@slaw - I just put my Herron 360 Ref up for sale on A'gon over the weekend; really fine preamp and I spent 5 years enjoying it, but it was time for something different and got an Aric Audio Super 6SN7 with the upgrades. Big step up. And I hate that tiny remote with the Herron! But I am keeping my Herron phono preamp...
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@inna Here’s a reason for a tube phono section: If we are talking about a LOMC cartridge, its inductance in parallel with the capacitance of the tone arm cable sets up an electrical resonance at Radio Frequency (RF) frequencies. For example a Lyra Titan might be at about 5MHz. Because of the design of the coil in such cartridges, the electrical peak is pretty sharp (in radio parlance, high ’Q’). It can go into oscillation just from the energy of the audio signal sending it into excitation (another radio term). That RFI (since that is what it is) can be as much as 30dB higher than the signal level itself! That can really mess with some preamps, especially solid state where the RFI can be rectified by the input stage, causing distortion, usually perceived as brightness. You can also get ticks and pops if the front end of the phono section overloads. Hence the ’cartridge loading resistor’ which detunes the resonant peak, and by so doing reduces distortion. Its much easier to built tube preamps that don’t have this problem! If the designer was aware of this problem it can simply be plug and play with no concern of the load resistor and far less ticks and pops (just the ones that are actually on the LP surface instead of ones generated by the phono section as well). Since a lot of people find ticks and pops pretty annoying and since taking away a setup problem makes the whole thing easier, win win.
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@atmasphere Nicely explained. Is that the only reason (RF) that increasing the load resistor value appears to brighten (open) up the top end of a MC? |
- 27 posts total