[DVV]

Actually sliding bias does not have to work quite the way DVV describes. The topology that I am presently using in the LNPA 150 does not use an op amp but has discreet circuitry that "feeds" the bias control transistor. The bias will change as function of signal voltage. At idle and up to approximately one watt the DC bias is pretty much constant. As it starts to move above the one watt the DC bias will increase. Propagation delay for the amp is a constant 1 microsecond to the best I have been able to measure.
Mr. Audioengr raised a concern earlier in this thread about parasitic capacitance on P.C. Boards and power amps. I have not found this to be at all applicable to date. The capacitance that I have encountered is due to the "Miller Effect: on the class a drivers which represent the second stage of the amplifier.

Dan, I did say "typically". Of course there are alternatives, and in fact, Nelson's system also uses no op amps, just discrete components.

The reason why I said "typically" is because quite a few commercial class manufacturers have, at one time or another, used this system (e.g. JVC, Akai, etc). As you would expect, the price constraints in these models caused them to use op amps as the fastest and least expensive solution all around - but not necessarily the best, and certainly not the only one.

As for stray capacitance, this can be a problem, however, it will become a serious problem only in very poor outlays. Pay attention to your outlay, make it as small as is practical, and you're not likely to have any problems with it, just as Dan says. And I second the Dan's comment on the Miller capacitance.

Unfortunately, this problem is all too often resolved by simply throwing in a bootstrap capacitor. If used without good measure, it can limit the effective slewing rate of the amplifier. It is charged by the current drawn by the input stage, typically a differential pair, so if this capacitor is relatively large, it will limit the speed with which it can be charged, and hence the slew rate. However, this is a well known and well documented problem, so I seriously doubt anybody but the shoddiest of designers still has problems with that.

Before the tube fans out there start to glow too brightly, let me just add that the Miller capacitance problem was first discovered and named in tube technology, which is also very prone to it. So there!

Cheers,
DVV

[DVV]

Thanks for the info, DVV.  Have a selection from the Canarvel Wagon on me.

Please forgive my ignorance, Max, but what's "Canarvel Wagon"? A beer (wishful thinking here)? If so, I'll be glad to collect the first time I'm in the US.

You know, if I just started collecting the beer people have promised me, I could drink my way around the world, with the notable exception of Japan, where not even a sake was offered me. Of course, by about London, England, I'd be so sloshed I wouldn't know where I was going any more, so a rest would be in order before I terrorized the US with beer consumption.

Cheers,
DVV

[hairofthedawg]

Isn't the Carnival this time of year?  Something to do with Easter or something like that.  It was Fasching when I was in Germany and was generally a lot of fun!

cheers,

Dick

[DVV]

Isn't the Carnival this time of year?  Something to do with Easter or something like that.  It was Fasching when I was in Germany and was generally a lot of fun!

cheers,

Dick

Dick, you disappoint me. I was hoping somebody would mention the Bierfest in Munich - millions of gallons of beer drank in two days. Bad doggie!

Cheers,
DVV

[MaxCast]

Thanks for the info, DVV.  Have a selection from the Canarvel Wagon on me.

Please forgive my ignorance, Max, but what's "Canarvel Wagon"? A beer (wishful thinking here)? If so, I'll be glad to collect the first time I'm in the US.

You know, if I just started collecting the beer people have promised me, I could drink my way around the world, with the notable exception of Japan, where not even a sake was offered me. Of course, by about London, England, I'd be so sloshed I wouldn't know where I was going any more, so a rest would be in order before I terrorized the US with beer consumption.

Cheers,
DVV

I didn't think anyone would get that.  It is from a talk show in Chicago and it is not the common phrase I thought it might be.  It basicaly is a cart which has anything you want on it (usually alcohol ).  Things to sooth you carnal mind in a happy carnival kind of way Whatever you desire it is all on there.  Even down to the little miss pushing the thing.

[JoshK]

Isn't the Carnival this time of year?  Something to do with Easter or something like that.  

Doh!  You would have to remind me.  This is the first Carnaval in Brazil I have missed in three years.  If anyone is looking for the wildest party they have ever been to or could imagine, I recommend the Carnaval in Salvador de Bahia!  Boy or boy do I have fond memories of that trip!  Not for the week of heart though.

[DVV]

...

I didn't think anyone would get that.  It is from a talk show in Chicago and it is not the common phrase I thought it might be.  It basicaly is a cart which has anything you want on it (usually alcohol ).  Things to sooth you carnal mind in a happy carnival kind of way Whatever you desire it is all on there.  Even down to the little miss pushing the thing.

Naughty Max!

DONE!

Cheers,
DVV

[DVV]

I think I might be about to experience why amps sound different.

Some time ago, I ordered replacement caps for both my Harman/Kardon integrated amps. The older one, dating back to December 1993, model 6550 (2x50W/8 ohms), is well past its due to have its caps replaced, and I figured I might do the same for the newer 680 (August 1999). Anyway, I got the spare parts today, as were shipped to their local distributor by H/K.

