My review of the M3 Turbo S is finally live!

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Wind Chaser

Re: My review of the M3 Turbo S is finally live!
« Reply #40 on: 23 Feb 2018, 09:59 pm »
Yeah, it’s worth hanging onto them because as you said, you never know if you might have a use for them again.

The problem with a SET as isn’t just low impedance, but severe swings/spikes in the impedance.



Even though the above pertains to the Triode Master, it is still useful as the plot to the M3 Turbo S would look quite similar except instead of bottoming out at 16 ohms, it bottoms out at 3 ohms. That first peak around 30 Hz at 95 ohms is followed by another peak around 1.5 KHz which literally is off the charts! At 3 kHz the impedance is still over 50 ohms. Depending on how one uses the Speltz autoformers, they will amplify those peaks by a factor of 2x, 3x, or 4x, which only makes a difficult load all the more difficult. SET amps need not apply.



poseidonsvoice

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Re: My review of the M3 Turbo S is finally live!
« Reply #41 on: 24 Feb 2018, 01:02 am »
Here is a quote from the Absolute Sound review on the Coincident Dynamo:

Quote
One of the factors that can make an amplifier shine with one speaker and stink with another is its source impedance. A typical push-pull tube amplifier’s source impedance is likely to lie in the range of one-to-two ohms, which only slightly perturbs the speaker’s frequency response. I measured a source impedance of 10.2 ohms off the Dynamo’s 8-ohm taps. The net effect was to reduce speaker response in the upper bass and lower midrange, the power range of an orchestra, where the speaker’s impedance magnitude is lowest. It didn’t sound exactly like the bottom dropped off the map, but the balance was distinctly lightweight. This was especially an issue with symphonic music, which was reproduced without a convincing orchestral foundation.

A 10.2 ohm output impedance from the 8 ohm tap! That would be a 5.1 ohm output impedance from the 4 ohm tap! Wow.

Best,
Anand.