| Update on Previous Info on Oddwatt Amp issue [message #97474] |
Sat, 02 March 2024 20:35  |
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gofar99
Messages: 1903
Registered: May 2010
Location: Southern Arizona
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Illuminati (5th Degree) |
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(also posted on diyaudioprojects.com) Hi everyone. This is an update of a potential long standing issue. In the past 16 years there have been numerous variations and sizes of Oddwatt amplifiers. All share one design feature that may or not be known by all builders. Since it has been some time since I mentioned it, it seemed now would be a good time. Especially as it just occurred to a new builder. They all use the output transformer to invert the signal in the power output stage. This makes the amp non-inverting and ensures the phase of the small amount of NFB to be correct. If the phase is not correct the amplifier will sound thin and lacking in bass and possibly unstable. At least one set of early instructions pictured the primary side wires on the output transformer going to the wrong tube. If you use Edcor transformers the tube that receives the signal from the driver uses the brown wires. The blue ones go to the slave. For other brands of transformers, they are often marked on the specs with a dot. This dot would correspond to the blue set of wires on the Edcor ones. I hope that no one has been listening to an amp with the incorrect phase. A way to tell on a built amp is to temporarily disconnect the feedback loop. If the phase is correct the sound should get a little louder. If it get quieter then the phase is wrong.
Good Listening
Bruce
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