Simple or Complex Circuit Preference?

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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 ( 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]
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...
I Agree


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 Krell’s 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]
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...
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.
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.

Well, of course, test equipment is no replacement for a good set of ears :D 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...
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 ....


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 can’t 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]
Which and why

>Which amp is "better"?

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


'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.

If I had ever once noticed a consistent trend that amps that measured better also sounded better, I'd still be pounding the pulpit for multiple zeros in the distortion specs. In fact, I found that distortion specs are virtually meaningless as an indicator of sound quality.
--Some amps that measure poorly sound bad. The trivial conclusion here is that "of course" the amp sounds measures badly. But is it necessarily so?
--Some amps measure poorly but sound good. This invariably seems to lead people into the old thing about "...well <i>obviously</i> you must like 2nd harmonic distortion...", usually trotted out when the amp that sounds good is tubed. The quickest way to quash that argument is to pull out a solid state design that doesn't measure very well, but sounds good. It's always amusing to hear them try to get out of the corner they've painted themselves into.
--Some amps measure well and sound good. Again, the trivial conclusion is that it's <i>because</i> they measure well. that a valid conclusion?
--And, finally, there are amps that measure well and sound like breaking glass. This case is the saddest of them all, because there are invariably people who will convince themselves that it sounds good--because, look, the specs are so good! It <i>has</i> to be good...right? The only cure for this sort of delusional thinking is a concert hall, but rarely do people of this sort care to put their preconceived notions of 'good sound' to the test.
I've heard amps in all four classes. I've owned amps in all four classes. After years and years of defending specs, I finally learned to buy the equipment that sounded like what I heard in the concert hall. All else is simple sophistry.
Is the sound quality related to the simplicity of the circuit? Partly. But also partly due to the parts quality, topology, operational class, the choice of gain devices, etc. There's no magic, per se, just an accumulation of wise choices. The more right decisions made, the better the circuit will sound, but no one choice will 'kill' the sound, nor will a single decision make a circuit a classic, respected years later as a breakthrough. If enough good choices are made then the scales will tip towards a better sounding piece of equipment.
As someone said above, if band-aids have to be applied, it's time to rethink the basic approach, rather than try to beat the poor thing into submission. Back up and pull out a clean sheet of paper. In my guise as author, I once heard some advice: The more you labor at a scene that isn't working, the worse it will read, and the less likely that you'll admit that there's something wrong. Something similar is undoubtedly true for audio.
I just wish I had back all the money I wasted over the years in pursuit of good specs.


[Edited by GRollins on 11-05-2001 at 05:57 PM]
I am taken with Einstein's comment too, but in truth it has only entertainment value, and says little about creative process. I believe we know what he means only if we have created something innovative ourselves....

I am not as fortunate as John and have little test gear; signal generator, CRO, lots of DVMs. However, I indulge a little design, and I read a lot, and I agree that Doug Self's site is very erudite, and very useful.

Of particularly interest to me is the musicality of the amp. Horrible word, but it simply means listening to the amp as the consumer would listen; to see if it tugs at the heartstrings. Not very scientific, but then, the ear is extraordinarily sensitive, and I have found that much of the math and measurement approach leads me up blind alleys.

I think I follow John's comment about circuit complexity. One can use a very simple circuit, but to make it work properly may require a fair degree of supporting infrastructure; constant currents, regulated voltage, etc.

Some circuit concepts are counter-intuitive; who would have believed, for example, that dielectric qualities of the lag compensation cap in an audio amp have profound influence on the bass? We are talking 100pF or so here; but it's true. And who fully understands why the wonderful impedance characteristics of a constant current source can greatly complicate the stability of an audio amp?

I am confident that the subjective listening test remains the criteria by which the market assesses an audio amp. There is growing cynicism about good specifications, whose day might have come and gone amongst the cognoscenti, but which looks like reviving with the new digital amps (which are immediately stunning, but pall after an hour's listening.)



Hugh R. Dean
Re: Which and why

ALW said:
>Which amp is "better"?

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


'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.

Ok, but my whole point is: what sound goods to you, invariably sounds good to everyone else? This is what i mean by "listening test being VERY subjective". I'm not trying to drop my ears for an oscilloscope; i (anyone) can design an amp that will show near-zero THD and sound like crap when real music is run through it. We all know there's more than THD, bandwidth and stuff to an audio amplifier, but, sadly, that's all the OBJECTIVE we can get to describing it.

In the end, some people like Krell amps, other like Willamson valve ones, it's all about tastes.
I've got a question for folks that have been at this a while. I want to educate my ears, so I'm looking for some examples. I looking for a couple of products (tube and solid state) that fit each of the groups below:

1. Measures good and sounds good
2. Measures good but sounds bad
3. Measures bad but sounds good

1. Measures good and sounds good
2. Measures good but sounds bad
3. Measures bad but sounds good

1. Not a lot that i'm aware. A friend of mine just built the ESP 60w AB, which measures wonderfully and, to my ears, sounded just as well.

2. Lots of examples, both on DIY and comercial... let's take Krell; they measure great but some people told me they found them "sterile"... couldn't tell for myself. Again, "sounding" bad = enterely subjective. Most mid-fi amps have rather good specs the sound does not follow.

