Hey there! I’m fairly new to (but still not too versed with) the world of Hifi, yet I’m slowly building my system. So far I’ve purchased a used Russco Fidelity Pro phono preamp that I don’t know much about except that it was designed for broadcast and has very low noise, apparently a decent fit for moving coil cartridges. Has anyone used this? Will it be able to handle any low output carts like the Hana ML without distortion? I’ve attached photos of the Fidelity Pro and its specs sheet for reference.
Phono preamp question
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I've owned a few of these, Moving Magnet input.
You can convert using a Step Up Transformer which works fantastic...
You can convert using a Step Up Transformer which works fantastic...
The gain specification is a bit cryptic but it equates to 58dB (unless I've made a blunder in my calculations). That seems unusually high for an MM phonostage. If it's true, that's enough for a LOMC cartridge. Yes, it will amplify a Hana ML without distortion. However, the input impedance is 47k, which suggests that MM cartridges were what this phonostage was designed for. A load impedance around 100 ohms would be more typical for a LOMC phonostage, but 47k still works. I'm not convinced that the S/N ratio would be spectacular with a LOMC cartridge though.
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W9TR
Super Member
Your calculations are correct. 0 dBm into 600 ohms is 0.775 Vrms. So gain is 58 dB. That’s typical for a broadcast operation looking for 5–10 dBm at the console input.
Since it is designed for MM cartridges, (no broadcast station I know of used MC carts, too fragile) the noise performance is unknown. Worth a try, though.
W9TR
Super Member
Let’s look at the noise spec. It doesn't say what measurement bandwidth was used, or the load impedance used, so this is just directionally correct.
-108 dBm into 600 ohms is 3.085 uV.
V= 0.775 * 10^(-108/20)
The Hana ML has an output of 0.4 mV.
SNR = 20*LOG10(3.085 uV/0.4 mV) or - 42 dB.
So it will work, but not very well. A step up transformer or MC preamp will do this fine cartridge justice.
Also somebody check my math please, I’m on my first cup of coffee.
Can give it a go but I agree the loading isn't really right for an LOMC. Could probably solve that by changing the input resistor, or a Y cord with some loading resistors. Basically need an RCA plug with whatever resistor the Hana wants to work into. Plug that into one side of the Y, plug the leads from the turntable into the other. The resistor will be across 47k but if its a typical several hundred ohm load, the 47k across it won't skew it by very much.
1/desired ohms - 1/47000 = 1/needed load resistor if you want to be more precise about it but realistically I think you'll find this doesn't matter enough to lose any sleep over.
1/desired ohms - 1/47000 = 1/needed load resistor if you want to be more precise about it but realistically I think you'll find this doesn't matter enough to lose any sleep over.
Looks good to me. About the same as I came up with.
There are R/L level adjustments accessed via a screwdriver through the front panel.
I don't know if they adjust the gain or if the gain is fixed and they just trim the signal, though.
The Grado phono preamp (PH-1) employs a single op amp and switches between 40dB and 56dB of gain, and users seemed satisfied with using these preamps with lower-output Grado cartridges.
I don't know if they adjust the gain or if the gain is fixed and they just trim the signal, though.
The Grado phono preamp (PH-1) employs a single op amp and switches between 40dB and 56dB of gain, and users seemed satisfied with using these preamps with lower-output Grado cartridges.