Regarding pros and cons of the options, and having a good collection of 12AX7/AU7s, I need to make a pest of myself (again) with some more questions for you preamp gurus out there.
First of all, does anyone around here think this dual plate follower design would produce enough second-order harmonics to be worth building? I like the idea of not having to screw around with cathode follower filament bias.
Will this thing have low enough impedance at both ends to drive a solid state amp from a computer's line level output? I lack fancy-pants math ability beyond beyond calculating resistor value for a desired voltage drop at x amps... and even then I just cheat with an online calculator.
Does anyone know of a safe vendor for the Chinese kit? They're all over eBay, but the sellers are all overseas and seem a little shady. There's nothing to be found on Amazon unless I'm looking in the wrong place. Otherwise I'll have to make it from scratch, which isn't too daunting except for rounding up the parts.
If I have to use a B+ voltage drop resistor, should it be calculated for the average plate current of both tubes, or the maximum?
Does the filament center tap really need to be 9 feet away from the ends as described? 🤣
Thanks for any and all opinions on this.
First of all, does anyone around here think this dual plate follower design would produce enough second-order harmonics to be worth building? I like the idea of not having to screw around with cathode follower filament bias.
Will this thing have low enough impedance at both ends to drive a solid state amp from a computer's line level output? I lack fancy-pants math ability beyond beyond calculating resistor value for a desired voltage drop at x amps... and even then I just cheat with an online calculator.
Does anyone know of a safe vendor for the Chinese kit? They're all over eBay, but the sellers are all overseas and seem a little shady. There's nothing to be found on Amazon unless I'm looking in the wrong place. Otherwise I'll have to make it from scratch, which isn't too daunting except for rounding up the parts.
If I have to use a B+ voltage drop resistor, should it be calculated for the average plate current of both tubes, or the maximum?
Does the filament center tap really need to be 9 feet away from the ends as described? 🤣
Thanks for any and all opinions on this.
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The feedback network won't work as expected, due to the loading by the tube.
But this is NOT a clone of any Marantz preamp, and should not be described as such.
But this is NOT a clone of any Marantz preamp, and should not be described as such.
It is indeed not a Marantz clone.
By “feet” they mean the pin number of the tube.
The voltage drop resistor has to be calculated on the average current.
What is the input impedance of the amp you want to connect it to?
By “feet” they mean the pin number of the tube.
The voltage drop resistor has to be calculated on the average current.
What is the input impedance of the amp you want to connect it to?
O/L gain of 30 and C/L gain of 11. High distortion certainly, and maybe clipping due to the DC feedback.
"4 Feet for the tap" is a mis-translation, the heaters (filament) are wired to Pin 9 and Pins 4&5 in the 12A_7 family.
You want a tube preamp between your computer and your SS amp? Check out this 12AU7 preamp. It acts as a buffer to match the impedance your amp needs. If you don't want to spring for the tube rectifier you could use a SS rectifier and a power transformer like this, bring the cost of the project down a bit.
You want a tube preamp between your computer and your SS amp? Check out this 12AU7 preamp. It acts as a buffer to match the impedance your amp needs. If you don't want to spring for the tube rectifier you could use a SS rectifier and a power transformer like this, bring the cost of the project down a bit.
That's why I said "fake." The grammatical error seemed obvious, but my making fun of it may not have been. Couldn't find any specs on the web, but I imagine the line level input impedance is typical, around 50K.
It is nothing whatsoever like a phono preamp. They would be 47K, or 100R for MC. And have much more gain, and EQ.