Randy Slone: Opti-MOS - diyAudio
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Old 27th February 2001, 05:12 PM   #1
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I'm going to build an amp from Randy Slone called the Opti-MOS.

Go check this out: http://www.sealelectronics.com/

It's a traditional amp with incredible specs. Has anyone else built or looked at these amps?

I called and talked to Randy Slone. He's an incredibly nice guy. He didn't know me, but we talked Audio Philosophy for a half hour. The main theme of the conversation was amplifier transparency. Which I agree with, wholeheartedly. That's one reason I bought the book, "High Power Audio Amplifier Construction Manual" by none other than Randy Slone, of course.

I was looking for a high power transparent amplifier. It can be made to be 80-200W. The worst case distortion is about .04 according to Mr. Slone. That's not the 1kHz 0dB number which is 0.005. That's the worst case anywhere between 0-infinite dB and 20-20kHz. That's awesome!

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Old 27th February 2001, 07:36 PM   #2
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Don't get too besotted with distortion specifications. They mean virtually nothing. Tube amps typically have distortion specs an order of magnitude higher (or more) and just as routinely trounce solid state amps for sound quality. (Note that there's no spec for 'transparency,' although it's a commonly accepted term to describe the sound of audio equipment.)
If it's power that you want then fine, but there are lots of amps out there (viz. 'pro' amps for PA or what have you) with vanishingly low distortion specs...but most don't sound all that good.
Phrased another way: Negative feedback is a cheap, easy fix.
Tube amps generally have NFB on the order of 6 to 12 dB. Solid state amps...well, the sky's the limit, and the specs get better and better all along the road. But, funny thing, the amps sound worse and worse. Dry and lifeless. Sure, the music comes through, but does it have that magic?
The disclaimer here is that I've never heard the amp you're describing, although I looked at the website once upon a time. It may be just wonderful. I hope so. We can use all the great sounding gear we can get (whether tube or solid state).
Good luck.

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Old 28th February 2001, 02:27 AM   #3
blmn is offline blmn  Brazil
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You bought a very good book. I think you have already read the chapter two (misinformation in audio) so that you have a consistent basis now to understand why these standardsare important. I'm sure you will make a very good amp.

Tell us the results, please.

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Old 28th February 2001, 03:23 PM   #4
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I think you need to pick up this book and read Chapter 2.
There is no magic in power amplification. If I want to add
that "magic", I can buy a tube pre-amp to add the 2nd order
distortion you love.

Personally, I own a McIntosh that I love. It's distortion meassurements are the same as the Opti-MOS. I won't say it sounds wonderful. I would say it has no sound. It doesn't change what the artist put on the recording. That is the ultimate goal here!

I've held these views for years. I bought the book by
Mr. Slone because he agrees with me. When we talked, he
stated an even more convincing argument. If you add
harmonics to an already harmonically rich recording like
piano or guitar, it will sound muddy. I personally have
experienced this. I had an amp that when it came to
Mozart's piano concerto #21, it sounded like the
piano was under a heavy blanket. With my McIntosh the piano sounds like... a Piano!

That's the best counter argument I can come up with at the
moment. Any more takers on this Grey's side? I love a good
debate on Audio Philosophy. There can be no winner! It's
a matter of personal taste. If Grey wants to watch a TV
adjustmented so the faces are greeen. Then that's his
perrogative. Personally, I wouldn't buy a TV that is
factory standard that way though. If I did, I wouldn't
be able to watch the TV in real colors. I would buy a real
TV and add a Blue-Red filter to the input.

