What’s the deal with brands of Transformers and Upgrades?

If you are into amps you probably have heard lots of hype about different transformer brands.  There always seems to be a person who replaced their transformers and claim that they suddenly had a magical sound.  Sounds too good to be true…but is it?

Different transformers do differ in sound but if they are wound to the same specs the differences in tone are very minor.  However, many cheaper transformers sound less toneful because they are simply wound differently or made with cheaper materials. In some cases using a different transformer with different specs will give a player a sound they like better. To really understand what going on let’s go over the types of transformers and their function. By knowing this we can separate the hype from the truth.

The four types of Transformers:

Power Transformers:

Power transformers provide power to the amp.  Basically, the power transformer plugs into the wall voltage and turns that into the voltage your amp needs.  The power transformer is not in the signal path so it does not directly affect the sound, but it can affect the sound as a secondary effect. Two power transformers from different companies that have the same specs and materials operate exactly the same way and sound exactly the same! The main consideration is reliability.  A really well-built transformer will last longer and be reliable.

There are many companies that use cheap power transformers in lower end models---the transformers are poorly made or under spec'd.  The Fender Blues Junior is good example of one of these.   An under spec’d power transformer causes additional power supply sag since it cannot keep up with current draw of the power tubes at high volumes. This can make the low end of the amp mushy. Such under spec’d units are in more danger of blowing but they do have an affect on the tone. You do not want to skimp on a power transformer.

Another possibility is the use of an over spec’d power transformer. This ensures long life and good power regulation. By using a power transformer with ample power, you can improve an amp’s power supply’s regulation. This will introduce less sag but fortunately a designer can always add sag to an amp if more compression is needed

Chokes:

Some amps use a small inductive device called a choke.  It is not a transformer but looks like one.  A choke basically smooths out the power supply ripple to prevent hum. Again, these do not affect sound if the chokes are rated the same.  You want quality materials for reliability, but it is not in the signal path. 

There is a current trend of replacing a resistor in an amp without choke with a choke as a modification. This will change the feel since it’s likely to change the power supply’s impedance and the voltages. It might be perceived as step up in an amp with a poorly filtered power section since it would reduce hum. This same goal could easily be achieved with more capacitance or active regulation. Each approach will have its own sonic effect. I would not recommend adding a choke as universal mod. Certain amps will benefit and others will not. Many modern amps have eliminated chokes to reduce the possibility of radiated hum and because of advances in capacitor and semi-conductor technology that allow for quiet power supplies without chokes. In amps that have vintage amounts of filtering (often under filtered) a choke is very helpful.

Reverb Drivers:

In most amps that have a tube reverb have a reverb transformer or driver.   This transformer’s job is delivering the signal to the reverb tank. Since signal passes through it you want a high-quality transformer here.

Output Transformers:

This is the really important one. The output transformer basically transfers signal from the power tubes to your speaker. This is the most critical transformer in any amp and really makes a difference! Your whole sound passes through it. Quality is a must but there are other factors too.

Different transformer models are wound differently.  Typically, guitar amps have either straight winds or interleaved/sectionalized windings.  Straight winding is cheaper to manufacture and yield more distortion and less frequency response. Sectionalization or interleaving is a winding technique made to overcome those issues and give the transformer better frequency response. There are different styles of interleaved windings that also have different sounds. The more elaborate the interleaved windings are the more expensive the transformer will be to produce. Output transformers used in Hi-Fi applications have more elaborate winding scheme while guitar output transfomers need less frequency response and it less critical how much distortion they introduce.

Transformers can differ in type of material used in the laminations. Again, high quality materials are what you want. However, traditionally guitar amps use lower grade steel in comparison to hi-fi amps. Upgrading the transformer to one with better quality steel will increase the frequency response. Another factor is the thickeness of the laminations. In general, thinner laminations make for a better transformer than a transformer of the same size with thicker laminations.

Some folks will judge an amp by the size of the output transformer, but this is matter of taste.  Some designs sound better with a small output transformer while other sound better with larger transformers.  A larger output transformer will have broader frequency response puts out more power, and thusly have more headroom.  Larger output transformers are more expensive and traditionally the output transformers in guitar amps are undersized in comparison to hi-fi amps. You want to avoid tiny output transformer.

Output transformers have different primary impedances.  Tubes are fairly flexible so the specs on transformers can be too.  For example, a Deluxe Reverb uses a 6.6K primary impedance while a 5E3 Tweed Deluxe has an 8K.  These two winding impedances sound slightly different and produce differing amounts of output power if the same voltage is applied.

Finally, there is an ongoing debate about whether paper bobbins confer some tone advantage over modern nylon bobbins. In short, they do not. A bobbin is inert.

What about brands?

There are a few different brands with the best-known ones in US are Weber, Heyboer, Classic Tone, Hammond and Mercury Magnetics. There are also many manufacturers that do not have name brands. They make transformers for different builders or companies that retail transformers.

One important thing to note is that while transformers are not complex to manufacture but they must be designed correctly and have strict quality control. Materials can also differ. Chinese steel may not be same grade as US or Japanese made steels. An incorrectly designed transformers or loosely wound transformer will buzz. I’ve personally had to return whole batches of transformers to a well-known company for this issue.

