Fender Blender 3 Knob

Sideways again. Will fix this at some point.

Here's a trace of the rare 3 knob Fender Blender. Pots date late '75, early '76, so this one was born no earlier than '76.

This is a wacky one. It has a multi function rotary switch plus "Gain" (conventionally: Volume) and "Sustain" (conventionally: Gain).

1 = FET Boost

2 = Fuzz Filtered

3 = Fuzz Less Filtered

4 = Fuzz Filtered Differently

I can't really remember what all the different filter effects had on the fuzz, but overall it was an underwhelming concept.

The FET Boost was actually a bit louder than the filtered fuzz, so I purposed to the owner that I mod it so that the fuzz actually went through the boost. So #1 was still clean boost, but #2-4 could be as louder or louder. I routed the fuzz through a simple volume trim before hitting the FET so the fuzz volume could be balanced or boosted with respect to the clean setting.

My original notes to the owner of a 3 knob I repaired:

"Preamp" mode is completely separate from the "Fuzz" mode, thus explaining the disparate levels between the two. It is a shame that this "Blender" has no blend control. I thought the selector switch would provide some degree of blend, but it does not.

The preamp circuit is a JFET, "common source" inverting amplifier. The device is a 2N5352.

The "Gain" control is common to all modes. It is the last component before the output of the circuit board. The label "Gain" is misleading. "Volume" or "Level" would be a more appropriate label. "Gain" is simply the master attenuator for all the modes.

"Fuzz" mode switches away from the JFET amp over to a 3 bipolar transistor circuit. The 3 transistors are all tied together to form 1 functioning amp. The gain of the first 2 transistors is controlled by the "Sustain" control. The "sustain" is actually being used as a variable resistor, not an attenuator like the other control. The first two transistors are tied together as a "Darlington pair." This boosts the input impedance and the (potential) gain of the circuit. The 3rd transistor functions as a voltage follow/output buffer.

At the output of this amp is a pair of 1N4001 silicon diodes that connect back to the input of the fuzz amp. This completes a clipping negative feedback loop popularly used in pedals like Big Muffs and Tubescreamers.

At the same node as the diodes, there are 3 different tone selective paths that are presented to the amp's output. The selector switch chooses which tone path is completed to the "Gain" control/main output.

Pots date to the mid 70s, specifically, 1975 week 52 for the sustain, and 1976 week 13 for the gain.