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Chip Amps Amplifiers based on integrated circuits

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Old 12th November 2012, 07:20 PM   #21
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Default lower cost

Stereo amplifier chip $7. No costly lethal transformers to buy or touch.
TDA1554Q Manu Philips Encapsulation Zip 2 x 22 W
The TDA155Q amplifier has a smooth treble that's not raspy, and therefore I'd propose that it would match up with the remote control head units at post 12.

The efficiency is very high for a class B, so heatsink expense is minimal--could use a plastic project box, drill holes in the bottom of the box, cut most of the top out of the box, and bolt the typically included metal plate atop the box, forming a convection cooler, in which case the chip mounted on the metal plate would hang down inside the box. Air goes in at the bottom (if you add rubber feet) up to the chip and then hot air is expelled at the small gap that is all the way around the top edge.
It would look like a black box with an aluminum top.
Or it could be done in color (optional):
Click the image to open in full size.
My own amp is black, silver and 1/3rd larger.
Enclosure expense is minimal for cool running amp with external power supply.
It looked better and ran much cooler after I added the square rubber feet (1 cm square by 2/3rds cm tall, feet to make the air vents work).

The amplifier is built with:
Inexpensive 15v cord from post 17
2200u 25v cap
100u 25v cap
22u 25v cap
100n cap
2 of 330n cap (wima polyester or nichicon electrolytic)
2 of 10k resistor for input loads
10k resistor for mute (un-mute)
Plastic project box (with flat metal shelf included)
Can use remote control head-unit from post 12 instead of the mechanical volume control.

TDA1554Q amplifier is extremely easy, inexpensive and durable, but does not naturally have either a laid back or euphonic sound. However it is possible to add those features via simple external circuits.
Optional "open sound" effect:
1). BlareBuster circuit at input with 1 20k pot, 2 of 47u cap and 2 of 100n or 1uF ecaps.
2). Power filter made with 1 fast silicon diode, a 1 ohm resistor and a 22u or larger cap.
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Last edited by danielwritesbac; 12th November 2012 at 07:24 PM.
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Old 13th November 2012, 10:20 AM   #22
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One thing worth saying is to buy casework and power supply plus heat-sinks is expensive . Giving it a little thought I would build these as Monoblocs ( a power supply for each channel ) . For arguments sake we could say 4 x 20 to 25 V DC (4 x 22 000 uF 35 V ) . The transformers 160 VA . This would allow to build a bridge amplifier or conventional 100 W stereo design later ( 2 x 40 to 50 V 320 VA ) . The heat-sinks 0.7 to 0.5 degrees per watt . With the heat-sinks I have listed one should be enough . The casework could be bought large enough to take one more if required . As a rule of thumb AB amps push out the power they give to the speakers as heat ( 50% realistic efficiency , not 67% theoretical ) . It is said 1/6 the stated output if undistorted music is the true average maximum ( 1/3 if Techno ) . That suggests even one of my recommended heat-sinks should work for 2 x 100 W real music if typical class AB . There are complicated ways of calculating this which I have found to be a bit unrealistic in real life . Mine is if you can not hold the heat-sink for 10 seconds it is too hot ( > 60 C ) . If you have the unit in a cupboard or the ambient temperature is high then pay attention to this . For a power amp that has generous heat-sinks one can use a wooden box , hum and noise should be OK . Some Audiophiles prefer it ( DNM ).

Some people say a good amplifier is 80 % power supply ( Naim of old ) . I suspect that is true . The point about Monobloc is the cost is not greatly more and it will make a small difference . My assumption if going to 100 W conventional is to use it as a single shared power supply ( +/- { 40 to 50 V } ) . Then one can duplicate as a Mononbloc if wanting better . 160 VA is about right for a real world design 100 W ( 320 VA both channels ) . Remember 160 VA is the safe operating point , the transformer will give a littler more on a transient with complete safety . Even Techno music should be OK . I would say even if using a switchmode PSU etcetera plan as if one day doing it the conventional way . Switchmode can make the efficiency better so might be justified . Like butter and margarine I prefer butter . In truth both have merit .

