12AX7 MM/MC Phono Preamplifier PCB ref VTL - Page 7

gabrielbecheanu · 11th June 2012, 06:51 PM

I bought only the pcb, all the parts are very good quality caps from Nichichon and the semiconductors from Farnell non polar caps from Vishay but the hum still is

patti · 11th June 2012, 07:15 PM

...maybe even see something wrong but it is correct that the grid goes to GND?
how does the tube controlled?

patti

Stephen R · 12th June 2012, 07:34 AM

Valve is "controlled" by grid-cathode difference. Doesn't matter which is at "ground".

jeffreyrow · 13th June 2012, 03:33 PM

I have checked the solder connection n they seem good, I made a aluminium coated plastic cover for the transformer n nearly all the hum went away, the rest went when i cleaned all the earth terminal. No more hum but a little buzz which i attribute to placement of input wires...I have intermittent signal on left channel but i will wait till i get new rca sockets n valves. I am using a Thorens TD280 Mk II, coupled to a Acurus L10 line pre amp and Acurus A250 power amp. Bass is ok but what can I do to increase it.

marsvolta · 18th June 2012, 12:40 PM

I am at 400k in R14. Bass is pretty good. The output will start to oscillate much over 500k.

I have very little hum or buzz.

Klimanski · 18th June 2012, 02:50 PM

Some years ago I also have purchased this kit from Analogmetric. It seems to me, that sound was a bit better after C8, R15 ( shortened ) and R14 were removed, but R16 changed to 56K, capacitor C11 consists of two 10n in parallel, C6 - Russian K72-6 0.033uF, you can see it on e-bay x8 0.033uF 500V AUDIO teflon capacitors K72P-6 | eBay. I listened it with MM only.

morinix · 18th June 2012, 04:49 PM

Is the MC quiet enough?

Klimanski · 18th June 2012, 05:02 PM

Havn't tested. Sorry for mistake is last post - C11 - two 10n in series.

jeffreyrow · 20th June 2012, 06:24 PM

400 k sounds good, still getting buzzing in both channels at 1/2 volume. Btw, my power supply is really hot esp the 12volt regulator..any advice?

marsvolta · 07:12 PM

Did you connect the heater GND and B+ GND together or elevate the heater GND?

Did you connect both 260v B+ together? I see only 1 being powered in your pic.

I would also twist the mains on the right side tighter and without the earth GND and get them away from the power supply board.

11th June 2012, 07:15 PM	#62
patti diyAudio Member Join Date: Nov 2009	control voltage to GND ? ...maybe even see something wrong but it is correct that the grid goes to GND? how does the tube controlled? patti

18th June 2012, 04:49 PM	#67
morinix diyAudio Member Join Date: Jun 2006	Is the MC quiet enough? __________________ Robert Lounge Audio

20th June 2012, 07:07 PM	#70
marsvolta diyAudio Member Join Date: Apr 2012	Did you connect the heater GND and B+ GND together or elevate the heater GND? Did you connect both 260v B+ together? I see only 1 being powered in your pic. I would also twist the mains on the right side tighter and without the earth GND and get them away from the power supply board. Last edited by marsvolta; 20th June 2012 at 07:12 PM.

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11th June 2012, 06:51 PM	#61
gabrielbecheanu diyAudio Member Join Date: Jun 2006 Location: Constanta	I bought only the pcb, all the parts are very good quality caps from Nichichon and the semiconductors from Farnell non polar caps from Vishay but the hum still is

12th June 2012, 07:34 AM	#63
Stephen R diyAudio Member Join Date: Oct 2002 Location: Folkestone	Valve is "controlled" by grid-cathode difference. Doesn't matter which is at "ground".

13th June 2012, 03:33 PM	#64
jeffreyrow diyAudio Member Join Date: Jun 2011	I have checked the solder connection n they seem good, I made a aluminium coated plastic cover for the transformer n nearly all the hum went away, the rest went when i cleaned all the earth terminal. No more hum but a little buzz which i attribute to placement of input wires...I have intermittent signal on left channel but i will wait till i get new rca sockets n valves. I am using a Thorens TD280 Mk II, coupled to a Acurus L10 line pre amp and Acurus A250 power amp. Bass is ok but what can I do to increase it.

18th June 2012, 12:40 PM	#65
marsvolta diyAudio Member Join Date: Apr 2012	I am at 400k in R14. Bass is pretty good. The output will start to oscillate much over 500k. I have very little hum or buzz.

18th June 2012, 02:50 PM	#66
Klimanski diyAudio Member Join Date: Oct 2007 Location: Riga, Latvia ( Lettland )	Some years ago I also have purchased this kit from Analogmetric. It seems to me, that sound was a bit better after C8, R15 ( shortened ) and R14 were removed, but R16 changed to 56K, capacitor C11 consists of two 10n in parallel, C6 - Russian K72-6 0.033uF, you can see it on e-bay x8 0.033uF 500V AUDIO teflon capacitors K72P-6 \| eBay. I listened it with MM only.

18th June 2012, 05:02 PM	#68
Klimanski diyAudio Member Join Date: Oct 2007 Location: Riga, Latvia ( Lettland )	Havn't tested. Sorry for mistake is last post - C11 - two 10n in series.

20th June 2012, 06:24 PM	#69
jeffreyrow diyAudio Member Join Date: Jun 2011	400 k sounds good, still getting buzzing in both channels at 1/2 volume. Btw, my power supply is really hot esp the 12volt regulator..any advice?

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