Harry Haller's Passive Pre

[transducer]

Many months ago HH posted a schematic for a passive volume control using a fixed series resistor and variable shunt element using a pot. I put one together according to his schematic, only to have two problems. The first is that I had very little range of control, it was either off or blasting. To solve this I adjusted the value of the fixed series resistor from 11k to 26k. I also had a hum that got louder with increased volume. It wasn't really noticable when the music was playing, but when there was silence it was there. Thanks to Arne's help, I put in an 18k resitor across the input to ground, and that solved the hum problem. The pre is now dead silent, even at maximum volume. And as if that wasn't good enough, it is also more transparent (I think ) than my DIY active stage using a BB OPA627BP. I used cheap metal film resistors and a Radio Shack volume pot, all in a plastic box.

I highly recommend this design to anyone in need of a passive controller. I've attached a modified schematic.

Thanks Harry, wherever you are and thanks to Arne for putting the final touch to the project.

Cheers,
RonS

[Morello]

Why is HH banned?
(He was banned before I visited this forum för the first time)

\Morello

[halojoy]

Hayy Haller is a man who likes to express himself
A sort of Jim Morrison (Doors) person.
He would make a great lead-singer (front-face person, front-page story)
in a rocking band!
"That's the way he gets by
that's the way he were born"
and he has to courage to be Harry Haller and not anything else.

[jh6you]

O... my...
If you do not mind my honesty, you really like to express yourself and be a lead singer.

JH

[halojoy]

that is right
we are a few born with that defect

[halojoy]

Originally posted by transducer
The first is that I had very little range of control, it was either off or blasting. To solve this I adjusted the value of the fixed series resistor from 11k to 26k. I also had a hum that got louder with increased volume. It wasn't really noticable when the music was playing, but when there was silence it was there. Thanks to Arne's help, I put in an 18k resitor across the input to ground, and that solved the hum problem. The pre is now dead silent, even at maximum volume.
I highly recommend this design to anyone in need of a passive controller. I've attached a modified schematic.

Thanks Harry
RonS

transducer,
You have the input at the schematic. It is also important what is connected to the output. And what is connected to the input?
Can you tell me some more? Anyway it seems to work excellent for you.

[transducer]

halojoy,

The input gets connected to my CD player, and the output to the amplifier. Is this what you meant? There is no other circuitry in the preamp.

For the rest of you, can we keep this thread on topic? I was hoping to stir up some discussion or inspire someone to build this preamp, not dredge up why HH is no longer here. I was just paying homage to him as the originator of the schematic.

RonS

[halojoy]

yes, transducer
that is what I meant.

In most CD-output - poweramplifier connections
you really do not need any active amplification.

So the idea is very right!
It is a way to keep the signal way
short and clean.

If poweramp has 10Kohm input and CD-output have normal
drive capacity, there will be more currents transported
through the cable.
That I like.
A big current flow will not as easily be disturbed by forreign small currents.
If a preamp has 100Kohm input, only 1/10 so much current
is transported.
1.000 volt signal/100Kohm= 10 uA - That is not much!