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Old 31st August 2005, 09:49 PM   #41
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Join Date: Jan 2002
Location: Puget Sound
I like the XR45 a lot. I picked one up around the buzz of its digital amplifiers with the intention of modifying it. But ultimately it's been great to have as a backup and to deal with issues such as this.

People talk about running the DCX gain as close to clipping as possible to get max resolution. But your suggesting I get everything zeroed? What should my input gain be at?
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Old 31st August 2005, 10:01 PM   #42
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Konnichiwa,

Quote:
Originally posted by ultrachrome
People talk about running the DCX gain as close to clipping as possible to get max resolution. But your suggesting I get everything zeroed? What should my input gain be at?
I think you misunderstand (and there may be where some of your hiss stems from).

You MUST run the INPUT as close to clipping as you can, for what you consider you want full level to be.

THEN attenuate the outputs in the analogue domain to match your amplifiers. The result, maximal input and output dynamic range.

Ciao T
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Old 31st August 2005, 10:03 PM   #43
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Location: Dallas, TX
Ultra,

Not the DCX gain as high as possible, but the input signal as high as possible.. To get the best quality results you want to do as little gain or attenuation in the DCX as you can get away with.. You should drive the maximum signal you can into the DCX, do as little "gain" change in the DCX as possible and then attenuate at the amplifer.

--Chris
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Old 31st August 2005, 10:21 PM   #44
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Speaking strictly about DCX settings, the gain on inputs A and B should be set as high as possible, avoiding clipping. Or should the input gain be 0 as well?

The gain on outputs 1 through 6 should be as close to 0 as possible.

Correct?
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Old 31st August 2005, 10:28 PM   #45
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Konnichiwa,

Quote:
Originally posted by ultrachrome
Speaking strictly about DCX settings, the gain on inputs A and B should be set as high as possible, avoiding clipping. Or should the input gain be 0 as well?
The input gain should be set to 0db gain, the INPUT SIGNAL should be as high as possible while avoiding clipping, for what you consider to be the highest possible Volume control setting on the preamp you use.

Quote:
Originally posted by ultrachrome
The gain on outputs 1 through 6 should be as close to 0 as possible.
Yes, that too.

Ciao T
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Old 31st August 2005, 10:31 PM   #46
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Okay. Understood. Thanks for the clarification.

My preamp is a grounded grid modified to use 12AT7. Rosenblit says it should be good for 30dB of gain.
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Old 31st August 2005, 10:49 PM   #47
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Quote:
Originally posted by ultrachrome
Okay. Understood. Thanks for the clarification.

My preamp is a grounded grid modified to use 12AT7. Rosenblit says it should be good for 30dB of gain.
Here is what I would do to set your input levels..

1) Turn off the power amps.

1b) mute all DCX outputs just in case

2) Turn preamp volume control as high as possible

3) set the gain of the inputs on the DCX such that you are just avoiding clipping with no pre-amp attenuation. Watch the LEDs do not have the power amps on!!

4) turn pre-amp volume ALL THE WAY DOWN

5) turn on power amps

6) Set gain on power amps as low as possible or add the maximum inline attenuation

7) slowly increase the pre-amp volume level until the sound is at a normal-high listening level.

8) if the pre-amp is turned all the way up and the sound volume is too low, increase the power amp gain

Ideally you'll be almost maxing out the pre-amps volume control at normal listening levels

--Chris
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Old 31st August 2005, 10:57 PM   #48
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Konnichiwa,

Quote:
Originally posted by ultrachrome
Okay. Understood. Thanks for the clarification.

My preamp is a grounded grid modified to use 12AT7. Rosenblit says it should be good for 30dB of gain.
More than too much gain.

A normal CD Player will give 2V with digital full scale or +8dbu.

The DCX input sees "overload" at +22dbu, so 14db gain are needed for that, having an extra 6db gain (so 20db in total) is perfectly sufficient.

Then you may want to attenuate the outputs so that "full scale" or +22dbu leaves 6db overload headroom in the crossover, that is +16dbu or around 5V is either Amplifier clipping and/or speakers sensible SPL Power limit for the lowest sensitivity part of the system.

This way you leave 12db gain headroom and 6db level headroom in the crossover, which is ample for any system.

If your woofers have the lowest SPL/sensitivity in your system then first match the Adcom Amp to the required level, which suggests to me 12 db attenuation IN THE ANALOGUE DOMAIN for the Adcom Amp.

The work out the difference in input sensitivity between the Amp's and the difference in SPL between the drivers, add up and attenuate mid and treble apropriatly.

Assuming 94db/2.83V/1m Woofers and 100db/2.83V/1m Midranges and tweeters and with the Adcom giving full output at 1.125V and the XR45 at 0.2V, in other words the Pannie requires 15db attenuation to have the same power output as the Adcom and the Drivers are 6db more sensitive, so you need to attenuate the signal to the XR-45 IN THIS EXAMPLE CASE by 15db+6db MORE than the Adcom on the woofers, or in this case by 12db+15db+6db = 33db.

If you have trouble with Voltages vs db and all that, if you list the rest of the system (drivers etc.), I'll have a bash in terms of giving you set of fixed attenuators for each channel which leave you some scope for tweaking the levels on the crossover (that is what 6db headroom are good for) but also maximises dynamic range.

Deal?

Ciao T
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Old 31st August 2005, 11:14 PM   #49
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I appreciate that.

I think I have everything that I need to pretty much eliminate the hiss and optimize the DCX gain settings.

The system is:
Fountek NeoPro5i 102dB
Audax PR170M0 100dB
Lambda Dipole12 (qty 2) 90.2dB
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Old 1st September 2005, 02:28 PM   #50
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Konnichiwa,

Quote:
Originally posted by ultrachrome
I appreciate that.

I think I have everything that I need to pretty much eliminate the hiss and optimize the DCX gain settings.

The system is:
Fountek NeoPro5i 102dB
Audax PR170M0 100dB
Lambda Dipole12 (qty 2) 90.2dB
I allowed myself to take the whole thing into a new thread:

Settig up active Speakers with Behringer DCX2496

as I thought there may be some more general interest.

Sayonara
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