Hi all-
I’ve been working on several phono stages lately and have discovered a nice headroom test that capitalizes on how the Quantasylum QA401/QA402 analyzers work.
They both use a flat drive signal to excite the DUT, and subtract out the RIAA curve from the received data. Because RIAA has 40dB more gain in the bass than the treble, a phono stage can be interrogated to reveal its overload structure at low frequencies, where a flat drive signal, and a real world turntable, will always overload first.
Here is the exact same preamp before and after changing the opamp rails from ±14V to ±17V. This proves the phono stage overload got a lot better! Very cool these boxes can do this.
I’ve been working on several phono stages lately and have discovered a nice headroom test that capitalizes on how the Quantasylum QA401/QA402 analyzers work.
They both use a flat drive signal to excite the DUT, and subtract out the RIAA curve from the received data. Because RIAA has 40dB more gain in the bass than the treble, a phono stage can be interrogated to reveal its overload structure at low frequencies, where a flat drive signal, and a real world turntable, will always overload first.
Here is the exact same preamp before and after changing the opamp rails from ±14V to ±17V. This proves the phono stage overload got a lot better! Very cool these boxes can do this.