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Old 4th November 2001, 02:35 AM   #1
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I have been wondering what the thought of the DIY audiophiles that are involved strictly with home audio systems is in regards to circuit simplicity. Having looked a many circuit designs done by very well respected individuals such as Erno Borbely, Nelson Pass and Douglas Self and there is a good mix from very simple to fairly complex.

I very seldom design a circuit that is simple because it is not possible to control many circuit aspects without making a circuit more complex. A good example is DC drift. If a way to control DC drift is required to allow DC coupling into the next stage a simple circuit will need to be made more complex. Capacitive coupling of course eliminates the need to pay real close attention to DC drift. There are of course also other parameters such as DC drift that can be enhanced by the addition of various parts to a good working simple circuit. Thus I prefer to refer to a more complex circuit as a enhanced simple circuit.

My question is then, are there more individuals who prefer simple circuits over enhanced simple circuits?

Having just looked at the Douglas Self site (http://www.dself.demon.co.uk/ampins.htm) it appears that his site may no longer be updated by him due to lack of time. I would encourage all to visit his site since it is a great source of information on the art of building audio amplifiers. Douglas Self of course has written an excellent book on power amplifier design and many use it as a reference, even when doing patent applications.

John Fassotte
Alaskan Audio

[Edited by alaskanaudio on 11-03-2001 at 09:43 PM]
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Old 4th November 2001, 03:25 AM   #2
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Arrow Mixed feelings here...

Well, as usual, it depends. My personal taste is simple amp circuits; it's a proven fact (from the hundreds of good sounding designs available) that you don't need a lot of dc-servos, current mirrors, bizzare topologies and stuff to have an amp sounding good. From where i stand, if an amp really NEEDS such things, it's a bad design from scracth...

What i mean is, that a good amp is one with a basic design that offers (relatively) stability, linearity and low distortion; then negative feedback, current sources and stuff are added over it to make it work BETTER, not just to make it work as it's intended to. At least that's what i look on audio myself...
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Old 5th November 2001, 01:22 AM   #3
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Default I Agree

Lisandro,

I agree with you fully, especially your second paragraph.

I do not add parts that have no function, every circuit design I work on is checked using the test equipment I have available, along with computer simulations when appropriate. When, and only when all the technical aspects of a circuit are worked out, refined and verified are listening tests begun. I was surprised to hear Dan Agostino, of Krell say that he uses the same principals in designing Krellís very fine equipment at a Stereophile Magazine show not to many years back..

You could call me a technocrat since I strongly believe that this is the only way to design equipment. Perhaps this is due to the fact that I have been a electronics technician for over thirty five years. It does require a very large investment in test equipment to do this and a extremely understanding spouse.

One of the things that are of great benefit to the DIY community are the very high quality sound cards for computers along with good sound editor software. These allow testing with real music and other special signals. Not just tone, multi tone, pulse and others tests. A musical segment can be recorded before and after going through a piece of equipment, and then time aligned at any point and subtracted. Within the limits of any phase shifts induced by the equipment over a specific bandwidth the resulting A minus B signal can be a very accurate representation of the distortion products produced.

With a high speed 24 bit sound card measurements to extremely low levels of distortion can thus be measured using actual segments of music. There is no need to find someone with a golden ear whose opinion will vary from day to day and who may also be happy with a one percent distortion figure due to the harmonic re-structuring of the original signal. These new tools will aid greatly into taking away our individual biases.

Or will they?

John Fassotte
Alaskan Audio



[Edited by alaskanaudio on 11-04-2001 at 08:24 PM]
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Old 5th November 2001, 01:38 AM   #4
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I know what you mean. Audio equipment it's no magic; and servos & stuff HAVE their place, it's just i beleive you don't see them a lot on the DIY ground because they tend to be rather irksome to design and build... even when most of the times the results are rewarding.

I haven't tried using my soundcard as test equipment yet, but i've heard from people using cheap 16-bit ones, and they, all within their limitations, obtained great results. I beleive scientific measurements (THD, noise, crosstalk, bandwidth, etc) are important, and perhaps even a bit more than actual "listen" tests, which are subjective most of the time. A test i found very informative is the square wave response, specially on complex loads. Unfortunately, they're rare to come by...
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Old 5th November 2001, 11:56 AM   #5
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What we need to remember is that audio measurement equipment, currently in use are not designed on psycho-acoustic models and convey very less as to how human beings would perceive sound. Good measurements are good indeed when they translate into 'subjectively' appreciable sonic qualities. For example, a high NFB will enable good THD measurements to be obtained from common circuitry; however, sonically what it means can only be inferred from a real listening test. Instruments are not substitutes for human beings and they were not meant to be.

