Mofien har det ja, men hvis jeg skulle ha byttet ut den med feks Gold Note PH-5, som ikke har en egen mono switch.. Er en mono switch noe man enkelt kan få tak i et sted?
Jeg håper jeg får tid og ro til å lese å forstå alt ( eller iallfall nok ) av artikkelen til å skjønne hvordan støy fra en mono LP kanselleres når kanalene summeres, men vi snakker om så svake signaler at det har betydning hvor og hvordan summeringen skjer.
Skjemaet vist i artikkelen plasserer summeringen mellom trinnene i en RIAA-topologi. Hvis jeg forstår det rett er det for å unngå å innføre ytterligere dempeledd på signalet hvis summeringen må skje mellom PU og RIAA eller etter RIAA.
Kan hende var det slik Mofien din var bygget.
« Summing the outputs of the phono stage by simply bridging the line output with an SPST switch is also quite undesirable for several reasons. Most competent designs will have an output impedance in the range of a couple of hundred ohms determined by resistor in series with the output; enough to prevent parasitic oscillation of the amplifier stage connected to the line and its inherent capacitance, but certainly not enough to prevent current limiting overload from taking place should it be bridged onto the adjacent channel with any appreciable voltage difference between the two channels. Some low-quality single-stage designs get around this by increasing the value of these load stability resistors, turned current sharing resistors, by a factor of ten all the way to 1kΩ so that the amplifier stages for both channels aren't fighting each other so hard through a low impedance load. A few op-amps may still struggle to drive 1kΩ worth of current sharing without a significant loss in linearity.
Further considering the fairly heavy loading that a low impedance and therefore low noise RIAA equalisation network places on a single-stage design there may not be very much current capability left to throw into the mono summing network and the resistors are sometimes increased all the way past 3kΩ and sets the output impedance of the phono stage high enough that almost a 3dB loss in level is experienced when it is connected to a common line input impedance of 10kΩ, diminishing to a still rather unhappy 1dB loss if 1kΩ current sharing resistors are used. Many of the designs that the author has seen use 2.2kΩ current sharing resistors which will not only cause a level loss of 1.64dB but also increase the effective line impedance an order of magnitude from what it might ideally be, increasing the susceptibility to electrostatic coupling of interference. The higher output impedance can also cause the frequency response to droop at the high end if the phono stage is going to be connected to a length of cabling and line input with considerable input capacitance, capacitance being added to most line inputs for the purposes of filtering out radio frequency interference, often without consideration of line source impedances of more than a few hundred ohms.»
michaelfidler.com
