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Offline Simon Briggs  
#1 Posted : 25 October 2020 15:33:39(UTC)
Simon Briggs


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One for Martin to consider with his wealth of review experience.

I have always been fascinated by the combination of Krell KSA & The Apogee Scintilla and in the late 1980s and into the 1990s this was a combination I wanted to own.

Things have moved on but am sure that in fine fettle would still be a worthy combination.

My question relates to Krell amps only and have wondered which generation of Krell power amplifiers is the most load tolerant and capable of driving a one ohm load?

My guess would be in the original fan cooled KSA & KMA series all up to the newer fin cooled KSA 250.

in the mono series up to KMA 400 & MDA 500

Reference series in particular the KRS 100 and 200 probably the most load tolerant of all the Krell amps? Loved the KRS-200 driving Divas as I heard at the 1987 Penta show,

later on the Krell KAS the 2 box reference and latterly the big EVOLUTION ONE ?

I think even my little S550i could be capable?

Investigating later models I am not so sure that the FBP series could do it, may be the 402e could, but not the others in that later Evo series, excepting the EVOLUTION ONE ?

This is a question I think Martin may be able to answer

Simon

Edited by user 24 November 2020 23:21:57(UTC)  | Reason: Not specified

Offline phil page  
#2 Posted : 25 October 2020 19:31:34(UTC)
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Simon, I'm sure that the 700cx could do it - I inadvertently had mine driving a less than 1 Ohm load at one point. But you've just sold yours!
Phil
Offline Martin Colloms  
#3 Posted : 28 October 2020 19:18:01(UTC)
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Originally Posted by: phil page Go to Quoted Post
Simon, I'm sure that the 700cx could do it - I inadvertently had mine driving a less than 1 Ohm load at one point. But you've just sold yours!


Each contact in a connection loop, amp to loudspeaker can be 0.1 ohm never mind the soldered contacts in the loudspeaker and the amplifier.

So let's count per single channel. At least two inside the amp to the terminals then two for the spades or bananas then the joints to the speaker cable then two joins at the other end of the cable, noting a minimum of possibly 0.4ohm loop for the cable, then the cable terminations to the inside of the loudspeaker. I make that 1.4ohms (neglecting the amp output impedance) driving a '1 0hm load'

not very sensible!

never mind the approx quadrupled distortion from the power amp at these high curents.....

Martin
Offline Simon Briggs  
#4 Posted : 28 October 2020 19:59:53(UTC)
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Thanks Martin,

Thinking about Krell amps that could drive the Scintilla is purely out of curiosity only, I blame Covid-19 causing this related boredom driving my brain and curiosity to dig up old and unresolved questions. This cam out of reminiscing about the absolute Sounds system I heard at Penta 1987 where Krell KRS-200 / Krell 6 pack Pre was driving a pair of Apogee Diva loudspeakers, I went on to talking about amps that could drive the 1 ohm Scintilla. From my research the KRS-200 seem s like the most load tolerant amp of all time.

My list of Scintilla driving Krell amps

Originals, fan cooled KSA50 KSA100, KMA100, KMA200

mid 80s Big fins KSA80, KMA160, KSA200, KMA400

Reference KRS100 and KRS-200

later gen amps KSA150, KSA250 MDA Monos not sure?

Plateau biased amps S and FBP series, not sure of their load tolerance into 1.0 ohms and lower?

later gen amps Evolution One had a stiff PS

S550i integrated is very load tolerant and probably can.


anyway......



Unrelated to this I am not sure what I will replace my 700cx with to drive my big new speaker, but it must have bass as good as or better than the 700cx, minimum must be the 402e but will not rule out going as far as Krell 900 evo monoblocs, I just like the Krell sound in a bigger amp. I have about 18 months or so before I need to cross that bridge.

The Krell KRS-200 Monos are so old now, I doubt they can be serviced anymore?


I am sure that my little Orelle SA100 EVO integrated could make music with my new speaker, albeit at lower levels and with some concessions in the bass.


Simon

Edited by user 28 October 2020 20:39:04(UTC)  | Reason: Not specified

Offline sandyk  
#5 Posted : 05 November 2020 23:23:30(UTC)
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Originally Posted by: Martin Colloms Go to Quoted Post
Originally Posted by: phil page Go to Quoted Post
Simon, I'm sure that the 700cx could do it - I inadvertently had mine driving a less than 1 Ohm load at one point. But you've just sold yours!


Each contact in a connection loop, amp to loudspeaker can be 0.1 ohm never mind the soldered contacts in the loudspeaker and the amplifier.

