Preamp Noise with High-Efficiency Speakers

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.

Atmasphere,

Did you mean to say "without" instead of "with"? If not, then I am confused by the statement.

"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."

Wow, I did not know my thread can attract so many responses in days! It looks like noise is more attractive than music.

Georgelofi, I currently do exactly what you say: set the input impedance at max (57k Ohm on RCA) and run DP-777 directly. I normally listen at -30 dB on my DP-777, so you are right, modern electronics have too much gain and we are throwing the signal away. And I have to either throw it away at DP-777's internal volume control, or at an external preamp. I don't know which way is better because the noise issue doesn't allow me to evaluate preamps.

I appreciate your (and Nelson Pass's) belief on the preamp-less approach, but I am not convinced that the volume control inside the DP-777 is a world beater; and I am not sure the DP-777's output impedance (at more than 100 Ohm) and the FL-100's input impedance (57k Ohm) is a match made in heaven.

When I use conventional speakers (85-92 dB), having a good preamp is a clear winner. Audia's own Flight Pre actually worked much better than Cary SLP-05 due to impedance matching, and running AMR DP-777 direct sits somewhere between these two preamps. With a Cary V-12R power amp the results is totally reversed in favor of the Cary SLP-05.

I don't want to turn this thread into another arguement over preamp/preamp-less comparison, but we all know system matching is key and there's no way better than all others. At one point I bought an all Audia system (CD/Pre/Pwr), and an all Cary system to reduce the hassle of system matching. But at the end of the day it is still not simple. Now I am thinking about buying a Devialet D-Premier and sell everything else.

Cheers!