Variable XLR Line Level Attenuator..?

[Snatchman]

Hello..Is there a build for a good passive variable line level attenuator ..?

 

[ruffrecords]

Do you want it stepped or continuous?

Cheers

Ian

 

[Bo Deadly]

Hello..Is there a build for a good passive variable line level attenuator ..?

It depends greatly on what you want to use it for and what the min / max attenuation is. Every attenuator has a characteristic impedance. So the source will see a certain load impedance and the load will see a certain source impedance. If you need the load and source to appear constant, you would need a bridged H attenuator which requires a three section variable resistor with specific values. For that you might find a Daven attenuator on Ebay but ones with a lot of steps and the right impedances are usually pretty expensive. If the load is truly balanced, like a transformer or active like a THAT 120x, then you could get away with just a simple pot across the lines. But again, every passive attenuator is going to present a source impedance that must be considered. For example, in this last case, you would not want your pot to be more than 5K or so if the cable is vaguely long. If it's unshielded, any series resistance could be a problem.

So again, state the requirements. What are the load and source impedances, attenuation range, how long is the cable, is it shielded, is the load balanced or single-ended, ...

 

[Snatchman]

Do you want it stepped or continuous?

Cheers

Ian

Hello..Ian...Yes, I'd like to have it continuous...Thanks...

 

[Snatchman]

It depends greatly on what you want to use it for and what the min / max attenuation is. Every attenuator has a characteristic impedance. So the source will see a certain load impedance and the load will see a certain source impedance. If you need the load and source to appear constant, you would need a bridged H attenuator which requires a three section variable resistor with specific values. For that you might find a Daven attenuator on Ebay but ones with a lot of steps and the right impedances are usually pretty expensive. If the load is truly balanced, like a transformer or active like a THAT 120x, then you could get away with just a simple pot across the lines. But again, every passive attenuator is going to present a source impedance that must be considered. For example, in this last case, you would not want your pot to be more than 5K or so if the cable is vaguely long. If it's unshielded, any series resistance could be a problem.

So again, state the requirements. What are the load and source impedances, attenuation range, how long is the cable, is it shielded, is the load balanced or single-ended, ...

Hello..Thanks for your reply..I'm wanting something to put behind my pres that doesn't have an output fader to control level going to DAW...Cables not long ( 3 ft'ish)...

 

[Bo Deadly]

Hello..Thanks for your reply..I'm wanting something to put behind my pres that doesn't have an output fader to control level going to DAW...Cables not long ( 3 ft'ish)...

For this I would just make a cable with a fixed pad on the digital interface end. Just a U pad using resistors soldered directly to the jack. You should be able to make it fit inside the shell.

Crank the mic pre until it clips and measure the output level. Then calculate the values for U pad for 100R output characteristic impedance and attenuation to 6dB below dBFS of your digital interface. Then it will never clip the interface. Even though the signal will be seemingly low at typical mic gain settings, it doesn't matter because the noise floor of your digital interface will still be well below the noise level of your pre output. So you can amplify digitally in the DAW without any noise penalty. The pad could literally be 40dB and it wouldn't matter.