So let's count per single channel. At least two inside the amp to the terminals then two for the spades or bananas then the joints to the speaker cable then two joins at the other end of the cable, noting a minimum of possibly 0.4ohm loop for the cable, then the cable terminations to the inside of the loudspeaker. I make that 1.4ohms (neglecting the amp output impedance) driving a '1 0hm load'

not very sensible!

never mind the approx quadrupled distortion from the power amp at these high curents.....

Martin


Spot on!

Why on earth would any sensible person design a High Fidelity speaker of such a low impedance? As Martin said, the power amplifier distortion would be much higher mainly due to Beta droop in the Output
transistors into low impedance loads.
Added to that, you would need to have a pile of them in parallel. Large power transistors also have quite a bit of input capacitance, and this increases with the number of parallel output devices.
Then there is the much lower input impedance of the pile of output devices as well .
This much heavier loading also reflects back into earlier stages of the amplifier,l degrading the performance before negative feedback, as well as most likely resulting in overall distortion figures well in excess
of what can be obtained these days with amplifiers designed to suit more modest loads .

Please feel free to correct any misunderstanding on my part.

Kind Regards
Alex
Offline phil page  
#6 Posted : 07 November 2020 02:55:06(UTC)
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I suppose that Apogee just weren’t sensible. Plenty of people probably said so at the time!
Phil
Offline Simon Briggs  
#7 Posted : 07 November 2020 14:03:04(UTC)
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This is making for some interesting research.

Totally impracticable daft and illogical yes.

Sound quality as a combination, probably likely excellent even now.

Would I own it dunno!! unlikely. This is just for interest only.. Blame Covid a desire to avoid boredom and an over active / curious brain

Has my question been answered yet? No so learning and research continues.

Personally speaking I am pleased that both of the Loudspeakers I am currently working on are a sensible load.

Edited by user 07 November 2020 17:16:21(UTC)  | Reason: Not specified

Offline phil page  
#8 Posted : 07 November 2020 17:05:07(UTC)
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As I recall, Doug Brady used to have a pair of Apogee Scintillas at home, driven I think by a big old MF amp.

Phil
Phil
Offline Simon Briggs  
#9 Posted : 07 November 2020 17:14:27(UTC)
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Originally Posted by: phil page Go to Quoted Post
As I recall, Doug Brady used to have a pair of Apogee Scintillas at home, driven I think by a big old MF amp.

Phil


Read that somewhere too, not sure it was an A370 which was a capable amp at the time, but think he had an SA470?

I think there were also MA570s as well IIRC?

Edited by user 07 November 2020 17:16:03(UTC)  | Reason: Not specified

Offline phil page  
#10 Posted : 09 November 2020 02:44:41(UTC)
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Doug told me himself, but I don’t remember which MF amp he used.

There’s a thread on Audiogon on the subject - ‘Apogee Scintilla Power’ - that you might find interesting, Simon
Phil
Offline Yeti  
#11 Posted : 10 November 2020 04:37:42(UTC)
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KSA 80B if you find the profile of member bailyhill on the Naim forum.
Offline bailyhill  
#12 Posted : 23 November 2020 22:35:31(UTC)
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Thanks all for the kind words about Apogee after all these years. As a founder and designer of the first two Apogee Speakers, I have some input on this.
The first product, the Full Range Ribbon loudspeaker was a 4 ohm unit, driven by transformers to match the impedance. Most folks used two 100 watt+++ amps biamped--one driving the woofer panels, and one driving the MRT. It was 80 inches tall, 32 inches wide, and had a shipping weight of 785 pounds. I know that because our Korean Distributor ordered the first two for that country, and he had them air freighted--$$$. The word was that they went to the CEO of Audio Technica.

The Scintilla was a cost reduced version of the Full Range, but with some innovations. It turned out to sound even better as a result. It had a combined midrange tweeter with 5 ribbons, all in the same magnetic field, with the 4 tweeter ribbons straddling the midrange, in what was nearly a perfectly time aligned arrangement. It saved magnets, which were the most expensive part. It was 60 inches tall, but retained the trapezoidal ribbon woofer (now called a magnestat but there was no such word in the vocabulary at that time). It leaned back several degrees to tame what would otherwise be a quite beammy line source. I discovered that the transformers were quite lossy, even though they were toroids, and realized that we could just use a ribbon resistor and have increased efficiency. That also meant that the speaker could be direct driven with no transformers. Audiophiles loved it. We had a version that was one ohm and one that was four ohms. The one ohm always sounded a bit better. Probably because of the limitations of high power amps, which were mostly class AB at the time. Of course they would put lots more power into one ohm. Some worked better than others. I have no idea about the later Krell amps. I had mime recapped last year by the factory and adjusted for one ohm operation. Absolutely no regrets. Would do that again. I researched the forums and other sources when I decided to activate the Scintillas 3 years ago, and the two amps recommended were the KSA-50 and KSA-80 as best with the Scintillas.

