Audeze LCD-2

[spritzer]

That seems to be pretty common these days. The datasheet is clearly just a rough outline that one can work around with enough audiophile parts...

[dsavitsk]

Well I do feel picked on. In this case it's been fairly well documented by Woo owners that the WA6 and WA22 change sound noticeably with a rectifier change. They REALLY do. No BS.

The fact that a different rectifier tube changes how your amplifier sounds does not imply that rectifier tubes have some inherent sound to them. Understanding why this is the case is actually of some importance.

As KG noted, different rectifier tubes will drop different voltages. Some may also change the impedance of the power supply. This, in turn, changes the operating point of the amplifier itself. Thus, the rectifier simply changes the parameters at which the other active components are operating. Sometimes this may lead to one sound, sometimes to another. But it is not sound imparted by the rectifier. While a particular rectifier may warm up one amp, this does not mean it will have the same effect on another. If you are just swapping out rectifier tubes, there is nothing systematic and no predictability.

A variable regulator with a variable output impedance can accomplish much the same thing. For instance, in this circuit, one can change both the voltage, and the power supply’s output impedance.

By doing so, one can adjust an amplifier for lowest distortion, or whatever parameters one is interested in. This is much the same thing that is accomplished with the changing rectifier, except that in this case the designer knows what is going on rather than haphazardly changing things, and it is repeatable so that a customer hears what the designer heard and can thus actually judge the merit of the design. To me, an amp that is excessively responsive to tube rolling, particularly one that is responsive to rectifier rolling, is simply a sloppy design.

Tube rectifiers do have some real use. They provide an easy slow start circuit. They have lower switching noise than many solid state parts, they dissipate heat above the chassis (heat, of course, that might not exist in a sand rectifier), and they can drop excess voltage which is useful if one is using an off the shelf power transformer. But, if you are using them to tune your circuit, you have an underdeveloped circuit.

Well there are many out there that would disagree with you. Perhaps this falls into the same category as cables?

In that there is not a single person on the planet who can hear a difference in a double blind test? Could be.

[kevin gilmore]

To me, an amp that is excessively responsive to tube rolling, particularly one that is responsive to rectifier rolling, is simply a sloppy design.

Absolutely true. But also a way for the vendor to get way more discussion on the various websites, and to sell lots of very overpriced tubes.

Other than the soft start part which is deliberately designed into tube rectifiers, about $1 in a pair of silicon diodes is a much better idea.

In many cases the soft start is not needed. Every single mcintosh tube amp built after about 1958 had silicon diodes. So did the marantz

amps.

Edited December 17, 2011 by kevin gilmore

[wink]

How would one of these go?

http://www.webervst.com/ccap.html

[recstar24]

Damn you Doug and your science!!!

[kevin gilmore]

How would one of these go?

http://www.webervst.com/ccap.html

just fine. I have a few of them installed in various places.

A number of different companies make these things.

[FrankCooter]

The fact that a different rectifier tube changes how your amplifier sounds does not imply that rectifier tubes have some inherent sound to them. Understanding why this is the case is actually of some importance.

As KG noted, different rectifier tubes will drop different voltages. Some may also change the impedance of the power supply. This, in turn, changes the operating point of the amplifier itself. Thus, the rectifier simply changes the parameters at which the other active components are operating. Sometimes this may lead to one sound, sometimes to another. But it is not sound imparted by the rectifier. While a particular rectifier may warm up one amp, this does not mean it will have the same effect on another. If you are just swapping out rectifier tubes, there is nothing systematic and no predictability.

A variable regulator with a variable output impedance can accomplish much the same thing. For instance, in this circuit, one can change both the voltage, and the power supply’s output impedance.

By doing so, one can adjust an amplifier for lowest distortion, or whatever parameters one is interested in. This is much the same thing that is accomplished with the changing rectifier, except that in this case the designer knows what is going on rather than haphazardly changing things, and it is repeatable so that a customer hears what the designer heard and can thus actually judge the merit of the design. To me, an amp that is excessively responsive to tube rolling, particularly one that is responsive to rectifier rolling, is simply a sloppy design.

Tube rectifiers do have some real use. They provide an easy slow start circuit. They have lower switching noise than many solid state parts, they dissipate heat above the chassis (heat, of course, that might not exist in a sand rectifier), and they can drop excess voltage which is useful if one is using an off the shelf power transformer. But, if you are using them to tune your circuit, you have an underdeveloped circuit.

In that there is not a single person on the planet who can hear a difference in a double blind test? Could be.

Great post Doug!

Besides the slow warm-up, the main advantage of tube rectifiers was their lack of switching noise. With the advent of high voltage Schottky diodes, this problem has pretty much been eliminated.

Most non-regulated tube power supplies are pretty bad. In order to do it right you need multiple high quality chokes that few manufacturers or consumers are willing to devote the space, weight and resources to. One the other hand, there are lots of terrible solid state power supplies used in tube amps. Think of 80's style amps with banks of 6550's and power supplies consisting of nothing more than generic rectifiers, a resistor or two, and massive banks of cheap electrolytic capacitors.

With the exception of mercury vapor types, I've pretty much abandoned tube rectification, although I still like tube regulators. Still have a problem with the electrolytic capacitors though.

