Help in using pre-amp outputs with receiver. - AVS Forum
Audio Theory, Setup, and Chat > Help in using pre-amp outputs with receiver.
chanc's Avatar chanc 09:35 AM 06-10-2013
I have an Onkyo TX-NR809 which has pre-out. Pre-out can be connected to an external amplifier to provide additional power to the Onkyo. I hesitate to buy the additional amplifier and want to experiment some more before spending more money. It happens that my old receiver Pioneer is available.

Is using the older Pioneer receiver as an amplifier possible or advisable? I only want to drive the R and L front speakers of my 7.1 setup. Another issue I noticed it the preouts are single RCA connections and where the inputs on the Pioneer or Onkyo are double RCA connections ( Red an White). How does one solve this issue?

Really appreciate some help here.

absolootbs's Avatar absolootbs 10:11 AM 06-10-2013
You won't be providing additional power, you'll be providing power in place of the onkyo's amps. In order to use a second receiver strictly as an amplifier*, you would need to run rca's from the preouts of the first receiver to the multichannel analog inputs of the second receiver (one rca for each channel). And if the second receiver doesn't have a multichannel analog input, then there's no way to use it strictly as an amplifier*. The red/white rca inputs you see are the regular 2-channel analog audio inputs. You could theoretically connect the preouts for your front left and front right channels to one of those inputs, but then you'd be using the second receiver as a receiver (pre/pro and amplifier) in addition to still using the first receiver as a pre/pro. So the signal would have whatever processing and volume control is being applied by the first receiver plus whatever processing and volume control is being applied by the second receiver. I can't think of a single reason you'd ever want to do that. And even if your second receiver does have multichannel analog inputs, the only reason to ever use two receivers in this fashion would be if one receiver has a far more capable amp section than the other (and i do mean far, as most receivers amp sections aren't different enough to make much real world difference).

*Technically, you're still not using it strictly as an amplifier, as the master volume will still be in the signal path. But at least you're avoiding any and all processing, etc. that way.
chanc's Avatar chanc 11:08 AM 06-10-2013
In freeing the Onkyo needs to drive the front speakers, there will be additional power for the remaining speakers. Since the Onkyo and most other AVRs tend to rate their power as 2-channel driven, I would assume that if all channel were driven, the RMS power would be far less. That is my rationale for considering additional amplifier.

Thanks for clarifying for me the multichannel analog inputs and the difficulty to use the second receiver as an additional amplifier. My problem is I do not know if adding an amplifier will help my 7.1 set up at all. I suspect that in movies, when playing fairly loud, the Onkyo 809, rated at 135W/channel 2 channel driven might be underpowered for my other channels. My set up is mostly Klipsch and Acoustech speakers.
absolootbs's Avatar absolootbs 12:54 PM 06-10-2013
Quote:
Originally Posted by chanc View Post

In freeing the Onkyo needs to drive the front speakers, there will be additional power for the remaining speakers. Since the Onkyo and most other AVRs tend to rate their power as 2-channel driven, I would assume that if all channel were driven, the RMS power would be far less. That is my rationale for considering additional amplifier.

probably true, technically. but will it be enough to matter? highly doubtful. keep in mind that you have to double the output power to gain a meager 3 db.
Quote:
Originally Posted by chanc View Post

My problem is I do not know if adding an amplifier will help my 7.1 set up at all. I suspect that in movies, when playing fairly loud, the Onkyo 809, rated at 135W/channel 2 channel driven might be underpowered for my other channels. My set up is mostly Klipsch and Acoustech speakers.

luckily, theres no need to guess, or even experiment (although we all know experimenting can be fun). all you should theoretically have to do is run the numbers. start with how loud the loudest you think you'd ever listen is. lets say its 10 db below reference. that means you need to be capable of 95 db at your listening position from each speaker. you lose ~6 db for each doubling of distance, so add 6 db times the number of "doublings" of distance beyond 1m that you sit from your speakers. lets say you sit 12 ft away. thats ~4m, which is 2 "doublings" when starting with 1m. 6 db for each doubling * 2 doublings = 12 db. 12 db + 95 db = 107 db @ 1m that your system needs to be capable of. now take the efficiency of your speakers (speakers are generally rated at a certain number of db @ 1W and 1m. thats why we converted the needed output to the 1m figure). since you said you use klipsch speakers, i'll guess they're a fairly efficient 95 db @ 1W/1m. as i said before, to gain 3 db you have to double the power. to get from 95 db to 107 db you have to gain 3 db 4 times ((107-95) / 3), which means power needs to double 4 times from the 1W that the rating started with. so the power needed to reach 95 db at a distance of 12 ft using speakers that are 95 db efficiency is 2^4 = 16W. in other words, in this exact situation, as long as your receiver can put out 16W or more with all channels driven, adding an external amplifier isn't going to gain you anything (assuming that you subscribe to the point of view that all properly designed amplifiers sound the same when operated within their limits).

