DIY Audio Projects Forum

I made the circuit and tried to drive the same using 12-0-12/3 Amp transformer. I feed the Audio input to the circuit and switched on the power supply. But I got zero output from the speakers. After 2-3 secs, 7912 negative voltage regulator got fried . The I disconnect the power supply at that instant.

Check:
Diode polarity.
Make sure that you want to put 24V on the diodes.
Capacitor Polarity.
All connections are clean, complete and without solder-blobs.
And, that all heat-sinks are in place.

Let us know.

Hello ravi.bppimt. In reading your post, a couple of things come to light.
You say the negative reg blew. Both the pos and neg regs are in the same package but the electrical connections are different.

First (left to right)
Pos = 1,2,3 where 1 is input, 2 is ground, 3 is output.
Neg = 1,2,3 where 1 is ground, 2 is input, and 3 is output. (note the difference)

Second
Pos reg TAB = ground.
Neg reg TAB = input.

The second point means --you MUST isolate the tab. This is done using mica or silicon washer so the tab and what it is bolted to do not electrically touch, (thermal connection only) and second a shoulder washer which will keep the bolting screw from touching the side of the hole .

I would add, do not connect the amp to the power supply until you have the regs working properly.

I hope this helps.
Laurie

Hi Peter,

I checked the Negative regulator pin configuration and I was assuming the pin configuration same as 7812 In-Gnd-Out. That assumption costs me the fried chip. . But as instructed by Laurie I checked the same and found that it is Gnd-In-Out.

And after replacing the chip I checked the same and it was working fine. And I was getting the Left & Right speakers output . But when I connected the Sub-woofer, it was oscillating continuously and delivering only noise. Then I killed the power and disconnected the Sub-woofer instantly. I guess there is a terrible noise was getting amplified and it was driving the woofer. Can you please share you thoughts on this!

After disconnecting the woofer I started the amp again with two speakers and it was working fine. Then after 10 mins all of sudden, the electrolytic capacitor connected to the negative regulator (7912) exploded like a mini bomb . Two of my friends sitting next to me got scared and fled away from the room. Then I killed the power instantly. I have attached the pic.

My question is, I bought the 4700uF 25v Capacitor from a local store but according to the circuit diagram I need 4700uF 35v. I repeatedly asked them that I need 35v capacitor. But they insisted me to use the 25v one and told me that it will work fine [ image attached]. Any way I have bought the correct one now [ image attached]. Can you please confirm whether the new capacitor will work fine or not.

Currently I am using 12v-0-12v, 3A transformer. Do I need to put less ampere transformer. I mean to say, instead of 3 A shall I use 1.5 A or 1 A. As I am not using heavy duty speakers.

Regards,
Ravi

_________________
Regards,
Ravi

Hi Laurie,

Thank you so much for helping me out. I got more doubts now as one of my electrolytic capacitor got exploded. Please read the previous post for detailed info.

Can you please share you thoughts.

_________________
Regards,
Ravi

If a 25V cap exploded, either you connected it backwards, or you are operating at substantially more then 25V. Double-check the polarity, and use (at least) a 50V cap in any case.

Hi hi. Glad to help. Your cap probably exploded because it was in backwards. That'll do it for sure. In the positive supply the cap + goes to V+ and cap - goes to v-. But remember the pos and neg supplies are in series. The "negative supply" is really another positive supply with "it's positive" connected to the neg leg of the positive supply. The connection point between the two supplies is therefore referred to as the common ground point.

(( here i drew out an example for you to see with your eyes but when i submit it the order changes so it makes no sense. Ha ha ha )) We are ALL armatures at something.

Now then, as for the voltage rating on the cap. A cap's voltage must always be as large or larger than the voltage supply it is being placed across. If the cap has an even larger rating than the voltage it is across it simply means the cap will never be in danger of being close to it's limits.
Think of it this way. You have "one" cup of water, (for you it's 4700 mfd ). You can put it into a one cup container which will hold it, but will spill easy. OR you can put the "one" cup of water into a gallon bucket and there will be no worries of it spilling out when being moved or jarred. Either way you still have one cup of water which in your case is the 4700 MFD. Weird way of explaining it i know and i am sure lots would chastise me for explaining it this way but you get the pic i am sure.
As for the exploding cap placed in the cir backwards. We've all been there, so you are in good company. lol Welcome to the club.
As for your friends running out of the room. Ha ha ha ha ha ha look at em go lol !!
Finally somewhere in this thread i read a comment about lowering the trans to a smaller current rating. Remember the circuit is drawing the current from the power supply. (( the supply is NOT pushing the current into the cir)). Therefore having a larger that necessary power trans supplying the current to the amp just means the trans will not have to work as hard and so will not get hot or even warm. This is a good thing, especially if you decide to add more cir's on later such as a pre-amp, or remote control working from the same supply.

