Can I use DC voltage instead of AC voltage in the PCB?

[iori3310]

Hello.

I am posting here after a very long time. In my previous post, I had a solution regarding the IC being faulty. Right now I am just asking a simple question here.

Is it okay to use an 12v adapter DC voltage instead of 12v AC in the PCB power supply section? (Picture attached below)

In the picture above, red circled area is where the two AC power wires are supposed to be attached.

Should I attach two DC power cables in the same spot?

Please, do answer my question.

Thanks in advance
Iori

 

[Nigel Goodwin]

It depends entirely on the circuit - bear in mind the 12V AC will be close to 18V once it's rectified and smoothed.

Does the unit have the option of battery power? - I'm presuming it's an effects pedal or something?.

 

[Diver300]

The components to the left of the power input are probably the rectifier diodes. Their arrangement and connection relative to the input would be correct for four diodes in a bridge, and the two components further to the left look like they are connected the way that electrolytic smoothing capacitors would be connected.

If that's correct, 12 V dc should work, but at Nigel said, it may need a bit more voltage than that. You don't have to worry which way round to connect the dc supply.

The possible problem is the PNP transistor to the right. I can't see if it's got any connection to the ac power input. If it has, there is something on the board that needs ac, which won't work with a dc input.

Almost all electronics is dc. Transformers only work on ac, so there has to be a rectifier somewhere. When that board was designed, which looks to be over 20 years ago, manufacturers would use ac power supplies if they needed to have an ac signal on the board, for timing or something. I've also seen that done to run a small synchronous motor. However, an ac input was also often used to avoid needing to package rectifiers and capacitors in the transformer housing, when those components could often be fitted to the main circuit board more cheaply than having a whole separate circuit board inside the transformer. If you are lucky, that's what they've done here.

AC input are very rare nowadays. Power supplies are usually switch mode as that now makes them smaller, lighter and cheaper, so there is no such thing as a low voltage ac signal at mains frequency. The rectification has to be done on the switch mode board, and as there's always a circuit board with a switch mode power supply, fitting the rectifiers there is just as cheap as fitting them elsewhere.

 

[Les Jones]

I think the answer is PROBABLY yes. I am guessing that there are four diodes on the component side of the board just to the left of the two connections and these diodes form a bridge rectifier. IF there are ONLY two of these diodes connected to each of these connection points then I would say the answer is yes. (You have the advantage over us of being able to see the other side of the board.) It may be a double sided board with etch connection on the component side to these two AC input points. Bear in mind what Nigel has said about the higher DC voltage that would be produced bu rectifying 12 volts RMS.

Les.

 

[Nigel Goodwin]

It may be a double sided board with etch connection on the component side to these two AC input points.

It looks entirely like an old single sided board - nothing there to suggest it's double sided.

 

[gophert]

I'm presuming it's an effects pedal or something?.

An effects pedal with separate Bass output? Oh, I see you hedged with a second option, "or something". I guess that "or something" could be anything (everything) from a data logger to a wifi router to a 2.1 channel audio amplifier?
You're a funny guy.

the two rows of twelve are likely a SIP-12 amplifier chip like below..

 

[Mickster]

^^
Or even a CD6282CS, which was referenced in OP's initial post:

Guess very few look at links any more, even you ^^.



iori3310 What voltage was originally supplied to the PCB at the location you circled in red?
The original thread you linked to said this:
2) Direct power touch from 220V AC without any switch.

Can you clarify, and perhaps show a picture of the PSU section of the PCB, on the component side?

 

[gophert]

Or even a CD6282CS, which was referenced in OP's initial post:

Upc1185/CD6282 - I've heard It both ways.
And looks like you agree that Nigel is in left field.
Also, looks like you've taken up some graphics editing - nice work. I like the hollow arrows.

 

[Mickster]

Upc1185/CD6282 - I've heard It both ways.

Not seeing a direct cross-reference from a cursory search, so I'll take you at your word...

And looks like you agree that Nigel is in left field.

Looks like both of you failed to read the OP's link and correctly identify what was being discussed....

Also, looks like you've taken up some graphics editing - nice work. I like the hollow arrows.

Thanks, been working on that for ages. Got any tips for better presentation? Might try to add some contrast and fill in the arrows next time....purple glitter do it for you?

 

[gophert]

next time....purple glitter do it for you?

I'll send a PM with my preferred formatting rules. Your eagerness to please me is quite
[deleted by mod]

 

[Mickster]

I'll send a PM with my preferred formatting rules. Your eagerness to please me is quite
[deleted by mod]

Cool.

 

[gophert]

Oh, stop restraining yourself. It's clearly more than just "hero".

 

[Mickster]

Oh, stop restraining yourself. It's clearly more than just "hero".

You're right.
When you submit posts that make you look like a twat, I think "Oh my God!"


EDIT:
BTW, do you have anything to help the OP, or is it just Nigel who currently gets you bent?

 

[gophert]

EDIT:
BTW, do you have anything to help the OP, or is it just Nigel who currently gets you bent?

Wow, double level irony. I love irony. Thanks.

 

[iori3310]

Hey guys, sorry for replying so lately on the same issue again.

So, this is what is happening again -

I had a very faulty Transformer which caused pain to me since the last 2 years in a row. The same issue occurred to my speakers again. So, I tried to replace the AC transformer with the DC and asked in this section. I understood the whole suggestions provided to me. But I still could not wait to find a proper 12v AC transformer for the speakers.

The first transformer that was installed inside the speaker was 12v AC with 1.6 AMP. The new ones before the last ones were 12v AC with 3 AMP.

I think this was the reason that all my transformers failed or both the ICs' are drawing more power from transformers than it needed. I could not find the 12v AC 1.6 in the local market. But there were 12v 3 AMP available. My focus went to the transformer immediately and started searching for online shops.

I ordered and installed a 12v 1 AMP transformer inside the speaker and voila, everything seems to be working like magic. Until this week, I had no issues with speakers but I noticed something difference.

The sound quality of the speakers went low, I mean very low. Even with 30-40% of the PC sound I could only hear it on normal level. Also, since the last couple of days, the buzzing sound started to come out of the speaker again. And this buzzing sound is very much annoying than the low sound quality.

Now I am getting fed up because you could see my posts that I have been suffering since 2019. Thing is, both speakers are okay and from one little mistake caused me 3 years of pain in a row.

How can I stop this buzzing sound? Should I change the transformer again? There are no 1.6 AMP 12v AC transformers available in the market. And the 1 AMP transformer installed inside the speaker, I think this is the one causing the buzzing sound problem.

I am hoping to get some useful suggestions again.

Here is the original problem post.

Thanks in advanced.
Iori