full details on creating good sound

I have been here several times trying to create a good audio amplifiers and amplifiers so far I havent had any help creating an amplifier so I tend to resort to Chinese made amplifier boards that I buy on ebay I am not sure if its my preamp that seems to be giving me some sounds that arent so clean, there is not much of a hum in the sounding but once music is playing at a certain level its not very clean and its not clipping. I would lean to beleive thast its the amplifiers that aren't playing all that clean.

I would like to know all the major sections of an amplifer not in a fine comb detailed way but laying it out like a lock diagram it doesnt have to be all that needed for example speaker protection circuits which I have never used before.

so for my builds I would generally have:
power supply stage
fan circuit
preamp stage
amplifier
and thats it.

I havent even been able to find a simple VU meter or peak detection circuit which doesnt use many lights possible 4 or less LED's.

Another thing is I would love to build a high quality preamp board which I can use on all amplifiers from bass to tweeters 2 channels and stereo, so that would generally be 20hz to 20khz.

I have always asked for help to create an amplifier class D seems be a challenge so I would work with a class AB amplifier also something using FETS which can be easily upgraded interms of power rating since I would generally go for high powered amplifiers and 2ohms would be the target for connected speakers 2 channel also.

I have been busy coding with arduino and teaching myself and doing some projects that I couldn't do much audio projects but I have already bought resistors and caps of various sizes and Fets and single and dual opamps.

It would be nice to get some help and I would like to document everything as I go also.

I have been here several times trying to create a good audio amplifiers and amplifiers so far I haven't had any help creating an amplifier.

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Ask good questions and expect good answers...

So in other words you don't see any good questions in my previous post?

There are basically good questions in your posts, and I see many Edaboard members answering it. I remember that you sometimes got lost in strange circuit issues which can be hardly debugged from a distance. Saying "I haven't had any help" is rather unfair against the Edaboard members engaged in the discussion.

I know that several thread contributors are professional electronic engineers who probably managed to design and repair similar audio devices many times. Somehow their expertise didn't arrive.

Don't want to guess about the reasons, I can just suggest to try again.

I guess my Statement was too open but when I said I didn't get any help I was refering to the part about creating an amplifier design.

This is a helpful forum I could never say that.

I think i need to learn how to design circuits properly so that I can start asking more appropriate questions also I tend to realize my questions are basic and I tend to forget somethings because I don't document alot of critical details but I'll change that this time.

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before I start to design Ill check out circuits and see if I can understand them first.

I found this in a book called 101-200 transistor circuit



does it look like a working amplifier and how can I look at it and differentiate sections of it.

Do you want to design discrete transistor audio amplifiers?

If so, I would suggest the book "Handbook of Audio Circuit Design" by Derek Cameron.

Another is by noted audio designer Dough Self, reference books: "Audio Power Amplifier Design" and "Small Signal Audio Design".

Your schematic shows a rudimentary, but workable audio power amp.
Its simplicity reveals some shortcomings. For insance, the circuit would be barely be working class AB, it does require some sort of bias adjustment.

The amplifier you found is simple so its distortion just before clipping (about 2W into 8 ohms) is about 1% which causes the sound to be fuzzy. The distortion of good amplifiers is 0.01% or less.
Most of its distortion is caused by the BD140 that is simply turned on by a resistor (470 ohms to ground at its base) that delivers less and less current when the transistor needs more current (when the output swings low).
The 220uF output capacitor cuts the power in half at 91 Hz so lower frequencies are not produced.

EDIT: Of course a poor quality speaker sounds awful.

I just found that circuit to show as an example and how you guys can analyse it so easily I want to be able to that but not sure how to start.

I was wondering if I should start from just designing some pre-amplifiers. I think its easier for now than starting with power amplifiers unless you say otherwise.

I have tl072 and tl071 opamps I would like to make a high quality pre-amp with a frequency ranging from 20hz to 20khz I also want to build any circuit you guys reccomend that's built buy anyone or if you chose to help me make something from scratch I plan to make them and test them and share results I need to test each section of these circuits.

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I just found that circuit to show as an example and how you guys can analyse it so easily I want to be able to that but not sure how to start.

I was wondering if I should start from just designing some pre-amplifiers. I think its easier for now than starting with power amplifiers unless you say otherwise.

I have tl072 and tl071 opamps I would like to make a high quality pre-amp with a frequency ranging from 20hz to 20khz I also want to build any circuit you guys reccomend that's built buy anyone or if you chose to help me make something from scratch I plan to make them and test them and share results I need to test each section of these circuits.

To design a preamp you need to know the input signal level from the source and its recommended load impedance which will be the input impedance of the preamp.
You need to know the sensitivity of the power amplifier so that the preamp gain can be calculated and set.
Do you need tone controls?

I use various things to play music like phones, cd players passing through mixers ect.

I'm not sure where the signal level would be but I'll assume it's atleast 316mv which is the standard as you always say.

I won't be able to tell the load impedance either even though I have never checked that before, in most cases I think i would be leaving from a cross over to the input of the preamp I'm not sure if there is a standard for load impedance so I can work with a guideline.

