Bypassing A Preamp With Volume Pot In Amp

06-03-14: C_avila1
I did notice that the attenuator is turned to 12 o'clock with merely average listening level. Does that mean that 10Kohm resistors would allow for more head room with volume?

Head room will remain the same, position will be different, lower. This could psychologically make you think it's got more headroom.

Remember Nelson Pass's quote:
Nelson Pass:
"Quote We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.End Quote"

You may like the 10kohm better it will have better impedance coupling with amps that are down to around 33kohm input impedance, higher than that is no problem.
But your source should be of the industry recognized low output impedance say below 1kohm, usually this means solid state, and only a selected few tube ones.
As there are many weedy tube output sources that are high output impedance, some I've seen that are a ridiculous high 3kohm sometimes 5kohm output impedance and should never be put for sale on the market, these will prefer to see 50kohm pot or even higher.

And if you find you need to use a source switch box, select ones with rotary type selector switch. These tend to have better contacts than push type, you can also put your passive in there as well, this way you can change amps when you need, just use interconnects that are less than <100pf (picofarad) per foot, which most all quality ones are.

Cheers George

Lse, it's not a pot (potentiometer).

It's just like a direct connection between source and power-amp with none of the contacts or preamps active components in the signal path, like a pots very lightweight wiper contact or switched resistor pots contacts in the signal path.
It's just a single fixed soldered resistor, that just happens to be able to change it's resistance value by being light sensitive.

It's the most transparent, uncoloured, dynamic way of getting the signal of the source to the power-amp, without any active tube or solid state components or contacts in the signal path.

You can read all about in these two threads.

http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1276356977&&&/Lightspeed-Attenuator-Best-Preamp-Ever-

http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp.html

Cheers George

Correct Jetrexpro, nearly all sources these days have output voltages higher than what the maximum input voltage is needed to drive amps into full output.

So there is no need for preamps with gain.
And if you have a source with low output impedance (<200ohms) as well, which most are anyway. All you need is a passive volume control, does'nt matter if it's inside the poweramp or outside connected by a meter of quality low capacitance (which most are) interconnect.

Cheers George

You'll find a lot of so called intergrated amps these days are exactly just that, a power amp with a passive and input switching, many of these are coming from EU and Asia and some are "Hi-End" tube mostly but now some solid state as well.
Cheers George

C_avila1
You haven't mentioned the input impedance of your poweramp.

I say 10K as a general even when direct connected, as most amps are 47kohms (industry standard) input impedance.

If you have say a Rogue tube poweramp which are 1mohm input impedance then yes a 50kohm pot will be more than fine.

Just remember it's easier to manufacture a 10kohm stereo log pot so that both channels track each other within a db or so than it is to manufacture a 50kohm stereo log pot to track that well.

Cheers George

C_avila1: Great idea, if your source has equal or higher output voltage than the input sensitivity of your amp great, you are almost there.

If your source has a nice low ouput impedance say below 100ohms, this will happily drive down to 1kohm (1:10 ratio).

EG: The combined load of say a 10kohm passive and a 47kohm input impedance (industrie standard of most amps)amp is still 8.2kohm, the 100ohm source will happily drive this (1:82 ratio), then this will be the most transparent/dynamic sound you will get.

Cheers George