Amplifier design parameters required for a good match for high (16+) ohm speakers?
Most SS amp will output half the wattage @16ohm than @8ohm, you
need to check if a amp has enough output power to drive the 16ohm speaker to
desired
loudness/SPL. https://www.crownaudio.com/how-much-amplifier-power |
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 |
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. |
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. |
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. |
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. |
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 always found that the ST-70 played better bass if it was possible to use the 16 ohm tap. This is assuming of course that the speaker was at least 16 ohms in the bass region! The power rating of the amp actually goes up a watt or two as the output transformer is more efficient when used on a 16 ohm load. |
Rodman, my ST-70 has the 5AR4 rectifier tube made by GE, and the 7199 driver tubes made by Conn in USA. Currently using JJ EL34 output tubes. I know the JJ EL34 could be replaced with a smoother tube. Any particular Mullards you might recommend? Ralph, I am using the 16ohm output with the Contrasts, which are rated at 16ohms. I am not sure about actual impedance within the bass frequencies. |
If I still owned an ST-70, I’d be forced to purchase four of these(Did I mention, "salty"?): https://www.tubedepot.com/products/el34-mullard-double-o-getter-welded-plates I might be disposed to try the NOS, 1970s, Siemens version, toward the end of this page(and keeping a matched pair in each channel, if a matched quad couldn’t happen): http://www.audiotubes.com/el34.htm That page contains a lot of good info, if you’re going to shop EL34 types. How old are the Conns? Assuming you enjoy experimentation, here’s an easy/inexpensive way to enable you to try various NOS 6U8 type tubes(cheaper and more plentiful than the 7199), in your amp: https://tubedepot.com/products/6u8-to-7199-adapter Should you find a 6U8 tube, the sound of which pleases your tastes(Tung-Sol made some nice ones, in the 60s), it’s simple to move a couple leads on the tube sockets, obviating the adapter. https://tubeworldexpress.com/collections/preamp/6u8a Again- if the power supply capacitance is still stock(or aged), it’s still inadequate(by modern standards). Have fun and happy listening! |
@jroberson did you get an alert or is there an email in mailtrap? |
what about user @mesch |
@jroberson @robersonj2 did any of those get notifications? |
