The problem with the Woo Audio 3ES

[spritzer]

This week I was browsing the net and I came across this:

http://bbs.erji.net/forum.php?mod=viewthread&tid=2239622

Now it is all in Chinese but these were the first pictures of the insides of the Woo Audio 3ES.  This was an amp I never really paid any attention to, I'm so fedup with Woo and their sub-par crap, but finding internal pics does warrant a look.  First off the pics aren't great but at least there are some schematics there and we need to try to verify they are correct.  We have no further info than this as I can't find any more internal pics, so this is what know at this point.   First the PSU:

Now, nothing new here, same old crap Woo have been building for years but why place the output sockets right next to the power transformers like that?  I mean the whole idea behind a two box solution is to place the noisy power transformer away from the amplifier and thus the output, not run the signal back into the PSU and have the output sockets right next to the, rather large, radiation field of the EI power transformers.  Makes no sense but things are about to take a turn to the worse: 

Now... here is where things start to look a bit off and I'm going to see if anybody can spot it without venturing further.  Now neither Kevin nor I can read Chinese so the markings on these two schematics that were included meant nothing to us:

We focused on the tube schematic and wondered how this could work, I mean it is a simple grounded cathode 6SN7 input with a 300B cathode follower output.  We are not dealing with a lot of gain here so at first the schematic had to be wrong, no way to drive electrostatics from this.  Then Kevin figured it out, this is just a preamp, the latter schematic is the output for the headphones and what is that... it's a fucking Apex PA97 opamp!!!

https://eu.mouser.com/datasheet/2/156/pa97u-1853045.pdf

Go on, double check the pinout against the datasheet and look at the recommended values.  Now look at the internal picture again and follow the wires, input selector is on the left and the preamp/headphone selector is on the right with the red wires.  What's there next to the back panel with 4 identical modules and a shit ton of hotglue?  The electrostatic module... which is made up for 4 of these which cost around 100$ each in bulk.  This is a 14k$ amp! 

Now we don't know what is on the heatsinks next to the tubes, has to be a TO220 size part but no way to see what it is.  The rest of the schematics make sense though.  B+ goes directly onto the 300B plates and there is a grid resistor next to the "G" pin with the cap from the 6SN7's right next to it.  Two large resistors next to each filament pin too.  Then we have the large, brown, resistors going off the B+ to feed the 6SN7's and two identical plate resistors for it too.  . 

Now what is the problem... well I can't see anywhere on the Woo site which says this is a hybrid amp, they talk about the 6SN7's, 300B's and the rectifier but nothing about a basic opamp outputs for the electrostatic outputs.  Let's just quote them: "The new 3ES achieves the most ambitious dream in the audio world".  Yeah... not so sure about that... 

Funny enough, clones of the Stax D10 are surfacing in China now and I have one.  Guess what that one uses?  Apex opamps....  and I bought one for 250$ shipped to me and it fits in the palm of my hand. 

Below are the rest of the pics from that Erji post for posterity.

Edited February 3, 2023 by spritzer
Fucking typo's....

[spritzer]

Since I was asked, here is the cheap China amp with the Apex opamps

[kevin gilmore]

i've been searching for over 24 hours now and cannot find a single example of a 300b used as a cathode follower. All 300b preamps seem to use an output transformer. And this completely makes sense as the voltage grid to cathode for a 300b is 75 volts. used as a cathode follower its performance has to be poor.

and the opamp used for the headphones, from the apex website, this device runs class C. no output stage bias. furthermore the maximum voltage swing bandwidth is 3khz. and the slew rate is 8 volts/us.  this has got to be a miserable sounding thing.

there seems to be another amp just like this (for over $30k) that likely has some significant amount of solid state on the internal heatsink.

300b are great tubes when used as outputs in a push pull circuit. thats about it.

 

[luvdunhill]

Maybe these folks, though the schematics are no longer published:

https://www.transcendentsound.com/

[kevin gilmore]

that does look like the right thing. 12au7 for gain driving 300b cathode follower. 70ma definitely pushing the tube pretty hard. not balanced.

