Heat issue with Lamm M1.2 Reference

I'm having a heat issue with one of my Lamm M1.2 Reference mono blocks or rather a lack of heat.

One of them is suddenly putting out less heat than previously, especially at the rear of the amplifier, where it is almost cold to the touch even after 3 hours of playing.

Neither my wife nor I noticed any difference in the sound tonight, but we were playing soft music all evening so nothing to really challenge the amps.

Anyone experienced anything like this before? Any thoughts on the cause?


You should contact Lamm. If the two amps are operating at different temperature under similar conditions I would suggest the bias needs to be adjusted. I had a similar situation with a Classe amp in which one side was warm while the other was extremely hot. I contacted Classe for bias adjustment instructions. It seemed straight forward enough so I made the adjustment. After setting bias both sides operated at same temp.
Although the temperature was noticeably different I hadn't noticed a sonic degradation.
Something wrong happened for sure. It could be that half the tube went bad - I've had some tubes test bad but their sound was still good. Not sure how that happens but I have experienced it twice. You could replace the tube and see what happens. While you are at it, check for fuses on the main board. If after that it still doesn't work normally, it's time to call Lamm.

Interesting observations. Thanks, Arthur and Tim.

I was checking Lamm's web site and saw this feature of the 1.2
The M1.2 Reference is a masterful blend of design and engineering simplicity. It is a pure class A amplifier featuring high-speed MOS-FET transistors in the output stage with no overall feedback and special switch-selectable bias/voltage settings for 8- or 4-Ohm operation. The bias setting switch assures the pure class A operation of the M1.2 Reference when matched with a speaker load of either 4 or 8 Ohms, whereas conventional class A designs double the power into 4 Ohms resulting in one fourth of the doubled power in class A and the rest in class AB.
Are the switches in the same position?
Yes, Tim, the switches are both in the 4 Ohm position and my Wilson Sophias are 4 Ohms.

I'm going to shut them down now, let them cool off and later today replace the tubes, then try them again. If that does not work, I'll call Lamm on Monday.