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OTL, Output Transformerless Amplifier User Group.

RE: a jolt

Obviously Direct Drive amps are the correct way to drive and ESL. The Model 3 requires 750 Volt-Amps (VA) to play Miles Davis at high levels. The problems with transformers are many and the load presented to a conventional amplifier is about 1 ohm at high frequencies. The transformer I designed for the Model 3 added quite a bit to that load due to winding capacitance. Since the load is capacitive it causes transistor amps with load line limiting to clip at low volumes, this is why ESLs are best driven with transistors with no limiters, but those are rather rare. No wonder tube amps tend to drive ELS as they have no limiters but now we are going through two transformers and still not enough current. Low voltage OTLs, though some like them, are not the best choice either as they cannot supply any where near the high currents required by a 1 ohm load.

The virtue of an DD amp is its high operating voltage. At 1500 volts one needs only 1/2 amp to get the 750 VA required to play trumpet music. I only make these amplifiers for sophisticated users who are comfortable with high voltage.

On the safety factor let me remind all the high voltage DC is not the same as AC. Its not the voltage but the current that matters and it's path through the body. AC causes the heart to fibrillate and DC defibrillates (as seen on TV with the paddles). I have unintentionally taken a shock across the chest several times. Most recently with 3 KV on a Bev 2SW amp from arm to arm and more recently while packing the amp being discussed here by a similar voltage. All got was a burn the size of a pin head on my finger and a jolt. I said one bad word and moved on. If used normally the warm tubes will discharge the B+. The polarizing has to be discharged manually but it is DC in a capacitor.

One should be careful while playing music however as that is AC, but only the bass is dangerous around 60 HZ. High frequencies are not as dangerous.

There are far more dangerous things around us every day. Of course we dont want a child or pet to stick there nose in these things. You probably dont want them in near your turntable for obvious reasons.




Edits: 05/06/16

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