amplifier SET Music
Angel XD845 with mighty 845 triodes
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,
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 !
- 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
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
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.
about 10 parts per channel everything still worked well.
Then I upgraded
horrible coupling caps (10 c garbage) with Arcotronics
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)
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.
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
amplification - input and driver).
PROCESS OF TWEAKING
LATEST SCHEMATICS _ LAYOUT
19 Oct 2007 - LATEST REVISION OF SCHEMATICS
by Lukasz Fikus
C1 = 150-220 uF
/ 450 V
R1 = 10K : 15 K
V1 = 400:420 V DC
I 1 = 10 mA
V2 = 230 V DC
V10 = 350 VDC
R2 = 680 Ohm /
R3 = 200:500 K /
C2 = 0,22 uF : 1
uF / 250 V
C4 = 1uF:4uF/450V
V5 = 130 V
V5 = 130V
R6 = 47K:62K/1W
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.
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.
General rule is that for driver stage (second) the tube
should be a high current one. I use the readily provided 6sn7GT in
On first - input
stage the better tube is also 6sn7 but the amplification factor is
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.
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.
note about 845 tubes:
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.
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)
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
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
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
that, it is hard to get it, even factory-direct.
MODIFICATIONS OF AMPLIFIERS
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
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
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
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
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.
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.
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
The design idea for the ultimate Angel mod: 6H13C driver (never tried
The input tube -
as above - 6sL7GT or 6H9 (Ru) or 6N9 (Chi)
6N13S (cyr: 6H13C) double triode just like Megalampizator.
Connect only one
half - the current will be enough.
1. Power voltage
2. Design Ia =
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
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.
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)
resistor: This resistor adjusts current. Start from 400 Ohm and adjust
until Ia = 40 mA +/- 20 %.
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.
LAST MOD RECIPE - FROM DIETMAR
The best angel at the time of writing -
June 20 2008
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
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.
recommend this mod over my own proposal.
MUSIC ANGEL - 300B
Angel 300B factory circuit
Angel 300B new circuit
The first tube should be 6N2P noit 6N1P
MUSIC ANGEL - KT88 push-pull
The facts about
It is made in
china by a factory called SHENGYI, their website is www.yogoo.com.
They have 10
amps and a pre.
The amps are:
300 B SET
845 SET (XD845MK
(XD500 Mk III)
MINI P14 (EL84
gems from China, easy to re-work because wired point to point, are:
is this one:
CAYIN amplifier - description of