I have a Nakamichi PA-7 that is acting strange. It has a boost of about 5 db from 3-8khz. At first I thought it was my speakers but I measured them on another amp and the speakers were fine.
Any idea what could cause this?
Only thing can think of is a cap in the feedback network that shunts to ground being electrolytic (like 47-100uf, maybe up to 220uf) fizzled. Wonder also if has like old bipolar electrolytics on the input circuit (there for dc blocking). Though both of those I mention more bass rolloff symptom than a pass band boost (or top and bottom rolloff leaving that 3-8k)
You’re like damn, this sounded bright as f**
Plus imagine across both channels where very coincidental to have matching problem severity.
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Nice amp! Definitely worth fixing. Hope you get it figured out.
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Wow, just googled that amp, it is a beast! Really nice looking too.
I’m from a technician, but fwiw I second the culprit likely being an old cap. It’s at the age where it probably could really benefit from (and is worth) a re-cap and tuneup (bias and offset check). The large power supply caps are likely still fine if they aren’t leaking or bulging. The little electrolytics should go though. Just repeating what I have read and been told, no real knowledge on my end..
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Nelson Pass is pretty active over on diyaudio he has been very helpfull in identifying issues like this. From what I can tell he is a genuinly nice guy.
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Thanks for the replies. I kinda figured it would be a cap or 2 or 26.
A full recap was in the plans anyway but now I will have to do it sooner than later.
That looks boss!!! I am assuming i wouldn’t want to lift it!
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Yeah, it weighs about 60 or 70 lbs.
Stumbled upon this today. A few nice tips to avoid confusion and big headaches durring the repair.
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