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Old 20th September 2006, 09:37 PM   #1
noubar is offline noubar  Lebanon
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Question 2 stk4050v bridged amplifier

I'm building a power amplifier right now, it will be the 3rd one i build and i'm only 16 years old so i'm not a pro...

i've already tried a 2 ohm load on stk4048 IC's (150W RMS @ 8 Ohm) and it worked fine even at full power so my question is will the stk4050 IC (200W RMS @ 8 ohm) can handle a 2ohm load so i can bridge two of them and use a 4 ohm load...?

i need a little help as i don't know what pre-amp IC's to use to invert the signal of one channel and to keep the same gain at the other channel...

i also have to ask about the transformer as in the datasheet it is said that the stk4050 can handle 95V but the recommended voltage is 66V so i'm a little confused because i've already used a 60V (30V+30V) transformer for the stk4048 IC... so i was thinking to build a 90V (45V+45V) transformer for the stk4050 but i'm afraid to burn the stk4050 out...
i have good heatsink i never had overheating before, i always use fans so everytime i touch the heatsink it's cold even when the amp is running at full power (stk4048 amp). So does anyone have an idea how i can get the best power performance and without burning everything out...?

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Old 21st September 2006, 01:52 PM   #2
ronnieb is offline ronnieb  Netherlands
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Hey Noubar,

I've been working with the STK 4050 for some while, also as bridged amplifiers for stage amplification, where we normally use 4 Ohm loads. A lower load then 4 Ohm is not recommended in bridge application mode, because of the current capabilities of the STK 4050, if you really want to use 2 Ohm loads, you should consider building a Power Mosfett amplifier, which is also easier to expand in output power, but the cost of it will be higher.

The power supply is the difficult part of the 4050 and ic's like them (I also often use the TDA 7294 mostly for it's small size) To fully use the capabilities of the 4050 you need a split power supply, that is, you need 2 x 66 V (66V + 66V) RMS for optimum results. Using 2 x 45V as you were planning to do, isn't a problem, but you won't get the full output power.

The only problem in building the power supply is regulating it to 2 x 66 V RMS. The efficienty factor of a fully loaded power supply is about Vin x 0.9 = Vout RMS (but this is at full load), so you need a transformer of 2 x 73 V AC, the problem is that if the cirquit hasn't got any load, the input voltage isn't 2 x 66 V, but (2 x) 73 x sqrt(2) = (2 x) 103 V, which exceeds the capabilities of the STK 4050. You would have tho regulate the output voltage down to 66V, else you get some nice fireworks

So if you want to be on the safe side, use a transformer of 2 x 45 V and use a bridge rectifier with a couple of big elco's of at least 2 x 10.000 uF per channel. Your output voltage won't go higher than 2 x 66 V then.

For the pre amplifier, you could use ic's like the TL 081/082, they have a very low noise production, so at full power it won't sound like you're standing on the beach with a big storm going on

Hope this helped,

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Old 21st September 2006, 08:54 PM   #3
noubar is offline noubar  Lebanon
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Default thanks 4 the reply

hey Ronald

Thanks for the reply it helped me but i'm still confused the "Vcc max" (maximum supply voltage) is it the voltage between the amplifier ground and the "Vcc -" or "Vcc +" ?? or is it the voltage between the "Vcc +" and the "Vcc -"

i'm going to invert the input signal of one of the channels so i can make the amplifier bridgeable. then can i connect a 4ohm load on the bridged output (that will be a 2 ohm load on every 4050) or i'm going to see some smoke after doing this? i've already used a stk4048 to drive two 4 ohm loads and it worked fine at full power all the night... Is it the same with the 4050?

finally i want to know what's the best choice of transformer to get the best power output... regulating it to 2 x 66v wont be a big trouble i'll just have to add some load... but i'm afraid that the 4050 can't handle more than 47.5v x 2 which makes the voltage betwenn "Vcc+" and "Vcc-" 95V.

and i have a question, whats the easiest way to invert the input signal of my stereo amplifier (STK4048 x 2) so i can make it bridgeable... i don't want to add any other circuit inside as there is no more space...
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Old 22nd September 2006, 07:22 AM   #4
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Maximum supply voltage on the STK4050V is +/-95V, which means a +95V supply, and a -95V supply.

