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Old 15th April 2002, 03:29 PM   #11
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Thanks for the comments!

Again with great effort to avoid becoming anoying I must reply to your comments:


2N3055 = Slow:
They are fast enough for a near perfect 50KHz square wave without any overshoot and a bandwidth beyond 200KHz. Their Ft(=0.8MHz to 4MHz) prevents high frequentie oscilation. I consider it useless to use faster ouput transistors if that mean installing of an compensation cap which I now do not need. This design is inherent stable.

2N3055 = bad gain linearity:
Well considering that this design uses the 2N3055 at 1.2A Iq thus so only at a 0.1 to 2.2A current swing, the devices are used in their lineair regeon (well according to D. Self in his book). Add to that that I discoved I do not need mor then 0.5A current swing for high SPL levels I considerd it as not so important

2N3055 = not robust
Well they are use at an Iq of 1/7th of the rating and a power dissipation 1/10th of their rating. I do not have to expect any failers.

Seems to me that no argument against the 2N3055 can be made other than the most important:
Subjective Experience.
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Old 15th April 2002, 04:00 PM   #12
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Default 2N3055

The NAD 3020 used the 2N3055 as did the Bedini 25/25. Both these amps have practically cult status. The John Curl JC-2 used 2N5884s and 2N5884s which were also 4 MHz devices. Many construction articles are designed for ease of build and availiblity of parts. My favorite surplus store has plenty of 2N3055s and no 2SC3281s. These transistors are fine for a beginer to cut his teeth on and are more tolerant of non-optimum layout and compensation than the new fast stuff. And they really don't sound too bad.

H.H.
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Old 15th April 2002, 04:16 PM   #13
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Hi HarryHaller..

Nice to hear from you on this thread..

Do you happen to have a link for me on those Bedini 25/25 and JC-2 schematics? Or are you gonna tell me I'm lazy and must find them myself?

cheers,
thijs
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Old 15th April 2002, 04:28 PM   #14
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Default JC-3

I meant JC-3......http://marklev.com/marklev/ No source on Bedini.

H.H.
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Old 15th April 2002, 04:36 PM   #15
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Thanks.
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Old 15th April 2002, 04:37 PM   #16
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Default best of british.......

Hello tschrama and Harry, thanks I was going to mention the 3020, but left it out.

My recollection of these is that they achieved their cult status mainly due to the British hifi press extolling their virtues in the context of low cost, minimalistish, synergystic systems that worked well in a small (British) listening environment.
In a small room, with 6 1/2" or 8" 2 way, yes indeed they worked quite well.

They were never great shakes hifi and they were never intended to be - their strength was british designed circuit and layout, european semiconductors ( I reckon they sound different to Jap and US semis), minimal parts count, cheap construction and built in Taiwan, and hence relatively cheap and easily available.
They also had nice sounding tone control section in addition to reasonably pleasant overload characteristics - ie compression and soft clipping, that enabled overdrive without getting unduly nasty.
Overall this was quite a pleasant amplifier for its day but goes nowhere near the detail, resoloution and cleanness of more modern circuits and devices.
A penalty of 'slow' output devices is increased HF and IMD distortion, and this is sonically evident.
The resultant sound can be a bit like Musak, and that can be pleasant enough in it's own right too.

Lets hope you try substituting the 3055's and report your results,
Regards, Eric.
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Old 15th April 2002, 04:42 PM   #17
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Thanks for all the info ... I am searching the farnell catalog for the upgrade devices.. I post a thread when I've got something...

greetings,
Thijs
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Old 15th April 2002, 05:05 PM   #18
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Default NAD 3020

Many of the short comings of the NAD were the usual short comings of many amps built to cost targets. I put Cadas input RCAs, Edison Price Music Post output connectors, Panasonic HFQ power supply caps, and HexFred diodes in the thing. No other changes. The amp sounded seriously good driving modified Magnapan MGIIIs. I did not change any transistors in the amp. It is really easy to attribute the sound of an amp to preconcieved notions. Attention to details, passive parts quality, power supply design, and stability can easily count for as much as semiconductor choice. I also find that better the topology, the more sensistive the design is to these factors. Simple topologies lend themselves to less parts and make using good parts more an option at a given cost. some of the old topologies are competetive with todays designs. I bet a Curl JC-3 wth Toshbia Jfets and Toshiba and Sanyo Bipolars would rock your world and that is a 25 year old design.

H.H.
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Old 15th April 2002, 05:21 PM   #19
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Harry, sounds like those parts cost as much as the amp itself.
Yes, although the NAD 3020 semis were european, the passive parts were most definitely the cheapest asian that they could find !.
I recall that although not wonderfully clean nor uncoloured, they were always musical, even erring on the slightly polite side, which is perfectly acceptable to me.

Harry, my comment on the subtle sound character/origin of transistors is from long sonic observations - do you agree ?

Regards, Eric.
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Old 15th April 2002, 07:14 PM   #20
Geoff is offline Geoff  United Kingdom
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JLH

Originally quoted by Sidney:

"So in my final version of the amp I used hq parts and matched 2N3055's with Hfe's of 200 for the output trannies and 160 for the 2N3055 current sources (per the JLH site better to have the one lower than the other)."


There is (or should be :-) nowhere on my site that states that it is better to have one output device with a higher or lower gain than the other. The best performance for this circuit is achieved when the two output transistors are matched. If matching is not possible, then the lowest distortion is obtained if the higher gain device is used for Tr1. See Table 2 in the 1969 article.

A number of people have reported an audible improvement when changing from the 2N3055 to MJ15003. Care must be taken if other alternatives are considered since the JLH circuit does not have any fixed compensation and relies on component characteristics to achieve stability. Higher speed devices such as the 3281 may or may not work. I am aware of one constructor who has used the 2SC3281 in a 1969 version without any apparent problems whereas another tried the MJL3281A in his 1996 version and the result was oscillation.

NAD2030

Eric

I'm afraid I have to disagree with you that the sound of the NAD is due to its use of European transistors. If you look at the schematic you will find that there is a mixture of Japanese (2SC1400), European (various BC and BD devices) and American (2N6551, 2N6554, 2N3055 etc) devices.

I think it is far more likely that the performance is due to the circuit topology. The amplifier avoids the use of long tailed pairs (differentials) and constant current sources. If I have read the schematic correctly, the power amp section has a single input transistor (current feedback) followed by a VAS with boot-strapped current source and then a Darlington EF output stage. The phono stage uses a cascoded single transistor input stage and the pre-amp section also manages to work without the current, seemingly mandatory, differential input.

I agree with you about the quality of the passive devices. All bar four of the resistors in each channel were 1/4W or 1/2W carbon. The only non-carbons used were the series resistor in the phono input (1/4W metal film), the output Zobel resistor (1W metal oxide) and the output stage emitter resistors (2W cement). Non-electrolytic capacitors were either ceramic or Mylar.

It would be very interesting to hear this circuit built with quality components.

Geoff
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