Hi,
I need a preamp with selectable 3, 6 and 12 db gain between my dac and headphone amp. I don't need volume control as my headphone vol control is pretty good. I need a balanced input and balanced output. I would like it to be simple and as few components as possible. What options do I have?
I need a preamp with selectable 3, 6 and 12 db gain between my dac and headphone amp. I don't need volume control as my headphone vol control is pretty good. I need a balanced input and balanced output. I would like it to be simple and as few components as possible. What options do I have?
An INA2137, which is a dual balanced to single-ended converter, followed by a dual opamp with switchable feedback resistors to select the three gain levels, followed by a couple of DRV134 single-ended to balanced converters. It can be single supply if you want to power it with a dongle. I can draw you a schematic if you like.
Edit: or, even simpler, a switchable voltage divider instead of the opamp, I realized the INA2137 can be configured for 6dB gain, plus another 6dB of the DRV134, there's your 12dB and then you only have to attenuate in between for the other two gains.
Cheers,
Cabirio
Edit: or, even simpler, a switchable voltage divider instead of the opamp, I realized the INA2137 can be configured for 6dB gain, plus another 6dB of the DRV134, there's your 12dB and then you only have to attenuate in between for the other two gains.
Cheers,
Cabirio
The circuit in figure 2, with an extra op amp at the output to provide an inverted signal, would work, and is pretty simple.
https://www.edn.com/variable-gain-superbal-circuit-preserves-cmrr/
Original circuit is from Burr Brown's Jerald Graeme in the 70s.
https://www.edn.com/variable-gain-superbal-circuit-preserves-cmrr/
Original circuit is from Burr Brown's Jerald Graeme in the 70s.