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In Reply to: RE: Tube amp driving speakers w/ unstable impedance posted by mondial on August 02, 2016 at 23:07:09
Not too many amps have 16 ohm taps anymore!
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-and it matters not whether the amp is tube, solid state or class D. You can see this in the specs- distortion is always lower into higher impedances.
The distortion is usually higher ordered harmonics, which are very audible to the human ear as brightness and hardness.
Of course transistor amps don't make as much power, but they become easier to listen to.
distortion is always lower into higher impedances.
That doesn't seem to be the case with my VTL amps according to this Stereophile test .
It's true at low power levels, but not at higher ones where the distortion differences are wider and a 4 ohm load seems to work best.
Yes- that is true in your case as the VTL does not have 16 ohm taps. If it did though, not only would the distortion be lower but the output transformer would run cooler as it would be dissipating less power. You would also get more bandwidth, maybe even as much as an octave on the bottom.
...as it would be dissipating less power.
Actually, there are times when I really would like more power to handle really dynamic works.
You would also get more bandwidth, maybe even as much as an octave on the bottom.
Actually, that would not necessarily be desirable in my case. I get flat to 30 hz in-room response already (see my gallery) and sometimes it is excursion limited at higher outputs.
If the output transformer is dissipating less power what that means is more power is available to drive the loudspeaker.
It is more this reason that nearly all tube amps that have a 16 ohm tap will make more power into a 16 ohm load than they will into 8 or 4 ohms even if they have the taps for it. Mind you, its not a lot but there is a difference.
More bandwith usually translates to less phase shift. In a nutshell its a pathway to sounding more like real music.
It is more this reason that nearly all tube amps that have a 16 ohm tap will make more power into a 16 ohm load than they will into 8 or 4 ohms
Perhaps that's great for speakers with broad band high impedance. Mine, however, are not.
They are at or above 16 ohms for the first octave only. From 100 to 10k, they range from 8 ohms down to 3 ohms where it continues to dip above that frequency.
-So any tap would be a compromise.
Hence my moniker. :)
Sound Lab U-1PX
We've showed with Sound Lab a bunch over the last 30 years...
That speaker has a peak in the bass of about 30 ohms. Since the VTL runs a bit of feedback (tends to act like a voltage source) I would expect it to run a bit bass shy. How do you have your jumpers set?
I also run Acoustat 1+1s in the home theatre system. Again, pics are available by clicking my moniker and following to the galley. I became an instant full range electrostatic fan when I first heard Dr. Cooledge's (JWC of TAS) Dayton-Wrights when I was a teenager. While not perfect, they sounded so "right" on most content. I purchased my first pair of Acoustats when I was 20 in '77.
We've showed with Sound Lab a bunch over the last 30 years...
I heard Brian Walsh's pair driven by a pair of your MA-2s. Sounded perfectly wonderful, but occasionally clipped them on demanding material.
I would expect it to run a bit bass shy.
That may well be the case for a Virgil Fox fan. :)
With my previous front end arrangement of GamuT CD-1 direct to amps via attenuators, I was getting flat to 25 hz in room response. When I switched to using a Touch as the player, I lost a few cycles. With my current Sonore µRendu, I sense the bottom octave has been restored. As for me, I find the results completely satisfactory. I need to perform the test again with the current setup.
Here's the third octave plot with the GamuT player:
How do you have your jumpers set?
Jumpers? If you refer to the three rotary controls on the backplate, they are all set to their nominal flat settings.
-
Aren't speakers voltage driven? Speaker manufacturers quote the voltage sensitivity, not the power sensitivity. While the power of a transistor amp into 16 Ohm will drop, its voltage swing will not.
A 16 Ohm speaker will have 3dB less voltage sensitivity though vs an 8 Ohm one.
Well a speaker's excursion is proportional to current, not voltage. Current and voltage are also proportional - but there's some nuance. If you connect a low impedance load to a voltage source that can't supply the current at the designated voltage, the voltage will drop to match the current it can supply (or perhaps your source will fry or catch fire).
How that relates to matching amps and loudspeakers, a bit above my pay grade.
They are the same if the load is 8 ohms.
If 2.83V into the load:
4 ohms is 2 watts
16 ohms is 1/2 watt
Hi BCR ,
The big amps of ARC still have the 16 ohm tap ( REF 150SE , 250SE , 750 ) My 610T also has them .
Mondial
Hi Mondial,
You are lucky ,like I said, very few have that option.
BCR
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