Transformer for guitar amp.

[ubaid88]

Hey there I am working on a project for guitar amplifier. So project requires 25-0-25 step down transformer. What is this. I mean how will it output voltage. Would 25+ and -25, +25 and 0 or something that will result total pd of 25. Well i will be testing my circuit in software simulation so i required help for it. I am beginner in electronic (Science student of A-levels).

Here is the description of project regarding transformers. I am bit confuse about output 25-0-25 transformer but +/-35 output.?

The amplifier is designed for a maximum loaded supply voltage of +/-35V, and this must not be exceeded. Normal tolerance for mains variations is +/-10%, and this is allowed for. The transformer must be rated for a nominal 25-0-25 volt output, and no more.

[Rick Erickson]

I am beginner in electronic (Science student of A-levels).

Are you enrolled in an electronics class? Your instructor should have taught you this stuff before unleashing you on a design project.
There are basic formulas that you should understand first. I learned this stuff in High School Electronics class. I'm sure there are plenty of articles on the net discussing basic AC theory.
A quick answer: the 0 reference is your center tap. A standard two diode Full Wave rectification circuit should net you at the filter cap: (25 x 1.414) volts, or 35.35V. In the real world you will likely see more voltage at the filter, as the transformer is rated at 25-0-25 or 50V C.T. (Center Tapped) at its rated output current. Draw less current from it and the voltage will rise slightly.

[and this must not be exceeded]

Why? Will it explode? If you must keep the voltage at 35V you may need to employ some sort of voltage regulation circuit. Most guitar amps don't use regulation on the output stage. If your output device can't handle more than 35V then run it a bit lower, maybe 28V for some safety margin. (Different power transformer) Mains AC levels fluctuate all over in the real world and this must be considered when desiging equipment. I have seen a major manufacturer's amp designed on the edge of the cutoff voltage for a TDA2050, and the amp had intermittent operation & nasty sounding distortion as a result. Fluctuation must be considered to ensure stability.

RE

[ubaid88]

I am beginner in electronic (Science student of A-levels).

Are you enrolled in an electronics class? Your instructor should have taught you this stuff before unleashing you on a design project.
There are basic formulas that you should understand first. I learned this stuff in High School Electronics class. I'm sure there are plenty of articles on the net discussing basic AC theory.
A quick answer: the 0 reference is your center tap. A standard two diode Full Wave rectification circuit should net you at the filter cap: (25 x 1.414) volts, or 35.35V. In the real world you will likely see more voltage at the filter, as the transformer is rated at 25-0-25 or 50V C.T. (Center Tapped) at its rated output current. Draw less current from it and the voltage will rise slightly.

[and this must not be exceeded]

Why? Will it explode? If you must keep the voltage at 35V you may need to employ some sort of voltage regulation circuit. Most guitar amps don't use regulation on the output stage. If your output device can't handle more than 35V then run it a bit lower, maybe 28V for some safety margin. (Different power transformer) Mains AC levels fluctuate all over in the real world and this must be considered when desiging equipment. I have seen a major manufacturer's amp designed on the edge of the cutoff voltage for a TDA2050, and the amp had intermittent operation & nasty sounding distortion as a result. Fluctuation must be considered to ensure stability.

RE

No no, this not a school project. This a diy guitar amp project.
[QUOTE=Rick Erickson;67111]I am beginner in electronic (Science student of A-levels).
This was just tell my level of understanding about electronics stuff.

[Rick Erickson]

[This a diy guitar amp project. ]

Well, there's nothing like jumping in with both feet, but it helps to make sure there's water in the pool first. If you give more specifics about your circuit design there are many knowlegable people here who can and will help you through it. A schematic diagram would be best, or at least details like what output device(s) you are planning to use, and what you plan to get from it power wise to a chosen speaker load. I assume this is a soid state project from your voltage requirements.

RE

[ubaid88]

[This a diy guitar amp project. ]

Well, there's nothing like jumping in with both feet, but it helps to make sure there's water in the pool first. If you give more specifics about your circuit design there are many knowlegable people here who can and will help you through it. A schematic diagram would be best, or at least details like what output device(s) you are planning to use, and what you plan to get from it power wise to a chosen speaker load. I assume this is a soid state project from your voltage requirements.

RE

http://sound.westhost.com/project27.htm ok here you go full details

[Steve Conner]

You need a transformer like RS part number 223-8106:
http://uk.rs-online.com/web/search/s...duct&R=2238106

If you don't understand what this means, get help from your teacher or something.

[Enzo]

Here is your confusion. Transformers work on AC voltage. That 25-0-25 means there is 50volts of AC on that secondary with a tap in the center. So there is 25v of AC from that ceter tap - CT - to either end.

The circuit runs on DC voltage, in this case +/-35VDC. The two 25VAC sources - the transformer - must be rectified and filtered to make the two DC voltages: +35VDC and -35VDC.

If you are studying electronics, you should know that AC volts are measured in what we call RMS voltage - that means more or less the average voltage over time. SInce AC sine wave voltage from the wall starts at zero volts, swings to a positive peak, then swings to a negative peak and on and on. You should also know by now that the peak voltage of that AC is appiorximately 1.414 times the RMS value. Multiply 25VAC RMS by 1.414 and you get... 35VDC.

It works the other way too. To find out what AC voltage you need for a given DC voltage, multiply the DC value by .707. 35VDC x .707 means approx 25VAC would be needed. Of course the same answer.

I can't imagine why a circuit was limited to 35v other than if the design used 35v caps or something. Or it is a really old design using 60 volt transistors.