[simmconn]

I wonder what’s in those black boxes marked ‘phase splitter’, 1:1 transformers? I see 4 coax cables going into them. 

[luvdunhill]

4 minutes ago, simmconn said:

I wonder what’s in those black boxes marked ‘phase splitter’, 1:1 transformers? I see 4 coax cables going into them. 

I am guessing two jfets and a pair of bjts and some resistors - my assumption is based on the J113 marking (but not sure what a PST22 is?)

edit: maybe not I don’t see where the bipolar power rails would come from

Edited February 3, 2023 by luvdunhill

[swt61]

2 hours ago, luvdunhill said:

 bipolar power rails

Easy glum, easy glow.

[spritzer]

Those phase splitters are also in the WA22 and I believe they are just transformers.  I can't see any power wires going to them there either. 

[kevin gilmore]

back board in the power supply next to the high voltage opamps has what looks to be a pair of 3 terminal regulators.

one low voltgage power supply needed to drive all the input relays.

[mwl168]

@spritzer: You are correct - re: the two hand-drawn schematic; first one says “3ES pre-amp section”, second one says “3ES electrostatic headphone amp section” on top and “same for 4 channels” at bottom, the script in the rectangle in the schematic says “3ES amp module”.

According to the OP, the pre-amp section is “ tube-input and tube-output”, headphone amp section is “transistors”.

Edited February 4, 2023 by mwl168

[spritzer]

Thanks for confirming that, the google image translation threw up something similar but one can never trust it. 

Maybe that small PSU in the back is the HV +/- supply for the Apex chips?  The sister amp WA33 has a similar B+ supply for the tubes from the few pics I could find. 

[luvdunhill]

Spritzer, any good source (or left overs) for the PA97 at around $100 each? How did that little amp cut the cost down so much, I presume they are genuine Apex parts?

[kevin gilmore]

pa79 mouser price is $56 each.  but limited to +/-175 (its a dual opamp)

i can't imagine there are any fake parts in that package so likely parts are disappearing out the wrong end of the factory. similar to the shure earbuds.

mouser price on pa97 is $150 each.  there are better apex parts to use in that voltage range for about the same price. you should be able to do a pair of carbon boards for the same $600, probably less.

that $250 price for the portable includes the headphones. what it does not include is a lithium ion battery pack.

 

Edited February 4, 2023 by kevin gilmore

[spritzer]

I was quoted some prices from a Chinese seller last year and these were around 100$ each.  Genuine parts and not pulls either.  No idea who that seller was but it was through one of those marketplace sites, UT source or one of them. 

No idea how they can make that amp so cheap but part prices are usually around half in China compared to what we see.  Also plenty of stuff that gets "lost". 

[rizena]

Isn't that a scam?

[spritzer]

That can be debated but I fail to see where they state that the electrostatic output is opamp or even solid state based.  They only talk about the tubes in the preamp section. 

[luvdunhill]

One persons preamp is another persons gain stage I guess.

[spritzer]

It's a D10 clone so just as bad as the D10. 

[kevin gilmore]

the d10 absolutely does use the pa443. same style of bent heatsink to get the heat to the case.

birgir can post pictures of the d10 if he wants, and there are other pictures of the d10 with the heatsink removed.

you might want to look at the datasheet, a single resistor programs the output stage bias current

 

Edited February 10, 2023 by kevin gilmore

[kevin gilmore]

a little high voltage opamp porn

 

[spritzer]

The D10 uses Apex and the listing for this thing clearly states it is a D10 clone, run a bit hotter.  I'll take pics tomorrow if I can find some time. 

[kevin gilmore]

here you go   pa443D

 

Edited February 10, 2023 by kevin gilmore

[spritzer]

Yup... Apex. 

[spritzer]

Yeah and this one has more power it seems.  Still pitiful but a bit more.