Want Big Bass? Deliver Big CURRENT ....

or Layman Follows the River to the Sea

Let's assume:  a). You are somewhat inexperienced in terms of electronics; b). Your amplifier is a weakling, with a very lousy bass performance;  c). You are an intelligent person;  d). You know how to follow the thread to the end, or how to follow the River to the Sea;

e). You are determined to do something about that inadequate bass performance. If all of the above is True / True / True / True / True,... then this article is for YOU. 

I want to tell you a story of a very basic amplifier, of times that are long gone and past: the times of my youth, times when I had limited financial means, but at the same time, a big heart for BIG sound. 
An amplifier, that after 4 years of usage, I sold for 3 times the price as compared to the original purchase price, and on top of that, shortly after the transaction, I got a surprise present from the purchasing guy - in the form of a crate of beer cans. 

As a student, I purchased a very basic piece of equipment, a TECHNICS SU-500 amplifier, for the price of present day peanuts.   Obviously, I got what I paid for - a sound that resembles the price tag. 
Please do not understand me wrong - in itself - this was not a "bad unit" - it was a budget product providing a budget sound. 

Now, I was very unhappy with what I heard from this unit - from the very outset, from the very beginning. 
I wanted to modify that amplifier in some way, ... but there was a small problem: 
a).  I was totally green grass / beginner / inexperienced in terms of electronics. 
b). My amplifier was obviously a weakling, with very lousy bass performance. 
c). I think that I had a fair degree of technical imagination 

.. So I decided to do something about it. 

Now, in those times, they suppliers of amplifiers did not readily and happily provide you with complete schematics of what you are purchasing, so I had to "imagine" how the internals of the amplifier look like. 
I tried to "imagine" where the high currents flow, because it is the high currents that I have intuitively associated with the big lung slamming bass that I was lacking. 
I adopted a common sense derived strategy of following the thread to the end, or .... to follow the River to the Sea. 
The big current is supposed to flow to the speakers. But ... Where does the big current come from ?  What path does it follow ? 

This is the schematic that I drew based upon a brief mental inspection of what "might" be the insides of that device. 

It just so happens, that this (oversimplified!)  schematic is universal, and valid in 99% of the cases .. even today.    Now .... Look closely at this schematic.   
It consists of the yellow area, full of some fuzzy-buzzy electronics, which are totally complex,  totally uncomprehendable,  ... and totally irrelevant for the LAYMAN. 
So let's just imagine, that all that complex yellow area electronics - that they are a "black box"  (actually, a yellow box), that only provides "control" to the executive power transistors  .. and that we do not fight with the things that are beyond our comprehension and out of our control. Let's just imagine that all this yellow stuff is as good as you can get - at this specific price point and price tag.

Now, we shall focus on "all the rest"  (pun intended) .... being the "THING" that constitutes the two circuits providing the current that actually flows through my speaker. 
And what do we see ? 

a). We see a symmetrical voltage supply (in most of the cases).  The common connection - is in the middle.  I represented this symmetrical supply as two batteries, for the sake of simplicity.  But we do know that there is some power supply circuits behind those simple symbols.  
b). We see two serial pass elements, transistors (or transistors embedded within integrated power amplifier IC's) that control the flow of the current from the "top circuit"  ... the "plus" current, and/or from the "bottom circuit" ... or the "minus" current. 

{{ B.T.W.  I   ***AM*** presenting very complex issues in a very trivial and simplified fashion.  But I am doing so on purpose }}

c).  If the current flowing in the "upper circle" is equal to the current flowing through the "lower circle" ... then, from the speaker's point of view - nothing is happening.  The speaker does NOT see any net current whatsoever, as the two currents compensate each other. 
This is the case when no music is playing and we have total silence. 

d). Any imbalance of the amount of conduction between the upper and lower circle, or specifically, it's pass element (transistor Q1, Q2), results in a "net imbalance" within the two loops, 
and hence, as a result, a net current flows through the speaker, one way or the other.   ( Rock and Roll ! ). 

All this can be derived from plain common sense and a brief inspection of at least a few basic amplifier topologies. 

OK.   Now, look at that picture AGAIN.   Something does not "click".  And guess what ?    
What I am lacking there is the SHEER BRUTAL FORCE of the CROSS SECTIONAL AREA of those feeble little wires that are presented as above. 

The following, as below, is what I would find to be much more satisfactory: 

Actually, this picture is also not quite OK, if you think about it.   
Have a closer look ... What you see here are two independent batteries. 
But ...
What I am lacking here are two pocket sized nuclear power plants. ... Or something similar.   
But we will get to that .... 

Before I get back to the pocket sized nuclear power plants issue ... let me ponder a little about the problem of GEOGRAPHICAL DISPERSION. 

