Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Yosser on April 07, 2026, 04:07:45 am

Title: Adding a treble control to a Carlsboro 60 pa thoughts
Post by: Yosser on April 07, 2026, 04:07:45 am

This is just an idea, is it possible to add a treble control or treble boost to this amplifier, it has a presence control (which maybe a treble control in disguise) but no treble control named as such, could this be an easy mod or would there be performance trade offs?
The stack seems to be like a James stack or based on baxandall - any thoughts?

Title: Re: Adding a treble control to a Carlsboro 60 pa thoughts
Post by: sluckey on April 07, 2026, 04:34:56 am

The Presence pot ***IS*** a treble pot. Nothing to do.

BTW, I just noticed your very dangerous bias circuit. The bias pot allows the bias voltage on pins 5 of the EL34s to be adjusted to zero volts! Doing so will quickly kill the EL34s.

Title: Re: Adding a treble control to a Carlsboro 60 pa thoughts
Post by: Yosser on April 07, 2026, 04:44:50 am

Quote from: sluckey on April 07, 2026, 04:34:56 am

The Presence pot ***IS*** a treble pot. Nothing to do.

BTW, I just noticed your very dangerous bias circuit. The bias pot allows the bias voltage on pins 5 of the EL34s to be adjusted to zero volts! Doing so will quickly kill the EL34s.

Ah, I thought as much in this case
I have modified the bias circuit be a marshall design to prevent that from happening.