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Old 23rd February 2010, 05:19 PM   #1
sekhar is offline sekhar  India
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Default 200w amplifier under development help needed

hi,
everybody let me introduce myself I am Sekhar..... newbie in this field of solid state amps ..... I was trying to make a quasicomplementary amps for a few weeks...every time i assembled a circuit that i took from the net something or the other went wrong.......so i decided to make my own amp ....... it is just a very simple circuit that i design of what i understood from the book of G RAndy Slone... Plz have a look at it and help me make the amp better ........ Sugessions r highly recommended ..... any type of help would be great

hERE ARE CIRCUITS AND SIMULATION DATA;

AT 10HZ
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AT 20HZ
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AT 1KHZ
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AT 20KHZ
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AT 30KHZ
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Old 23rd February 2010, 05:25 PM   #2
wahab is offline wahab  Algeria
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It would be better to replace the TIP41 by a BD139 and to connect
a capacitor of about 47/67pF between base and collector of this
transistor..otherwise, the amp will oscillate..

Anyway, the BD139/140 are rated at 80V VCE, so you should reduce the
supply volatge by a few volts or replace these devices by more adequate ones
if you want to keep the volatge at that level...
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Old 23rd February 2010, 06:13 PM   #3
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Hi sekhar

Well looking at it you certainly don't need the diodes in parallel with the mosfets as they already have built in intrinsic body diodes, that'll save a few pence. I'd be very tempted to disconnect the diode that connects to the BD140 on the negative side (remove it) & then connect the emitter of the BD140 to the lower side of the 0.22 ohm resistor on the output. As it is now the BD140 has no control over the output current on the negative half cycle.

If you reconnect it as i suggest then it'll operate as as complimentary feedback transistor with the lower power mosfet in a feedback loop that will control current much better.

You do realise that you'll never be able to swing the output voltage on the negative half cycle to near the rail voltage. This is due to the IRFP250 needing substantial gate voltage to turn it on & then some to draw heavy currents & approach the negative rail. You have it sorted on the positive side as you are using a bootstrap capacitor.

E2A:- As wahab pointed out the BD139 & 140 need to be replaced with higher voltage components.

I'm glad you are simulating it first, best of luck
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Old 23rd February 2010, 08:04 PM   #4
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-----bc pairs in the input will not be very happy at this rail voltage mpsa series might be an option ....

----- your bias circuit is generic .... it needs one more resitor on the down side and also needs to be recalculated

----- your ltp pair seems miscalculated and ofset will be present at the output... R9 and R14 have to be of the same value either 22or 27 k depending on the gain you want

----- it is not safe to think of this amplifier as dc coupled ....capacitor and resistor must be installed in the input

----- then again there is no filter in the input ( capacitor in parallel with R 14 ) that will determine partially the uper end of your amp

----- Wahab sugested a very correct thing ... a miller is to be added in the VAs section tip 41 something that is also to be replaced with a BD 139 or even an MJE 340... miller cap needs to be configured with scope load and generator and 47PF is optimistic and above 100pf is too much and safelly kills your sonics .... a more realistic valuse will be between 68 and 82

----- zobel created by 10 R +100 nf is a must for this amplifier and to my opinion this will HAVE to be together with an inductor in the output

----- event horizon comment is correct there is something wrong there but i dont have time enough to see exactly what ...i will get back to you on this one

----- you may fish some info from NP project a mosfet citation 12 it is a similar circuit without so many goodies like yours but still you can get some info from there ...it is avery detailed article

-----most importand

---- at this configuration and at this rail voltage you expect this amplifier to produce a litle more than 90W@8 ohm with good power supply and good construction .... that is almost the double in @4Ohm loads ...180W of power for only two tranistors like that is way too much .... not even 4 will be enough

you see at 90W @8Ohm depenting on your type of speaker often except the typical resistance of 8Ohms stated behind the speaker as a load is always depenting on the frequency so the same speaker sometimes might "dive" to 6 or even lower resistance ...this will stress the transistors and then smoke....

so either you low your rails and recalculate everything or smoke is arround the corner ...keep in mind that with your topology is even worst since youre doing quasi coplementary that behaves even worst under reactive loads since the lower output tranistor cannot actually "follow" the uper one

---- god i hate fu****cking simulators they tell you fu****cking nothing about how to built an amplifier

i will end up this very long opinion by telling you to take a look and read and understand the diference of various mosfets and a very good place to start with is post related to P101 from ESP pages or the Quasi pages that you may find in the forum

kind regards sakis

oooops i have just seen the top of your post : " 200W amplifier under construction " ....hmmmm you seriously need to thing about this once more my friend .... safely with this circuit you may be able to produce arround 60W
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Last edited by east electronics; 23rd February 2010 at 08:10 PM. Reason: seen the top of the post
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Old 23rd February 2010, 08:15 PM   #5
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a small advice outside the post ....

almost 4 years ago i was in the exact same position like you are now ...at the time i received from kind forum members a similar bunch of information ( i dint come like that in one post ) but many members added a few things here and there ....

i said to my shelf :::: NO !!! THIS CAN BE RIGHT .... IT A NICE AMP IT SHOULD WORK !!!

trust me my friend ...they were right and i was wrong
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Old 23rd February 2010, 08:18 PM   #6
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Quote:
Originally Posted by wahab View Post
It would be better to replace the TIP41 by a BD139 and to connect
a capacitor of about 47/67pF between base and collector of this
transistor..otherwise, the amp will oscillate..

...
Also the BD140 needs a cap from collector to base or you will get oscilation on the output.
I found that in my own quasi design.
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Old 23rd February 2010, 08:27 PM   #7
sekhar is offline sekhar  India
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I am trying to simulate the circuit with all the above mentioned changes but for some or the other reason the simulator is crashing ..............
Will keep trying .................
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Old 23rd February 2010, 09:25 PM   #8
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good ...let us know there is a bunch of very nice guys here willing to help

regards sakis
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 27th February 2010, 10:53 AM   #9
sekhar is offline sekhar  India
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hi
I simulated the following circuit "MK2" and got standard results...........I had a few queries before making the amp..........
1. in simulation the amp gives a offset of 3-4V........ Which after a long time settlest to 20mv.... WHy?????
2.Has any body made the "legend MK2 amp" .......... If so kindly give the reviews about the amp and its problems if any..........
3.I desperately need a high power amp with good sonics......is MK2 good enough ???? Is any changes needed to the given circuit

Circuit.
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Last edited by sekhar; 27th February 2010 at 10:58 AM.
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Old 27th February 2010, 02:28 PM   #10
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Sekhar,the designer of this amp suggested me if you want good sound take the Legend Stage Master it is more suitable for home use the MKII is more for PA(read better PA)
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