3. Most quality valve amps and some of Nelson Pass' amps, the SOZ for example.
1. I actually think the top Krell amps definitely fall into this category.... After listening to ANY of the FPB amps, I find them just absolutely stunning to listen to. You can add Levinson to this category too.

2. I'd put most stuff that's considered "mid-fi" in here too... Take NAD for example, I'd consider most of their stuff to sound bad but it measures pretty well....

3. Lots! Just about any Cary or Conrad Johnson Valve Amp for starters....Cary stuff measures ABSOLUTELY TERRIBLY but there are a LOT of people that think they're beautiful sounding amps.....
Interesting discussion.
Its is actually very subjective, we all seem to hear the same things at the same time completely different. We all agree on a certain musicality factor ( - which touches you when you listen - ) but we get to this point on different paths, I suppose.

My "three" pence:
For me personally Krell amps sound absolutely terrible, and so do Levinsons. They are clear and big sounding, but when I am listening I fall asleep immediatly or my mind turns elsewhere.
I always regarded the NADs, at least the older ones, as not so bad, very good in an average and cheap setup. They actually measure worse than they sound !
I once had the chance to listen to a Audionote ONGAKU for a certain time, with an all analog setup: That sounded really good ! And if it would measure anyhow, I do not care at all.
Strangely I have heard good sounding amps with both complex and simple circuit topology. It seems more a matter of synergy.


ps: In my kitchen and eating room I listen to an 1970s transistor radio I once found at a junkjard (!) and repaired it. It was made by HEA, a long defunct Austrian company, uses an oval speaker from Celestion in a wooden box, with an amplifier with two germanium transistors with approx. less than 1 watt. Yes, there is no bass and a lot subtle information is lost, but this little beast sounds absolutely great ! I use it everyday, for news and music, classical and rock, the sound fills the room with ease, sometimes I think my local independent rock music radio station nowhere sounds as good ...
Low Feedback and Low Damping Factors

I believe that many power amplifiers have damping factors that are just too high to make loudspeakers sound as good as they can.

Many amplifiers that claim to have very high damping factors usually have significant amounts of feedback around the output stages. This feedback is primarily used to reduce measurable distortion to insignificant levels. But secondary function of this feedback is to increase the damping factor through the regulation of the amplifiers output voltage that the feedback produces.

Thus if we can regulate the stability of output voltage versus amplifier loading through the use of feedback we can control the amplifiers output impedance or damping factor as it is commonly called.

Damping factor is also a function of the type of output devices used and their configuration in the circuit. MOSFET’s in general will offer lower damping factors than BJT devices. MOSFETS are usually operated at or near class A bias conditions to achieve the best performance with minimum feedback. I personnaly do not care to use emitter or source followers in the output stage since they have to much self feedback in such a configuration.

As I recall there were a number of excellent power amplifiers available in the past that had a way of adjusting damping factor thru the use of selectable amounts of negative feedback. These adjustments were used to optimize amplifier damping factor for a particular loudspeaker. A change of two to four Decibels in negative feedback around a low feedback amplifier can change the sound produced by the loudspeakers substantially.

Personnaly I prefer amplifiers with relatively low damping factors and thus relatively low amounts of negative feedback around the output stages. This does not mean that other stages in the amplifier need low feedback levels when such feedback is applied around short local secondary loops. A damping factor of 10 to 20 is what I would consider optimum for best sound quality in a power amplifier. Anything higher would tend to resemble a power supply and not an amplifier designed for best sound quality.

I suspect that many individuals prefer the sound of amplifiers with low damping over those with high damping factors. This is likely one of the prime reasons why many tube and simple solid-state amplifier circuits are preferred. Both tend to have lower damping factors..

John Fassotte
Alaskan Audio
First let me say that I do NOT wish to offend anyone by what I am about to say, after all it’s only my personal opinion. What a interesting discussion it has been so far.

I think that we humans are basically an arrogant bunch, (my self included, comes with the genes) and we find it hard to admit or remember that our perceptions aren't all that accurate, (OK I know yours are).

I like what sounds good to me, often new sounds. I love some systems that I could not live with. An example of this was the first time I heard Klipshorns, WOW! Possibly the most dramatic speakers I ever heard, you know you're alive! But I wasn't born yesterday, after an hour of listening I had to keep turning the volume down, (some call it horn loading fatigue).

Amps for me have been the same, I recently listened to another valve amp, and gee it sounded nice. "Here see what it does with this track." "No, I thought not, oh well." Suppose I need a number of amps for different music.

If I listen to amps blindly, not knowing anything about it, not even seeing it, (a shelf full of amps at the HIFI store) it often sounds nice? Interesting? Good? Whenever I look at the specs, they enlighten me to possible deficiencies that I can then hear. Can I really hear them, or am I imagining them? Well sometimes I know that I can hear them, they are that obvious, it was just that I was being entranced by this new sound before.

I now listen first musically, check the specs and them listen again critically and try not to forget how fallible my ears are. Don’t let your ears or minds fool you, use both of them, in the end you probably need to please both.

Regards WALKER

PS I've heard some great amps, simple and complex, MOSFET, BJT and THERMIONIC, and I've got at least one of each, but then I'm probably deaf as a post.
mlloyd1 said:

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).


could you elaborate on this? I have read everything that is on the D. Self site but this does not ring a bell.


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