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jessie.dazzle wrote:

For now, the amplifiers I use are a pair of Lamm M1.1s (was going to look for a pair of used ML2s, but more and more considering building a pair of Meliquaides). Using the M1.1s with a pair of V.A. Parsifal/Encore (direct radiating) speakers there is a little background hiss, but nothing you would hear from the listening point.

First of all about the Lamm M1.1. It is a common knowledge that SS PP amps is very much not the correct amp to use with horns but here we enter a little secret of mine. It is known that ceramic drivers do not do good HF and particularly in horns. However, when you drive the ceramic horn driver with SS PP amps then the drivers begin to sing. I had some very good results with Lamm M1.1s and various none-alnico drivers.

jessie.dazzle wrote:

However with the S2s, this background hiss is much stronger; the level is constant and does not rise or fall with volume adjustment. It can be heard from well beyond the listening point. The hiss is equally present in all (4) S2s I have, so I don't think it is a question of the driver. With the S2s I can hear much further "into" the hiss, and observe all kinds of detail (fluctuations in the electricity?).

Jessie, this is very normal behavior of S2. The S2 has 22dB more sensitively then Parsifal/Encore. In addition you drive S2 with 20 times more power and gain then they should be driven, and with the amp (Lamm 1.1 that is not partially quiet. What do you want form those drivers. They have no noise  - then juts present to you what was given to them.

jessie.dazzle wrote:

The hiss remains when disconnecting the ground wire for all circuits powering the system. My question now is... Do other S2 users have the background hiss when using appropriate SET amps? Is it possible that the M1.1s generate more hiss? I should also mention that the associated preamps are either an L1 or an L2. I recently replaced all tubes in both pre and power amps (hiss present with both L1 and L2, so the preamp is probably not the source of the hiss).

Ok, what you have for noise perspective is the worst combination for a high sensitively system. 80% of your noise comes from Lamm L1 or an L2. They are MOSFET preamps and MOSFET have own MF output noise that is not depending form the volume control (it is not gain noise but the indispensable MOSFET noise). It is not auditable with 90dB sensitive acoustic system but with 110dB sensitive and too much gain in power amplification the noise is right in your face. Bypass the Lamm preamps and you loose most of the think MF hiss. The minor noise that will be left will be own Lamm M1.1’s noise. This amp is also quite noise for high sensitively speakers. The solution could be various. Find low noise 5W-10W power amp and drive it with Lamm preamp. The amplitude of the hiss will go all the way down. Bypass the Lamm preamps and use any low power amps and the noise will be gone for good. In the end do not forget the S2, according to this paper has 10W max power handling. Could you believe now severely you discharge this magnets when you drive them with 110W of PP power? Anyhow, even with Lamm preamps and reasonable power/gain power amp (20-24db no noise gain) you will not be able to be bothered by Lamm L1 or an L2 MOSFET’s hiss. ML2 is very-very quite amp, virtually silent, there are many other SETs… but when you go into the world of properly assembled (and consequentially quietly operating) single ended amplifiers then you will not have any hiss issues with your S2 drivers.

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