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Few questions about the leach amp
Few questions about the leach amp
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Old 30th March 2001, 12:11 PM   #21
carlmart is offline carlmart  Brazil
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Importing parts from Europe is not expensive and it's very easy. Usually pay no taxes when coming into the USA.

So getting caps from there might be a choice. A friend of mine is using Ansar polypropylene caps, that you can get from Cricklewood.com or rswww.com. Many say they are much better than Solen and very close to Hovlands for very reasonable prices.

But I would also like to get back to what this thread originally was: Leach amps. Or solid state amps at least.

Since I started DIYing, many years ago, my quest has been to find what made things sound "right", lifelike, as live instruments do, and to investigate how designs or parts collaborated for or against that fulfillment.

What "gets in the middle" is distortion, dynamics, bandwidth, acoustics, you name it. When you get a balance of some of them you usually stick to it. And that seems to be what, IMHO, tubes and horn speakers do when they work together.

At a price though, because the extremes (high and low ends) in tube designs merely come through. The mids seem to be the prize, but I refuse to get a Golden Globe when I can get an Oscar...

Solid-state, also IMHO, is more "diyable" than tubes: cheaper, low risk (lower voltages), usually works right away.

So what it misses as a total experience? Coherence with the sound, as most solid-state circuits don't shine through in a particular range as tubes do in the mids. Solid-states output more bass, important on some music types, but some are criticized on the highs response, when compared to tubes. Which sounds funny comparing to a design that is highs shy...

So how to do solid-state amps, and particularly DIY projects, sound better? When I came into following this DIYforum I hoped to find some answers.

Douglas Self did a very thorough research on distortion and how to improve on it, though he never showed (rather disregarded) listening tests results.

But why don't we stick to solid-state and try to get "tube-like", coherent results from these circuits? Or are they doomed? I think not. I think we can add clean, "liquid" mids to the bass, cleaning it also as well as the highs. How can we do that?

The Leach amp, which BTW I never listened to, has been one of the most popular among DIYers, so why not try to improve on it?

Why not adding low current regulators on the voltage amp stages? Why not trying different regulator types, discrete or not, to see if the sound improves? If we want to build a house the structure comes first, so why not consider the supply as our amp's structure to build upon it?

Listening is something we DIYers can all do, though measuring most cannot. Why not report on what block changes (say a current mirror instead of a cascode or viceversa) do to the sound, or what happens when better constant current sources are added? What happens when parts are improved or changed?

The Leach amp was just mentioned as an example, as it's known, easy to get and several suggestions on how to improve it have been mentioned on this Forum. It might be legitimate to experiment on it as a common ground to start from.

How do Spice or similar simulations relate to sound? In the same way as objective measurements do? How far can you get with them? What do they leave out?

A lot of questions indeed, maybe deserving a whole new thread of their own. How far can we commit to go on this quest?

Sorry for the long text.


