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PostPosted: 09 Sep 2009, 03:17 
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Location: Duesseldorf, Germany
This is the support thread for the DIY TDA2050 Hi-Fi Chip Amplifier Project. Please feel free to ask your questions and post photos and details about your build.

FAQ
:?: How do I wire a Dual Secondary or Center-tapped (CT) transformer?
:arrow: See this post: Rectifier setup for Dual Secondary and Center-tapped (CT) transformers.

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 02 Oct 2009, 05:39 
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Hi Tom,

I built your TDA amplifier and worked pretty well at my first try (which is great because it's the first time I try something like this). I was really excited when the first channel was finished and started throwing out perfect un-distortioned sound.

But now that the 2 channels are done I find the sound somehow 'boxy'. What I try to say is that it is not crisp, I sounds like if its behind an obstacle or something like that. No distortion, the sound is 'whole', all the details are there, but no shinning as I would expect.

I used standard cheap components that I found in my local electronic store and changed the power supply to use two 18V 2 Amp transformers instead of the one in your diagram that I couldn't find. I also changed the potentiometers to a 50k one (the 25k were sold out).

Could the standard quality components be reducing the sound quality? Or the 2 amp transformers maybe? The potentiometers?

Thank you and best regards!


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PostPosted: 02 Oct 2009, 05:43 
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Hi again,

Forgot to say that I'm connecting all the stuff directly to the amp: computer, mp3 player, cd rom player, etc. Not using any preamp. Could that be the problem?

Cheers!


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PostPosted: 02 Oct 2009, 15:26 
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Hi ixcoatl!

Now - i thought a while about which answer would be good... It is hard to say what you have there. This is something like "fishing in the fog" and more guessing than knowing what's up... My amp is running without any problems and with a very high and clear sound...
Not boxy - promised! Even with my cheap ole crappy boxes in my "work room" the amp sounds - hmm - good.

The amp can drive a lot of sources from (afaik) 500mV up to 2-3V. So - it can handle nearly all sources but no phono or mic. inputs. That's not your problem. Your pots are very OK. I'm using 50K ALPS (blue velvets) since one week. The old ones (Radiohm) were not symetrical and they've worked like a bunch of crap. ALPS keeps papa smiling! But - that's also not your problem. The transformers shouldn't be a problem too. If they are matched a bit, they both should have the same output power and they should work parallel at the end. Just a little question - to be sure - how did you connect them?? Each to one rectifier bridge, or the outputs in serial to get a centre tap??

OK - what i think now is that you have bad connections somewhere. At the moment i'ld guess that you didn' connect the RCAs seperately to each channel. Each RCA positive and negative lead should go to its own amp channel (the pot ground included). That will say, that each input channel must be completely connected to one amp channel. Even the "ground" should be connected to its own amp channel ground. Maybe you've got a complete crosstalk. To keep each channel away from the other (imo) is very important for this little piece of magic. (I had a problem with the first layout because the RCA grounds were sticked together. That sounded like 4 boxes in a small bathroom - or whatever like).

The next suspicious one is the input cap and the "C2" that is shown here: Application Circuit Shematic
I don't know which kind of input cap you've used. "C2" must have the value shown on the scheme and good quality (It's a frequency setting component). The input cap is one of the mainparts on this little amp. This cap must be able to pass all details from the incoming signal. A high(!) quality cap is recommended for the input section. (Not a "high end - high price" - simply a good one). It might be the case that you use an - hmm - "cheap" electrolytic type here. That wouldn't be a good idea! E-caps have the characteristic that they often don't pass higher frequencies correctly.

OK - please check all connections again and again until you're sure that it's all right. As said - all ground connections must go to each channel seperately. Please refer to the schematic on the project page. Each single wiring (for one channel) is shown on the scheme and should be followed. For the wiring and the parts connections refer to: HiFi Amp Scheme.

I now must remark also that this little amp is not a "state of the art" super duper "top of the tops" high end device for 30 bucks... It's just simple to build and yummy yummy good!

Sry - i don't have some other ideas at the moment - but i hope that was a little help now ;-)
If not - i'll take the time to make it work right - with your kindly help...

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 03 Oct 2009, 04:53 
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Hi Tom,

The transformers are connected each to its own-independent set of rectifier bridge, capacitors and resistors.

The RCAs are connected independently to their own amplifier and each amplifier is connected to its own power source.

I think that the problem is that I´m using the same ground for everything including the RCAs. My common ground it's the one that comes out from the union of the +/- wires after the rectifier bridges, resistors and capacitors.

I have no idea how to manage the wiring to have 2 independent grounds per channel. As far as I understand the only way to do so would be to build inderpendent power sources.

Could you please explain me with a little bit more detail how to separate the grounds for each channel?