[shellylh]

With Woo amps there may also be something else at play since they routinely use large caps right after the rectifier and that may cause issues.

Yep, another mikhail fail too. So the datasheet says 40uf max after the rectifier. So mikhail put in a 40uf cap.

Then paralleled it with a 200uf cap.

These statements concern me a bit (as an owner of a Woo WA5-LE). Is sounds like you are trying to say that there are issues with the design of the Woo amps. I assume this is the case for the WA5-LE as well. Are these issues actual safety/reliability issues like in Mikhail's amps? I surely don't want a 300b amp blowing up or causing a fire, etc.

[kevin gilmore]

The woo stuff is built for a specific price point as is just about everything else these days.

The transformers are appropriately sized, and none of mikhail's famous 800 volt stupidity.

And none of the 25 ampere DC filament things either.

So they are not going to blow up, or cause a fire etc.

The issue with putting big caps after a tube diode without a large choke in the middle

puts much more strain on the diode than is normal. So they don't last as long and

eventually sag quite a bit. Meaning the resistance of the diode goes up permanently.

Mercury rectifier tubes are something different entirely, are very low impedance, can

work at thousands of volts, are still used today in some applications, and are toxic

if you break one.

It is possible to do a fully regulated all tube power supply. Tektronix did it by the tens of thousands.

You need a tube rectifier (5u4), a pass tube (6l6) a gas tube voltage reference (0a3)

and an error amplifier (6au6). No one seems to want to do it right. In fact if you do it this

way, you don't need huge hunks of iron and stacks of expensive black gate caps either.

So it could be way better, and way cheaper. But it does take up a bit more space.

It would end the "my rectifier tube sounds better than your rectifier tube" sillyness.

Remember mikhails "fully regulated" ESX power supply with the 10 gas tubes on top.

This is the WRONG way to do a regulated power supply. I doubt that any of those lasted

more than a few days.

Edited December 17, 2011 by kevin gilmore

[shellylh]

The woo stuff is built for a specific price point as is just about everything else these days.

The transformers are appropriately sized, and none of mikhail's famous 800 volt stupidity.

And none of the 25 ampere DC filament things either.

So they are not going to blow up, or cause a fire etc.

That is good to know.

The issue with putting big caps after a tube diode without a large choke in the middle

puts much more strain on the diode than is normal. So they don't last as long and

eventually sag quite a bit. Meaning the resistance of the diode goes up permanently.

What kind of timeline is this, months, years? Can one test or look for signs of this? Would the tube just measure with a short life in a tube tester or is it more complicated?

[mikeymad]

^^ this...

(full disclosure - WA5 owner)...

[dsavitsk]

What kind of timeline is this, months, years? Can one test or look for signs of this? Would the tube just measure with a short life in a tube tester or is it more complicated?

Probably too many factors to predict. Older well made rectifiers can handle a lot more abuse than some of the new cheapies. If you search around, there are tons of stories of cheap modern 5AR4's failing where old tubes worked fine (seems especially common in guitar amps -- partly because a lot of relabeling goes on).

In the most extreme cases, you'll see a flash in the rectifier where they arc. This can kill a tube instantly. Assuming this has not happened, then either measuring for voltage changes over time, or putting the tube in a tester is probably the best bet.

[shellylh]

Ok, that is good to know. I am currently using a pair of "old" (not sure of the year) RCA JAN 5u4g ("coke bottle" shaped) so hopefully these will last for a while. I also have a pair of the Sophia Princess 274b but maybe these might fail faster than the mil-spec RCAs. I noticed that the glass on the SP 274b is darker than the glass on my SP 300b tubes (and I think darker than when I first got them). I wonder if this is due to the design of the power supply in the Woo products or if this always happens with the SP 274b.

Edited December 17, 2011 by shellylh

[The Monkey]

Yet another revision...

[recstar24]

I see the angled connectors, anything else that is different?

[Tari]

The wood is a bamboo composite. It's supposed to be more readily available and consistent than the Caribbean Rosewood.

[The Monkey]

The choice of bamboo is interesting. I have bamboo floors in my apartment. They look nice, but overall they suck. All you have to do is give them a hard stare and they dent. It's also impossibly easy to scratch them. I wonder if these cups will exhibit similar tendencies. I prefer wood to grass.

[Tyll Hertsens]

I prefer wood to grass.

I'm having a hard time with this statement.

[swt61]

If it's a composite, then it may be stabilized with resin, in which case it'd be harder Dinny. I can understand why they'd move to something more consistent, but for the money you should have a choice of exotic hardwoods to choose from.

[Fitz]

I'm having a hard time with this statement.

Yeah, why not both?

[K3cT]

Some close-up shots from ALO.

I have to say I prefer the overall aesthetics of these than the LCD3 although the wood choice is a bit suspect. I definitely prefer the older rosewood's looks but if this bamboo composite is lighter then I guess the trade-off is worth it.

[guzziguy]

I'm sure that it's worth it for Audeze. I imagine that switching from rosewood to this bamboo composite is adding a healthy boost to their profit margin.

[Pars]

So what will they have in store for LCD4? Balsa?

Edited April 2, 2012 by Pars

[swt61]

^ Thatch

[wink]

As hard as it is to believe, balsa is classed as a hardwood..........