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Old 28th February 2001, 05:06 PM   #5
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Pixie, blmn, et. al.:
Trust me, I'm well aware of all the arguments about specifications and tube vs. solid state. I've been at this for a long, long time. I've worked in stereo shops, both mid-fi and high end. I've listened to many, many systems, ranging from beginning to ultra high end.
Here's what I found:
When I began, I, like many others, wanted to make the best choices I could when plunking down my hard-earned money. I thought that the numbers on a piece of paper correlated to the quality of the sound coming from the equipment. I bought accordingly, to the tune of tens of thousands of dollars. (That 's' is not a typo...I spent a lot of money--enough to buy a very nice car.) I was one of the 'cool' people. I bought politically correct equipment...look, the specs prove I'm right! The techno freak in me was a very happy critter. Hell, I still get a kick out of hardware for hardware's sake, it's all part of the hobby. But...but...after I'd had all these various pieces of hardware for eight or ten years or so, I came to realize something, and trust me, this was damned hard for me to admit out loud at the time, for all their technological prowess, there were systems that were simpler and cheaper that sounded better. There were aspects to the sound that I had always blown off as hyperbole at best, and possibly downright lies, that were not only true, but actually correlated to what I heard when I heard music live. Things like image, for instance. I thought I had image. I was only partially right. What I had was a lateral spread, from left to right, so that I could point at, say, a guitarist. I thought that was all there was. I was wrong. With a system that can image, you can hear *deep* into the stage; it becomes three dimentional. Spooky, the first time you hear it. But I couldn't hear that on my system--just the lateral spread. But my prized low-distortion equipment! How could it *not* do everything right? Isn't getting the waveform through intact enough? The answer is: No. What's going on, here? Frankly, nobody knows what the whole story is. Phase shift plays a role in it. I'm reasonably certain of that. I'm also 100% certain that it's not going to be the whole story, either. I have an analogy with medicine. There are diseases out there that can kill you. That's a given. Medical science has made great strides in treatment of some of them. We have a vaccine for smallpox, for instance. Cheap, effective. Good stuff. But just because you have in hand an effective treatment for smallpox and pneumonia and can control some forms of heart disease does not mean that cancer does not exist. Cancer exists. Back to audio. Distortion, to me, represents an audio disease that has been cured, or at least managed. But to pat one's self on the back over having slain one beast whilst others are still on the loose stikes me as foolish. Let's be honest, audio is a niche market. The amount of money that the audio industry can bring to bear on studying pathologies of the sound is miniscule, compared to what's spent in the medical industry in a single day. Will some clever young lad (or lassie) uncover another pathology of sound? Yes. When? I dunno. In the meantime, you and I have to muddle on with what we have. I'm not saying that distortion specs aren't useful--they are--down to about 1% or so. After that, it's time to go looking for other problems. Yes, yes, yes...I'm fully aware of all the 2nd harmonic arguments, but there's nothing like a stereo shop on a slow afternoon, with five or ten really good (spec-wise and/or sound quality wise) amps/preamps/what-have-you to teach you that specs are virtually meaningless in the real world. And I had many slow afternoons in the trade. Even before that I can tell you that the day I bought my Linn Sondek LP12 (yes, I go back that far) was the first time I did something *right* in my audio system. I could hear more detail and the beginnings of a rudimentary image. And this from a turntable (turntables were commonly regarded as having no effect on the sound) that had lousy specs as far as rumble, etc. However, Ivor (head guy at Linn Sondek) had this idea he called Loss of Information Theory. In other words, he'd identified a pathology, and set out to cure it. Others later went far beyond his work, and didn't even bother formulating theories to cover what they were doing, but turntables got better because Ivor had the essential breakthrough idea. Thanks, Ivor. Mind you, I'm not aware that anyone has ever bothered to come up with a method to measure LOI in a turntable. All they did was tighten up the tolerances on the bearings and make all the mechanical parts fit together tightly. But just because no one bothered to make up a spec doesn't make the concept invalid, nor does it mean that you can't hear the difference.
Regarding hearing differences: It has been my experience that there is a breakover point, a threshold below which improvements to an audio system are inaudible. Let's take a gross example. Put the finest, most elaborate turntable/CD player into a table radio (we're assuming phono/line in jacks). Ya can't hear it. How good does a system have to be before you can hear a difference? That's hard to say. It depends on what you're trying to hear. Image, for instance, is particularly fragile. I've never heard a mid-fi system image. Only in rare cases have I heard anything like an image from a (forgive the hodge-podge) lower high-end system. There's also the hurdle that you have to educate your hearing. Huh? You know how to hear, don't you? Well, yes, and no. When people are stricken blind, they report that their hearing acuity increases. Your hearing can be 'taught.' The trick is to heighten your hearing, while retaining your eyesight. Try this. You know your home, right? Try navigating from room to room purely by your hearing, eyes closed (or at night). Listen for the walls. They're there, and you can hear them in subtle ways by the sound that reflects off of them. The ticking of clocks, the shuffle of your feet. Listen! You lose points every time you slam into a wall. Give it time. You're learning a new talent here. You're learning imaging. Then go back to your measurements and tell me where what you're learning about imaging fits in. It doesn't. Neither does transparency, which I happen to think is a very important descriptive term. I can hear transparency, but I'll be damned if I can think of a way to measure it, bottle it, and put it on the shelf along with harmonic, IM, and TIM distortions, S/N ratios, etc. Pixie, if you can figure out a way to quantify transparency, my hat's off to you, tell us all how to fix it, and we will. In the meantime, speaking as one who spent many, many dollars chasing spec sheets and ended up with a pretty flat sounding system, I'll keep going to hear live music (not rock concerts--no longer--too loud and too processed) to keep my hearing tuned up and going for sound quality instead of specs.
Oh, and as a footnote, I own both tube and solid state (Would you believe Nelson Pass era Threshold S-500's? Putting a couple of film caps across the electrolytics in the power supply does wonders for the high end.) equipment, and like both...for what each does well. I have just reconfigured my system for quad-amp (tweeter/mid/woofer/sub) using solid state for the lower frequencies, tubes for the mids, back to solid state for the highs. The dust hasn't settled yet. I have projects in the works which may be of interest to some of you. I'll post when I have results to report. (I seem to remember that there was a post a few months ago about an active crossover question-> Would an emitter/source follower work with a Sallen-Key topology? Yes, it does. If anyone is interested in active crossovers, and if I can figure out a way to get the schematics up, I'll be glad to share. I plan (pax, Pixie) to try a tube version and compare sound-wise, as soon as I can clear out a few other things, like the amp I'm building.)
Jason: Sorry about the length of the post.

