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#76974 - 01/23/06 04:20 PM Voltage gain which is correct
ford1215 Offline
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Registered: 01/03/03
Posts: 10
Loc: Decatur Al
Voltage gain: XLR 34dB, RCA 28dB This is for the 7700.

Voltage gain: XLR 28dB, RCA 34dB This is for the 7500.

Which one is correct? I would think the Voltage gain on the 7700 was posted correctly. What is the advantage of having a larger voltage gain?

Fletcher

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#76975 - 01/23/06 09:46 PM Re: Voltage gain which is correct
gonk Offline
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Registered: 03/21/01
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The manual (which applies to both of them) is 34dB (XLR) and 28dB (RCA), so I would expect that to be the correct one.
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#76976 - 01/23/06 09:56 PM Re: Voltage gain which is correct
Doug917 Offline
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Registered: 08/10/05
Posts: 238
Loc: Shawnee, KS
There is a standard in which balanced connections are supposed to be 6dB above RCA connections. Gonk is correct.
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#76977 - 01/23/06 09:57 PM Re: Voltage gain which is correct
Ritz Offline
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Registered: 07/03/05
Posts: 547
Loc: NJ/Beijing
And more importantly, how are they able to extract 6dB more gain from the balanced connection? That's an astonishing difference. Perhaps I just don't understand the inner workings of amp design (I'm slow that way). Can someone shed some light on this?

Cheers,
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#76978 - 01/24/06 07:48 PM Re: Voltage gain which is correct
ratpack Offline
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Registered: 05/26/05
Posts: 110
Loc: Alabama
I'd also like to know where the extra 6 dB comes from. I just don't think that it is from the difference in the connections. Maybe there is a difference in the amps, somehow.

It is my understanding that the balanced inputs only make a difference with long cable runs where noise pickup may become a factor with the RCA type cables.

If I am mistaken, I would like to know the differences.
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#76979 - 01/27/06 02:37 AM Re: Voltage gain which is correct
Kevin C Brown Offline
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Registered: 12/11/01
Posts: 1054
Loc: Santa Clara, CA
For a balanced connection there are two legs sent not just one. The 2 legs are 180 deg out of phase wrt each other. They are then subtracted from each other, so:

+S - -S = +2S

So the signal strength is doubled, which gives you the 6 dB gain. Also, when you do that subtraction, voila, noise present on both legs is subtracted out.
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#76980 - 01/27/06 01:58 PM Re: Voltage gain which is correct
gband Offline
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Registered: 10/19/05
Posts: 65
Loc: Central NJ
Just to add to Kevin's elegant explanation, a doubling of voltage is a 6db gain [20log(2)], and yes its not just the connections, its the differential design overall.

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#76981 - 01/29/06 09:53 PM Re: Voltage gain which is correct
ratpack Offline
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Registered: 05/26/05
Posts: 110
Loc: Alabama
Thanks guys! I obviously forgot how the balanced input works.
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#76982 - 02/05/06 04:26 AM Re: Voltage gain which is correct
Kevin C Brown Offline
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Registered: 12/11/01
Posts: 1054
Loc: Santa Clara, CA
It's a very elegant solution to noise in interconnects. Simple, but very effective. smile
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#96019 - 09/12/16 07:46 PM Re: Voltage gain which is correct [Re: ford1215]
LAH Offline
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Registered: 08/28/16
Posts: 4
I own the Outlaw Audio 7700 amplifier which I used to power my 3-way active open baffle loudspeaker pair, but I was planning on building another 4-way active system. Of course, this necessitated buying an additional amplifier, hopefully with the same voltage gain. I ran across this thread, along with a couple of others from different forums, where the 7500/7700 voltage gain was in question. I noticed on the ATI site on their specification sheet for different amplifiers, the ATI AT2000, which closely resembled the Outlaw 7500/7700, that for RCA inputs the voltage gain was listed as 34 dB, whereas the Outlaw Audio manual stated a 28 dB gain for RCA. Also, the XLR input gains for the ATI AT2000 were stated as 28 dB, but the Outlaw Audio with XLR inputs were stated as 34 dB. I began to suspect one or the other was wrong, with the Outlaw Audio manual being highly suspect.

Then it occurred to me that I could simply measure the voltage input and output and calculate the voltage gain of the amplifier. Note that this is all a moot point since I have purchased a used 7500, so I can be assured of an identical voltage gain regardless of whether the stated gains are reversed or not. But I figured I would post this here for future reference, just to set the facts straight.

I used a 400 Hz sine wave output generated by TrueRTA to a USB sound card to test all 12 channels of both amps with no loudspeaker load. I measured the output from the sound card (the amp input) and each amplifier output with a Fluke 87-V, a true RMS multimeter with a wide bandwidth. If you have an inexpensive multimeter, you may use 60 Hz as the sine wave output since most meters are accurate at that frequency. The measured sound card output was 248.2 mV (.2482 V) with RCA outputs and between pins 2 & 3 on XLR outputs. I then averaged all 12 channel outputs, which turned out to be 12.59V with an RCA input and 6.485V with an XLR input. Notice right off the bat the roughly 6V difference in channel output between the two. It sort of lets you know what's going on here and what the calculations are going to reveal, and why the voltage gain is 6 dB lower for XLR. Remember, by its differential design, the input voltage will be double that of RCA.

