The 5 Pound Bag (A Documented Build)

[jrohlf]

I recently finished an ambitious 3 year build which I've documented at:

The 5 Pound Bag

Its architecture is pretty unusual and consists of 12AT7's and EL84's in the preamp. The site has lots of documentation, photos, and clips but here are a few teasers:




Medium distortion clip (12AT7 clipping only)
Super heavy distortion clip (12AT7 + EL84 clipping)
Light distortion clip (only EL84 clipping)

[cminor9]

gave that a listen, and I've got to say that sounds really good! It doesn't give me that scooped mid sounds-like-everyone-else vibe that I was afraid I'd hear when I saw all those knobs

Looks like you put a lot of thought into your design. Very cool to use 12at7s.

What value LED's do you use for the 12at7 cathodes? I have heard of people putting those on the cathode but I cannot figure out what values to use there (most of the LEDs I have come across are very low voltage).

Nice work!

[jrohlf]

LED bias

I've found red leds are around 1.6V, green and yellow are around 1.9V, blue around 3V and infrareds go even higher. You can always put leds in series with each other or with ordinary diodes to increase voltage drop.

A red led should work just fine for a 12AX7 and I even like them for 12AT7s which bias them much warmer relative to a 12AX7.

I suggest starting with a variable resistor + big cap in the cathode, tweak until desired tone reached, then replace with proper combination of leds/diodes. Then make sure to mount the leds on the front panel to increase your amp's bling factor .

LEDs in heavily overdriven stages can actually help you track down blocking problems because they will go dark when the stage shuts off.

[MarshallPlexi]

Man sounds great! Would love to see a better pic of the schematic. I'm sure I'd learn a TON from your build! Again great work, very clear and crisp OD tones.