ReMusic interviews Alberto Guerra from AGD Production


Today we will be interviewing Alberto Guerra, CEO of AGD Production, not so much on his recent and incredible exploits in the world of modern audio amplifiers, but more on his precise and documented experience in the power semiconductor sector. We have already presented his products here and here, the AGD Vivace and The Audion. Let’s remember briefly Alberto’s competence in his CV, updated here, and lets start with the questions pertinent to the topic of this interview, which is the following: why has it become a fact that in the not-so-distant-future of the audio amplification field there are only D class amps or something superior?


Prezzo Sanken 2SA1295



The price, at the time of this interview, for a classic bipolar transistor – BJT, PNP, Sanken 2SA1295, now out of production.


Question: Alberto, from some time now I have been hearing directly from the manufacturers of Audio amps, they have a really hard time finding “classic” power transistors components. For example, the bipolar transistors made by Sanken. Can you confirm this? What can you tell us about this?

Alberto Guerra: All electronic components have well-defined manufacturing-life. Technological development and competition are the factors that guide the decisions that companies make on the economic convenience of maintaining a product line, its availability, and obviously, its price.

The “Golden Age” of the bipolar components was over 30 years ago and the manufacturing technologies (processes and methods) of these products are immensely challenging to maintain, in terms of infrastructure that is now obsolete and the know-how of engineers and technicians that is no longer there. Not to mention the material and silicon wafer sizes and material specs, that are no longer available. All in all, the whole supply chain of these products becomes more and more difficult to sustain considering a great reduction in demand too.




A bipolar transistor not originally intended for audio, 2N3055, but with its complementary MJ2955 made possible the boom of the Hi-Fi market – also used in the integrated amplifier NAD 3020.


Question: The global market makes us believe that we can have any product produced in this modern age at any time. Even now, you can find replicas of turntables, vintage radios, and tape recorders. Some manufactures are even producing new VCRs. Is this possible with components like final power transistors or MOSFET?

Guerra: Obviously, it is not possible for semiconductor components. The infrastructure necessary to keep the manufacturing of any specific semiconductor cannot be maintained or reproduced once its disassembled. So once the resources are expended, there will not be a possibility to reopen the production.


Question: Interesting. What happens then when we see a “replica”, or a remake, or a revisiting of a product years or decades later? Are we seeing a new iteration, as in a new circuit in terms of design and components but the same end-product as the original? Or, worse, in your technical opinion in this sector, are we left with the only similarity in the product being the name?

Guerra: It depends; there are a few possibilities. Sometimes there exists a legitimacy in a product because of the well-known brand that backs up its origin. Other times-more often than not- only the aesthetic part of the product is kept true to the original.

Therefore, we must make a distinction.

For example, in the case of the discrete semiconductors it is almost impossible to find original components after 30- or 40-years production is stopped. Therefore, if the circuit gets duplicated, although identical in terms of electric schematic, it can’t help but be different in terms of its complete characteristics. I say “different” without stating a quantitative amount because sometimes the new components that are used can definitely be much better than the products with the obsolete technologies of decades past. In any case, a copy is a copy and it can never have the same value as the original product.



Fake 2N3055


Hunting for vintage components has its risks: here a fake 2N3055.


Question: We are used to thinking that vacuum-tubes, the NOS one for example, have virtually the same characteristics and offer the same performances as when they were first made: can the same be said of solid-state components manufactured decades ago?

Guerra: This is certainly true for semiconductors, but the effects of storage in humid or corrosive environments can have nefarious effects on their practical usage. For example, the metalized parts suffer from corrosion, the plastic containers can become delaminated from temperature changes, consequentially the hermeticity of the product can be compromised. When this happens, the contamination and corrosion of the semiconductor chip inside, is practically guaranteed and so its function is compromised as well as its reliability.

However, if the components are maintained correctly, certainly the original characteristics will not be altered at the time of use. The life of a semiconductor, like I said, is superior to almost any other electro-mechanical product. We are talking centuries…


Question: So, transistors behave differently if they are really used rather than just stored? Certainly, there exists a classic mortality curve, for example.

Guerra: Yes, obviously, if they were used and if they are past the infant-mortality part of the classic “bath-tub” life curve, the component will be operating in the plateau of the curve and in complete stability. This time is in fact measured in decades, at the least.


