Thank's for sharing your expierience Alex.
In the future I think I will leave two stage choke filters to the true gurus. I put 200uf of capacitance across the power supply output and the woofers stopped dancing. It is too big to put in the supply so I will try to jam it into the phonostage.
There is still more hum than I would like. I yhink it must be a
ground loop or hum pickup on the input wires. I used twisted
pair telephone wiring instead of shielded cable. I will try the
ground breaker I have been reding about on this forum. Two
back to back diodes across a resistor. If that doesn't work, then
it's shieled input cable.
I will let you know how it goes. How is your project coming along?
Let me know how your power supply works out.
Rolf.
In the future I think I will leave two stage choke filters to the true gurus. I put 200uf of capacitance across the power supply output and the woofers stopped dancing. It is too big to put in the supply so I will try to jam it into the phonostage.
There is still more hum than I would like. I yhink it must be a
ground loop or hum pickup on the input wires. I used twisted
pair telephone wiring instead of shielded cable. I will try the
ground breaker I have been reding about on this forum. Two
back to back diodes across a resistor. If that doesn't work, then
it's shieled input cable.
I will let you know how it goes. How is your project coming along?
Let me know how your power supply works out.
Rolf.
I finish my phonostage earlier than I expected.
With AC heating, it is quiet as a mouse!
And it sounds excellent too! I used the PSU schematic I posted earlier. I used 500ohm/20uf polypropylene for the last RC filter instead of the 1K/10uf that was used by RJM on his schematic.
My heaters are center tapped and I just twisted the wires tightly and connect the CT to ground. I use stargrounding on this phonostage. I was really expecting noise/hum, when I fired it up, I thought I did not turn on my preamp or amp, can't hear hum with my ear on the speakers using a 92db speakers.
Pictures to follow as soon as I finish the plinth.
With AC heating, it is quiet as a mouse!
And it sounds excellent too! I used the PSU schematic I posted earlier. I used 500ohm/20uf polypropylene for the last RC filter instead of the 1K/10uf that was used by RJM on his schematic.
My heaters are center tapped and I just twisted the wires tightly and connect the CT to ground. I use stargrounding on this phonostage. I was really expecting noise/hum, when I fired it up, I thought I did not turn on my preamp or amp, can't hear hum with my ear on the speakers using a 92db speakers.
Pictures to follow as soon as I finish the plinth.
38dB?!
very little gain. so are all you guys using additional preamps after the phonostage or what? My phono amp has about 58dB gain for a high-out MC cart. All my poweramps are passive attenuated and need 1.5-2Vrms for full output. Just seems backwards to have an additional preamp with gain for normal, 2V, line level sources. Keep seeing these phono stages with less than 50dB of gain and wondering why people do it this way.
very little gain. so are all you guys using additional preamps after the phonostage or what? My phono amp has about 58dB gain for a high-out MC cart. All my poweramps are passive attenuated and need 1.5-2Vrms for full output. Just seems backwards to have an additional preamp with gain for normal, 2V, line level sources. Keep seeing these phono stages with less than 50dB of gain and wondering why people do it this way.
zarniwoop said:
I use a low gain transformer coupled dht line stage (4dB)because I have so many sources and several amplifiers I swap back and forth - too much wiring to disturb every time I want to make a minor change or repair. I use stepped attenuators, high end rca jacks and the transformers are permalloy so replicating even the stepped attenuators and jacks in multiple amplifiers would be far too costly.
My phono stage like yours does have quite a lot of gain at around 50dB with a Grado Platinum Reference..
Your comments are well taken, but there are still a lot of people running line stages with >20dB of gain and with those phono stages having gains of 40dB or so work well. People with old analog sources need the additional gain in some instances as well. Everything in my system is generally 2V output, but none of my tuners are - fortunately there is adequate gain available to get loud even with these sources. I am about to get a reel to reel, and most of these will have maximum output levels of less than 1Vrms.
zarniwoop said:
This phonostage is my first attempt of making a phonostage.
Anyway, am using a high gain linestage so the lowish gain of my new phonostage is not really too much of an issue.
Next phonostage will be a higher gain phonostage, next time I think I am more proficient of dealing with hum and noise issues of high gain phonostage.
Sorry. My english is so bad... I maked this phonostage about year ago. In begin, it used a 6n1p, but now it used a 6n23p (russian 6dj8). Sound of this phonostage is nice. In PSU I used a HFA06TB1200 rectifiers and IRF840 regulater. Case is plywood? no screening? but no hum.
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mashaffer said:
I did not modify the circuit, I checked the loadline of the 6dj8 and checked if it is optimal with the 6n1p, it does seem optimal. I have not tweaked the circuit yet, but I used polyester caps on the RIAA and I want to replace them with silver mica. The resistors used on the RIAA are carbon and I want to replace them with metal film.
This phonostage is quite a good performer.
I started tweaking the circuit, first I used red LEDs to bias, sounded too harsh for me.
I also tried to bias the 6n1p hotter, replaced the bias resistor with 470R and then 330R, went back to 500R, the sound is much better with the 500R cathode resistor.
Since the gain is a bit on the low side, am thinking of using 12at7 for the first stage and then 6n1p for the second stage. Passive RIAA equalization in between the two stages.
Does anybody knows to compute for the resistors and capacitors of the RIAA if I replace the 6n1p with 12at7? Thanks.
I also tried to bias the 6n1p hotter, replaced the bias resistor with 470R and then 330R, went back to 500R, the sound is much better with the 500R cathode resistor.
Since the gain is a bit on the low side, am thinking of using 12at7 for the first stage and then 6n1p for the second stage. Passive RIAA equalization in between the two stages.
Does anybody knows to compute for the resistors and capacitors of the RIAA if I replace the 6n1p with 12at7? Thanks.
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