How much do I need to spend to get a preamp that sounds better than no preamp?

Hello @georgehifi

We've had a similar discussion about preamps:
https://forum.audiogon.com/discussions/bypassing-a-preamp-with-volume-pot-in-amp
I knew I've seen that Nelson Pass quote before.

I have had great success "bypassing" a preamp with a Khozmo stepped attenuator using Z-Foil TX2575 resistors inside an amp.

I ditched the volume attenuator completely in my current setup and only control the volume from the computer. I prefer to lose a few 1s and 0s from the computer volume than to add a preamp that brings so much favorable and unfavorable distortion/coloration from tubes, resistors, capacitors, regulators, diodes, interconnects, power cords, etc.

Who needs an preamp when you have a Pass XA25? (jk) This amp is amazing.

c_avila1
Who needs an preamp when you have a Pass XA25

Hi again Ciro.
Your XA25 (very nice poweramp btw) is 47kohm input impedance and I believe you used a 50kohm Khozmo stepped attenuator as a passive pre?
You really should of used a 10kohm Khozmo passive pre, it would have been a much better better impedance match to the XA25’s 47kohm.

But your now going direct from source to XA25, even better again, so long as you don’t lower the digital domain volume control of your source below 75%, as you will start to "bit strip", 14bit resolution instead of 16bit ect ect.

Cheers George

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.

I suppose if I had to floor the accelerator to drive 55 mph, maybe I’d think the life was being sucked out of my driving. Then again, maybe I like 55. Nice and safe, good gas mileage…

Is impedance matching an issue? Passive volume controls do have to make a trade-off between input impedance and output impedance. If the input impedance is high, making the input to the volume control easy for the source to drive, then the output impedance is also high, possibly creating difficulty with the input impedance of the power amplifier. And vice versa: If your amplifier prefers low source impedance, then your signal source might have to look at low impedance in the volume control.

This suggests the possibility of using a high quality buffer in conjunction with a volume control. A buffer is still an active circuit using tubes or transistors, but it has no voltage gain – it only interposes itself to make a low impedance into a high impedance, or vice versa.

As per usual, George omits the rest of Nelson's words **after** the quote he usually trots out. I've included more of that text above, seems to me not for the first time on this thread.

As you can see, it points out that passives can't do the best job on their own, and are helped out by the use of a buffer. I've pointed this out many times on these threads about passive vs. actives.

What Nelson does not address is that a buffer at the input of the control is useful too. However, a buffer with no gain is going to have some signal loss. Its also *very* tricky to build a circuit with only a little gain without being on the edge of linearity with many devices, tube or transistor. So if you have a no gain buffer at the input of the control and a no gain buffer at the output, you may wind up with not enough voltage to drive the amp to full output. This is why there continue to be active line stages made, despite digital sources having higher voltage outputs for over 35 years.
My best surmise is that George consistently leaves out Nelson's complete remarks because they don't fit his world view.

So, impedance matching, and gain, are both important ?