Tubes can hiss. It's a common problem. You can try different tubes one set at a time (preamp tubes, power tubes). That's where I would start.
These are good suggestions but this problem is different. It seems like the hiss is coming from the preamp because I don't hear it when the preamp is muted or off. But if I use a different amp, I don't hear hiss at all. I've swapped tubes. That's not the issue. It seems like something incompatible between the Lamm and the Ayon. I'm going to try another preamp next week.
How are you connecting the Lamm preamp -- via the direct in or one of the selectable inputs? I looked at the specs for the Ayon and they don't say what the input sensitivity is. It could be that it is a mismatch for the Lamm. If you are using direct in, try switching to one of the selectable inputs and then reduce the volume on the Ayre until the hiss goes away. This will mean that you'll need to turn the volume on the Lamm up higher.
If you are using the selectable inputs on the Ayon, it could mean that the preamp tubes are aging and need to be replaced, or once again, just a mismatch with the Lamm.
Thank you @mlsstl!
I just realized there is a gain switch on the back of the Ayon and a attenuator switch on the Lamm. By reducing the gain on the Ayon and going to -15 on the Lamm, the hiss is almost gone. I've learned over the years that with tubes you're never getting a completely silent idle. Just didn't want to hear it from 10 ft away!
System gain structure. This happens when you have high gain preamp, high gain amp, and sensitive speakers in various combinations (usually 2 or 3). The signal-to-noise ratio of the preamp really matters here. Tube preamps and tube amps tend to have higher gains, combined with lower signal-noise ratios. Hence the hiss.
You can mitigate the hiss by adding inline attenuators between pre and amp (e.g. 10dB), and then raising volume to match your prior levels. This works "like magic" because you’re mitigating the noise floor from the preamp by re-apportioning some attenuation from before the circuit (the volume knob) to AFTER the circuit. In either case, you’re throwing away the same net amount of gain, but it matters WHERE this happens - because in the latter case you’re now also throwing away hiss noise generated by the circuit itself!
Then of course not all preamps are equal on signal-noise ratio - tube gear is especially diverse in this matter. I’ve had some super high gain tube preamps that were much quieter than lower gain tube preamps from a different manufacturer! The ARC Reference preamps have an exceptionally good signal-noise ratio for tube gear (I think it may be helped along by a few SS parts though). VAC preamps also tend to be pretty stellar here, and are pure tube.
@dhcod -- glad you found a solution! One thing about amps and preamps is that there are no universal standards regarding gain and sensitivity. This can make certain combinations of preamps & amps problematic, though the issue can usually be fixed with some experimentation.