Jazid
05-05-2019, 19:42
SOLD, SOLD, SOLD
OK here's something unusual. In my line of op-amp investigations I came across this offering on DIYAudio a month or so back. It's built by Kim Bay Smidt who I have had many happy dealings with and used as his own 'destination' phono stage until he sold up his analogue end.
The Hans Polak phono stage is a no compromise design by a talented designer, produced commercially as the reference stage for Allard Audio in Holland, and at one point in time as unpopulated PCBs for DIYAudio. The circuit is explained in Linear Audio Vol 12 but I cannot reproduce it because of copyright infringement. His brief was to compete with commercial products in the £10-20k price point, specifically Boulder and Ypsilon. Originally it was a MC stage, however Kim wanted to stick with his 5mV/cm cartridge and so got Hans to adjust the circuit for MM stages.
The phono stage is fully differentially balanced with floating RCA inputs and balanced output connectors. It has the usual 47kOhm input impedance and adjustable cartridge capacitive loading via a pair of toggle switches on the rear which offer 0 - 47 - 100 pF on each channel. It also has a defeatable rumble filter operating at off, -3dB@11Hz, and -3dB@15Hz. Overload margin 30dB, ultra-precision passive RIAA filter with accuracy within +-0.1dB 20Hz-100kHz, phase angle
OK here's something unusual. In my line of op-amp investigations I came across this offering on DIYAudio a month or so back. It's built by Kim Bay Smidt who I have had many happy dealings with and used as his own 'destination' phono stage until he sold up his analogue end.
The Hans Polak phono stage is a no compromise design by a talented designer, produced commercially as the reference stage for Allard Audio in Holland, and at one point in time as unpopulated PCBs for DIYAudio. The circuit is explained in Linear Audio Vol 12 but I cannot reproduce it because of copyright infringement. His brief was to compete with commercial products in the £10-20k price point, specifically Boulder and Ypsilon. Originally it was a MC stage, however Kim wanted to stick with his 5mV/cm cartridge and so got Hans to adjust the circuit for MM stages.
The phono stage is fully differentially balanced with floating RCA inputs and balanced output connectors. It has the usual 47kOhm input impedance and adjustable cartridge capacitive loading via a pair of toggle switches on the rear which offer 0 - 47 - 100 pF on each channel. It also has a defeatable rumble filter operating at off, -3dB@11Hz, and -3dB@15Hz. Overload margin 30dB, ultra-precision passive RIAA filter with accuracy within +-0.1dB 20Hz-100kHz, phase angle