Just picked up an early Quad 405. I did the basic upgrades of adjusting the input sensitivity, replacing the op amp, upping the op amp supply voltage to 15V, upgrading C5 and C10, and putting in new bulk caps.
Quad 405 Upgrade
I also put on new feet, and replaced the screws with uncorroded ones.
Next up - maybe - is a new DIN socket, phono jacks, new speaker posts. The original stuff is a bit corroded. I am not excited about rewiring with better cable, the design doesn't look like it cares that much about the internal resistance of the power and speaker wires - there's a 47 ohm resistor in the output path anyway.
I also have to think about the buffer mod for the 15V supply. This version of the 405 has no speaker clamps, and I am a bit concerned about popping a voice coil.
I'm not really ready to do the more advanced upgrades, much as I appreciate Keith and Bernd's work. I prefer to measure to make sure that I don't introduce errors, and am not set up for that. I'm limited to basic bench testing with sine waves, square waves and a scope.
Here's the Mouser parts I used. You can pretty much use this list as a guide to parts to replace for the basic mod. I had the 0.1uFs lying around: I would not recommend leaving them off.
Mouser P/N Description .Qty Price
R6 71-RN60D-F-102K 1/4watt 102Kohms .2 0.07
R4 71-CMF556K8100FKEK 1/4watt 6.81Kohms 1% .2 0.14
C4 594-222230342154 0.15uF 5% 250volts .2 0.64
DIN 502-60HA4FX 4 PIN DIN JACK .1 4.98
C5,C10 647-UKW1J101MPD 63volts 100uF 4 0.47
D1,D2 78-BZX85B15 15 Volt 1.3 Watt 2% 2 0.07
512-MPSA42NPN Transistor .2 0.28
IC1 595-OPA604APG4 FET-Input Audio 2 3.15
C13,14 661-ESMH630VNN153MA 15KuF 63volts 2 9.27
C13,14 539-VR3A CLAMP 1.375/1.44 .2 1.95
0.1uF MLCC ceramic .4
Rubber feet 4
Quad 405 Upgrade
I also put on new feet, and replaced the screws with uncorroded ones.
Next up - maybe - is a new DIN socket, phono jacks, new speaker posts. The original stuff is a bit corroded. I am not excited about rewiring with better cable, the design doesn't look like it cares that much about the internal resistance of the power and speaker wires - there's a 47 ohm resistor in the output path anyway.
I also have to think about the buffer mod for the 15V supply. This version of the 405 has no speaker clamps, and I am a bit concerned about popping a voice coil.
I'm not really ready to do the more advanced upgrades, much as I appreciate Keith and Bernd's work. I prefer to measure to make sure that I don't introduce errors, and am not set up for that. I'm limited to basic bench testing with sine waves, square waves and a scope.
Here's the Mouser parts I used. You can pretty much use this list as a guide to parts to replace for the basic mod. I had the 0.1uFs lying around: I would not recommend leaving them off.
Mouser P/N Description .Qty Price
R6 71-RN60D-F-102K 1/4watt 102Kohms .2 0.07
R4 71-CMF556K8100FKEK 1/4watt 6.81Kohms 1% .2 0.14
C4 594-222230342154 0.15uF 5% 250volts .2 0.64
DIN 502-60HA4FX 4 PIN DIN JACK .1 4.98
C5,C10 647-UKW1J101MPD 63volts 100uF 4 0.47
D1,D2 78-BZX85B15 15 Volt 1.3 Watt 2% 2 0.07
512-MPSA42NPN Transistor .2 0.28
IC1 595-OPA604APG4 FET-Input Audio 2 3.15
C13,14 661-ESMH630VNN153MA 15KuF 63volts 2 9.27
C13,14 539-VR3A CLAMP 1.375/1.44 .2 1.95
0.1uF MLCC ceramic .4
Rubber feet 4