Creating a Cornell Amp

 

 


When we see an object for the first time, we look at it in its entirety, but most things can be broken down into more than is immediately obvious. Inside every amplifier are various electrical components, all intended to make the amp work as it should and as has been promised. So, why do they vary so much in price? Needless to say, anything to which the descriptor "hand-built" or "handmade" is attached, will always cost more, but there is no mystery here, or rather, there shouldn't be.

The following is intended to explain what the essence of a Cornell Amp is, and how we make the decisions we do relating to quality and cost. There is no mystique. The simple answer is that we care very much about the quality of our product and take a pride in producing the best amp possible while maintaining realistic costs.


Inspiration and Idea

Having a problem-solving type of mind, I have always been able to produce ideas or suggestions on just about any practical subject. The explanation for this is, in part, because I like to think myself to sleep at night; in my opinion, counting sheep is for those with little imagination! In fact, most of my best ideas have come from dreams. Having said that though, input from friends and existing, proven designs are most important. Of course, my experience of custom designed amps, built over many years, always plays a major part in the formation of new ideas, and it is now rare for me to be asked for or about something that I haven't done before.

Perhaps I am making this sound easy, but I have spent all of my working life as an electronics engineer. Due to ill health, and preferring to play guitar than do my homework, I didn't achieve well at school and so counted myself fortunate to be accepted into an electronics apprenticeship. This was my introduction to the valve, how it works, and what it can do, and was when I built my first amp. What this represents is nearly 40 years of education in and experience of the production of tone. So, it would be a poor show indeed if I could not do what I do.


Design


So, the beginning of amp creation is through inspiration and idea, but these are useless on their own; to put any design into practice you must first understand the physics involved. During this part of the creation process, I often refer to my battered copy of "The Radio Designer's Handbook" by Langford Smith to help me. However, I must admit that trial and error, and the experience of years of experimentation are probably my most common methods of resolving design problems.

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Design is also related to cost and this is where the first mistake or confusion can easily be made. Do we build to a price or to a specification? No-one ever asks me to create an amp for a certain price, what I am presented with is always a rough outline spec. Generally, guitarists know what the end result is to be, that is, what they want to amp to do; the problem for me is how to achieve it.

When I was part of the design team for "Dallas Arbiter", very often the design request for a new product would come from the sales management department, but this was always followed with a ceiling cost. Being an engineer, it was always difficult for me to understand how cost could be brought into the equation. I felt that the idea was to be designed and developed and that that was where my job ended, not understanding that to maximise sales and profit was the major goal of my employer. Now I am able to decide what I want to do, and I revert back to what I enjoy - the design and development of the ultimate amplifier without consideration of cost. However, I do not intend to build just one amplifier in the hope that someone will understand it and want to buy it. There is little point in trying to create the ultimate amp unless it fulfills the customer's requirements, and so practical considerations must form a part of the creation process.


Components


A part of my commitment to what I do is that I want my customers and potential customers to understand that I create high quality amplifiers. There should be little need to justify which components are used, but our customers have the right to know that we promote good pratice and that the components we use have a good pedigree in quality and reliability.

Unexplained descriptions, such as "hand-wound transformers," "powder-coated chassis," "highest quality components", to justify high cost are confusing and unreliable. Just these three statements explain nothing about the quality of the amplifier, in fact, I would question them closely. For example, in the case of powder-coat painting, the chassis could be positively dangerous because the paint insulates the components from the essential earth connection to the chassis. Cornell Amplifiers stand on their own merits in both quality and design, but we ask you to question everything. Should you see a statement referring to quality, question it, if you do not understand it call us and we will explain the facts and the myths.

Our policy is that every component must be determined by its use and its reliability, not by its cost. This is where we first meet the need for specifications; a component manufacturer's spec should not always be taken as fact. For this reason, we decide and dictate all component parameters and install a policy of fitness for purpose. (See component specifications below.)

We would much prefer to buy all components in the UK, but in order to maintain our high standards, many of the components we use are sourced from abroad. Wherever possible, we make or specify our own; chassis, cabinets and transformers are made in England to our own rigorous specifications. Even the handles on our cabinets are made from leather at a local saddlery. We buy valve bases from Japan, potentualometers, capacitors, resistors, and coverings from the USA and Canada.

Valves can be problematic, thus we have tried various manufacturers and as a result we have made own own testing gear to check valve quality. We carry out our own matching of output valves during the final test, and re-test each amplifier after a final soak test.

Carbon composite resistors are no longer generally available, yet we use them throughout our range of products. We found that there was a marked difference in tone between these and any other modern alternative. It is true that metal film, metal oxide, and high stability resistors are an improvement on the old carbon resistors, but the sweetness of tone has been lost with those improvements. To improve the standard of the old carbon composite resistors and make them more reliable, we have adopted the Ministry of Defence practice of conformal coating. The circuit design is laid out on a component board using eyelets and turret tags, the components are then mechanically formed and soldered. The conformal coating seals the components and soldered joints preventing the effects of vibration and reducing moisture absorption which causes noise and carbon breakdown. The board really is built like a tank, because this is exactly how tanks are built!


Board Layout


The essence of the amp is in the circuit design, and when the components for it have been established, it is an unwavering rule that ALL Cornell Amplifiers will have a component board layout as opposed to the more frequently used tag strips. Again, the board is made to our own specification using eyelets and turret tags. I believe that this is the best way to transform the circuit design into reality. The major benefits are control of the positioning of sensitive components and control of the earthing relating to valve characteristics, which enables uniformity of components and their protection by using conformal coating.


