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Old 6th January 2013, 10:43 PM   #3791
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Join Date: Oct 2005
Quote:
Originally Posted by don2007ksa View Post
can't wait the schematic of mr. engel's nmos 500,more power to you sir.
everything is here sir,
https://sites.google.com/site/quasisdiyaudiosite/
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Old 14th March 2013, 01:48 AM   #3792
SAMCPI is offline SAMCPI  Iran
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Join Date: Sep 2012
Location: Tehran
Default NMOS 350/500 and Soft start CCT

Hi Quasi and all

I have 2 question

1- about Amplifier NMOS350

Item 7 in Construction Guide – Nmos350/500

7. All being well switch off, back off the bias control trimmer (VR2) and replace the 100 ohm
resistors with 10 ohm 1 watt resistors. Switch on again and re-adjust VR2 to get 0.3 volts per
per FET pair across the positive rail 10 ohm resistor.

I should For a 6 FET board set for a voltage of 0.9 volts ?
and For a 10 FET board set for a voltage of 1.5 volts?

2- About slow turn-on cct circuit
i want to use 9v AC Transformer for 12v DC output and turn on 12v relay . so i have problem with R1 & R2

Pleas help me. Thank you very very much

BEST REGARD
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Old 14th March 2013, 10:41 AM   #3793
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
Measure the output bias currents across R29 ....... R34.
The schematic tells you 30mA per pair.
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Old 14th March 2013, 01:13 PM   #3794
SAMCPI is offline SAMCPI  Iran
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Location: Tehran
Thank you Andrew

i build nmos350 , and i use IRFP460
I adjust VR2 to get 0.9 volts on
across the positive rail 10 ohm resistor. so all mosfet very hot

i am sorry for my Eng language , because very very por
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Old 14th March 2013, 01:17 PM   #3795
SAMCPI is offline SAMCPI  Iran
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Join Date: Sep 2012
Location: Tehran
Quote:
Originally Posted by AndrewT View Post
Measure the output bias currents across R29 ....... R34.
The schematic tells you 30mA per pair.
Thank you Andrew

i build nmos350 , and i use IRFP460
I adjust VR2 to get 0.9 volts on
across the positive rail 10 ohm resistor. so all mosfet very hot

i am sorry for my Eng language , because very very por
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Old 25th March 2013, 03:06 AM   #3796
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Join Date: Dec 2008
Hi all,

I want to make the nmos 200 with a pair of power mosfets. What is the change should I make to the original schematic of nmos 200? I still don't know what type of mosfet i will use (maybe 240p, 260p, or a 250p, depends on the availability)

The other question is about ground lift of the amp (the 10R resistor), is it necessary to put this lift resistor? What if I don't use it?

Thank you.

Best regards,
Roy
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Old 11th April 2013, 11:02 PM   #3797
FQR is offline FQR  Germany
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Join Date: Nov 2012
Location: Bad Birnbach, Bavaria
Hello, guys, and hello, Quasi!

first of all: Iīm (brand) new in this forum. Plese help me, although this may be a little offtopic (canīt load all the sites, so donīt really know if it is), ok?

2 days ago I found the Actrk 400/600 schematic on this site:

600 Watt Quasi Amplifier With Mosfet IRFP460

I posted it with addition of many, many questions... but the only thing, i "heard", was:
"Not bad, but search for the apex." Although apex has not the "quasi-comp" output, that i need. Aaargh... donīt want to tell you the feelings, that i had, and till now, further, and (different but) stronger, have.
Plese guys, read the thread (only 3 posts all), and tell me, what you think:

Subamp with ~ 1000 W RMS at 4 Ohms, built at low cost

After the advice of JMFahey, from noon to now, with waiting for every site between 1 and 10 Minutes to load (cause my UMTS is bad enough on my "very special" domicile in the middle of the "Pampa", but since a few days itīs limited in rated max. speed (since I reached my 3 GB), too. Only GPRS/EDGE...), I searched for any pure vertical-n-channel output, which would be good for me.

Just a few Minutes ago, feeling more and more hopeless, and REALLY slowly rising headache about my sh%§*'!" situation, I - found - the - word (or better: name) - "Quasi" - mentioned - in - the - (felt) 500.st thread (THIS thread), that I found with my bad tags and keywords (I am absolute beginner in audio, and english language is not too easy for me).

It seems to be, that THIS WAS an approved design in "diy", from the BEGINNING!!!

Please: Would you help me? Could you tell me the specs of/for the parts? (1.Inductor; 2.Diodes; 3.What means the slightly diagonal "fork" with three prongs? I saw many german schematics, but this sign, i have never seen; 4.Types for Capacitors; 5. Resistors (as I mentioned in the thread before)

6. And: Do you know a "trick" for getting a voltage, 10 volts higher than rail V, without having further taps? (My transformers got only three taps, for two identical voltages. Only idea i have is add some windings - not real good, I think.)

