Simple high damping factor current drive amplifier

My head hurts, I’ve been reading other peoples rantings about what makes the best audio amplifier, it’s not rocket science but does require an understanding of the laws of physics.

Firstly it is current not voltage that determines how far the cone or ribbon of a voice coil or ribbon speaker moves, as the current produced by a specific voltage varies with frequency, voltage drive will not produce an accurate representation of the original audio.

Secondly the inertia of a speaker can accurately be represented by the parallel LCR circuit used to simulate the resonance of a speaker.

Thirdly a high damping factor can reduce the amplitude of any overshoots and resonance produced on a high speed pulse input.

I used a resistor in series with the speaker back in the early 60’s when I modified a Radio & Hobbies (early electronics mag.) Playmaster Valve Amplifier and noticed a much cleaner audio result.

I worked on various solid state designs over the years eventually achieving the result I was after.

I recently decided to design a simple DIY project to demonstrate these facts and was surprised by the sound quality from a mediocre OP Amp.

The THD was improved by two orders of magnitude, and the bandwidth is now insane and completely stable even with a short circuit across the speaker.

The following circuit diagrams show the change required to convert a voltage amplifier to a current amplifier. Note:- the microvolt input required to zero the DC output before connecting the speakers.

To see the full specifications and complete DIY design visit my website at https://www.inja.com.au/diy.php

Note also :- speaker box design is different for current drive amplifiers. Start by mounting your driver in an infinite baffle and taking measurements.

The damping factor may appear at first glance to be low ie 1.2 ohm resister in series with the 8 ohm speaker. However when you divide this resistor by the open loop gain of the amplifier you get the real figure to divide into the 8 ohm speaker.

 

Professional quality DIY Amplifier

Fidelity Audio is the degree of perfection of the reproduction of the original sound.

To me perfection does not have levels it is either perfect or imperfect, so why do we have terms like hi fidelity (Hi Fi) and Ultra Hi Fidelity. What next Super Duper Hi Fi?

There are many factors that affect the fidelity of audio reproduction.

Room reflections and resonances have a significant effect and can be improved or eliminated by some simple changes.

The resonances within the speakers are the second most significant problem, and this can be almost eliminated by correcting a basic design error that exists on most amplifiers. This change produces a huge damping factor on the speaker forcing the speaker to accurately follow the input signal reducing the overall distortion and phase error without any additional production cost.

I don’t have tone controls or graphic equalizers. The room has been optimized and the pair of speaker were designed, optimized, to take advantage of the new amplifier design.

I use this correction technique in my DIY amplifier and change an average audio IC into a high end 3.5 Watt amplifier.

Why only 3.5Watt output.

Even in a large home listening room (unless you have an auditorium full of people in your house.) 3.5 Watt is louder than required. It is not uncommon for people to purchase a 300 Watt amplifier, convinced by a sales person that this is the way to have the best sound system (Sales Bulls…), and it is then listened to at a power level of less than 2 Watt.

If you were to continually listen to it at the 300 Watt level in a normal listening room it would result in severe hearing damage.

Yet the difference between 3.5 and 300 Watt is less than 7 just audible steps or only 4 times as loud.   — Sound Quality is NOT sound level —

I also have designed a professional audio system originally 3.5 Watt, the market place forced me to increase the output to 30 Watt to match the (Sales Bulls…). This is 3 just audible steps above the 3.5 Watt Amplifier or twice as loud.

The specifications tell part of the story, the specially designed speaker system and the room modifications are the final things that complete the package.

I enjoy listening to one with the volume turned down to below 2 Watt per channel, I shut my eyes and feel the presence as if I am at the venue live

I now use the term “Live Audio” by which I mean as close as I can get to being at the live performance, and that is a lot closer than any equipment I have listened to.

For design details https://www.inja.com.au/diy.php

DIY Audio Amplifier

Yes at 75 Years young I am a student studying Website development. The students in this intake have restored my faith in the future. I’m most impressed!

My first Qualification in Victoria 1962 to 1967 Telecommunications Technician followed my childhood interest in electronics.

After a brief training period I spent the year 1968 at Mawson in the Antarctic.

Over the next two years I worked in research from antenna design to design of test equipment used in the testing of data transmission equipment (in those days it was all discrete component ie no LSI).

I attended night school to study computer programming, my calculator is more powerful than the school computer in 1970.

Moving back to Perth, my Wife’s home, in 1971 I started my new career in the computer industry.

From computer operator, to programmer, to maintenance programmer then to systems analyst.

Then I changed to micrographics enhancing the capability of the hardware and programming in machine code and writing software to control an Australian designed Micrographics camera that was sold worldwide.

I then started my own company and after a shaky start I branched into Record management. The company grew and soon had seven camera operator/data entry staff.
I now found myself not satisfied in a management role.
I new two people, one who had management skills and the other sales skills, so I convinced them to join the company.

This left me free to return to systems design where I had many large successful projects.

At age 65 I retired. This lasted less than 4 weeks I was bored, so I accepted a job managing an electronics shop. This re-activated my interest in electronics which had never really stopped as I had been working on a new designed audio amplifier and speaker system.

At age 70 I retired to concentrate on my research into my hobbies.
This now produced results. It included a concept I had designed back in the Valve era early 1960’s.

Now you have met me I will continue with my studies and will start to release some of the concepts and projects that I hope will be of interest.