The Amp Garage

I don’t think you have done anything wrong as maximum attenuation is about -20db with a 16 ohm speaker load. That would equal about 1W with an input of 100W. Speaker sensitivity is usually around 100db which means that 1W will be pretty loud. This statement is from DR Z homepage. (The Air Brake has ...

Download this Line Out schematic/calculator and it will give you the resistor values. Default values assumes a 50W amp at 8 ohm but it will work for just about anything if you use a pot for R2.

Mike

I have set up an Excel calculator so feel free to use.

Mike Lind

Some numbers and links to get you started. IEC standard might be a good starting point and it stipulates 5V, 120R. A voltage divider circuit should be sufficient for this purpose so you first need to calculate the output power of your amp and to what load you are connecting it to. 100W into a 4R loa...

By switching your amp to 8 Ohm you are actually decreasing the mismatch as the Airbrake will start at around 10 Ohm with a 16 Ohm load. The load will then increase with attenuation to about 22 Ohm with a 150R Rheostat. Ken Fischer quote: "On these high powered British amps, due to their unique trans...

I have added a Minimum Attenuation Calculator so it automatically gives you "Min Att" for different input and output loads.

Mike

I have added a spreadsheet document in the files section containing calculators for L, T and Pi attenuators. This will make comparison easier as you only have to fill in values once for all calculators.
Power Dissipation is included and also Impedance Matching for T and Pi.

Mike

*Updated 16-Apr-2010 rev1 with "Min Att" Calculator.

This spreadsheet contains L, T and Pi attenuators with Power Dissipation.
T and Pi also has Impedance Matching.
This arrangement should make it easier to compare resistor values etc.

Mike

Pi updated with Impedance Matching.


I have added a Pi Attenuator and a L-PAD calculator in the files section so check them out.

Mike

Replaced by Attenuator spreadsheet. Updated with Impedance Matching. This is a Pi Attenuator calculator with power dissipation. The main purpose is to give correct impedance at both the input and output and give you the minimal power rating for the resistors. I have not included impedance matching a...

Replaced by Attenuator spreadsheet.

I have included power dissipation in this L-PAD calculator which may be useful if you decide to build one.

Mike

I have not tried the VVR3 but maybe Dana can fill in. Power Scaling have a dynamic range of about 40db which should be enough for home use. I feel that this have less effect on tone that any attenuator I've tried but someone might disagree. It works great on Marshall style amps but might not work as...

R1=pararell resistor or shunt R2=series resistor R3=rheostat Zo=speaker load Zi=input impedance The Airbrake attenuator is basically a Pi Attenuator with the speaker replacing the last shunt. R1 sets the maximum impedance of the circuit and R2-R3 sets the maximum attenuation. With a 25R R1 the sprea...

You need to increase series resistance. With a 25R shunt and 25R series resistor the maximum attenuation with a 8 ohm load is about -10db. With an added 150R rheostat you will get down to about -23db. Probably to loud for home use as you might want to reach at least -40db. The version with the adjus...

The switch in this layout is of the "shorting" or (Make-Before-Break) type. If you use the "non shorting" (Break-Before-Make) type you might experience a pop when you switch attenuation levels. From a technical standpoint a BBM switch would be more suitable for higher currents, but the jury might st...