advertisement


Nac92/90.3 Service+

A

Ant

pfm Member
Evening all.

I recently purchased a one-owner 92/90.3 with little use, to which I really like what I hear for the most part. Pro's: Vocals sound great and there's a surprising kick on the mid-tones for 30(ish)w/pc, initially which is quite impressive. Cons: the strings are all over the place and after 30 minutes or so at moderate volumes the punchy notes seems to roll off and becomes a bit too mellow for my liking.

There is a definite L/R channel imbalance too up until 9 o'clock on the pot and any further clockwise becomes a bit untidy. I measured the supply/rails and bias and everything looks good - the 10000/4700uF BHC's are dated '98 with a very slight bulge to the top as if compressed with air. Based on that I'd like to replace the PSU capacitors and swap out the in/out/feedback tantalums for new. I've read Martins excellent acoustica site start to end, which is very informative and I plan to decouple the output transistors together with updating the 90's 10000uF 40v (35mm height) BHC's like for like, same for the 4700uF BHC supplying the 92. Swap out all feedback (4) tants for 47uF 25v BC128's, and in/out (8) for BC128's of the 25v 10uF variety, and with 4x Panasonic 470uF 50v FC's for the output transistors, to what I can establish - keeps it close to Naim 'sound'?

Question - anybody have an idea where I can purchase the above capacitors from all in go from the U.K please, happy to pay additional for the convenience since I've added it all to my Farnell basket but some components are coming from the States with 6-7 week delays.
 
Just my opinion and others may disagree but for me BC128s definitely change the Naim sound. I'm not saying that it's for the better or the worse but it's definitely different. I'd advise sticking to like for like replacements of the tantalum beads using the best you can get - AVX or Kemet.

What is it you're having to get from the States? Everything you need is usually available in the U.K.
 
I agree with Malcolm that modding the 92/90 is a bit of a No-no. It's really only a slightly beefed up Nait in disguise and nobody's modding those since the original design was spot on for the price/performance.

If you do anything replace res caps like for like if possible.

The Nap90/3 uses BHC which are now branded Kemet but are exactly the same thing.

Agree kemet or AVX tants like for like.

for the electrolytics in the pre amp there are several sensible ways to go

You could use the samwha 47uF caps Naim use for servicing

Or use 47uF Elna stargets instead

Or use 47ufF Elna Silmic II's throughout

Or use new old stock 56uF OSCON SP's for decoupling and the Silmics only for feedback.

Or use 47uF Nichicon Muse KZ's all round.

In practice though your experience is likely to be that you spend some money on servicing and actually get very little improvement.

Your "imbalance" issue is unlikely to be cured by any form of servicing. The 92/90 is known to be "coloured" in its presentation, and if that doesn't suit you then just move it on.
 
Dont forget to refresh the tant in the 24v feed while you have the board out of your 90.
I may have some of the coupling/feedback tants knocking about, will have to look. I recently purchased some of the Samwa electrolytics mentioned in another nait thread, prob have a few spares too.

It seems quite difficult to get the 10,000uF and 4700uF from the same place, Ive been looking for the kemet ALC10

Another thought, Kendeil is one of PFM`s favorite flavours, if you have a look at the K05 spec sheet, theres a couple of likely lads in the 40v section (look right)

http://www.kendeil.com/Portals/0/pdf/K05_type.pdf

K05040472_PM0D025 - 4700
K05040103_PM0E030 - 10000

Anyone know if Witch Hat or Avondale may stock or be able to order?
 
It would seem people generally agree that the tantalum beads contribute to the Naim sound, films are more open, Silmics are a preferred choice for 'lytics in feedback, os-cons for decoupling and Nichicon KZ's are good/popular in DIY.

After using KZ's in previous projects with good results - I initially thought about swapping out all the Buffer/Gain/Poweramp electrolytics & tantalums for Nichicon KZ's for a low cost experiment, inquisitive to see what change they made over the tants, and replace like for like back to beads if I don't like what I hear, any thoughts?

Replacing the PSU caps are the first step though - preferably for Kendeils (thanks juz), which I've sent Avondale a stock/order enquiry for the K05 10000/4700uF, so hopefully they're available. Alternatively - the 10000uF BHC (Kemet) are available from Farnell.


Thanks
 
The 10,000uF/50v K05 Kendeil caps don't fit the majority of cases where the BHC/Kemet 10,000/40 was used. The only amp with enough clearance is the 140/180 and they really shine there.
 
Thanks but as posted by juz 3 up - Kendeils K05 spec sheet shows 40v variants of 4700 and 10,000 in 25/30mm height respectively.

