JoaMat

Happy Birthday!

Yes, heat sinks and front/rear panels are from modushop.biz. Brackets and aluminum plates for top/bottom covers from local shops. Drilling, tapping and other crafting done in kitchen.

Today I joined the Qobuz family. They don’t like Sweds but with a little from NordVPN they think I’m an English Brexiteer. Found this on Qobuz - in flac 96kHz 24bit: Esbjörn Svensson Trio - Live in Gothenburg

I have been using Roon for some time now and I really like it. Roon points at (my own library and Tidal) 300+ tracks of Bye Bye Blackbird – and Sarah Vaughan did one in Tokyo, 24 September 1973?. 2CD - great album.

The new T2 has behaved in a good manner for a whole month. Now qualified for old good tubes... ...Amperex Bugle Boy to the left and Brimar to the right.

Great! …then I found this...

FedEx came an hour earlier than expected. One amplifier has now “new” op amps OPA197. The other has new OP27, one channel with 10K instead of 25K at -input pin. So now I just have to wait and see. I expect the OP27 with 25K resistor to fail sooner or later. For the rest - wish me luck!

and

No, that’s no nonsense. I’ve been thinking of that possibility as well. But… There is the balance servo also OP27 on the same power lines which works alright. Second, the offset servo works and keeps the balance quite stable but not at zero as supposed. When I built my three layer Carbon a few years ago I experienced the same problem with offset OP27. So until today I’ve had five OP27 deteriorations/failures. Anyhow, ordered LF356 and OPA197 with same footprint as OP27 today. Expected to arrive on Friday 1 p.m.. According to OPA197 datasheet the OPA197 has an unique input protection. As I understand OP27 has diode input protection that might be less robust than OPA197’s input protection… but this is probably well beyond my understanding.

My two mini T2 have been working for half a year now. I’m still pleased with them. But when I checked the outputs I got offset voltages for all four channels in the range 2 – 20 volts. They should be close to zero. After some investigations I found that all OP27 measured zero volt between + and – input pins in diode test mode both ways. After replacing opamps the offset and balance are perfect again. I’ve no idea why four opamps have deteriorated. But I do feel that it will happen again so I appreciate any ideas and thoughts that could make the offset servo more reliable. Below is schematic of the offset servo. Reduce resistance of R38 to 10K? Look for another opamp? More?

nice cars... ...