Single ended amplier

[Mark Hennessy]

What I'm puzzled by is that if we use a ECC83 we get 60v P-P out, which I thought would overdrive the OP valve causing distortion.

Just a general point here about "gain structure".

If your triode has too much gain, then yes, it would be capable of "over-driving" the OP valve.

However, this doesn't matter because the OP valve will clip first when it runs out of headroom. And when the user hears clipping, they should turn down the volume.

The output stage should always clip first. If an earlier stage is clipping before the final output stage does, then something has gone wrong with the gain structure, and the amplifier will never be able to deliver its full output power.

Also wouldn't it mean that the volume knob would only go to "3" say?

That's more like it. In other words, the amplifier will have too much gain.

At which point, we use negative feedback in some form to reduce the gain to the desired amount - bearing in mind we need to have slightly more gain that we might think because some recordings are made at a lower level, and some sources are quieter than others - commercial hi-fi amplifiers usually have between 10 and 20dB of "gain in hand" for that reason. Which means that most commercial amplifiers are into clipping at about 12 o'clock on the volume control when playing a modern CD with high peak levels.

Negative feedback - stating the obvious, I know - will make a good amp better in every regard, providing you get it right. Some audiophiles think there is something wrong with NFB, but I assume we don't need to go there