The audio world's pursuits should be (1) to arrive at psycho-acoustic models based on criteria that actually determine our appreciation of reproduced music and (2) to change the parameters that we measure, based on these models. Only then will there be a corelation. Or we would just be participants in this endless debate.
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Old 5th November 2001, 01:33 PM   #6
ALW is offline ALW  United Kingdom
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Default I like Einstein's take

He said 'Everything should be as simple as possible - but no simpler'

Sometimes circuits need to be complex to do the job, it's all about acheiving the end result in a set of circumstances.

The passive preamp is a classic example, given the right situation it can sound great. In others though it's a disaster.

Andy.
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Old 5th November 2001, 07:38 PM   #7
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Well, of course, test equipment is no replacement for a good set of ears But i feel that most "listen test", while necesary, are very, very subjective.

Let's take a valve amp, 1% THD. Now take another amp, identical specs but much lower THD (solid state probably). Most people will feel that the valve amp is better sounding, and probably will be, as the distortion will be mostly 2nd harmonic. But is that amp "better"? I mean, if i wanted 2nd harmonics, i'd add an exciter or something... to me, it might sound better, but we're not talking hi-fi anymore, because, well, the signal coming out of the amp has little to do with the signal that got into it. I'm not saying that valves are bad or or anything like it (i'm a guitarrist and wouldn't trade valves for anything ), it just goes to show that listening test, while valid, are not all.

On the other hand, an audio amp is all about listening, so if someone's happy that way, why bother? Well, that's about everyones taste...
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Old 5th November 2001, 08:05 PM   #8
mlloyd1 is online now mlloyd1  United States
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This is one of the issues I wrestle with:

Let's say I can make an amplifier with current mirrors, etc. that has lower total distortion "energy" across the audio band than a "simple" topology amplifier. However, the "simple" topology amplifier will have a different distribution of the harmonics across the audio band.

I can make the frequency response (bandwidth) and rise times ("speed") identical. I can use the same grounding schemes, attention-to-detail in the layout, etc. to control noise, hum, etc.

I also assuming "normal" operation (not near clipping, no out-of-band products, etc.). Some may argue, but in my application, this is a valid assumption.

Which amp is "better"? Why?

I think given the current available technology, some "complexity" is necessary. For example, for most amp designs, cascoding the 2nd stage brings about sonically benefical and measureable improvements.

I've been curious about mating a reoptimized Leach low TIM amp with Doug Self's clever Class A bias regulator (I'd drop the rails to cut down the heat problem - lower output power is OK to me). All things being equal, would this be a better amp than a reoptimized version of Nelson Pass's 20W class A project from Audio many years ago?

I think my biggest problem is time to play with all the ideas you folks put in my head :-)

Gotta go, the soldering iron is hot now ....

Michael

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Old 5th November 2001, 08:16 PM   #9
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Default THINGS of VALUE

ALW I have heard this before and also use this principal. The complexity of a circuit is in general determined by the goals set by the designer.


I have read Samuels post and thought about away to answer it since it is not uncommon for ears to be used to counter the use of test equipment designed for audio testing.

Here is what we may need to do.

We build a perfect amplifier by what ever means are required. What comes in goes out with no coloration of any kind.. Then we add controls to this perfect amplifier to vary the amount of distortion, phase shift and frequency balance to make the reproduced sound the most pleasant to a particular set of ears under unknown but varied conditions.

After this is done we can use the test equipment to see what control settings were required to make each ear happy. The left and right ear of course may not require identical settings. We then consolidate information from many such tests and build amplifiers that reproduce the exact amount of desired signal modification required to satisfy the majority of ears. Now we should have the perfect amplifier for sound reproduction. At least for most ears.

Striving for outstanding technical performance could thus be limited to generating the proper amount of signal modification instead of striving for no signal modification at all. This would relief a lot of stress for a lot of engineers.

The one drawback is that the ears used in each listening test canít be calibrated. Thus there is no true reference point that is good for all ears under all conditions. This leads me to believe that building equipment to satisfy a particular ear may not be good for all ears.

But building equipment in this manner may still be good since I would be able to use all my test equipment to some degree and thus my investment in it would not have been a total waste of money. Each potential listener could provide information on just exactly how his ears need a particular amplifier to modify the signal for best listening quality in his particular setting. DSP may be the best to do this user specific tailoring. Thus I may need to purchase some DSP programming and test equipment.

John Fassotte
Alaskan Audio


[Edited by alaskanaudio on 11-05-2001 at 03:19 PM]
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Old 5th November 2001, 09:32 PM   #10
ALW is offline ALW  United Kingdom
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Default Which and why

>Which amp is "better"?

The one that sounds best (i.e. most enjoyable).

>Why?

'Cos that's what it's all about. As an engineer I like to measure things and design the 'best' but ultimately if it's not enjoyable it's not doing it's job.

Given good recordings by talented musicians one should be involved in the musical performance. It matters not one tiny bit whether it measures 'perfect' or not.

Andy.
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