Aleph-X builder's thread.

[still4given]

Sorry if this has been asked.

The input is set up for balanced line. I have some equipment with balanced outputs but most of my stuff is unbalanced. For testing I shorted the - input to ground and just used the shield terminal and + inputs. If you set up the amp to use both, do you need to short the - input to ground when using RCA's? Seems like I got a hum without doing that.

Do you use a switch to ground it when going with an unbalanced source?

Thanks, Terry

[wuffwaff]

Hi Terry,

yes -IN needs to be grounded (via the same value of input cap you use on the +IN side).
You can either use a switch or shortign plugs between PIN 1 and 3 on your XLR inputs.

William

[still4given]

Originally posted by wuffwaff
Hi Terry,

yes -IN needs to be grounded (via the same value of input cap you use on the +IN side).
You can either use a switch or shortign plugs between PIN 1 and 3 on your XLR inputs.

William

Not sure what you mean by the input cap. Could you explain a little more?

Where would I find shorting RCA's?

Thanks, Terry

[wuffwaff]

Hi Terry,

to keep DC from entering the amp you need input capacitors in series with +IN and -IN. (around 10uF will do nicely).

To use the amp unbalanced you connect the -IN cap to ground.

You don´t need shorting RCA´s (wich are very easy to make yourself) but a shorting plug for the balanced input connectors or a switch that connects -IN to ground

William

[Netlist]

To avoid input caps I corrected the DC with the preamp connected. This of course only works well if you don’t plan to change preamps at a regular basis.

/Hugo

[still4given]

Originally posted by wuffwaff
Hi Terry,

to keep DC from entering the amp you need input capacitors in series with +IN and -IN. (around 10uF will do nicely).

To use the amp unbalanced you connect the -IN cap to ground.

You don´t need shorting RCA´s (wich are very easy to make yourself) but a shorting plug for the balanced input connectors or a switch that connects -IN to ground

William

Do you mount those caps on the input jacks themselves?

Why would I use a shorting XLR? If I'm using a balanced input I wouldn't want to short the - input to ground would I? Or are you talking about a 1/4" jack that shorts when nothing is plugged in?

Thanks, Terry

[BobEllis]

The caps could mount directly to the jacks or anywhere convenient between the jacks and boards.

Only short the - input to ground when using unbalanced sources.

Depending on how you implimented it you have some choices:

An RCA to XLR adapter cable that shorts your - input

A switch to short the - inputs to ground when using the RCA jacks

An XLR plug that shorts the - input inserted into the jack when you use the RCA input.

[hieroglyphics]

Couldn't you also use some sort of inverting op amp between the + and - sides? By shorting the - side, aren't you only using 1/2 the amp?

[BobEllis]

Both halves of the amp get used through the "magic" of the differential, but the gain is lower with a single ended source.

[wuffwaff]

Hi Bob,

like you said both halves are used but the gain should be more or less the same balanced and unbalanced.

William