Mingda mono block amplifiers

MC300-C and


Lampized in July 2010


Ming-da amplifiers have been "polluting" the google search for the key words like 805, 300B or Amplifier - for quite some time. I realized that this is a Chinese brand that makes "Chinese high end". Their top model (featured here 805/2A3 called MC3008-A
is really intriguing, especially for 1490 USD plus shipping.  Yes - PER PAIR. )

The cheaper cousin is MC-300-C which is a push-pull 300B triode amp. Very sexy looking , resembling (maybe even too much) the CARY and Jadis amps. It has a nominal power of 25 Watts, and that is A LOT in my book.

This pair sells for just a little bit above 1000 USD, just a hair on the wrong side of a grand. (on ebay, because the internet shops have 1500 price)  I mean nobody could make a DIY project so cheaply, not mentioning a good month needed to make DIY like that.

OUTSIDE - all looks really Gucci - nice chromes, gold plated ring inserts, rock solid potted encapsulated transformers, button, binding posts,  RCA's - everything is up to high end standards. The Music Angel was a Chinese interpretation of almost high end - this one IS high end full stop.

Next:  INSIDE - looks better than any amp I have seen from China, (or in fact - the Cayin / Spark brand is mounted equally well).  The wiring, the part selection, the overall neatness - all is first class. I remember many western high end products looking waay less good - like Mephisto 1 transport, or Theta Data transport, or VAC DAC, or Meridian 226 player, or even VTL160 monos that I used to own.

Now wait a minute - high end is about the sound, not the looks. At least not only the looks.

So I played them in factory form.
The sound is surprisingly good: quite loud, quite dynamic, with tons of low bass, with okay everything else. I would rank this sound c- meaning - almost acceptable.

After full reverse engineering of the schematics I found that:
First tube is a dual triode - 6sL7 and they used it God knows why in paralleled mode. We gain NOTHING by paralleling two triodes, but we loose one precious half of triode for nothing plus we waste energy needed to heat it etc. And I must make a confession here - I hate 6SL7 - I never liked it and as a routine I replace it with 6SN7 or 6H8C. And so I did. I used only a half of 6SN7GT which plays much better than even paralleled 6SL7.

The second tube - this time 6SN7GT - was used as phase splitter and driver at the same time. From that tube signal goes to the two grids of the push-pull pair of 300B's.
Why push pull / Because compared to SET with one tube and 6 Watts, in push-pull we get quadruple power at the price of one additional tube. And the output transformer is halved in size.  6Watts for a 300B SET amp is kind of shy power, but 25 - that is another story. In tube world 25 Watts of 300B sound is like having a V8 engive.

The first tube is connected to feedback loop which goes under the cathode resistor. Why would anyone want to shell out a grand for triodes like 300B and HAVE A FEEDBACK LOOP ? At least I wouldn't.
So I cut off the loop completely.
Then I noticed some tricks to manipulate high frequency response on the anode resistor of the first signal triode. I removed that too.
I also noticed an input capacitor before the first grid - This can be removed too.

There were numerous changes which are visible on my schematics below. I changed operating points of small tubes because they were set for tooo low current for my taste.
Finally I tried the amps with my muuuch simplified schematics and it worked just great. It is much more open, 3D is deeper, sound goes beyond speaker base very wide, the mids are much more 300B'ish so to speak and bass is less "one note" kind and more colorful full spectrum bass.

Overall - the amp is really good now, its modification is simple and innocent. And we don't have to rework half the amp like in the Music Angel to even get to the safety issues like grounding etc. Here all is almost as good as it gets.
If your budget is a grand - go for it, however if you can shell out a grand and a half  (and I suggest that you do) - then  there is a better amp from ming da - just read on !!!

Above: note the well made star ground scheme.

Above: these are two big Philips caps of very high quality. They are connected in series with the voltage balancing diodes and resistors, so the overall voltage rating becomes double. This is circa 900 V DC.

Above: note the metal clamps which hold the caps - they are additionally insulated from capacitor body wy some insulating material. (green-ish). This is such a nice touch - shall the cap break from the electrode to the body - it will not affect the safety of the amp chassis. Well done.

Above: the 300B sockets  with blue resistors which supply negative bias voltage to the grids, and big green resistors which make de-humming circuit for the cathode.  It would be much better to replace these two resistors with a 1 Watt potentiometer of 50 or 100 Ohms  with center wiper going to the cathode resistor.

