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Help needed for my preamp

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Hi
Well after 2 months of building I powered up my preamp based on the Comet Octal Phono preamp courtesy of Hagerman Technology and,for the line amp, a 6sn7 SRPP.
I have managed to build a dual mono power supply utilising 1 5u4g 1 6080 1 AT7 and 1 5651 per channell.
2 questions.
1. the phono preamp has a 300k resistor to ground at its output. this output is connected to the phono section of the input selector switch. The line amp takes the input from the selector strait into the grid via a 100k pot (alps Blue).
I have the feeling that the impedances are not matched in this case. Is this correct? If this is the case then how should the output of the phono connect to the input of the line amp with respect to matching impedances?
2.my amp's tubes are all above the enclosure... the input tubes for the phono amp (6SL7) are obviously getting some induction in them.. if i put my hand over them the noise is louder... The next thing i am going to try is cooper canisters over them.. does anyone have some hints as to what else may help reduce this phenomenon?
I will post some pics of my amp.. now to building my parallel 300B monoblocs with outboard power supply.....
Thanks A bunch in advance for any help
regards
Nick
Australia
 
Why do you want to match impedances? In a voltage drive situation not involving transmission lines (which is the case for 99.999% of home audio), you want the lowest possible source impedance and the highest practical load impedance; one hits diminishing returns pretty quickly once the ratio of the two is larger than 20 or so.

I don't have a schematic of your particular unit, but I'd guess that the 300k resistor is largely irrelevant to the source impedance- it's probably there to prevent pops and bangs when switching sources.
 
and the line amp

Here is the line amp stage
 

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I agree

I must admit that i have never been more mesmerised sonically than from this simple but beautiful sounding line stage.. to think that 1 tube and a hanful of components can leave everything i have heard behind is mind boggling but then again does keeping the signal path simple surprise me? Not at all.
The phono section is equally brilliant.. although i need to reduce rfi in the 1st stage (6sl7) i will try copper tubes over them....
If anyone has any ideas then please let me know
Meanwhile i will enjoy the amazing sound...
I must advocate tube regulated power supplies as well.. the difference is palpable...
Regards
Nick
 
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