Welcome to SAS Audio Labs. SAS Audio Labs came about in December 1996 (after 16 years of research) and continues to play a leadership role in the evolution towards audio perfection. I hope the knowledge presented over the years in my "White Papers" has helped you in understanding what makes a great sounding audio design and helps you when evaluating a component.
Afterall, this hobby is about you and your journey toward more satisfying and realistic music. I am beholden to neither recent technology nor old, but my own innovative designs but only after thoroughly investigating each design.
I start each topic with general easy to understand information and then get more technical. If you wish to bypass the technical information, just scroll down past the technical information in each section.
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A) SAS Audio Labs believes that the entire design is important, which includes the power supply, the active circuitry, individual parts incorporated, and even the layout. For instance, although a particular design may look good on the surface and may even have a lot of support, digging deeper may reveal reveal an inherent weakness that renders it inferior. I use proprietary sohphisicated listening tests that are very sensitive at revealing flaws in that particular part or component.
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B) I start with the layout as virtually no one ever mentions this aspect of design. Does it have hot parts or tubes (especially octal tubes) in close proximity to temperature sensitive parts, such as capacitors? A 250-490 degree octal tube within two inches of a 170 to 220 degree maximum rated capacitor risks power supply failure sometime in the future. Some electrolytic capacitor's life span is halved with every 20 F degree rise in temperature. To understand what I mean, put your fingers close to a light bulb and feel the warmth.
A blown power supply could cause an expensive down stream component to fail which both you and I do not want. One indication of how knowledgeable and experienced a designer is is by the layout. In todays world, I think it is always a good idea to inspect the internals of a component before purchasing. I keep all hot parts well away from other parts, and since SAS Audio's inception in 1996, no 10A has ever required a repair.
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C) SAS Audio Labs was the leader in the concept and use of "lead to lead tm" connecting (December, 1996 white paper). "Lead to lead" connecting refers to connecting part leads together thus bypassing the need for connecting wires. This reduces the number of connecting wires and solder connections.
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D) In December, 1996 I published a "White Paper" listing both the positive and negative virtues of both hardwiring and PC boards. The trick to using PC boards is, of course, avoiding the negatives while incorporating the positve of each method.
Two big pluses of incorporating PC boards are consistency between components and higher frequency response because of less capacitance between adjacent parts and from parts to ground. Using "lead to lead" connecting reduces the number of foil traces and wire, thus the number of solder connections. Others manufacturers have also followed my concept in their designs.
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E) In October, 1997, I presented a "White Paper" that discussed the issue of frequency dependent sonic feedback from stage to stage, through the power supply. This type of feedback is prominent in almost every design, even if not stated. (Actually, I was prompted to write this paper by what I read in the "RCA Radiotron Designers Handbook," 1960, 4th edition, written by 26 engineers, so this issue is not new, just brought back to life.)
Musical feedback extends from near zero hertz through the midrange frequencies and its consequences are generally more pronounced than global feedback as huge phase shifts occur within the audio band, unlike conventional global feedback which generally has phase shifts well outside the audio band. A smaller feedback problem may occur at the high frequencies as well, but with much less phase shifting.
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F) Another philosophy is the absence of any buffer stages, cathode followers, or Mu stage (which uses a cathode follower), with their inherent ultra high negative feedback. For future reference, I shall simply use the term "buffer stage" to mean any ultra high feedback stage. They are usually mentioned as simple impedance matching stages, producing low output impedances. Unfortunately, the inherent high feedback is rarely mentioned. In the below quotes, notice the phrase "common-plate"/cathode follower.
- From "Semiconductor and Tube Electronics, An Introduction," by James
G. Brazee:
"The common-plate or cathode- follower circuit configuration is an extreme example of degenerative (negative) feedback, since all output signal is fed back in such a way that it appears in the input (grid to cathode) voltage loop in phase opposition to the signal voltage." - From the "Radiotron Designer's Handbook," page 316-7:
"It is therefore frequently referred to as "cathode loading" in distinction to the conventional "plate loading". As a result of 100% negative voltage feedback inherent in the cathode follower...."
The feedback is so high that the gains are less than 1. (The gain a Mu follower stage creates is from the lower tube while the upper tube/FET is the high feedback cathode follower stage.)
I prefer triode regulation any day over solid state regulation.
