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Old 29th March 2011, 10:57 AM  
Pano is offline Pano  United States
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Location: Milliways
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Default What is Gain Structure?

Gain structure (AKA Gain Staging) is a concept that gets talked about a lot in pro audio, but most home audio folks have never heard of it. Understanding gain structure can help you get the cleanest signal possible out of your system and avoid some nasty things. Things like noise and clipping,...

Last edited by Variac; 1st April 2011 at 11:34 PM.
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19th December 2011
454Casull
diyAudio Member
Conrad, your sig made me LOL.
19th December 2011
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nigelwright7557
diyAudio Member
Gain structure can be found in audio mixers.
You can have line inputs to the mixer which dont need much gain.
It starts to get a bit more complicated with low output microphones where the signal can be very small. Simply having loads of gain will also amplifiy noise or ground hum.
So often mixers can have a variable microphone pre amp gain to keep the gain low but the signal at a good level.
19th December 2011
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RCruz
diyAudio Member
Now that is a very good idea. A variable gain preamp.
RC
19th December 2011
nigelwright7557's Avatar
nigelwright7557
diyAudio Member
My Peavey mixer works that way. The mic inputs have seperate gain controls.
19th December 2011
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RCruz
diyAudio Member
I must study this very carefully... I am actually using a line buffer instead of the "normal" 16x preamp I used for so long and the gains in stage size, dynamics, clarity and control are uge.... but sometimes I would like to have a louder listening session and just canīt. I would like to have some gain in the preamp but not always. Variable gain is the way to go for me now.
RC
20th December 2011
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Pano
diyAudio Moderator
Don't confuse variable gain with variable attenuation. Variable attenuation is how almost all volume controls work, even the mic preamps on a mixer strip.
Having a preamp with a bit of voltage gain is not a bad idea, as Mr. Cruz points out. 6-12dB gain can sometimes be useful.
Actual variable gain is not all that common because variable attenuation is so much easier to do.
29th January 2012
Antoinel
diyAudio Member
I advocate the design doctrine of Nelson Pass which is: "keep it simple". A CD player has a volume-controlled headphone amp. It is a high fidelity mini power amp ~15-20mW (rms) into 30 Ohm loads. The CD player's volume control may be manual (e.g. Marantz), or motorized via a remote controller (Sony). The resultant output then goes directly to the input of the power amp. This approach is a high efficiency and least-noise gain structure.
30th January 2012
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adason
diyAudio Member
"I advocate the design doctrine of Nelson Pass which is: "keep it simple". A CD player has a volume-controlled headphone amp. It is a high fidelity mini power amp ~15-20mW (rms) into 30 Ohm loads. The CD player's volume control may be manual (e.g. Marantz), or motorized via a remote controller (Sony). The resultant output then goes directly to the input of the power amp. This approach is a high efficiency and least-noise gain structure. "

Antoinel,

while it is feasible, to put headphone cd output straight to the amp, it usually does not sound very good. The reason is that the best cd players do not have headphone output at all, those who have have it for some sort of monitoring, not for real listening. Well, I tried it, it just does not compare with dedicated high quality headphone amp fed by line signal. The line level out can be high quality, but headphone amp inside cd player is usually of mediocre quality. Most of the time one OPA. Rarely discrete. Never tube headphone output. If yes, please point me to such cd player.
30th January 2012
Antoinel
diyAudio Member
Sorry, I do not not know of a CD player to report. The CD players I have are a Marantz (manual vol control) and an older Sony which uses a motorized unit. A very handy feature. Is this feature found on high end CD players? I do not know; but I hope/guess it can be. You are correct. The headphone amp of a typical CD player is an OPA used as a unity gain buffer. It is driven directly by the output signal which appears simultaneously at the RCA outputs. No reason for the signal to be mediocre because it is processed by an OPA. Its distortion is low and will be even lower when it feeds the input of a power amplifier of impedance ~47 K. It is barely doing any work. Its fidelity may beat that of its externally processed RCA signal. One needs to consider the balance between the added cost and the performance of the external preamplifier or attenuator. Your following thought is valuable. It is preferred for a high end CD player to have an internal volume controlled high end headphone amp.
30th January 2012
AndrewT
diyAudio Member
I would never use the headphone output of any commercial grade audio equipment as the mains audio feed to my stereo system.

Even the dedicated Line Level output can be substandard and needs upgrading to become the mains stereo feed.
regards Andrew T.

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