class A eq amp - part 1

I'm looking to replace the simple preamp I've been using for many years now. Basically I want to rework the tone control. I could use some modern opamps but there is not much satisfaction in designing with opamps other than tweaking the filters. Tubes is a bit costly and bulky so this leaves us with transistors.

design goals

• circuit as simple as possible, preferably class A
• low power consumption
• supply voltage as low as 5V (for USB power)
• filters need not be symmetrical for cut and boost
• 2Vpp output voltage is sufficient
• no potmeters, only switches

gain block

I found this John Linsey Hood design on the web.

source: http://www.angelfire.com/sd/paulkemble/sound3.html

There are also variations with single ended power supply. The design does not seem to be very critical. I spiced my own version and it works out quite well down to 5V.

Next step is to breadboard it. I was happy to find out that it works as intended.

The idea is to use the shunt at the input to 'cut' and to replace R7 to achieve 'boost'.

Obviously some compromises will be needed but I experimented a bit and it looks (and sounds) quite well, more on this in part 2.