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Old 2nd January 2014, 12:38 AM   #1
cut is offline cut
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Default Building from a pair of MA-9S2 boards, first project

I just bought this pair of boards which implement a clone of the Marantz MA-9S2. They're all assembled and look more or less like the picture on the vendor's page at Wholesale Product Snapshot Product name is Assembled 150W+150W HIFI audio power amplifier clone Marantz MA-9S2 AMP C5200/A1943 free shipping. Each board is one channel.

Although I think I understand pretty much what to do next, I am getting the feeling I also might be in over my head as this is my first amplifier project, close to the first thing I've done with analog electronics, and the first project which requires that I build a power supply from parts. I am really just starting to learn and so there are gigantic gaps in my knowledge. I'm hoping that finishing this project will end up allowing me to banish at least some of the major gaps. I'm confident I can eventually puzzle this thing out, but would sure appreciate some help!

I understand that each of these boards wants a nice toroidal power supply to give it around 25v DC, so I figure I will get this toroid: 300VA Toroidal Transformers and then hook each output up through a bridge rectifier like this: Wholesale Product Snapshot Product name is KBPC5010 Bridge Rectifiers DIODE RECT BRIDGE 50A 1000V, followed by a capacitor or two for smoothing--that last part I'm less sure of how to do right since I am starting to think there are probably some important subtleties.

Does it sound to y'all as if I am more or less on the right track? I also still need to figure out where to attach things on these boards. The places that look like attachment points on the board, followed by what I think they're for, are:

GND: to be attached to the earth from the wall power

-VSS: to be attached to the negative side of the DC power

+VCC: this must be the positive side of the DC power

a pair, one of which is labeled INPUT+ and the other is unlabeled: this must be the audio input


OUT: One speaker wire must get attached here, but where's the other wire go? Does it get hooked to the same GND?


Okay, that's where I'm at now. I will probably end up searching down some books on power supply design next, and order the toroid as above unless with your help I figure out that that's not the right one.

Oh yeah, one more thing: I am also going to need to figure out how to add a volume adjustment knob/knobs. From my initial reading it looks like a voltage divider circuit might be the thing, but I'm just starting to read about that and would very much appreciate advice or pointers.

I feel like there is probably a book which I should read to tell me a lot of this stuff. If there is one that folks here would recommend, I would love to find out what it is.

Whew!
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Old 22nd January 2014, 10:09 AM   #2
esgigt is online now esgigt  Netherlands
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Hi,

Looking for an amplifier for my daughter, I came across the same amplifier. Compared to the original MA-9S2 the schematic appears to be copied with some alterations regarding Power-stage (one transistor pair less), Bias setting and the protection circuit, which has been omitted. on the other hand a DC-servo has been added (does nothing if the power-stage fails).
The original MA-9S2 uses the big (Toshiba?) power transistors, which are of higher spec (power/current) than the 5200/1943 (only 2 pairs) used in the clone. My idea would be to modify the clone's power-stage and add at least one pair of 5200/1943.

Power supply:
the ad. I've found, states that the amp requires +/- 30V to 63V (max. rating of capacitors). So a 2x25 Volts will answer to that requirement. On the top level, the load regulation (5 to 7%) of the transformer MUST be regarded. Thus the max. voltage would be 2x40V.... or change the caps on the board to 80V or 100V types. For Vss and Vcc: use enough smoothing capacity. At least 2x15.000uF (and an inrush limiter). And preferably a double rectifier.

Grounding:
Try using STAR-grounding. Also the "-" of the speakers ought to be connected there. Be sure the leads to the star-ground are well connected!
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Old 22nd January 2014, 11:36 AM   #3
sajti is offline sajti  Hungary
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Just one note:

That is not a clone of the Marantz MA9, and absolutely not any relation with that! Marantz MA9 is more sphisticated, fully balanced from input to output.

Sajti
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Old 22nd January 2014, 11:57 AM   #4
esgigt is online now esgigt  Netherlands
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Quote:
Originally Posted by sajti View Post
Just one note:

That is not a clone of the Marantz MA9, and absolutely not any relation with that! Marantz MA9 is more sphisticated, fully balanced from input to output.

