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Old 10th June 2014, 10:45 PM   #11661
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it seems you boyz weren't recently at PL board

amp* is an amp is an amp

be it from sand or filled with no air

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Old 10th June 2014, 10:52 PM   #11662
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I've yet to hear an amplifier (or DAC) with no added "electronic" coloration, or conversely, able to reproduce the full gamut of tone colors and vividness of live music.

Gary Pimm's Class A amplifier, though, is pretty close. Out of all the amps I've heard, it's certainly in the Top Ten.

Last edited by Lynn Olson; 10th June 2014 at 11:09 PM.
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Old 11th June 2014, 12:23 AM   #11663
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You haven't been around enough, Lynn, - I abhor "electronic colouration", normal audio stinks of the stuff, I think "copper" and "heat" when I hear it - and so that is always the main focus of my efforts, to get rid of that ugly taint ...
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Old 11th June 2014, 01:49 AM   #11664
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Lynn.
As I said I understand and remember reading your reasons for using a class A tube amp. I also see no problem with using a hybrid SS/tube amplifier. Where you just can't do that and expect 20 watts to do the job is with a common direct radiator type of loudspeaker. you just run out of power and into major distortion. Now your insistence on zero feedback I think would have many designers in disagreement even if they are tube aficionados. I think you have just learned to like and expect the type of harmonic distortion that you will produce with a non-feedback amplifier, I don't believe that it truly has an inherent superiority to a feedback design, it is just a different harmonic content. Feedback has been used to linearize tube amplification going back to at least the Williamson type of amplifier circuits. I can't and wouldn't argue your tastes in music reproduction, we all like what we have come to expect and what we are exposed to. Your chose is just as relevant as anyone else. I am amazed that the old Altec drivers have remained and are reproduced today, I remember them well though back when we did PA work even with A2's and such we had decided that we liked the old JBL drivers of the time better.
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Old 11th June 2014, 02:35 AM   #11665
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Quote:
Originally Posted by Kindhornman View Post
Where you just can't do that and expect 20 watts to do the job is with a common direct radiator type of loudspeaker. you just run out of power and into major distortion.
Incorrect. If you do the maths, that demonstrates that such is not true; however, most 20 watt amps also have miserable power supplies, which totally cripples the ability of the amp to do the job - sort all that out, and the 20 watter will easily produce deafening sound, with minimal audible distortion, into those types of speakers.
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Old 11th June 2014, 02:57 AM   #11666
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Zero-feedback amplifiers, if competently designed, have a soft clipping characteristic, very much like a limiter for a radio station. This gives them about 3 to 4 dB of progressively compressed headroom where distortion gradually increases.

The Karna has 0.1% distortion at 15 watts, almost entirely 2nd and 3rd harmonic. Steady-state, it can put out 30 watts at 3%, and for transients in the 100 millisecond range, 50 watts or more. Slewing is pretty good too: it can put out full power at 500 kHz, although I didn't have the nerve to try that for more than a few seconds.

The 20-year-old Ariels are 92 dB/meter, and I listen at a distance of 11 feet. Peak sound levels are typically center-dominated (instead of hard left or hard right), so power from both channels is available. The system as a whole is audibly compressing at 105 dB (at the listening position), which is consistent with 40 watts (both channels) steady-state, and 100 watts for brief transients.

Raising the efficiency by 5 to 8 dB is a simple way of gaining headroom while retaining an amplifier that I prefer over all others. If I want to listen to transistors, I switch over to the Marantz MM8003 power amplifier, which is mostly used for home theater duties.

The external crossovers of the Ariels have a set of DPDT input switches that quickly change over from the 2-channel triode system to the 5-channel home theater system. The crossover input selector switches grounds as well as "hot" signals, so the grounds between the two systems are isolated from each other. I can listen to either transistors or triodes, and upgrade the 5-channel transistor side of things if I want ... maybe Class D, maybe a more sophisticated solid-state amp. But it's not a priority.

If the readers of the DIY forum prefer Class AB transistor amplifiers, good for them! It saves a lot of money, and greatly widens choices of potential loudspeakers. If 200 watts or more is on tap, then you can choose electrostats, magnetic-planars, MBL or Ohm radial omnidirectional speakers, or the traditional favorite, direct-radiators with efficiencies in the 85~93 dB/meter range.

Last edited by Lynn Olson; 11th June 2014 at 03:12 AM.
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Old 11th June 2014, 06:50 AM   #11667
g3dahl is offline g3dahl  United States
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Quote:
Originally Posted by ra7 View Post
Gary, what is your listening distance and average SPL at the listening position?
My speakers are 11 feet away from the main listening position (coincidence Lynn?), with their centers 11 feet apart. Average SPL is around 75-80 dB, according to my iPhone app.