To put this into perspective.   Imagine that you have a very expensive, Hiend-Audio Amplifier, consisting of 4 boxes. A stereo set of split chassis mono-blocks. 
They are so much super hyper Hiend-Audio stuff, that they actually come in separate boxes:  a). the power supply box, and b). the signal processing box.

Now,  imagine the following setup:  
a).  The power supply boxes of your super hyper Hiend Audio Mono-blocks are set up ... in Alaska. 
b).  The signal boxes of your super hyper Hiend Audio Mono-blocks are set up .... in Texas. 

{{ c).  .... not to mention the speakers being set up yet elsewhere, ... but that is the subject of a totally different article ... }}

Now, after you connect all the cabling .... do you get that "intuitive feeling", that such a setup might not perform to the fullest extent of it's capability ? 

I do. 

The following picture presents the geography of your amplifier.   
Alaska - is on the right hand side.   
Texas - is on the left hand side. 
The speaker ... is in the middle. 

I hope you agree that something "does not click" in this geography / topology. 
I't simply can not perform to the best of it's capability. 

Now, ... What if we were to establish a *** LOCAL BRANCH OFFICE ***, or    REPRESENTATIVE office, of our ALASKA power supply in Texas ? 
Here, in Texas ? See picture below. 

But what's more ... what if we anticipate that this branch office in TEXAS will enjoy such a lot of traffic, so much demand and sooooo many customers, 
that we purposefully oversize this office ... to such a seemingly absurd extent, that this branch office in TEXAS is actually BIGGER than the headquarters in Alaska ? 

See picture below. 

There is also one more issue to cover here.  
Even if our branch office in TEXAS has a very big storage room for goods to be delivered to the local customers in TEXAS,
 ... it will not do us any good, if we have inefficient logistics between the headquarters in Alaska and the storage in TEXAS. 

So we need to equip ourselves with some decent logistics, with a lot of trucks, capable of handling the FLOW of goods in BIG QUANTITIES. 

Only then, with an adequately sized storage, and with an efficient logistics throughput capability, can we successfully  DELIVER, each and every time that the DEMAND ARISES.  
Irrespective of the SIZE of the DEMAND.  

The local storage should be as close as possible to the final customer, being the respective pin of the power transistor, from the one side, and the minus terminal of the speaker, on the other side. 
Please also bear in mind that your enterprise is selling TWO kinds of products ...   the PLUSES  and the MINUSES.   You need to build adequate local storage capability for each of them separately. 
The local storage capacitors that I used were of some very extravagant, full of excess CAPACITY, up to the limits of common sense, and they were soldered DIRECTLY to the pins of my customers. 
Actually, my storage as installed in the local branch was THREE times BIGGER than that in the headquarters.   {{ poor old rectifier diodes ! }}. 

Obviously, you can and should add some high frequency polypropylene bypass capacitors to those storage monsters, so as to enhance the performance throughout the whole of the frequency band. A minor detail, but a nice one. 

But what about the empty trucks ?   They obviously need to travel back to the ALASKA headquarters.   
What I am getting at is that ALL of the three logistic routes: the PLUS delivery, the MINUS delivery, and the EMPTY TRUCKS return paths .... They all need to be of adequate cross section.
In my amplifier, I followed the printed circuit board tracks.  I followed the rivers to the sea, whereby the sea - being the power supply. Then, I took a wire from a Russian KAMAZ truck motor starter coil (as cheaply obtained from a local junkyard) and soldered such wire on top of those feeble pcb tracks.  
The wires had a diameter of probably 3 millimeters and were made of some very soft and easily bendable copper   (high purity, military grade ?). 

All of this tweaking was a result of a layman's, very naive analysis of the geography, the logistics and the storage facilities that were available in a budget class amplifier. 

The results were ... interesting.  Both the sonics, as well as financially.
Sonics: That bass slam - simply blew my boots off ! 
Financials:  I sold that SU-500 unit, as a "second hand", after 5 years of use,  for a price that was three times higher than the original "brand new" purchase price. 

Best Regards, and 

Happy Soldering !



P.S. The article as above contains certain mental shortcuts and purposeful (and brutal) simplifications, so as to better "visualize" certain concepts, problems and issues. In my humble opinion, this simplified representation of physical phenomena is cruel, but justified, for the sake of clarity and keeping it "short". This is not an attempt to provide classes on the theory of entry level electronics, but a layman belletristic visualization of some of the effects arising thereof, and how we can get some "action" and quick results without the boring maths. 
Alas, it always is a good thing to read a book or two on electronics and stuff, just to be certain that you know what you are soldering. Have Fun !  Oh, and PLEASE ! ... do not get your self electrocuted while you are at it.  Common sense - applies.  Specific general safety guidelines can be found on my website.

Matej Isak. Mono and Stereo ultra high end audio magazine. All rights reserved. 2006-2013. www.monoandstereo.com. ..:: None of the original text, pictures, that were taken by me, links or my original files can be re-printed or used in any way without prior permission! ::..