Dennis Had Inspire Amps...what speakers are you using?

[Bombadil]

A very basic question, but I can't recall knowing the answer.

Are the Inspire amps optimized for 4 ohm or 8 ohm speakers?

[bearcity]

Originally Posted by Bombadil

A very basic question, but I can't recall knowing the answer.



Are the Inspire amps optimized for 4 ohm or 8 ohm speakers?

This quoted from his latest add,

“DESIGNED TO DRIVE LOUDSPEAKERS IN THE 90 dB SPL RANGE OR BETTER AT 2 OHMS TO 20 OHM IMPEDANCE.”

[Bombadil]

Originally Posted by bearcity

This quoted from his latest add,

“DESIGNED TO DRIVE LOUDSPEAKERS IN THE 90 dB SPL RANGE OR BETTER AT 2 OHMS TO 20 OHM IMPEDANCE.”

I was hopeful of getting a bit more information.

There is no way a SE tube amp can deliver the same amount of power from 2 ohms to 20 ohms. Nor will it be as linear over such a wide range of impedance.

This is why many tube amps provide multiple taps.

Look at Stereophile tube amp measurements. They vary wildly into different loads. For example they tested the Cary CAD-805RS single-ended amp with 845 tubes. At 3% THD they measured a max of 13 wpc into a 4 ohm load and 31 wpc into an 8 ohm load, both of these were measured with 10db of feedback.

When set to no feedback, they measured 10 watts max power into 4 ohms.

Note that Cary advertised the CAD-805RS as being a 27wpc amp.

So this Cary SE amp produced more than double the power into 8 ohms. They recommended using the amp with high impedance, high efficiency speakers.

[bearcity]

Originally Posted by Bombadil

I was hopeful of getting a bit more information.

There is no way a SE tube amp can deliver the same amount of power from 2 ohms to 20 ohms. Nor will it be as linear over such a wide range of impedance.

This is why many tube amps provide multiple taps.

Look at Stereophile tube amp measurements. They vary wildly into different loads. For example they tested the Cary CAD-805RS single-ended amp with 845 tubes. At 3% THD they measured a max of 13 wpc into a 4 ohm load and 31 wpc into an 8 ohm load, both of these were measured with 10db of feedback.

When set to no feedback, they measured 10 watts max power into 4 ohms.

Note that Cary advertised the CAD-805RS as being a 27wpc amp.

So this Cary SE amp produced more than double the power into 8 ohms. They recommended using the amp with high impedance, high efficiency speakers.

From Dennis just now, "To answer the output impedance question …. Nominal output matching impedance design center is 9 ohms on most Inspire amplifiers."

[Bombadil]

Originally Posted by bearcity

From Dennis just now, "To answer the output impedance question …. Nominal output matching impedance design center is 9 ohms on most Inspire amplifiers."

Thanks. That is great to know.

[Bombadil]

Originally Posted by bearcity

From Dennis just now, "To answer the output impedance question …. Nominal output matching impedance design center is 9 ohms on most Inspire amplifiers."

Not that Dennis needs any validation or that I am qualified to pass judgement, but I will say that setting the optimal output impedance to 9 ohms is a very solid decision.

I suspect that Inspire SE amps produce somewhat less power into 4 ohm speakers than for 8+ ohms. This can be a concern as 4 ohm speakers need more power to reach higher volume levels. Note that speaker sensitivity specifications are derived from measuring how loud it is when driven by a 2.83V signal and at a distance of 1 meter. 2.83V into 8 ohms is 1 watt. However 2.83V into 4 ohms requires an amp to produce 2 watts.

Consider the Cary CAD-805RS which I mentioned earlier. It was measured as producing 31 watts into 8 ohms, but only 13 watts into 4 ohms. If one was driving 4 ohm speakers with the 805, not only would the amp be producing significantly less power, the speakers would need more power to reach a particular volume level. Thus a system with an 805 and 8 ohm (or higher) speakers would be able to reach much higher volume levels and have much more dynamic headroom.

An example: Say one has an amp which produces 8 wpc into an 8 ohm load but only 4 into a 4 ohm load. A person owns two sets of speakers, both measured at 93 dB, one is 8 ohm and the other is 4 ohm. Both measurements are industry standard 2.83V at 1 meter. So to hit 93 dB, the 8 ohm speaker requires 1 watt whereas the 4 ohm speaker requires 2 watts. With this combo of amp & speaker(s), the amp is capable of driving the 8 ohm speaker to a maximum of 102 dB, however can only drive the 4 ohm speaker to 96 dB (2 watts needed for 93, 4 watts needed for 96).

This isn't as much a concern for most solid state amps, as they double (or close to it) their output into a 4 ohm load. Many (most?) push-pull tube amps produce more watts into 4, 5, or 6 ohm loads. But many single-ended amps do not.

[Isaacc7]

I'm curious how the output impedance plays onto this. I can run a wide variety of output tubes with the firebottle kt88 and they have a significant spread in output impedances. My speakers have a nominal 4 ohm load and are rated around 90db sensitive. I tend to listen at fairly low levels, when I rock out I might hit 86db from 8 feet away.

After trying lots of tubes, kt88, 7581a, 807, 6ar6, el38, I have settled on the 6v6 sounding the best to me. The best bass, tonal balance, etc. Haven't noticed any issues with power but I assume that's because of the modest volumes.

I'm pretty sure the 6v6 have the highest output impedance out of all of the tubes I've tried. I'm left scratching my head because if the amps are optimized for a 9 ohm load and my speakers are 4, surely tubes having lower output impedance would be better right? I would expect the kt88 to be the best but it actually sounds kind of thin. Or am I thinking about this all wrong? Maybe what's more important is the speaker impedance at specific frequencies?

I like how my system sounds with the 6v6 and that's the most important part. I would like to understand why though.

[Jdsmoke]

I recently picked up a Firebottle amp and was looking to use a Bluesound Node as the preamp. Has anyone tried this combo? Any concerns? I’m paring w Klipsch Heresy IV. It’s set up for low volume/background listening via streaming in my bar area.

[Bombadil]

Originally Posted by Jdsmoke

I recently picked up a Firebottle amp and was looking to use a Bluesound Node as the preamp. Has anyone tried this combo? Any concerns? I’m paring w Klipsch Heresy IV. It’s set up for low volume/background listening via streaming in my bar area.

You should be able to do it, but note that the Bluesound Node is a lower-quality preamp (and DAC). They use lower quality parts throughout the preamp & analog outputs, power supply, and DAC. However it does stream very accurately (when run to an external DAC) and has good control software.

When measured on test equipment the analog output from a Node was roughly 14-bits. So even if you stream 24-bit files, you will be listening to 14-bit resolution unless you use an external DAC.

[Jdsmoke]

Originally Posted by Bombadil

You should be able to do it, but note that the Bluesound Node is a lower-quality preamp (and DAC). They use lower quality parts throughout the preamp & analog outputs, power supply, and DAC. However it does stream very accurately (when run to an external DAC) and has good control software.

When measured on test equipment the analog output from a Node was roughly 14-bits. So even if you stream 24-bit files, you will be listening to 14-bit resolution unless you use an external DAC.

Thanks - I didn’t know this. It’s mostly for Spotify so I will have to try this out and assess if I need an upgrade on the source.