I am thinking about replacing the electrolytic capacitors in a NAD 302 that I purchased new in Thailand in 1993 and that consequently uses 220 volt power. I have used a step-up transformer to operate it in the U.S. for many years. Nowadays, it seems less peppy than it was, so I am thinking about replacing capacitors.
Does anyone have experience with recapping the 220 volt version? I am wondering if the capacitor values of the 220-volt version are different than those listed in the U.S. service manual, for 110 volts. The U.S. service manual is here.
Which capacitors are the most important and most likely to need replacement after nearly 30 years? There are a lot of electrolytics? Do any of the other non-electrolytics need replacing?
If I changed the transformer to 110 volts, how would that affect the capacitor values? After the power gets past the rectifier, and is DC, is it the same for the 220 and 110 volt versions? I'm thinking I could measure the DC voltages after the rectifier to see if they match what's in the U.S. service manual posted on HiFi Engine.
Is this a good way to mess up a really nice amp?
Thanks for any and all advice.
Does anyone have experience with recapping the 220 volt version? I am wondering if the capacitor values of the 220-volt version are different than those listed in the U.S. service manual, for 110 volts. The U.S. service manual is here.
Which capacitors are the most important and most likely to need replacement after nearly 30 years? There are a lot of electrolytics? Do any of the other non-electrolytics need replacing?
If I changed the transformer to 110 volts, how would that affect the capacitor values? After the power gets past the rectifier, and is DC, is it the same for the 220 and 110 volt versions? I'm thinking I could measure the DC voltages after the rectifier to see if they match what's in the U.S. service manual posted on HiFi Engine.
Is this a good way to mess up a really nice amp?
Thanks for any and all advice.
the cap values will be the same, as they operate on the DC side of the transformer. Changing the electrolytic caps should be straight forward, use quality caps (Nichicon, Elna, Nippon Chemicon etc) from a reputable distributor (Mouser, Digikey. Newark etc).
There is a wealth of information here on recapping amps, but patience, learning as much as possible before starting, a good solder iron and desolder tool and a reasonable DMM, if the amp is fully functional, is the minimum that you should need.
The challenge with all recap/refurb is that if a mistake is made , then diagnosing that can take some skills.
good luck and enjoy!
There is a wealth of information here on recapping amps, but patience, learning as much as possible before starting, a good solder iron and desolder tool and a reasonable DMM, if the amp is fully functional, is the minimum that you should need.
The challenge with all recap/refurb is that if a mistake is made , then diagnosing that can take some skills.
good luck and enjoy!
Thank you pwdiya12! I will look forward to this project. Any thoughts on how to find a suitable 110 volt replacement transformer? I was thinking I could measure the DC output voltages put out by the 220-volt transformer (to make sure they match the values on the schematic in the service manual) and then find a 110 volt transformer with those same DC voltage values and hopefully a similar footprint.
It's quite possible you may not have to get a new transformer for 110V operation.
The existing transformer might have dual primaries connected in series for 220V.
The procedure to separate the primary windings and connecting them in parallel for 110v use and with the correct phasing might be more involved than perhaps your electronics experience will allow,but is doable. There are threads here that describe the process.
Cheers
Thanks Junior35. Are there visual clues to whether it has dual primaries? I did have a technician look at it many years ago - before I knew anything about electronics - and he said it was not an easy fix to convert the voltage, which makes me think the transformer lacks duel primaries. The service manual does not seem to state what the output voltages are before they go into the rectifier. Is it even possible to order such a transformer from Digi-key or Mouser?
One picks a transformer with windings of the voltages required by your circuit, in current rating twice what the rated output power is, times 2 again for stereo if the unit uses only one power transformer. Then one has to find the size that will fit your unit. Then one has to adapt the mount scheme. NAD tends to have 2 windings, one high voltage for the rails, one lower for the input stages. These voltages are not usually rail+15 v as is usual for models using op amps for input stage.
Two black or brown wires set one pair to the fuse & line cord, the other two connected together, are the signs of a dual voltage transformer. Huge volume models as NAD don't usually have that feature.
I've found EI transformers were a little cheaper from alliedelec.com than from newark. Triad is the usual old fashioned brand, but all are produced overseas these days. Allied sells garbage grade (1000 hr service life) electrolytic caps, but most of their other products are industrial grade. Toroid transformers from antecinc.com are what the diy builders are using, but these require a different mounting method and also usually are wider and shorter than EI transformers for older products. Toroids may require a soft start circuit to avoid tripping a breaker designed for EI transformers of the same rating.
Two black or brown wires set one pair to the fuse & line cord, the other two connected together, are the signs of a dual voltage transformer. Huge volume models as NAD don't usually have that feature.
I've found EI transformers were a little cheaper from alliedelec.com than from newark. Triad is the usual old fashioned brand, but all are produced overseas these days. Allied sells garbage grade (1000 hr service life) electrolytic caps, but most of their other products are industrial grade. Toroid transformers from antecinc.com are what the diy builders are using, but these require a different mounting method and also usually are wider and shorter than EI transformers for older products. Toroids may require a soft start circuit to avoid tripping a breaker designed for EI transformers of the same rating.
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Thanks indianjo. It looks like the transformer will need two different output (DC) voltages: +/- 28VDC and +/- 33VDC according to the schematic and the power supply diagram in the service manual (see below). There is also a +38v line. Whaaat's that? This may be a lot more trouble than it is worth, considering that my trusty Radio Shack step up transformer has worked fine for years. But it might be a fun project if it was possible to order a replacement for and then solder and mount it in place. Curious if anyone has done something similar and what the degree of difficulty is. My experience includes building a tube guitar amp from a kit, rebuilding a Hafler DH-200 with new filter capacitors and new PCB boards, building small Ruby guitar amps using op-amp chips and also making a booster guitars. I also successfully replaced the filter capacitors on another NAD amp, which solved a humming problem.
Hi,
Please note the red circles on bottom right of the attached schematics. You will notice that it shows transformer connections for both 220v as well as 110v. NAD as well as other manufacturers often use dual primary transformers and reconfigure as needed for the various world markets and their respective line voltages.
That said, it is quite possible that your particular unit (due to supplier issues etc) has a single primary winding transformer. You will have to do some digging and see how many wires are present on the primary side. There should be at least 4 wires.
Cheers
Please note the red circles on bottom right of the attached schematics. You will notice that it shows transformer connections for both 220v as well as 110v. NAD as well as other manufacturers often use dual primary transformers and reconfigure as needed for the various world markets and their respective line voltages.
That said, it is quite possible that your particular unit (due to supplier issues etc) has a single primary winding transformer. You will have to do some digging and see how many wires are present on the primary side. There should be at least 4 wires.
Cheers
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