Will changing gain affect frequency response?

George makes a good point that sonic consequences can particularly be expected if a gain change is implemented in a circuit via a change in the value of a resistor in a feedback loop.

Regarding Dentdog’s Zesto Leto, there doesn’t seem to be any indication at the website or in the manual as to how the gain change is implemented. (Although the manual states in bold-face type, in the paragraph dealing with the internal gain switch, that "due to high internal voltages there are no user adjustable switches, only authorized representatives can make these adjustments," and also states that the "warranty is void if the product has not been used in accordance with the instructions found in this owner’s manual.")

A schematic for the McIntosh MC60 can be found on the web and shows that its gain control is simply a resistive pot (potentiometer) used as a voltage divider and connected to the input through a capacitor.

As I see it the bottom line to Dentdog’s question, and to such questions generally, is that whatever sonic effects might result from changing how the overall gain is apportioned between components figures to be highly dependent on the specific designs that are involved. So in most cases the only way to find out is to try the various alternatives in the particular system, IMO.

Does trimming the gain on the amps give me less headroom when listening at higher volumes?

No, assuming that you don’t turn the gain controls on the amps so far down that you can’t drive them to full power (when and if that is required by the music and your volume preferences).

Regarding the ZBOX, it sounds like it uses the tube in a cathode follower configuration, and has an Alps pot at its input for gain control. It is described as using "large hi-end coupling caps," so perhaps the specified output impedance of "less than 1000 ohms" is conservative, even at 20 Hz. In any event, I would think that the key to its sonic effects, in addition to possibly allowing the gains of other components in the system to be optimized, is the mention that it "works by creating a starved voltage condition in the filament of the tube that in turn causes an increase in favorable harmonics and a decrease in objectionable distortion." Although I suppose the reduction in "objectionable distortion" may not really be a reduction, but rather a masking by the "favorable harmonics" that are introduced.

John ("Ivan"), thanks for the nice words.

Regards,

-- Al

I don’t believe this has been expressly mentioned. You can significantly effect how you "drive" your speakers by adjusting the gain and therefor the volume the speakers put out. I would be Very cautious however about over-driving the speakers and burning out the crossovers, blowing out the speaker surrounds or similar speaker or other damage. A friend of mine blew out the speaker surrounds of his speakers 3 times before he caught on that he had the gain adjusted too high. Adjusting the gain too high can also cause your equipment to "clip". The best setting for gain is just before your equipment begins to clip. This is the point at which you are driving your speakers and your equipment to the max - which is what you want to do- but you are not over driving it. I understand all of the discussion of volume and our perception that louder is better. Gain is really a different issue although it also results in variations in volume. Again, I would be most cautious about turning the gain up with careful consideration of the overall effect it is having on all of your equipment.

In addition to the points already made, an additional issue is that a room can sound brighter at higher volume levels!

I run into this all the time at audio shows where the rooms are hotel rooms that aren't built as well as rooms you might have in your house. At lower levels reflective surfaces such as windows and framed pictures might seem innocuous but if the room is driven too hard you might find it painful.

In a nutshell the room is at least 50% of the total system quality! I have lots of LPs and they have proven to be good room diffuser elements when neatly stored in their shelves (rather than stacked on the table beside by my turntable...). This is why there is a room treatment business.

One other thing that can affect tonality when the volume is increased is the effect of the volume control on the surrounding circuits. This usually affects tube preamps more than solid state. There is this thing called Miller Effect, which is the input capacitance of the amplifying device interacting with the outside world. It can affect frequency response! A classic example is a loss of high frequencies in the middle of the control (the impedance of the control interacts with the input capacitance of the tube or transistor) If you happen to use that part of the control a lot, turning it up past that point might make for more HF response.

This problem can be controlled by careful design.