Phono stage success!

rman · 30th June 2008, 02:48 AM

Hi all.

I just got my version of Richard Murdey's 6DJ8 phonostage
up and running, and it sounds just fine.
http://www.geocities.com/rjm003.geo/.../diy_pho3.html

I don't hear any real difference beetween it and my Hafler DH110
which by what I have read has an excellent phono section.
My turntable is nothing very special however.
Here are some pics.

rman · 30th June 2008, 02:49 AM

Or here they are

rman · 30th June 2008, 02:51 AM

That's inside the psu. I haven't drilled vent holes in the lid yet.
this is the phonostge itself.

rman · 30th June 2008, 04:12 AM

Also, thank's to Tubewade and Hotbottle for their input when
I was planning this project.

alexg · 30th June 2008, 05:31 AM

Looks great.

I need to do a phonostage soon (am using a crappy SS phonostage) and I was looking at the hagtech's cornet octal (6sl7 and 6sn7) and this phonostage (6dj8) but since I have tons of 6n1p, I might do a 6n1p phonostage with slight modification of the circuit.

Great job on your 6dj8 phonostage.

alexg · 30th June 2008, 02:52 PM

BTW, how is the gain of the RJM phonostage?

I read in another thread that the estimated gain of this phonostage is around 35db.

My preamp does not have too much gain so I am a bit worried about the low gain of the phonostage.

Thanks.

rman · 2nd July 2008, 12:51 AM

Hi.

Richard Murdy's page on this amp says 38db. Should be about
90x. 30x per stage with a 10 (20db) loss in the passive filter.

I am using a Hafler 110 preamp. the volume settings are about
the same as when using the built in phono section. The sound
is just as good too. The Hafler phono has a very good reputation.
So I didn't really need the tube phono but it was a fun project.
Watch out for hum. I just left the heaters floating and got alot of
hum. I have grounded one side of the heaters at the outboard
psu and the hum has dropped alot. I am going to ground them
in the amp instead and see how that works. I don't really want
to reference heater supply to a positive voltage because the
rectifier diode heater uses the same supply.

Since taking theese pictures I have fiished the lid for the psu.
Now I need to finish the case for the phonostage.

Rolf.

mashaffer · 2nd July 2008, 01:01 AM

Are you using an IDH rectifier? If so then, I think, referencing the heater at a higher voltage (within reason) should not be a problem and I would think that it would make a world of difference. Tightly twisted heater wires is of course recommended as well. I did this on a high gain guitar amp and there was absolutely no audible hum.

just a newbie's opinion.

alexg · 2nd July 2008, 01:51 AM

I gather that your heater supply does not have a center tap for ground. I don't think you need to reference the heater to a positive supply, the cathode voltage is very, very low.

If you don't have a center tap heater supply, try connecting each leg of the heater supply to ground with 100 ohm resistor. This seems to work for me.

I started drilling my chassis for this preamp, but I will be using 6n1p because I have tons of them. Thanks.

rman · 2nd July 2008, 02:10 AM

Hi Mike.

Yes it is an indirectly heated diode a 6x4. I would't think it would be possible to share heater supply with the amp triodes otherwise.
Thank's for sending those plugs. I did go with a different
connector however.

alexg,

I think I will try you idea. good luck with your build!

ps. I did twist the heater wires.

30th June 2008, 02:48 AM	#1
rman diyAudio Member Join Date: Oct 2007	phonostge sucsess! Hi all. I just got my version of Richard Murdey's 6DJ8 phonostage up and running, and it sounds just fine. http://www.geocities.com/rjm003.geo/.../diy_pho3.html I don't hear any real difference beetween it and my Hafler DH110 which by what I have read has an excellent phono section. My turntable is nothing very special however. Here are some pics.

2nd July 2008, 01:01 AM	#8
mashaffer diyAudio Member Join Date: Jun 2004 Location: Indiana	Are you using an IDH rectifier? If so then, I think, referencing the heater at a higher voltage (within reason) should not be a problem and I would think that it would make a world of difference. Tightly twisted heater wires is of course recommended as well. I did this on a high gain guitar amp and there was absolutely no audible hum. just a newbie's opinion. __________________ mike - www.keepingsundayspecial.org

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30th June 2008, 04:12 AM	#4
rman diyAudio Member Join Date: Oct 2007	Also, thank's to Tubewade and Hotbottle for their input when I was planning this project.

30th June 2008, 05:31 AM	#5
alexg diyAudio Member Join Date: Jan 2005 Location: Philippines	Looks great. I need to do a phonostage soon (am using a crappy SS phonostage) and I was looking at the hagtech's cornet octal (6sl7 and 6sn7) and this phonostage (6dj8) but since I have tons of 6n1p, I might do a 6n1p phonostage with slight modification of the circuit. Great job on your 6dj8 phonostage.

30th June 2008, 02:52 PM	#6
alexg diyAudio Member Join Date: Jan 2005 Location: Philippines	BTW, how is the gain of the RJM phonostage? I read in another thread that the estimated gain of this phonostage is around 35db. My preamp does not have too much gain so I am a bit worried about the low gain of the phonostage. Thanks.

2nd July 2008, 12:51 AM	#7
rman diyAudio Member Join Date: Oct 2007	Hi. Richard Murdy's page on this amp says 38db. Should be about 90x. 30x per stage with a 10 (20db) loss in the passive filter. I am using a Hafler 110 preamp. the volume settings are about the same as when using the built in phono section. The sound is just as good too. The Hafler phono has a very good reputation. So I didn't really need the tube phono but it was a fun project. Watch out for hum. I just left the heaters floating and got alot of hum. I have grounded one side of the heaters at the outboard psu and the hum has dropped alot. I am going to ground them in the amp instead and see how that works. I don't really want to reference heater supply to a positive voltage because the rectifier diode heater uses the same supply. Since taking theese pictures I have fiished the lid for the psu. Now I need to finish the case for the phonostage. Rolf.

2nd July 2008, 01:51 AM	#9
alexg diyAudio Member Join Date: Jan 2005 Location: Philippines	I gather that your heater supply does not have a center tap for ground. I don't think you need to reference the heater to a positive supply, the cathode voltage is very, very low. If you don't have a center tap heater supply, try connecting each leg of the heater supply to ground with 100 ohm resistor. This seems to work for me. I started drilling my chassis for this preamp, but I will be using 6n1p because I have tons of them. Thanks.

2nd July 2008, 02:10 AM	#10
rman diyAudio Member Join Date: Oct 2007	Hi Mike. Yes it is an indirectly heated diode a 6x4. I would't think it would be possible to share heater supply with the amp triodes otherwise. Thank's for sending those plugs. I did go with a different connector however. alexg, I think I will try you idea. good luck with your build! ps. I did twist the heater wires.

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