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Old 30th March 2001, 05:23 PM   #22
GRollins is offline GRollins  United States
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I have a friend who listens, almost exclusively, to rock & dance music on a good system. He's not so much a DIY as a heavy modifier. Very heavy. Amongst other things he reconfigured the passive crossover on his speakers. A classical concert came up with some pieces that he thought he'd like to hear (he does listen to some classical). I met him in the lobby during the intermission. He was shaking his head. I asked him what was wrong. He sheepishly admitted that he'd gotten the balance of the highs all wrong--too much--when doing the crossover work.
It has been my experience that people frequently go for too much high end. Detail! Nuance! Accuracy! they cry. Just listen to the tinkle of the piano! That's accuracy!
"When's the last time you listened to an unamplified piano live?" I ask.
Some, out of pride, or because they truly don't care, never get away from that search for a bright sound. The ones who don't care I have no quarrel with. At least they're honest. Like a fellow I work with, if the words are intelligible enough to sing along with, he's happy. Maybe their interests are elsewhere. The world needs bird watchers and collectors of stamps. But those who, out of pride, or out of being too lazy to check their assumptions about what 'accuracy' is against the real world...I sigh.
The reference for accuracy is unamplified music. Period. Get that right and the rest will fall into place. Mind you, I'm not even saying that people have to *like* what they're listening to--just use it as a reference. I know that my system was *way* off of reality until I started going to something other than rock concerts. It was flat, it was low disortion...and it sucked.
Oddly, I learned in the process that I liked jazz and classical. Thought I hated them before. (Still hate opera, though.)
Along the way, you find that people tend to follow an arc from a brighter, soi disant 'accurate' sound to something that's somewhat less forward in the highs. I know it was true for me, and for innumerable others I've known. Many of them were repeat customers back when I was selling audio. I note with interest that Nelson Pass describes much the same progression in his own work--see the link to AVS that Mark (mefinnis) offers elsewhere. For that matter, read the whole thing. Nelson has some interesting things to say, overall.
Carlos, per your remark about Self/Slone (to me they are tied by philosophy) never listening. I agree wholeheartedly. But not only do they never seem to actually listen to their circuits, not once do either of them mention ever listening to live music. Sad, but instructive. Live music, not a meter, is the benchmark. They remind me of armchair quarterbacks. Lotsa talk about what should be done, but no action. It takes more than an oscilloscope to build a good amp.
Incidentally, tube amps can be very good in the highs. Very good. Yes, the lesser circuits go soft at both extremes, but the better tube equipment can do highs. The low end? Rarely, rarely. I've only known a small handful of tube amps that were good in the deep bass. The odds definitely favor solid state in that part of the spectrum, as even comparatively inexpensive solid state can do a decent job.
As far as modifying the Leach, I'm not sure it would be the best test bed, but there's certainly no reason to take that circuit as sacred any more than anything else. By all means, whip that thing within an inch of its life. Do I not recall that it uses a current mirror in the front end? I'd like to hear a report from someone on the sound quality of a current mirror vs. resistor load. Yes, I know what the numbers say, and yes, you'd lose gain in the process...I'd like to know what it *sounds* like.
Carlos, I suspect that Spice vs. real life is really the same question as do distortion specs mean better sound. Do you have some reason to suspect that Spice can tell us other things? If so, I'm all ears (so to speak). I'm all for measurements...as long as they correlate to the real world. Most of them, unfortunately, do not.

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Old 30th March 2001, 10:08 PM   #23
carlmart is offline carlmart  Brazil
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First of all let me say that I agree with you 100 percent on using live, unamplified music as your reference.

In fact that is my background, as I was a film location sound man for almost 15 years. Now I have my own small
audio & communications equipment rental business, so I have to keep in contact with whatever comes along, for better
or for worst.

In my recording years, the question was how to get a clean sound when recording and a vivid one when mixing. Unfortunately those were mono years, but the recording medium was excellent (Nagra recorders), as well as the mix medium (17.5mm sprocketed tape). Analog all over, even if I have absolutely nothing against digital... as long as you know what you are getting. But that's another story.

On the other side, my electronics knowledge is limited, but maybe that also gives me some freedom to judge things both as they sound as compared to what they measure. It's also the reason why I am asking for some guidance.

Striving for a live sound experience might be the word then, even if that becomes an impossible task.

On the other side, when you listen to the sound coming through a high quality microphone, through quality
headphones, you listen to a lot more than what you thought was there. The mind plays tricks with our hearing,
something that is even used (quite effectively) by some noise reducing systems or even low-bit digital media to do their job.

So when people talk about "the sound of a piano", or "the sound of a guitar", they are talking of what their mind reminds about it. Only traces of the "real" sound are there. But this is turning too philosophic, I think.

Something I would advise every audio lover is to walk to your closer music instruments center, where they will
probably have some quality microphones, and listen to your own voice and the salesman's through quality
headphones. Don't try speakers because they will deceive you: use headphones.

