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Old 25th August 2012, 03:03 AM   #51
Aniket is offline Aniket  India
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Thanks Sir Vostro and Sir Andrew, i would do so and mention the results, also update schematic.
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Old 25th August 2012, 04:21 AM   #52
Aniket is offline Aniket  India
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Default Schematic

updated schematic attached
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Old 25th August 2012, 09:52 AM   #53
AndrewT is offline AndrewT  Scotland
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Add local decoupling both at the output devices and on the main supply rails.
Add degeneration resistors to the LTP.
Add a trimmer resistor to the 3k3 (lower one connected from Zener to LTP). This trimmer to set LTP in balance.
Add degeneration resistor to VAS

Add a third 3k3 in the supply to the Zener/LTP. The Zener can manage with a bit less than 9mA. Or try splitting the upper 3k3 into two off 2k2. Then add a smoothing cap between the 2k2 for extra filtering to the LTP tail. 10uF to 100uF would do.

If you feel you must run at lower bias currents in the output stage, then double the emitter resistors to 0r47. This will allow ~45mA of bias through each pair for near optimal ClassAB.
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Last edited by AndrewT; 25th August 2012 at 09:55 AM.
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Old 22nd October 2012, 02:12 PM   #54
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Hi Aniket .

Andrew's suggestion of a VAS emitter resistor is interesting ( I presume as that would degenerate the VAS ) . This can be up to 22 R as a rule of thumb . One amp I built recently was 16R . What you might hear is that the sound is punchier at 0R and softer as the resistance increases . A friend I built an amplifier for definitely preferred 0R . My quick guesstimate is that 4R7 will be about the trans-conductance point , l assuming gain to be about 100 for the BD139 . I suspect the critical values to be 0R 4R7 and 10 R . As your VAS current and voltage is low you might find a higher gain transistor for this application . I think 2N5551 would be OK ( often about g = 150 ) . Sanyo have excellent devices if you can get them . As you have 47 pF VAS cap I think it will be OK . The BD139 will be adding to that . You might start with 68 pF if trying something new as a precaution . Looking at the difficulties of changing a transistor a small emitter resistance seems an easy option . One other transistor is MPSA 42 . It's gain is lower so a higher value emitter resistor might be required . It has a good reputation and is cheap .

Technically speaking some say a VAS resistor is a bad idea as it reduces available negative feedback to correct crossover distortion ( as does the VAS cap ) . This is true . I find if a little is used and trans-conductance is reached or slightly exceeded then IM distrotion is lower . A trade between IM and crossover distortion is a nice game for the ears .

I like your bootstrap constant current source . Generally the 100 uF costs as much or more than a BD140 . How many have ever tried one ?

Study the Quad 303 output stage . It works very well . It could be adapted with extra output devices . The Quad can work with only 10 ma standing current . Rotel used 44mV @ 0R22 to set bias = 20 mA .
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Old 2nd February 2013, 08:52 PM   #55
PetruV is offline PetruV  Romania
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This seems interesting,what modifications can i use to get 300-500w in 4 ohms
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Old 3rd February 2013, 10:21 AM   #56
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I think read up on bridging . It allows a stereo power amp to be converted into a high power mono unit . The advantages are compound . Not least no great investment to give it a try . If liked upgrading of heat sinks and power supplies comes next . A brief trial ( 10 minutes max ) should be possible before things get too hot . 4 ohms will need many output transistors .
Bridging Adapter For Power Amps
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Old 3rd February 2013, 07:23 PM   #57
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Is there a possibility that we can get a PCB for your amp. worth trying out
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Old 5th February 2013, 04:36 AM   #58
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Quote:
Originally Posted by djk View Post
"@djk how could i get more power out of this amp."

How much power?

What is it for?

Crown made the M600, M2000, MA10K all using the 2N3773.

The more outputs the more power (and a bigger power supply).

The M600 is a bridge amplifier.

The M2000 and MA10K are bridged bridge amplifiers (although the MA10K would only do 7KW continuous, 10KW on program material).

The M2000 was frequently used to generate a clean 120V/60hz for medical equipment.
Quote:
Originally Posted by AndrewT View Post
The 3773 is a good output device for one that is limited by 140Vceo.

let's start with a +-65Vdc supply, that allows for a bit of overvoltage for the mains electricity supply. That supply will allow a maximum output of ~60Vpk into a suitable load.
60Vpk into 1r0 is equivalent to 1800W.

Now design and build those 3773 into a +-65Vdc balanced amplifier.

We can expect 3600W into a 2r0 load.

If sufficient capacity is built into the amplifier it could even be designed using a lot of skill to drive a 1r0 load to ~7kW.

Is that close enough to 10kW?

But, I would never recommend putting all my assets into a one amplifier PA duty. I would much rather have seven or eight 1kW amplifiers driving the speakers for my paying audience.

10kW with 2N3773 could be done by bridging 2 sets of grounded bridge amplifiers.........

I think that is why DJK quoted 10kW range.

Last edited by Workhorse; 5th February 2013 at 04:40 AM.
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Old 5th February 2013, 05:52 AM   #59
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Default 887 watts with 2n3773 70-0-70 volt d.c.

Here is a circuit of 2n3773 8 pairs,70-0-70 volt d.c. 42 volt output at 0.497% distortion power output 887 watts into 2 ohm
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Old 5th February 2013, 10:07 AM   #60
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Default 2n3773 10 pairs 1.766 k.watts with 70-0-70 volt d.c. output can put upto 1 ohm2n3773

Same circuit now further modified 2n3773 10 pairs 1.766 k.watts with 70-0-70 volt d.c. up to 1 ohm output Load
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File Type: jpg 2n3773 1.766 k.watts with 70-0-70.JPG (239.5 KB, 495 views)
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