When you see a spec for voltage that says '+/-60V' or some such, that means a +60V supply, and a -60V supply, referenced to ground.

As far as the STK4050V, I think I'd keep the supply rails under +/-80V.
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Old 23rd September 2006, 11:37 PM   #5
noubar is offline noubar  Lebanon
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Default 10x 4 the reply

i'm going to build a MOSFET amplifier circuit coz the stk4050 is very expensive here, and if i'm going to buy the power IC's and the transformer, i can buy a brandnew MOSFET power amplifier but i want to do it myself so i can learn their secrets... does anyone knows some website where i can find some help on these stuff?? i only want to build a circuit that can fully power my new Pioneer subwoofer TS-W306C (1000W max. 400W nom.)
and btw i'm looking for a crossover circuit as i've completely burned out the one i had bought (80 bucks )
I just don't understand how to "kill" every frequency more than 40Hz from the audio signal!
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Old 27th June 2007, 09:25 PM   #6
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Default power supply and power

Itís great that your fooling around with thick film and thin film hybrid modules.
But with the high end stk4048 and 4050 you need to understand power.
Remember ohms law always applies so the open voltage of the transformer is what will charge your caps. If you ran the 4048 at Fcc+30 60v-ct you never brought them up to their full power.
In my last thread I posted
that site has a 2.2kva dual ct toroidal that a killer but for you I would say go to
they have a used ct that cost $65.00 use that transformer and start from there.
A very basic power supply with at least 10000mf per side and a 500ohm load resistor per side
If you need a schematic email me and Iíll send it to you. Then go back to your 4048ís
This is going to give you a lot of power so look for a soft start circuit and use it
Make sure you have a load on the 4048 when you power it up but not speakers
Use about 10 ohms wire wound and test your outputs. I could go on for ever
e-mail me and Iíll send you the titles of a few good books that will really help.
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Old 27th June 2007, 10:05 PM   #7
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Default variac

One thing I left out that I find very helpful when your dealing with power (analog)
I always use a variac so I can adjust the input to the primary transformer it's worth the cost.
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Old 28th June 2007, 12:11 AM   #8
noubar is offline noubar  Lebanon
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hi dave
i've already build an stk4048 amplifier it stopps working when input votage exceeds +/- 40v so i've built a +/- 35v PSU with 4 caps (4700mf each 2 per side) and 370 ohm load resistors per side.

for the stk4050 if i ever plan to build it i may build the transformer by myself, variacs are useful but very expensive here

i'm really interested about the books so could you please e-mail me the titles

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Old 30th June 2007, 01:19 PM   #9
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Default Books of interest

Noubar Hi,

Sorry it took so long to get back to you itís been a bad week!!!!
Anyway, my books are scattered but here are a few.
Remember be diversified itís the best way to build the relationship between all things.
The more you reed the more you see.

Some books worth having, Iíll send you some other titles as I dig them out.

Visual dictionary of Science, published by Barns an Noble Books
Copyright 1998 dorling kindersly limited, London
A really nice book

Basic Optics and Optical Insruments (I would tell you to buy this book also)
Prepaired by the bureau of naval personnrl
Dover publications, inc. NY

Analog Circuit design, (not that great but so good old insight to the beginning of analog)
Butterworth-heinemann, edited by Jim Williams

High performance Audio Power Amplifiers (not as good as it sounds but worth having)
Ben Duncan, newnes

Practical Electronics for Inventors (This is a great book full of everything)
Donít let its seeming elementary style fool you buy the book!
Paul Scherz, McGraw-HillÖ.. Great Book

The Art of Electronics (I have two of these itís like a bible to me)
Horowitz Winfield Hill, Cambridge university press

Noubar buy the last two for sure. The reason for the others is so you can see the relationship between all things. Thatís why I say Ohms law always applies

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Old 11th July 2007, 07:56 AM   #10
billbo is offline billbo  Australia
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Default stk 4048

I have built a stereo stk 4048 amp on vero boards with +/- 58 volts dual 300va toroidal power suplies. One of the simplest amps I have built. Have a look in the photo gallery on page 28. I have posted pictures of the amp. Its still running well. The STK 4048's were very cheap here in oz. $23.50 each from WES components in Sydney.
Billy D...
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