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Old 28th February 2001, 06:30 PM   #6
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Something I forgot to put into my previous posting that I find to be food for thought. In my experience, there have been many, many people who have gone from believing that specs count for something to actually listening and comparing what they hear to real music. But not a single person have I ever known, nor have I ever even *heard* of, who 'saw the light' and went from listening to believing the specs. The uni-directional flow is instructive.
There are people who get disgusted with the pricing of good gear and quit the hobby. There are people who hit hard times and have to accept cheaper gear because they no longer have the resources to buy something better (but don't get in their way when better times come along, because they're headed for the nearest audio shop). There are people who fall to the Spousal Acceptance Factor and have to either drop back or get divorced. There are those who get irritated over the hocus-pocus factor put out like a fog around some manufacturers' product (some of the product sounds good, and some doesn't--absolute dreck--but the hand-waving is highly annoying). And there are those of us who turn to DIY.
But never have I known someone who went back to specs...

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Old 28th February 2001, 09:04 PM   #7
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You supported my arguement. The turntable is the place to add the "imaging" or "warm sound". Even the pre-amp.
But, the amp will have no effect on that sound if it accurately reproduces the input wave. There is no way adding more distortion in the amp phase is the answer.

If we can illiminate the amp as a sound shaping element,
we can add shaping to any input. Which means we could have the nice 60's warm valve sound from the turntable, but have nice perfect sound from the DVD player.

Personally, I want that option. I don't want a separate set of amps for each medium.

If it's price you're worried about. The Opti-MOS is $162 plus the cost of the power supply. That's incredibly cheap. It would cost less I'm sure if you make your own boards and price shopped for the parts. I'm buying the kit for simplicity. I went through the whole process of etching my own boards and buying the parts for the Zen. I've had that experience, I don't really need to do it again. But, the Zen didn't sound as good as my McIntosh. So, I'm going for quality this time, not an illusive sound.

I absolutely do not want the amp to shape the sound for me.
As Randy Slone puts it,
"The holy grail of amplifiers would be a wire with gain."
Or from Nelson Pass,
"Areas of criticism of the design(Zen) all relate to the objective, measurable performance, but in addressing them, I found that the subjective performance improved with the measurements."

That's the end of the arguement from me. This has been a facinating debate of philosophy, but like I said there can be no winner. We are the extremes of a age old debate. If the hundreds before us haven't come to a conclusion. Then neither will we.

Thank you for the stimulation in my otherwise dull day.