One may ask, what about feedback in a regulator stage. Luckily its affects are fairly small due to its location in the circuit. But even then one must be careful with the design.
What about hum and interference pickup, from outside sources? I live on the second floor of my apartment building facing two 2.2 million watt television transmitting towers about 5-6 miles away and I can put my ear on the speakers without any interference being heard. None. So hum and interference are non-existent. The next section will deal with frequency response.
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G) I use the 10:1 ratio to be safe. That is the input impedance (Z) of the amplifier is 10 times that of the output Z of the preamplifier, or source. The RCA Radiotron Designers Handbook recommends 5 times, or 5:1. For example, at 5:1, if the preamplifier/source output impedance is 2000 ohms, the amplifier input impedance needs to be only 10,000 ohms minimum. Using 10:1, the amp input impedance should be 20,000 ohms.
Some teach a 100:1 ratio, which actually creates problems because one almost always needs an additional buffer output stage to obtain the very low output impedance needed. However, the additional stage itself deteriorates the musical quality.
Understand that teaching the 100:1 ratio attempts to legitimize the use of a buffer stage and unfortunately infers that those who don't use it are inferior designs. Adding a buffer stage increases frequency dependent feedback, increases the complexity, and adds to the cost and increases the profit margin. But there is another obvious question.
That obvious question is why not just design a single stage, low output impedance, wide bandwidth, and low distortion design to begin with and forget the additional buffer stage with its problems? Proponents claim a lower output impedance of, say 100 ohms is better, thus higher frequency response, lower distortion, and less interference/hum. Let's investigate.
Decreasing the ratio from 100:1 to 10:1 results in virtually no increase in harmonic distorion. For example if the total harmonic distortion at 2v rms output measures .01% (-80db) using the 100:1 ratio, changing to 10:1 raises the distortion by approximately .012% to -79db, a rise of approx 1db. Not much difference is it.
Let's check for any high frequency response advantages. If one uses a high capacitance interconnect cable (IC), say 250pf of capacitance, and the output impedance changes from 2000 ohms to 100 ohms, the frequency response changes approx 0,4db at 100,000 cycles per second.
Using a 50pf interconnect cable results in less than 0,02db change at 100khz. By the way, everyone knows that capacitances should be minimized with interconnect cables. (However, rarely, a longer IC with higher capacitance is neccessary as there is no choice.) Actually a major portion of the loss in high frequency response is due to the volume control resistance/input tube capacitance relationship.
The added buffer stage does not do much except contribute artificial flavors.
As far as hum/interference, it all has to do with proper grounding/shielding scheme. I live in a second floor apartment approximately 5-6 miles from two, 2.2 million watt visual and 200,000 watt aural producing television stations. I hear no interference with my ear on the speaker cones.
In conclusion I will not add anything that is harmful to the music. Enough is enough, and more is simply too much.
Acknowledgements
Each page is designed to help educate the consumer when purchasing gear. From time to time, other articles and products will be added; so stay in touch.
I would like to thank God for inspiring the designs and parts used. It has been a real adventure, with His inspiration leading the way.
The articles covering theory require a special thanks to Walter G. Jung for discussions and his articles entitled "Picking Capacitors". Without these articles and discussions, these pages would be of lesser quality.
Thanks to Svetlana and JJ for allowing us to use their vacuum tube graphics on our site.
SAS Audio Labs
1901 N. Morton Ave. Suite 184
Morton, Illinois USA 61550 (10 miles east of Peoria)
TEL: (309) 263-0736
1:00 PM - 6:00 PM CST Monday - Friday
Auditions on weekdays, nights and weekends available
Email, sasaudio@omnilec.com
Totally Confidential. No email will ever be sold or given away.
*sas audio labs, SAS Audio Labs, SAS AUDIO LABS, and the SAS AUDIO LABS banner are trademarks of SAS Audio Labs."
*copyright©: 05-17-2008 Updated 10-17-2008. All contents of this page article (except Sovtek, JJ, and Svetlana Tubes) are copyrighted. Any and all
designs and schematics, layouts of all our components, term "lead to lead wiring", "lead to lead connecting", "we make music come alive", "we make music truly come alive", and "the last watt is as important as the first watt" are copyrighted. All rights reserved. No portion of this article may be reproduced without written permission from Steve Sammet at SAS Audio Labs.