New to me Nikko Alpha III

uncynd

uncynd

Member
Purchased a Nikko alpha 3 and beta 2, the beta 2 pots (guessing the balance) were creating an almost inaudible left channel. After some cleaning all seemed great. Alpha 3 was actually a bit brighter than I expected and overall after cleaning the beta I was very happy.

Today I decided to check the amp's (Alpha III) DC offset at the terminals. The left channel was perfect near 0, however the right channel tests almost exactly 30mv offset consistently. While I have some electronics experience I haven't got a clue what to do, if anything, about this. I could clean every board in the amp (literally the only thing I can think of) I thought about adjusting the bias but I don't think that would help since one channel is so clean. I'm looking for some guidance on how to diagnose and repair this. Thanks!

P.S. I have tested the output from the preamp and both leads test 0 offset.
 
You need to learn about the amp. 30 isn't too bad but I know you want it at zero. Most here live with anything less than 15 some as high as 50.

But you need to find the service manual on the amp and see what is used to control the offset. Whether it is adjustable, good, or is set by a pair of matched transistors which over the years may have become unmatched. You have electronics experience so there is what I have learned over the years, having swapped the transistors in a Hafler DH-200 to get the offset close to zero.
 
Ahh ok found the manual and looks like there is a pot to adjust DC balance, thanks! II don't really understand why I am to short the DC inputs on adjustment but I'll do it anyway lol.
 
The shorting plugs on the direct input, volume at zero, keeps the signal as limited as possible. No extraneous atmospheric crap getting into the Direct input and causing false DC. So you set the DC offset once with the shorting plug then with a different VR to lower it without the plug and repeat until you get it to zero 10mV. Don't forget to use mini-grabber clips so we don't have to visit how to repair a Nikko Alpha III amp. Too many people have decided that the no user adjustable components inside is not directed at them and we spend the next month or two walking them through a repair that should not have needed to be made. I did it once, learned a lesson after popping a resistor with a loose probe. Fairly easy fix but it was a turntable no power amp in that one.
 
well I've used plastic sticks cut to adjust pots, screwdrivers with heat shrink on them.

Mini-grabbers for poking a probe into an amplifier that will be powered up. Hook up the grabber than turn the unit on to avoid that instantaneous small spark and new post on how to fix a broken amp.
 
Blue I really appreciate these tips - most of my electronics experience is on pinball machines, the boards are big and schematics are easy to read, everything is accessible. Amp circuitry seems far more complicated and hard to work with - in no way did I want to overstate my position here, I am a complete newbie.
 
In my book anything under 50 mv in fine. The closer to 0 the better. My nikko alpha 2 has 0.1 mv and 21 mv on the other channel. I could drop it with a new pair of diff transistors. However it doesn't bug me that much. Unlike yours mine doesn't have a trimmer for dc offset just idle current.
 
FWIW I have not done anything about it yet - but I likely will when the snow flies. I love the analog gauges on the Alpha II thanks for the heads up!
 
Hey....

The aforementioned channel (left) has started doing something weird - what would cause the channel to work for hours and then slowly fade out? Maybe that pot needs a cleaning is all I can think of? I thought maybe the RCAs but why would it degrade after a certain point and work perfectly until then? Thanks again for any insight...thinking about getting in the amp to morrow and adjusting/cleaning.
 
uncynd said:
Hey....

The aforementioned channel (left) has started doing something weird - what would cause the channel to work for hours and then slowly fade out? Maybe that pot needs a cleaning is all I can think of? I thought maybe the RCAs but why would it degrade after a certain point and work perfectly until then? Thanks again for any insight...thinking about getting in the amp to morrow and adjusting/cleaning.
Click to expand...
Sounds like maybe bad relay contact. Does it come back if you turn the volume up? (don't keep it that way...) Another test is to tap the relay when the problem occurs, and see if the volume comes back. Some people open up the relays, and burnish contacts and maybe mechanically adjust for better contact, but best procedure is to get replacements, if that is your problem....
 
Thanks Steve, the fix so far is either power cycling the amp OR the pre-amp. Couple times now it has completely cut out on the left channel only. - Scott
 
Hmmmm - could be the preamp. IIRC the beta 2 also has a relay - reverse your preamp leads to the amp and see if the same channel fades out.
 
Just want to update the thread with my progress - I isolated the left channel issue to the amp after reversing inputs and also substituting a different amp for a full day.

So I go into the Alpha 3 and I discover these DC offset pots are FILTHY and barely turn, the commercial round style (crap). The readings were pretty tight and adjustable to 0 but then I attempted to clean the pots and that upset all values for both channels. Now I can't adjust to 0 because of the 1 turn orientation of the pots LOL - they are no where close and not in sync (2 adjustment pots per channel). I have resolved to replacing the pots with multi-turn quality parts and will get back.

I honestly think the pot was creating the cut out condition and degradation of the sound in the left channel - while the DC offset at the output was fairly consistent at 30mv it would jump and did not seem stable.

Am I off base in thinking this? The relay looks perfect (no visible dust, joints are clean and look to have integrity) - protection seems to work efficiently.

This is the trimpot which I think will replace the B22kohm circle pot from factory (the 1k pot is the same but in the proper leg configuration).
https://www.digikey.ca/product-detail/en/3296W-1-223LF/3296W-1-223LF-ND/2535906/?itemSeq=272588902

They don't stock the "Y" configuration so I'm thinking bending the middle post slightly forward will have to work.

Please let me know if anything sounds terrible from above. - Scott
 
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Will be changing the pots on this tomorrow as I have some time - can't help but admire the layout inside this amp after toying with a couple Pioneers this week. Everything makes sense - two separate PSBs / channel component layout is seemingly organized!

Edit: Job done - Balanced!!! For anyone replacing the bias pots on this amp you should modify your calibration procedure from the manual because despite having separate power supply boards each channel is influenced by the other. Adjust bias for each channel to + or - <60mv then go down to + or - <30mv for EACH channel THEN fine tune.
 
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Thanks NAD and all who contributed to this!

Edit: Thanks again - MAN it sounds great balanced!
 
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