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Old 11th June 2014, 01:00 PM   #11668
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Originally Posted by Lynn Olson View Post
A great thread if you're interested in high-power transistor Class AB feedback amplifiers; the simulated distortion is extremely low, stability and slew rate are high, and many variations on a theme. Maybe somebody will bring one to the RMAF show this fall; I'm curious to hear what one of the Slewmaster variants sounds like.

My interest is in amplifiers with zero feedback (local or global), amplifying elements with very low intrinsic distortion, and no switching artifacts. The Karna is one approach; Gary Pimm's is completely different, with MOSFETs, FETs, and bipolar transistors, but full (thermal) Class A and operating as a high-voltage differential steered current source.

Interestingly enough, both amplifiers sound pretty similar to each other, but both are sonically quite different than commercial SETs or transistor Class AB feedback amplifiers. (Gary Pimm built my Karna amplifiers, and we've done a lot of direct comparisons between the two. Both amplifiers use Gary's cascoded MOSFET current sources.) I'm contemplating a Mark II version with direct-coupling between the differential input and driver section, with a center-tapped reactor/audio-grade choke to keep the input section dynamically balanced and voltage offsets between the pair low.

Thermal Class A limits the power to 20 watts/channel or less if you want to keep heatsink size reasonable or B+ voltages less than 550V. Twenty watts isn't a limitation if the speaker efficiency is high enough, there is no requirement to fill an auditorium, and a separate amplifier is used to the cover the below-60 Hz range.

100+ watts/channel of (thermal) Class A power gets us into the rack-sized range, serious cooling requirements, and either very large heatsinks or B+ voltages in the 1 kV to 2.5 kV range ... something the size of a small radio-station transmitter.

Gary Pimm, Gary Dahl, and I are not building rack-sized amplifiers, and we like the sound of Class A operation (direct-heated triode, MOSFET or bipolar transistor). So ... a more efficient loudspeaker, which Gary Dahl is enjoying right now.
Lynn, I think almost all serious DIY ers who have been around would have a similar view on this. What Gary Pimm enjoys in the US, likely I enjoy here in the UK but achieved differently but with similar basic electronic principles. Certainly your Karna reflects a nice circuit and balance of selected parts, and mine are again, like the Gary,s different than yours and theirs. This type of friendly stuff no doubt happens at the meetings of small audiophile groups i.e DHT, PA , Theatre music

This is good because it does give hope to many new DIYers that there are quite few options open to them. And I like the Ariel replacement speakers of Gary Dahls, which are beautifully made. I would make them different again jsut for fun and the ywould work too. There is a slight rivalry in there with all DIYers and that is human nature. And the guy from Israel , disarmingly makes his own valve amps and his may be exceptional, while he asks for unique circuit diagrams for state of art solid state Gary Pimm amp. This is waht really does keep DIY going and its has needed it in the world recession. I rue the day if and when you could only buy complete manufactured units. Digital may have brought that a little too close.
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Old 11th June 2014, 01:06 PM   #11669
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Quote:
Originally Posted by Lynn Olson View Post
Zero-feedback amplifiers, if competently designed, have a soft clipping characteristic, very much like a limiter for a radio station. This gives them about 3 to 4 dB of progressively compressed headroom where distortion gradually increases.

The Karna has 0.1% distortion at 15 watts, almost entirely 2nd and 3rd harmonic. Steady-state, it can put out 30 watts at 3%, and for transients in the 100 millisecond range, 50 watts or more. Slewing is pretty good too: it can put out full power at 500 kHz, although I didn't have the nerve to try that for more than a few seconds.

The 20-year-old Ariels are 92 dB/meter, and I listen at a distance of 11 feet. Peak sound levels are typically center-dominated (instead of hard left or hard right), so power from both channels is available. The system as a whole is audibly compressing at 105 dB (at the listening position), which is consistent with 40 watts (both channels) steady-state, and 100 watts for brief transients.

Raising the efficiency by 5 to 8 dB is a simple way of gaining headroom while retaining an amplifier that I prefer over all others. If I want to listen to transistors, I switch over to the Marantz MM8003 power amplifier, which is mostly used for home theater duties.

The external crossovers of the Ariels have a set of DPDT input switches that quickly change over from the 2-channel triode system to the 5-channel home theater system. The crossover input selector switches grounds as well as "hot" signals, so the grounds between the two systems are isolated from each other. I can listen to either transistors or triodes, and upgrade the 5-channel transistor side of things if I want ... maybe Class D, maybe a more sophisticated solid-state amp. But it's not a priority.

