Does anyone have a quick tutorial of proper bias procedure for Nakamichi PA-5 available? I have the owner's manual and it says to use shorting pins on inputs. Does this mean just run a small rca from red-to-black on left channel and then do the same on the right channel?
What you are describing sounds like the outputs (speaker terminals), not the inputs (the RCAs on top).
To short the inputs, you could just insert a small alligator clip into each one, which will connect the center-pin position to the shield for each channel. Alternatively, you could sacrifice an old RCA interconnect cable by cutting it in the middle to make two separate cables, one of which to short the left channel and the other to short the right channel. To do this, just twist together the leads for each cable at the cut ends (one lead is the center conductor, the other the return/shield). If you want to make it look nice, put some shrink wrap on the exposed wires. Then insert the RCA end one of these cables into the left input RCA and the RCA of other cable into the right input RCA.
Or, you could just forego the shorting altogether. It will usually be fine that way, as long as you are not in an electrically noisy environment. I normally don't bother to short the inputs.
Gee, I have shorting RCA plugs on the bench. They are needed often. Besides, it is so easy to make a pair you should just simply use them as instructed in the manual. By the way, no loads or speakers connected for bias adjustments. Allow time for the circuit to settle and check your adjustment again.
I was authorized warranty for Nakamichi for years. These are very nice, reliable amplifiers.
-Chris
I was authorized warranty for Nakamichi for years. These are very nice, reliable amplifiers.
-Chris
Thanks Chris.
Well it looks like one side was at .048 and the other was .042. After turning the idle current adjustment down a hair on both sides (counterclockwise...?), I'm now having difficulty getting a good reading at all (TP101/TP102) and (TP201/TP202). Both read now 0.00. Any thoughts?
Hi zkottke,
My first concern is that by the reading you are giving, your meter hasn't got the accuracy or resolution for this reading. Looks like a 1 VDC scale. Please tell me, what meter are you using? What you need is one with a 100 mV scale (or thereabouts). You should be able to read at least 0.1mV with a decent meter in order to have any confidence in your readings at this level. Your test leads are also important, cheap ones can lead to false readings. Same with leads that are too old to be reliable. $10 leads are junk, please use half decent ones. Just for reference, I use leads that cost $45 or more. They probably went up in price in the last few years. You can pay upwards of $150, there is no need for that. You just need decent leads. Holding by hand when adjusting bias is a good way to blow things up.
At this age, the trim controls could be intermittent. If the control goes open or high resistance the bias current will drop to some minimum level (it fails safe). So before replacing anything, note where the control was before you started. I always take pictures because I often get equipment that was messed with by hacks. Next, with the amplifier off, gently rotate the control back and forth a few times. Put it back where it was when you started. If you feel very carefully and turn gently with light pressure, you can feel the dent where the control was for years. Put it there and turn the unit on again. Please use "micro-clips" to connect the test points to your meter. Note what the readings are when it is cold, then again after 20 minutes. Note the top cover must on in place to get a proper reading so the internal temperature stabilizes to where it would normally be.
Please let me know how this works out.
Now, this is critically important. If the controls do in fact need replacement, use the same type of trimmer control. DO NOT use 10 turn controls.
-Chris
My first concern is that by the reading you are giving, your meter hasn't got the accuracy or resolution for this reading. Looks like a 1 VDC scale. Please tell me, what meter are you using? What you need is one with a 100 mV scale (or thereabouts). You should be able to read at least 0.1mV with a decent meter in order to have any confidence in your readings at this level. Your test leads are also important, cheap ones can lead to false readings. Same with leads that are too old to be reliable. $10 leads are junk, please use half decent ones. Just for reference, I use leads that cost $45 or more. They probably went up in price in the last few years. You can pay upwards of $150, there is no need for that. You just need decent leads. Holding by hand when adjusting bias is a good way to blow things up.
At this age, the trim controls could be intermittent. If the control goes open or high resistance the bias current will drop to some minimum level (it fails safe). So before replacing anything, note where the control was before you started. I always take pictures because I often get equipment that was messed with by hacks. Next, with the amplifier off, gently rotate the control back and forth a few times. Put it back where it was when you started. If you feel very carefully and turn gently with light pressure, you can feel the dent where the control was for years. Put it there and turn the unit on again. Please use "micro-clips" to connect the test points to your meter. Note what the readings are when it is cold, then again after 20 minutes. Note the top cover must on in place to get a proper reading so the internal temperature stabilizes to where it would normally be.
Please let me know how this works out.
Now, this is critically important. If the controls do in fact need replacement, use the same type of trimmer control. DO NOT use 10 turn controls.
-Chris
Ok great. Yes, my multimeter leads are junk and now i realize this. I now have both sides set as close to .040 after 2 checks in between music for 20 minutes then performing same routine to check. My left channel was extremely hot and the idle adjustment was much more erratic than right. I'll give it some more time and see how close to spec i can manage.
Thank you!!!
Thank you!!!
Okay, sounds great.
Please get better leads as they will eventually cost you dearly. Same for your meter. I would highly recommend Fluke or Keysight, not the bottom of the line models but something reasonable. That would be more than $200. However, these meters will last you decades and will not lie to you.
Please get better leads as they will eventually cost you dearly. Same for your meter. I would highly recommend Fluke or Keysight, not the bottom of the line models but something reasonable. That would be more than $200. However, these meters will last you decades and will not lie to you.
I think i will make the investment into a better meter and leads. 1 amp down 2 to go. Now on to Classe CA-300 then Parasound HCA-2205!
Thanks again!
Thanks again!
I have a Nakamichi PA-5 Power amp now intermittently generating loud staitic (regardless of volume on the CA-7 Control (pre) Amp. I have to shut if off immediately so can't tell if it's one channel or another. Any ideas from the DIY'rs out there?
Hi Gary,
I have a good idea what is wrong. It requires skilled service by a very competent audio service technician not bent on "improving" everything he touches. The parts involved require matching using a jib, not a meter function.
-Chris
I have a good idea what is wrong. It requires skilled service by a very competent audio service technician not bent on "improving" everything he touches. The parts involved require matching using a jib, not a meter function.
-Chris
Anyone having to ANY work on an amp, preamp, etc should invest in a set of shorting plugs.
They're cheap, so why not have the proper tools on hand for such work.
They're cheap, so why not have the proper tools on hand for such work.