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sickly nac 92

Z

zanash

pfm Member
I've just pick up said pre .......Its making a bubbling noise [pops clicks etc] on the right channel with vol pot at zero or mute engaged. left chanel is quiet music plays over the top of the pops and clicks on right channel ......suggest caps died dying output stage ? does anyone have the schematics ...or better still able to point a finger at the problem?
 
Difficult to say. I guess I'd change the gain stage's feedback caps first, you probably know their position (47uF, bottom right, the pair, not the single one). But then again, I'd change the caps anyway.

Best,
Oliver
 
cheers yes my gut feeling too would you swap the tants for say cerafines ?.....having had the thing running through my system should its presentation be warmer and richer than a valve pre [beard ca506] .....my previous experiences with naim gear lead me to expect forward touch bright. I'm getting the overblown central image and compressed extreme left right ...and its not as resolving as the beard. That's not to say its not an interesting listen, just rather different ! What the experiences and recommendations of replacing the alps blue with something a little more transparent ?
 
I, too, had gut feelings about the use of "boutique" caps in Naim amps once, but experience tought me otherwise. I'd swap the tants for Kemets, they are cheaper than Cerafines and easy to buy via eBay. AFAIK, these are used by Naim nowerdays.
I swapped all electrolytic caps in the buffer and gain stage for Nichicon KZ types (47uF/50V). Some say these caps are sonically close to the old red Roederstein ones used by Naim in the 80ies and early 90ies.
Beyond that, I'd add filters, change existing ones and add the best PSU you can build. :)
 
Aren't these preamps essentially the same as the other Naim preamps with down rated components and poor earthing?
In which case the schematics will be on acoustica or Neil's pages.
Regards Andy.
 
^ yes. 92 = 62 = 42 in terms of actual circuitry.

Or in 72 parlance, source is switched into a 324 buffer feeding the volume/balance pots, then a 321 gain stage feeding the output. Tape outputs are not buffered but fed from a 680R on the switched input. A 725 delay circuit mutes it for a few seconds when you turn it on.
 
I'm sure it's just a typo but I think MJS meant to say - a 325 delay circuit
 
I did mean that! Thanks. My head was in full Naim nomenclature mode. It would have been a 725 if it had been designed for the 72, but it was for a 32 hence 325. Now the 729 on the other hand..
 
Incidentally the one-board pre-amps used to use the x21 suffix. So a NAC92 main board is a 921 for example even though it had buffers as well as the gain stage on board.
 
Ok thanks for that info ......Work so far has not eliminated the fault , but sound quality and resolution are streets ahead. Components changed are as the previous thread coredumps nac92 a second life, with the exception of the alps blue being swapped for a TKD 2CP-601, and yes I did forget to check if it was a pitch match, and no it didn't. but happily with legs bent to the correct hole pitch, the pot is lowered to the exact height required. This has done astonishing things to the sound quality ....gone is the warm dull rather lazy/hazy presentation. Its now fast clean taught rich clear ...who'd have thought the blue was that bad ?......The 1k that coredump changed was swapped for a pair of amtrans amrg carbon films ....The larger electrolytics were replaced with Nichicon`s FG [fine gold]. I've narrowed the fault down to a tan but can't find a supplier rs are charging £3 a pop min order of 25 , thank you no thank! So have got some standard electrolytics and will swap the ones of each channel and see if thats fixed it .
 
So following a bit of investigation the fault was in fact the first tantalum cap on the input of the first stage after the pot , this was duly replaced on both channels .....
All bubbling and farting noises have been eradicated.
 
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