now i'm not saying this is proof you have no use for an external amp - these were all just guesstimate sample numbers. take out my sample numbers, plug in your real numbers, do the same math, and see what you come up with. also, this is all assuming that your speakers are capable of handling the necessary power to reach the volume desired without exceeding their mechanical or thermal limits in the first place... which they may or may not be, depending on just how loud you want to go.
commsysman's Avatar commsysman 01:20 AM 06-11-2013
The simple fact is that almost any receiver you can buy for under $1000, and a lot of more expensive ones too, have a power supply that is not large enough to supply 5 or 7 channels with adequate peak power for HT use. You don't get that kind of power supply for that kind of low price; not possible.

Adding a separate 2-channel power amplifier, which probably will have a bigger power supply than the whole receiver, adds a relatively huge amount of peak power for the front channels while taking that load off of the receiver so it can do a better job with the remaining channels. That is the ideal solution.

Using the Pioneer receiver, with its limitations, is not nearly as good IMO as getting a dedicated 2-channel power amplifier, like for example the Marantz MM7025.

Find a good 2-channel power amplifier and you will be a lot more pleased with the results.
Nethawk's Avatar Nethawk 03:36 AM 06-11-2013
The second paragraph above is the only piece of accurate information you've provided in years. The rest is pure hogwash.
chanc's Avatar chanc 05:09 AM 06-11-2013
@commsysman, I did a lot of readings about receivers over the years and I have to confess, I suspect you are right. I bought the Onkyo TX-NR809 because it has a relatively heavy and powerful power amplifier section and I have a 7.1 set up. I have had a nagging feeling that adding a 2-channel power amplifier would help. I only mentioned the Pioneer for experimentation as I know that it was never optimum or even desirable. I will look at the Marantz MM7025. Although I am inclined to the Emotiva XPA-2 because of cost.

@absolootbs, I did read MichaelJHunan Amplifier FAQs sticky and your calculations were right on. My horn speakers are fairly efficient and I do not play movies too loud. When I play a BD disk the Onkyo gives a pretty good loudness level. But when I play mkv files, the volume had to be cranked up much higher which is the reason I thought adding a 2-channel power amplifier would help. But I want to be reasonable sure of the benefit before committing to another piece of electronic gear (plenty of computer and electronic gears already). I have had receivers with preouts before but I have never added a power amplifier to it. If I remember correctly, it takes about 10 times the power to double the loudness. So adding a modest 2-channel power amplifier (150-200 W/channel) might not do anything but lessen the load of the rear and surround speakers. So the benefit is only at peak level when playing real loud. Thanks again for tips about multi channel inputs. My Onkyo has 5 single rca preouts.
chanc's Avatar chanc 05:17 AM 06-11-2013
Quote:
Originally Posted by absolootbs View Post

probably true, technically. but will it be enough to matter? highly doubtful. keep in mind that you have to double the output power to gain a meager 3 db.
luckily, theres no need to guess, or even experiment (although we all know experimenting can be fun). all you should theoretically have to do is run the numbers. start with how loud the loudest you think you'd ever listen is. lets say its 10 db below reference. that means you need to be capable of 95 db at your listening position from each speaker. you lose ~6 db for each doubling of distance, so add 6 db times the number of "doublings" of distance beyond 1m that you sit from your speakers. lets say you sit 12 ft away. thats ~4m, which is 2 "doublings" when starting with 1m. 6 db for each doubling * 2 doublings = 12 db. 12 db + 95 db = 107 db @ 1m that your system needs to be capable of. now take the efficiency of your speakers (speakers are generally rated at a certain number of db @ 1W and 1m. thats why we converted the needed output to the 1m figure). since you said you use klipsch speakers, i'll guess they're a fairly efficient 95 db @ 1W/1m. as i said before, to gain 3 db you have to double the power. to get from 95 db to 107 db you have to gain 3 db 4 times ((107-95) / 3), which means power needs to double 4 times from the 1W that the rating started with. so the power needed to reach 95 db at a distance of 12 ft using speakers that are 95 db efficiency is 2^4 = 16W. in other words, in this exact situation, as long as your receiver can put out 16W or more with all channels driven, adding an external amplifier isn't going to gain you anything (assuming that you subscribe to the point of view that all properly designed amplifiers sound the same when operated within their limits).

now i'm not saying this is proof you have no use for an external amp - these were all just guesstimate sample numbers. take out my sample numbers, plug in your real numbers, do the same math, and see what you come up with. also, this is all assuming that your speakers are capable of handling the necessary power to reach the volume desired without exceeding their mechanical or thermal limits in the first place... which they may or may not be, depending on just how loud you want to go.

