Guitar Aplifier

[fikic]

Greetings,
Did anyone bulid this project already? Can you tell me your experience. And if someone made PCB, can he past it here. I will past mine..

Thank you

 

[audioguru2]

The capacitor part numbers on this site are strange. Go to RED Circuits to see the correct parts list for the project.

 

[fikic]

What is strange?  ??? There are capacitors from 1 to 13..

 

[Hero999]

I've never seen a 2200΅F capacitor, I presume it means 2200

 

[fikic]

yes yes, there are uF. It is logic.

Here is my schematic and PCB:

amp_fill.pdf

amp_fill_layout.pdf

amp_fill_shema.pdf

 

[Hero999]

Thanks for posting the PCB.

It's still a good idea to check the schematic here against the original because lots of the schematics here have been copied incorrectly..

 

[fikic]

I don't have transformer with 3 contacts and I used 2 way one. Can anyone check, if schematic is correct?
I have tryed circuit, but I didn't connect the speaker and one of the transistors died becouse of the too big current through it. I am now waiting for new trasistor to try my PCB.

 

[Hero999]

Using a non-tapped transformer and bridge rectifier won't make any difference so long as you reduced the secondary voltage to 24V.

Which transistor failed?

Simply blindly replacing it won't help, the chances are it'll fail again.

There is potential for Q5 or Q6 to go in to thermal runaway, especially if R9 is adjusted incorrectly. Did you correctly follow the instructions, setting R9 to its lowest value and increasing it until the quiescent current is 25mA to 30mA, wait 15 minutes and adjust if required? I'd recommend doing this with a speaker or 3R9 to 8R2 dummy load resistor connected.

Adding emitter resistors to Q5 and Q6, also might be a good way to prevent thermal runaway..

 

[fikic]

Yes, I followed the instrucions, but I am afraid you're wrong about the transformer. The schematic I made is similar to original one, just that I used rectifier bridge and 48V transformer. If I understood you right, I used too high input voltage ??? Why I should reduce it to 24V?

 

[audioguru2]

Yes, I followed the instrucions, but I am afraid you're wrong about the transformer. The schematic I made is similar to original one, just that I used rectifier bridge and 48V transformer. If I understood you right, I used too high input voltage ??? Why I should reduce it to 24V?

The project uses a 48V center-tapped transformer. Since you used a transformer without a center-tap then your transformer should be 24V, not 48V.

 

[Hero999]

Yes, I followed the instrucions, but I am afraid you're wrong about the transformer. The schematic I made is similar to original one, just that I used rectifier bridge and 48V transformer. If I understood you right, I used too high input voltage ??? Why I should reduce it to 24V?

The circuit failed because the input voltage was double what it was designed for.

Look at the original schematic.

The transformer's centre tap is connected to 0V so the voltage at either winding (with respective to 0V or neutral) will be 24VAC.

The voltage at one winding will be 180

 

[fikic]

Yes. I know that. I just didn't look good and now I understand it all. I have transformer with 24V secundary and I connected it's another secondary, so I got 48V. But I was wrong and now I will use original patent of this transformer. At least I know what was wrong now. As they say, we learn on mistakes and I learned something new today. Thank you all for your help. I will report on my project on monday, when I get new transistors.

 

[fikic]

Can anyone just tell me please, how do I check NPN and PNP transistor with multimeter with range for testing diodes or with ohmmeter without any testing circout?

 

[Hero999]

A quick test for an NPN transistor is to put the positive on the base and check for a 0.6V to 0.7V voltage drop when the negative is connected to either the collector or emitter.

To test PNP transistors, just reverse the positive and negative connections.

Unfortunately these tests aren't perfect, a transistor might pass but won't work properly because it's not completely broken but badly damaged, for example the gain might be deverly reduced so it no longer amplifies enough.

Because the circuit was connected to too higher voltage, it's possible that some of the other components have been damaged, drastically shortening their lives. If you replace the transistor and reduce the transformer voltage, it might work for awhile, then fail again as a result of the damaged caused by the over voltage.

 

[fikic]

Which components are in danger thoug?

 

[Hero999]

Any of the semiconductors could have been damaged as well as some of the capacitors, especially C13 as it's connected directly across the power supply.

Providing this project is not for sale, don't worry about it, just keep a supply of spares.

 

[fikic]

C13 is good. I made a conuctivity test betwen + and -. It conducts for 1 second, then capacitor is unconductable for few seconds. I think, that Q5 is ok, becouse it conducts between collector and emmitor. It also show resistance between Base and Emitor of about 600 Ohms and in other direction is about 2kOhms. Is That ok? I haven't check other transistors yet..

 

[Hero999]

C13 is good. I made a conuctivity test betwen + and -. It conducts for 1 second, then capacitor is unconductable for few seconds.

Yes, it might work now, as I said earlier, that doesn't mean its life hasn't been shortened.

I think, that Q5 is ok, becouse it conducts between collector and emmitor.

That means its broken, it shouldn't conduct between the collector and emitter without a base signal.

Did you try to test the transistor whilst it's still in the circuit by any chance?

It also show resistance between Base and Emitor of about 600 Ohms and in other direction is about 2kOhms.

it shouldn't conduct in the reverse direction, unless your test voltage is higher than 5V which is too high and might damage the transistor.

Is That ok? I haven't check other transistors yet..

From the results given above, it looks like you've tested the transistors whilst there still in the circuit..

To do any meaningful testing, the transistor must be removed from the circuit before it's tested, otherwise other components in the circuit can influence the result: for example a resistor connected in between the base and collector can turn the transistor on.

I think you need to read up a bit more on transistors before continuing.

 

[fikic]

I tested transistor Q5 out of circuit. I know, I can't test them inside of it. I will see. If amplifier will work and if one day woun't work anymore, I will simply rechange components that are now life shorted probably.
PS.: Can you please check my PCB and tell me if it's good with original schematic?