Unique Design Features


A passion for tone places high demands on all areas of the creation of a Cornell Amp, and this has led to the design of unique features throughout our amps. For example, our transformers, stainless steel chassis and brass cabinet fittings are all specially designed. However, these are just a few of the unique features, and we have a number of tone circuit designs developed over the years which we would prefer to keep to ourselves.


Prototype


It would be nice to be able to say that we get it right first time, but sometimes it is not until we have built an amp that we can see how to improve it. Therefore, the prototype is an important part of the design and development process. It is at this stage that the circuit design is finalised and the overall tone established.

Testing the various speakers and matching the tone characteristic of the amp to the speaker can only be done with the assistance of a number of guitarists. To design and develop an amplifier involves not just the "archetypical" electronics engineer, but also a guitarist's "ear". Having said that I have found it unsatisfactory to accept any single opinon, which could result in a single tone in a range of amplifiers. All sounding the same, that would suit just one guitarist or musical genre. We offer a variety of amplifiers with a range of tones which we feel can only be produced through good engineering skills and several guitarists. Most importantly every Cornell Amp is a product of a long history of designs established over the years and used by a world of guitarists.


Assembly proceedure


Making a single amplifier can be a joy, being involved from the beginning to the end is very rewarding. However, when the time comes to build ten or even 100, changes occur and gremlins arrive and the end result is often something that sounds completely different to the original tone. In order to avoid these problems, we use an assembly procedure that puts each product through a number of assembly stages. Each stage includes instructions on which component is to be used, how to assemble it and even which type and size of screw, nut, bolt and washer. These stages may include an inspection and/or test process to maintain not just the quality but also to make sure that each amplifier is the same in its visual and tone characteristics.


Testing


With such a rigorous assembly procedure, we find that each Cornell Amplifier works first time in the majority of cases, however at the testing stage we measure and record the voltage and signal at various points of the amplifier. Valves have a wide range of parameters, so we select valves for gain and noise and these are used in sensitive areas of the pre-amp section of the amplifier. For the output valve stage, we have made our own valve tester which does not only test the valve but also matches the parameters to be used in amplifiers where doublets or quadlets of valves are needed. Each amplifier is also tested on a guitar and then re-tested after three to four hours of soak testing.

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Valves testing and matching

Specification


We do not intend to provide a detailed specification for each component, however a general list of some of them will enable an easy comparison with other amps. Should there be anything that you do not understand please ask us. We are also happy to supply any preferred component specification at your own request. Along with the carbon composite resistors in our customised amps, we also use Orange Drop capacitors, Mallory capacitors, silver-plated wire, 24mm pots or just about anything you request. We have special transformer designs and the lingo to match, if you have the imagination, we have the know-how
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Chassis

Our chassis are made of 16 gauge stainless steel with each corner welded. Stainless steel is the ultmate material to use for a chassis because of its obvious non-corrosive and rust-free characteristics. Stainless steel is also non-magnetic and does not transfer AC hum through the chassis. Our attention to detail extends to the polished and etched stainless steel front panels on some models.

Transformers

Every mans transformer is a drop-through, high efficiency dual primary type with 115 and 230 volt wiring suitable for use worldwide. Output transformers include interleaved windings on paper. Custom designs include features such as cross-coupling, ultra-linear, cathode or grid feedback tappings and independent anode windings.

Component board

SRPB drilled and riveted with eyelets and Harwin turret tags. Components are sealed with conformal coating.

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Capacitors

Massive 220uf and 330uf Samwha decoupling capacitors ensuring minium hum levels. Other decoupling capacitors used include Sprague and Mallory. Signal couplings include Sprague Orange Drop and Mallory.

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Resistors

Our high power resistors are made of Vitreous enamel, cement or metal oxide. Signal resistors strictly 1/2 watt carbon composite.

Potentualometers

We use strictly Mouser, USA or Precision Electronic Components from Canada.

Switches
   
Arcolectric supply all toggle switches for Cornell Amps.

Reverb

The reverb in Cornell Amps is transformer/valve driven made by Sound Enhancement, their long spring provides lush reverb.

Jack Sockets

Supplied by Cliff Electronics or Switchcraft.

General Wiring

PVC tinned steel wire, silicon rubber-coated steel, multi-core single and twin screened signal wire, silicone rubber-coated silver wire (used in our custom designed amps). Mostly supplied by Belden and Alpha.

Speakers

Jensen, Tone Tubby, Celestion; we also modify Celestion speakers for a rounder tone.

Cabinet

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Jointed pine with Russian birch ply baffle or all plywood. Coverings of various styles and types including Classic Tweed, embossed leather or rexine. Various grill cloths including basketweave and salt & pepper type. Metal or leather corners. Leather handle with brass or stainless steel brackets. Brass or stainless steel grill vents. Rubber feet. Custom designs in hardwood are also available.

 

 

Customer Service

We are at the end of a phone, call us and you will not be greeted by an automated answering system or a rehearsed fob off. We will do our best to advise you on what is best for your needs. Cornell Amplifiers range from good quality at sensible prices, to our customised service for those who want something special.

Our customer service policy is very simple: if you like us, you will come back. We value your opinion on our products and are always happy to listen to your comments because this may be the start of the development of our next project.

 

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