Chinese amplifier SET Music Angel XD845 with mighty 845 triodes

EXECUTIVE BRIEF: In this page I describe how I searched the world for a tube amp that is easy to buy and everybody can afford it. To meet this criteria one must modify a cheap amp to make it better - otherwise a "proper" amp in the shop would cost at least 3000 dollars.
A ready kit is also an option, but the Angel is cheaper than any kit I know, and works better than most of them.
So I found FOR YOU a diamond in the dust and as a self proclaimed Prometheus - hereby I share the knowledge with all of you.
Your search for the amplifier is OVER.

What a story!!! Me and an audio buddy of mine we found this amp on the ebay and after some thinking we decided to give it a try. We all don't trust the Chinese high-end yet, do we? They make cheap imitations which do not sound nearly as good as "our" western originals. Right?
But these toys for boys look so tempting.
Wait a minute - 845 SET ? 8000 dollars? 2500? not? how about a thousand? Not yet?
This amp retails for 570 USD tubes included.
Lets risk it.
If it is shit - the loss is 600 bucks.
After paying all the money up front to the e-shop in HK days seemed like weeks. 20 days later - no amp, no info, no answer to emails. 30 days - still silence.
At the end - 6 weeks after purchase - Rafal (the brave guy) accepted the loss and decided to write it off his books.
Nex day the postman brought the Angel.
(by the way, since I wrote this text 2 years ago, more than 20 angels arrived from the same eshop - LESHELE - and most of them arrive in 5 working days maximum, without any problems, without a single issue).

In the carton, instead of 4 bricks - arrived real amplifier !
Upon examination - it looked real. Good body, good finish, professional tube sockets, transformers - potted and encapsulated. Connectors - highend. EVERYTHING looks good.
Lets plug it.
The amp WORKS!!!
But how does it sound?
It doesn't even sounds like a boombox. Not bad. Horrible. The  muddy sound resembles the neighbours fighting behind the wall, not music. And DEFINITELY not Music Angel...
One week later Rafal decided he does not want it - it is not listenable at all.

What could I do - before dumping the Angel  to serve as a doorstop I would take a good look inside.
What I found is that the amp is made strangely - there are twice as many parts inside as on the attached schematics.
Even on the schematics - there are too many parts.
So what I did I hooked up the oscilloscope and a generator and I started removing parts observing the signal.
After removing about 10 parts per channel everything still worked well.
Then I upgraded horrible coupling caps (10 c garbage) with Arcotronics MKP.
And in the end I fixed a wiring error on the input tube.
In fact the input tube is SRPP - just like Lampizator circuit.

845 ORYGINAL SCHEMATICS (real life drawing)

845 FACTORY SCHEMATICS (not real life)

Back to listening
BINGO! This is a real SET 845 amp. It plays fantastic music, it is powerful, dynamic, transparent, wide, deep, 3D - and what have you.
If we could upgrade further the output transformers we would be talking world class. But even with the 10 $ upgrade which I did - this is the big amp killer. I think it is the best value in the world market. I cant think of any amp in the 3000  $ range that could seriously beat the MA845.
As a matter of fact, the same factory makes also a 300B variant (not nearly as good as 845 in my subjective opinion) they also make KT88 which is actually interesting alternative, although not as good as 845 because push pull can never beat SE class A.
There are also variants with EL34 push pull and some cross breed of 300B and 845. If you want the real McCoy, go for 845.

After re-doing 10 of Angels, including one 300B, one KT88 and 8 times the 845, I am absolutely positive this is the best secret of hifi market.
Just buy it cheaply and follow my instructions and you will be amazed !
BE CAREFUL - 900 V DC inside will kill you if you touch it.

All these parts and more - went straight in a dustbin.

New circuit - 1 kHz square wave amplified from 60 mV at the input to 70 V pp at the 845 tube grid.
(two stage amplification - input and driver).



19 Oct 2007 - LATEST REVISION OF SCHEMATICS by Lukasz Fikus

Comments to drawings:

C1 = 150-220 uF / 450 V
R1 = 10K : 15 K 2 W
V1 = 400:420 V DC
I 1 = 10 mA
V2 = 230 V DC
V10 = 350 VDC
R2 = 680 Ohm / 1/4 W
R3 = 200:500 K / 1/4 W
C2 = 0,22 uF : 1 uF / 250 V
C4 = 1uF:4uF/450V
V5 = 130 V
V5 = 130V
R6 = 47K:62K/1W
C3= 47uF:100uF/400V
R4=R5=680 Ohm /1/4W

I deliberately removed the values from drawings for two reasons: one - I need to be able to adjust one part every now and then without re-drawing. The circuit goes through constant progress.

Two: I need  to be able to discuss the schema with other people and it is easier to talk about  "R5" than "this resistor between cathode V1 and grid V2" - you understand.

ON TUBES: General rule is that for driver stage (second) the tube should be a high current one. I use the readily provided 6sn7GT in parallel mode.
On first - input stage the better tube is also 6sn7 but the amplification factor is rather small.
So for folks who have a lampizator - their CD signal is circa 20 V pp so they do prefer a better albeit weaker tube 6sn7.
For low CD level folks - 6sL7 provides more kick.
In the first stage these tubes are interchangeable, in second stage - they are NOT.
Obvious choice for driver is 6N13C (megalampizator) - same octal socket, but over 50 x the current of 6sn7. I am working on this solution - ULTIMATE one in this case. The 6N13C needs a lot of voltage amplification so the input MUST be the 6sL7.

