NAD 3020 Transformer Specs

[SilverNAD]

Hello There,

I’m a diagnosed 3020 nutcase and collect silver face and Series 20 gear. Several of my collection have blown/fried transformers and I was discussing this with a company supplier in China who thinks they could do a small run (100 units - 50 at 110v and 50 at 220-240v). If it were possible (and vaguely affordable) I would cover cost and set up some way of getting them to other 3020 die hards.

I’m aware the early models had a bottom chassis mount whereas later were attached to rear of chassis, however does anyone know if the outputs were the same?

I need to supply them the power and output values of the transformer- can anyone help me with a written list from the schematic, which I’m hopeless at reading?

Thank you.

 

[IndianEars]

The circuit diagram that you have posted is not legible enough to read voltages...
The NAD 3020 was an Iconic, 20 Watts / channel RMS @ 8 Ohms amplifier, with a very punchy sound.

The secret sauce was its Mains transformer that was designed to a price point..... believed to provide sufficient juice at 50 Hz to sound punchy, but would not sustain that power delivery @ 20 Hz, which most systems at its price point were incapable of delivering.

A Circuit diagram or Service manual will at best provide you the No Load voltages of the power Trnsformer, and at best the rated current.

The key yo the NAD 3020's transformer were its transient behaviour and frequency behaviour... I doubt you will get detailed enough winding and core details to make the same transformer from scratch.

Your best bet would be to get the original transformer rewound by a good rewinder.

 

[reubensm]

A couple of years ago, a good friend of mine and fellow forum member had sent me a 3020 for repairs. I had a power transformer with a fried secondary. This was a second generation original 3020 with the transformer bolted to the back panel (not to be confused with the 3020A). The power fuses had blown previously and a local mechanic had shorted out the fuses with jumpers and as a result the amp was working without fuses. After some use, the transformer was shorted when the power transistors shorted. I got the transformer rewound and had the issues with the power transistors addressed, removed the jumpers over the fuses and had the amp back in action.

Its an open secret that NAD never shares the specs of their power transformers on paper but I was able to obtain the specs from my contacts with various NAD service centers across the world and verify what I got by reverse engineering my own NAD 3020.

Let me share what I know:

Primary: Has essentially 2 winding sets, both for 120 volts, with each having a 110 volts tap. This is in line with NAD's attempt to market the 3020 in different global markets as one can simply wire the primary by combining these sections in various configurations, to obtain compatibility with the following AC mains voltages, depending on the country or continent - 110 volts, 120 volts, 220 volts, 230 volts, 240 volts. Here is a snapshot of the wiring possibilities:



Secondary: This is where the transformer gets interesting. I would say that the design is like having 2 transformers with center tap secondaries, built into one unit. But before going into the logic of the transformer, a short note about the 3020's design. From the perspective of the power transformer secondary, the powersupply of the amplifier is divided into 2 sections:

• Section-1 is the high current un-regulated section which powers a bridge rectifier with a filter capacitor bank, solely for the output transistors and the driver transistors of the power amplifier section. The unregulated nature of the powersupply and the capacitor bank enables the powersupply to accomodate sudden spikes in current requirements when playing at higher volumes or alternately the higher current drawing required when driving difficult loudspeaker loads (can go as low as 2 ohms)
• Section-2 powers a relatively lower current regulated powersupply for the pre-driver stages of the power amplifier section and the entire preamplifier section including the phonostage.

Additional notes: When upgrading the powersupply filter caps, it is better to use 50 volt ones instead of the existing 35 volt ones (which is rather borderline). Also I have come across several DIY clones of the 3020 wherein 2 separate power transformers are used for performing the intended functions of section-1 and section-2 independently. Also I have come across a few DIY versions using toroidal transformers instead of the conventional type. In hindsight, both these are a bit more expensive but possibly, better-sounding options.

 

[IndianEars]

SUBERB, detailed info, reubensm.

 

[shafic]

Today Santa gifted me a mint condition NAD 3020 and enjoying the 'warm' sound of this little wonder now.

https://imgur.com/R5z0P64

https://imgur.com/DnHvbxy

 

[kspcbe]

Beautiful ! Enjoy music !!

 

[tufty]

Very interesting information, particularly the writeup from @reubensm. I believe the transformer in the 3020 is the same or very similar to that in the 3225PE, which is my current problem...

Threadjack time.

A while back, my 3225PE, bought in 1987 or 1988, suffered from a neutral fault on the line outside the house, and basically got fed a hyooge 380V spike. It wasn't the only bit of electrical gear to get fried, and although the power company's insurance paid out, I kept it around with the intention of eventually resuscitating it. A friend gifted me his old Scott A436, one thing led to another, and the NAD has lingered, unused, unloved, and above all unfixed, for the better part of 15 years. Time to fix that, I think.