With all channel driven, the Onkyo TX-NR809 is said to put out about 80W RMS/channel although I have not seen any official published data. So my adding a 2-channel 150W/channel for the front speakers will not do anything much for loudness, but probably helps headroom (?) .
arnyk's Avatar arnyk 06:16 AM 06-11-2013
Quote:
Originally Posted by chanc View Post


With all channel driven, the Onkyo TX-NR809 is said to put out about 80W RMS/channel although I have not seen any official published data. So my adding a 2-channel 150W/channel for the front speakers will not do anything much for loudness, but probably helps (?).

Since music and operational conditions vary, its exact power output is hard to predict exactly. In general adding an external power amp in the 150-200 wpc range will be pretty futile. It will be even more futile if you have a good subwoofer (recommended).
chanc's Avatar chanc 06:32 AM 06-11-2013
WOW!!!! So you just saved me from upgrade hell!!! smile.gif

I do have a SVS subwoofer with a pretty good power amplifier built-in so the Onkyo power amplifier is not needed for LFE. I am considering the 150-200 W / channel for a 2-channel power amplifier because I thought the front speakers should not be driven much more than the rear and surround speakers and obviously because of costs involved. The last thing I need is a humongous and heavy electronic gear (not to mention expensive).

I found this calculator for the power amplifier:

http://www.crownaudio.com/elect-pwr-req.htm
Nethawk's Avatar Nethawk 10:10 AM 06-11-2013
^^^ It doesn't have to be humongous, heavy or expensive. Look into Crown XLS, I just purchased the XLS1500, 300W for $288. Not that I'm talking you into an external amp or anything wink.gif
chanc's Avatar chanc 12:05 PM 06-11-2013
Quote:
Originally Posted by Nethawk View Post

^^^ It doesn't have to be humongous, heavy or expensive. Look into Crown XLS, I just purchased the XLS1500, 300W for $288. Not that I'm talking you into an external amp or anything wink.gif

AZ is selling it for $359

http://www.amazon.com/Crown-XLS1500-Power-Amplifier/dp/B003HZV2JS/ref=sr_1_1?ie=UTF8&qid=1370973636&sr=8-1&keywords=crown+xls+1500

Specs look good, weight only 13 LBS shipped. Most AZ reviews are from mobile users, i.e. DJ, musicians, etc... Do you like it in a home set up? Where did you buy it?
Nethawk's Avatar Nethawk 04:00 PM 06-11-2013
Hi chanc, yes, it's great. A caveat - I'm not one to argue that amps sound different. I hooked it up, turned gain to full and listened for noise from my speakers and heard none. Then started playing tunes and smiled. This was an all new system though - receiver, amp and speakers - so I had lots to smile about.

I bought mine from Guitar Center. Sweetwater, Musicians Friend and Guitar Center all have price match agreements, by playing the game and producing some rather complicated mathematics they agreed to sell for $288. You can get the XLS1500 for $309.99 at Guitar Center now, and I'm betting if you ask Sweetwater to match the price you can possibly save sales tax.

Here's a good thread from Audioholics that's worth reading through. Based on the sentiment from a lot of folks whose opinions I respect, I had no doubts.
chanc's Avatar chanc 04:19 PM 06-11-2013
@nethawk, thanks for the feedback. I love the idea this is not another monster box and great cost/performance ratio. I am still researching how to integrate this with the Onkyo 809. Does not look like the Crown have a 12v trigger connection. Does it go into standby automatically when there is no signal and wake up when the Onkyo sends the signal ? I would assume the Crown has no remote control so no easy way to turn it on or off. Is leaving it ON all the time an option?
Nethawk's Avatar Nethawk 05:06 PM 06-11-2013
No. You can buy power strips with switched or delayed outputs or find a reasonably priced 12v power source. Heat output is not an issue, but I wouldn't advise leaving it on all the time.
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