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OTL, Output Transformerless Amplifier User Group.

RE: Questions

>What treble transformer are you using? The original toroid or the new toroid from SL?

Both treble transformer and bass transformer are original ones.

>What would be unsafe about removing the 8-ohm resistor?

In Dr. West’s article, the impedance of speaker can be close to 1 ohm without RC filter if I recall it correctly. Therefore, I think it is safe to connect a 8 ohm resistor in parallel with treble amplifier’s output.

>With either of the two SL transformers, you probably would need a capacitor in series, to create a hi-pass filter, but not the resistor.

You are right. I have tried to use a capacitor in series to create a hi-pass filter. But the sound is not as good as without hi-pass filter unless I can find a capacitor without any sonic signature. There is a dip at about 300 hz without the capacitor in series. But I just don’t want to give up the improvements for sound to get smooth response. I used a electronic crossover before but not now. Please see the image above.

>I am surprised if you are using either of the SL toroids and NO capacitor that you are not having issues, but that's good news, if so. I am assuming your 8R resistor is in parallel with the amplifier output; yes?

So far, all things are fine. But I do realize that the frequency response is not as smooth as with a capacitor as I mentioned above. I also used a swatch to change the inputs of toroid so I can increase +3db output if I need to.

>What amplifier? This is most important, because if you are using a solid state amplifier, then you ARE probably better off with the 8-ohm resistor. With a tube amplifier, no.

I use Wolcott P400’s for high frequency and Spectron Musician III for low frequency.

As I know, the original SL transformer's low frequency limit is 400 hz. I am wondering if I can connect two original SL toroids in parallel so two toroids act as one to further extend its low limit.



Edits: 05/11/14 05/11/14 05/11/14 05/11/14 05/11/14

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