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Old 29th April 2011, 01:31 PM   #1
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Default Trafo bad, or am I bad

Hey guys, I guess I could say I am a relative newbie to the world of electronics. I have soldered many audio kits with no issues and am running a couple right now. I seem to be having an issue with the following setup though:

I have the following 2 kits:

NE5532 Preamp Kit

TDA2030A 2.1 Kit, basically two single TDA2030A's for front left and right, and a pair of TDA2030A's "bridged?" for the subwoofer. Also has NE5532 active filtering for low pass for the subwoofer.

Powered by the following transformer:

24V W/center tap 1.5 Amp Transformer

With the above setup, it runs great except I feel that 1.5A transformer gets a little too warm because it doesn't have enough power (amps). So I decided to upgrade to this transformer:

Triad F-187U 28VCT 4 Amp Transformer

It was purchased by a well known and respected vendor, Steve @ Apex Jr. He is baffled that it doesn't work, says it is new but didn't get a chance to test it before shipping, since it was new. One of the supports was bent, and I clipped off the leads shorter to remove any tarnish in case of poor contact. It looks like it has seen some years on the shelf (maybe they all look like that, IDK), but other than that looks new, even came in original box. I trust Steve, he is an excellent guy to work with.

For some reason, when I hook the new 4 Amp-28VCT trafo up, I get a lot of pops at about half the volume of the old 24VCT 1.5 Amp transformer. I can "just" hear it before it distorts. So I hooked the 1.5 Amp back up, runs great once again (I originally had it like that for almost a month with no issues whatsoever). Tried all of the above 3 times, same deal each time. I checked the newer one with a voltmeter, and with no load it reads around 30 VCT, 14.8 V per output. The older one reads 13.6V per output (27VCT ballpark).

Could the newer trafo be bad? It seems to not be putting out enough amperage possibly?? Is there any way to test it with just a couple of voltmeters, as that is all I have at the moment? Surely that extra 1-2volts +/- wouldn't do this, would it....??? The active filtering on the 2.1 setup along with the entire NE5532 preamp have voltage regulators, +-12V and +-15V respectively, and and am I correct in the chips should be OK with that voltage?

I can give more info/details to the best of my ability when I get home later today/tomorrow.

Thanks for any help/suggestions.
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Old 29th April 2011, 02:15 PM   #2
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Here are the instructions, they won't provide the actual schematics
Attached Files
File Type: pdf TDA2030A 2.1 instruction.pdf (36.7 KB, 34 views)
File Type: pdf NE5532 volume control board INSTALLATION INSTRUCTION.pdf (144.8 KB, 28 views)
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Old 29th April 2011, 03:23 PM   #3
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Some photos are necessary i think. Maybe TDA kit not need preamp?

Last edited by Professor; 29th April 2011 at 03:27 PM.
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Old 29th April 2011, 10:44 PM   #4
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Nah, this kit doesn't need a pre, I just wanted to add one since this is a low budget build for my PC. Therefore, I currently eliminated it from the equation. Still have the same problem.

I'm having issues with my camera right now, got a couple of pics to come thru, let me know what else you need and I'll try to get more pics of it.

The 1st one is of my PC sub, the 2nd one is the 2.1 Amp, the 3rd is the Triad trafo hooked to the amp alongside the MCI 1.5 Amp transformer for size comparison or whatnot (no, it is not hooked up too).
Attached Images
File Type: jpg Cheap Sub #1.jpg (32.5 KB, 151 views)
File Type: jpg 2.1 #1.jpg (25.1 KB, 143 views)
File Type: jpg Triad 2.1 #1.jpg (29.4 KB, 141 views)

Last edited by caxxxxxx; 29th April 2011 at 10:58 PM.
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Old 30th April 2011, 03:00 PM   #5
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Try to connect transformer to dummy load, wirewound resistors for example. You need a pair of 6.8 ohm resistors to provide 2.17 amperes for two half of winding. Measure V1 and V2 with load
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File Type: png Безымянный.png (10.8 KB, 120 views)
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Old 30th April 2011, 03:32 PM   #6
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Professor:

The closest thing I have is 5.4 Ohm in the 5 Watt variety, the only 6.8R resistors I own are in 1/4 Watt. Do you think the 5 watts are close enough for a short timespan?

Edit: I also have a pair of 1.5 ohm resistors of the 5W, could series them in with the 5.4 to give me 6.9R (Ballpark, they are 5%), if you think the 5W are safe enough.

Last edited by caxxxxxx; 30th April 2011 at 03:38 PM.
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Old 30th April 2011, 03:44 PM   #7
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Quote:
Originally Posted by caxxxxxx View Post
Professor:

The closest thing I have is 5.4 Ohm in the 5 Watt variety, the only 6.8R resistors I own are in 1/4 Watt. Do you think the 5 watts are close enough for a short timespan?

Edit: I also have a pair of 1.5 ohm resistors of the 5W, could series them in with the 5.4 to give me 6.9R (Ballpark, they are 5%), if you think the 5W are safe enough.
6.9 ohm is Ok but with 5W you need operate quickly or use heatsink or put resistors in a cup with water. Another way use fan.
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Old 30th April 2011, 03:47 PM   #8
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OK, just went ahead and did it super quick as the resistors heated up rather quickly, the voltage readings are 14.4V per output. If I am correct, this seems OK but wish I had some higher wattage resistors to let it sit a little while longer.

Now I'm really stumped.

Oh, I measured a pair and it read 6.7 ohms.
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Old 30th April 2011, 03:54 PM   #9
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Quote:
Originally Posted by caxxxxxx View Post
OK, just went ahead and did it super quick as the resistors heated up rather quickly, the voltage readings are 14.4V per output. If I am correct, this seems OK but wish I had some higher wattage resistors to let it sit a little while longer.

Now I'm really stumped.

Oh, I measured a pair and it read 6.7 ohms.
I think your transformer good. With 50% load output voltage drop on 0.4 volts.

Last edited by Professor; 30th April 2011 at 03:58 PM.
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Old 30th April 2011, 04:01 PM   #10
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Quote:
Originally Posted by Professor View Post
I think your transformer good.
Yeah, me too. I just got another 2.1 kit in the mail a couple days ago, I may try and solder that one up this weekend and see if I have the same problem.

Other than that, I'm still open for suggestions. I just don't understand how the weaker trafo is more powerful than the stronger one.

After A/B-ing the 2 so much yesterday, I even notice a little more bass with the weaker trafo at the same volume level.
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