TDA2030A board with LM1875T? - diyAudio
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Old 12th April 2015, 08:25 PM   #1
djduck is offline djduck  Estonia
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Default TDA2030A board with LM1875T?

Hey everyone!

I recently purchased this kit from fleabay: TDA2030A Audio Power Amplifier Arduino DIY Kit Components OCL 18W x 2 BTL 36W | eBay
It came in just a few days ago and I'm both impressed and disappointed at the same time. The PCB is super quality, so are the resistors, volume pot, screw terminals and bridge. Caps are genuine Panasonic and United Chemicon. Input caps are BP but they are mismatched. On is KME I think and the other one was KMC or something - yea never seen that on either. Only power supply caps were a bit disappointing, as they were ACON brand. Not that filter cap brand really matters, but still. They also forgot one thermal pad. Kit was supposed to come with TDA2030A but came with TDA2030 instead. But that's not really a problem as I never actually intended to use them.
You see, I read somewhere that TDA2030 and LM1875 chips are pin compatible. After comparing the schematics, I figured close enough and soldered in the LM1875's. But I thought I'd check in here before actually installing it in a chassis to see if there are any changes I should make.
Here is what the board uses:
22K feedback resistor with 680R shunt and 22uF cap
1Ohm+100nF Zobel
2.2uF input cap with 22K loading
3300uF per rail filtering + 22uF closer to chips

Also what power supply voltage should I go for? I'd like to get about 20Wpc. In case the voltage exceeds 23V I'll have to buy different power supply caps as the ones included in the kit are rated for 25V.
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Old 12th April 2015, 09:17 PM   #2
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sure, the pinout is identical.
You would want something close to + - 25 volts as rail voltage.
so you should get some higher rated supply caps.
in my personal opinion i would go for the largest you can fit on the pcb.
and bypass them with something around 100 nf 63v + rated foil type caps.
should work.
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Old 12th April 2015, 09:25 PM   #3
djduck is offline djduck  Estonia
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Thanks, Arty!
I'll see what my local electronics store has, I think they had some 35V 5600uF I could use. Should I bypass the main filters or IC pins directly?
I'm thinking of finding a cheap stereo amp with a good chassis but blown or poorly designed amplifier for cheap and fitting this in there, that way I won't have to come up with an enclosure
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Old 13th April 2015, 06:44 AM   #4
djduck is offline djduck  Estonia
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Also, should I add the 1M resistor that's used in the datasheet schematic?

Thanks!
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Old 13th April 2015, 03:05 PM   #5
johnr66 is offline johnr66  United States
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With my own bench tests, I have found you need a minimum of 2,200uf per channel of amplification. If less, max output suffers due to high ripple on the rails limiting clipping headroom. More than that, diminishing returns. With two channels, 4,700uf caps should work.

No 1m ohm resistor needed. It just keeps residual charge off the input cap and there is already a pot.

If using 4 ohm speakers, use no more than +/- 18v. The LM1875 has a maximum non clipped output of 10v rms with this supply voltage. That is 2.5a rms or ~3.5 amps peak output current and this leaves PRECIOUS LITTLE current head room for driving reactive loads (e.g. any loudspeaker). +/- 16v would be safer. With 8 ohm loads and +/- 25v rails, current is only 1.89a rms, so you actually have more headroom (and 28.5 watts of clean, unclipped output!). Good example of why low impedance loads are a bear to drive.

Since the main filter caps are close to the ICs, I'd rather see the nearby decoupling caps be .22uf film.

Of course, be sure the IC's are authentic. Not likely off of eBay.

Last edited by johnr66; 13th April 2015 at 03:09 PM.
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Old 13th April 2015, 03:15 PM   #6
djduck is offline djduck  Estonia
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Quote:
Originally Posted by johnr66 View Post
With my own bench tests, I have found you need a minimum of 2,200uf per channel of amplification. If less, max output suffers due to high ripple on the rails limiting clipping headroom. More than that, diminishing returns. With two channels, 4.700uf caps should work.

No 1m ohm resistor needed. It just keeps residue charge off the input cap and there is already a pot.

If using 4 ohm speakers, use no more than +/- 18v. The LM1875 has a maximum non clipped output of 10v rms with this supply voltage. That is 2.5a rms or ~3.5 amps peak output current this leaves PRECIOUS LITTLE current head room for driving reactive loads (e.g. any loudspeaker). With 8 ohm loads and +/- 25v rails, current is only 1.89a rms, so you actually have more headroom (and 28.5 watts of clean, unclipped output!).

Since the main filter caps are close to the IC, I'd rather see the nearby decoupling caps be .22uf film.

Of course, be sure the IC's are authentic. Not likely off of eBay.
Thank you so much for the reply!
My ICs are definitely authentic, I bought them for a member on another electronics forum who bought a whole pile some time ago directly from National. He uses them to modify old amplifiers with blown or crappy output stages.
I'll add decoupling caps to the 22uF caps then. My power supply is currently 21.3V per rail after rectifying and filtering. I'm using B&W DM310 8 ohm speakers, which are quite efficient and don't need a whole lot of power, so the LM1875 is a good amp for these, I think.
Right now I need an enclosure. I'm on the lookout for an old dead junk amp to pull the guts and install my LM board
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Old 13th April 2015, 08:13 PM   #7
djduck is offline djduck  Estonia
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I have another quick question. I bought two chips from the seller but he gave me four for the price of two. Two chips had identical serial numbers so I installed those in my board. But the other two have mismatched serial numbers and look slightly different, I'm assuming one is from an older batch of chips perhaps? I was wondering whether I could use these in stereo or would the channels be slightly different sound wise?
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Old 14th April 2015, 07:23 AM   #8
AndrewT is online now AndrewT  Scotland
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National's datasheet should show what the codes mean and where/when made.
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