amp and the inputs for 5 & 6 need to be "summed" together if your head unit only provides a single channel for the sub. 

You will be fine running a single pair of RCA's to the amp in *2 channel input mode * and effectively running the output in 3 channels.


----------



## Thumper26 (Sep 23, 2005)

mcintoshi said:


> Go back and re read the manual for the 900/5. You only need y connectors if you run the amp in* 6 channel input mode*. This is because the amp is only a 5 channel amp and the inputs for 5 & 6 need to be "summed" together.
> 
> You will be fine running a single pair of RCA's to the amp in *2 channel input mode * and effectively running the output in 3 channels.


Whole lotta this. Before I buy anything like that, I first download the manual to get familiar with things like crossovers, physical size, bridging options, etc. The manual has a section dedicated to this, and includes pictures.


----------



## jhsellers (Jan 7, 2012)

mcintoshi said:


> Go back and re read the manual for the 900/5. You only need y connectors if you run the amp in* 6 channel input mode*. This is because the amp is only a 5 channel amp and the inputs for 5 & 6 need to be "summed" together if your head unit only provides a single channel for the sub.
> 
> You will be fine running a single pair of RCA's to the amp in *2 channel input mode * and effectively running the output in 3 channels.


The 6-channel mode will need a y-cable for the subwoofer only, if there is just a mono signal available. (This presumes you'd use Front and Rear HU outputs for the input, instead of y-connecting HU L&R to amp Front/Rear for the bridging. Without rear stage, I don't want F/R fader to unbalance the inputs to the bridged amp channels, should it be inadvertently adjusted. 

But, the 2-channel mode requires the RCA inputs be connected to L&R of FRONT channels, and the REAR inputs are unused. If I'm bridging front amp channels for my left speakers, and rear amp channels for my right speakers, then this won't work, according to the manual. (maybe it would, but all output would consist of the summed L&R HU signals?) 

However, I did re-read as you suggested, and it made me realize that 4-channel mode should work, with y-connected inputs. And I won't need separate inputs for the subwoofer channel. 

It looks like I might need y-cables all around, just to be mostest-safest. 

Thanks,
John


----------



## mcintoshi (Feb 22, 2011)

jhsellers said:


> The 6-channel mode will need a y-cable for the subwoofer only, if there is just a mono signal available. (This presumes you'd use Front and Rear HU outputs for the input, instead of y-connecting HU L&R to amp Front/Rear for the bridging. Without rear stage, I don't want F/R fader to unbalance the inputs to the bridged amp channels, should it be inadvertently adjusted.
> 
> But, the 2-channel mode requires the RCA inputs be connected to L&R of FRONT channels, and the REAR inputs are unused. If I'm bridging front amp channels for my left speakers, and rear amp channels for my right speakers, then this won't work, according to the manual. (maybe it would, but all output would consist of the summed L&R HU signals?)
> 
> ...


You only need the two channels of input to drive the 900/5. You will not be able to use the fader of the head unit, but to answer your initial question, you can bridge the front and rear channels to your mids/highs and run the sub stage to a single sub. No need for y connectors at all. 

As long as you have the input selector in 2 channel mode, the amp can send that signal to all the crossovers and you can do what ever you want with the output.


----------



## jhsellers (Jan 7, 2012)

mcintoshi said:


> You only need the two channels of input to drive the 900/5. You will not be able to use the fader of the head unit, but to answer your initial question, you can bridge the front and rear channels to your mids/highs and run the sub stage to a single sub. No need for y connectors at all.
> 
> As long as you have the input selector in 2 channel mode, the amp can send that signal to all the crossovers and you can do what ever you want with the output.


Well, not that I'm doubting your obvious confidence (I'm thinking you have used one of these before?), but does this lose the stereo separation of L/R signals? 

That's what I'm reading from text in the manual - states that bridging requires the same (mono) signal into both inputs of the bridged channel pairs. The amp needs both inputs of a bridged pair energized. 

If I use 2-channel mode, and L/R signal to Front inputs, then is front bridged output the sum of L&R signals, or does the amp have internal signal routing such that it will send L signal to Front-Right channel? (Similar/same for R signal to Rear bridging?) 

Or, does output of each bridged channel pairs just become the sum of the stereo L&R signals? 

Does this better explain my confusion? Will I end up with a monaural system?


