I have been so busy the last few months that I didn't realize I forgot to rig up the second part of my report on the little Harley Benton 5W Blues Junior clone which is itself a tweed Princeton.

Well it's has grown...




Here are some interesting documents if you would like to work on a Harley Benton yourself:

See through Main PCB
See through tone control PCB
Harley Benton Stock Tone control schematic
Fender Princeton 5D2 schematic
Harley Benton - Circuit Description in French
Harley Benton - Circuit Description in English
Freestompboxes.org thread on this amp



I have done the following changes:

R1 = 1M pull down instead of the 68k
R2 = 33k that I could have lowered even down to 10k, but as analogguru points out, that heaps of gain in reserve, so figured I'd go with the Princeton Tweed value
R6 = jumper
R8 = 1k5
R9 = 2k2
C3 = 4.7uF
C4 = 4.7uF

Changed the tone pot to a master volume control:




Took the ROG Umble schematic and took out the tone stack:



Soldered up this little tone stack on a piece of perfboard:



And put the tone stack hidden at the back of the amp, as a secret weapon.



Although the tone stack could be improved, and there's the sound of pigs being slaughtered when both GAIN and MASTER are near to maximum, this is in no way a problem since the amp has so much more gain aboard then before. You can hear the amp now when it's turned on, which is normal for a fender type camp you expect at least also to get some nice clean tones from.
With the gain turned down and the master all the way up, it renders near to acoustic clean tones of the jazzier kind, especially since the the mid cut and bass control allow perfect fattening up of the clean tones without distorting. The other way around, gain maxxed out and master down, grittier tones arrive. Distortion you turn up the master volume, but also the tone stack may be useful in generation and shaping the disortion at lower volumes. With mid cut completely engaged, screaming distortion can be gotten at very basic levels. This is because the mid cut take a bit from your volume.
The amp is very sensitive to humbuckers, even a little too much to my taste, so I might have to work on the input, or adding another one with a higher in series resistor. Ir"s hard to keep the amp clean at any volume with humbuckers.

In short, it really has the ka-ching that I want from an amp and that I've yet to find in a commercial < 500 EUR amp. When I see a Harley Benton head on ebay, I'll bid again.

have fun,
modman