Preamp Noise with High-Efficiency Speakers

Amen Atma!

It is a banaid fix because his AMR has to drive the input of a preamp through the same interconnects and pre amp inputs are usually 47kohm (industrie standard), his FL100 is acually higher and easier to drive at 57kohm through the same interconnect and 1 pair less as well.
And gain doesn't even come into it as he has an abundance. and as a bonus it's all direct coupled, no "masking" capacitors in the signal path as it would be with many preamps.
A preamp in this case in the path can only add colouration/distortions that some may like because it's masking a problem elsewhere.

Like I said Nelson Pass's quote says it all, to contradict it is almost blasphemous. read again carefully.

Cheers George

A Quote from the master Nelson Pass

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.

Cheers George

Hi Ying - I highly recommend buying the Jensen noise troubleshooting kit. It is inexpensive (or you can make the devices yourself - they give you the directions) and will come in handy for years to come as equipment, rooms and homes change.

I have 101dB/m speakers and recently installed a new and quite expensive Linestage and immediately noticed the buzz that was always present, but low in level, grew in volume to where it was annoying at the listening seat during quiet passages. With the help of Jensen's troubleshooting guide, I tracked it down to noise being induced in the 3m unbalanced IC's I run from Linestage to amp. With IC's plugged into the amp, but not plugged into the Linestage, the noise was loud and variable depending on how the IC was moved around. Isolation transformers on the IC's won't fix this and I couldn't move IC and equipment that significantly. My solution: my Audion amps have a gain control knob. I turned the gain down on the amps and use more gain in the Linestage. Noise has vanished.

Get the troubleshooting guide with special RCA couplers ($12.50) or print out the guide at the link below and make your own. You'll then be able to unequivocally identify the source of the noise. Dave and Bill from Jensen are also great and very helpful if you need help.

Jensen Noise Troubleshooting Guide

Good luck. You shouldn't have to live with noise nor should you have to settle running DAC direct if you don't want to.
Jordan

Neat post, German B. And that guide book is pretty clearly written. Nice contribution!

George, you can't count on a preamp having a 47K input impedance- that is for phono, not a line section, which might often be more like 100k.

Amplifiers frequently have 100K input impedances too. When you run impedances that high and then introduce a high impedance (passive volume control) between the source and the amplifier, the result will be that the system is going to be extremely sensitive to cable colorations. There will also be a loss of bandwidth as capacitance in the cables take their toll. In addition, if there is any input capacitance in the amplifier it will not matter if the source is direct coupled- you will loose bass impact.

There is no 'blasphemy'. As much as I respect him (I think of him as one of the top ten designers worldwide) Neslon Pass is simply wrong about this although I agree that it makes no sense to have a lot of gain and then burn it off. There are more elegant ways to do it than passive controls though.

A simple solution is a buffered volume control. This offers proper volume control performance with it acting as a mild tone control or hindering dynamic impact.