306 vs. One Small Day

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29-Feb-2020 10:56 PM

Fabian

Fabian

Posts: 107

This is probably not of any importance to anyone, but I still want to mention it. I'm currently running my KEF R7 through two 306 in bi-amping configuration, one 306 per  channel. Today I was listening to the 12" maxi single version of Ultravox' One Small day with the tilt control of my Quad 34 set to +3dB. Of course, pre and power amps are upgraded to the highest Dada specs.

The thermal protection kicked in on both of my 306 at the very same point in time. Wow! That's awesome! I never managed to get to that point before.

Kudos to the KEF R7 for taking me absolutely clearly to that insane sound pressure leveland to the revised 306 for shutting down exactly at the same time.

This is the final hint to start working on my pair of 606. The Dada revision kit and new power capacitors are lying around for a couple of months now. Will start the rebuild tomorrow!

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02-Mar-2020 05:22 AM

EJP

EJP

Posts: 1742

Amazing. I could understand it a little better if you were using one channel of each to drive a subwoofer, as they would both be seeing more or less the same signal in those channels, but I suspect that most people are like me and use one for the main speakers and the other for the subwoofers.

EJP

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02-Mar-2020 11:28 AM

Fabian

Fabian

Posts: 107

I think it’s not that surprising looking at the details. KEF’s current speaker line-up is amazing, but for reasons beyond me they falsely declare their speakers as “nominally 8 ohms”. In reality, the R7’s impedance is below 4 ohms between 85 and 300 Hz, with a minimum dipping as low as 3.2 ohms in the 130 Hz area.

https://abload.de/img/kefr7impedancea7kez.png

I love my revised 306s for their sound and their perfect looks, but they don’t have excessive headroom into lower loads. And Quad only ever specified max. output with one channel driven.

Add the fact that I had set the tilt control to +3 dB “party mode” which will increase the output by 6 dB at 50 Hz (and even 10 dB at 30 Hz) and yes, I’ve been listeningreally loud.

Even when used in bi-amping configuration these are still passive speakers. Both amplifier channels are fed the same input signal. The output of the “high pass channel” is only reduced by the capacitive load of the crossover while the “low pass channel” sees the mostly inductive load of the filter network above ~400 Hz. I know Quad amps are unconditionally stable into any load. I have never seen a measurement how much max. power might drop into reactive loads, though. Anyway, this is probably the least contributing factor.

For almost all listening conditions the 306 does have sufficient power. But since I also own a pair of 606 it’s probably just the right time to finally start the overhaul.

 

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02-Mar-2020 01:07 PM

EJP

EJP

Posts: 1742

There is a power versus impedance graph in the user manuals of the Quad 303, 405, 306, 606, 707, and 9o9 power amplifiers. The one on page 12 of the 306 user manual also shows time to trip the thermal protection.
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02-Mar-2020 05:59 PM

Fabian

Fabian

Posts: 107

Yes, my statement regarding the somewhat limited power into lower loads was based on that very graph. 606 is certainly a different beast.
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