Using an AV Receiver as a PreAmp ... via the headphone jack?

lawdogg

I am a proud new owner of 3.1TL's, but I unfortunately have an odd couple of av receivers which individually are not up to the snuff of the SDA's 200W/channel requirement. I have two receivers: a Technics SA-AX530 (that I am using solely as a phono pre-amp for my Sony PS-LX520), and a Pioneer VSX-523 I am using as the central A/V receiver for its HDMI inputs / output.

I have read that it's of course possible to use an AVR as a pre-amp if the main unit has pre-amp outputs ... but unfortunately, neither of mine do.

Could I achieve the same result by using the headphone jack, with a headphone to stereo RCA cord from the headphone jack of one to a random input of the other?

Both the Technics and the Pioneer are rated at 80W/channel at 8ohms. What would be the total W/channel if I used this headphone-jack pre-amp method?

I have them hooked up as such right now, and both volume knobs work (versus using the tape output as I was before). So this should be the signal is getting the benefit of both amps, correct?

I am hoping this means they will be up to snuff to handle the Polks. Looking for pros / cons, advice, personal experience, etc.

Thanks in advance,
Ryan

(I may have missed previous discussions of this, I apologize ...)

F1nut

I have them hooked up as such right now, and both volume knobs work (versus using the tape output as I was before). So this should be the signal is getting the benefit of both amps, correct?

I've never heard of that and don't think it's a good idea. Basically, it would seem you have two separate power supplies, which means there is no common ground and that's bad juju without the AI-1 SDA cable.

That said, you don't need 200 wpc to drive those speakers. I've driven 1C's off a 75wpc tube amp and heard 1C's driven with a 40wpc tube amp, both with excellent results. The minimum recommended power for your speakers is 50wpc, so as long as you don't expect rock concert volume levels, you'll be fine until you can get something better.

F1nut

To drive my point home a little further, it's the quality of the amp and not the wpc that matters. I'd take a 100wpc BAT amp over a 200wpc Emo any day of the week and twice on Sunday knowing full well that the BAT will outperform the Emo on every level.

Schurkey

lawdogg wrote: »

Could I achieve the same result by using the headphone jack, with a headphone to stereo RCA cord from the headphone jack of one to a random input of the other?

You need the Technics because it has a phono input, and the Pioneer doesn't? You want the Pioneer because it has HDMI in/out, and the Technics doesn't?
You're taking the stereo signal present at the headphone jack of the first receiver and using that to power a stereo line-level input of the second receiver?
I think you could, but there'd be no point. You'd have all the distortion added by the first receiver's preamp and headphone circuitry and switching, plus all the distortion of the second receiver.

I won't promise that a headphone jack will properly power the input of another receiver. If anything, it'll over-power the input of the next receiver if the volume knob on the first receiver is turned up too high.

lawdogg wrote: »

Both the Technics and the Pioneer are rated at 80W/channel at 8ohms. What would be the total W/channel if I used this headphone-jack pre-amp method?

I have them hooked up as such right now, and both volume knobs work (versus using the tape output as I was before). So this should be the signal is getting the benefit of both amps, correct?

Nope. The first receiver is putting a fraction of the output power into the headphone jack. The headphone jack won't even use the main power amps built into the receiver--it'll be likely be powered by an "amp on a chip" based on the preamp section's voltage. The only power driving the speakers comes from the second receiver.

If both receivers are of approximately the same quality and rated output into the load of the speakers, you've more-or-less doubled the distortion while gaining nothing in terms of power to the speakers.

F1 and I occasionally disagree, but not in this case. Better one "good" receiver/amp than two mediocre receivers daisy-chained. In your case, unless you get a dedicated phono preamp, you'd be better off using the Technics tape-out jacks into a line-level input of the Pioneer; at least that way you avoid the headphone circuitry and the impedance/voltage mis-match the headphone jack likely causes.

Sea

I agree...not the best idea. If you have no other choice I would keep the volume of the feeding Reciever very low to simulate a line level input.

lawdogg

Thanks all, and Schurkey, yes to all questions. I need the phono input on the Technics because the Pioneer has no phono input (and thus no RIAA curve amplification); I need the Pioneer to send the HDMI signal to the TV. I didn't know that the headphone jack gets its signal from a separate amplifier than the speaker outputs.

In any event I'll just run the speakers with just the Pioneer and see how it sounds before getting any other crazy ideas. To be clear, either way I'll only be running the speakers from one receiver, which has commonly ground channels. Also, I'm more interested in the highest quality sound at reasonable volume levels rather than the highest volume sound.

