DIY - Attenuator for Quad 405

attenuator for QUAD 405

Some examples of dividers bridges (Metal Film Resistors 1/4 W) for attenuator without potentiometer.

Vcc In (Volt) Entry R1 values (Ohms) R2 values (Ohms) Vout (Volt) Quad
0.775 60 110 0.5
0.775 600 1100 0.5
0.775 6000 11000 0.5
1.0 60 60 0.5
1.0 600 600 0.5
1.0 6000 6000 0.5
1.2 60 44 0.5
1.2 600 440 0.5
1.2 6000 4400 0.5
1.5 60 30 0.5
1.5 600 300 0.5
1.5 6000 3000 0.5
2 60 20 0.5
2 600 200 0.5
2 6000 2000 0.5

I made this attenuator for my power amp QUAD 405, not yet Quad 44, a preamplifier fully adapted to the 405.

With a divider bridge made with resistors made of metal films of 1/4 watts , I can say that the result is successful, a beautiful dynamic and almost no breath, it's tiny, you really have to have your ear stuck on the tweeter.

I realized this little editing with the components that I already had. I used a 8 kohms watermark potentiometer (SFERNICE) and a 0.22 µf capacitor for interference on the switch.

I think the sound is much better than with a preamplifier, a lot less components on the signal path.

In seeking to remedy this little breath in my speakers, I realized that it came from the Quad and not the attenuator.

You will notice that the wiring is in star, a way of wiring to avoid the loops of masses. I also incorporated a switch to be able to disconnect the attenuator and connect the amplifier to a Quad 44 later. The switch button is located on the back of the unit.

Coming soon in a second version of this attenuator, I will bring some interesting modifications, (delay of the loudspeaker outputs, headphone jack, vu-meters)

Bridge divisor formula

Voltage Divider Bridge

ResDivider is a program to calculate the output voltage of a bridge voltage divider resistive value of the resistors and the input voltage. The program also gives the dispersion in tension with min and max values according to the tolerance value of the resistors used for deck divider. More information on the article about the bridge voltage dividers.

attenuator schematic for Quad 405

attenuator schematic for Quad 405

attenuator schematic for Quad 405

attenuator schematic for Quad 405

Potentiometer without attenuator, cabling according to schematic.

attenuator for Quad 405 Quad 405