Unity coupled power stage

[tecnophil]

Hello,

I am a new member ,located in Germany 49 years old and since the age of 14 I have been fascinated by some glowing parts in a radio.
After some years of being occupied with other things, I would like to build another tube amp.
I have been attracted by a design called "unity coupled" formerly used by McIntosh.It seems that it might be possible to design a tube amp with all the advantages of such a unit combined with a higher damping factor than in conventional tube amp designs.
I own some Telefunken V69's and like them much but would prefer a better speaker control the low frequency range.
Has anyone made some experiences with a unity coupled design,perhaps with the Van der Veen toroidal output transformers?

Greetings from Germany Ralph

[Eli Duttman]

If you are going to get involved with unity coupled design, study Frank McIntosh's designs, like the MC240.

Completely different in topology is the Harman/Kardon Citation II, but it too controls woofer voice coils very well. Plitron offers toroidal O/P "iron" with the bandwidth needed to "replicate" Stu Hegeman's design.

[smoking-amp]

Jan V. did a Mac project:
BigMac, Unity coupled output amplifier

Likely some threads here on diyAudio too. Seach for McIntosh or CFB or unity gain.

[Bandersnatch]

search also for 'LW6-180' an design using TV sweeps.

The unity coupled design requires large drive voltage swing; it is moderately troublesome. There are a few ways to solve it. Examine the 12BH7 part of the McIntosh circuits( on the 75/275 for example ). There is positive FB there to deliver the headroom required. One can deliver the headroom without positive feedback by substituting a CCS for the 12kOhm resistors( the 12BH7 plate loads ).
cheers,
Douglas

[tecnophil]

Hi,

thank you for all the answers.I knew that the unity coupled design is a bit tricky because of the recommended high voltage swing for driving the output tubes.I considered a common cathode phase splitter as first stage followed by a mu stage driver in combination with a white cathode follower.(comments welcome...)When I find the time needed I will mount these stages for doing some measurements before buying the "iron".

Ralph