The Canadian Guitar Forum banner

1 - 12 of 12 Posts

·
Registered
Joined
·
676 Posts
Discussion Starter #1
As Volume is controlled by amplitude, Tone by spectrum, or bandwidth, then how, or what is the best physical description of Gain? It’s represented by a control knob on many amps, but what is actually being controlled? What action is the underlying circuitry performing?
 

·
Premium Member
Joined
·
4,698 Posts
The signal gets clipped. Normally you have a nice rounded sine wave, gain causes the top round part to be clipped off
 
  • Like
Reactions: J-75

·
Premium Member
Joined
·
1,230 Posts
Gain is basically how much bigger the output is than the input. Typically stated as voltage gain. So mathematically Vout/Vin. Can also be stated in decibels as 20log Vout/Vin.
The control on most amps labelled gain is usually not a gain control at all, but just a volume control. A true gain control would actually change the gain of an amplifier stage, a volume control lowers the signal going into that gain stage.
 

·
Registered
Joined
·
676 Posts
Discussion Starter #5
Gain is basically how much bigger the output is than the input. Typically stated as voltage gain. So mathematically Vout/Vin. Can also be stated in decibels as 20log Vout/Vin.
The control on most amps labelled gain is usually not a gain control at all, but just a volume control. A true gain control would actually change the gain of an amplifier stage, a volume control lowers the signal going into that gain stage.
OK, I get it. Thanks.
 

·
Premium Member
Joined
·
25,103 Posts
A great many confuse "gain" with distortion. The tonal consequence of increments to gain, however, depends on context. So the amount of gain applied to a voice mic, to get a nice clean-but-hot signal to maximize S/N ratio, is often well in excess of the amount of gain applied to a guitar that would send an amp into clipping. But that's because a) a voice mic starts out as a much lower-amplitude signal than a guitar, and b) the mixer or mic preamp is designed to apply gain cleanly, with lots of headroom, where a guitar amp applies additional gain, internally, and is designed to anticipate a signal only a bit hotter than a slightly boosted guitar.

dtsaudio nailed the definition nice and clearly. I would only add to it that what is often referred to as a "buffer" generally has a gain of 1, where Vin = Vout. That is, no amplification is applied. At the same time, because the buffering action will prevent against potential loss of higher-frequency content, buffers can result in an audio output that sounds "louder" because less top end was lost. Still, no gain. Weird, huh? No shame in being mystified by it.
 

·
Premium Member
Joined
·
12,559 Posts
Yea, @dtsaudio explanation covers it.

Wrt guitar amps, before the mid 70s, amps had one level control (Volume). This was the preamp volume, the power amp was always hardset to '10'. The big breakthrough was separating those two controls, adding a Master Volume. The original volume in the preamp stayed, but I guess two 'Volume' controls (pre and power) was confusing, so lots of companies called the preamp volume control a 'Gain' control.

As mentioned, it adjusts the preamp's level that then feeds the power amp. This allows you to hammer the power amp with a distorted preamp signal and control the overall level of the amp (the actual volume) with the master. Result --- distortion at quiet to moderate levels.
 
  • Like
Reactions: J-75

·
Premium Member
Joined
·
25,103 Posts
It actually depends on the specific type of amp and design. You are quite correct in stating that what is labelled "Gain" in some amps (chiefly tube) is really just a volume control after (though sometimes before) the tonestack. However, in a great many amps, particularly solid-state and hybrid (SS+tube) amps, the gain control really IS a gain control. For instance, in this Marshall 8240 Valvestate, the gain control really does change the gain of the op-amp stage it is part of.


 

·
Premium Member
Joined
·
1,230 Posts
Good point mhammer. Typically I see true gain controls in opamp circuits like the one you show. Traynor uses true gain in some of their amps as well. One thing to note, when a gain control is used, you can't get zero volume at the minimum setting. The lowest you can achieve is unity gain. I've seen this in some traynor's and I've actually had people think there was something wrong with the amp because sound was still coming through with the gain control at zero.
 
1 - 12 of 12 Posts
Top