I have mine running at one ohm with a Krell KSA-80B, which is pure class A, rated at 80 watts into 8 ohms. However it will double down to one ohm, giving 640 watts of pure class A, which is spectacular. Nothing like 9KW which the Statement is rated, but Naim did not advise using the Naim amps into one ohm according to my Naim dealer at the time.

I am about to make a big purchase of a set of Mundorf Caps for rebuild of the crossover from woofer to MRT. It should be quite an upgrade. However, the original Scintillas had Sprague Metalized Polypropylene caps, which were the best available at that time. It takes 24 caps, 10 uf each, for a parallel array of 240 uF--and that is per side. That is more expensive than the magnets in them.
thanks 2 users thanked bailyhill for this useful post.
Simon Briggs on 23/11/2020(UTC), Pete_w on 24/11/2020(UTC)
Offline Simon Briggs  
#13 Posted : 24 November 2020 23:20:58(UTC)
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Originally Posted by: bailyhill Go to Quoted Post
Thanks all for the kind words about Apogee after all these years. As a founder and designer of the first two Apogee Speakers, I have some input on this.
The first product, the Full Range Ribbon loudspeaker was a 4 ohm unit, driven by transformers to match the impedance. Most folks used two 100 watt+++ amps biamped--one driving the woofer panels, and one driving the MRT. It was 80 inches tall, 32 inches wide, and had a shipping weight of 785 pounds. I know that because our Korean Distributor ordered the first two for that country, and he had them air freighted--$$$. The word was that they went to the CEO of Audio Technica.

The Scintilla was a cost reduced version of the Full Range, but with some innovations. It turned out to sound even better as a result. It had a combined midrange tweeter with 5 ribbons, all in the same magnetic field, with the 4 tweeter ribbons straddling the midrange, in what was nearly a perfectly time aligned arrangement. It saved magnets, which were the most expensive part. It was 60 inches tall, but retained the trapezoidal ribbon woofer (now called a magnestat but there was no such word in the vocabulary at that time). It leaned back several degrees to tame what would otherwise be a quite beammy line source. I discovered that the transformers were quite lossy, even though they were toroids, and realized that we could just use a ribbon resistor and have increased efficiency. That also meant that the speaker could be direct driven with no transformers. Audiophiles loved it. We had a version that was one ohm and one that was four ohms. The one ohm always sounded a bit better. Probably because of the limitations of high power amps, which were mostly class AB at the time. Of course they would put lots more power into one ohm. Some worked better than others. I have no idea about the later Krell amps. I had mime recapped last year by the factory and adjusted for one ohm operation. Absolutely no regrets. Would do that again. I researched the forums and other sources when I decided to activate the Scintillas 3 years ago, and the two amps recommended were the KSA-50 and KSA-80 as best with the Scintillas.

I have mine running at one ohm with a Krell KSA-80B, which is pure class A, rated at 80 watts into 8 ohms. However it will double down to one ohm, giving 640 watts of pure class A, which is spectacular. Nothing like 9KW which the Statement is rated, but Naim did not advise using the Naim amps into one ohm according to my Naim dealer at the time.

I am about to make a big purchase of a set of Mundorf Caps for rebuild of the crossover from woofer to MRT. It should be quite an upgrade. However, the original Scintillas had Sprague Metalized Polypropylene caps, which were the best available at that time. It takes 24 caps, 10 uf each, for a parallel array of 240 uF--and that is per side. That is more expensive than the magnets in them.



Welcome to the forums bailyhill and thank you for posting the insight. It was great to read some history about both the Full range and the Scintilla development.

I was interested to read about the KSA80B as a recommended amplifier, would be interested to learn about the adjustments made maybe they were re-biasing the amps to suit the 1 ohm load best?

Owning a pair of Scintillas is on my bucket list so to speak since hearing the Divas as a youngster at the 1987 Penta show driven by the KRS-200.

I sold a big Krell amp recently to finance my latest loudspeaker design and build, and plan to get back on the big Krell ladder in the next couple of years. My next Krell amp purchase will be based upon the ability to drive the 1 ohm Scintilla just in case I do get a pair.

So I will be researching carefully which amplifier to purchase.

It may be one of the bigger older Monobloc amps

KMA 200 (Fan cooled) / KMA 400 / MDA500 or one of the later sliding bias amps KAS two box or

FPB again the 750mcx or EVO 900

I have a bit of time to research this further….

ATB

Simon


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