2SK175 Hitachi

Invented by Bell Labs, here is an example of a MOSFET, the 2SK175 and its pair 2SJ50 developed by Hitachi mainly for Audio. They were used in some vintage products like the amps from the New Zealand Perreaux.


Question: Are there still companies, factories, or assembly lines out there for this type of component?

Guerra: In contrast to the vacuum-tubes, for which in the 1970’s literally all of the production lines were transferred from western countries to Russia, China and many other in the east and far-east, this did not happen for many semiconductor components, like the bipolar ones. In their case, the costs of transferring the production line did not make economic sense. And moreover, once production was dismantled, there was no continuity in the supply chain. ON Semiconductor and Sanken for example, still have in there catalog some decades-old parts, but their numbers are very minimal and the famous products of Motorola, ON Semiconductor, Sanken, Sanyo, or Toshiba are now literally extinct.


Question: So, what happens to the sound of these amps if we replace the old transistors with components, since that is all we have? For example, does a class A or AB manufactured now, behave differently than the original of 40 years ago made with the old components? This argument is valid for the repairs as well.

Guerra: The sound is a result of the effect of many components, active – semiconductors, IC etc. – and passive – resistors, capacitors etc. Today the material science is extremely more advanced compared to the one of decades ago. If a design or redesign of an old project takes advantage of that, the result can only be positive.

Unfortunately, however, though this may be true for most passive components like capacitors and resistors, is not necessarily true for active components.

This may be the case if those active components are substituted with new parts with characteristics intended by the manufacturer to operate in switching rather than in linear mode or if they are replaced with other part number with worsen thermal performance – i.e. due to a different package metal case to plastic case. So, we need to always understand which compromises the designer has chosen in order to utilize what is available.



12AT7 RCA Black Plate


The NOS or NIB valves, Now Old Stock or New in Box are not by definition forever available, here is one of the most appreciated ones, the 12AT7 RCA Black Plate.


Question: Vacuum-tubes have made a comeback and will stay in a niche of a niche market. Bipolar transistors and many vintage MOSFET are no longer manufactured- they are very scarce if not already disappearing- nor will they be produced again. What will be left of the past or what will be left for the future in the dispositive/component field of audio amplification?

Guerra: You cannot stop innovation and I am more than convinced that the impact of the new technologies in the field of audio will be nothing but positive. The developments in materials, in power-semiconductor and in integrated circuit technologies can only bring more improvements and substantially continue the mission of reproducing an even more realistic sound message.


Question: So, is Class-D practically inevitable? Is that all that is left, like Highlander? Or will be go beyond?

Guerra: I think that Class-D, with its topographical variations, will be more and more dominant, maybe because it is inherently better in linearity, in power-density, and, let’s not forget, in its impact on the power losses, aka efficiency. Moreover, I think that the reduction in size of the amp systems, due in great part to the elimination of heatsinks and the ability to use more advanced power supplies, will give more freedom to industrial designers to search for products with alternative designs.


Guerra: I think that Class-D, with its topographical variations, will be more and more dominant, maybe because it is inherently better in linearity, in power-density, and, let’s not forget, in its impact on the power losses, aka efficiency. Moreover, I think that the reduction in size of the amp systems, due in great part to the elimination of heatsinks and the ability to use more advanced power supplies, will give more freedom to industrial designers to search for products with alternative designs.

Guerra: Maybe we need to urge them to use a Q-tip? I am kidding, obviously, but not too much. What can I say: personally, I have never understood this biased “fundamentalist” argument. Technology and science are not a dogma and to think that we can remain tied to systems with 15% efficiency and with an operating life of hundreds of hours is not a sustainable choice. The problem is not in the absence of “soul” in a product, but more in the ability of the designer to create an object that sounds good, never mind the topology, to understand the elements that influence the sound quality and correctly interpreting them scientifically, physically, electronically and not in the esoteric/miraculous sense.

Either you have skills, or you do not.

I suggest that those self-proclaimed purists not hide behind a dogma when with a little humility, curiosity, and consideration, one can make some illuminated discoveries in the field of audio.



For further info: to AGD Production website

by Giuseppe
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