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Interesting article on A/V receivers - and preout question

Discussion in 'Amplifiers & Receivers' started by nelmr, Dec 8, 2010.

  1. nelmr

    nelmr Active Member

    http://www.audioholics.com/education/am ... gy/trading

    I think we all agree about the trading of features for power on most receivers. Among other things, I was interested in the More Gain is Better? section.

    My new receiver has preouts and I haven't used them yet (don't have any amps, but may one day). But I was wondering if there was a way to know what Vrms rating they have. The audio specs are found here (page 21). I assume it's probably 1.2V (under the audio output rating, though it lists 2V for digital, whatever that means).
     
  2. soundhound

    soundhound Well-Known Member

    Re: Interesting article on A/V receivers - and preout questi

    I could go on about esoteric electronic design decisions made by the manufacturer, but the short answer is that essentially all (can't speak for Bose) consumer audio gear is gain and output voltage /drive compatible with any other manufacturer's gear.

    I didn't find the "more gain is better" part, but that again is a design choice by the manufacturer and will yield a compatible component with other manufacturer's gear.
     
  3. nelmr

    nelmr Active Member

    Re: Interesting article on A/V receivers - and preout questi

    Here is the section I was referring to (and specifically 2 volts vs. 1.2 volts):

    I once picked on Emotiva for creating their latest series of amps with higher than usual voltage gain (32dB unbridged, 38dB bridged). A typical high performance amp only a few years ago had around 29dB of gain via the unbalanced inputs meaning if a preamp drive level was around 2Vrms it would be capable of driving a 400 watt amplifier to full rated power without clipping itself and turning off. I found many budget receivers couldn’t drive their preamp outs any higher than 1.2Vrms without clipping and distorting or shutting down. That meant an amplifier with a similar gain structure would only be capable of being driven to 142watts when that receiver was used as the preamp! In the case with the Emotiva XPA-2 amp of 32dB of gain, that same 1.2Vrms would drive it to its full rated 250 watts/channel specification. When I spoke to the company President, Dan Laufman, he said they deliberately sacrificed a bit of SNR in order for their amp to be more compatible with receivers being used as preamps to drive them.
     
  4. yromj

    yromj Well-Known Member

    Re: Interesting article on A/V receivers - and preout questi

    That means they sacrificed one of the primary reasons for using an external amp. Bad call, IMHO.

    John
     
  5. nelmr

    nelmr Active Member

    Re: Interesting article on A/V receivers - and preout questi

    Would you rather have a slightly higher noise floor and be able to use all 100% of an amplifiers output, or have an amp with a lower noise floor but never be able to take advantage of the majority of its power due to low voltage preamp outputs on a receiver? That is in essence what the issue is about.
     
  6. yromj

    yromj Well-Known Member

    Re: Interesting article on A/V receivers - and preout questi

    The lower noise floor, w/o question. As I said earlier, a primary reason for using outboard amplifiers is to decrease the noise floor. Most receivers will play most speakers plenty loud w/ their own amps. Also, as you well know from your volume calculator, the difference between 250W and 300W isn't very much as far as sheer volume goes.

    I'm not saying that the increased headroom is bad. I am saying, though, that it's not worth sacrificing a quiet amp for, IMHO.

    John
     
  7. nelmr

    nelmr Active Member

    Re: Interesting article on A/V receivers - and preout questi

    I agree with what you are saying as noise floor is an issue already in most receivers. The example though was using 400watts at 2.0volts vs. 142watts at 1.2volts for the preout. That's a difference of ~4.5dB (1.2 volts vs. 2.0 volts).

    That's a lot of head room to give up for a quieter amp. Now at 400 watts most speakers wouldn't be able to handle that anyway, so cutting back to 142 watts is still a ton of power. But if the amp is smaller, say 150 watts, the 1.2volt penalty brings it down to around 50 watts.

    Regarding receivers able to power most speakers, true, but 4ohm speakers are a different story. One may be buying a separate amp for load reasons. At 4ohms, powers likely to be high anyway so a 4.5dB penalty may not be that big an issue. I'm just saying I haven't really thought about these differences until I read the article.
     
  8. yromj

    yromj Well-Known Member

    Re: Interesting article on A/V receivers - and preout questi

    So, I buy a 200W amp to use behind a receiver with 150W amps. In this instance, what have I gained?

