OK, here is a thread showing another NAD 3020 that I rebuilt. This one has been a real labor of love compared to the first one I did, I bought a pile of parts from a fellow AKer with the hopes of getting it back together again.
Here is what I started with. As you can see, the output transistors and heatsink are missing, along with the power amp driver transistors, headphone jack, and volume control. I did buy a 7020 receiver for parts, but there were very few bits I could use for this 3020.
Here is the board removed from the case. I already mentioned no heatsink right?
I had to make my own heatsink out of a piece of aluminum L-section, as the heatsink in the parts 7020 receiver wasn't the same. This took a while to get together, as I was waiting on borrowing a friends band saw to make a nice clean cut, and to use a friends drill press to make the holes. Eventually, I bought a cheap cut-off saw, and drilled the holes myself using nothing but a picnic bench for clamping. It sucks not having our own house, I'll be glad when we find something, all my larger vices, clamps etc. are in storage. What I did was use a heatsink from another 3020 amp, screwed this to my L-bracket, and got drilling. My old metalwork (metal shop) teacher would be proud.
Jumping ahead big time here, this is a shot of the interior all completed. It's easier to list the parts that are original rather than what has been replaced. The bass, treble and balance pots are all original, as are all the switches except the power. The ceramic and green film caps are the originals, as is the one zener diode on the power amp board, and the power level meter IC. Everything else has been replaced : all electrolytics (using Nichicon KW and KL), all diodes (both signal and power rectifier), all transistors, all resistors (changed to 1% metal film).
Close-up of the phono pre-amp. The two big browny/red film caps replaced some 4.7uF electrolytics. The cap indicated by the yellow arrow was also changed to one of these films, as was the one on the other channel. The only problem was, it interferred with the location of the pre-amp power supply board. After trying to move it out of the way and lifting a solder pad, I admitted defeat and went back to a Nichicon KL cap. NAD do not use any special caps in signal path locations in this amp, unlike Kenwood, Pioneer, Sansui etc.
Pre-amp power supply board, the two caps circled in yellow are the ones that were going to be replaced with films, but there wasn't room.
Close-up of the power amp section. I added trimmers to adjust the bias, the NAD service manual says to swap out resistors until the correct reading is obtained.
Front view.
Rear view. I decided to do away with the switched and unswitched power outlets on the rear panel. In all the years of messing around with audio gear, I don't think I've ever used these once. It cuts down on a lot of 110v AC wiring that goes over the power amp stage, I don't know if it will reduce hum. I just covered the holes up with a piece of aluminum.
You may also notice the speaker terminals. The originals were broken, and these were sourced from the parts 7020 I mentioned earlier. However, even these were not a straight forward drop-in replacement, I had to bend the pins to make them line up with the holes in the PCB.
I also removed the soft-clipping switch, since the soft clipping circuit is not longer functional as I removed those components.
Here is a view of the front right corner, showing the Alps blue pot I bought from eBay. This was a real pain to fit, the 7020 volume pot bracket wasn't the same as the 3020, of course I only found this out AFTER I'd got the front panel on. I ended up making another one out of a piece of aluminum.
Front left view this time, and you can see the new power switch and the spark suppressor I fitted. I also tied up the transformer primary wires here, since they no longer went to the power outlet sockets on the rear panel.
You see the two browny/red film caps beside the bass control? These were originally blue electrolytics looking very similar to the blue Sanyo ones that fail in other brands.
So, does it work? The answer is YES! I powered it up, and was able to set the bias and offset well within specs. There are a few little teething troubles though...
The power lever meter doesn't work. I put new LEDs in here, I hope I didn't put all five of them in the wrong way. I have a spare board to try just in case.
The balance control doesn't work. I had to repair the one that was on there as it had broken off the board. I will check to see if there is a broken solder pad, if not then I'll replace it with one from one of my "parts" 1020 pre-amps**.
Not sure about the heatsink. The original NAD one was just a folded piece of aluminum about half the thickness of mine, but with more surface area. I might see if I can find some extra heatsinks to bolt onto this one I made, not that I have been using it at very high volume to generate much heat yet.
Lee.
** parts pre-amps they might be, but at least one of them might be getting a turbo boost and get turned into a 3020 amp. The one thing the parts 7020 receiver did provide was a nice big transformer, bigger than the 3020 one...
