The Interview

Bonne Dittmar [Bonner Dittmar]

L.V. - Maybe you would like to talk about the design of the 'Alto' main amplifier. B.D. - It has a unique circuit design for the amplification stage and it has also a very high tech power supply. There are a lot of regulators to keep all the voltages very stable.
L.V. - Is the circuit a secret, or can you be more specific about it? Why don't you use a switching power supply? Although it is still not widely used in the Hi End, a few manufacturers are doing it. Would you call the amp a fully regulated design?
B.D. - A switching power supply has too much distortion. When you have fast signals, you will destroy the edge of the signal, so it won't be what it originally was! In the 'Alto', the power transistors are regulated and the input stage is doubly regulated by it's own regulator, so that the noise of the output power supply does not affect the input stage. We use very big capacitors in the power supply so we can get a lot of current. We do not give the circuit design to the customer and there are some aspects of the design that we do not talk about for obvious reasons.
L.V. - How many transistors do you use in the output stage?
B.D. - It's only one pair per channel because I don't like to put them in parallel because they are never the same and the music gets distorted.
L.V. - What about the transformers. Someone makes them for you? In the past I've seen very expensive amplifiers with big transformers that not only did they buzz, but if you placed your hand on the chassis, you felt it shaking! Do you test them for noise?
B.D. - Yes. We have a very special material inside the transformer to keep it a low noise one! Our transformers are the best you can get at the moment. It is certainly not easy to design a very good and noise free transformer. We never had a noisy one but we certainly check them out! Transformers tend to make a noise when there is a small amount of DC in the mains, and if you use a hair drier you can put this DC on the mains and this way you can check if your transformer is low noise or not! Most hair driers have two steps. When you put it on step one, it is cutting half of the wave from the mains and since half the wave is not used, a small amount of DC is produced.
L.V. - In the 'Alto', those round things at the sides, are they for heat dissipation?
B.D. - Yes. They are non-resonant heat sinks. Normal heat sinks resonate. The power transistors, they vibrate with the music! If you put a power resistor at the output of the power amplifier and turn up the volume, you can hear the music through the transistor! It is without bass, as in the telephone, but you can hear the music. If the signal is coming to the room from the speakers, everything tends to vibrate, the heat sink will vibrate, the transistor will vibrate and this will cause distortion in the vibration inside the transistor, and the transistor will not be able to perform at it's best.
L.V. - These "heat sinks", can be had in black or silver? Are they hollow? The black ones, are they painted black? The black one has the same sound as the silver one? (Laughing)
B.D. - They are made from solid aluminum. The black one is anodized, not painted. Sprayed with small glass particles and then anodized. The side panels are also made in this way. The silver ones are made in the same way, sprayed and anodized. I haven't noticed any difference in the sound of the different colors!
L.V. - What kind of cable do you use inside the amp? Those binding posts on the 'Alto', three pairs, are they only for bananas? Can the customer specify another kind?
B.D. - We do not use cabling from a hi end manufacturer, but a professional cable we think is very good. The normal binding posts we use are for bananas and they are very good. The customer can specify any kind of binding post or internal cable he wants. This is very easy for us to do, since our products are handmade.
L.V. - What kind of transistors do you use for the output stage?
B.D. - We use, for both the 'Alto' and 'Lato' amps, Japanese Sanken bipolar transistors. We also tried FET transistors, but I don't like them so much. They add something to the sound which is not right. We tried FETs at other places in the amp, in the power supply, the driver stage, but i still didn't like them. All of the transistors found in the amps are bipolar!
L.V. - Are you using any op-amps in the circuit? Some people think that op-amps are underrated. They say that the best of them can compete or surpass discreet circuits.
B.D. - We use op-amps for DC control, out of the signal path, and in the power supply. We have our own circuit on the 'Timpano' and the 'Alto' and I think they are better than any integrated circuit. A disadvantage of IC's is that they cannot integrate resistance very well. They can put in lots and lots of transistors, but when it comes to resistors, sound quality suffers. We checked, both by measurement and by ear, lots of resistors before we decided which ones to use. They come from Italy.
L.V. - Some people say that for different circuits you might need parts from a different manufacturer to have the best sound. Part "a" from "x" may be best for your circuit, but part "b" from "y" might be better for another circuit (of course we are talking about the same kind of parts here).
B.D. - That is a very difficult question, maybe... but I have to say that we don't do that. When a resistor is the best sounding on the input stage of the phono stage, where the biggest difference can be heard, than we know that it is the best for the whole amplification stage.
L.V. - Since the amps are fully regulated, they should be less affected by changes in the quality of the AC current than other amps. Do you think that is true?
B.D. - Yes, they are decoupled very good, but the mains cable on Bonnec equipment makes a lot of difference because they are on a very high level of sound quality and resolution, and you can easily hear whatever change in the system!
