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RJM 6DJ8 phono section

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F

fergs1

Member
Joined 2005
#1
greetings everyone. just wondering who has built the rjm 6dj8 phono and would like to share their views and experieces here.Ive looked at dozens of schems but I keep coming back to this one to build. It will be my first try at a valve phono and this one looks pretty simple and i like the fact that it uses 6dj8. also what output level could I expect running a mm at 0.5mv thru this stage. Also are there any particular things to whatch out for in building this circuit. Any help would be greaatly appreciated.
cheers fergs
 
#3
I haven't the foggiest idea what the rjm is, but the Bottlehead Seduction is built around the 6DJ8 too. Rigged out with CCS loads, the Seduction yields 40 dB of gain. The 6DJ8's mu is 33. That equates to 30.4 dB. Double that and deduct 20 dB. for the EQ network and, voila, there's 40 dB. If resistive loading is used, the net gain will be under 40 dB.

Boosting a 5 mV. MM cart. by 40 dB. yields 0.5 V. That will not be enough drive for many power amps. So, a line stage with a little gain is needed.

FWIW, 52 dB. of gain is needed to raise 5 mV. to 2 V., which is the O/P of a CDP.
 
#4
Eli Duttman said:

Boosting a 5 mV. MM cart. by 40 dB. yields 0.5 V. That will not be enough drive for many power amps. So, a line stage with a little gain is needed.

FWIW, 52 dB. of gain is needed to raise 5 mV. to 2 V., which is the O/P of a CDP.
Click to expand...

Don't know the circuit, but I'd be inclined to put at least a buffer between most phono stages and power amps...possibly with some amount of additional gain to insure flexibility for both cartridge and amplifier options for the future.
 
#5
greetings everyone, here is the link to the rjm phono stage. i,m just curious about the gain. my amp is ideally driven with 700mv and if i can get close to 500mv out of this circuit then isn't it just a case of simply giving my power amp a little more grunt or is there something I am missing as to how a amp behaves when not properly loaded.volume is not an issue in my flat so i'm just wondering how important an extraa gain stage is. thanks for all your replies
cheers chris
 

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#13
Eli Duttman said:
The schematic is for a resistively loaded, passively equalized, circuit. Net gain should be approx. 35 dB. A GENEROUS "guesstimate" is an O/P of 300 mV. You NEED a line stage with gain.
Click to expand...

If I replace the first triode (6dj8) with 12at7, how much gain would I expect?

Do I need to revise the RIAA portion of the schematic?

Thanks.
 
#15
reinhard said:
Think the RJM is a design of Jean Cristophe Morrison (JC)

He is employed at New Sensor Corporation in NJ as a senior
engineer.

Reinhard
Click to expand...

Lee35210 said:
I believe that RJM refers to Roger Modjeski. Excellent sound, but a bit tempermental preamp, according a friend who has one.
Click to expand...

Richard Murdey is RJM. Some very simple detective work (actually going to the site) can clarify this.
 
#16
OOPS!

I stand corrected!
People need to be more creative with their names!
I guess just too old to keep it all straight.
Thanks


PS: The Modjeski preamp was by RAM, as in the tubes. It was/is a 6DJ8 based pre also, so my mind leaped to the wrong conclusion.
 
#19
Hi.

I just finished building this phono. It sounds great but I am
having some hum issuse that I need to work out.
I am using a Hafler DH110 preamp. The volume settings are
about the same as when using the Haflers built in phono section.
sound quality to me seems about equal as well. I used multi-turn
pots for the filter resistors and carfully matched the capacitors
with a capacitance meter. I will keep working on the hum, DC
heaters might not be a bad idea.
 
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