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I got this tuner this weekend. The sound is very good and the sensitivity is beyond what I thought about tube tuners.I heard that some people are modifying the deemphasis on Fisher tuners. I always thought that the deemphasis on tuners sold in North america were settlled at 75 µs
Is Fisher tube tuners have a deemphasis of 75µs ? If no, what are the R and C values I need to upgrade it?
Thanks
The de-emphasis on the Fisher tuners, at least through the MPX, is higher than the standard. Some have complained of a darkened top end. But it does not significantly impact matters enough to warrant correcting it in my opinion. Bear in mind that the FM format only requires audio performance to 15kc and is naturally lacking the highest range already.A common mod several years back (advocated by a kit vendor) involved tearing out the filters, which I do not recommend after seeing the results on a scope. Otherwise, you can play with the resistor values at the back end of the mono stage and the MPX subchassis to nominally brighten up the top end. I recall posting in detail about the particulars and all the pitfalls some time ago. It should be somewhere in the archives.
But considering the magnitude of the result, correcting the de-emphasis is not usually worth the effort. A tweak of a tone control, or even a different audio output amp tube will yield a much greater result if you feel the tuner presents a rolled off top end. The effects of varying compression levels are more audibly significant than the de-emphasis error at this point.
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