The external symptoms are that it no longer powers on, no LED, no hum, nothing. The fuses are OK, and although the big caps look like they need replacing, nothing inside has obviously let the magic smoke out.

I was suspicious of the transformer, so pulled the fuses to avoid potential damage elsewhere and hit the power switch. Can't work out where the centre taps earth to, I'm guessing the chassis, but even between the supposed unrectified ±50V outputs for section 2 I'm not seeing significant voltage. Like an idiot I didn't make notes, though, so I guess that needs to be redone. I've attached the relevant bits of the schematic from the service manual.




So, I guess, dead transformer, and given that they're seemingly unobtanium, I guess it's also dead amp, unless there's some other option. Any ideas?

 

[tufty]

OK, transformer is definitely at fault. On this amp, only neutral is switched (well, one of live and neutral, all of which depends on which way your plug is wired, or plugged in for a 2 pole plug, and mine is wired with live to brown and neutral to blue. Because I'm an electrician). On the switched side I have connectivity with reasonable resistances to all but one of the primary taps, which is the one that runs to live. From the live side, nothing.

Secondary sides look OK, at least they give reasonable looking resistance values.

This *could* mean that it's just the thermal fuse which has gone south. "just". The transformer does not look like it's fun to get into.

 

[tufty]

Verdict : It was the thermal fuse. Tore into the transformer as far as the primary connections.

The "live" wire (black on my model) from the distribution board to the transfo goes direct to the thermal fuse. The other end of the fuse surfaces elsewhere, and connects both to a winding proper, *and* to a wire that comes out to the distribution board (white wire labelled 0V in my case).

So I shoved it all back together, unsoldered the mains wire, connected live to the switch in the place of the neutral (I do not like an unswitched live) and connected neutral to the white wire's terminal. Fuses out, cross fingers, power on. OK, reasonable looking voltages on the hot side of the fuse terminals. Power off. 1A fuses back in (regulated preamp secondary). Power on. We have LED, we have no smoke or spitzensparkzen. Power off, all the rest of the fuses back in, line input, cans in the headphone output, power on and .... YES!

Currently we have 54-46 was my number, warm NAD sound. I'd forgotten how much I love this amp. Been running for the better part of an hour, no hotness, no funky smells.

Remains to be seen what happens when I put it through the big Cabasse boxes, but I am very optimistic. Once I have that all tested up, I'll probably pull the trigger on a recapping set. Not sure what the potential downsides of no thermal fuse are, though. Apart from the next loss of neutral probably being properly fatal, I guess.

 

[reubensm]

Very interesting information, particularly the writeup from @reubensm. I believe the transformer in the 3020 is the same or very similar to that in the 3225PE, which is my current problem...

Threadjack time.

A while back, my 3225PE, bought in 1987 or 1988, suffered from a neutral fault on the line outside the house, and basically got fed a hyooge 380V spike. It wasn't the only bit of electrical gear to get fried, and although the power company's insurance paid out, I kept it around with the intention of eventually resuscitating it. A friend gifted me his old Scott A436, one thing led to another, and the NAD has lingered, unused, unloved, and above all unfixed, for the better part of 15 years. Time to fix that, I think.

The external symptoms are that it no longer powers on, no LED, no hum, nothing. The fuses are OK, and although the big caps look like they need replacing, nothing inside has obviously let the magic smoke out.

I was suspicious of the transformer, so pulled the fuses to avoid potential damage elsewhere and hit the power switch. Can't work out where the centre taps earth to, I'm guessing the chassis, but even between the supposed unrectified ±50V outputs for section 2 I'm not seeing significant voltage. Like an idiot I didn't make notes, though, so I guess that needs to be redone. I've attached the relevant bits of the schematic from the service manual.

View attachment 75623


So, I guess, dead transformer, and given that they're seemingly unobtanium, I guess it's also dead amp, unless there's some other option. Any ideas?

Sorry to hear about the neutral fault, you are right, the 3020 (the i-version) and 3225PE are similar with the 3225 featuring a different power supply design with PE mods producing an additional 5 watts output. Alternately, the 3020 series features an un-regulated power supply design for the power output and driver transistors.

 

[reubensm]

Verdict : It was the thermal fuse. Tore into the transformer as far as the primary connections.

The "live" wire (black on my model) from the distribution board to the transfo goes direct to the thermal fuse. The other end of the fuse surfaces elsewhere, and connects both to a winding proper, *and* to a wire that comes out to the distribution board (white wire labelled 0V in my case).

So I shoved it all back together, unsoldered the mains wire, connected live to the switch in the place of the neutral (I do not like an unswitched live) and connected neutral to the white wire's terminal. Fuses out, cross fingers, power on. OK, reasonable looking voltages on the hot side of the fuse terminals. Power off. 1A fuses back in (regulated preamp secondary). Power on. We have LED, we have no smoke or spitzensparkzen. Power off, all the rest of the fuses back in, line input, cans in the headphone output, power on and .... YES!

