Pics of Tamas' Preamp

[Flatpicker]

[quote author="tk@halmi"]...The servo sounded like it was messing with the mids and lows (several observers reported so). Most likely, it was an implementation problem on my part...[/quote]I donno... I've had knowledgeable folks tell me they sound like that when they are working correctly. :wink:

 

[MikoKensington]

Hot tits!

 

[CJ]

Incredible!
What is the pad like? T or H network? How many db cut?
Thanks!

 

[PRR]

> I just removed the grounding wire.

Still a closed-loop conductor through the can and case. If the case is painted, it may not be closed today, but when the can scratches-through the paint, it will carry about 0.1VAC-0.3VAC in about 0.001 ohms, 100 AMPS, which could get awful hot.

I love the bean-can but I think you do not need it, and would be better off without it.

 

[soundguy]

so much for getting all excited about the can... If you were to loosely wrap the transformer with a mumetal shield but leave the top open, I would guess that you wouldnt run the same risk as in this scenario, right? Even with torroids, Ive had lots of trouble using 1578's in the same chasis no matter where I put them.

dave

 

[Flatpicker]

[quote author="soundguy"]...Even with torroids, Ive had lots of trouble using 1578's in the same chasis no matter where I put them...[/quote]Yep... Folks like to slam wall-warts, but there's a huge advantage to having the transformer outside of, and away from the preamp chassis.

 

[tk@halmi]

[quote author="PRR"]> I just removed the grounding wire.
Still a closed-loop conductor through the can and case. If the case is painted, it may not be closed today, but when the can scratches-through the paint, it will carry about 0.1VAC-0.3VAC in about 0.001 ohms, 100 AMPS, which could get awful hot.
I love the bean-can but I think you do not need it, and would be better off without it.[/quote]

For the sake of safety I have removed the can. How would one install such a shield properly? I have seen pictures of some preamps that feature mu-metal (not beancan) shield? What if I isloated the bolt through the toroid so it does not contact the chassis ?

Thank You,
Tamas

 

[tk@halmi]

[quote author="cjenrick"]Incredible!
What is the pad like? T or H network? How many db cut?
Thanks![/quote]

Hi CJ,
I think it is called a U-pad. It is the run of the mill pad seen in the Jensen appnotes. I measured 19dB cut so nominally it is a 20dB pad.
Thanks,
Tamas

 

[kevinc]

The stray field from a toriodal transformer is greatest where the leads emerge from the windings, due to the disturbance of the winding symmetry. It's often good enough just to orient the transformer so that the leads emerge from the side that faces away from the input circuitry. If not, then you can make an effective shield by cutting a strip of ferromagnetic metal (out of a tin can, if you like; I have) the height of the toroid and wrapping it around the periphery of the toroid. I am told that it is is best to insulate the ends where they overlap, so that there is no electrical contact there. Tape it all in place (make sure that the shield doesn't cut into the insulation of the leads) and you have a shield.