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Old 28th February 2001, 11:04 PM   #8
grataku is offline grataku  United States
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Randy Slone is a very nice guy indeed. However, if you read his web site, you will find that he is also a jesus freak, a creationist that, when it comes to his spiritual beliefs, refutes the scientific evidence to the contrary. He completely turns around and takes the objectivist approach as his audio philosophy. Here only the hard experimental data matters. Therefore, an amp with low measured distorsion will always sound more transparent. As a result of this conflicting views it hard for me to believe the man. I guess that at the end of the day he was able to sell you an amp and I hope you are happy with it.
There is a review of his book on the Jan issue of Audio Express that I recommend you read. The reviewer points out some of the more objectionable and bad-sounding choices for example the back2back tantalum decoupling capacitors.
As far as I am concerned I take an empirical approach: change both the circuit topology and the components until you get the best possible sound to your ears.
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Old 1st March 2001, 03:04 AM   #9
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Just for fun, I checked out the Slone book from the library. And, for the record, I agree with perhaps 30% of the things he says in Chapter 2. As for the rest...well, there are some real howlers in there.
One thing which I find distressingly common is the setting up of a straw man, i.e. intentionally (or, to be charitable, unintentionally) wrongly stating a case in order to make it fallacious, hence easily knocked down. Case in point: The "Trade Secret" at the bottom of page 19, where he states,"Monoblock construction always [sic] provides audible sonic improvement." Sometimes, perhaps. Definitely a good idea if you're running a smallish power supply because of inability to get, say, a 20A transformer, but can get two 10's and use one for each channel. (Something DIYers come up against frequently.) But that 'always' makes it very easy to take the moral high ground and 'prove' that you're right. It's all in how you phrase it.
His insistence that high end amps are of necessity complex flies in the face of reality, witness the Zen amp Pixie built. In fact, it is generally the simpler ones that sound better.
He mentions the recording (aka 'pro') industry as being well supplied with 'high-end' gear, and holds it up as an 'example' in the sense of someting to emulate. Whew! That's a good one. In reality, much studio gear is not even up to the standards of an ordinary mid-fi system. When he said,"Their livelihood [recording enginneers] depends on the highest quality sound obtainable at any price," I nearly fell out of my chair. In fact, the recording industry is, like everyone else, obsessed with the bottom line, and even in the cases where the folks in the studio want better quality gear, the brass won't let them have the budget to buy it. The product they're putting out is selling just dandy, so why spend more money to improve it? That's on page 30, by the way. Hysterical.
P 17, (yes, I know I'm jumping around, page-wise) he says,"If elusive audio subtleties were actually degraded by solid-state processing, as many subjectivists claim, how could they even exist on the sound medium?" Thanks, guys, this guy's a card. I laughed so hard I nearly wet myself. I guess by Slone's 'logic' if one tiny spck of dirt gets on my window pane, then no light will come though at all, right? By definition, degraded means that the original quality has deteriorated...not stopped entirely. Yet, Slone seems to feel that it's an all or nothing proposition; a brick wall.
The word sophistry comes to mind.
I could go on and on and on. There's hardly a page in Chapter 2 that doesn't have at least one seriously flawed statement. My problem with this is that (aside from the fact that the distortion figures don't correlate with reality--if they did two amps from different manufacturers with the same specs would sound the same, and they most assuredly do not) for a philosophical stance that claims to be based on logic...it isn't. The 'logic' is seriously flawed, and it's all right out there in public. The story The Emperor's New Clothes comes to mind.
When the Hafler apply-the-input-to-the-output cancellation strategy came out, I was pleased. Finally, I thought, we'll get to the bottom of some of these things. So simple. So elegant. The only problem is that amplifiers did *not* take the expected quantum leap forward.
So what gives?
I'd love to know, myself. I hear things that no one has (yet...I'm still hopeful) tracked down in measurements. Does that mean they don't exist? Not by a long shot. Maybe we're hitting transient problems. (N.B: *Not* TIM; I'm not impressed by slew rates. I'd love to figure out a way to look at real music transients in slo-mo, compared to the input. Steady state specs don't cut it when we're dealing with a moving target.) Back to the lab, guys, we're going to have to figure this one out ourselves, because it's a cinch that we're not going to get a grant from Washington. But we won't get anywhere by claiming that the differences/problems with sound reproduction aren't there.
I listen, then try to figure out why I'm hearing what I'm hearing. Sometimes I succeed, sometimes I don't, but that doesn't mean that I retroactively do an Orwellian doublethink and blot out the fact that I heard something. Other folks seem to prefer to tell their ears what to hear, based on what they've read, whether specs or soi disant logical arguments. I'd like to note also that there's an element of self-fulfilling prophecy here--people make up their minds that high end is bunk, so of course they're not going to 'waste' all that money on something that costs as much as good gear costs. Reasonable, on the face of it. (I'll be the first to admit that the pricing of high end gear is horrendous these days.) So they end up with a system that doesn't have sufficient resolution to let them hear the difference between, say, capacitors or speaker cables, then they say (Suprise! Suprise!) that there's no difference to be heard. Moral of the story: Don't buy a Walmart microscope and expect to see paramecium--you'll be lucky to see your fingerprint.
So...what to do? Not an easy question to answer. The quick and easy answer *should* be to visit a high end shop and listen for yourself...something 'objectivists' (Slone's word--I prefer to reserve that term for another use.) are reluctant to do. Why? They've already made up their minds there's nothing to hear...another self-fufilling prophecy. And frequently the sales staff are over-egoed and under-trained, sometimes downright greedy...they want that commission, or they're facing a sales quota (ugh--not a bright thing to saddle a fella with when he needs to take time with a customer). It's not uncommon to find the systems in disarray. Sigh. The problem isn't a new one.
I'm more than willing to have people listen to my system, but I don't think any of you are in my area. As I said above, my system is in transition at the moment, but I can probably demonstrate the reality of a few things that 'objectivists' love to pick on. Then we can put our heads together and try to figure out why such reasonable-seeming things as why the Hafler test don't show what they ought to show. Man, I had high hopes for that one! Trust me, I want to be able to measure what I'm hearing, so as to figure out ways make it even better.
Oh, got the Douglas Self book, too. Will try to at least skim both over the next few days. Yes, I saw that Self has a chapter on objective/subjective. Haven't read it yet. Only so many hours in a day and I've got three audio projects in motion, stories to write, and a full time job.
Jason: I know we're not killing trees, here, but do you have a limit on post lengths? (Assuming that we stay more-or-less on the topic.)

