rogers cadet opt replacement

[Paul Rayson]

Hi everyone, I have built a rogers cadet 3 power amp, I have used replacement opt transformers that only have 4 + 8 ohm speaker connections, is there anybody who can help regarding the feedback connection to 8 ohms as it comes from a 15 ohm terminal. Many thanks, Paul

 

[Eli Duttman]

The key fact to getting the requisite value adjustment is that the impedance ratio is the square of the turns ratio. Remember, the signal at an 8 Ω tap has been stepped down further than the signal at a 15 Ω tap. Therefore, the % of the O/P voltage fed back has to be reduced.

 

[Alan4411]

I think the answer will be the same as previously mentioned.
rogers cadet

Without test gear trial and error. Reduce the value of the resistor used for 15 ohm (6.8k). Try 100pF to 390pF in parallel.

 

[Steve Morley]

Did you try what was suggested in your previous thread? What was the result? Don't get to bent out of shape about it. Put on some music, open some wine (or whisky) and enjoy!

 

[Galu]

Worth compensating when going from 15 to 4 ohm, but going from 15 to 8 is not worth losing sleep over.

It can do no harm to your amplifier if you experiment in the way that's previously been suggested. Simply adjust for best audible result.

 

[Alan4411]

We should mention too, that if you get oscillation with the feedback connected (anything from a loud squeal right down to a low rumble) then reverse the 2 primary anode connections. So do not use your best speakers for initial testing.

 

[Paul Rayson]

Thanks to all of you