Frankly, I was a little disappointed. Originally, both units use Elna for Audio caps (2x15,000uF/63V for 6550, 4x8,200uF/63V for 680), but what i got today were some Korean caps. Worse, they were made to resemble Nichicon caps so closely that unless you carefully read the text, you'd swear they were Nichicons.

I could be wrong, but I suspect these are not up to the originals. Of course, never having tried them before, I'm willing to give them the benefit of doubt, but this Nichicon mimicry got me a bit down. If you have a good product, why do you need to emulate someone so closely?

Oh well, we'll see. Good thing I have some Fischer & Tausche caps also coming my way.

Cheers,
DVV

[tmd]

Dejan,
Why did you bother ordering H/K caps anyway. Would you not have looked for a 'better' aftermarket cap in the spirit of tweaking?
Neil.

[DVV]

Dejan,
Why did you bother ordering H/K caps anyway. Would you not have looked for a 'better' aftermarket cap in the spirit of tweaking?
Neil.

Neil, I don't like mucking around with other people's designs, even if I do have the schematics. Also, there's the matter of physical size - not easy to find direct replacements.

But as i said, a pack of Fischer & Tausche caps are on the way. Just in case.

Cheers,
DVV

[Dan Banquer]

As I started to develop the LNPA 150 I came rapidly to the conclusion that lowering noise in a power amp was going to be based not on the transistors themselves but what was going on around the amplifier. Using the Small Signal Transistor Data book from Motorola. I found that Motorola stopped giving noise figures for transistors rated at higher voltages and currents needed for power amps.  Plenty of stuff at line level though.
That being the case I decided to apply a few classic techniques and some of the suggestions of the engineers that I was working with at the time. The following is a basic outline of those techniques.
Solid state designed for low frequency can have some real noise problems when it is exposed to H.F. and R.F. so reducing any of these artifacts will help. How the amp is grounded and shielded is crucial here so I will describe to the best of my ability what I have done.
One of the grounding techniques I use in all my equipment  has been called the “pseudo balanced” approach. Big name, a simple technique. The chassis of the unit is earth grounded through a 3 prong AC line cord, but the audio signal ground is NOT connected to the chassis ground. Using this technique, I have just wrapped an earth ground shield around the more sensitive audio circuitry. Given the amount of interference we have around us these days, this is not a bad idea. Now that my chassis ground is separate I can use a “star ground” and direct my audio signal grounds to one place. This is usually the power supply. Double sided ground plane on the P.C. Boards directing the ground currents back to the power supply is also done.  In one fell swoop so to speak, I have  reduced radiated interference and reduced ground loops in the unit.
To knock down conducted interference through the AC lines I use a single stage AC line filter in a can right at the AC input. This probably the best place for it, right inside the unit to reduce any pick up from the line cord that connects the unit to the wall. ( I am considering experimenting with some Dezoral Bricks in the near future)
All of the above is dependent on a 3 prong outlet, but since home computers and other assorted household appliances now come with a 3 prong plug I don’t consider this a drawback.
I also use a regulated Power supply for the entire amp, not just the voltage gain section. This acts not only as filter for low frequency noise, but gives me the benefit of a very low output impedance source that the amplifier can draw on. The equivalent amount of capacitance that it would take to do that would be capacitors that looked more like 5 gallon drums, than the cans we mostly see inside a power amp. If I can paraphrase Doug Self, (author of numerous articles on amplifier distortion) “I’d hate to do a low noise amp without a fully regulated supply”
I hope the above helps people to understand how I do things, and I hope some of the DIY guys try some of these techniques.
If there is one thing I am convinced of at this point it's that if there is less noise, there is more music. Especially for digitally sourced acoustic music.

[DVV]

As I started to develop the LNPA 150 I came rapidly to the conclusion that lowering noise in a power amp ...

If there is one thing I am convinced of at this point it's that if there is less noise, there is more music. Especially for digitally sourced acoustic music.

Agreed, Dan, but I would like to add some of my experiences. Over the years, I have experimented quite a bit, given that I am a certified power supply freak, always was.

In my view, while full regulation is better overall, I feel the price penalty for including the current gain stages is simply too high. It's not much of a problem as long as you stay below the say 70-80W line, but after that, it starts to cost a lot.

On the other hand, what 90%+ of amps offer these days, meagre decoupling with a resistor and a capacitor, with maybe a diode thrown in, between current and voltage stages is simply poor design.

In my view, the best all around compromise is to use full regulation for the voltage gain stages and the predriver, while leaveing the driver and output stage proper on unregulated lines, albeit with hefty supplies. This allows for say 90-95% of full regulation, but saving say 35-40% of the costs and about as much in space (less heatsinking required). All this is very loose of course, actual figures will depend on specific products.

This has another, not so obvious benefit. It allows for split power supplies, so for any given power, you can always allow your output transistors to work at say 4-5V less voltage than otherwise. The benefit is that they stay more inside the good half of their SOAR, or if you like, that you can get that much more current from them.

Just my 2 cents' worth.

