This site originates from my desire to propose amps and preamps of quality, using, as each case indicates, the patterns  and the technology which bring out the best in musical quality.

For example, single-ended circuits give a more detailed sound, along with greater precision and focus, while push-pull circuits give greater bass control and an overall scene which is more realistic.

This is why I am of the opinion that the first choice is better for driving the higher frequencies while the second is better for the lower ones, although not everyone opts for bi-amplification.

Even among active components, as you probably well know, some types give certain qualities while others give different qualities. In the end  the types of components plus the types of patterns render variegated solutions.

Another important factor could be defined based on the final power stage;

  1. final stage as a voltage generator;

  2. final stage as a current generator

These two express different and often complementary dynamic behaviour, and so, of course, the sound they produce is different.

The bottom line is that we can obtain


better energy production (Type A) for high frequencies, as if there were more extension


better energy production (Type B) for low frequencies, to permit greater sound production.

 In any case, it must be observed that nowadays virtually 100% of the power amps on the market are structured with the final power stage being of the A Type. This means that very often amplifiersócommercial and nonóare seen having 20 or 30 devices per channel, trying to better their low-frequency characteristics.  But then, besides higher costs and other technical problems for the designer, the focus and detail of the higher frequencies actually diminish because of the multiple paths the signal is forced to follow.  In fact, when a signal is divided between different devices and has to follow different pathways (and therefore differing lengths), and when the various parts of the signal do not terminate at the same time or with the same phase, the harmonic structure of the original signal is hopelessly lost proportionally as the frequency rises; the sound becomes less precise and focused. This is why so many audiophiles maintain that a 2A3 single-plate has a more crystalline and defined sound than a 2A3 double-plate.  And this is just one example. It is not by chance that the tubes judged to be highest in quality are all single-plate (45,  71,  AD1,  VT25,  etc.).


My choice

So, after this brief introduction you see the reasons behind my working philosophy, which will always be to

  1.  use single-ended circuits whenever possible;

  2.  use one device for single-ended circuits or one couple when it is necessary to use a push-pull circuit;

  3.  use currency generators in final stage;

  4.  limit the number of amplification stages (in the A35 there is only one);

  5.  use direct couplings whenever possible;

  6.  use Audio-grade components;

  7.  use inductive/capacitive filters in the feeders.


My idea is that the sound of an amp is influenced not only by the types of active devices used, but also by two other factors:


the configuration of the circuit,


the characteristics of the single components used.

The first determines overall behaviour, while the second defines accuracy and detail.  Itís obvious that both must be carefully evaluated to obtain the best performance.


 My reasoning

Here is a brief list of the criteria which guided me in my selections:



Transconductance amp as final power stage

The reasons for this choice are based on personal experimentation.  For example, the structure of the transconductance power stage permits better interaction with the woofers and heightens their potential (I donít want to go into detail here, but those interested can go to the link Ultrasound).

The basses are compact and full, as those you get from a tube amp, but with an energy and control (damping factor)  impossible to obtain with a tube amp. The mid-levels are natural-sounding and projected into the foreground as can be found in few other solid-state electronics. The high tones are delicately present though never excessive, rendering listening a pleasing and relaxing experience. With the right speakers, an excellent balance in tone is manifest, together with a first-class drive and energy, plus a scenario of characteristics one would never expect.

It handles voices and solo instruments with sensitivity meticulousness, like a tube amp, but with more recent types of music it pounces with vigor, command, and an emotional involvement unknown to tube or semi-conductor amps with output voltage followers.



Active devices

An amp with a transconductance output device represents, to me, the best alternative, because tubes have limits here due to the high output impedance and the low level of current .To be specific, for a singolo guadagno di stadio/single stage gain like the A35, the choice has fallen to the MOSFET, which behaves outstandingly as a transconductance amp, having both a low output impedance and the capacity to manage elevated currents.


To potentiate the properties of symmetry and overall balance, I choose not to use complementary devices (which are complementary only in theory)in favour of exactly identical devices (having the same polarity).

And lastly, for the abovementioned reasons, I opt to use a single couple of devices that allow the erogation of 35 effective watts,  at an 8ohm load, and which function in true class A. This is more than enough power for domestic environments, when one takes into consideration the unique function of the output stage in relation to the scenario and the dynamics it is able to furnish.



Phase shifter

The phase shifter Iíve chosen is a transformer because it is absolutely the most balanced when itís well made.  The one I use is custom-constructed by a noted Italian constructor, and was originally personally supervised by myself. It reaches the desired result of excellence.  It is made of high quality grade materials and boasts particular winding techniques specifically developed to avoid introducing significant limitations and to exalt the advantages of this choice, namely;

  1. galvanic separation.  This feature heightens dependability;

  2. the removal of the ground loop, and;

  3. the possibility of piloting the final with both balanced and unbalanced signals.

This choice, when added to the precedent one regarding the use of devices having the same polarity, allows the realization of the most symmetrical and balanced configuration imaginable.




The overall sound quality of an amp depends on the quality of every element, active or passive, inserted in the circuit (as someone has said, the sum of all the components is heard, even the power cable!).  Therefore, besides the aforementioned transformer, the other passive elements I use have been chosen with great care, while the active devices , because of my choice to avoid using negative feedback, are selected with more than great cure; in fact they are for all intents and purposes, identical. 

Since the axiom demonstrates the fact that every component really IS heard, Iíve chosen to minimize them.

So, relative to itís stature, this amp very probably incorporates the fewest components, active and passive, notwithstanding the necessary presence of the phase shifter.



Power supply

In the amplification sector of the A35, there are no condensers on the pathway of the signal. However, unless a battery is used, in all amplifiers the audio signal circulates in the power supply capacitors , even in those with direct coupling.  In the A35, the capacitors are of the Audiograde type.  Besides this, several inductances have been incorporated, which give a series of advantages, including;

  1. a superior grade of clamping;

  2. the reduction of the necessary overall capacity, which permits the use of higher performance capacitors,

  3. the separation of the audio frequencies from the spikes generated by the rectification or from the various disturbances coming from the electrical grid.

 The structure is, however, dual-mono, so each channel has itís own power supply, including transformer. Moreover, to avoid any type of interaction with the audio circuits, the power supplies are in a separate housing and isolated.

 To sum up, the guidelines used in the realization of the A35 were the sound and the listeners, so great attention has been paid to each and every aspect so that the best  overall sound production could be achieved.