    John
     
  9. soundhound

    soundhound Well-Known Member

    Re: Interesting article on A/V receivers - and preout questi

    I find it incredible that a manufacturer could design the output to NOT put out more than 1.2 volts. Using today's integrated circuits and the typical power supply voltages used for them, ANY unit should not clip until at least 7.5 volts or so for + - 15 VDC rails.

    Also, the standard gain for a power amp today is 28dB, which is the THX spec also.

    Admittedly, I've been dealing with at least decent grade of gear for the last several years, and have not touched the really cheap stuff, but I still find it amazing that someone could use modern ICs and not manage to get a decent output from them.

    Stick with the good stuff......
     
  10. yromj

    yromj Well-Known Member

    Re: Interesting article on A/V receivers - and preout questi

    Don't confuse lower impedance with lower effeciency. 4 Ohm speakers can be just as effecient (or conversely, ineffecient) as 6 or 8 Ohm speakers. The difference is the ratio of amps to volts. The lower the impedance, the higher the amp draw. The power draw will be the same.

    John
     
  11. yromj

    yromj Well-Known Member

    Re: Interesting article on A/V receivers - and preout questi

    :text-+1:

    Words to live by right there.

    John
     
  12. soundhound

    soundhound Well-Known Member

    Re: Interesting article on A/V receivers - and preout questi

    Signal to noise ratio and gain are NOT mutually exclusive! In good equipment, you can have high sensitivity and a good signal to noise ratio. Its the cheap stuff where this cant hold true apparently.
     
  13. nelmr

    nelmr Active Member

    Re: Interesting article on A/V receivers - and preout questi

    My mid-level Denon 3310 (MSRP $1499, I paid $600), only is rated for 1.2volts (and I believe 10k ohm) on the preamp outputs. Their next model up (MSRP $2000) is the same.

    Now I don't know if it actually can go higher, but that is what the spec lists.
     
  14. soundhound

    soundhound Well-Known Member

    Re: Interesting article on A/V receivers - and preout questi

    Many times the listed output is a reference level, not a level where clipping starts. Only getting the gear on a test bench will tell one way or the other. Still, It's awfully hard to create a circuit which will NOT put out at least 7.5 volts into a 2K ohm load unless they're cutting some pretty severe corners.
     
  15. yromj

    yromj Well-Known Member

    Re: Interesting article on A/V receivers - and preout questi

    FWIW, I had to alter my gain structure w/ my Mackies to lower my noise floor. I turned the gain on the amps down, which effectively limited my peak volume. No one ever complained that my system wasn't loud enough, and that's in a nearly 5,000 cu. ft. room (16'x28'x11').

    In other words, I did exactly the opposite of what they did. I sacrificed peak volume for lower noise level.

    John
     
  16. nelmr

    nelmr Active Member

    Re: Interesting article on A/V receivers - and preout questi

    What preamp/receiver where you using?
     
  17. soundhound

    soundhound Well-Known Member

    Re: Interesting article on A/V receivers - and preout questi


    Again, healthy signal level and signal to noise ratio should not be mutually exclusive. In a decently designed piece of gear, you can easily have both.

    Maybe I've been hanging around pro gear too long........ :cry:
     
  18. yromj

    yromj Well-Known Member

    Re: Interesting article on A/V receivers - and preout questi

    SH, I agree. Effectively what I did was take advantage of the higher S/N ratio in the pre/pro because to achieve the same SPL, I had to have the volume at a higher setting.

    The wiring for one of the light circuits in my room made a near cirle around the perimeter of the room and another made an "S" in the ceiling. Both of these, along w/ a couple of others were dimmed and I screwed up and didn't have the amps on the same circuit as the pre/pro.

    The hiss/buzz wasn't overbearing by any stretch, but it was there.

    nelmr, I used a Yamaha RX-V2400 for a while before I upgraded to an Onkyo Pro SC885 pre/pro.

    John
     
  19. Flint

    Flint "Do you know who I am?" Superstar

    Re: Interesting article on A/V receivers - and preout questi

    This is why I wrote that long article on gain structure tweaking to reduce the audible noise in a well designed systems. However, the only way to adjust the gain structure is to have components with gain controls. If an amp doesn't have a gain control you are stuck with whatever gain it offers.
     
  20. soundhound

    soundhound Well-Known Member

    Re: Interesting article on A/V receivers - and preout questi

    Technically, a power amp's level control does not control gain. Gain is always fixed, and will always remain at its native gain no matter what position the level control is in. The level control only controls the signal voltage being fed to the input stage of the power amp.
     

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