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Old 1st March 2001, 05:11 AM   #10
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I've now read the subjective/objective portion of Self's book, and am pleased to report that he, for the most part, resists painting himself into logical corners quite as baldly as Slone does. I also enjoy his slightly harrumph-harrumph British tone of writing. That said, yes, he makes some of the same logical errors, albeit more subtly. I find it interesting that he, on page 22, seems to see no problem with a current-limiting amp, i.e. one which is incapable of doubling its power when going from an 8 ohm load to a 4 ohm load. I would think it a trivial observation even to someone who puts their faith in specifications that, given that speakers rarely (yes, there are exceptions) have flat impedance over their entire operating range, an amplifier which could not deliver sufficient current to meet demands would not be the proverbial 'straight wire with gain' that we all desire.
This is, I find, a common failing. Components measure one way on the bench, but differently when faced with the real world. Putting a capacitor on the output while on the bench is, perhaps, a start, but since real-world speakers are more complex RCL networks, I would think that it would be obvious that someone should try more global measurements involving entire systems, just as an illustration of the sorts of things that could go wrong. Yes, I realize it would only show the interactions between that one set of components--this is not to propose some global table of every extant component where one could run a finger across a column and see how preamp A would behave with amp B, running into speaker C in terms of frequency response at rated power. But a limited subset might prove instructive in the sense of revealing interactive errors capable of objective measurement.
In the case above, presumably subtractive ones where, as an example, amp that delivered a rated 100W at 1KHz, and possibly at 200Hz, but only two-thirds of the power required at woofer resonance, or at a crossover point where the impedance dipped.
Pixie, would you not agree that this would be a measurable problem...one with real world consequences? If so, then we have a starting point...no 'magic' involved, just pure math, meters, and oscilloscopes.
Simple enough to cure, of course, bigger power supply, for one, possibly bigger output stage. All this means money. Compromises would be in order, either in performance, or in price. Or both. But it would provide us with a philospohical starting point for dealing with real honest-to-goodness objective measurements of hitherto 'subjective' issues.

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