Also note many tried to drive low imp speakers with Futterman OTL which looked for high imp ( such as KLH Model Nine 16~30 ohm ) loads. When driving low imp designs when the impedance dipped to 4 ohms or less it would oscillate. ALL speakers have a varying impedance, it depends at what frequency is being delivered to the speaker when the measurement is being taken.
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Early ones had stability issues. http://www.atma-sphere.com/Resources/OTLs_Defined.php Reading more, it seems JF improved the circuit and fixed the issue. |