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DIGI-125 Kit Amplifier Module
DIGI-125 Kit Amplifier Module
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Old 20th September 2012, 09:10 AM   #111
east electronics is offline east electronics  Greece
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....i wonder what excuse anyone will have to comment this work as nice and tidy while a bunch of errors and some of them quite critical

--twisted cables are very wrong for such an application
--even worst if all of them tied up all together
--crosstalk figures will hit the sky
--even worst when input and output cables also tied together ( oscillation will be waiting around the corner )
--i see no decoupling anywhere in the power supply ( s)
--i wonder if any adjustments needed how they are going to be done
--I see no inductor but may be i am wrong and trust me in a six ch amp is obviously needed

nice looking job doesn't mean that is also proper ...
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 20th September 2012, 09:14 AM   #112
east electronics is offline east electronics  Greece
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just seen the decoupling ...my mistake
just seen the non existing vbe multiplier
thermal run away will be there
even worst when common heat sinked on a common heatsink while the one amplifier will warm up the other .

at least take the cooling and ventilation advice given
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 30th October 2012, 09:44 AM   #113
rakesh_sharma23 is offline rakesh_sharma23  India
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Thanks for feedback..
Amp is running fine..
Few problem in found are
1. Some noice can be heared when audio is muted ( May be twisted cables issue as pointed by "sakis" above) or some circuit layout design problem (Power supply in on the same board).
2. MFD Cabinet and Poor Heatsink result heating... but not too much..

Solution .. will be making new layout, Powersupply will go on saprate board..and a new cabinet and some good heatsinks..
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Old 21st March 2014, 04:32 AM   #114
Mayan is offline Mayan  Hungary
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Default my build

digi125_mayan.gif

Picture 006.jpg

Picture 007.jpg

Hi there, I built it too, sounds so good ! Very good deep bass and clear, sweet mid and trebles. PS +-36V, 24mA /channel. I'm very happy with it.
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Old 21st March 2014, 06:46 AM   #115
Mihkus is offline Mihkus  Estonia
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Has anyone ever done any measuring on this amp? THD+N and bandwith, fq response?
Got pretty much everything to build it little subwoof amp
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Old 21st March 2014, 11:32 AM   #116
Ian Finch is offline Ian Finch  Australia
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The original design is a utility amp. i.e. for general purpose use in audio for musical instruments, monitors, desk amplifiers etc. Not hi-fi. THD is ~0.05% @ 50W/8R.

That assumes the original design parts lineup which included MJ802/4502 output transistors for 125W/4R. The remainder were all small-signal T092 transistors, BC546/56 types, including the drivers. Without decoupling, noise is largely power supply dependent, so a really well designed and built power supply is going to improve hum and noise substantially.

Here is a link to Greg Erskine's site, showing a test build on a commercial PCB with the T092 transistors.
However, I would be concerned about the use of this design for subwoofer duty which is the highest average current duty for amplifiers. I think there are better designs for woofer amps and they usually involve more output pairs for a given power rating. That means more drive current and gain too.

The design is the basis for AKSA 55 and B-AKSA. To all accounts, they sound just fine and AKSA 55 sold as an audiophile kit product internationally, so something must be good about this ultra-simple, minimum parts count design.
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Old 24th April 2014, 02:18 PM   #117
rawbas is offline rawbas  Philippines
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Hi, can this circuit operate at +/-45V or do I need to increase the values of the bias resistors?

Thanks..
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Old 24th April 2014, 05:19 PM   #118
Ian Finch is offline Ian Finch  Australia
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Quote:
Originally Posted by rawbas View Post
Hi, can this circuit operate at +/-45V or do I need to increase the values of the bias resistors? ...
If you want to use 2N3055 output transistors , the simple answer is no. +/- 40V is the maximum supply allowed for them, in AB power amplifiers with 8 ohm loads. +/-35V would be considered a safe maximum for hard use with lower impedance loads. The rail (+/-power supply) limits are set by the transistor Vceo and output voltage level. It has little to do with amplifier design or bias resistors, though it may be wise to change a few values in more complex Vbe multiplier designs.

The alternative is to upgrade the transistors to higher voltage and current types suited for the 100W/8R or even more, that may be possible with 45V rails. The amplifier was originally specified for 125W/4R as stated earlier, so all components would have to be assessed for uprating to suit the increased voltages and currents.

Looking at rakesh's transformer though, I would not be surprised that its regulation was poor enough to allow the rails to sag well below 40V at maximum power. If you find one like that, it might save your transistors - or it might not
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Old 25th April 2014, 12:44 AM   #119
rawbas is offline rawbas  Philippines
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I see,
I am considering using BD139 or C2073 for the VAS, BD139/140 for the driver and 2SC5200 and 2SA1943 for the output.
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Old 25th April 2014, 02:21 AM   #120
AKSA is offline AKSA  Australia
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The Digi125 was in fact my start point for the AKSA.

I heard this amp in 2000 for the first time and was impressed with the sound for such a simple, elegant circuit. I resolved to refine it more, and in just a few weeks had the first prototype of the AKSA 55, which sold in hundreds as a kit.

During the development I spent time on the choice and dimensioning of all components. And since I did not have an Audio Precision 2, and no intention to buy one, I did long term listening tests with many friends, audiophiles, and lots of different music.

I commend this design, the designer, Graham Dicker, is a very, very clever man.

Hugh
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