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Old 13th July 2002, 05:46 PM   #1
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Default And this is how it all started

It seems that there is certain interest in my work , so I present here my actually first creations done some 20 years ago.

My first all out project was a preamp with all possible features. At that time it was running on 220V and was using DIN connectors. You might not believe me but only knobs and a groove across the front face were custom machined, all other openings were drilled out and filed by hand. As I remember it took me a whole day to do it.
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Old 13th July 2002, 05:55 PM   #2
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All the boards were designed and etched by me and as usually I wanted to avoid excessive wiring. The circuits are arranged in two levels, where bottom contains phono EQ and power supply and top actual preamp and elaborate filters. I think there was not a single feature I didn't put there. But then, I was more influenced by Japanese makers then by Mark Levinson.
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Old 13th July 2002, 06:04 PM   #3
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At that time I was also into mini systems (315mm width) so both preamp and amp were of that size. The amp was low distortion class B, nothing particular about it if not the small size. It delivered 50 W and I never needed more. The chassis is not done from 1/4" aluminum, but from steel I used from other equipment chassis and cut to size.
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Old 13th July 2002, 06:07 PM   #4
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The one thing I like about it, is the compact arrangement and good use of space. Also symetrical layout and separate transformers for ea. channel. If you read the small print on the caps you will know where I'm coming from.
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Old 13th July 2002, 06:07 PM   #5
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Cool stuff, you got a good touch with construction
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Old 13th July 2002, 06:14 PM   #6
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Very nice!

The front panel looks very nice as well. Rub on transfers for the letters?

Just as a matter of interest, why the different transformers per channel?

One transformer of twice the size is usually cheaper than two, so I'm interested in your opinion given you used two transformers here.

Also, what transformers are those?
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Old 13th July 2002, 06:25 PM   #7
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The transformers were changed later for 110V since original used 220V. Two of them fitted better in available space, I also think that using separate transformers for ea. channel is better (you know true mono construction). Now I would use much bigger transformers thou.
Dry transfer lettering always worked good for me, and even after 20 years you don't see much wear.
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Old 13th July 2002, 07:08 PM   #8
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I must agree that seperate channel transformers are a very good idea indeed. This method gives greater channel seperation and much better power figures. I have a Harman/Kardon HK402A
and it uses seperate trannies. It's only rated at 60W a channel into 8 ohms, but I can load it with four or 2 ohms and easily get more power than expected. Thus, this amp uses (harman/kardon watts) which is like RMS compared to Peak.
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Old 13th July 2002, 08:04 PM   #9
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I'm not arguing, just asking some questions.

If the amp design has a high PSRR, why would separate transformers give bettern separation?

If a channel needs more power, wouldn't be easier to pull from a supply that's twice as large? (i.e. more transient response possible).

What do you mean by 'better power figures'?

I measured my Technics 55w power amp supplies a while ago and was surprised to find they are much higher voltage than expected (I can't remember the number now). It's sized to be a 150w amp as far as the voltage goes, but they rate it at 55w. I'm wondering if this is the same thing you're seeing in the Harmon Kardon. (Not trying to compare the two, it's just interesting).

Part of the reason I'm asking is that for my home theater, 10 power transformers is a whole lot more expensive than 1 or 2 :-)
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Old 13th July 2002, 09:55 PM   #10
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OKay, to answer your questions:

first of all, when you draw large transients of power from a PSU, you'll cause a voltage drop no matter what even if small. WHen you have a seperate PSU for each amp, the amps haven't got much ease in interfering with eachother. Essentially, one amplifier causes a voltage drop on a bass transient or something whil the other is trying to produce vocals, the vocals on the other amp get reduced in amplitude at each transient and this can become noticeable. Basically, it's an easy way to get away with minimal size supplies and still give each amp less disturbance in the line.

For home theater it really depends on what your willing to pay for or listen to. You can achieve exceptional results with only one transformer for a pair or more of amps, but this transformer and it's supply capacitors mustn't let transient voltage drops occur.
Most dolby and DTS recordings have very very bad distortion figures on transients anyway so it doesn't matter too much with home theater. And try not to believe in THX labels either, it's a publicity stunt.

BTW, my next set of amps will run off of the same PSU and trannie and deliver: 2X600W into 4ohms, 2X100W into 8ohms, and 1X80W into 16ohms all from a 5kva transformer but I'm going to use 1 farad supply caps to eliminate transient problems. As you may see, it isn't a necessity to have seperate PSU's, it just a luxury if you can afford it...


Well... many limiting factors do occur in amplifiers and also, there are many ways of rating output power. In the Harman/Kardon industry, they often made huge understatements in the ways of power. Also, Harman/Kardon amplifiers are very very well designed for high current capability and excellent current handling. They will not drop off or flake out like many amplifiers these days when you demand bass from them. Thus, they seem way more powerful than the usual amp of the same rating. One good example of HK current abilities is that I could run my amp into a set of 4ohm and 8ohm speakers in parallel which results in a total load impedance of 2.6 ohms. I could crank the amp until it's gain stage distorted and the output transistors didn't even get hot, while if you did this to a modern home reciever or amp, it would turn into a nice fireworks show!
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