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Old 22nd August 2013, 02:32 AM   #241
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Hey guys i made tda7294 and 2sc5200/2sa1943 with a toroid 30+30 5+5 amp, but not sounds good under 8 ohm load and distorts a lot on high volume, example 4 ohm 2/8 ohm woofers in parallel , i did exactly of the schematic, the heatsink which i m using it's good at high volume the ic and transistors are always cold.

what could be the problem?
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Old 22nd August 2013, 05:16 AM   #242
gootee is offline gootee  United States
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How much capacitance did you use, for each power supply rail?
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Old 22nd August 2013, 03:07 PM   #243
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I m using 2x 4700uf 50v for each supply rails
Maybe it's the low capacitance that is causing this problem?
What do you think? Gootee
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Old 22nd August 2013, 03:41 PM   #244
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Have a look at the output with a scope and then you will see what kind of distortions that you are having.

It will be either clipping (flat topping of the waveform's) or crossover distortion (notches at the center points of the waveform).

If your power supply can't supply enough current then these types of distortions can occurr when attempting high power levels.

jer
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Old 23rd August 2013, 12:21 AM   #245
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thanks for reply geraldfryjr!

So i don't have a scope, but i will see what i can do this weekend!

I forgot to say which when the amp is running at 4 ohm load the sound distorts at low volume also, as you said start to clipping

In 8 ohm it's completely clean and no distortion at maximum or low volume

And one more thing, i don't found the resistors 0,15R, i just found 0,47R, i don't know if that change anything
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Old 23rd August 2013, 11:13 AM   #246
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You could use three of the 0.47R in parallel, to get (0.47/3)R.

You need more rail capacitance. I am not at my computer but would guess that you need at least 4x as much.
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Old 23rd August 2013, 03:14 PM   #247
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Thanks for reply gootee

So,i don't understand what you said about the resistors,parallel is for have more watts or less resistance?
About the caps, i will buy more four, two each rails
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Old 23rd August 2013, 04:05 PM   #248
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Quote:
Originally Posted by charleslokko View Post
Thanks for reply gootee

So,i don't understand what you said about the resistors,parallel is for have more watts or less resistance?
Both. Paralleling a number, n, resistors all of same value gives result of value/n. Power handling is also increased, since the current in each resistor is also divided by n, and power = iČR.

Quote:
About the caps, i will buy more four, two each rails
You can calculate the minimum required capacitance, instead of guessing. The equation, and a spreadsheet for that, are in the post at:

Resevoir capacitors for Chip Amps
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Old 24th August 2013, 07:03 AM   #249
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Hi guys !! I have a few questions about the amp design. I'm going to use the following: simetrical power supply 35-0-35 AC (about 45-0-45 DC after rectifier) TDA7293 + 2SC5200 + 2SA1943 and a 4 ohm speaker. First: how much power will I get with this configuration (+ losses). Second: how do I control the bias voltage ? Third: will the 15A limit of the transistor be an issue and if I use 2 pairs of 2SC5200/2SA1943 in paralel will it be less risky for me to burn the bipolars ? My goal is not to obtain more power with the second pair of 2sc5200/2sa1943, but to make it less risky for them to burn out. Thanks in advance !!

EDIT: Fourth: how much voltage can I pump into the 2sc5200/2sa1943. Can I go up to 90-0-90 v for the bipolars, and 45-0-45 volts for the TDA7293 ?? And do I need more pairs of 2sc5200/2sa1943 (like 6x2sc5200/6x2sa1943)to cope for the new voltage rating, power output, maximum amps output, so they won't burn out ??

Last edited by Xerpentor; 24th August 2013 at 07:25 AM.
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Old 25th August 2013, 07:40 PM   #250
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Well, 45 VDC minus the Vclip voltage across the amplifier itself will probably be around 42 VDC and if we assume the ripple voltage will be <= 2 V then we have 40 V max peak across 4 Ohms which would push 10 Amps max peak. But that's "peak" and power ratings are given using RMS. So dividing by sqrt(2) gives 28.28 V RMS sine wave voltage pushing 7.071 Amps RMS sine wave current through 4 Ohms. Rated max power is then either vČ/R or iČR, which both equal 200 Watts RMS rated max output power.

But that depends entirely on the ripple voltage being less than or equal to 2 Volts. And the ripple voltage limit depends entirely on the value of the reservoir capacitance.

For the conditions assumed, you would need at least 44000 uF per rail, to get 200 W rated max power. With 20000 uF, you would get about 179 Watts rated max. And with 10000 uF you would get about 148 Watts rated max.

If the Vclip voltage is different than the assumed 3 Volts, those figures would change somewhat.

You can see how to calculate that, and download the spreadsheet for it, in the post at:

Resevoir capacitors for Chip Amps

Cheers,

Tom
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