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RE: TU-879S and TU-875 mods

Change to ultra-triode connection
When you add a small signal transistor to the first stage, it becomes an ultra-triode connection by using the 12AX7 triode as the feedback device. (See below.) You can obtain high quality bass as this will reduce distortion drastically - home page for the ultra-triode connection.

Reduce the amount of NFB or turn to no feedback
You can reduce the amount of NFB by increasing the resistance Rnf towards triode cathode that is running NFB from the secondary output transformer. (In reverse, the amount of NFB will be increased by decreasing the resistance. This is not recommended as the performance will not be stable.) Once you remove Rnf, it becomes a non feedback amplifier. (Cg can be removed if it is preferred.)

Advantages of NFB:
Better frequency response, less distortion, less gain or voltage drift,

Disadvantages of NFB:
Less gain.
Possible oscillation if not properly designed.

Regarding TU-875:The chasiss of Tu-875 is too small to add 3 or 4 bank eq.

Edits: 10/23/11

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  • RE: TU-879S and TU-875 mods - vkung 21:19:12 10/23/11 (0)


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