7. Why would it be "better" and "safer", to use only the lowest given voltage of them?
(The exact type of both is: SIEMENS 4AM6542-8DD40-0FA0. Rated 2.5kVA(cont.), 13.3kVA(short.) with several primaries, from 550 to 208 Volts, and secondary rated at 2 x 115 Volts. So the given voltages (w.o. diode losses) are like mentioned, but I canīt get 10 "extra" Volts too simple... ^^) Cause I want to use (min.) +/-85 V or so. I need ca. 1000 W RMS on 4 Ohms.

8. My IRFP450 (Harris) are lower (150W) power rated than original "IRF"P450 (190W).
But fortunately they have (but only slightly) lower gate charge. Could i use 8 pairs instead of 5, by lowering value of gate resistors to 20 (10 + 10) Ohms?

9. Are there any PCBīs to get? Only thing I know about PCB is using UV-lamp. Such a magnetic ballast i got at home (125 W). But I have no printer. Thatīs bad. (But not impossible, someone would have the right printer...) ...the RIGHT printer, right? I mean, one need some special ink, which is dense enough not to let through the UV light, or not?
But the thing on making PCB, why I never tried to make one til now (although for some small electronic projects Iīve had good usage for), is, that many people say many different things, what substance one needs to "etch". (And one more question: If using etched PCB for the output, how does this work? With some friends, some years ago, living in a little bigger "village" than now, we made some high-power-electronics, rated to similar ccurrent(s). But we used platines with very thick copper plate, milled by a cnc.
What is the difference? Should/must one wire point-to-point, although he uses PCB?)

Sooo many questions, I know, probably too much! (But my head works and works, cause so many hours of stupid and senseless searching.)

Greets, and hoping for (positive) reply,

FredQR
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Old 12th April 2013, 09:36 AM   #3798
AndrewT is offline AndrewT  Scotland
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Location: Scottish Borders
FQR,
build a simple low power amplifier before you go to a complicated and high power amplifier.
You could try a 40W to 60W chipamp on a 160VA transformer.
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regards Andrew T.
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Old 12th April 2013, 11:26 AM   #3799
FQR is offline FQR  Germany
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Join Date: Nov 2012
Location: Bad Birnbach, Bavaria
Hello, again!

Now I found schematic of "NMos 300 / 500" - this could be a good solution for using my parts, (not having a transformer with 10 "extra" volts, for building Actrk600) but I donīt found a description for it. Should/Could I use higher rail voltage (probably NOT! Would not fit with given part (resistor) values, I think),

or (with the simplification P = Uē / R; 75 V could feed about > 1400 W RMS into a 4 Ohm load --- so much is not needed, only 1000 W, but if rail voltage would get down under load of 4 Ohm to, say, 65 Volts, each complete rail should be able to deliver about 15,5 Amperes continuously, right?) is it possible, to use 8

(or more? but donīt think it would fit to the driver circuit, cause gate driving current eventually would be too low/not more adequate... hmmm... Circuit "only" should drive a subwoofer in frequency not over 80 Hz, doesnīt this change the possibilities? Cause at lower freqs gate driving current must not have this value, I thought -- or am I nuts?)

pairs of my "very special IRFP450" from Harris, which have only 2/3 the gate charge, only 3/4 the Ptot, as "normal" IRFP450 have? And if this could work, which value of gate resistors would be best (for, say, 8 or 10 pairs)?

And if NOT: Can I bridge 2 of them into a 4 Ohm / 1000 W RMS load? I doubt it. Isnīt there any OTHER schematic which gives min. 800 W RMS into 4 Ohm load (as it IS, without changes), where most of my parts would fit in?

Now I know, what kind(s) of parts to use. Foil capacitors 100V, metal film resistors rated at 0,5 or 1 Watts for general, 1 or 2 Watts for little higher current in driving circuitry, and ceramic 5 Watt types for the source resistors.

But not much more, unfortunately...
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Old 12th April 2013, 11:54 AM   #3800
FQR is offline FQR  Germany
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Join Date: Nov 2012
Location: Bad Birnbach, Bavaria
Hello, AndrewT!

Thanks for your reply. Coulnīt see it, cause sometimes for hours I got no connection, and couldnīt actualize the site.

I know, my posts are too long (probably most of you would NOT read all of them, or the whole post...

But I wrote "please read other thread". There I had written, that I already built a chipamp (very simple, LM3886 without tone or volume control. Cause this functions were in the preamp).

I donīt mean, that Iīm "experienced" now...

The problem is: I have to build this amp in the next time, before I have to move away from this beautiful place, where i got access to much more tools, than belong to myself, and know many peple, which could help me, find solutions for problems with my non-existing car/drivers license.

Only thing getting better for sure is internet connection.

So I hope again, someone would answer my (now slightly decreased number of) questions.
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