----------



## mcintoshi (Feb 22, 2011)

jhsellers said:


> Well, not that I'm doubting your obvious confidence (I'm thinking you have used one of these before?), but does this lose the stereo separation of L/R signals?
> 
> That's what I'm reading from text in the manual - states that bridging requires the same (mono) signal into both inputs of the bridged channel pairs. The amp needs both inputs of a bridged pair energized.
> 
> ...


I do have a 900/5. I can't convey it any better than the manual. Take a stereo signal from your head unit and plug that to the FRONT inputs of the amp. Put the input selection switch to 2 channel input. Bridge the front channels of the OUTPUT to your left speaker and the rear channels to your right speakers. Subwoofer to the subwoofer output.

The amp is designed to send the L & R signals to all the appropriate output stages. You will be able to adjust the balance, but not fade front to rear since you will not have a rear speaker set. 

You would only need those Y adapters in the event your head unit only had a mono signal coming from it. This is not the case for your set up since you are using a stereo signal to the amp. (No mono signals)


----------



## jhsellers (Jan 7, 2012)

mcintoshi said:


> I do have a 900/5. I can't convey it any better than the manual. Take a stereo signal from your head unit and plug that to the FRONT inputs of the amp. Put the input selection switch to 2 channel input. Bridge the front channels of the OUTPUT to your left speaker and the rear channels to your right speakers. Subwoofer to the subwoofer output.
> 
> The amp is designed to send the L & R signals to all the appropriate output stages. You will be able to adjust the balance, but not fade front to rear since you will not have a rear speaker set.
> 
> You would only need those Y adapters in the event your head unit only had a mono signal coming from it. This is not the case for your set up since you are using a stereo signal to the amp. (No mono signals)


Thanks, mcintoshi - I'll do as you suggest. 

I appreciate the help,
John


----------



## mcintoshi (Feb 22, 2011)

No worries John! Glad to help. You are going to love the amp. I still cant believe JL was able to cram all this power / features into this small chassis and still make it sound this good.


----------



## Mike West (Nov 17, 2011)

mcintoshi said:


> I do have a 900/5. I can't convey it any better than the manual. Take a stereo signal from your head unit and plug that to the FRONT inputs of the amp. Put the input selection switch to 2 channel input. Bridge the front channels of the OUTPUT to your left speaker and the rear channels to your right speakers. Subwoofer to the subwoofer output.
> 
> The amp is designed to send the L & R signals to all the appropriate output stages. You will be able to adjust the balance, but not fade front to rear since you will not have a rear speaker set.
> 
> You would only need those Y adapters in the event your head unit only had a mono signal coming from it. This is not the case for your set up since you are using a stereo signal to the amp. (No mono signals)


This is incorrect. If you plan to bridge the front channels to the left speaker and bridge the rear channels to the right speaker, then both front inputs need to see only the left information and both rear inputs need to see only the right information. A pair of Y-adaptors will be needed if you want to keep it in stereo, and you cannot have the input mode switch in the 2 channel position.


----------



## jhsellers (Jan 7, 2012)

Mike West said:


> This is incorrect. If you plan to bridge the front channels to the left speaker and bridge the rear channels to the right speaker, then both front inputs need to see only the left information and both rear inputs need to see only the right information. A pair of Y-adaptors will be needed if you want to keep it in stereo, and you cannot have the input mode switch in the 2 channel position.


Thanks for this clarification, Mike. 

When bridging a pair of channels for subwoofer use, can the HD series inputs handle the slight difference between stereo L & R signals, or do the inputs need to see exactly the same? (e.g. - sum of either L or R in both channels, but not summed together?) 

It seems there might be a little loss in either case - lose the stereo, or lose the difference in either left or right signal. Not a big thing for subwoofer frequencies in most media, but still - price you pay for bridging? 

Best regards,
John


----------



## Mike West (Nov 17, 2011)

When bridging a pair of channels to a subwoofer, you still want to use both inputs, but using both a left and a right input signal is fine.


----------



## thereddestdog (Feb 21, 2017)

Sorry to bump such an old thread, but are Y-splitters necessary on only these JL HD amps? I had an old Sony amp that I didn't need to use splitters, but it was a simpler design. Because the HD can drive different impedances, the splitters are required? (Friend wants to use the HD900/5 in 3-way mode)


----------

