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Amplifier design parameters required for a good match for high (16+) ohm speakers?

Though I have a reasonable understanding of, or at least am satisfied with, the requirements for an amplifier asked to drive low impedance speakers, I am wondering about specific design parameters that might need be considered when mating an amplifier to high impedance ones. Asked another way: Are there specs that one should seek out when searching for an amplifier to be mated to such speakers?
mesch
audiokinesis
2,750 posts
 

As long as the amplifier has enough power that it won’t be clipping into the 16 ohm load, it should work just fine, unless there is some other mis-match going on.

I have made speakers that are user-configurable as either a 4 ohm load or a 16 ohm load. As long as the amps weren’t pushed into clipping, to the best of my knowledge all of my customers who tried it both ways preferred the 16 ohm configuration. I have been told by multiple amplifier designers that distortion is lower into a high impedance load.

At least one amplifier designer, Ralph Karsten of Atma-Sphere, recommends high impedance speakers particularly for his lower-powered OTL (output transformer-less) amps, which unlike solid state amps actually make MORE power into a 16-ohm load. If you haven’t already, I suggest taking a look at his amps. (Disclaimer: I’m a dealer for Ralph, and have been making speakers with his amps specifically in mind for 14 years.)

Duke

mesch OP
3,527 posts
 
Thanks for the responses. 

I am using a Dynaco ST-70 (35wpc) into Contrast Model One As3 speakers having a rating of 16ohms and 92dB sensitivity.  I believe the sensitivity rating might be a little high, even considering that 92dB equates to 89dB with an 8ohm speaker. I have no knowledge about the impedance across the frequency range, however the manufacturer states that it does not vary much.

I guess then, when considering an amplifiers rating into an 8ohm load, one should half that rating into a 16ohm load as a way of assessing that amplifiers ability to provide enough power for a particular circumstance.  

I might add that Ralph of Atmosphere refurbished my ST-70. 



 

rodman99999
6,171 posts
 
Your Dynaco ST-70 is a tube amp. While SS amps reduce output, as speaker system impedance rises, the typical tubed amp does not(given a correct impedance match/output connection). You might find this article enlightening. Especially, the comments immediately below graph 7, regarding output and distortion figures, into various loads. https://www.stereophile.com/content/dynaco-stereo-70-ii-power-amplifier-measurements Use your 16 Ohm tap, for best results.
mesch OP
3,527 posts
 
Rodman, Thanks much for your input and the link. I can't believe I did not find this review myself. It seems that the input impedance of this amp is not the reason I didn't find it as enjoyable using a Schiit SYS passive pre as with my Jolida active pre. Bass was lacking with the SYS.

I have always know that he tube rectifier in the original ST70 was a weak link. Though I would not want to replace with SS rectification. This was why I spent so long looking for a high impedance speaker to use with it. I was also looking to find one with greater than 92dB sensitivity. I have been using the 16 ohm taps with the Contrasts. I have used the 8 ohm taps with other 8ohm speakers, however approached use with them with caution as they all drop below 4ohms in the bass region. I never considered these speakers ideal for this amp.
rodman99999
6,171 posts
 
Does your ST-70 still incorporate the 7199? If so- not much available, as far as tube rolling, now days. The EL34/6CA7 has never been known for a lot of dynamics, regarding bottom end. Sylvanias or Mullards, are what I had always kept in mine. They were much more plentiful(and- way less salty too), back then. No experience with what’s being manufactured now, so- can’t comment on their bottom-end performance. What rectifier are you using?  The Mullard(Blackburn plant)GZ34, is what I always recommend. Not that it offers any more juice, but- that it sounds so nice and lasts so long. I tried SS rectification(didn’t like it). You might contact Ralph and ask about beefing up your power supply(capacitance, etc), if that wasn’t already part of his refurb work. It’s been my experience, upgrading power supplies has always resulted in improved reproduction/greater dynamic impact, across the board.
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