Monday, February 8, 2016

A Delicate Balance

A few days ago a customer asked me about using the Eminence 820H speaker in the Memphis Mini amp.  I tried that speaker long ago and considered offering it as a substitute speaker but I had to reject it:  The 820H comes only as a 4 ohm speaker and the MM amp expects to see an 8 ohm load at the speaker tap.  This would cause the amp to run hot, leading to transformer failure.  Nobody likes to see smoke coming out of the back of his amp.

Any amp based on the Classic 5 platform will have the same problem unless the builder has gone to the considerable trouble and expense of swapping out the OT to accommodate the 4 ohm speaker.  Even worse, if you are running a 6L6 power tube along with the 4 ohm speaker you are likely to burn the power transformer. 

We have hundreds of Memphis Mini amps in use, many for up to two years on stage.  We know what works and what doesn’t.  A well-designed vintage-style tube amp is a Rube Goldberg contraption of moving sonic parts that work together to produce a wonderful tone.  It can be a delicate balance.  Ask your amp maker before using a lower impedance speaker or bigger power tube.  It could fry your amp.