The C2 capacitor brand is MPE and it is a polyester one. The electrolitic caps are either REC or capXon.

Thank you for your time and patience with a newbee :D, I'm having quite a lot of fun with this project.

Best regards


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PostPosted: 03 Oct 2009, 14:18 
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Hey again,

it seems that your build is basically OK...

OK - at the end, the supply has two common grounds - taken from the PS + and - potential. Maybe we should take a second view on it to see how the thing works: The ground for each channel is build "on board" on each channels amp board. There are TWO wires from the supply to each amp board. One wire is the plus, one the minus. Each board has 2 buffer / power supply bypass electrolytic caps. The caps "supply" and buffer the TDAs again after the power supply leads to the boards. Each of this cap supplies its own potential (one + rail and one - rail). The ground for each channel also is done by this caps. You could see the caps on the amp boards as a second supply. With their own potentials they form their own ground at each board with the dependence to the power supply. All RCA and pot ground connections (each channel seperately) are connected to this gnd potential on the amp boards. The common ground shown on the supply schematic only is symbolic and has nothing in common with the amplifiers grounding system! The symbol is shown (as usual) to see the relation for the supply rail potentials. The heck is - how you have the view onto the whole circuit and how it works. Simple is not simply simple.

I hope that was good to understand how the grounding works on the channels (i don't know to write it better - feel free to ask!...).
Afaik - this technique usually is used to have the lowest possible crosstalk on each channel and to get a wider sound stage. In each case - it's logic and accurate.

Now - i have no further ideas what could be wrong (if there really is something that went wrong). For me, it seems to be ok what you've put together.. All i can say now, is to check the circuit again. Sometimes you don't see the trees in the forest.
Maybe you'll show us some detailed pics from your build. Just to see, if we can find something else...

One of my mates, here in Krautland, has build the version from the project page and he's very pleased and impressed by his amp.. I also must say, that he builds speakers.. A lots of them.. He was looking for amp to test his speaker builds and for his own use... He promised me, that the amp sounds very clear (sometimes a bit sharp) and very detailed - with a high resolution and a wide sound stage. I asked him for some pics but he didn't answer til today.. (it's weekend).

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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 04 Oct 2009, 04:07 
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Hey again,

here is a little scheme to show the basic layout and wirings. This scheme also shows the grounding technique and should clear up, how it works.
Attachment:
amp layout scheme.GIF
A short explaination for this scheme: The scheme shows the whole amp in 4 parts. Transformer, supply and 2 amp channels on the right side. The supply section has 2 large caps for the current filtering and smoothing. This caps are centred on their potentials to get the "+" and the "-" voltage rail. The supply has its own ground to neutralize the caps at the centre. Without doing this, it wouldn't be possible to get the "-" rail. The PS ground is independent from the amps ground. The amps grounding works by the same way. Each amp has its own caps to build a neutral point in centre of them, and so - they have its own gnd. The in- and output RCA / Plugs ground points are connected to this amplifier ground points. By this way it's possible to have 2 independent ground points for each channel.

Very hot thing ;-)


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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 05 Oct 2009, 18:22 
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Hey again,

Here you can see the wiring and layout scheme for the amp section (amp boards):
Attachment:
TDA amp wiring scheme + layout.GIF
The scheme is slightly different to "Photograph 2: TDA2050 Hi-Fi Amplifier ProtoBoard - Bottom View" from the project page but the connections are the same anyway. The speaker out / gnd should be clear. At this point, the headphone output network is connected too. The headphone ground is connected at "Aux GND" (below UB+). The Pot is connected to "Pot GND" (2nd. below UB+). The rest also should be clear. UB+ and UB- (supply + / -) are connected to the caps!

Now - i hope that's one more help ;-)


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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 10 Oct 2009, 17:06 
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Hey again,

one next solution for a good grounding:
Attachment:
Grounding and wiring - optional.GIF
on this scheme, the ground IS directly coupled with the Power supply. (This scheme shows some more details, but basically it is THE SAME as the scheme posted before). Only the ground is different. This time both amp grounds are connected to the supply ground. This can be very useful, if some "ground rail" differences occur (Not really often). There is one very important thing, if you want to go this way: The amplifier grounds must be connected to the supply ground at the nearest possible point. Best way - close to the supply cap's ground rail. Each channel seperately (with 1 wire for each channel).

All signal inputs and outputs are still connected to their own amp channels (to reduce crosstalk, noise or loops where it's possible).

Have fun!


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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 16 Oct 2009, 01:22 
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Hi again,

a little addendum:

Nearly one week ago, the input potentiometer was changed to one ALPS 50K "Blue Velvet". Now - i can tell that it is a real improvement. The sound is not different or better, but both channels work very symetrical now. Both volume levels are now the same and there is no more fading between the channels. IMO - it was a good descision to engage a good potentiometer.

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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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