I am curious to get your opinions on the conventional method of using receivers as pre-amps - wondering if you're implying there would be more distortion using an avr's amplifier as a pre-amp instead of a dedicated pre-amp's amplifier? If both amps are in the same class (e.g., A/B), I wonder why using an avr as a pre-amp would introduce more distortion than a dedicated pre-amp?

Maybe you guys meant it in terms of the headphone signal not getting the same amplification as a pre-out jack. But if you also meant the main amp in the avr too, I have been reading some discussions on the topic elsewhere in the series of tubes ...

http://www.audiokarma.org/forums/showthread.php?t=362179 wrote:

I've had great luck over the years using the pre-out section of many different recievers and integrateds. Some of their preamp sections will surprise you at how nice they sound. Right now I'm using the pre-out on a Pioneer sx1010 to drive a Proton d1200. I'm quite happy with that pairing.

https://www.avforums.com/threads/anyone-using-a-av-receiver-as-a-pre-amp.1759080/ wrote:

AV amps make great processors in my opinion.

I've used various Onkyo av amps as processors and I find the performance excellent. I've also tried Anthem and Yamaha and they are also good.

I have an old Onkyo PR SC 886 which is a great processor and even though it is more than 4 years old, the performance levels it produces are on par with todays av amps in sound quality. The newer Onkyo receivers have better room eq than my processor and in some respects are better.

etc.

tonyb

Pre amps don't have amplifiers, you buy those separately. Can you use an AVR as just a pre amp ? Sure you can, but a separate pre is better especially for 2 channel listening.

lawdogg

Thanks. I'm very much on the upward slope of the learning curve here. So using an avr as a pre-amp doesn't mean the signal is amplified by its own amplifier before the main amp? Thanks again.

tonyb

Once you add an amp to the receiver, you take the receivers built in amp out of the equation.

halo71

Assuming that AVR has 'proper' pre-outs to accommodate hooking up a power amp.

F1nut

Ya know, I don't think either of those guys has heard a dedicated 2 channel pre amp in their rigs.

lawdogg

I think I get it now ... no adding wattages. I don't know why I had that idea in my head.

I haven't heard a dedicated 2 channel amp either. Any members in the bay area?

lawdogg

Today's dumb question / observation is: using the surround channels of a 5.1 or 7.1 AV receiver to "bi-amp" your front channel speakers.

I figured I would update with another point on my learning curve. I ended up using the surround channels of the VSX-523 to "passively bi-amp" the speakers. In other words, I removed the 3.1TLs' tweeter to woofer terminal jumpers. Then I ran the main L/R of the receiver to the woofer inputs, and ran a separate pair of speaker wires from the surround L/R channels to the tweeter inputs.

I read a lot on the topic and decided to try it out. Well, it sounds much better to my ears. I haven't taken any measurements yet to see if I'm actually getting 80watts RMS to both the low and the high inputs, so I have no objective data to back that up. But the bass seems like it is stronger without loosening up at all, it really sounds fantastic.

What made me try it out was thinking that if, for example, my VSX-523 is rated at 80watts / channel by 5 channels, if all channels fed off the amp equally, it should be rated at (80 * 5) / 2 = 200 watts per channel just driving the front 2. But instead, any channel will run 80 watts RMS regardless of whether or not the other channels are driving anything, at least as far as Pioneer's documentation goes. So it seems like each channel acts kind of like its own 80 watt monoblock. That means that using the surround channels to bi-amp should in theory result in twice the wattage (assuming all channels are equal), and result in a total of 160 watts / channel RMS.

Any idea if there's a best way to measure the total wattage in this configuration? I'd like to see what's really going on.

Schurkey

80 watts delivered to the tweeters will result in the total destruction of it's voice coil.

Fortunately, there's not a huge amount of treble energy in most recordings; so by the time the signal is filtered by the high-frequency crossover, the tweeter should be safe.

What you've done is to double the amount of current available to the speaker, while not affecting the voltage a bit. If the regular two channels weren't current-limited, the best you can say is that your doubled-up speaker cables now have half the resistance of the single-run you used before.

You're happy...leave it alone. I'm surprised you hear a difference.

F1nut

What made me try it out was thinking that if, for example, my VSX-523 is rated at 80watts / channel by 5 channels, if all channels fed off the amp equally, it should be rated at (80 * 5) / 2 = 200 watts per channel just driving the front 2. But instead, any channel will run 80 watts RMS regardless of whether or not the other channels are driving anything, at least as far as Pioneer's documentation goes. So it seems like each channel acts kind of like its own 80 watt monoblock. That means that using the surround channels to bi-amp should in theory result in twice the wattage (assuming all channels are equal), and result in a total of 160 watts / channel RMS.

