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NAP 180, early versus late models

P

peterm

pfm Member
I recently bought a 180 with the intention of fitting a pair of LesW's new boards to drive my shahinian obelisks as recommended some time ago by MJS. I found that my 250 didn't produce much (any!) output from the tweeters in the obelisks and I gather the regulator boards in the 250s and135s can be incompatible with the 2 ohm load resulting from 4 parallel connected tweeters. My old 180 did a much better job than the 250 so it seemed a good plan (and reasonably cost neutral) to sell the 250 and use the proceeds to buy a 180 plus a pair of Les's boards.

My old 180 (used in a second system) is an early version, the serial number dates it to 1993 whilst the "new" one appears to date from late 2001.

On receiving the newer one I looked inside and found it had a 500va transformer rather than the 430va version in the old one, I was pleased.
When I connected the new amp in place of the old one I was less pleased - I thought the stylus needed cleaning on my cartridge (it didn't). The new amp is much less dynamic than my older one (it doesn't really matter since I'll be ditching the NAPA boards in favour of Les's) and I see why some say the 250 is a better amp than the 180. I didn't hear any difference when I replaced the 180 with a 250 some years ago but I would have done if my 180 had been the one I just bought.

This begs the question - did Naim downgrade the 180's performance to stop it stealing sales from the 250, or is it just sample variability?
Does anyone have similar experience or information (perhaps someone who was at Naim at the time!)?
 
Get them both done then, I would imagine they will be sounding quite shouty by now.

Pete
 
peterm said:
I recently bought a 180 with the intention of fitting a pair of LesW's new boards to drive my shahinian obelisks as recommended some time ago by MJS. I found that my 250 didn't produce much (any!) output from the tweeters in the obelisks and I gather the regulator boards in the 250s and135s can be incompatible with the 2 ohm load resulting from 4 parallel connected tweeters. My old 180 did a much better job than the 250 so it seemed a good plan (and reasonably cost neutral) to sell the 250 and use the proceeds to buy a 180 plus a pair of Les's boards.

My old 180 (used in a second system) is an early version, the serial number dates it to 1993 whilst the "new" one appears to date from late 2001.

On receiving the newer one I looked inside and found it had a 500va transformer rather than the 430va version in the old one, I was pleased.
When I connected the new amp in place of the old one I was less pleased - I thought the stylus needed cleaning on my cartridge (it didn't). The new amp is much less dynamic than my older one (it doesn't really matter since I'll be ditching the NAPA boards in favour of Les's) and I see why some say the 250 is a better amp than the 180. I didn't hear any difference when I replaced the 180 with a 250 some years ago but I would have done if my 180 had been the one I just bought.

This begs the question - did Naim downgrade the 180's performance to stop it stealing sales from the 250, or is it just sample variability?
Does anyone have similar experience or information (perhaps someone who was at Naim at the time!)?
Click to expand...
I use a 180 from 1998 with Obs2. The amp has been recapped and works well with the Obs2. I briefly used a 250 and that was not as good a pairing, although I would not say it was alarmingly bad. Tweeters functioned. I would be curious to hear how the Avalon boards work for you. Good luck.
 
Pete MB&D said:
Get them both done then, I would imagine they will be sounding quite shouty by now.

Pete
Click to expand...

The unserviced 180 (old one) sounded as good as my recently serviced 250, not at all "shouty".
I'm not going to have the newer one serviced just so I can put the newly serviced NAPA boards in the loft once I've fitted Les's boards in their place!

Thanks Linus, it was your post from last year that alerted me to the fact that 250/135 regulator boards and obelisk tweeters were a bad combination, up to then I was thinking of taking the obelisks back as faulty.

Peter
 
I have serviced a 250 that was probably as old and it sounded very hard and shouty, yours must have had a easy life!

Pete
 
Well I hope things get better. My 180 seems to do the job. I have heard that the Obs1 was a much harder load to drive versus the obs2 or a late model 1.
 
I've now got round to looking inside the amps to compare them.
The older one with the smaller transformer runs the boards at +/- 37.9 volts, the later one +/- 39.3 volts.
I next checked the bias current using LesW's instructions (multimeter connected in the +ve supply to the board with no load connected and no signal input).
The recommended range is 36 to 38 ma, the old one measured 37.5 on one channel and 40.5 on the other. Since it is suggested not to exceed 40 or else risk thermal runaway I tweaked the higher figure down to 37.5 to match the other channel.
The newer amp had 30.3 and 30.8 ma bias currents! I increased them both to 37.5 to match the other amp.
I have now listened to both and they sound the same, my earlier reservations about the newer model have been resolved.
I'm suspicious about the low bias on the newer model, both channels were similar suggesting they had been deliberately set that way but it certainly sounds better with the higher settings.
 
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