What is Gain Structure? - Page 5

29th March 2011, 10:57 AM
Pano diyAudio Moderator Join Date: Oct 2004 Location: SW Florida	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,... Click here to read the entire article Last edited by Variac; 1st April 2011 at 11:34 PM.

16th April 2011

Conrad Hoffman

diyAudio Member

I can't recall ever building a power amp with a gain much higher than 10X. Going over 10X seems like the first step towards the troubles described. OTOH, trying to go too low can lead to stability problems; notice how many high bandwidth opamps have a minimum gain of 5X, or you have to add phase compensation networks to avoid building an oscillator.

Signal to noise performance is set at the first stage of any amplifier. It can get no better than that downstream, though it can certainly get worse, as the article shows. Complexity is bad; I've no experience with true pro audio, but it seems obvious that complicated (many stages) systems get a huge benefit from standardizing on larger signals. It's a wonder modern PC stuff works as well as it does, given 5V power rails.

[begin dumb idea] We have an environmental chamber at work with a refrigerator and a heater. It controls the temperature by running the fridge full blast all the time, and simply changing the heater power to get the desired temperature. Maybe the ultimate answer is to run the audio system wide open, just below clipping, and put a power attenuator right at the speaker! The numbers work out well unless efficiency is one of them. [end dumb idea]

I may be barking up the wrong tree, but at least I'm barking!

16th April 2011

Pano

diyAudio Moderator

Ha! Actually I was going to suggest just such a thing, if only as an example.

Run it all flat out (barring clipping) and turn it down at the speaker with an L-Pad or transformer attenuator. Inefficient, and probably won't sound good, but it should keep the S/N ratio pretty high.

But then you run into problems such as trying to mix consumer and pro levels, such as the DCX2496 example in the article. If you are using the analog inputs, your CD player signal may still be a little weak. Use the digital input and you'll get more than enough level out to run any amp.

Take the Speaker Voltage Test!
planet10 needs your help: Let's help Ruth and Dave

17th April 2011

AndrewT

diyAudio Member

The F5 or F5x (+16dB) will be must first Power amp with a gain of less then 20times (+26dB)
Not many Power Amps will perform well if the gain is significantly lowered cf. what the designer intended.

regards Andrew T.
Sent from my desktop computer using a keyboard

19th April 2011

roscoeiii

diyAudio Member

What a great article and thread. One of the most useful I have read here. Wish I'd been more aware of this a year or so ago. After moving to a tube amp (an OTL Atma-sphere S-30), I was delighted that I was able to get jumpers to replace 2 of the 6SN7s and reduce the gain of my amp. Speakers are much quieter as a result and I get a greater range of travel in my preamp.

To get more fine-tuned control from my preamps attenuator, I have also lowered the output voltage from my DAC to 1.35V. But after reading this thread, I feel that the sound quality might benefit from bumping it back up (options are 5.48, 2.74, 1.78 or 1.35V output). With the lowered amp gain, maybe I will have an acceptable sensitivity in my volume control and improved sound quality from having a hotter source?

19th April 2011

AUDIODH

diyAudio Member

I guess I am confused here about at all the post regarding Amp gain....did I miss something all my professional career???
Did your favorite XYZ bands, sound company's/Pro audio designers, recording studios, etc. miss the collective boat?
WHY is amp gain such a big issue - did the rest of the world skip a beat???? Did the DIY counsel find something the rest of the audio engineering world missed??? Help me out here...please! Dang these industry pro's sheesch
- Dave

19th April 2011

Pano

diyAudio Moderator

Why? Because of the costs of gain. Why have 40X voltage gain if you only need 4x?
The DIY crowd tend to be frugal. Frugal with their money and also their designs. Many like to uncomplicate things.

The costs of more gain than you need include things like noise, distortion, higher parts cost, more complicated circuits, etc. While I can't swear that low gain systems are great just because they are low gain, many of the best systems I've heard were low gain. Certainly noise is low in such systems.

And there is a certain elegance in "enough, but not too much." Nothing wrong with that as a goal.

19th April 2011

Pano

diyAudio Moderator

Quote:

Originally Posted by roscoeiii

I was delighted that I was able to get jumpers to replace 2 of the 6SN7s and reduce the gain of my amp.

That's cool that you were able to do that.

Quote:

With the lowered amp gain, maybe I will have an acceptable sensitivity in my volume control and improved sound quality from having a hotter source.

That's been my experience. A source that is a little hotter than it "needs to be" somehow sounds better. I don't know why, but to me it does. Going to 2.74 volts is an increase of 6dB. The change is worth a listen.

19th April 2011

KaffiMann

diyAudio Member

So basically, you should have a power amp with short signal path, that you could adjust the psu voltage on...?

So I could use for example 2x3-30VDC power supplies for the power amp (in series, middle to ground), and replace the pot for voltage adjust with a stereo lightspeed attenuator, or just a regular stereo pot (one part for each psu).

But what kind of power amp would handle such a variable psu?

Edit:

I noticed that this has been discussed before:
https://www.diyaudio.com/forums/solid...e-control.html

19th April 2011

Pano

diyAudio Moderator

Let's not get bogged down in amplifier design, it's not the subject of this article. There are many threads that cover the subject.

The idea is good management of signal levels all along the path. Choosing devices with modest gain is often a good way to do this for a home system. Finding the right amount of gain and attenuation is what you really want.

19th April 2011

KaffiMann

diyAudio Member

Yes, the right amount of gain in the right place.

I was just thinking how you could apply that in a practical way. You have to be able to adjust the gain somewhere, I have no intention of listening to music on 10 different audio systems, pending on the volume i desire.

The consensus seems to be that high gain sources are nice, so that would translate to voltage buffers - stepped attenuator (because a lot of potmeters cannot really cope well with more than a few volts) - current gain stage.

But then the gain would be higher in one stage than the other, and regulated by variable resistance on top of that. Isn't some of the idea that the gain should be somewhat balanced throughout the entire chain?

Unless you have some way of adjusting the gain directly, by for example adjusting the supply voltage of the circuits, provided that they can handle that without going into "crappy snr mode".

I may be lost in some chain of thought here, but the article got me thinking, which is completely foreign to me.