How to reduce output from Class-A tube amp?

lo mein · « **on:** 6 Oct 2003, 05:19 pm »

How can I reduce the output of Class-A tube amp (guitar amp) to 1 watt (one watt) or less?

Thanks.

Curt · « **Reply #1 on:** 6 Oct 2003, 05:36 pm »

Reduce the input

That's an easy solution.

Use a voltage divider on the input (two metal film resistors) or even a pot (easy to adjust) since it's just mono.

lo mein · « **Reply #2 on:** 6 Oct 2003, 07:25 pm »

Quote from: Curt

Reduce the input That's an easy solution.

Use a voltage divider on the input (two metal film resistors) or even a pot (easy to adjust) since it's just mono.

Thanks for the quick tip. Curt.

But can you be more specific, like exactly what parts, value, to use, etc. Maybe even a wiring diagram.

The amp that I want to reduce the power is the Vox AC-15. I do have the schematic already.

I want to be able to get full power tube compression sound but without the loud noise. Even 1 watt is loud when driving a 4x12 cab.

Thanks again.

Curt · « **Reply #3 on:** 6 Oct 2003, 08:25 pm »

You have an e-mail with a schematic. It was easier than linking to my server.

lo mein · « **Reply #4 on:** 6 Oct 2003, 09:39 pm »

Quote from: Curt

You have an e-mail with a schematic. It was easier than linking to my server.

Got it. You're DA MAN! Curt. Thanks. Best of all. I don't even have to butcher the amp.

Thanks.

biggerdog · « **Reply #5 on:** 8 Oct 2003, 02:05 pm »

That method will not run the amp into the power compression region you are seeking, it will simply reduce the level, just like turning down the volume control.

You'll need a couple of high power resistors. The values will depend on the speaker impedence, and the amp's power output at clipping.

Can you supply this info?

lo mein · « **Reply #6 on:** 10 Oct 2003, 12:56 am »

Quote from: biggerdog

That method will not run the amp into the power compression region you are seeking, it will simply reduce the level, just like turning down the volume control.

You'll need a couple of high power resistors. The values will depend on the speaker impedence, and the amp's power output at clipping.

Can you supply this info?

Curt's method works. I wired it just before the amp's output to speaker's terminal.

The amp is a Vox AC15(Not reissue.) The speaker is 8 ohms. I believe.

I'll experiment with different ways as well. I do have a couple more amps to doctor. As I do run everything in stereo. Need only about 0.5 watt for recording.

And I don't like to play loud anymore at home.

Thanks.

Curt · « **Reply #7 on:** 10 Oct 2003, 07:50 am »

The circuit I sent was to go between the source (instrument) and the amplifier, not between the amp and the speaker

biggerdog · « **Reply #8 on:** 10 Oct 2003, 10:47 am »

Ooh! I don't know exactly what ciruit diagram Curt sent you, but if you're using metal film resistors or a volume pot between amp output and speaker, it probably won't last very long.

biggerdog · « **Reply #9 on:** 10 Oct 2003, 10:54 am »

Also, with tube amps, you're supposed to keep the output loaded down with something close to a speaker's impedance. If you don't it's possible (when you crank it) that the output transformer or tubes will arc internally, from excessive voltage.