Hi Peter,

Thank you for the suggestion. Now I made the power rail using 35v capacitor and its working fine now.

Checked the polarity thrice just to make sure everything is correctly connected.
I connected the speakers to the output of the Amp and the out is simply a Hissing noise. I think it is the Ground Loop issue.

Is there any suggestions for resolving the issue!!

_________________
Regards,
Ravi

Hi Laurie,

I got a complete picture from your example.
Thank you for making me understand and its my pleasure to be a part of the club.

I made the circuit and its working fine now. But when I connected the speakers to the output of the Amp, its giving simply Hissss noise even after disconnecting the audio input. After few googling, I came down to a conclusion that it is happening due to Ground Loop. Have to check the extra ground i made which creates the loop.

It would be very helpful for me if you provide a hint to find the loop easily!!

_________________
Regards,
Ravi

HI Ravi. Sorry for the delay. I don't believe a ground loop would cause the amp to hiss. A ground loop will cause a hum. When you make a ground loop in a cir. The signal going down the line which is normally being shielded by the outside ground shield, no longer is because of the physical loop created by the connection making the loop. Normally the signal goes in one end of the wire, travels down it and comes out the other end. Any magnetic fields the wire passes which would get into the signal wire, is stopped (and bled to ground) by the outer shield. However if the shield is part of a loop, the magnetic induction will induce into the shield and travel round and round the loop in an endless circle. While it is doing this it also gets into the signal wire and is passed on to the amplifying stages as part of the signal and thus is "heard". The loop is a hum because most injection of outside magnetic interference is produced by transformers and house wiring carrying current to something at it's end. These sources are operating at 50 or 60 cycles (Hz). So they are heard as a HUMMMMM. Higher frequencies also get in but we hear the harmonic of them and thus again humm.

It is said over and over threw a hugh percentage of the threads that ALL GROUNDING should be done as a "STAR GROUND SYSTEM". This means all wires which are ground wires will be brought to ONE common point. Thus avoiding the possibility of loops being created.

A hiss usually comes from transistors and resistors which are in the cir's power or signal path. It is the micro amount of heat coming off the device (res, trans, etc) which occurs when current is passed threw them. Remember all devices have a resistance. This means a resistance to the current flowing threw it. This resistance causes a buildup of excess of energy which is expelled as heat. Even if it is such a small amount of heat one could not ever detect it, IT still exists and is happening.

Your source of hiss could be the fact that you have built the cir on breadboards plugging in each part in it's entirety. Each part is connected by way of the metal clips in the breadboard. Not nearly as good as solder connections. Also a biggy is,, the parts on the breadboards are not shielded AT ALL. Especially when building an amplifier which by it's very nature is designed to amplify any signal connected to it, having no shield around the cir will cause a worst case scenario to be present.

Printed Circuit Boards are desirable for their ease of construction but also,,,,, a wire is "round". So any emissions from it in or out are on a 360 deg plan. But a PCB does not use wires it has copper foil on the surface making the connections. If you picture a PCB cut down the middle and you look at the cut edge you will see the foil lines are varying widths (depending on the amount of current it is to handle), but more importantly the foil is very thin (top to bottom). So any emissions coming off or getting into the foil track are much LESS side by side as the majority of the emissions field is from the wide surface so away from the board and not into/from neighboring components on the board.

Really building up and working with any electronics and understanding it and what is going on just takes time and the experience gained by doing so. Don't get discouraged just keep plugging away at it.

Thank you very much for clearing things up for me. I also thought it was issue with the bread board. I tried 2 times, disassembled and again created the same circuit. But the output was same. Thank you very much for boosting my confidence. I will surely try the circuit in new bread boards now.

_________________
Regards,
Ravi