Dear All
Today I have problem about power amplifier.
From the spec of circuit it can drive max 80 watt but the transformer that I have it max 24 VAC , 500 mA which is not reach 80 watt.
When I use this transformer it will overdrive sound if potentiometer reach max position.
How do I need to adjust the resistor it the circuit ?
Circuit refer below
Best Regard
Today I have problem about power amplifier.
From the spec of circuit it can drive max 80 watt but the transformer that I have it max 24 VAC , 500 mA which is not reach 80 watt.
When I use this transformer it will overdrive sound if potentiometer reach max position.
How do I need to adjust the resistor it the circuit ?
Circuit refer below
Best Regard
You will need a bigger transformer. The one you have cannot deliver the power needed, far from it.
In short - YES! 😵
You said the amp "can drive max 80 watt" - if that's 80w per channel then (including power transformer losses) in order not to 'throttle' the amp's performance ... you should use:
* either one at least 300w power traffo
* or at least a single 160w power traffo for each channel.
I would find another DIY amp. The transformer should be with two secondaries (24V - 0 - 24V) and not with one 24V
https://www.st.com/resource/en/datasheet/tda7296.pdf
Or TDA7293, 7294, LM3886. There are ready-made kits or just PCBs for amplifiers and power supplies on ebay/Aliexpress. All together with DC speaker protection. There are also various D class amplifier modules with 24-48VDC single power supply. Speaker impedance should also be taken into account, if it is 4 ohms, the transformer/power supply requirements are doubled compared to 8 ohms.
Or TDA7293, 7294, LM3886. There are ready-made kits or just PCBs for amplifiers and power supplies on ebay/Aliexpress. All together with DC speaker protection. There are also various D class amplifier modules with 24-48VDC single power supply. Speaker impedance should also be taken into account, if it is 4 ohms, the transformer/power supply requirements are doubled compared to 8 ohms.
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If you already have that circuit, you can keep it and just use a proper power supply for it. The transformer need to supply 2x25 VAC and the power rating must be more than the output of the power amplifier. If it is 2 channel amp, double the wanted output. If you want a 4 Ohm capable amp, the required power rating of the transformer need to be increased even further.
That is true only if the transformer has two independent 25 vac windings that can be tied together at + and - to make a center tap. You'd need 2 bridge rectifiers & 2 filter caps. If you buy an e-core transformer, you need 50 vacCT. A 25 vac winding rectified will make 35-1.2 DC at low watts. 25*1.4 - 1.2v for the rectifiers. I have several transistor amps with one transformer that drives 2 channels. A 650 VA transformer one with 3300 uf cap made 75 w/ch on 8 ohms for 5 seconds on 2 speakers. Using class AB MJ15003.
80 w is a bit optimistic for single 2n3055 mj2955. As On Semi TO3 are all the same price, I would use MJ21194/21195 or MJ15024/15025. Or to avoid drilling 3 holes per transistor in the heat sink I would use MJL3281/1302. If you can access Indian transistors C something is preferred by posters from that country. In USA I buy On parts from authorized distributors. Don't forget a substantial heatsink. 10 cm x 16 cm x 2 cm with 6 fins might be okay.
LF351 is an old part. I'd use 5532, 2 halves for stereo. The dropping resistor from the rails needs to be changed to make the +-15 supply for the op amps. Or TL072. I prefer to regulate op amp rails with zener diodes, with a diode and filter cap for each op amp supply. The pinouts of the other op amps, the datasheets can be downloaded from datasheetcatalog.com .
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Yes , I see for the answer that with this transformer will not reach 80watt
But for my using I don't want more than 12 watt because I will use for music listening in my bedroom.
I use this circuit cause I can buy the complete PCB in local shop then I think I can adjust the circuit to be suit my using.
How do you think It will be possible ?
Best Regard
But for my using I don't want more than 12 watt because I will use for music listening in my bedroom.
I use this circuit cause I can buy the complete PCB in local shop then I think I can adjust the circuit to be suit my using.
How do you think It will be possible ?
Best Regard
In that case put up with the LF351 the shop is selling. It has some voltage noise. Don't neglect to add DC adjustment as post 2, perhaps by drilling holes in the board and adding wires. I would use a 100 k pot with the ends to the +-15 rails and the wiper through 10 k to pin 3.
If you use two 24 vac transformers per channel, for +-33 v rails, and each has 2 amps capability, you can get 2^2 * 8 = 32 w/ch with enough heat sink. 1 amp capability gets 8 watts. That is on 8 ohm speaker. 0.5 amp transformers would only get 2 watts. You stack the transformers + to - to make + and - rails.
That amplifier would most likely run fine on a +/-15V supply and give you the power level you are after. You will need a new transformer of +/-12V, 50 or 60VA, or a +/-15V SMPS.
English please:
"You can increase the value of the 2 resistors R15, R16 to 4.7 Ohm or 10 Ohm and see."
If you wish to post in a language other than English, you must also provide a translation.
Thank you.
I understood the original question not as what transformer or power supply to buy, but how to adapt this circuit to a 24VAC 0.5A transformer that is already on hand. I must say though I'm not convinced that this transformer is such a great find that it makes sense to go to the non-negligible expense and effort of building an amplifier (and power supply) around it.
I'm also a bit confused: In the first post you (the OP) say the amp sounds bad ('overdrive sound') when you turn up the volume ('potentiometer'), but then later in post #14 you say you can buy this PCB, which to me would imply you do not have the amp yet. Which one is it?
Also, how did you or do you plan to attach the AC output from the transformer to the circuit? Do you have a DC power supply with this transformer as a part of it, or did you just hook up 24V AC to the +/-35V rails of the amp? I'm surprised that anything resembling the input signal would come out of the amp in that case.
If you don't have the amp and do have a complete 24V DC 0.5A power supply, then I think Nixie62 had some amp kit suggestions for you. It still might not be the most cost-effective and satisfying solution though (compared to ditching the transformer and going for something else).
If you have neither the amp nor a complete DC power supply but just a transformer, then it might be more promising and cheaper to find an amp and a power supply that go together than building this amp modified for +/-15V DC and building the corresponding power supply that uses the transformer you already have.
I'm also a bit confused: In the first post you (the OP) say the amp sounds bad ('overdrive sound') when you turn up the volume ('potentiometer'), but then later in post #14 you say you can buy this PCB, which to me would imply you do not have the amp yet. Which one is it?
Also, how did you or do you plan to attach the AC output from the transformer to the circuit? Do you have a DC power supply with this transformer as a part of it, or did you just hook up 24V AC to the +/-35V rails of the amp? I'm surprised that anything resembling the input signal would come out of the amp in that case.
If you don't have the amp and do have a complete 24V DC 0.5A power supply, then I think Nixie62 had some amp kit suggestions for you. It still might not be the most cost-effective and satisfying solution though (compared to ditching the transformer and going for something else).
If you have neither the amp nor a complete DC power supply but just a transformer, then it might be more promising and cheaper to find an amp and a power supply that go together than building this amp modified for +/-15V DC and building the corresponding power supply that uses the transformer you already have.
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