Designing output transformers is not rocket science but is beyond the experience of many engineers. Many engineers are not experts in archaic tube audio. This is one of the reasons so many cheap output transformers don’t sound very good. They are not engineered well. This is where using an established brand is helpful—-those companies have engineers that know what they are doing. Another possibility is to use a vintage or high-quality transformer as a template for a company to copy—-most companies can do that.

Weber Transformers:

Weber transformers are made overseas (by which I mean China or elsewhere in far East for the guy who keeps emailing me about how I’m not being respectful of European made transformers which are usually very high quality) and are cheaper than the other brands. They actually sound fine to my ears but they do not appear to be as vintage correct (if that matters in your build).  They are built reasonably well for the price, there is wide selection, and have useful features. I have seen few power transformers fail over the years.   That said I think that higher end output and reverb driver transformers do sound a bit clearer and punchier. Overall, these are budget units.

Heyboer:

I have used lot of Heybeor Transformers and they are nice American made transformers.    They sound great.  Trainwreck (for part of their production) used them, and Dr. Z Amps use Heyboer’s as do many other high-end builders.   Since Heyboer does not retail transformers, the public usually gets them through a supplier. Weber, Tube Depot and Mojotone carry them.  They are well designed, and the folks over there really know what they are doing.

Hammond:

These Transformers are made in Canada and are of high quality.  I would not hesitate to purchase an amp with Hammond Transformers. They have been around a long time and were used in Traynor Amps which have reputation for reliability.  I have used them in my amps and find them to be very nice and extremely well built. The power transformers are especially useful with their high filament current ratings allowing for more tube swapping possibilities. They have a wide line up of models that has continued to expand to cover lots of vintage reproduction styles.

Classic Tone Transformers:

Note: Classic Tone and Marvel have gone out of business.

I often used Classic Tone Transformers in my builds. They sounded really good and are built very well. Unfortunately, they have gone out business.

Mercury Magnetics:

These are the one people talk about.  They are great transformers but function and sound no better than Classic Tones, Heyboer’s or Hammonds to my ears.   They use modern nylon bobbins which ensure long life. Many people like them, and sound is very good as is the quality. They also offer upgraded versions of classic amp transformers adding additional capabilities or upgrading the steel cores.  At 2 to 5 times the price you will pay a premium for them, but you are paying for their expertise. They are great for replacing a hard-to-find models.  I use Mercury Magnetics upon request or to replace a difficult to find transformer because Mercury has a wide selection of odd ball vintage replacements.  

Others:

There are other transformer makers. Pacific Transformers makes great transformers for OEMs and supplied Trainwreck Amps during part of their production. There are other out there too doing good work. My rule of thumb is that US made, Canadian, or European brands are generally pretty good but overseas transformers are better avoided unless they have been designed and commissioned by a well-known company or unless the company producing them has specialization in audio transformers.

The plants in Mexico, Taiwan, China and other places can do good work provided the company commissioning the transformer specifies high quality materials and takes an interest in the engineering. The rub is that there are manufacturers from those regions that make cheap low-quality products to fill the demand for low-cost parts. These companies make them all look bad. Often those low quality of parts are what is found in production line amps. Only some of these companies have expertise in audio transformers. A transformer should not be dismissed purely on its place of manufacture.

Over time more domestic suppliers are likely start manufacturing overseas and overseas manufacturers are likely to displace some domestic manufacturers as their brand recognition improves. This is happening already. Right now, many transformer companies that have factories in multiple countries and the quality is similar in their US and overseas made models.

The Truth:

If you judge an amp simply by the brand of transformers in it, you are doing yourself a disservice.  Transformers are important to tone but not because of the brand name. Instead, is it because of the choice of transformers in relation to the circuit design and quality and design of transformer.  Transformers are simple devices to make, and many companies make quality transformers.  Quality is very important, but hype is only a shelter for the under-educated or under experienced.

An amp designer with the proper knowledge and experience will not have to rely on brand names and hype to get great tone.  A good amp designer can make great amp with many different brands of transformers since they will use judicious transformer selection (specs, size, quality etc.)  and have the ability to tweak the circuit to sound it's best.  No matter what brand of transformers an amp has if an amp has a poorly design circuit it will sound bad. 

   If you are considering changing transformers as an upgrade, you should consult the schematic and know why or if the upgrade is going to achieve your goals. If you cannot properly access that question, ask for help from an expert.  Do not rely on the sample size of one experiment on internet forums for enlightenment or adverts from transformer companies. There are cases where changing transformer makes sense and cases that it does not. In many cases changes elsewhere in the circuit are all that are needed.

Note on copying old designs:

Much of the amp makers (my amps included) are making amps that are similar to famous vintage models. Unfortunately, with the advent of magazines, YouTube channels, and forums novices assume and “experts” reenforce these various models are “magical” and the parts in them “perfect”. This is far from true. In regard to transformers Marshall, Fender, and other sometimes used low quality transformers and there is wide variation in quality among their products. Some vintage transformers are great and other do not sound very good. All these vintage parts do have a tone to them, but the assessment of the tone should be seen as subjective. Often the lower grade materials mean less clarity and frequency response. Sometimes this is desirable other times it holds an amp back. Sometimes using a better transformer than what a vintage amp had is right way to go.