NAD 1000 Pre-Amp Recap question.

[Ronj]

Hello All,
I am about to re-cap a NAD1000 pre-amplifier. Gonna change all the electrolytics, as all of them must be almost 20years old and are a Taiwanese Brand called TEAPO. I anyway happen to have all the required values with me in Nichicons so thinking why not? While I was at it I noticed that there are some electrolytics in the Signal path...

I have copy pasted parts of the schematic in the below image and marked these suspected signal path electrolytic caps in Red circles(Only represented one channel here, the other obviously is identical)

Now the question is while I re-cap should I opt for Non-Polar caps? Or should even try to squeeze in some polypropylenes? Or just generic Nichicons would do? Really appreciate your inputs...

 

[Mooly]

I would go with good quality like for like parts. One thing I would do (and just saying this quickly looking at the circuit) would be to confirm by measurement of voltage across the caps that they are fitted the correct way around. Sometimes when offsets are in the millivolt range you find caps can be incorrectly biased.

 

[sgrossklass]

Teapo, eww. Not exactly high-end.

The caps before and after the phonopre should be bipolars, as they see no bias voltage to speak of. It still isn't very much for number 3, as well as the one in the feedback network that you missed (C321, oh, and C215 for the RIAA).

BTW, looking at the schematic of the 1000S, I don't like the headphone output much. It would be suitable for vintage 600 ohm cans but little else. Tons of gain (>30 dB) and high output voltage, impedances not particularly well-balanced, limited output current. At least they were smart enough to place muting before the amp rather than behind it, as some Japanese mfrs did. I'd want to revamp this - lower supply voltages, put in a NJM4556A configured as a unity gain buffer with equal impedances +/-, and decrease output series impedance considerably. I could go into more detail if you're interested.

 

[Ronj]

Teapo, eww. Not exactly high-end.

The caps before and after the phonopre should be bipolars, as they see no bias voltage to speak of. It still isn't very much for number 3, as well as the one in the feedback network that you missed (C321, oh, and C215 for the RIAA).

BTW, looking at the schematic of the 1000S, I don't like the headphone output much. It would be suitable for vintage 600 ohm cans but little else. Tons of gain (>30 dB) and high output voltage, impedances not particularly well-balanced, limited output current. At least they were smart enough to place muting before the amp rather than behind it, as some Japanese mfrs did. I'd want to revamp this - lower supply voltages, put in a NJM4556A configured as a unity gain buffer with equal impedances +/-, and decrease output series impedance considerably. I could go into more detail if you're interested.

Hey thanks a lot. But I am not really gonna use the Headphone Out. But I surely wanna use the Phono stage. So what you suggest is, use Bipolar for Phono stage?

 

[east electronics]

Teapo at the time was quiet reliable been pulling plenty of them from old Nad equipment for replacement but most of them have been measuring quite ok still replaced to be on the safe side ...

For what it worth company exists also today so yeah they are not totally crap but yes these are cheap things...

As for replacements i will go also with mooly's suggestion and at some points i could play with film bypassing down under the board in the area of 0.1-0.47 if time was available for playing around .

Kind regards
Sakis

 

[Mooly]

Teapo at the time was quiet reliable....

Yea, I've come across Teapo caps many times over the years. They are a typical reasonable quality cap.

At least they are not noVer.

 

[Ronj]

Finally after a month's delay, today I finished the re-capping of my NAD 1000 pre-amp. Have a doubt about Capacitors C321 and C322, Originally they were electrolytics 47uF/25V. As I did not see any "biasing' so to speak I replaced them with 22uF Jantzen polypropylene. is 22uF too small a value? should I add another 10uF in parallel to the 22uF Jantzen polypropylene?

I have kept C315 and C316 electrolytics. Used 100uF 63V Elna Cerafine I had in hand. I always use "tone defeat" anyway . I did not do any critical listening yet. But when I switched between tone defeat on or off with Bass and trouble at mid points, I couldn't hear any difference. So is 22uF good enough? or is it because of my speakers Usher V601, that don't go very low. around 44Hz... Is that I don't hear any difference?

Attached is the schematic with said capacitors circled.

 

[Mooly]

Not easy to analyse at a glance because the settings of the pots all alter what the cap sees impedance wise. All you can say with certainty is that you will have raised the lower roll off point of the amp... as a ball park figure look at the specs and see what its supposed to go down to and then add say 100%. Not very accurate but is should cover worst case scenario.

 

[Ronj]

Here is the spec. For frequency response it says +/- 0.2db. Of what I wonder... 20Hz - 20Khz +/- 0.2db?

 

[Mooly]

Indeed... of what. The figure is meaningless on its own.

 

[Ronj]

I added two ugly 30uF APC polypropelene behemoths in parallel, soldered directly to Jantzen's leg and hot-melt glued in "doggy" position on the side. 😀 Luckily I dont hear any noise pickups.. So 52uF in total... Hope that settles it... Music is playing now.. Running in.. So far no noise, no crackles. A tad bit brighter than before.. Or so I feel... May be in time that shall settle as well. Now back to the Nikko Project...