Valve Itch phono

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#803
woodturner-fran said:
OK,

It was easier to sketch it than photograph. That would have meant turning it off..... 🙂


So bear in mind that the layout used here is most likely not ideal. I used it because it suited a case I already had (holes drilled etc). So I'm sure having the 4 valves nearer one another or laid out in a different way would be better.

So, the basic premise is that 1 long bar runs along the lenght of the 4 valves. Low current grounds (inputs and input valve cathodes) are connected right at one end. Next up along are all the RIAA grounds (close to the input grounds) and then right at the far end of the bar I have connected the PSU ground, output grounds, heater ground, connection to chassis and the output cathode grounds. The shields on the 2 x 6N2 are along the bar.

As I said, I'm sure there are better ways, but I now have very low hum.
http://www.diyaudio.com/forums/attachment.php?attachmentid=222297&stc=1&d=1304973716


Fran
Click to expand...

Thanks for pic Fran, I have several questions about grounding:

-Where do you connect 47K load resistor, togheter output cathode gnd & output RCA gnd?
-Where do you connect RIAA components (R6, C3 & R8), between 6N2 pin 9 and output cathode gnd & output RCA gnd ?
-Where do you connect R13, togheter output cathode gnd & output RCA gnd?

Felipe
 
#804
Fran can't read, could you help me?
 

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#807
Hi Felipe

I would dearly love to make 'an Itch'...
...but for various reasons, I concentrate on doing Salas's NJFET just now...
...Yes, balanced...I think...
...might PM you on that Felipe.

I am keeping my beady little eyes on progress here though !
You gonna have a great preamp there Felipe !

How about 'Star Grounding' also...
...all ground wires, straight 'back to the source'...
...ie. Right on the 'negative terminal' of your main PSU capacitor...
...Absolutely NO current mixing then.

People don't seem to do it so much these days, with PCB's and the like...
...just needs loads of wire ( & good routeing ).

To me the 'Star Grounding' scheme, is just a bus-bar anyhow, but comprised of 'seperate' wires.
Just a thought...
...I like 'Star's'.

Cheers

Si.
 
#808
Oh also Felipe...

...Dunno...you may already have this...
...but I have bumbled around with valves for quite a while...
...but never had a REALY GOOD text-book on the subject.

I just got 'Valve Amplifiers' by Morgan Jones...
...published by technical book company 'Newnes'.

It is utterly SUPERB !...
...and even a brain-dead amateur like myself, can understand it ( Not TOO much maths, Just the right amount ).
Morgan's writing style is highly readable also; not like some awfull technical books.

I am sure Newnes's proof reading is 101% also, which helps.
4th Edition...about 700 pages ( phew ! )...not cheap...but I think it will be worth EVERY penny to me.

Nice.

Cheers

Si.
 
#811
The Space Egg Corp said:
Hi Felipe

I would dearly love to make 'an Itch'...
...but for various reasons, I concentrate on doing Salas's NJFET just now...
...Yes, balanced...I think...
...might PM you on that Felipe.

I am keeping my beady little eyes on progress here though !
You gonna have a great preamp there Felipe !

How about 'Star Grounding' also...
...all ground wires, straight 'back to the source'...
...ie. Right on the 'negative terminal' of your main PSU capacitor...
...Absolutely NO current mixing then.

People don't seem to do it so much these days, with PCB's and the like...
...just needs loads of wire ( & good routeing ).

To me the 'Star Grounding' scheme, is just a bus-bar anyhow, but comprised of 'seperate' wires.
Just a thought...
...I like 'Star's'.

Cheers

Si.
Click to expand...

I use Star Ground in my Simplistic NJFET RIAA🙂
 
#812
merlin el mago said:
Fran can't read, could you help me?
Click to expand...

"Input ground and input cathode connect here"

Bad handwriting I know!!! Sorry for that.

The general principle is that the lowest ground currents are off at one end of the buss, and progressively bigger ground currents are positioned up along the bar until the output cathodes, output RCA gnds, the shunt ground etc right at the opposite end.


Also, I used shielded wiring for the inputs, plus I followed that link posted earlier about tyng the RCA input grounds to the chassis via some cheap ceramic caps - IIRC this has to be done right at the entry, every few mm really matters.

From Aiken amps:

While the star ground is excellent for eliminating ground loop hum, it is not always the best scheme for preventing radio-frequency interference (RFI). Fortunately, there is a simple addition to the star ground scheme that will make for a very quiet amplifier with no RFI. Simply add a 0.01uF capacitor from the chassis to the ground lug of the isolated input jack using very short leads. This will shunt all of the RF "riding" on the shield of the cord straight to the chassis ground before it can get into the amplifier and cause problems. Any kind of ground lug can be used for the chassis connection of the capacitor. You may be able to find a solder lug that slips over the shaft of the isolated input jack for a convenient ground lug. Use of an internal-toothed lockwasher is recommended for these types of connections to insure a good "bite" into the chassis for a good ground.
Click to expand...

from Star Grounding



Merlin: I know how you feel right now!!! Been there so many times. But with the help here, Salas and reading around I managed to finally understand grounding much more. In fact, the stuff I've learned making the itch really helped me sort out several other amps that had a little hum etc. Through enough sh*t and it eventually sticks in my head!!

Fran
 
#816
woodturner-fran said:
"Input ground and input cathode connect here"

Bad handwriting I know!!! Sorry for that.

The general principle is that the lowest ground currents are off at one end of the buss, and progressively bigger ground currents are positioned up along the bar until the output cathodes, output RCA gnds, the shunt ground etc right at the opposite end.


Also, I used shielded wiring for the inputs, plus I followed that link posted earlier about tyng the RCA input grounds to the chassis via some cheap ceramic caps - IIRC this has to be done right at the entry, every few mm really matters.

From Aiken amps:



from Star Grounding



Merlin: I know how you feel right now!!! Been there so many times. But with the help here, Salas and reading around I managed to finally understand grounding much more. In fact, the stuff I've learned making the itch really helped me sort out several other amps that had a little hum etc. Through enough sh*t and it eventually sticks in my head!!

Fran
Click to expand...

merlin el mago said:
That's correct grounding
Click to expand...

Post 805 link: http://www.diyaudio.com/forums/analogue-source/140635-valve-itch-phono-81.html#post3218544

Thanks Fran, more or less I understood your grounding way, was only to be sure.
 
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