In Reply to: Re: Best inductors for RIAA? posted by chaslieb on October 29, 2001 at 17:42:11:
Hi Charles,So far I have built 5 Phonostages with LCR RIAA. I have no
schematic. They are so simple that's not necessary to draw
them. All of them are transformercoupled. Three use the
Tango RIAA and are based around the Telefunken EC8020.
Unfortunately this tube is very difficult to get. But there
are alternatives. One of the other two is an all DHT preamp
with 801As. For this one I built a 'discrete' LCR RIAA.
The last one was an experimental phonostage with 6HV5.
For this I built a RIAA with UTC variable inductors. This
one led me to the analysis of the Tango RIAA. Obviously
the DC resistance of the UTC coils is very high which for
example leads to a early bass roll off.I will try my calculation scheme with those UTC coils to
see if it's valid.
Typically I drive the LCR with a step down transformer,
so that it's fed with a source impedance of 200 Ohms or
less. The DC resistance of the driving transformer is not
critical. It will only generate some loss, but it's not
frequency dependant.To get enough gain I always place a 1:4 step up transformer
after the RIAA.There is a schematic of a LCR phonostage in the latest
VALVE magazine. The article is from a friend of mine.
His Phonostage is very similar to my EC8020 based
one.Regards ... Thomas
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