K05040472_PM0D025 -- 4,700/40v, 30x25mm
K05040103_PM0E030 -- 10,000/40v, 35x30mm

Would it be possible to order these ^ please?
 
MJS said:
The 10,000uF/50v K05 Kendeil caps don't fit the majority of cases where the BHC/Kemet 10,000/40 was used. The only amp with enough clearance is the 140/180 and they really shine there.
Click to expand...

The 10000uF cap PN: K05025103_PM0D030
Is listed as 35mm Diameter and 30mm High, is that a little too fat to fit the 90?
 
juz400 said:
The 10000uF cap PN: K05025103_PM0D030
Is listed as 35mm Diameter and 30mm High, is that a little too fat to fit the 90?
Click to expand...

That ^ PN is for the the 25v variant - the 35x30 40v 10,000 is K05040103_PM0E030. IIRC the original10,000 BHC's were 35mm in diamenter?
 
From memory, and I'd wait for MJS to confirm this, but I seem to recall that the NAP90/3 (and Nait3/3R) amplifier boards run off +/- 29v rails rather than the +/- 39v rails in the other NAPs of the period. If I'm correct there's no need to go for 50v capacitors when 40v types would be more than adequate. Remember Naim used 40v capacitors on the amps with 39v rails.

Alternatively there's plenty of spare room inside a NAP90/3 and you could mount the two main power supply capacitors horizontally off the pcb.

The capacitor for the +24v preamplifier supply is far less critical and you could go down to 3,300 uF which Naim used in some of the earlier NAPs.
 
Thanks for the info on the 3,300 misterc6 - Farnell stock the 10,000 and the smaller 3300uF BHC in ALC10 Series, so good to go :)

I've placed an order for the following...

92:
Input/output: 10uF 35v Kemet/AVX Tantalum beads
Decoupling: *in search of Sanyo Os-con SP
Feedback: 47uF 50v Nichicon KZ

90:
Input: 10uF 35v Kemet/AVX Tantalum beads
Transistor Decoupling: 47uF 50v Nichicon KZ
Feedback: 47uF 50v Nichicon KZ
Output Transistor Decoupling: 470uF 50v Nichicon KZ

*Does anyone know of a source to purchase NOS 47uF 25v Os-con SP's in the U.K please?

Thanks
 
I've had Nait 3 from new ('97 I think) and have been very content with the sound. Still don't think it's in need of recapping, but I've not used it for a couple of years now. If you're replacing the caps anyway, I'd be interested to know what capacitance value the old ones are now giving.

I found powering my Nait 3 pre board with a TeddyCap made a big improvement, but this isn't a particularly cheap option, even if you made your own *Cap.
 
I tried to get to the bottom of sanyo os-con replacements here but I am not sure I really got there ... I think sq225917's suggestions are the best starting point. I will go update that thread with my findings so far ... but they are just availability / spec searches at the moment as I have yet to try any. I would avoid ordering os-cons from unknown sources, they haven't been made for years, may just get grey market or worse rather than the real thing ...
 
Thanks nobeone. I looked into the Wurth WCAP-PTHR Series from Farnell - spec wise they seem in the same ball park as the Sanyo Os-con SP's
 
I've just swapped out the reservoir caps and 10uF tants in the power amp and noticed the Rubycon electrolytics decoupling the transistors are 10uF. *edit* SOA Circuit
 
As far as I'm aware the Naim power amplifier circuit does not have any Rubycon decoupling transistors. The Acoustica site deals with the NAPA power amplifier boards which are fitted across the range of this vintage except for the Naits (1, 2, 3, 3R) and the NAP90 and NAP90/3 which have a simpler lower power circuit running from lower voltage rails as I mentioned previously.

The only electrolytic capacitors in the power amplifier circuit you are dealing with are:

10uf 35v tantalum bead for the input capacitor
47uF 6.3V tantalum bead for the feedback capacitor
2 x 10uF 35v tantalum beads in the SOA circuit (is it these you are talking about?)

The circuit diagram for the NAP90/3 shows no integrating capacitor on the bias transistor.

I've just spotted a photo of a 90/3 board on the Internet that has two small light blue electrolytics but these are in the SOA positions which have zero effect on signals or sound. Many people feel that the SOA circuit should be disabled or removed entirely.
 
Apologies. They are in the SOA circuit, they are 10uF 50v but not tantalum beads; Light blue Rubycon 5M168's.
 
You must log in or register to reply here.


advertisement


Back
Top