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Gain Structure for Home Theater Discussion Thread

13480 Views 85 Replies 22 Participants Last post by  Maxino1969
Please use this thread for any comments or discussion about my article Gain Structure for Home Theater.

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Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Hi Wayne,

Let me first say thank you for your expansive treatment of this consumer/pro line interface issue. I have been trying to use my Crown K1 pro amp for two weeks now, and couldn't find much information into finding this article a few days ago. I really appreciate your enthusiasm and thorough explanations!

I have a 7.1 system with a Yamaha HTR-6160 AVR at the helm. It is rated at 110 watts/channel with all 7 channels running, although I don't believe that. I recently upgraded my fronts to Polk RTA 15tl's (91db 8 ohm 250 watt rms, four 6.5" drivers) and decided it was a great opportunity to outsource their amplification to a 350 watt/channelCrown K1 I had sitting around. I wanted more heft behind the speakers, and also wanted to ease the burden on my AVR. Initially I simply used an rca-to-1/4" cable from my pre-outs to the Crown, but I couldn't get the same volume that I got from the Yamaha. Today I realized that the 1/4" plug was not a balanced TRS but the other kind (TR?) So perhaps I should get another cord? I didn't realize this though until today. FYI The Crown has an input sensitivity of 1.4 vrms and the Yammie (according to the manual) passes a 1 volt signal from the pre-outs.

I ended up getting a Samson S-Convert, ran XLRs into the Crown, and it was much, much better. The bass was awakened compared to when the Yamaha drove them. I did some guessing here and there, though, since now I had three knobs to affect volume (gain knobs on the Crown, gain knob on the S-Convert, and of course the AVR's control. My Yamaha's volume spread is -80 -- +16.5. When I calibrated my speakers for 7.1 a while back with an SPL, I used 75db as my reference. I rarely go past -18 on the Yamaha, and my front speaker levels are set at 4.5 on a scale 1 -10. I like not maxing out my system in any setting, so I left everything alone when testing out the S-Convert. Just going by my ears, I noticed a lot more hiss during the music's quiet passages when I maxed out the sensitivity gain on the amp. And when instead I maxed out the S-Convert's gain and moved the Crown's knob back to its middle setting I could hardly hear any noise. The AVR was also playing a lot louder than normal at -11. I was pretty impressed with the results, but still felt there were other ways to measure than my ears and my gut. The next day I found your article.

I decided to do the voltage test on my Yamaha pre-outs. I got a digital multi-reader and downloaded your sine waves and pink noise.

I unplugged all my speakers and raised the L and R speaker evels on the AVR to max. I connected a DVD player with a digital coax connection and bipassed all tone and signal processing with the "pure direct" feature. I played the 60hz sine wave track. I turned up my Yamaha and got to about -7, then it promptly shut off. The voltage reading was always about 2-2.4 volts when this happened.

First off, should I be concerned about damaging the receiver? Why is it going into protection mode? Considering max volume is +16.5, I'm surprised that -7 volume is overloading it. I understand that I've also maxed out my L and R levels from 4.5 to 10, so that contributes. But I was really not expecting this shut down to happen. This receiver has given me no trouble before.

Next thing I did was reconnect the pre-outs to the S-Convert and take a voltage reading from the balanced XLR cable that's headed to the Crown. The S-Convert was at it's middle setting on its gain knob, which the manufacturer refers to as its "unity gain". This time I got to -12 on the Yamaha, also just over 2 volts on the multimeter, before the receiver turned itself off.

The next step was running the 1 khz sine wave through a speaker. I had to go through the S-Convert but left it at unity gain, and the Crown's sensitivity gain was just at the 2nd notch, the first notch that made the sine wave audible. I got to -34 on the AVR and just quit. It was loud enough to hurt my ears, but no harmonic overtone. I guess that wave is so pure it just sounded extra loud.

So I'm kind of at a stand still because:

After my amp shutting down so much I'm concerned about busting speakers when the 1 khz distorts through my tweeters.

2 I don't understand why my voltage test shut the AVR down. BTW Just out of curiosity I tested the voltage on the back of the DVD player, also with the 60 hrz track. Both with the analog rca and the coax digital outs the signal was 4v, and in fact even more because it was going immediately to error on the multimeter since I was measuring in the 4v range. I just checked the Yamaha manual and noticed a "maximum input voltage (effect on, 1khz, 0.5% THD)" = 2.3v. I know I was testing with 60hz, but is it possible the Yamaha shut down because of it's input limit, not output limit? Does its volume knob simply control its own input sensitivity just like the knobs on the S-Convert and the Crown K1?

3) I'm also wondering if I should return my L and R speaker levels to it's SPL calibrated levels on my Yamaha, put the volume to -20 (a median movie watching level for me) and see what voltage it's delivering to the S-convert, and concurrently the amp.

4) Maybe I simply need to get a rca-to-TRS interconnect? It will balance the signal? But not boost it?

5)There also is another piece of hardware called the Ebtech Line Level Shifter. It does the same as the S-Convert except it's passive circuitry, and requires no power. So theoretically it is sonically transparent and conveys no noise floor of its own?

The S-Convert has a s/n ratio of 90 db
Yamaha: "s/n ratio (IHF -A Network) CD, etc (effect off, 250mv) --100db or more
Crown has >100

I hate to overthink all this considering it sounded good, but in respect to all the data you provided, I'd really rather know the signal chain is running clean and trouble-free.

Sorry for trying to write more words than your article had! This is my first post, but I plan on easier topics after this! Like, "Name your favorite subwoofer movie?"

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