So this is the doner amp that is going to be used for the project, its in almost mint condition and i dint want to break it(unless i have to lol)
Its what i call a mk3, this is the same board they used as they moved onto the 'A' version
So things that need to be done
Modify the base of the heatsink so it will accept the FETS
Modify the print so it maches the pin out
so this is the scheme that needs to be used for this one
ive never been able to find an official 'A' service manual, but this is close
Its easily recognised by the fact the regulated supply is now on the main pcb
Its what i call a mk3, this is the same board they used as they moved onto the 'A' version
So things that need to be done
Modify the base of the heatsink so it will accept the FETS
Modify the print so it maches the pin out
so this is the scheme that needs to be used for this one
ive never been able to find an official 'A' service manual, but this is close
Its easily recognised by the fact the regulated supply is now on the main pcb
Attachments
The same basic design often works with little or no modification other that the adjustment range on the vbe multiplier. You get a few watts less with the mosfets, unless the drive voltage can be enhanced to drive the gates a bit above the rails. Even thats not essential, you can just live with 3 volts or so less output swing.
Some people just like lateral mosfets. Another cult which you can join 😎.
They can also handle a momentary overload which would normally kill 2N3055’s.
They can also handle a momentary overload which would normally kill 2N3055’s.
If I remember well the 3020 is only a 20W amp: difficult to abuse 2N3055's with that amount of 'raw' power 🤣.
No SOA protection + shorted speaker wire. 3055’s won’t always tolerate it. Laterals don’t either, but your chances of winning that lottery are MUCH higher.
Still not convinced that a NAD3020 in 'almost mint condition' deserves such a butchering.
let's not kill the bear before we sell the skin.
I'm waiting to see the final result and anyway, it will surely advance the debate on the "for or against" in general 😜
I'm waiting to see the final result and anyway, it will surely advance the debate on the "for or against" in general 😜
In case anyone is wondering... so you're not OK then 😀
Well it started back here:
https://www.diyaudio.com/community/...ct-strip-down-and-upgrade.386581/post-7084088
Uncharted territory.
Given the choice, I’d start with one that needed work anyway if I was doing this. Like the one that got stripped down. Or at least one that needed new output transistors.
i've never looked at the NAD3020 sch before. does it really use the 2n3055 and no emitter resistors?
Yes, but those are original hometaxial type 2N3055s, not the present day epitaxial type. Certainly, we'd need to add the emitter resistors and re-arrange the bias to use more readily available epitaxial product. There are actually many 3020 product series repair threads here that cover or at least draw attention to this.
Hi Ian,
Can you discriminate between the two types using some measurement (without opening them🙂) ?
I got a bunch of different brands recycled from old equipement.