Then see if there's some guitar playing in the room (guitarists are always trying one), and listen what it sounds like direct and through the mike/headphone chain. You can't get better than this on what reference you should have (even if guitars have limited bandwidth).

Then go home and find a good guitar recording, play it and listen how it sounds like. Use it as a way to fine tune (or gross tune) your audio system. You might be surprised.

My asking to get back on the solid state thread didn't have to do with any kind of despise for tube equipment, but with my experience that what they provide is not completely accurate. A friend of mine who also read that post says that only poorly designed tube gear is high shy, just like you say, and you are both probably right. He says that they do not have poor bass, and I don't agree.

The question might be on how to take advantage of things from each field. A hybrid maybe, or a solid state
designed as to sound valve-like on what valves do best, if that is remotely possible. Some say it is not.

As I mentioned I don't have any plans to build the Leach, and if I did I would add some things to it, like cascodes and/or current mirrors at the front end. On my present amp, that I built based on Graham Nalty design about 15 years ago, cascodes are used everywhere. To good effect I think. A similar design, with different part values though, was used by a highly regarded Classé Audio power amp at the time.

That correlation of measurements and the real world is also something I have many times insisted on, as audio mags are not too good at looking for ways to make that intercross.

Sound, as well as photography, is quite good as long as you are on its linear area, but when you go into the black (lows) and white (high) areas things get complicated. It's there where the instruments should go measure, instead of taking boring measurements in the linear areas, as I think they do.

Gray, it's a pity you don't give access to your e-mail address. If you can please e-mail me.

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Old 30th March 2001, 10:50 PM   #24
Damon Hill is offline Damon Hill  United States
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The Leach amplifier does not use a current mirror or a true active current source; the designer felt they weren't worth the additional complexity. However, I'm taking my old driver boards and at least trying out some current source circuits on the diff amp. I believe Leach feels he has a predictable and stable design that is easy for beginners to build successfully, so he hasn't tried many radical departures from the design; all designs are tradeoffs in complexity and stability and you just have to set standards at some point.

I'm also interested in Sziklai (complementary feedback) output stages, though these are not as stable as emitter output designs. A Sziklai has 100% local feedback, and this might be especially useful in reducing distortion in a Class B output stage. I think it's worth experimenting, and I'm planning a new chassis and the necessary wiring changes to be used with my modified older boards.

There are some output transistors that are characterised for lower distortion, but I've stayed with MJ15003/4 because of compatibility and availability at lower cost.
One might want to consider the 2SA1302/2SC1328, though these are plastic case types with lower SOA.

Because the Leach design has a lot of decoupling and an inherently high PSRR, a regulated power supply is generally not worth the effort. But there's no reason it couldn't be done for the VA and diff amps; one might want to have a separate supply for those circuits.

Making significant design changes piecemeal is risky because it can change bandwidth and stability in unknown ways, though I did find that modifying the ver 2.something board's diff amp circuits to the ver 4.5 works perfectly well.

I did find it helpful to put in bleeder resistors for the power supply because it doesn't bleed down the rails symmetrically for whatever reason. But there is little turn-on thump and turn-off has usually been graceful, too.

I set bias on my Leach amps by monitoring THD at a low power lever and stopping at the point where the crossover glitches on the 'scope display disappear. I've tried high
levels of A/B bias and found that near-B operation sounded a little better.

My amplifier was built as a dual mono chassis with 60.000 uF per rail; I later added lots of film cap bypassing on the
caps and circuit. I think this cured some oscillation on
one channel, and overall may have improved the sound. At any rate, it does improve ripple without the trouble of a regulated supply. I like to think it sounds better with a massive power supply, but of course I really don't know. I simply had the parts and nobody to stop me from building the amplifier that way!

My present audio system is in my bedroom, using a pair of (original) Acoustic Research AR-11 speakers, rescued from Goodwill for $18 and upgraded with polyprop caps in the crossovers. These are four ohm speakers, so the amplifier is working harder now, but I can't drive them at REALLY high levels in my small room. But it's awfully nice having a real midrange; with the addition of Kimber 4TC speaker wire, I'm getting fairly good imaging that compares well with other good systems I've heard. I couldn't afford 8TC wire.

