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Old 20th February 2014, 02:14 PM   #1
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Join Date: Sep 2011
Location: Waco, Texas
Default First ChipAmp Attempt (TDA2050)

Hello all - This is my first post here.

Normally my interest lies in developing and creating guitar/bass effects pedals. Maybe I'll post some of that stuff here. Anyway, I decided to try and create an amp that could be used either for guitar or to replace the LM380 amp I made and use for music in my cave. BTW, it is running a couple of very old Radio Shack speakers (you know, back when Radio Shack had some good quality stuff) and it sounds quite nice and can get moderately loud.

I followed the main ideas for the single supply application from the 2050 datasheet. I rarely do exact, I would rather experiment and change it up so that I have a better idea of what is going on. Oh, and always try to beef it up a bit.

2050_amp_1.png2050_amp_2.png

The power supply is driven by a couple of (once again) Radio Shack transformers I found in a box of donated capacitors. They are the 12V 3 amp variety wired in series to get the voltage up. So, after rectification and capacitation, I'm getting around 30V (approx 34V without load). I put it in a PS case from a computer. It is a nice fit.

2050_ps_1.png2050_ps_2.png

Things to learn from this project:
Originally, I built it and tested on my 12V bench PS. Both channels worked fine.

Then I tested it on the PS I built for it. I failed to check the voltage limits on some of the capacitors (namely the output snubber caps) and explosively let the smoke out of one of them. I found that they were only rated at 25V, which worked for my 12V supply, but evidently did not like the 30+V supply. Especially when I forgot to put a dummy load on it. So I replaced the blown cap with one that was rated at 100V. However, in my frustration, I missed soldering correctly and soldered the snubber resister straight from the output to ground. It did not seem to like that and let all the smoke out of the attached 2050 chip.

So, as you see it, only one channel (the left one) is working. The fan is not connected, as it is only a 12V fan and the new PS would smoke it. I have a different fan setup for it that I'll show when I post the completed pictures.

Once the blown chip is replaced, I am going to experiment with bridging the two chips using a couple of unity gain buffers, one inverted, one not. I thinking that should get me roughly around 50-75 watts for a guitar amp. I'm too lazy to do all the math right now, but 30V at 3A, bridged into 8 ohms - that should be loud, right?
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Old 20th February 2014, 03:43 PM   #2
johnr66 is offline johnr66  United States
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Join Date: Mar 2009
Not bad for the first time out. I do have some suggestions. Use a dual supply so you get +15 and -15 volts and the ground. That way you can do away with the large output coupling caps and the 1/2 supply reference for the +input pin. Read up on star grounding if you haven't. Try to condense the size of your layout.

If you go bridged, you can do away with the output coupling caps. You will not get 50-75 watts bridged into 8 Ohms.

Lets say you have 30 volt supply (under load). In bridged configuration with 8 Ohm load, you get about 25 volts output peak. Convert to RMS, multiply by the inverse of the square root of 2 which is .707. So, the max nonclipping AC output voltage the amp can make is 17.7 volts. Square that and divide by the load impedance and you get 39 watts.
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Old 20th February 2014, 04:23 PM   #3
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Join Date: Sep 2011
Location: Waco, Texas
Thanks for the info (and the math)! I'm so used to single supply constraints (for my pedal work), so I just default to it. I haven't done any dual supply projects, but it sounds like I am going to start. The bottom is one large mass of individual ground lines, lol, almost making the standoffs unneeded.

Making it smaller... Yes. Being my first attempt, I just slapped it on vero and "keyboard composed", so to speak. So there wasn't a whole lot of layout planning put into it, and I just used a lot of components that I have laying around.

I've learned a lot from this project so far, mainly that the PS takes as much planning (if not more) than the amp itself. I had read that an amp is just a power supply that supplies its power in the form of an audio signal. It makes sense. Too bad transformers aren't as cheap as the chipamps, its hard to justify large expenditures to the boss (er, wife).
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Old 20th February 2014, 05:16 PM   #4
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Join Date: Jul 2010
Location: northern minnesota
looks like u have been bitten by the diy bug! when looking for parts go to garage sales pawn shops ect look 4 older amps,recievers powered subs 4 cheap. 100 watt recievers usually have a split power supply 40 or so vac transformers big expensive caps ect lots of good parts out there
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Old 3rd March 2014, 05:43 PM   #5
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Join Date: Sep 2011
Location: Waco, Texas
Thanks, good advice. Found a few laying around in old equipment at the house already. I also took some other advice and switched to bipolar supply. I'll never use single supply again, except on the guitar FX pedals (because I have to).

I converted my existing power supply for this project to bipolar (easier than I thought). I also then just made a new chipamp using LM1875 chips. It sounds very good, but was not as loud as expected. It is still louder and better sounding than the old LM380 based amp I was using. But I am using this for powering a system that will sometimes be for outdoor "party" music, so I need a bit of volume but still good quality at low volumes.

I think I can get more volume by having a good preamp ahead of it. If I amplify the signal up a few volts headed in, that should help (1875 will take input voltage up to rails). Also I'm thinking of reconnecting the power supply transformers in series to get a higher voltage - 32V vs the current 16V. I'll have only 3 amps instead of 6, but I don't think that will make a difference, and I think it will be louder. Datasheet seems to confirm this.

Here is new amp picture
1875 Amp 01.jpg

I'm also thinking of building another identical setup, making a crossover, and bi-amping the whole thing. I'm liking the looks of the lightspeed attenuator to do volume, and maybe modifying that circuit to handle a basic tone control. Just 'cause I've got some optocouplers laying around and I don't have any dual gang pots.
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