Power Amp Distorion Issues - Please Help - diyAudio
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Old 4th May 2007, 03:39 PM   #1
Syko is offline Syko  Slovakia
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Default Power Amp Distorion Issues - Please Help

So I'm building a combo (solid-state only), and I've decide to build the poweramp first, so I can listen to how the preamp sounds during the preamp development. I wanted something bulletproof and simple, without any chances of messing up and I've decided to use the TDA2050 and I used the typical application circuit, they have suggested. I've added a voltage splitter infront of that and a voltage follower infront of the splitter. Check out the attached pic.

This should be a linear HiFi amp, so the only time it distorts the signal, is when it's overdriven and starts clipping, rite?

Well,....NO.

That S.o.a.B. distorts the signal, even if he's far far away from the max peak voltages. What's even more strange, if I turn it off and it still runs for a couple of seconds on the juice left in the supply capacitors, the distortion is suddenly gone, and the signal is clean. That is until the capacitors run out of juice, and the machine is silent, offcourse.

Please checkout this clip http://media.putfile.com/Technical-Project-Issue for the sound.

What sounds like switching between a clean and crunchy channel is actually turning the machine on and off. On = distorted, off = clean.

So please, I'm begging you, if u got any idea where the problem could be, give me some advice.

Thanx in advance.
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Old 4th May 2007, 04:02 PM   #2
Did it Himself
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Ahoj,

What is the point of the splitter? Is your source very loud?

I suggest your problem is your power supply, which you have failed to show us
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Old 4th May 2007, 04:11 PM   #3
Syko is offline Syko  Slovakia
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sorry, my bad

I use a modified transformer, originally it had a single secondary coil, now it has 2 outputs. I use a rectifier like the lower one on this picture.

Click the image to open in full size.

I use 4 caps for each polarity, with a total capacity of 13.6mF per polarity (and yes I mean mili, not micro) I get about +-17V of output without any load, and it shrinks to about +-16.6V when it supplies the power amp.

oh, and the splitter is there, so I don't risk overdriven the power amp, don't know if the ratio is really, good, should experiment on that, but dealing with this non clipping distortion has a highr priority
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Old 4th May 2007, 05:27 PM   #4
Syko is offline Syko  Slovakia
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crap..ok 1 more try

http://www.geofex.com/Article_Folder...s/plus-9v3.gif

I'm using the lowe one
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Old 4th May 2007, 05:34 PM   #5
BWRX is offline BWRX  United States
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Hi Syko. The link is broken because of the ... in the middle of the URL. You can edit your post and change it to the correct address.
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Old 4th May 2007, 05:48 PM   #6
Syko is offline Syko  Slovakia
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http://www.geofex.com/Article_Folder...s/plus-9v3.gif

hopefully this will be fine...it's the lower one
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Old 4th May 2007, 07:25 PM   #7
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I wonder if you have not put the centre tap of the transformer to the exact same point as the centre of the capacitors.
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Old 4th May 2007, 07:36 PM   #8
Syko is offline Syko  Slovakia
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Yes I have. At least if I think that "the centre of the capacitors" what it is, is that wrong?
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Old 5th May 2007, 09:15 AM   #9
AndrewT is offline AndrewT  Scotland
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Hi,
the amplifier with buffer and attenuator could be better implemented.
The overall gain is +24db.
This can be achieved using just the amplifier without that buffer and without the fixed attenuator.

Change R2 to 1k5 gain =[22/1.5]+1=16times (+24db). Is TDA stable at this gain?
With all that gain you may be overloading the chipamp.
Add a normal pot as an attenuator before the DC blocking cap on the non-inverting input.
The 100nF (C1) and 220k (R1) could be changed to 1uF and 100k. then you can use a 10k pot .

Now to the resistances on the chipamp input pins.
You have 220k on the non-inverting and 22k on the inverting. Have you measured the output offset?
You will probably need to make these much closer in value to remove most of that offset. R1=22k and pot=2k might be close (if your source can drive 2k).

R7 seems a bit low for an HF stabilising load. Try somewhere in the range 4r0 to 8r2. C7 seems a bit high, try reducing that to somewhere between 100nF and 220nF.
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Old 5th May 2007, 10:12 AM   #10
Syko is offline Syko  Slovakia
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Thanx for all the hints, but I finally found out what was wrong. Th speaker I was using was broken, I've just used a spekar with the same inpedance and the sounds was crytal clear.

MEans I gotta buy a new speaker, but the solution is easier than too lok for problems in th electronix.

Thanx a lot 1 more time.
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