Here is what I started with. As you can see, the output transistors and heatsink are missing, along with the power amp driver transistors, headphone jack, and volume control. I did buy a 7020 receiver for parts, but there were very few bits I could use for this 3020.
Here is the board removed from the case. I already mentioned no heatsink right?
I had to make my own heatsink out of a piece of aluminum L-section, as the heatsink in the parts 7020 receiver wasn't the same. This took a while to get together, as I was waiting on borrowing a friends band saw to make a nice clean cut, and to use a friends drill press to make the holes. Eventually, I bought a cheap cut-off saw, and drilled the holes myself using nothing but a picnic bench for clamping. It sucks not having our own house, I'll be glad when we find something, all my larger vices, clamps etc. are in storage. What I did was use a heatsink from another 3020 amp, screwed this to my L-bracket, and got drilling. My old metalwork (metal shop) teacher would be proud.
Jumping ahead big time here, this is a shot of the interior all completed. It's easier to list the parts that are original rather than what has been replaced. The bass, treble and balance pots are all original, as are all the switches except the power. The ceramic and green film caps are the originals, as is the one zener diode on the power amp board, and the power level meter IC. Everything else has been replaced : all electrolytics (using Nichicon KW and KL), all diodes (both signal and power rectifier), all transistors, all resistors (changed to 1% metal film).
Close-up of the phono pre-amp. The two big browny/red film caps replaced some 4.7uF electrolytics. The cap indicated by the yellow arrow was also changed to one of these films, as was the one on the other channel. The only problem was, it interferred with the location of the pre-amp power supply board. After trying to move it out of the way and lifting a solder pad, I admitted defeat and went back to a Nichicon KL cap. NAD do not use any special caps in signal path locations in this amp, unlike Kenwood, Pioneer, Sansui etc.
Pre-amp power supply board, the two caps circled in yellow are the ones that were going to be replaced with films, but there wasn't room.
Close-up of the power amp section. I added trimmers to adjust the bias, the NAD service manual says to swap out resistors until the correct reading is obtained.
Front view.
Rear view. I decided to do away with the switched and unswitched power outlets on the rear panel. In all the years of messing around with audio gear, I don't think I've ever used these once. It cuts down on a lot of 110v AC wiring that goes over the power amp stage, I don't know if it will reduce hum. I just covered the holes up with a piece of aluminum.
You may also notice the speaker terminals. The originals were broken, and these were sourced from the parts 7020 I mentioned earlier. However, even these were not a straight forward drop-in replacement, I had to bend the pins to make them line up with the holes in the PCB.
I also removed the soft-clipping switch, since the soft clipping circuit is not longer functional as I removed those components.
Here is a view of the front right corner, showing the Alps blue pot I bought from eBay. This was a real pain to fit, the 7020 volume pot bracket wasn't the same as the 3020, of course I only found this out AFTER I'd got the front panel on. I ended up making another one out of a piece of aluminum.
Front left view this time, and you can see the new power switch and the spark suppressor I fitted. I also tied up the transformer primary wires here, since they no longer went to the power outlet sockets on the rear panel.
You see the two browny/red film caps beside the bass control? These were originally blue electrolytics looking very similar to the blue Sanyo ones that fail in other brands.
So, does it work? The answer is YES! I powered it up, and was able to set the bias and offset well within specs. There are a few little teething troubles though...
The power lever meter doesn't work. I put new LEDs in here, I hope I didn't put all five of them in the wrong way. I have a spare board to try just in case.
The balance control doesn't work. I had to repair the one that was on there as it had broken off the board. I will check to see if there is a broken solder pad, if not then I'll replace it with one from one of my "parts" 1020 pre-amps**.
Not sure about the heatsink. The original NAD one was just a folded piece of aluminum about half the thickness of mine, but with more surface area. I might see if I can find some extra heatsinks to bolt onto this one I made, not that I have been using it at very high volume to generate much heat yet.
Lee.
** parts pre-amps they might be, but at least one of them might be getting a turbo boost and get turned into a 3020 amp. The one thing the parts 7020 receiver did provide was a nice big transformer, bigger than the 3020 one...
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