Most high-quality guitar amplifiers inevitably work with tubes: Widely praised for the pleasant-sounding distortion and warm sounds. In addition, I notice that many high-quality guitar amplifiers only really come into their own when the volume knob is turned wide open. The power is usually between 50W and 100W which causes serious sound volumes to be needed to get a greasy tube sound.

My idea is to build a small combo amplifier with limited audio power, just with the intention of getting a good tube sound at a lower volume.

The combo consists of 2 channels: a clean/crunch channel and a distortion channel. The channels are switched to a send/return switch with a toggle switch to be able to add additional effects after the preamplifier. After that, everything goes through a 3-band equalizer. The power amplifier is a module of KEMO. Reliable, good sounding and not expensive. ) For the master volume button I added a "soft-clip limiter" circuit with diodes to get enough sound volume with limited audio power, without transferring the output stage.

The idea is also to run the tubes of the preamplifier on an easily manageable 48V power supply. This is a lot easier and cheaper to realize than the 2 to 300V DC that is normally used. I started experimenting with this idea and to my great surprise a standard 12AX7 tube is perfectly adjustable with a lower supply voltage, without compromising on sound quality.

The guitar signal is connected to a mono jack connection and ends up on U2A via R1. This tube amplifies the signal 27dB (20 log (24), the working point is 23V DC, no clipping occurs.

The used loudspeaker is a Celestion Ten30. This is an affordable speaker that sounds great. It is a 8-ohm speaker. For more power you can put two in parallel as a 4-ohm load.

For more details please see the attached documents and the project updates below.