OK, I've got it. That's bad news because I need to attenuate more than half the signal.
It needs to be, not for my main amp but for a couple of 300B SE mono amps that don't have a pot at the input. Guess the easier thing would be to install the pots there but that means double work and I'm lazy. LOL. What a headache. Maybe I'll end up installing a 50k pot at the phono preamp outputs. Thanks for the explanation.
It needs to be, not for my main amp but for a couple of 300B SE mono amps that don't have a pot at the input. Guess the easier thing would be to install the pots there but that means double work and I'm lazy. LOL. What a headache. Maybe I'll end up installing a 50k pot at the phono preamp outputs. Thanks for the explanation.
That can work, but you need to make sure you measure that 50K dual pot. you might have to fine-tune it with additional (low values) resistors in series (hopefully not in signal path) to match channels. Input is quite sensitive at that point.
Another idea is to use a 1M pot in series with 1M resistor (that 1M resistor goes towards ground, or the -0.9mV raised level from the heater devider on the romy cat circuit). You can try other values, so long as the total in series equals 2M.
Yeah, but as Sheldon pointed out that will only attenuate my signal up to half. I have decided to leave the phono stage as it is and I will attenuate the phono signal inside the line stage that drives the mono amps (no volume control on those). I don't know how to do this properly yet, the line stage has gain, I'll have to do a voltage divider before the 100k pot.
Back to this phono preamp, everyday it was sounding better than the previous (maybe the PS caps settling in) plus I have changed the input Russian tube for an American NOS and this thing is beginning to sound REALLY good. Hehe, I'm happy.
Lowest noise is usually with attenuation just before input to power amp. You may want to also attenuate your phono amp (simple divider on the grid is fine), if the gain is too high for your preamp.
Sheldon
Sheldon
If you have a chance try to get some Amtrans AMCH for the RIAA. At the beginning they were only moderately similar to non-magnetic silver micas, but after running-in for a few weeks the sound is far more and more life-like.
Its as close to sounding like no phono stage, and like rolling a studio master tape as I have ever managed...
Its as close to sounding like no phono stage, and like rolling a studio master tape as I have ever managed...
also, I ended up shielding the entire phono circuit from the power supply with a box I made of copper sheet... At highest volume there was some hum, but now it is really silent. Best would be to put the powersupply on its own chassis.
About the RIAA caps - I will buy those if I ever build another one or if I decide to build a better power supply for this one, new chassis, etc.
Yeah, same thing here, but now I have two outputs one normal and another attenuated via 12k and 5k1 voltage divider. The attenuated output cuts down the unwanted noise to almost imperceptible levels so it really isn't a problem.
I attach a pic of someone else's phono preamp which is probably the best way to do it but I wouldn't take the trouble to do that.
Yeah, same thing here, but now I have two outputs one normal and another attenuated via 12k and 5k1 voltage divider. The attenuated output cuts down the unwanted noise to almost imperceptible levels so it really isn't a problem.
I attach a pic of someone else's phono preamp which is probably the best way to do it but I wouldn't take the trouble to do that.
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