Inverting operation of Aleph Amps

pozo1992 · 14th March 2008, 12:17 PM

Aleph amps are intended to be run in non-inverting fashion via RCA inputs or differentially via XLR inputs. Some gurus are reporting about advantages when you have your amplifier operating in inverting fashion together with shunt feedback. So you get an amplifier with virtual ground at the inputs avoiding the common mode problems and distortion associated with non-inverting operation and series feedback, emphasized when using FETs. So I decided to try this on my Aleph 0S clone: Feeding the single ended output signal from my Aleph P clone to the inverting input (XLR3) of the Aleph 0s and connecting the non-inverting input (XLR2) to signal ground (XLR1) at the Aleph 0S. Doing this, the gain of the Aleph amp will be halved. It will be obvious when you study the schematic. Now it was time to listen and compare to the other two possible modes.
Great surprise and not expected: The inverting mode sounds better to my ears than the others (even better than having a full XLR connection between preamp and Aleph 0S) , especially more detailed. Maybe some of the other DIYers on this forum have already tried the same. What is your opinion – experience?
Comments are appreciated. Maybe Mr. Pass could contribute his experience too.

pozo1992 · 14th March 2008, 12:18 PM

Detail of Aleph 0S schematic.

pozo1992 · 14th March 2008, 12:29 PM

Forgot to mention, that when using the inverting mode I swapped the output wires in order to keep things equal.

Nelson Pass · 14th March 2008, 07:32 PM

The gain should not be halved, but the input impedance is.

14th March 2008, 12:17 PM	#1
pozo1992 diyAudio Member Join Date: Jun 2004 Location: Bavaria	Inverting operation of Aleph Amps Aleph amps are intended to be run in non-inverting fashion via RCA inputs or differentially via XLR inputs. Some gurus are reporting about advantages when you have your amplifier operating in inverting fashion together with shunt feedback. So you get an amplifier with virtual ground at the inputs avoiding the common mode problems and distortion associated with non-inverting operation and series feedback, emphasized when using FETs. So I decided to try this on my Aleph 0S clone: Feeding the single ended output signal from my Aleph P clone to the inverting input (XLR3) of the Aleph 0s and connecting the non-inverting input (XLR2) to signal ground (XLR1) at the Aleph 0S. Doing this, the gain of the Aleph amp will be halved. It will be obvious when you study the schematic. Now it was time to listen and compare to the other two possible modes. Great surprise and not expected: The inverting mode sounds better to my ears than the others (even better than having a full XLR connection between preamp and Aleph 0S) , especially more detailed. Maybe some of the other DIYers on this forum have already tried the same. What is your opinion – experience? Comments are appreciated. Maybe Mr. Pass could contribute his experience too.

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14th March 2008, 12:29 PM	#3
pozo1992 diyAudio Member Join Date: Jun 2004 Location: Bavaria	Forgot to mention, that when using the inverting mode I swapped the output wires in order to keep things equal.

14th March 2008, 07:32 PM	#4
Nelson Pass The one and only Join Date: Mar 2001	The gain should not be halved, but the input impedance is.

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