nikko na-590

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hi sakis, thanks, I appreciate it, i will pm you

i emailed Norman from web Tekko suggested, but got no response yet, but it was just yesterday

i do have many service manuals from hifiengine
Nikko | Owners Manuals, Service Manuals, Schematics, Free Download | HiFi Engine
whatever similar models, just to have an idea of schematics

so here is a deal with NIKKO, few weeks back I got nikko beta 20 preamp and nikko na-590 integrated amp chieply of ebay, just for fun
there is a thread about beta 20 preamp, its a rather good preamp, mine has some phono section switch issue I need to address and I have already recaped the whole unit, it sounds great especially phono section, but lets not talk about preamp

NA-590 integrated amp came to me with three broken of pots on the front, not just shaft broken off, but shattered pots for bass treble and balance. I put resitors there for now and was able to test the unit. Basically the amp works, but was probably not used for a while, so it needs to be recaped definitely. It sounded bad from first, but it got better, and now its rather good sounding. I need schematics, in order to know what caps are in signal pass and I would like to bypass the tone control section completely, since I have that beta 20 preamp.
Now looking inside, this integrated amp is probably rather basic, very few parts here and there, even worse, I do not see output reley! There are most likely no caps on the amps output, since I see none on the board, and assuming its DC, its rater dangerous. For such an old amp if it fails, it may take speakers with it. I see no DC sensing circuitry. Thast why I would appreciate schematics, I'd like to make it safe, add delay and DC sensing circuitry. Besides, now it makes loud turn on thump, and when you turn it of, music plays till the power suply caps last! Rather primitive...
Phono section of NA-590 looks terrible, I did not even used I want to make NA-590 just a power amp and use it with beta 20 pream in the guest room, or in basement for speaker testing/building.
I believe these vinatage components deserve second life.
Thanks everyone for help.
I will post as many pictures as you like.
well is what i think

at first look an amplifier that generic might be bad practice to use for such an application again no protection for a ""testing "" amplifier is a very bad thing to do ...Shape him up if you like but use it for the correct purpus such a very secondary system with casual duty and with in expensive speakers .

if you are willing to go on in such a generic amplifier as said a complete recaping is a must and caution will be needed if the amplifier is bootstrap you dont mess up with that value and same goes for feedback capacitor ...all the rest can be seen with a naked eye ...
Post a picture of the board i will let you know a couple of things ...

as about the thump can be caused by dry electrolytics and may self curred after replacing capacitors and aditionally adding bleed resistors to quick ensure that the cans emty pretty fast

i remember the switch/preamp issue and if i rmember well i sugested replacing the switch with audio grade relay and a piece of wire and you are done ...should be a walk in the park to do ...

kind regards
PS been checking the schematics i have and sadly none of them is even close to your amp ..wrong from my side as a suggestion
i finally got the service manual and started recaping
here is bunch of pictures as promised
after most caps changed, no loud turn on, and most importantly sound is better then expected, I love it
I have ordered speaker protection/dc sensing and delay circuitry, which I will put in (plenty of space there as you can see)
bias was right on target, no adjustment necessary
funny thinng is that this version of amp does not have bleeder resistors on power suply, so when you turn it off, it keeps sort of making sound till it discharges
this is how it was designed, they addressed it in 590II model, but it reqired to replace power switch, which I am not going to do
this should be cured by the relay on the speaker protection, once it comes I will install it
I am very happy with this amp, I have not expected it to sound so smooth and clean


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adason could i get a copy of the service manual? I am trying to repair a na-590 myself and could use the specs along with the schematic. When i turn it on, a low rumble builds to a loader one that I have to turn the unit off to keep it from damaging the speakers. I used 2 200w @8ohm power resistors with better results. The left channel is affected more than the right. The signal is backing up into the power supply. I checked the caps in the ps,they are ok. I am going to pull the pre drivers to isolate the amp from the preamp section and see if that helps. Any suggestions? I really like this amp and use it in my sound lab. Ive had it since the 80's.Artinvegas
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