Currently we have 54-46 was my number, warm NAD sound. I'd forgotten how much I love this amp. Been running for the better part of an hour, no hotness, no funky smells.

Remains to be seen what happens when I put it through the big Cabasse boxes, but I am very optimistic. Once I have that all tested up, I'll probably pull the trigger on a recapping set. Not sure what the potential downsides of no thermal fuse are, though. Apart from the next loss of neutral probably being properly fatal, I guess.

View attachment 75639

Nice fix, the pleasure of fixing a NAD amp and hearing it play like before, is truly a great experience.
Btw, my apologies for the delayed reply, on travels currently hence the delay.

 

[drlowmu]

There should be enough information in this thread, for a competent transformer company to wind a replacement. You should certainly give them a burnt up XFR, which will allow them an even easier duplication job with an even surer result.

50 or 100 pieces minimum is exceptionally excessive IMHO. Find other winders !!

Copy the stock part, do NOT redesign the core, is my suggestion.

Jeff

 

[Ja1nuszK]

Hi there. Your diagrams seems to be pretty useful. However, would you be so kind to tell me which of this combinations is proper for a US 120V? I have 3020 wired for 240V/ 50 Hz equipped with 29-2037 Transformer. Thank you.

 

[drlowmu]

Hi there. Your diagrams seems to be pretty useful. However, would you be so kind to tell me which of this combinations is proper for a US 120V? I have 3020 wired for 240V/ 50 Hz equipped with 29-2037 Transformer. Thank you.

See the the primary diagrams in Post #3, after the wording " Let me share what I know "

https://www.hifivision.com/threads/nad-3020-transformer-specs.91128/#post-1023747

The wiring for the lower voltage 120 VAC USA use, parallels the two primary windings. For 240 VAC Use, the two primary windings are placed in series.

Jeff

 

[Ja1nuszK]

Thank you Jeff for your quick answer. I appreciate you! However I'm a bit confused because my present wiring for 240V is white and orange connected to main switch. This combination isn't appear on diagrams above. Which of the markings in the diagram is proper for US 120V UL or SI ? Thank you.

 

[reubensm]

Thank you Jeff for your quick answer. I appreciate you! However I'm a bit confused because my present wiring for 240V is white and orange connected to main switch. This combination isn't appear on diagrams above. Which of the markings in the diagram is proper for US 120V UL or SI ? Thank you.

CAUTION-1: Only a DIY enthusiast who is familiar with transformers and electrical wiring should attempt to do this at home. Mistakes can damage the transformer or/and pose electrical shock hazards. Proper care with cable layout, proper soldering techniques and appropriate insulating techniques should be used when attempting this task.
CAUTION-2: (If working on the older 3020s) It is common for the Red and Orange coloured wires to fade over time and look similar (also the blue and brown wires tend to look darkish). Examine the wire colours closely under natural light, preferably nearest to where the wires exit from the transformer, if you face this challenge.

The person who has wired your amplifier has interchanged the top and bottom ends of each primary winding and hence this confused you (with reference to the diagrams from the original NAD 3020 service manual). To make it easier for you, I have re-drawn your current wiring using your interchanged wiring configuration for easy understanding. When rewiring for 120v, it is recommended to use the wiring configuration mentioned in the original 3020 service manual in order not to cause similar confusing circumstances for service technicians working on your amp in the future

Here is the diagram of your existing wiring config and the proposed wiring config (Jeff has rightly proposed this one as well):

 

[Ja1nuszK]

CAUTION-1: Only a DIY enthusiast who is familiar with transformers and electrical wiring should attempt to do this at home. Mistakes can damage the transformer or/and pose electrical shock hazards. Proper care with cable layout, proper soldering techniques and appropriate insulating techniques should be used when attempting this task.
CAUTION-2: (If working on the older 3020s) It is common for the Red and Orange coloured wires to fade over time and look similar (also the blue and brown wires tend to look darkish). Examine the wire colours closely under natural light, preferably nearest to where the wires exit from the transformer, if you face this challenge.

The person who has wired your amplifier has interchanged the top and bottom ends of each primary winding and hence this confused you (with reference to the diagrams from the original NAD 3020 service manual). To make it easier for you, I have re-drawn your current wiring using your interchanged wiring configuration for easy understanding. When rewiring for 120v, it is recommended to use the wiring configuration mentioned in the original 3020 service manual in order not to cause similar confusing circumstances for service technicians working on your amp in the future

Here is the diagram of your existing wiring config and the proposed wiring config (Jeff has rightly proposed this one as well):

View attachment 76477

Hi Rubensm. I'm impressed what you've did for me. Thank you. I'm pretty experienced in electronic DIY, however existing wired in my 3020 was different than in all diagram that I've received. Thanks again.