Hi. I'm new here.
I just started building one of these amps in school for my project, I got the schematics of this amp from of the National site from their .pdf data sheet on page #8, it uses single power supply for two amps.
Here is!
Original:
(parts are displaced, move them to the right and up)
And mine🙁slightly redesigned)
Also I used the same parts that are used in the National version in .pdf file
So the problem is that it plays for 6 seconds then it stops, it's on 30V with low current. I cant hear it at 25V at all, for power supply I used school power supplies, I don't have one made yet.
But at home I used my home printers power adapter(31v 2.5A) it give me really buzzing sound mixed with music, also my GND is not connected anywhere.
Also can you help me out with the power supply?
is this one any good?
Power Supply
Thank you
I just started building one of these amps in school for my project, I got the schematics of this amp from of the National site from their .pdf data sheet on page #8, it uses single power supply for two amps.
Here is!
Original:
An externally hosted image should be here but it was not working when we last tested it.
(parts are displaced, move them to the right and up)
And mine🙁slightly redesigned)
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Also I used the same parts that are used in the National version in .pdf file
So the problem is that it plays for 6 seconds then it stops, it's on 30V with low current. I cant hear it at 25V at all, for power supply I used school power supplies, I don't have one made yet.
But at home I used my home printers power adapter(31v 2.5A) it give me really buzzing sound mixed with music, also my GND is not connected anywhere.
Also can you help me out with the power supply?
is this one any good?
Power Supply
Thank you
It looks, as if the big electrolytic capacitor for the negative rail was the wrong way round.fr1s said:
The printers power supply is probably a single supply. You need a split supply.fr1s said:
Pretty standard with little capacity. Try to make it bigger and use bigger capacitors.fr1s said:
Look at the schematic, you can see better in there.
I have two Big Caps, so which one is the wrong way round?
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
That's what I thought :/
For the power supply what Cap's should I use??😕
In your photo the capacitor next to the IC has the negative connection on the right side. In the layout that side is marked with a +. Turn the capacitor around and hope it is not broken.
There is no 0v terminal for the PSU. The terminal marked + is positive speaker out, the one marked - is the negative speaker out, and this could be used as the 0v connection for the PSU. V+ is positive supply, V- is negative supply. I suspect that your problems are due to using a single rail supply for a split rail amp, and the caps are shown the correct way round. I found that a small 100n 100v ceramic capacitor soldered directly between pins 3 & 5 prevent hf instability. 🙂
pacificblue said:
oh ****
but on the original design it doesnt say which side is - or +.
but which way is it supposed to be?
There are several clues.
Clue one is the schematic in the datasheet. Those capacitors are C6 and C7, and you have C6 reversed.
Clue two is your own layout. The yellow plus symbols belong to the capacitors. Both capacitors should be the same way round with the minus markings to the left.
Clue three are the potentials. Vee or V- has a lower potential than GND, therefore the capacitor's negative pin goes to Vee or V-. Vcc or V+ has a higher potential than GND, therefore the capacitor's negative pin goes to GND.
@johnnyx:
Compare the photo from post #1 (3rd link) to the layout in post #3. The capacitors are drawn correctly in the layout, but in the photo one is reversed.
Clue one is the schematic in the datasheet. Those capacitors are C6 and C7, and you have C6 reversed.
Clue two is your own layout. The yellow plus symbols belong to the capacitors. Both capacitors should be the same way round with the minus markings to the left.
Clue three are the potentials. Vee or V- has a lower potential than GND, therefore the capacitor's negative pin goes to Vee or V-. Vcc or V+ has a higher potential than GND, therefore the capacitor's negative pin goes to GND.
@johnnyx:
Compare the photo from post #1 (3rd link) to the layout in post #3. The capacitors are drawn correctly in the layout, but in the photo one is reversed.
hello.
it looks like that the elcap in opposite the opamp is built in reverse...........
greetings........
it looks like that the elcap in opposite the opamp is built in reverse...........
greetings........
hello.
perhaps problem caused by missing +position of the elcap in the schematic and so on..................
greetings.............
perhaps problem caused by missing +position of the elcap in the schematic and so on..................
greetings.............
johnnyx said:
there is 0v terminal, it's just not labeled. It's below the lower 1000uF cap
So it my redesigned schematic alright?
are the polarities right way on the big caps?
ohh thx
on the 3rd picture it's the way my teacher told me to put it in, but on the 2nd it' was my mistake at least that's what i thought 😛
and what caps should I use for power supply? 2200uF's?
on the 3rd picture it's the way my teacher told me to put it in, but on the 2nd it' was my mistake at least that's what i thought 😛
and what caps should I use for power supply? 2200uF's?
(Edited by mod)
Thx I got it working 🙂 it was the cap that had polarities backwards!
Now I need to put another one together and get power supply for it 🙂
Thx I got it working 🙂 it was the cap that had polarities backwards!
Now I need to put another one together and get power supply for it 🙂
That is a topic of hot discussions.fr1s said:
The role model for gainclones has nothing but the two 1.000 µF capacitors your amplifier has on the PCB. It has its followers due to the effect on mids and highs that configuration has. It actually has none, it is more a lack of bass performance that makes the mids and highs more pronounced.
Classic power supply rule of thumb is to use 1.000 µF per 1 A of nominal output. That leads to an acceptable amount of ripple for most applications. The correct capacity depends on the supply voltage and spaker impedance. Due to the LM1875's current limiting to 4 A, you would be on the safe side with anything above 4.000 µF per IC per rail.
That means you look at the capacitors mainly as filters. The next step in filter theory is to not only bring the ripple to an acceptable level from a technical point of view, but also from an audio point of view. In other words filter it, as if you wanted to get noise out of the hearable range. Then you calculate it like a speaker crossover according to the speaker impedance for a frequency below the hearing range, which leads you to something like 20.000 µF per rail for 8 Ohm speakers and 40.000 µF per rail for 4 Ohm speakers.
In audio many people see those capacitors as the real power source of the amp, while the transformer is only there to refuel them. In that case the rule of thumb is BIB = bigger is better. The upper limit is determined by your wallet.
10.000 µF per rail for a stereo amplifier should be a good starting point. From there on upwards you have room to experiment.
This is the schematic that I've put together lately.
any good? do I need to improve anything?
So from what I understand I need 4 of 5,000 uF caps on my power suply?
2 rails (+25 and -25) =4 of 5,000uF caps?
also which diode would be better? MUR860 or MUR1520
any good? do I need to improve anything?
So from what I understand I need 4 of 5,000 uF caps on my power suply?
2 rails (+25 and -25) =4 of 5,000uF caps?
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
also which diode would be better? MUR860 or MUR1520
change the PCB labels at the left edge.fr1s said:
The inputs are AC & AC, not + & -
The 0V should be labeled Centre Tap (CT).
use 1n540x
For a single channel I prefer to see 4off 10mF for 8ohm speakers for a dual channel on a shared PSU try 4off 15mF or 4off 22mF.
AndrewT said:
I'm sure the flat side is neg, so that needs rotating..
I get confused about the square and round pads on PCB's😕
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