Gain in dB = 20 * LOG10 ( Gain Factor )

RCA Gain in dB = 20 * LOG10 (12.59 / .2482) = 34.10 dB
XLR Gain in dB = 20 * LOG10 (6.485V / .2482) = 28.34 dB

So they have been reversed in the Outlaw Audio manual. But one thing that is still a mystery to me is that the Outlaw Audio 7900 and ATI AT6000 and AT4000 specifications state the voltage gain is identical for either XLR or RCA inputs at 28 dB. Hmmm...

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#96020 - 09/12/16 09:04 PM Re: Voltage gain which is correct [Re: LAH]
AvFan Offline
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Registered: 09/12/05
Posts: 619
Loc: El Cajon, California
First, welcome to the Saloon!

Second, I'm very interested to get your thoughts on how the Outlaw/ATI amps perform with your speakers for music. I just got a new-to-me 2-channel preamp and I'm looking for a amp. I have an ATI 2005 paired with my Outlaw 990 and it has been really reliable and I have been thinking about getting an ATI 1802 or 2002 to pair with the new preamp.

Originally Posted By LAH
...So they have been reversed in the Outlaw Audio manual. But one thing that is still a mystery to me is that the Outlaw Audio 7900 and ATI AT6000 and AT4000 specifications state the voltage gain is identical for either XLR or RCA inputs at 28 dB. Hmmm...

Lastly, you probably have already seen it but check out the amp comparison spec sheet on ATI's website. While it does have the gain for RCA and XLR the same 28db for the ATI 6000 and 4000, the 3000, which is the Outlaw 7900, is 34db for RCA and 28db for RCA. I have no clue why they are the same for the ATI 4000 and 6000.

Thanks for the insights on how the Outlaw/ATI amps work for music!
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#96021 - 09/12/16 09:55 PM Re: Voltage gain which is correct [Re: AvFan]
LAH Offline
Deputy Gunslinger

Registered: 08/28/16
Posts: 4
Thank you for the warm welcome!

I don't think you can go wrong with any of the ATI/Outlaw Audio amps. They are very robust and dynamic. Mine are dead silent, and my loudspeakers are very inefficient and are a heavy load. In fact, when I was checking voltage gains of both amps, just out of curiosity, I calculated the difference in voltage gain between the lowest output channel and highest output channel of the 12 channels to see if the difference in gain could be audible or not. The voltage gain difference was .07 dB for RCA and .05 dB for XLR, both inaudible, I would say.

[quote][/quoteLastly, you probably have already seen it but check out the amp comparison spec sheet on ATI's website. While it does have the gain for RCA and XLR the same 28db for the ATI 6000 and 4000, the 3000, which is the Outlaw 7900, is 34db for RCA and 28db for RCA. I have no clue why they are the same for the ATI 4000 and 6000.]

So it sounds like the voltage gain for the 7900 may also be misstated as well, if the 3000 is the Outlaw 7900. I don't understand how the voltage gain could be the same for the XLR and RCA inputs for the ATI 4000 and 6000. It would seem that the gain structure would no longer be equivalent to each other.

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#96022 - 09/12/16 10:44 PM Re: Voltage gain which is correct [Re: ford1215]
AvFan Offline
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Registered: 09/12/05
Posts: 619
Loc: El Cajon, California
Thanks for the insights on how the ATI/Outlaw amps work with your speakers. At some point I will pull my 2005 out of my HT cabinet and try it out with the new preamp and my speakers. And I'll do my best not to strain my back during the process! My speakers are 4 ohm nominal, efficiency is 87db and my current integrated amp has 180 watts at 4 ohms with plenty of headroom. Testing the 2005 will be about how quiet it is, soundstage and bass performance versus how loud it will go.
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#96023 - 09/13/16 10:37 AM Re: Voltage gain which is correct [Re: ford1215]
LAH Offline
Deputy Gunslinger

Registered: 08/28/16
Posts: 4
Yep, that is one of the downsides to these amplifiers: They are back breakers! And I occasionally show my active loudspeakers at audio events, so that entails lugging around the amplifier along with the loudspeakers. Now worse yet, when I complete the 4-way, it'll be two heavy amps.

I also have the Outlaw 990, but I only use it for digital source selection, keeping the signal in the digital domain into a miniDSP 4x10HD, which then performs the D/A conversion for my amps. Volume control is through the miniDSP. The sound is absolutely stunning, and I really don't anticipate much improvement with a 4-way, but who knows?. I would like to test the effects of using dipole behavior for controlled loudspeaker directivity.

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#96032 - 09/15/16 04:09 PM Re: Voltage gain which is correct [Re: ford1215]
LAH Offline
Deputy Gunslinger

Registered: 08/28/16
Posts: 4
I know this is off the original topic somewhat, but speaking of ATI and Outlaw Audio, here is a link to a PDF found on Linkwitz Lab, highlighting some of the history of ATI. Notice on page 10 that Outlaw Audio is listed, along with numerous other companies whose products have been made by ATI:

ATI Sales Story

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#96033 - 09/16/16 09:44 AM Re: Voltage gain which is correct [Re: ford1215]
butchgo Offline
Desperado

Registered: 06/22/07
Posts: 366
Loc: Beautiful Eastern Washington
Very interesting reading.
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