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Old 26th October 2007, 12:27 PM   #1
Paswa is offline Paswa  India
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Default A TDA2050 Victory but trouble with transformer

Hi. I've just finish makin' a Chip amp with TDA2050 with the circuit given in the official datasheet. It works very very fine.

The bass is very very clear but

midrange is quite noisy (may be the speaker probblem)

treble is powerful too

I've to supply +-22.5V to get full 32W-35W output. please help me selectin' the ps design.[/B]

1>how much current will draw the circuit

2>if I use a 7825 ic, and then down the voltage to +22.5V

3>if I use 7825, what ic should i use to get -22.5V

4>Or high capacitance capacitors(like 2200uF-10,000uF) will be fine
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Old 26th October 2007, 02:06 PM   #2
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As it is the 2050 sounds fine with an unregulated power supply. Typically 17-0-17 volts will be fine. You could use a standard 15-0-15 volt supply ( ac transformer secondary voltage). The difference in power will not be noticeable and you have a safe margin for power surges. You could use a 90 VA transformer . I've used a 50VA transformer but it's a bit too small.

I think a regulated supply is an over kill but some diy amps seem to sound noticeably better with regulated supplies. I'm not sure if this is one of them.
You can use a 7818 and 7918 regulator and bump up their output voltage using a zener or diodes in the ground leg . Check the app note.

The amp should be noise free . There must be something wrong in your wiring , loose wires etc. Get it working perfectly with unregulated supplies before trying out a regulated supply .
Cheers.
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Old 27th October 2007, 06:01 AM   #3
Paswa is offline Paswa  India
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please explain what is VA. Is VA means the multiplication(*) of voltage and current(Ampere).

in a 90VA transformer,
is the potential difference(volt) = 15V
the current would be= 90/15 A = 6A

am i right?

also, the official datasheet says the ic will prouce its highest RMS at +-22.5V, so if I use 20-0-20, 90VA trafo and then use 7820 and 7920, is there would be any problem?

also thanks for ur very early reply
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Old 27th October 2007, 03:22 PM   #4
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Yes VA is voltage into current and is the power that the transformer can deliver.
If you look at a transformer spec ( eg. Miracle 80 VA torroid ) for a 15 - 0- 15 V secondary th ecurrent ratingis 2.67 amps. That turns out to be 80 VA / 2x 15 volts = 2.66 Amps.

So for your example the transformer must be 90VA/ 30V = 3Amps.

Don't run the chip at the highest voltage possible. If you get a mains surge the chip will break down . With no output relay protection it will burn up your speaker.

I guess the safest might be +/-18 volts. If you go regulated then the higher voltage is OK .The standard LM78xx chip will not work as they can only handle about 1 or just over 1 amp. It will need a pass power transistor as shown in the application manual. You will require a heat sink also ! Make sure the regulator can handle surge voltages. Calcutta must have horrid mains supplies (?).
Regulated supplies are attractive but requires a lot of work.
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Old 27th October 2007, 04:07 PM   #5
Paswa is offline Paswa  India
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Thanks! Thanks! Thanks! for ur valueable suggestion. don't feel disturbed, please, let me ask some more q/a::

Quote:
If you get a mains surge the chip will break down.With no output relay protection it will burn up your speaker
output relay protection, what is that ? give the circuit please, i wanna know about that. u r right, some areas of kolkata really have horrid mains voltage.



Quote:
It will need a pass power transistor as shown in the application manual
in application manual means? the datasheet of TDA2050 has no any pass power transistor. can u give me the circuit of that.

is there any no regulator ic that can handle 3A of current? do u know about that?

ok, if i'm unable to find or make a good regulator, i'll go for 18-0-18 @ 90VA.

thanks a-gain
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Old 29th October 2007, 02:42 AM   #6
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Because I m a little bit lazy,I usually go with this:
-calculate the max continuous output power,esp at low ohms,
-then get a transformer with rating of 1.5~1.6 of the max output power of the chip,per channel.
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Old 29th October 2007, 03:11 AM   #7
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thanks, but i won't understand this line ::
Quote:
then get a transformer with rating of 1.5~1.6 of the max output power of the chip,per channel.
transformer ratin of 1.5~1.6 means?
will I calculate the RMS power or the PMPO ?
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Old 29th October 2007, 04:02 AM   #8
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Quote:
transformer ratin of 1.5~1.6 means?
will I calculate the RMS power or the PMPO ?
If the amp requires 100 Watts, then buy a transformer of 160 watts/VA but with the same voltage.

And do not forget to MULTIPLY by 4 when asking at the shop. I hate to mention this.

PMPO is an entity of advertisers and do not quote/ask about it to engineers.

Gajanan Phadte
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Old 29th October 2007, 04:37 AM   #9
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Default Search for answers before posting questions...

Please search on this forum for 'speaker protection circuit' and something should come up. There have been lots of designs presented on this forum.
It's great to ask a lot of questions and get answers. BUT you MUST do your homework too. Search the Web and this and other forums for answers to your questions before putting them up here. Many have been answered many times before and it's painful to keep repeating them over and over again.

About Leolabs post.
Calculate the power output into the lowest load ( say 4 ohms ).
Here it might be 25 watts into 4 ohms ( per channel ). Now multiply that with 1.6 and you get 40 VA .
However I have used 50 VA and it is not enough . So pick something between 50 and 100 VA. If you play music where the avarage content is low like classical or folk then 50 to 70 VA might be enough. If you play music with high average power like rock or techno or synthesisers , then 100VA migh be better.
The reason for this is that the smaller supply can handle short high level bursts before sagging ( voltage) and is OK if the average power required is low.

At 18 Volts ( regulated ) supplies your peak current per channel might be close to 4 amps with a 4 ohm load . That's 8 amps peak with both channels playing the same signal. So a typical 3 A regulator is not enough. I suggest that you drop the regulator plan and get the unregulated supplies working first .

READ more..... all the info is already available . Ask questions if the info is hard to understand. See what others have already done...........I mean read about it by doing a 'search' .

About transformers . If you buy a reputed brand like Miracle or Delta or those that have a web page , chances are you will get what you ask for . So 100VA will really be 100VA . Small time local transformer manufacturers will not match up to the specs. They will be much cheaper , last for a shorter time and be nowhere near your VA rating . No point "saving" money here because " you get what you pay for " is perfectly applicable here.
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Old 29th October 2007, 08:17 AM   #10
Paswa is offline Paswa  India
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ok ok ok, i've learned many things from u. that's right, now i'll search first, thought second then post diy forum. ok, DON'T THINK TWICE IT'S ALL RIGHT

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