I do feel that the sound varies a bit from time to time, and
sounds a bit hard and edgy, at other times it is sweeter and more transparent. There MAY be a bias tracking problem, I don't know. I don't have any other power amps at present to compare to.

I'm curious to hear the newer 4.5 boards, because they incorporate some layout and feedback circuit changes that may significantly improve the sound, especially at higher volume with complex music material, such as orchestral works.
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Old 31st March 2001, 02:25 AM   #25
GRollins is offline GRollins  United States
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You're preaching to the choir. I've been a musician for thirty years. Live vs. live feed vs. recorded is a terrifying experience for those who think they know sound. The one caveat I would add is to your suggestion to use your own voice for testing. Most people don't know what their own voice properly sounds like, freed from resonances within their sinus cavities, eustachian (sp?) tubes, etc. Better to use the voice of a friend or loved one. Being a bassist (as opposed to vocalist, for instance), I'd be reluctant to use my own voice for evaluation, since I'm not familiar enough with how it sounds outside of my skull.
As for tube amps and bass...like I said, only rarely have I come across a tube amp I'd use under 100Hz. In every case, they were high-powered (150-200W and up) and *very* expensive. Not cost effective. I myself use solid state on my subs. For that matter, I've got SS on my woofer panels (meaning below 250Hz in my system as it stands at the moment).
When you bring up hybrids, you make my antennae quiver. I've never heard a hybrid amp that sounded as good as I thought it should. But that doesn't stop me from hoping that one can be done. One of the things I've got tucked away in the back of my mind is a hybrid using 6DJ8s or 6SN7s for the front and MOSFETs for the back end. Whether it gets done this century or not remains to be seen. I've heard it said, and from personal experience (so far) reluctantly agree, that hybrids bring out the worst in both formats, not the best. But I'm still hoping.
Egad! My E-mail address not there! I apologize. It wasn't intentional, I assure you. I thought I'd filled out all the blanks. I'll try to get that fixed right away. Thanks for bringing it to my attention.
I must have had the Leach circuit confused in my mind with another circuit. I defer to you on whether it does or does not have current mirrors. Please report on sound quality at your convenience, as I'm itching to know whether resistors or current mirrors cound better. I know from personal experience that it's damned difficult to design a current source that sounds as good as a resistor, regardless of what the specs say about the superiority of the current source.
You said you have 60,000 uF per rail on your amp. Is that one cap or several in parallel? If it's a multiple, you could always take some out and see how it effects the sound. There are some things that I've found that it's easier to tell by taking them away after you're used to the sound with them. However, it does take patience. In your case, if the caps are single 60,000 uF, then it may not be a viable option unless you have a matched pair of smaller (or larger) caps in your parts bin...

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Old 31st March 2001, 02:52 AM   #26
GRollins is offline GRollins  United States
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You mentioned variable sound, and I forgot to respond. Have you tried measuring your line voltage during good sound and bad sound? I know that in my previous house the voltage was rock steady at 123V. In my current house, I have watched it vary from 121 to 126V and back again over about a two minute period. This was without heat pumps or other major loads switching on/off (at least within my own house). There's also the possibility that you may have RF or other hash coming in over your AC. I use regulated supplies on everything I've built except the power stage of my amp. That one runs raw DC straight off the bulk supply. There are times that I consider regulating it, but it'd be a bear of a job. (575V at about .5A/channel) I also use isolation transformers with caps across both sides to supress a lot of high frequency garbage. The one to my preamp is a little more complicated, but the transformer and caps thing only cost me about $25 total. I got the isolation transformers surplus for less than $20. It was one of the best (and cheapest) mods I've made.
Again...apologies...and to anyone else who wanted to cuss me out (or confess to a love of tubes and was afraid of being lynched by the solid state mob if they wrote a public message to that effect) and was prevented from doing so. My E-mail button should be visible now. I wasn't trying to hide--honest. Besides, you know where to find me...right in the thick of things, usually getting fussed at (and fussing back, I confess).