Nope, all those channels share the same power supply. Therefore, the more channels you use, the less wpc you get.

cnh

Pioneer units like that have a power draw of 250 watts or more. As mentioned above, they share ONE power supply. When Pioneer rates those for two channel they usually mean 80 watts x 2 at less than 1 percent THD. So, maybe, you have two channels at 80 watts. You certainly do NOT have more than 80 x 2.

As far as the surround rating continuous, you'd be lucky if you have 50 watts x 5, maybe even less than that? AVR ratings are notoriously misleading and usually smoke and mirrors.

lawdogg

Thanks guys. Well, that's not the answer I was hoping for. It seems like some form of fraud to misrepresent current like that. How do you know which ratings to believe and which not to believe? And whatever happened to headroom anyway?

About it sounding better this way - I guess I'm just a fan of bi-wiring!

F1nut

Understand that an AVR is designed and built for HT use first and foremost. Therefore, compromises must be made. Bottom line, you'll never get what those speakers are capable of using an AVR as an all in one solution or even as just a pre amp.

tonyb

lawdogg wrote: »

Thanks guys. Well, that's not the answer I was hoping for. It seems like some form of fraud to misrepresent current like that. How do you know which ratings to believe and which not to believe?

Current and watts per channel are 2 different things. It is somewhat of a misrepresentation with watts per channel ratings but you have to pay close attention to how it's worded. If your receiver has 80 watts per channel, and is a 7 channel receiver, it can't do 80 watts to all channels at the same time. Which kinda defeats the purpose for HT.

In reality though, even for HT, all 7 channels are usually not used at the same time or at the same levels. The more expensive receivers have better power supplies but even they too have their limits. The receivers with built in ice amps like the pioneer SC series hold their power better across all channels driven.

Bottom line is, if you have to use an entry level to mid level receiver your best bet is to stick with more easy to drive speakers. Which rests in the 8 ohm category with an efficiency rating of 90 or above.

Even speaker ratings too you have to pay attention to the wording. Some rate their speakers at 8 ohm but will dip down to 6 ohm or even 4 or 5 ohm on occasion. They say xyz speaker is 8 ohm "nominal", which means average and it can dip lower. Lots of marketing voodoo in ratings, much like anything else, all designed and worded to sell products not necessarily to tell the truth or give a good representation of the products usefulness to the consumer.

Schurkey

F1nut wrote: »

Understand that an AVR is designed and built for mass-market HT use first and foremost. Therefore, compromises must be made. Bottom line, you'll never get what those speakers are capable of using an AVR as an all in one solution or even as just a pre amp.

FIFY. Your response was almost perfect.

There's no reason a receiver--including AV receivers--can't be built to high-end specs. They aren't built that way because the consumer has been trained to shop based on price instead of quality (because they don't understand the thousand things that make up "quality", but they can easily spot a five-dollar difference in price.)

Consumers like "commodity" products. They want to trust the manufacturers to get everything "right" so that the only talking point is how much power, or how many logos are on the front panel, or what the monthly payments will be.

F1nut

^Good points^

lawdogg

Well, I went against all advice here and picked up a NAD C370 and I am now using my AVR as a pre-amp via the headphone jack. But, I understand the basic concepts now.

It sounds good. It sounds the same as running inputs directly to the C370. The only difference is where the input signal comes from, to which the amp's gain is applied. It's just like using your mobile phone or laptop for music via the 3.5mm to RCA adapter into your receiver.

Nothing has exploded.

Still, I'm looking for a pre-amp with HDMI inputs and actual amp pre-outs. Or a speaker to line level converter.

Thanks all for the input.

tonyb

What you want then is HT pre/pro and a separate 5 channel amp.....if you doing HT and 2 channel in one system. Marantz makes good pre/pro's at reasonable prices and amps can be found used for fairly cheap from Parasound or B&k.....Adcom, Sunfire, etc.

lawdogg

Thanks - I'm actually only using the front 2 channels and a sub. I'm not a huge fan of the 5 channel HT setup, so that was one reason to choose the C370, the main reason being NAD's great 3db headroom.

I've found some reasonably priced used Yamaha AVR's with HDMI in/outs as well as pre-outs on local craigslist, so I think I'll just go that route.