L.V. - I have to say that I strongly agree with you because in the last ten years we have been making a lot of comparisons, with different kinds of power cables and mains "improvement" products and we have found them to have unbelievable amounts of influence on the sound of all Hi End equipment.
B.D. - That is why we thought that it might be better to have a battery power supply, and we tried this, but with batteries we found out that you do stay on one level, but it is not the highest level! It is good if you want to always have the same quality, but if you have good quality AC power, if you use good power cables, you will have a better sound quality. So, overall in my opinion, a battery power supply is not an advantage and that is why there is not a battery supplied Bonnec piece of equipment.
L.V. - About the 'Fono', it can be, with it's own full size box or inside the 'Timpano'. When it is inside the 'Timpano', does it use the preamp's power supply? What are the differences between the two versions and how is someone to decide which one to buy?
B.D. - The 'Fono' has it's own power supply with two transformers, one for the MC and one for the rest. The only difference, if it is in its own box, is that the transformers are a little better screened. If you are going to use the 'Timpano' pre, than my advice would be to save your money and buy the Fono inside the 'Timpano'. The stand alone 'Fono' is for people that already own a pre, usually with valves, and who want to continue using their valved pre with their valved amplifiers.
L.V. - Have you made listening tests to determine if there is a difference between using the 'Timpano', with the 'Fono' as a separate unit or inside the Pre?
B.D. - I'm afraid we haven't. But you can do it and tell us what you found out! Anyway, the result would be greatly affected by the interconnect used in the test!
L.V. - I would like to have your opinion about cables. When I started seriously testing different cables about twelve years ago, I was very soon convinced that only with expensive cables you can really use the potential of your equipment, and maybe that was true at the time, but as years go by I seem to be moving away from this position! I have found that, today, there are a lot of inexpensive, by Hi End standards, cables, both by professional and Hi End manufacturers, that not only have jaw dropping value for money, but they can compete, seriously compete, with cables costing three, five and ten times the price. I am not saying this lightly, since I have owned and still own some of the expensive ones. For readers to understand what I'm saying, I have to add that, subjectively, I've put a ceiling on what I would consider reasonable or even ethical, in the price of cables at the admittedly arbitrary value of 1000$ or Euro for one stereo meter of interconnect. (This is about the price of the most expensive interconnects I have owned) I have come across cables, let's say, costing 250 to 350 Euro, which under controlled conditions, and in very good and very revealing systems, have competed, favorably competed, against cables costing 1000, 2000 and even 2500 Euro. That has come as a shock to me, and although I seem to be in the minority here, I find it difficult to recommend expensive cabling anymore. Not to be misunderstood, I have to add that I still consider cables a vital part of the system, as vital as I used to think they were. It is just that I currently think (unless somebody can practically convince me otherwise) that you do not need huge amounts of money to find great cables anymore.
B.D. - Well, there is little I can add, since I have to agree with what you said. I think that you should try and find some good value for money cables and not spend a fortune on them. We like to leave this decision to the customer, though, since our amps have no problem playing well with almost all kinds of cables.
L.V. - Some manufacturers, lately, seem to be leaving out the third, grounding pin of the IEC socket. What is your opinion about that? Also, are you using a four layer board in the preamp?
B.D. - Grounding in general is very important. In my opinion, as we are doing, the system should be grounded in the pre, were ours is directly grounded. The amps are indirectly grounded through a resistor. In cases of very bad house grounding schemes with bad AC quality I can see why some people might want to leave the third pin out, maybe it is better. On the other hand, the grounding, this is electrical zero for the whole system, so it is very good to have good ground. The Timpano board is two layered, for reasons of cost. The first layer is mostly used for screening purposes and the bottom layer for the signal A lot of people are talking about the shorter pathways you get with four layered boards, but in my opinion the real reason that four layer boards can sound slightly better is because of the better screening they can provide us with.
L.V. - How do you decide how much feedback to use in the various amplification stages? By ear or measurement?
B.D. - Both by ear and measurements, but the ear is more important to us. Feedback is always too late so you have to design the circuit so it doesn't need the feedback so much. Measurements are mainly used to see if everything is working properly.
L.V. - As you told me before, if there is any kind of improvement in any of your products, it can be brought to the new specification as an upgrade?
B.D. - Yes! All of our products can be upgraded to the newer model. Of course this is not going to be happening every year, but maybe, every three to four years. Usually, it is going to be something with a small cost to the customer, the change of some parts that will give better sound. In the extreme case of a board change, as with the 'Timpano' pre a year ago, the board can be changed with the new one for slightly less than half the price of the preamp.

L. V. = Lambros Valleras Vice President, Greece High End Club

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