+4db & -10db selectable output

I've seen gear with selectable switches for the output jacks... +4 or -10db.

Can you just use a pad in the output circuitry to do this? ... instead of fooling with the gain of the preamp stage?

yes

:grin:

Jakob, you mind giving a little more details plz?

Cheers,

Tony

:razz:

Yes, if you need a +4/-10 switchable output, you can simply use a pad at the output.

14dB is 5x (or 0.2x) gain.

For unbalanced, use a simple resistor divider with e.g.. 4K7/1K, for balanced use a H-pad with e.g. two 4K7's and a 2K2 (roughly)

You could even have both outputs at the same time on two connectors.

Jakob E.

[quote author="gyraf"]:razz:

Yes, if you need a +4/-10 switchable output, you can simply use a pad at the output.

14dB is 5x (or 0.2x) gain.
[/quote]

Don't forget that it's +4dBu, and -10dBV. The reference points are different, so the actual difference in level is closer to 12dB (or 0.25x).

[quote author="gyraf"]

For unbalanced, use a simple resistor divider with e.g.. 4K7/1K, for balanced use a H-pad with e.g. two 4K7's and a 2K2 (roughly)

You could even have both outputs at the same time on two connectors.

[/quote]

Often, but by no means always, a +4dBu output will be balanced, and a -10dBV output will be unbalanced. In the case of some active outputs, you can achieve 6dB of attenuation by just ignoring the -ve leg. In that case, only a further 6dB (0.5x) attenuation is required to get down to a -10dBV unbalanced output.

Steve.

Thanks all...

Ok, for anyone interested here are the R values for a 12dB balanced H pad.

R1=180 ohms
R2=360 ohms


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R1 are all horizontal resistors
R2 is the vertical resistor

and what would be the resistors for 6db loss?

If you are fine with going unbalanced, then; none. Just ignore the negative wire.

no, i need 6db and 12 db loss on an output of a neumann v475-2 which does not have the usual options for a pad in the feedback path...

I had to do a little gain staging on a transformerless line stage requiring about 4 db attenuation.

But I wanted to maintain a bridging configuration (low impedance driving a high impedance) as much as possible. I did not want to heavily load the driving device or match impedance.

I figured typical is 50 ohms differential driving 10k differential.

I threw an attenuator in spice and also did noise analysis.

I found a U pad (rather than H) worked best considering all factors. In this case I ended up with the 50 ohm driving device seeing about 2500 ohms, and the 10k recieving device seeing about 600 ohms with negligible johnson noise contribution.

Les
L M Watts Technology