If the readers of the DIY forum prefer Class AB transistor amplifiers, good for them! It saves a lot of money, and greatly widens choices of potential loudspeakers. If 200 watts or more is on tap, then you can choose electrostats, magnetic-planars, MBL or Ohm radial omnidirectional speakers, or the traditional favorite, direct-radiators with efficiencies in the 85~93 dB/meter range.
Lynn

I strongly agree with this view, and would add that one could even progress to making ones own electrostatic or Magneplanar equivalent. WE can if inclined make anything with the now available materials parts and circuits, so DIY ers are in the best position today to do this if so inclined and can reasonably afford it.
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Old 11th June 2014, 01:19 PM   #11670
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Quote:
Originally Posted by Lynn Olson View Post
A great thread if you're interested in high-power transistor Class AB feedback amplifiers; the simulated distortion is extremely low, stability and slew rate are high, and many variations on a theme. Maybe somebody will bring one to the RMAF show this fall; I'm curious to hear what one of the Slewmaster variants sounds like.

My interest is in amplifiers with zero feedback (local or global), amplifying elements with very low intrinsic distortion, and no switching artifacts. The Karna is one approach; Gary Pimm's is completely different, with MOSFETs, FETs, and bipolar transistors, but full (thermal) Class A and operating as a high-voltage differential steered current source.

Interestingly enough, both amplifiers sound pretty similar to each other, but both are sonically quite different than commercial SETs or transistor Class AB feedback amplifiers. (Gary Pimm built my Karna amplifiers, and we've done a lot of direct comparisons between the two. Both amplifiers use Gary's cascoded MOSFET current sources.) I'm contemplating a Mark II version with direct-coupling between the differential input and driver section, with a center-tapped reactor/audio-grade choke to keep the input section dynamically balanced and voltage offsets between the pair low.

Thermal Class A limits the power to 20 watts/channel or less if you want to keep heatsink size reasonable or B+ voltages less than 550V. Twenty watts isn't a limitation if the speaker efficiency is high enough, there is no requirement to fill an auditorium, and a separate amplifier is used to the cover the below-60 Hz range.

100+ watts/channel of (thermal) Class A power gets us into the rack-sized range, serious cooling requirements, and either very large heatsinks or B+ voltages in the 1 kV to 2.5 kV range ... something the size of a small radio-station transmitter.

Gary Pimm, Gary Dahl, and I are not building rack-sized amplifiers, and we like the sound of Class A operation (direct-heated triode, MOSFET or bipolar transistor). So ... a more efficient loudspeaker, which Gary Dahl is enjoying right now.
Hi Lynn ,

When you say zero feedback, is this truly a zero feedback design without any degeneration ....?

Quote:
Originally Posted by Lynn Olson View Post
Zero-feedback amplifiers, if competently designed, have a soft clipping characteristic, very much like a limiter for a radio station. This gives them about 3 to 4 dB of progressively compressed headroom where distortion gradually increases.

The Karna has 0.1% distortion at 15 watts, almost entirely 2nd and 3rd harmonic. Steady-state, it can put out 30 watts at 3%, and for transients in the 100 millisecond range, 50 watts or more. Slewing is pretty good too: it can put out full power at 500 kHz, although I didn't have the nerve to try that for more than a few seconds.

The 20-year-old Ariels are 92 dB/meter, and I listen at a distance of 11 feet. Peak sound levels are typically center-dominated (instead of hard left or hard right), so power from both channels is available. The system as a whole is audibly compressing at 105 dB (at the listening position), which is consistent with 40 watts (both channels) steady-state, and 100 watts for brief transients.

Raising the efficiency by 5 to 8 dB is a simple way of gaining headroom while retaining an amplifier that I prefer over all others. If I want to listen to transistors, I switch over to the Marantz MM8003 power amplifier, which is mostly used for home theater duties.

The external crossovers of the Ariels have a set of DPDT input switches that quickly change over from the 2-channel triode system to the 5-channel home theater system. The crossover input selector switches grounds as well as "hot" signals, so the grounds between the two systems are isolated from each other. I can listen to either transistors or triodes, and upgrade the 5-channel transistor side of things if I want ... maybe Class D, maybe a more sophisticated solid-state amp. But it's not a priority.

If the readers of the DIY forum prefer Class AB transistor amplifiers, good for them! It saves a lot of money, and greatly widens choices of potential loudspeakers. If 200 watts or more is on tap, then you can choose electrostats, magnetic-planars, MBL or Ohm radial omnidirectional speakers, or the traditional favorite, direct-radiators with efficiencies in the 85~93 dB/meter range.
This would put your system sensitivity at listening position @82db/w add in second channel and some room gain 85db /87 db ? 15 watts will not give you much in dynamic head room, of course 8db increase in sensitivity will increase it some fold ...
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