A note about 845 tubes:
without going int too much details, the situation with tubes is this:
The NOS tubes from USA we can forget. They do not exist.
If you find a pair, it is either a) fake Chinese or used and burned out. Do not waste time and energy looking for NOS.
The Chinese factory makes cheap and very good 845's and they brand them under tens of labels, the home label is Golden Dragon but all the World production is from the same plant - (from google)

Shuguang Electrical Factory No. 1

Owned by Korean firm Samsung. Shuguang makes most of the popular audio and guitar types, which are frequently rebranded by importers and OEMs. Types believed in production: 6L6GC, EL34 (3 types), 6550, KT100, 5AR4, 2A3, 807. Possibly 211, 845. The price is circa 170 USD per pair plus shipping. Close matching is unnecessary.
Recently a new variant is announced - a metal  plate high end version of Chinese 845 - the 845-M.(m for metal)  I heard it is much better sounding. Price is unknown.

except ..
there is a small exception - the KR tube from Czech Republic. It costs much more than the Chinese tube but it sounds MUCH BETTER in every respect than the standard carbon plate 845. It is a worthwhile investment.
Having said that, it is hard to get it, even factory-direct.

General note about the tweaking process

It is hard for me to describe every amp and every possible schematics - how we want things to be modified.
In general - western schematics are usually a  result of a very long period of preparations, testing and optimization. They are finished and optimized.
Chinese amps are strange animals. Good looking, with good parts, but totally strange schematics.
The circuits look like a result of un-qualified copying plus some "original creativity" plus unknown factors. All in all, the Chinese products have too many parts and unnecessary components scattered all over the place.
My short list of mods is this:

1. In pentode tube amps ALLWAYS make a triode mode conversion.(unless there is a switch to change the modes) This applies to ultralinear circuits etc.
Triode mode pentodes sound great, but in pentode mode - they sound really BAD. Bad bad bad. The mod is easy and costs nothing.

2. In the input section - remove and short all series resistors - we don't need any of them. Tubes are happy when coupled to each other directly.

3. sometimes there is too many parallel resistors which form - together with series resistors - some signal attenuators. Get rid of all of them except the resistor which goes from tube grid to ground. Every small tube needs grid grounding resistor, value between 200K to 1 M.
The first input tube may use the volume pot as a resistor - so the parallel R can go out.

4. I like triodes without the cathode capacitor. Most amps use an electrolytic cap across the cathode resistor. Remove it and maybe you can decrease the cathode resistor by half. This sounds much cleaner.

5. Coupling caps: all tubes connect to the next tube by a series cap. Use sizes like 0,47 uF or more in the first stage, and over 1 uF in driver stage. use the RADIAL wound, round type not the box type and not the oval. Radial is the way to wind a good cap.
The best type is paper in oil (PIO) type, copper foil is the best electrode material. (jensen or audionote) or any decent MKP.

That's basically all we need to do. The improvement depends on the circuit but usually the mods open up the sound a great deal. Triode mode is most important of them all. Theoretically we "loose power" but subjectively the sound is louder, more spacious and free. Very well worth doing.

The design idea for the ultimate Angel mod: 6H13C driver (never tried or verified)
The input tube - as above - 6sL7GT or 6H9 (Ru) or 6N9 (Chi)

The driver: 6N13S (cyr: 6H13C) double triode just like Megalampizator.
Connect only one half - the current will be enough.

1. Power voltage - 400V

2. Design Ia = 40 mA

3. R power drop from 400V to 200 V:    200V drop = X * 40 mA.     ->   X=200/40= 5K Ohm Power dissipation: 40mA * 200V =  8 000 mW = 8 W. This is a BIG RESISTOR.

4. anode power capacitor: 680 uF / 400V (even if anode supply voltage is 200 V, before warm-up the tube is not conducting current hence there is no drop and we will see full 400V on the anode.
The size of this cap is not critical, whether it is 400, 500 or 1000 micro, but if it is too small there will be some small humming.

5. Anode resistor: designing for midpoint on the voltage line, 200V / 2 = 100 V. - this is anode resistor drop on idle current Ia = 40 mA.
At 40 mA the drop of 100 V will happen if Ra = 100/40 = 2k5 Ohm (power dissipation will be 100V * 40mA = 4000 mW = 4W so a 5 watt resistor is a minimum (take 5 parallel 10K/1W)

6. Cathode resistor: This resistor adjusts current. Start from 400 Ohm and adjust until Ia = 40 mA +/- 20 %.
Power rating: P=Isquared * R    Uc=-16V, P=16*700 mW.
A 2 W resistor is a safe choice .

Second half can serve for the other channel, so we need only 1 tube. One octal socket  will remain unused.

The best angel at the time of writing - June 20 2008

HERE IS a special schematic - supposedly much better than mine - from a very nice and knowledgeable man from Linz Austria - Dietmar Gerhold whom I thank for sharing with us his good job.
Here is a detailed description.

I tried the schematics from Mr. Dietmar on both the Angel 845 and on the Liang amp and I must agree. It sounds better on bass, on width, on height, on depth, on details. Everything is stable. There is no hum, no noise, no overheating of parts. It is a top solution for today - June 20, 2008.
I departed from the supplied schematics here and there by no more than 10 % because I used parts available. Apparently everything is OK. Current below 4mA, voltages plus minus the same.

I recommend this mod over my own proposal.


Angel 300B factory circuit

Angel 300B new circuit

The first tube should be 6N2P noit 6N1P


The facts about music angel:
It is made in china by a factory called SHENGYI, their website is
They have 10 amps and a pre.
The amps are:
300 B SET (XD850A III)
845 SET (XD845MK III)
300B PushPull (XD8502A III)
6P1 PushPull (Mini P1)
KT88 PushPull (XD800MK III)
EL34 PushPull (MiniL3)
EL34 PushPull (XD500 Mk III)
MINI P14 (EL84 PushPull)

Other fantastic gems from China, easy to re-work because wired point to point, are:

especially nice is this one:
and this:

CAYIN amplifier - description of modification


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