This Nikko Alpha III giving me headaches.

uncynd

Member
Aligned for bias and idle produces an offset at the speakers that is unacceptable to me.

Work done: Bias pots replaced, unit cleaned. Aligned to spec (bias and idle) following manual. Scope is great everything is stable.

Result: Sounds incredible BUT bias at both speakers is 40mv (WHAT THE....?!?!?!)
 
Aligned for bias and idle produces an offset at the speakers that is unacceptable to me.

Work done: Bias pots replaced, unit cleaned. Aligned to spec (bias and idle) following manual. Scope is great everything is stable.

Result: Sounds incredible BUT bias at both speakers is 40mv (WHAT THE....?!?!?!)
Are you saying the DC offset at the speaker terminals is 40mv? That may not be too big of a deal, but if the amp doesn't have a DC offset adjustment, you would probably need to replace and closely match the driver transistors on each channel.
 
Are you saying the DC offset at the speaker terminals is 40mv? That may not be too big of a deal, but if the amp doesn't have a DC offset adjustment, you would probably need to replace and closely match the driver transistors on each channel.

Yea - there are DC offset pots but the procedure for aligning does not involve active input. Short the input adjust then remove shorting pin and adjust for each channel. After doing this however and hooking it up to an active input the offset at the terminals is 40 for each channel. I'm not sure if I should be adjusting those pots with an active input?

edit: I take my time adjusting those pots allowing for them to settle each time. Not sure if related my gut is it's not but the small caps directly adjacent to the bias pots are really touchy.
 
Check the DC offset at the speaker terminals without your preamp connected to the power amp to see if that's the source of the offset. If it is, use the Normal inputs instead of the Direct.
 
Check the DC offset at the speaker terminals without your preamp connected to the power amp to see if that's the source of the offset. If it is, use the Normal inputs instead of the Direct.

So disconnecting the input fixes the offset - now near 0mv at the terminals.

Please help me understand why because it's 100% something to do with the amp's direct input. My Beta II (preamp) has no offset on the outputs and does not cause terminal offset on my other amps...
 
The Direct input is directly connected to the input differential pair. The Normal input passes the signal through a 3.3 uF coupling capacitor.

If there's no offset from the preamp than I'm not sure what the issue is.
 
Aligned for bias and idle produces an offset at the speakers that is unacceptable to me.

Work done: Bias pots replaced, unit cleaned. Aligned to spec (bias and idle) following manual. Scope is great everything is stable.

Result: Sounds incredible BUT bias at both speakers is 40mv (WHAT THE....?!?!?!)
Bias and idle are the same thing and should have nothing to do with the DC offset/balance.
 
The Direct input is directly connected to the input differential pair. The Normal input passes the signal through a 3.3 uF coupling capacitor.

If there's no offset from the preamp than I'm not sure what the issue is.
I don't see any issue as well. Chasing a problem that's not a problem.:rolleyes:
 
Yea sorry, got mixed up, you're right.

The offset pots were replaced the bias pots are original - they weren't giving me trouble at the onset. Bias/idle is set to spec and steady on both channels, the issue is the offset on direct input.
 
I don't see any issue as well. Chasing a problem that's not a problem.:rolleyes:

I certainly hope you're right but my curiosity has now peaked...

edit: I'm taking my time and not planning on doing anything unnecessary - I want to understand what I'm doing before execution.
 
Are your other amps input dc coupled?
Does the Nikko offset with the preamp on the normal inputs?
 
Finally got back around to this, here are the results...

Beta ii pre-amp plugged into the alpha iii "NORMAL inputs" gives ~+8mv DC offset on both output terminals.

Beta ii pre-amp plugged into the alpha iii "DIRECT inputs" gives ~+28mv DC offset on both output terminals.

AND it sounds far better on the direct input.

Like...WTF.

Edit: Muck it I just adjusted the dc offset pots in operation to 2mv on direct, will report back after playing music for a few hours...

Edit2: Well regret doing that - as soon as the input changes on the pre-amp the dc offset goes bonkers. Will report back after re-aligning.

I feel as if I might be learning in the slowest most stubborn and ridiculous ways possible.

(Thank god for my Pioneer sa-7700 workhorse).
 
Last edited:
Back
Top Bottom