Sajti
Hi Sajti,

On what information did you come to this conclusion? As far as I've compared the schematics of the original MA-9S2 and this so called clone, I observed the following:
- The input circuits of both amps use exactly the same layout (1 on 1) except for the values of resistors and the transistors used. This is what I call cloning.
- The bias circuit is different in both amps, however performs the same functionality. This is more a way to keep the Lawyers from your door, by not exactly transposing the architecture of the MA-9S2.
- The power section is in architecture an exact copy of the MA-9S2, scaled down and with less powerful transistors.

In my view this amp is absolutely a clone. Sure the original MA-9S2 excels in building quality, better and matched components and better specs. But the clone is almost for free (less than $50,-)! But that is what cloning for DIY is usually about.

Imho it is quit easy to upgrade such a clone to a level close to the origional. buy 3 pairs of well matched Sanken 2922/1295 (yes, I've looked them up in the meantime) with the proper drivers, change all transistors and resistor values back to original... then you will be closer to the original at a fraction of the cost.

Regards,
Edwin
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Old 22nd January 2014, 02:34 PM   #5
sajti is offline sajti  Hungary
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Hi,

the most important difference is, that Marantz use separated voltage amplifier, and power buffer stage to eliminate the back EMF distortion as much as possible.
So MA9 (and even SM11, and PM11) has two individually feedbacked stages. The output stage has a gain about 10-12dB only. The mentioned clone has the gain of 30.

The MA9 is fully balanced from input to the output. The clone is not balanced.

The Marantz has triple darlington output, the clone has double only. (This is not downscale, as the small Maratz amplifiers such as 7001 still use triple darlington)

MA9 use no DC servo, the clone use it.

So this is not MA9 clone. I heard one of this clone, and I heard MA9 too. Believe me, the original is a different world.

Sajti

Last edited by sajti; 22nd January 2014 at 02:46 PM.
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Old 22nd January 2014, 03:07 PM   #6
esgigt is online now esgigt  Netherlands
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Quote:
Originally Posted by sajti View Post
Hi,

the most important difference is, that Marantz use separated voltage amplifier, and power buffer stage to eliminate the back EMF distortion as much as possible.
So MA9 (and even SM11, and PM11) has two individually feedbacked stages. The output stage has a gain about 10-12dB only. The mentioned clone has the gain of 30.

The MA9 is fully balanced from input to the output. The clone is not balanced.

The Marantz has triple darlington output, the clone has double only. (This is not downscale, as the small Maratz amplifiers such as 7001 still use triple darlington)

MA9 use no DC servo, the clone use it.

So this is not MA9 clone. I heard one of this clone, and I heard MA9 too. Believe me, the original is a different world.

Sajti
Hi Sajti,

I do not disagree with you that the original is a world apart from the clone. That's what I wrote, too.

Indeed the overall layout of the original amplifier is different from the clone. The clone combines the P501 and P601 board in terms of amplification, introducing sound degradation. The clone just resembles the P601 board.
And you are right: if the clone also consisted of a copy of the P501 board, it would be a different ball-game... also in court, for the guy selling the clone would have been sued for copyright infringement.

In the original however, one of the HDAM's performs the same function as the opamp DC-servo in the clone....

As far as the use of darlington's is concerned: I only see one in the original amp, which is in the bias circuit. the power stage uses Epitaxial planar transistors (Sanken).

Regards
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Old 22nd January 2014, 03:53 PM   #7
sajti is offline sajti  Hungary
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Join Date: Apr 2003
Location: Vác, Hungary
Hi,

in the original amplifier the 2SC3421/2SA1358+2SC4883/2SA1859+2SC2292/2SA1612 form a triple darlington on the output. In the clone the 2SC5171/2SA1930+2SC5200/2SA1943 form a double darlingoton only. This is what I mentioned, not the bias circuit.

Sajti
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Old 22nd January 2014, 04:04 PM   #8
esgigt is online now esgigt  Netherlands
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Hi Satji,

Now I understand what you meant with 3 Darlingtons

Regards
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