Buy Heat Sinks Heat sink,0.72deg C/W 200x125x25mm 25g AAVID THERMALLOY S586/B/125 online from RS for next day delivery.
MCTA160/18 - MULTICOMP - 160VA TOROIDAL 2X18V | CPC
ECOS1VP333EA - PANASONIC - CAPACITOR, 33000UF, 35V | CPC
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Old 13th November 2012, 11:06 AM   #23
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I suspect only when we get to 100 Watts is it worth the trouble to build something . Comparing a Quad 405 we might buy on eBay we could be doing better to make it ourselves . I totally beleive someone taking the trouble to learn the basics can make something better than commercial designs . If I take up golf I can not imagine I would get that far as a new hobby I could make my profession . With electronics it is totally realistic to rise that far and quickly with a little help .

http://www.ebay.co.uk/itm/Quad-405-2...item27ccbd84b9
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Old 14th November 2012, 06:09 PM   #24
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i suspect its worth building under 500 watts.
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Old 15th November 2012, 10:22 AM   #25
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I think it is worth designing the power supply as the primary component . My idea to have either approximately +/- 25 V or +/- 50 V available .

There is a secondary reason . If the +/- 25 V is over specified the first Audiophile principle is researched . Is it worth having an over specified PSU ? Mostly it is , if only that it can be used again . I suspect it is a totally good idea . I doubt the cost difference is more than $30 above minimum requirements .

Rightly or wrongly 2 x 100 W output is considered true hi fi . Many PA people will accept it as a minimum requirement also . I suspect most amplifiers would sound as good if using all the same parts and only 20 Watts . the Yamaha class A or class B design did . It was a great amplifier both ways , the class A was better . The PSU I described with heat-sinks to match work be fine . Alas chip amps must be forgotten if so . My poor cousin Velleman kit could be converted to do that . There are better options . However being class A might be a decisive victory .

My point remains . Take the case , heat-sink and PSU very seriously . The amp can be changed many times .

If you calculate carefully the 25 V 50 V option is one of the best .

Yamaha CA-1000 on thevintageknob.org

Last edited by nigel pearson; 15th November 2012 at 10:26 AM.
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Old 15th November 2012, 11:27 AM   #26
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Quote:
Originally Posted by nigel pearson View Post
..... Alas chip amps must be forgotten if so ....
Sorry, I lost your logic here. Can you explain?
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Old 15th November 2012, 12:14 PM   #27
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I dont blame you, that post is very difficult to decipher
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Old 16th November 2012, 06:59 AM   #28
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Sorry all . Writing would never make make fortune . The point I was making is the power supply is a critical decision if saying money determines our reason for starting the project . Like in most things it is the critical 20 % extra that should be spent . Fascination might cause someone to go further than intended . If so my 25/50 V option should be future proof . The Yamaha Class A + AB rearranged it's power supply and biasing to have either option . As far as I know chip amps do not convert to class A ,where as the simple Velleman kit could be converted . In life most people have goals , class A is a goal of most who build amplifiers .
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Old 16th November 2012, 07:35 AM   #29
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This is how many discover class A . Douglas Self makes it easier . Well worth a read .
http://diagramas.diagramasde.com/aud...od%20Class.pdf .

Perhaps even this amp would adapt to my power supply ( +/- 22 V is close ) .
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Old 16th November 2012, 08:00 AM   #30
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Quote:
Originally Posted by nigel pearson View Post
.. .Class A is a goal of most who build amplifiers .
To eliminate the audio effect of sticking, switching, glitching, etc. . . bias in the Class AB amp can be increased to play the 1st watt or even more in Class A. Thus the popular trick of swamping clumsy with bias is the cause of poor efficiency in linear audio. Personally, I find it most unfortunate if such inefficient practices are habitual.

So my goal is the opposite--I like well done high efficiency linear audio.
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