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hybrid - Ruby Tuby
Written by Administrator   
Friday, 26 May 2006
I have revised the schematic and everything should be fine with the schematic! The sound clips have been re-recorded with the modifications made to the new schematic. You can actually here my picking on some parts of the clip (that is how low the amp can be volume wise!). The clean clip and dirty clip were recorded with version 1.1 of the amp. Dirty Clip2 is recorder with version 1.2

This is my first attempt at building an hybrid amplifier. I chose an hybrid amplifier for several reasons:

  • I wanted to start playing with tubes but I am afraid of high voltage
  • I wanted to have a nice tube distortion
  • I wanted to use a simple single wallwart as a power supply
  • I wanted to use DC voltage only
  • I wanted to use an LM386 for the output power amp
  • I wanted a low power amp, i.e. less than 1 watt

Out of these requirements came this design. Please note that I got a lot of help from a lot of nice people from Aron's Stompbox forum. Without Tone God, puretube and the guys over at runoffgroove (check out their killer jfet amp emulators!), none of this would have happened!

Here are a few sound clips (Dirty Clip 2 was recorded straight into a ZOOM PS04, the two other clips were recorded with a ZOOM PS02 using the builtin mic):

Clean clip
Dirty clip
Dirty clip 2
P90_clip1 with second version of Ruby Tuby (2 x 12ax7 tubes)

A few notes on the design:

  • I use a wallwart that is 12V 1.5Amps. The actual voltage is actually closer to 14, so, I am using a voltage regulator (7812) to bring it down to a constant 12V
  • Pins 4,5 and 9 of the tubes are not present in the schematic. Pin 4 is connected to the 12VDC and pin 5 is connected to ground. Pin 9 is left unconnected.
  • If the sound is too 'farty' (i.e. when low strings are played, you get a rumble instead of intelligible sound) decrease C10, C2 or C3 (or a combination of them). The smaller the cap, the less bass gets through
  • Use an LM386-N3. When I tried with an LM386-N1, all voltages (including on heaters) mysteriously went down to 9V!!!

Here is the current design (click on the schematic to enlarge it):

Last Updated ( Friday, 23 February 2007 )