Well folks, I didn’t ever think being involved in the audio business would require this of me. I have filtered through this thread and assimilated what appear to be the primary accusations against the LL.
I know that the main objective is claimed to “document just how badly built and designed this amp is” as exposing “safety” concerns, not to mention the magnanimous claim that “We post the data for people to make up their own minds” but I rather suspect it is more than that.
I’ll address the concerns that I pulled out, but I should make it clear that this will be my first and only post on this forum. If anyone has concerns about my designs or amplifiers, please contact me through my website.
The direct soldered/exposed IEC connections
This is only an issue for someone who wants to open the amp and modify it while it is plugged in.
It is not a safety issue for a normal customer who doesn’t open the box.
Also notice the small jumper next to them, that selects between high and low bias. Not the best idea to run these at high voltage...
Jumpers are floating and not near any low voltage pads or terminals. The voltage between the pins is less than 50V. There is no risk of problem.
cold solder joints
EC standards require the use of lead free solder. It frequently requires higher soldering temperature and cools with a duller finish. This is normal.
thin board
Thin board is a matter of opinion. The board does not need to be thicker to do its job well.
“What is the cause of a poor soldering?
Worker without skill experience;
Thin PCB substrate and thin traces that cannot handle the temperature; or,
Soldering station without temperature control?
The amp uses ROHS compliant unleaded solder and boards. The boards for LL1 were done by a PCB assembly shop capable of and who regularly does automated and hand lead free soldering for many manufacturers around the US and globally.
However, anyone who manufactures complex electronics knows that a highly capable supply chain is essential. I have hired and fired 4 PCB assembly shops before finding the one I’m using now to get the best work possible.
No LL has reported failure due to soldering issues.
The bias supply is utterly fucked and not safe to use. Then I'll add loopouts to the back and rewire the input section.
The bias supply works as it’s supposed to. There have been no reported failures of this supply.
LL2 has loopouts. This was a shortcoming and has been added.
Only thing I've done is remove those bloody mosfets which should never have been there and fix the CCS. So now the output capacitance is cut down to less than 10pf and the huge bump in distortion from the old CCS is gone.
BJTs do have lower capacitances than Mosfets. They also exhibit thermal runaway. Mosfets have advantages, including not being prone to thermal runaway.
All those zeners add a huge quantity of noise and as a whole it's just unstable.
Measurements and owners do not support this notion and the amp is quiet.
Additionally, the amp is not unstable. It has exhibited no stability issues on any production amp. When built properly the amp biases and works every time.
As for the safety of the amp, of course it isn't safe , there are no output resistors
The amp was designed to current limit and shut down if overloaded. The CE sticker on the back of the amp is for real. The LL1 was certified for entrance into EU countries by Diversified T.E.S.T. Technologies Lab (http://www.dttlab.com). This includes safety and emissions testing. I have the report in case someone in the EU wants to enquire.
“the thing gets stinkin hot” , “extended use of stock LLmk1 and probably LLmk2 due to heat and other issues is going to definitely cause reliability issues, and out of warranty repairs are going to be nasty”
Thank you Kevin, this actually brought a smile. This is a little like the pot calling the kettle black.
The thermal conditions of the amp have been tested both theoretically and in reality using IR sensors. The transistor junction temperatures are not near any operational or dangerous limit and if the amplifier is used in a well-ventilated area as recommended, it performs perfectly alright.
You think that the screws on the current source triple and transistors are somehow replaceable by someone other than a magician
My amplifiers are not intended to be serviced by third party members or DIYers. Registered dealers and my assembly house will have no problem returning the normal function of the amplifier. In HV amps if one part fails there is sometimes other damage. In order to return an amplifier to its original condition, if necessary, the entire board will be replaced. I call this customer service.
““So I take it that figure of 0.0009% THD+N isn't exactly accurate?”
J176 input fets designed for switching (not linear applications) with an input noise of a minimum of 10nv per root hz and an amplifier gain of 50db is real? when alex could have used the real thing instead (2sj74 or lsj74)?
2SJ74s are not commercially available that I know of except, possibly, from sources who stocked up on them. They are sometimes counterfeits. As a manufacturer I prefer not to depend on any of these sources. Although if Linear releases new LSJ74 (limited release just a few days ago, rumored OEM late 2013 last time I looked) they will be an obvious choice.
Measurements were done by an independent lab here in Austin.
Mosfets don't belong in electrostatic amplifiers!
So you say Kevin. I have designed this circuit around the Mosfets with their behavior in mind. This amp works very well and this is affirmed by the owners who have communicated with me.
Modifications made in LL MKII have further improved its performance while making various other improvements.
As for other makers entering the market, would anybody doubt the design and build quality of a Stax amp sold by Schiit or Pete Millet? The difference is that they know what they are doing, Cavalli has no clue.
Although I have the highest regard for Jason, Mike and Pete, this is pure speculation regarding a theoretical electrostatic amp. Unless you are privy to all of their business dealings and more importantly, their schematics, you don’t even know that there haven’t been problems that have been handled in one way or another, nor whether any current product has a problem that hasn’t manifested itself yet. And you certainly don’t know what an electrostatic amp from any of them would look like (except, of course, it would no doubt be a copy of something you did first).
Furthermore, this is a rhetorical trick. Bringing in other people who are respected is a way to give your argument weight that it doesn’t possess. A casual reader might conclude that these guys are somehow aligned with you on these comments about my amplifiers. But, as far as I know, none of them have made such a public statement.
Folks, the audio world can be great place to be with lots of very fine people. I have had the great privilege in the last several years of meeting many of them, both online and in person. I hope you all find that to be true too.
