12AX7 MM/MC Phono Preamplifier PCB ref VTL - Page 8

marsvolta · 21st June 2012, 02:07 AM

My 12v regulator gets very hot also. Its about 600 ma. I've got 2 big sinks on it. So far so good.

Nonatron · 21st June 2012, 07:08 AM

Quote:

Originally Posted by morinix

Is the MC quiet enough?

Don`t think so. The 12AX7 / ECC83 is too much noisy for serious MC amplification. For grounded grid amp some high gm frame grid tubes are much better like 6DJ8 or EC86. There are many low noise high gm pentodes available as well like E180F, E280F, D3a, C3m, C3g which all are better than the 12AX7.

jeffreyrow · 21st June 2012, 10:08 AM

Heater gnd and B+ gnd together. Underside of board i connected the 260 together.

Mains twistered tighter without earth, I have uploaded a pic. Switch is in front n supply is at rear so cant reroute the mains wires.
http://i1153.photobucket.com/albums/...row1956/06.jpg

ecereb · 5th October 2012, 09:44 PM

Jeff,
I know it’s been a while since you posted. After looking at your picture of the placement of the components, I know what is causing the hum. I too had the same problem. It is the location of the transformer. It is too close to the input side of the main board. The input stage is very sensitive to magnetic fields. The transformer is giving off a 60Hz magnetic hum. The hum you are experience is probably more pronounced through one channel. Your solution is much easier than mine. Switch the power supply board and the transformer. Put the transformer as far away from the board as you can. You may still have to shield the transformer to get rid of all of the hum. I could not move the transformer, so I shielded the main board, the tubes, and the transformer. I still hear a slight hum.

Graffity · 15th October 2012, 04:06 PM

Hello guys!
I'm new to the tube stuff and now building this preamp kit. Please help me, I have some noob questions.
How should I connect power transformer? There comes two 6,3v lines and we need 12,6, I guess I should put this lines together 6,3+6,3 ?
How should I set DIP switch to work with MM 47k load? Pin 6 on and all other are off?

Uunderhill · 15th October 2012, 09:24 PM

Quote:

Originally Posted by geek_83

No

this project seems to bee pretty decent so i have decide to build it but if You know any better tube pre-amplifier support MC cartridges please insert schematic.

Tubes are great - but because of noise, I would not recommend them in a phono stage.

Suggest, you find a kit that uses jFET's - which have a low noise figure.
.

Graffity · 16th October 2012, 04:04 PM

If I apply 260v AC to voltage regulator, I have 392v DC out, and I need same 260v DC output. I should apply lower AC voltage, am I right?
Please help anybody.

Graffity · 16th October 2012, 08:35 PM

I've applied 200v AC and 6,3+5 = 11,3v AC, output set to 260 and 12,55, and it works!
No hum and NO HEATING of voltage regulator at all! I've read about LV heating problem, I think this is about 12,6v AC input, you should use lower input voltage.

Stratos858 · 12th November 2012, 10:08 PM

I try R14 1M and R15 24k, not not bad at all. I always trying for better MC.
I think an op before the first stage could be the easiest way...

Any news from you??

Jeff i try the same psu board and is terrible. In my project i had better results with the heaters gnd not connected with B+. I had mant hums, try a good star ground and will be quite. The problems is mainly in MC ...i think.

Graffity · 14th November 2012, 07:17 AM

I use 400k at R14, bass is like it should be or a bit lower, tried 500-800k but there is no difference. I used WBT silver solder on everything except power board. First time sound was high-toned, now it is balanced with a little bit more high freq to my ears.
About ground - less ground connections - less hum for my opinion. I only connected power and sound input/output grounds together. No ground on chassis, transformer, heaters.

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21st June 2012, 02:07 AM	#71
marsvolta diyAudio Member Join Date: Apr 2012	My 12v regulator gets very hot also. Its about 600 ma. I've got 2 big sinks on it. So far so good.

21st June 2012, 10:08 AM	#73
jeffreyrow diyAudio Member Join Date: Jun 2011	Heater gnd and B+ gnd together. Underside of board i connected the 260 together. Mains twistered tighter without earth, I have uploaded a pic. Switch is in front n supply is at rear so cant reroute the mains wires. http://i1153.photobucket.com/albums/...row1956/06.jpg

5th October 2012, 09:44 PM	#74
ecereb diyAudio Member Join Date: Oct 2012 Location: Cincinnati	Jeff, I know it’s been a while since you posted. After looking at your picture of the placement of the components, I know what is causing the hum. I too had the same problem. It is the location of the transformer. It is too close to the input side of the main board. The input stage is very sensitive to magnetic fields. The transformer is giving off a 60Hz magnetic hum. The hum you are experience is probably more pronounced through one channel. Your solution is much easier than mine. Switch the power supply board and the transformer. Put the transformer as far away from the board as you can. You may still have to shield the transformer to get rid of all of the hum. I could not move the transformer, so I shielded the main board, the tubes, and the transformer. I still hear a slight hum.

15th October 2012, 04:06 PM	#75
Graffity diyAudio Member Join Date: May 2009	Hello guys! I'm new to the tube stuff and now building this preamp kit. Please help me, I have some noob questions. How should I connect power transformer? There comes two 6,3v lines and we need 12,6, I guess I should put this lines together 6,3+6,3 ? How should I set DIP switch to work with MM 47k load? Pin 6 on and all other are off?

16th October 2012, 04:04 PM	#77
Graffity diyAudio Member Join Date: May 2009	If I apply 260v AC to voltage regulator, I have 392v DC out, and I need same 260v DC output. I should apply lower AC voltage, am I right? Please help anybody.

16th October 2012, 08:35 PM	#78
Graffity diyAudio Member Join Date: May 2009	I've applied 200v AC and 6,3+5 = 11,3v AC, output set to 260 and 12,55, and it works! No hum and NO HEATING of voltage regulator at all! I've read about LV heating problem, I think this is about 12,6v AC input, you should use lower input voltage.

12th November 2012, 10:08 PM	#79
Stratos858 diyAudio Member Join Date: Nov 2011 Location: Athens, Greece	I try R14 1M and R15 24k, not not bad at all. I always trying for better MC. I think an op before the first stage could be the easiest way... Any news from you?? Jeff i try the same psu board and is terrible. In my project i had better results with the heaters gnd not connected with B+. I had mant hums, try a good star ground and will be quite. The problems is mainly in MC ...i think.

14th November 2012, 07:17 AM	#80
Graffity diyAudio Member Join Date: May 2009	I use 400k at R14, bass is like it should be or a bit lower, tried 500-800k but there is no difference. I used WBT silver solder on everything except power board. First time sound was high-toned, now it is balanced with a little bit more high freq to my ears. About ground - less ground connections - less hum for my opinion. I only connected power and sound input/output grounds together. No ground on chassis, transformer, heaters.