Thoughts on these audio amp circuits?

[FvM]

Misleading title. Both amplifiers are regular linear class AB MOSFET output amplifiers.

Thread merged with previous amplifier thread.

 

[Enzy]

Now where can I find the post.... I actually want to get some feed back on them.

 

[schmitt trigger]

I'm going to jump in and provide my two cents worth:

When one attempts to build a power amplifier, the most difficult part to obtain is the power transformer. They usually require oddball voltages with large current ratings and sometimes multiple windings.
In other words; a custom-made transformer.

Therefore I'm going to suggest what worked for me when I was learning when I was also into building amplifiers: find yourself a complete amplifier kit.

You will get not only the custom transformer, but heatsinks and very important, a well made PC board.

I cannot over-emphasize that a project's success or failure rate is directly related to a good board layout. Also, they will have a solder mask and silk screened labels, which make assembly easier and actually enjoyable.

What I would do, after I had successfully built and tested the stock design and studied it enough by probing voltages around, is to customize it with my ideas.
You can learn a lot that way, and won't have the frustration of burning out a hundred dollar's worth of component because of a simple wiring mistake.

 

[Enzy]

That's true, but I actually have amplifiers so far that I have etched that's worked well and I have done changes to improve gain, changed from mono to stereo, I build to learn but I also use them, I play music all the time and I like the fact that I can build my own amplifiers to play.

Differently from what I built on bread boards and etched I also tried kits more than once, I never have problems with kits those are simple enough for me, my aim from the other day is to build more power amplifiers in range of say 700 watts and above, going class d would be good also that's the aim but I would still try out a couple class ab high power amplifiers too even just for the silly reason of me loving to see alot of fets in a circuit that's well designed and plays wonderful

 

[Enzy]

Re: [moved] Query about VU meters (led bargraph)

Finally got some time yesterday and today to do some work on this, I just went ahead with the preamp only seen at the bottom right in the case, no vumeter, I wont say for sure that I like the sounding 100% when I add the preamp but I need it since it has the volume control, I havent made a test as yet with a bass speaker and a cross over but hopefully it sounds ok when I do. The way it sounds now it has a distorted sound t it when I use the preamp and the sound is there even when its at low volume.

 

[Audioguru]

Re: [moved] Query about VU meters (led bargraph)

The volume control should be able to reduce the output down to silence so yours must be wired wrong.
Your pcb has dark blue lines that cannot be seen on a black background. It does not show the audio preamp.

 

[Enzy]

Re: [moved] Query about VU meters (led bargraph)

I was just saying it sounds a bit weird when its at high or low volume I didn't mean that It cannot turn all the way down to silence because it can, but I am gonna finish making the connections then do a final test to listen how it sounds and use the scope to test outputs.

 

[Audioguru]

Re: [moved] Query about VU meters (led bargraph)

A preamp made with a lousy old LM358 dual opamp has crossover distortion. A TL072 dual opamp has very low distortion that you cannot hear unless its supply voltage is too low, or it is biased wrong or if it is feeding a capacitance (even the capacitance of an output cable) without an isolating 100 ohm series resistor.

 

[Enzy]

Re: [moved] Query about VU meters (led bargraph)

Ok I made a final test today I have to turn the gain to max and then the volume control 5k pot I have it to a little over half testing it on a 12 inch 200w speaker It didnt sound very load, will be testing it on the correct speakers next week when Im at that side of the world.

The bad sound I was getting the board was cracked I had to run wires on it I guess it was opening and closing right in line with a cap, ill rebuild the board though. It sounded better after the mod I made the amp is playing clean now just kinda light weight not sure if that because of the speaker I am using or probably I need more gain, I tried a 1khz test tone without speaker connected and at max I was getting 15v Ac from the speaker out.

 

[Audioguru]

Re: [moved] Query about VU meters (led bargraph)

A multimeter cannot accurately measure frequencies above about 120Hz because it is designed to measure only 50Hz or 60Hz electricity. Turn down the frequency of the signal generator to see if the multimeter reading increases. A 15V RMS sinewave into an 8 ohm speaker produces 28.1 Watts of power.

A volume control is supposed to be logarithmic like our hearing so if the amplifier produces 28W with the volume control at halfway then the amplifier will try to produce 450W or more when the volume control is turned to maximum.

