the sale in the link below a kit consisting of 3 pcbs for the construction of the final stage of the Nad 3020.
https://www.ebay.it/itm/275392868133
https://www.ebay.it/itm/275392868133
somehow agree Jan, but as this is a really old amp and you cant get a new, I would think it's ok ..... could be considered a tribute to this game changer of an amp 
The 3020 was my first amp ... and man it was remarkable Good sound even driven to max, and very reliable.
I actually used 2 in bridged mode in the early 80's for DJ work ... driving a pair of Cerwin Vega .... those where days
Questions scafas:
The 3020 was my first amp ... and man it was remarkable
Good sound even driven to max, and very reliable.I actually used 2 in bridged mode in the early 80's for DJ work
... driving a pair of Cerwin Vega .... those where days Questions scafas:
- you have omited the output relay ... why? .... will get you a bug umpf at turn on/off ..... also there was a Over Temp sensor connected ... securing the relaiability
- The DB139 must of course be mounted on the heat sink
- Did you consider going for SMD to make a tighter and less noise prone setup?
- could have been fun to change the output transistors as well .... but will need some simulation ..... actually updating the transistors to new and available types would be fun and helpfull
- You also left out the soft clipping circuit ...
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two emitter resistors have been added for better stability, the whole circuit has been simplified, all transistors are easy to find, in my prototype I used Sanken amps and the amp sounds really good, the amp doesn't heat up, just lukewarm, it sounds great, stable and reliable .thanks
Parts of the retail audio market and DIYs are always seeking products and designs that are no longer produced - lost now to memories and nostalgia. There are also so few remaining topologies that haven't already been used many times over, that it would be virtually impossible to come up with a linear design that didn't just consist of existing design elements anyway. So I think we'd be fooling ourselves to consider that whatever design we can develop doesn't consist of existing topologies that have already been used extensively and could be counted as already ripped off, whether we were aware of them or not.
Personally, I don't think that having iconic products fade away as static museum pieces or confined to a wiki page of condensed facts and figures is as much a tribute to the design and designer as offering the necessary PCBs to clone them with currently available tech, whether for profit or simply to recreate a piece of audio tech. history for following generations to respect and enjoy for themselves.
Some hucksters deliberately use the name of the original design. So that's a rip-off.
I've seen designs sold as 'QUAD 405 clone' that had a completely different circuit.
With the NAD 3020 ripoff published above, the guy even admits that 'two emitter resistors have been added for better stability, the whole circuit has been simplified', but of course he still calls it a NAD 3020. Dishonest.
And you can still come up with original designs if you want, even with 10 parts there are 2^10 or 1024 different ways to interconnect them!
Jan
Huh? The 3020 has not been made for some 4 decades, most have died (and hopefully became parts), the PCBs were dirt cheap and easy to kill, and parts were skimped where they could, this is a tribute, and i for 1 am happy to see it. The 3020 amp stage is quite good.
dave
Who cares Jan. It is tribute, and given the shortcuts made with origianals, and new parts, ceratinkly something that could be / should be tweaked.
Lots of variations on classic circuits, and credit given to the originals/inspirations.
For instance, at what point does it become Not-a-JLH or a Not-an-ACA?
dave
Lots of variations on classic circuits, and credit given to the originals/inspirations.
For instance, at what point does it become Not-a-JLH or a Not-an-ACA?
dave
Well unless you can find real 2N3055/MJ2955 output transistors, you'll for sure need emitter resistors.
The pair used in NAD 3020 is rather unusual in this respect. (Old 2N3055/MJ2955 where homotaxial types whereas modern types are epitaxial)
All modern output transistors will need emitter.
Would be fun to do a tribute anyway, using SMD components where possible, and maybe cranking up the supply voltage a bit .... but yes it would not be a NAD3020 ....
The pair used in NAD 3020 is rather unusual in this respect. (Old 2N3055/MJ2955 where homotaxial types whereas modern types are epitaxial)
All modern output transistors will need emitter.
Would be fun to do a tribute anyway, using SMD components where possible, and maybe cranking up the supply voltage a bit .... but yes it would not be a NAD3020 ....
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I once went down the rabbit hole and did a spice sim of the original design, and also made an improved version. You are welcome to try it out.
I think for a tribute amp to make sense today it need to be able to do at least 100 W. Speakers today are not as sensitive as in the 70's and 80's, and why would you bother the effort if it would not really fit the purpose.
Looking at the improved circuit today I would even suggest to use a pair of ThermalTrak output devices to simplify design and improve performance (would allow for SMD drivers, and no bjt mounted to the heatsink for bias).
The tribute part would be the single-ended input and the VAC section.
Anyway if an amp works well and within it's given parameters I think you should not be able to hear any difference.
But on the other hand this would be a good nostalgia trip
Rename the transistors.txt to transistors.lib and place in same dir as the .asc files for simulation with TLspice
I think for a tribute amp to make sense today it need to be able to do at least 100 W. Speakers today are not as sensitive as in the 70's and 80's, and why would you bother the effort if it would not really fit the purpose.
Looking at the improved circuit today I would even suggest to use a pair of ThermalTrak output devices to simplify design and improve performance (would allow for SMD drivers, and no bjt mounted to the heatsink for bias).
The tribute part would be the single-ended input and the VAC section.
Anyway if an amp works well and within it's given parameters I think you should not be able to hear any difference.
But on the other hand this would be a good nostalgia trip
Rename the transistors.txt to transistors.lib and place in same dir as the .asc files for simulation with TLspice
I’m happy with my 18w SIT-3 (and the ACA mini and ACA work fine except when really cranked). I would be unhappy to see more than a pair of output devices.
dave
And Jan you are of course right in attacking copying others work ... fully agree.
... forgot to mention that the PSRR of the original circuit leaves much to be desired .... probably why the input section needed a regulated supply.
My changed version has good PSRR for the negative rail but not good at all for positive ( only 28 db) .... so development would still be needed to get that improved .... and you would of course get further and further away from the original design
... forgot to mention that the PSRR of the original circuit leaves much to be desired .... probably why the input section needed a regulated supply.
My changed version has good PSRR for the negative rail but not good at all for positive ( only 28 db) .... so development would still be needed to get that improved .... and you would of course get further and further away from the original design
The 'nod' 3020?
Thanks for those files - I must admit that I have a lot of learning to do now! The original question about board availability was because my knowledge is basic at best (but I can solder), so was looking for a project. This just accidentally got a whole lot more interesting with your contribution @Baldin, so I'll buy a simpler DIY kit to satisfy me yearning to build something while I study this.
Thanks for those files - I must admit that I have a lot of learning to do now! The original question about board availability was because my knowledge is basic at best (but I can solder), so was looking for a project. This just accidentally got a whole lot more interesting with your contribution @Baldin, so I'll buy a simpler DIY kit to satisfy me yearning to build something while I study this.