Preamp Noise with High-Efficiency Speakers

Yingtonggao, just read this quote from Nelson Pass, I think we could all aggree that we all here with our combind wisdom pale into insignificance compared to him. Remember your FL100 takes 1.4v input to clip. Your AMR DP777 gives out more than 2v and you have 104dB sensitive speakers.

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

The problem with a passive is that it can act to functionally reduce the value of the coupling cap that might be in the source, such as a DAC. In doing so this is how bass impact can be lost. The other problem is that the system will be a lot more sensitive to cable artifact. This is likely the why of Nelson Pass' comment.

In a high efficiency system, it is more elegant to simply not have the gain. Power amps typically have about 30 db because speakers might only have 87db efficiency. But what if the speaker is a good 15-20db more efficient? Then it makes sense to have less gain in the amp, so the preamp or source can have the volume control in a reasonable (higher) position.

If you think about it, amplifier and preamp manufacturers have a difficult dance; to have enough gain to work with lower efficiency speakers but be quiet enough to work with higher efficiency speakers too.

We solve the problem by offering a jumper plug for our amplifiers that replaces one of the voltage amplifier tubes, thus reducing the gain (and the noise floor) of our amplifier.

With regards to grounding: If your equipment is built correctly there should be no need to resort to exotic grounding solutions like a copper stake in the yard. 'Built properly' means that the chassis and the circuit ground are two different things. This has been challenging for a lot of high end audio designers; but if you are going to meet the directives for the CE mark or similar, this is a problem that will have to be dealt with.

Worth seeing if changes in location of preamp (and associated ICs, especially if not shielded) relative to surrounding gear and any other electric gear, power cords or appliances results in any change in the buzz level. If so, take note of where noise level is minimal and use that to help identify what the external source of the noise might be. Repositioning gear alone might be a practical solution. The further each piece is away physically from each other and other potential noise sources, the better. Flourescent and halogen lighting as well as dimming devices are also often culprits for causing noise and interference with other devices, as are many digital devices and devices with large power transformers, like many power amps for example. Use of mu-metal sheets to provide additional isolation is another cost effective option to help in many cases. I use mu metal as an external barrier around my phono step up transformer device. Low level phono sections/gear are the most noticeably sensitive usually to external sources of noise.

No doubt very high sensitivity speakers like Avantegarde up the ante in terms of need for that feeding them to keep noise levels minimal.

Wow, lots of good suggestions on possible cause of, and solutions to, the noise problem. I personally had a problem with hum and buzz that came from a different source. Although my audio system and video system are separate, they share the same branch of power from the main panel. When my system seemed to suddenly develop a noise problem, I looked at the usual suspects and then tried something else. I cut the 75 ohm cable feed to the video system. That completely cured the problem. It appears that the cable feed managed to contaminate the power line even though the buzz/hum was not that big a deal with the video system (audio system is relatively high in efficiency, and thus, more susceptible to noise issues). Even though the entire video system was itself on a Furman power conditioner, the noise managed to infect the power feed to the audio system. I tried isolation transformers on the cable feed, but that did not work. The problem had to be cured by the cable company.

Yingtonggao, just set the input impedance of your FL100 to the max, which is 57kohm and feed your AMR DP-777 straight in and use it's volume control, which quote is a "Direct-Coupled Analogue Volume Control." No extra caps in the signal path.
This will be the most transparent/dynamic sound you will get PERIOD! As it is basiclly then a straight wire from the 777 to the fl100 then (no impedance mismatches). And you will have bags of gain left over still on the AMR's volume control.
If after that you still prefer an active preamp, then it's the colouration/distortion of it you like, which is a bandaid fix for something else that's wrong. Remember it is impossible for an active preamp to extract any more music than what is on the disc and being presented by your DP777, it can just add artificial things, as it does not make music itself.

Cheers George

Just got an email from the maker of the FL100 and your amp is also dc coupled. No caps in the signal path from your DP777 volume control all the way to the speakers, that is a big plus always.