Cheers,
DVV

[JoshK]

Hey,

I had a thought.  Don't know if this was mentioned before because I am not sure I have read the entire thread, but I know I have read most of it. What if we put this thread into action and design an amp from this.  We could come up with a design, schematic and parts list needed and it would be up to the reader to make it happen.  I am a complete newbie in this arena but I'd be willing to help out how I could.  I think it would put an original spin on this forum.  If it is a sucess we could go onto the next thread, like a DAC or a preamp or whatever's clever.  Dejan, I know you have a lot of experience here and basically I think that 80% of the design has probably been laid out here in one way or another.  

How many people would be willing to try to make it happen.  Kind of like the Teres TT project started out.  I know there are differences in opinion but maybe we could majority rule on an approach and try to stick to it. Or whoever has the most input gets a little more control of direction, or whatever.  

???

Josh

[Jay S]

Sounds like this is the approach that was taken with Eric Hider's custom solid state amps (which he has discussed before on HD).  Seems like there are 3 critical elements - great design, great (or appopriate) parts, great execution.  As a learning experience, focusing on SS or tubes may be great.  But, given how good digital amps can be even while the technology is still in its infancy, you may want to consider focusing on digital if you want to make a performance breakthrough.  Besides, it is likely to be cheaper since you need less parts - smaller power supply (transformer, caps, etc), no heat sinks, simpler circuitry, smaller case, etc.  

Get a few ICEpower modules and go wild!

[JohnR]

Get a few ICEpower modules

Maybe one of us should start an audio company and organize a group buy  

[DVV]

Get a few ICEpower modules

Maybe one of us should start an audio company and organize a group buy  

Well, we already have Hugh and his Aksa line.

Maybe Dan could be talked into selling his products in kit form.

Cheers,
DVV

[JohnR]

Heh, that was a joke with a bit of history behind it... a certain Danish personality, claims, counter-claims, counter-counter-claims etc - you get the picture - concerning B&O's modulation scheme and what it does or does not do, and the fact that you can buy the relevant Class D modules for a hundred bucks but they only sell them to OEMs.

 

[DVV]

Heh, that was a joke with a bit of history behind it... a certain Danish personality, claims, counter-claims, counter-counter-claims etc - you get the picture - concerning B&O's modulation scheme and what it does or does not do, and the fact that you can buy the relevant Class D modules for a hundred bucks but they only sell them to OEMs.

 

John,

So far, I've heard three digital amps: TacT Millenium Mk.2, the Sharp power amp and a hand made Greek version based on the Tripath module (no longer commercially available, I'm told, seems Sony stepped in and bought them out).

Their resolving power is almost beyond belief, they can dredge out what's on the CD or LP like nothing else I've ever heard. Their bass wipes the floor with the likes of Krell, levinson, Kensonic, etc. Their midrange is good, but not in the same league as their bass.

It's their treble that sells them short. It is, I would say, just barely all right. Something is not quite right there, something is missing. It's as if they have a detached treble, like it was two amps working where one should be and not quite in synchronicity.

The Greek version was the best of the lot, in my view, and admittedly, the margin was not large, but it used Siemens Sikorel caps for filtering, and being very intimately acquainted with these products, I do believe they gave it the edge (fastest caps on Earth so far, most important when working with ultrafast amps).

My conclusion is that digital amps are still in their infancy. We can talk about them again in 10-15 years. Remember they actually work in switchmode, which is why they are so efficient and need such small, almost token heat sinks. Maybe somebody will devise a way to run them in class A, or something.

Cheers,
DVV

[JoshK]

Dejan,

Funny I would say the strengths of my Spectron (digital just in case you weren't familiar) were in its bass and its treble.  The bass isn't overdampened like some SS amps, it isn't underdampened either, like all the tube amps I have ever encountered. It has truely clean, deep and tuneful bass.  It also has the most delicate highs or at least matches that of the best tube amps I have heard.  Its midrange is neutral, and is what is critized by those that like the midrange glow (read coloration IMO) of some tube amps).  Add to that list that it runs completely cool, even when driven for lengths at extreme levels, draws moderate current and is fairly resilent to any power grundge and you have the rationale for why I chose mine.  They aren't going to be all things to all people and I don't think they are the best of the best but the best of what I would consider approachable (in terms of price).

[DVV]

Dejan,

Funny I would say the strengths of my Spectron (digital just in case you weren't familiar) were in its bass and its treble.  The bass isn't overdampened like some SS amps, it isn't underdampened either, like all the tube amps I have ever encountered. It has truely clean, deep and tuneful bass.  It also has the most delicate highs or at least matches that of the best tube amps I have heard.  Its midrange is neutral, and it was in critized by those that like the midrange glow (read coloration IMO) of some tube amps).  Add to that list that it runs completely cool, even when driven for lengths at extreme levels, draws moderate current and is fairly resilent to any power grundge and you have the rationale for why I chose mine.  They aren't going to be all things to all people and I don't think they are the best of the best but the best of what I would consider approachable (in terms of price).

Josh, I never auditioned your amp, heck, I never even saw one live, so obviously, I cannot comment on it. But if what you say is so, that means progress is a-foot, people are working and solving problems, and that's something I always like to hear.

As for your comments on the bass, well, you just phrased it your way, but let me assure we are in total agreement.

Cheers,
DVV