I'm using a Chinese amplifier like normal
Specs:
- Power: 300W 8R (+ -75V), 600W 4R (+ -75V), 1000W 2R(+ -75V)
- Power supply voltage: DC+-60V~+-80V, (recommend voltage DC+ -75V)
- Distortion:0.07 % THD+N 600W 2 R
- Voltage gain:33 DB
- Loading resistance: 2Ohm
- Total Idle Power Consumption: 13.2W
- System Efficiency: 80% 600W 2R
- Dynamic Range : 99.4 DB
- Residual Noise: 290 UV
- Damping Factor:>70 (1K HZ ,2R)
- Frequency Response: 20Hz-20kHz + -1DB


No I won't need tome controls when I'm making an amplifier design for myself then Ill test out the tome controls portion.

The power amplifier needs an input of about 1V RMS for full output. Since the input will be a player and not a phono cartridge, tape head or guitar pickup then the impedance does not matter much. To allow you to turn up low levels then the preamp should have a gain of about 32 (+30dB) so that a log volume control will be at halfway for loud output with normal 316mV input levels.
A TL071 single or TL072 dual audio opamp will be fine. So that it does not clip when the volume control at the input of the power amp is at halfway then the opamp should have a supply more than 14V (or plus/minus 7V).

OK i would use a Tl072 since I would be using 2 amplifier boards so a 15v supply would be good then.

Is it better to use dual polarity supply with these circuits?

I have designed and made many audio circuits and they never amplify DC so I have never used a dual polarity supply.

So what about power supply for your amplifier circuits aren't they suppose to be dual polarity also?

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On the other note is there a good design format that I can start off with for the preamp that you know of or should I start a design and let you see what I come up with

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On the other note is there a good design format that I can start off with for the preamp that you know of or should I start a design and let you see what I come up with

Enzy said:

So what about power supply for your amplifier circuits aren't they suppose to be dual polarity also?

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No, why should they? Audio has no DC in it so coupling capacitors are used at the input and output of my amplifiers so that the circuit can swing the signal up and down. The circuit is biased at half the supply voltage which is 0V when there is a dual polarity supply. When powered by a dual polarity supply the coupling capacitors do not block DC, they are simple highpass filters which are also needed with a single polarity supply.

On the other note is there a good design format that I can start off with for the preamp that you know of or should I start a design and let you see what I come up with

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Preamps with two transistors and AC and DC negative feedback were used 50 years ago to replace vacuum tubes. Audio opamps are used today.

ok sorry for the late reply I was just looking back at some of your past info and I was choosing a preamp I could use and redraw to my liking.



I used a high pass filter calculator for c1 and r2 creates a high pass filter of 1.59hz and c3+c2 and r10 creates another high pass filter of 0.79hz I ensured the frequencies were 1.5hz or below in order to have a wide range of frequencies pass through from 20hz up. I didnt understand the part about octaves and -3db.

with the 10k resistors on the negative feedback would that give a gain of 2 if so then the first stage of the opamp has a gain of 2 then its fed to the second stage which also has a gain of 2 would that make final gain =4

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1) The 7815 will not regulate when the transformer is only 12VAC. The peak of 12VAC is 12 x 1,414= 16.9V. The full wave bridge conducts a high current at the peaks of the 16.9V so the loss is 2V. The rectified and filtered voltage will be 14.9V but the minimum input of a 7815 is 17.5V.
2) R1 is not needed.
3) Why do you use two opamps? Only the first opamp is needed but it its gain goes down to DC which is not wanted. It should have an AC gain of 32 so the value of R4 should be increased to 330k and a capacitor in series with R3.
4) The circuit of your second opamp is odd, it has too many resistors and its gain is less than 1.

EDIT: Holy smokes! Your preamp rectifies the audio because its input is not biased at half the supply voltage.

I think i might end up going back to the same specs as the tl071 preamp that im currently using making these changes, and what I shold be doing is using the tl072 for 2 different preamp circuits instead of one.

in other words if I use it the way Im using it now it would just make sense i use the tl071 circuit I just cant seem to get very clear audio from it or im not sure if its a fault of the amplifiers im using

Now you are talking about a TL071 preamp but you did not post its schematic.
Maybe your cheap Chinese power amplifiers are crap.
Maybe your speakers are crap.
How is your hearing? I did not know I gradually got poor hearing. I got a free hearing test that revealed that my hearing was normal for my age (71) and that I needed hearing aids. I got a free 3 months demo then I bought them and they make a huge improvement. My hearing aids have selectable features that normal hearing cannot do like increased sensitivity, noise reduction, muting, a loudness limiter and directionality.

ok I made some changes anyway



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I keep saying probably the amps are the prob I guess your reading selectively, hence why I said in the post that I want to make each section of am amplifier in the post in stages (not exact words). so after the preamp then Ill want to make an amplifier also hopefully you can help me with that.

as for me im a youngster just getting in my prime for electronics, this forum is part of my schooling so ill take notes even on the criticism thats a norm in the technical field