Open reply from Convergent Audio Technology:
I've had some direct inquiries, some slightly hostile, about my comment made above concerning JL3s driving MBL 101s.
First, the "man" I referred to who reviewed the JL1 with MBL 101s was Michael Gindi. This review was published in the very first issue of FI magazine. That system was the toast of New York - a veritable Mecca for audio reviewers and upper crust dilettantes. I bought my MBL 101s after hearing this system with my prototype JL1s.
Second, I made NO disparaging remarks about any other amplifier company in my previous post. I mention two amplifiers only as 500 watt and 700 watt tube amps. My point being that power, as in raw wattage, is not the key to driving a difficult speaker such as the MBL 101. To decide that I must have meant some particular company and then take umbrage is not reasonable.
Third, a couple of people have asked me what makes the JL3 (and older JL1) capable of driving difficult loudspeakers when more "powerful" amplifiers cannot:
- Huge output transformer -- at 55 lb. bigger than any other amps output transformer (and much bigger than the 10-12 LB transformers typical of 150 watt tube amps). This means that this transformer runs at a fraction of its capability even at bass frequencies and even at full power for much better magnetic linearity.
- high turns ratio in transformer - the transformer could be driven by 2 pairs of output tubes to achieve the same power rating, but we use eight pairs (four in the JL1&JL2) to achieve the same power. This means that the load impedance - and variations of same - are reduced by a factor of four times versus similar triode amps from other companies. Obviously this makes the load less difficult for the output stage tubes.
- High energy storage/watt -- at over 1000 joules for a 150 watt amp (7 joules/watt) this is possibly the highest ratio in any production amplifier. This means the power supply is much stiffer at any given output level and therefore the sound will be more stable and authoritative at all levels.
- very wide high frequency bandwidth output transformer - gives high stability into capacitive loads. We actually test each amplifier with the 8ohm/2uf "IHF load". The resulting ringing is minimal - about 5 percent. Most tube amps will ring violently or even damage themselves when faced with such a load. Stereophile gave up testing tube amps on the IHF load several years ago. I have talked with one tube amp manufacturer who considered this load "unfair" to tube amps. We don't consider it "unfair" at all -- and I point to the CAT amps success at driving all sorts of difficult loads as proof that designing such abilities into an amp is a good thing. Electrostatic speakers tend to look highly capacitive. (Soundlabs for example, look a bit like a 4uf capacitor in parallel with a 30 ohm resistor -- most amps get hard at modest volume levels when driving Soundlabs. I've talked with some people who incorrectly blame the Soundlab for this hardness because it happened with all amps that they tried on the speaker. This won't happen with any CAT amps.)
Lastly, I would like to thank all of the people who posted such kind remarks about our amplifiers. Its gratifying to hear such high praise in an anonymous forum such as Audiogon.
I've had some direct inquiries, some slightly hostile, about my comment made above concerning JL3s driving MBL 101s.
First, the "man" I referred to who reviewed the JL1 with MBL 101s was Michael Gindi. This review was published in the very first issue of FI magazine. That system was the toast of New York - a veritable Mecca for audio reviewers and upper crust dilettantes. I bought my MBL 101s after hearing this system with my prototype JL1s.
Second, I made NO disparaging remarks about any other amplifier company in my previous post. I mention two amplifiers only as 500 watt and 700 watt tube amps. My point being that power, as in raw wattage, is not the key to driving a difficult speaker such as the MBL 101. To decide that I must have meant some particular company and then take umbrage is not reasonable.
Third, a couple of people have asked me what makes the JL3 (and older JL1) capable of driving difficult loudspeakers when more "powerful" amplifiers cannot:
- Huge output transformer -- at 55 lb. bigger than any other amps output transformer (and much bigger than the 10-12 LB transformers typical of 150 watt tube amps). This means that this transformer runs at a fraction of its capability even at bass frequencies and even at full power for much better magnetic linearity.
- high turns ratio in transformer - the transformer could be driven by 2 pairs of output tubes to achieve the same power rating, but we use eight pairs (four in the JL1&JL2) to achieve the same power. This means that the load impedance - and variations of same - are reduced by a factor of four times versus similar triode amps from other companies. Obviously this makes the load less difficult for the output stage tubes.
- High energy storage/watt -- at over 1000 joules for a 150 watt amp (7 joules/watt) this is possibly the highest ratio in any production amplifier. This means the power supply is much stiffer at any given output level and therefore the sound will be more stable and authoritative at all levels.
- very wide high frequency bandwidth output transformer - gives high stability into capacitive loads. We actually test each amplifier with the 8ohm/2uf "IHF load". The resulting ringing is minimal - about 5 percent. Most tube amps will ring violently or even damage themselves when faced with such a load. Stereophile gave up testing tube amps on the IHF load several years ago. I have talked with one tube amp manufacturer who considered this load "unfair" to tube amps. We don't consider it "unfair" at all -- and I point to the CAT amps success at driving all sorts of difficult loads as proof that designing such abilities into an amp is a good thing. Electrostatic speakers tend to look highly capacitive. (Soundlabs for example, look a bit like a 4uf capacitor in parallel with a 30 ohm resistor -- most amps get hard at modest volume levels when driving Soundlabs. I've talked with some people who incorrectly blame the Soundlab for this hardness because it happened with all amps that they tried on the speaker. This won't happen with any CAT amps.)
Lastly, I would like to thank all of the people who posted such kind remarks about our amplifiers. Its gratifying to hear such high praise in an anonymous forum such as Audiogon.