 

[Enzy]

Re: [moved] Query about VU meters (led bargraph)

unfortunately I cannot do any testing over the weekend since the project is at work, and i wont be there on the weekend but if the halfway mark is 28w isnt that a far stretch to get 450w if I turn the nob all the way? I actually turned it all the way today a couple times, normally I would expect to have an amp at about half way to drive the speakers, especially for base I need the drive or else it will sound horrible, atleast playing mid even if its not driving the speakers hard it can still sound good enough if its load and clean

 

[Audioguru]

Re: [moved] Query about VU meters (led bargraph)

Our hearing's sensitivity to loudness is logarithmic so we can hear a wide range of loudness from a pin drop to something very loud. Half or double speaker power is just a small change in loudness. 1/10th or 10 times the power sounds like half or twice as loud. To smoothly adjust loudness the volume control must be logarithmic. If you use a linear control then from maximum to halfway the loudness drops only a little. It will be difficult to adjust the loudness to a low level.

A speaker must have an enclosure designed for its spec's to produce low frequency bass sounds. Without an enclosure low frequencies from the rear come around and cancel bass sounds from the front. Two or more speakers must produce the same phase to add their sound. If two speakers are connected with opposite phases then their bass sounds cancel.

 

[Enzy]

Re: [moved] Query about VU meters (led bargraph)

Ok, by the way I wanted to build an amplifier something I fully understand, a class D amplifier which I was talking about in a earlier post, I did reading on the types of amplifier already.

How would I start off in the design stage, for example say I want to build an amp with 500 watt RMS Per channel (stereo)
I would start off with a linear power supply also just for now.

- - - Updated - - -

Ill probably have to make a new thread for this though.

 

[Audioguru]

Re: [moved] Query about VU meters (led bargraph)

500W per channel is VERY high power for an audio amplifier. Maybe for a discotech with hundreds of people. For a home then a 50W per channel amplifier is fine.
Are you the guy with a powerful sound system on a bicycle?

 

[Enzy]

Re: [moved] Query about VU meters (led bargraph)

No I am not the guy with the bicycle.

in my country we mainly do outdoor music, always on large field with more than 100 people not a first world country and we arent over populated and we are the reggae country so our music is always load with alot of speakers 50 watts is very light for my types of setup.

for a 50 watt or close amplifier I would just work with a class AB like I have that circuit already (TDA7293/94)

- - - Updated - - -

For the outdoor purpose I was thinking to start at 500 watts doing a mosfet class D style amplifier something that I could modify later without alot of changes.

 

[Audioguru]

Re: [moved] Query about VU meters (led bargraph)

we are the reggae country so our music is always loud.

Then it is Jamaica, yeah man! My wife and I had our honeymoon there in Ocho Rios a little more than 38 years ago. Today I was in the large park by the river in my city and there were people I guess Jamaicans playing reggae on two large speakers and a powerful amplifier powered from a Honda electricity generator.

 

[Enzy]

Re: [moved] Query about VU meters (led bargraph)

Kool, out here the smallest set up we use would be like either 8 or 16 bass speakers "18 inch", 4 low mid 15" speakers, 4 high mod 12 inch speakers alone with horns and tweeters.

The biggest sound systems out here I have been around all of them they all use very powerful amplifiers.

The international sound system we have out here names Bass Odyssey you can Google them or YouTube they use 2 amplifiers for bass both amplifier have 2 channels 10, 000 watts per channel, most other sounds use Qsc branded amplifiers and some other use amplifiers like spyn normally they are turned to about quarter the range.

How do I start a design.

 

[c_mitra]

Re: [moved] Query about VU meters (led bargraph)

the smallest set up we use would be like either 8 or 16 bass speakers "18 inch", 4 low mid 15" speakers, 4 high mod 12 inch speakers alone with horns and tweeters.
.

You need to decide first whether you are using three amplifiers for high, mid and bass frequencies (you will have phase problems).

Or, you can use one amplifier but use filters to feed the high, mid and bass frequencies to deliver to different speakers. You will need massive filters.

When you are separating the frequencies, you need to be careful about the speaker placements.

If you are planning to address a crowd, then it is wise to forget about splitting horns and tweeters... Just use a single speaker to deliver all the frequencies. Just place them (multiple identical speakers) carefully with the field...

That is because different frequencies are attenuated differently...

 

[Enzy]

Re: [moved] Query about VU meters (led bargraph)

I would never use 1 amplifier, I would use 3 amplifiers If I am doing a set up like that

 

[c_mitra]

Re: [moved] Query about VU meters (led bargraph)

I would never use 1 amplifier, I would use 3 amplifiers If I am doing a set up like that

High frequencies have rather short range and I guess you need more tweeters to have a fair share of the frequency. Speakers are more efficient at low frequencies and you will need less of them. What is interesting with music is that the brain hears what it wants to hear rather than what is actually there. - in other words, human brain is rather forgiving...