845/211 tube amplifiers with kef reference 5?
Bel Canto SET80 use 845R power triodes and output 70Watts per channel.This is why this amp won't work with the KEF: http://www.atma-sphere.com/en/resources-paradigms-in-amplifier-design.html The Bel Canto is a Power Paradigm device; the speaker is a Voltage Paradigm device. Anytime the two technologies are mixed, you run the risk of a tonal anomaly. In this case, it will be bass shyness. |
op listen to ralph (atmasphere) and scott (verdant) 211/845s won’t go well with big kefs... you want low watt sweet single ended amp sound to play at real volumes, you need to hunt HARD for the right speakers... i still have a set of gordon rankin’s lovely 300b wavelength cardinal xs’s from 20 years ago... still can’t find a speaker i like enough and can live with to use them as the main amps |
thegreenman OPYou should be fine with P/P 845 or 211’s, or even SE ones with the speakers being 90db, and if the amps have a 4ohm tap, and you don’t want to go too loud with the SE’s. The 8ohm tap will give more watts but "could" a problem in the bass. https://www.stereophile.com/images/1017KEF5fig01.jpg The impedance peak at 2.5khz will be bought back down by the increase in -phase angle around there also, so a fairly flat 4’ish ohm impedance will be seen by the amp This is what Stereophile had to say Fig.1 shows how the impedance and electrical phase vary with frequency. While the impedance lies above 8 ohms in the low treble, it remains between 4 and 5 ohms throughout the midrange and bass and in the top octaves. The minimum value was 3.3 ohms between 90 and 100Hz, but as the phase angle is generally benign, the Reference 5 should work well with tube amplifiers from their 4 ohm output transformer taps. Cheers George |
You should be fine with P/P 845 or 211’s, or even SE ones with the speakers being 90db, and if the amps have a 4ohm tap, and you don’t want to go too loud with the SE’s.What George is saying here is bad advice. The Stereophile comments apply only to tube amplifiers capable of acting as a voltage source (IOW, employing feedback). Since 99% of all SETs are zero feedback, they will tend to behave as a power source rather than a voltage source. Since the design of the speaker clearly is expecting a voltage source (and Stereophile clearly shows this in their impedance curve measurement) you'll encounter a tonal issue (weak bass or brightness, depending on how you look at it) with such an amp. One other thing to keep in mind with all SETs! You can't run them up to full power like you can with most push-pull amps; to really get the most out of any SET the speaker should be efficient enough that the amp never needs to make more than about 20-25% of full power. If this rule is broken, the SET will be making quite a lot of distortion at higher power. Almost any SET has about 10% THD at full power. If you keep the amplifier power under 20% its going to be a lot less- typically under 0.5%. When you push the SET harder, the additional distortion is perceived by the ear as 'dynamics' since the higher orders are showing up, initially on transients. The ear uses the higher orders to sense sound pressure- hence 'dynamics' but its really just distortion. Its just not a good match. If working with a tube amp of that power, (60-70 watts) a push-pull amp employing feedback is the way to go. |
What George is saying here is bad advice. That’s wrong you’ll encounter a tonal issueThat’s just what sets do, look at ANY SET into the Stereophile simulated speaker load frequency response graph, most sets act like tone controls. thegreenman OP As I had 805 sets drive just that same speaker off the 4ohm taps, like I said the max loudness wasn’t quite there, but it sounded great, for tube set. The Kef looks like a benign 4ohm load to an amp when impedance and combined -phase angle is taken into account. Cheers George |