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Old 31st March 2001, 06:35 AM   #27
Damon Hill is offline Damon Hill  United States
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The power supply consists of eight 30,000 uF caps @ 60V,
grounds all tied together with an aluminum plate. Would have done copper if I'd had it and might still--I've some
double-sided PCB material but I'd rather use solid copper.

I have a pair of Tripp-Lite power strips with plenty of LC
to filter the AC lines. I ought to set up a power monitor
though, as per your suggestion. The diff amps have zener
regulation for the current source, so they should be pretty stable--I've thought about using a 39 volt zener and a foward biased silicon diode to compensate for thermal drift.

As I lived in Georgia before moving to Washington State, I
put in the Tripp-Lites for lightning protection more than for RFI--out here we seldom get thunderstorms, the weather's boring!

I bought a couple of surplus split-bobbin 1:1 transformers
with the idea of putting them on my preamp/tuner/CD/whatever
for additional isolation, but haven't done it yet... This is a rental house and modifying the wiring for a dedicated
line probably wouldn't please the landlord.

I hardly recognize my own voice, I have a terrible chest cold. {gronk} I really should listen more to live music,
but hearing a friend's Martin-Logan electrostatic speakers was demoralizing enough!
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Old 31st March 2001, 03:47 PM   #28
GRollins is offline GRollins  United States
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Sometime when you have a few minutes to spare, disconnect half of those power supply caps and listen, then give us a report...
I'm certainly not saying that you should modify your house wiring! Run a power cable out to the circuit and an outlet on the other side. I just checked my power critters and found that I've got .25 uF Sprague Orange Drops (I think I posted elsewhere that I had .1 uF, although that will do just fine) across the front and back of the isolation transformers. Just junk box/pack rat stuff. Certainly not anything 'audiophile,' but the sound (at least here, Chez Bear) cleaned up considerably. Obviously, it does nothing for the voltage fluctuations. Consider making up two for starters; separate ones for the CD and preamp. The preamp because it's most vulnerable in terms of low level signals. The CD to catch any digital hash that may try to sneak back up the power line into your house wiring. Separate mainly because you'd like to isolate that CD in its own little universe.
Wish you were still in GA, as we could have visited once in a while. Your weather out there may be boring, but I get tired of thunderstorms 12 months out of the year. We had a nice one just before Christmas which I would rather have avoided, but the real cracker was at the end of September--took out the answering machine and a few other odds and ends. Nothing in the stereo. When it thunders, I unplug from the wall. There's no protection like being unplugged. I lost a CJ Premier One to lightning once upon a time. Now *that* was a bother.

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Old 1st November 2001, 08:39 AM   #29
bawang is offline bawang  Malaysia
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Thumbs up Leach Ver 4.5 amp

Damon, I've built the Ver 4.5 of the Leach amp recently, all 3 channels of it. I can recommend this amp without hesitation to anyone with good hands-on experience in basic electronic skills. I even make my own PCB using the supplied artwork and transfer paper named PnP Blue. Excellent stuff.

As I don't have extensive test equipment, I just have to stand back and turn the switch on! An guess what, all 3 boards work from the start! Impressive! I biased the amps at 150mA each. Absolutely no turn on/off pops/thumps. Just be careful to install bleeder resistors at the input caps, and let the caps discharged before re-powering up.

I only use 30,000 uF of capacitance per rail for the combined load of 3 channels. Tests done with as little as 10,000uF produced excellent results (by my tin ears).

The reason for the lowering of the capacitance - the inrush current melted the contacts of the power switch (rated 240V, 6A) installed at the primary side! My transformer is capable of 12A continuous at 40-0-40V.

The only changes from the original design was:-

1) 2N???? pair to 2SB649A/2SD669A
2) MJE15030/31 to BD243C/244C

An excellent design.
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