Above: the brown cylinder is the bottom side of the biasing pot. These tubes work in push pull so by definition they cant have automatic bias. ~To balance both tubes we need manual biasing.

Above: the power switch has a capacitor across the legs in order to extinguish arcing during switch off. Very nice touch. It extends the life of the switch more that tenfold.

Above: the socket of the driver tube.

Hahahahaha. What a capacitor! Just look - Rudoycon !  The creative people from China created a new hot brand. Hahahahaha !

Above is my version of the driver: change the tube to 6SN7GT or 6H8C and use only first triode  in anode follower scheme. Go directly from RCA to the grid of that triode.

My experiments with various schemes for the driver / phase splitter (the left hand side tube when looking at the amp from the top.

Above: note that the right tube was changed by the owner to an exotic nos predecessor of 6SN7GT which I dont remember but it had anode on top of the tube .

ming da 300b

For a brief moment I installed in place of these chinese graphite Dragons - a pair of Svetlana standard 300B's and I heard more details and better bass definition with the Russians.

Above is the stock form schematics as I found it.
Next week I will post the new scheme of my design  that worked great.

Enter the 805 monos

These babes are about twice the size and weight of the 300B amps. They are 50% more costly too. A striking feature is the usage of a well known power tube - 2A3 - as a driver of the big 805 tube.  Such powerful driver can handle high levels of voltage swing and it has very low output impedance so it is a known practice to drive the big triodes like 211, GM70, 845, 805 and 813 with tubes like 300B or 2A3.
Does it make sense ?

Above - you can see that we upgraded the tubes from stock Chinese to RCA's. While not much better, the RCA's offered more liquid and attractive midrange. But the Chinese were very close indeed.

The 2A3 was a stock Chinese Golden Dragon.

Unlike the 300B amp - this one has potentiometer as well as a second input which bypasses pot completely.  Good choice.

As you see, the mighty 805 is a tube with anode on the "head". I think this is quite dangerous to have 900 V DC hanging around on such wire.

This is the schematics from the internet which is not precise but almost.

Before my mods that amp was already much better than stock 300B amp. It was veery loud, meaning - sensitive. It also had the 50 Hz brum - which is really annoying.
But overall the music was good, tubey, powerful etc.
But it was not as good as my similar in class GM70 monos.
So I tried to improve it.
In order to improve the sensitivity issue I decided to remove entirely the first tube. It was unnecessary to have 3 tubes before the 805. Two should be enough.
I connected the input directly to the input of the second tube.
Since the second tube is a driver of 2A3 - I decided to use a powerful tube my beloved 6H6P as a driver.
It works in SRPP mode so I reduced the lower cathode resistor from 2K to 1 K to match the upper cathode.
To augment the bass and improve sensitivity of this setup I added a lower resistor cathode bypass by means of 470 uF / 16 V OSCON cap with minus to the ground.
The elimination of the first tube automatically removed the global feedback loop. So far so good.

To eliminate humming - I removed at both - 2A3 and 805 the two resistors between the cathode and their cathode resistor and the resistor pairs (on schematics 47 Ohms, in real life 25 ohms each) were replaced by potentiometers - 100 Ohms by 1 Watt - 10 turns precision type. By turning these resistors I was able to  dial in the silence.
FIrst - I removed 2A3 tubes and  I dialed the 805 silence, then I installed 2A3's and dialed them to silence.
This is the proper way of handling the hum issue.
I biased the 805s to 70 mA each.
I also eliminated the entire circuit between the lower cathode of my 6H6P and the 2A3 grid. I just kept the upper cathode signal input.

After these changes - the amp exploded with music. Space, detail, depth, dynamics - everything improved. Sensitivity was just OK with my normal source signal giving great loudness at 11 o'clock. I think the full power sensitivity has reduced from 0,7 V to 3 V which is great.

This amplifier is wonderful - with charming mids, deep bass, pure sound and silent background. While it is not Ongaku, it is damn close. It beat my own super duper GM70 with everything  the best I could find including Mundorf gold oil caps, E182CC drivers, copper plate power tubes, silver wiring etc.
The mods are 1 hour if you know what you are doing. Just bypass first tube, clear off its socket from the circuitry, change heating of the second tube to pins 4 and 5 like for 6H6P, reduce resistor from 2 K to 1K, bias the power tubes well and voila - you have a world class monos for under 2 grand.
Very much recommended.
(not even mentioning doing the same with premium tubes: e182CC instead of 6H6P, better 2A3, and US made NOS 805's. )

I will post the new schematics next week.