V-Twin wrote:

"Patrick Turner" ha scritto nel messaggio
...
I have used a 6DJ8 with a passive RIAA, followed by a 12AX7,
so total gain at 1 kHz is 30 x 70 /10 = 210, and the
divide by 10 is the loss at 1 kHz of the RIAA filter.

So if you have a 5 mV @1kHz cart at 1 kHz, you just over 1,000 mV at the
output.
But a cart of 2,5 mV, and a second phono stage gain of 35
would still make 250 mV.
But not so good with a Denon 103 MC, whose output is only 0.3mV.
Then you need more gain, or a step up transformer.

Maybe I don't do the calculations right:
MM cartridges usually have around 4mV rms output voltage and I must have
about 2 Vrms at the phono stage output to match the max output of my CD
player.

Have you measured the CD player output?
I bet it ain't 2vrms, even when measuring with a stream of
heavy metal grunge as a test tone, on an rms meter with 20 kHz of bandwidth.


Considering about 20dB (maybe 30?) over the nominal 5cm/sec level for the
higest music peak in the vinyl, I have 40mV coming out from the cartridge.

Its possible, but rare....


Ergo I need an amplification factor of at least 2/0.04=50, wich becomes 500
considering the nominal 20dB loss of the riaa network.

The RIAA losses are negligible at LF, -20 dB at 1 kHz, and about -38 dB at 20
kHz.

If you had rated 4mV at 1 kHz from the cartridge, and a gain of 5,000
in the amp, and -20dB loss in the RIAA filter,
you get Vo = 0.004 x 5000/10 = 2v.

Most of the signals from a cart are less than 4 mV.


A EC8010 followed by a 76 should do the work, giving a gain of 600.

Including RIAA losses?


Maybe the output impedance of about 9kOhm can be a problem. Should i add a
CF?

You need to measure the Ro to find out properly.
Assume nothing.

If the amp you propose has cabling to a pre or power amp
which has 200pF, and the input R is 100k, and the Ro of your pre is 9k,
then the HF roll off be at 100 kHz, but I bet its lower,
because Ro isn't as low as 9k, and stray C elsewhere won't allow such a
bandwidth.
And the cathode of the outout triode of you phono amp needs to be
bypassed to maintain the effective Ro.

Patrick Turner.