Hi,
some time ago two nice variations of the classical baxandall volume control came up, see Handy Non Inverting Active Volume Control and Active volume control with balanced output using 2 op-amps . Common to both circuits is to gain in the noninverting stage, which makes life easier when you need a balanced or a noninverting unbalanced output.
Recently John Broskie published a "dual opamp phase splitter" circuit, Unity-Gain Phase Splitters , intended for bridging amplifiers. This splitter fits perfectly in a active volume control. The feedback network is completly between the noninverting and the invering output, so the noninverting stage is not additional loaded by the low input impedance of the inverting stage.
This means we have the option for a balanced output as well as high drive capability of the noninverting output, which may come in handy e.g. when direct interfacing to a crossfeed network of a following headphone amp.
Comments are welcome
Cheers Thomas
some time ago two nice variations of the classical baxandall volume control came up, see Handy Non Inverting Active Volume Control and Active volume control with balanced output using 2 op-amps . Common to both circuits is to gain in the noninverting stage, which makes life easier when you need a balanced or a noninverting unbalanced output.
Recently John Broskie published a "dual opamp phase splitter" circuit, Unity-Gain Phase Splitters , intended for bridging amplifiers. This splitter fits perfectly in a active volume control. The feedback network is completly between the noninverting and the invering output, so the noninverting stage is not additional loaded by the low input impedance of the inverting stage.
This means we have the option for a balanced output as well as high drive capability of the noninverting output, which may come in handy e.g. when direct interfacing to a crossfeed network of a following headphone amp.
Comments are welcome
Cheers Thomas
Attachments
Last edited:
When I simulated this I found a small cap across R7 was sometimes needed for stability.
Note if you use this circuit as-is with bipolar opamps you have the loud-cracking issue as there is no DC-blocker capacitor on the pot's wiper, so that the briefest intermittency during operation of the pot will interrupt the bias current to the top opamp, forcing it to slam the rails.
Note if you use this circuit as-is with bipolar opamps you have the loud-cracking issue as there is no DC-blocker capacitor on the pot's wiper, so that the briefest intermittency during operation of the pot will interrupt the bias current to the top opamp, forcing it to slam the rails.
i have a question concerning opamp choice in this circuit: would it be stable to use a decompensated opamp in position U2, e.g. a ne5534 wich is stable fpr gain >=3 without compensation? i am undecided, in this constellation compared to the classical baxandall volume control the gain is provided by the noninverting amplifier, so honouring the minimum gain for decompensated opamps should be posible (btw according to the latest release of small signal audio design by d. self there is a slight noise advantage). on the othe hand the overall gain is depending on the pot position smaller than the minimum gain.
any ideas wether it would work stable?
any ideas wether it would work stable?