Naim Preamp Mods and Upgrades

page and links generously contributed by Ced Taylor: (opens new window)

For where to find parts, order codes and rough prices of components described here, please check on the components and supplies list pages. As usual here at Acoustica, you hack up perfectly good, working equipment completely at your own risk. Us getting away with it is no guarantee of a repeatable result. Season to taste, some settling of contents may have occurred in transit...
Nac 72- Pictures
  Nac 72 inners (fig 1) Nac 72 inners (fig 2) Nac 72 boards (fig 3)


Gain boards
  Nac 32.5 gain board (fig 4) Recent Gain board schematic (fig 5) Early Gain board schematic (fig 6)


Buffer boards  
Buffer board schematic (fig 7)


729 Time aligned boards
729 board schematic (fig 8) time aligned board parts(fig 9) time aligned board tracks (fig 10)


Preamp Internals
  Nac552 (fig 11) Nac252 (fig 12) Nac102 (fig 14) Nac52 (fig 13)


Board descriptions


NA323 K/S Phono MC
NA322 MM Phono
NA326 Fixed Line Input (link board)
NA328 Variable Level Line input with some HF filtering
NA324 Tape Output and pre potentiomenter Buffer boards
NA321 Main Gain, Output Drive
NA325 Switch on relay
NA729 Time-Aligned input buffer boards - AKA 72 Filter Boards

Nac 72 has:
324/7 (tape out buffer)
328/1 (Variable Level Line input with some HF filtering)
729/1 Time-Aligned input buffer boards
321/5 Main Gain, Output Drive
325/7 X 1 Switch on relay






Upgrading the preamp really boils down to 3 key areas:

1) power supplies
2) component selection
3) grounding issues

These are not really clearly seperate issues as there is some crossover between the subjects and also involve external psu's of various designs. However the gains that can be gotten from these areas are all large and can transform a humble little 32.5 into a total giant killer of a preamp that can stomp naims finest products.

POWER SUPPLIES to a large extent boil down to the quality of the regulator used and monolithic regs such as the lm317 are NOT up to scratch. See PSU page for more on thisl
COMPONENTSs. The quality of the capacitors is by far the dominant factor in preamps and to cut a long story short, the electrolytics (i.e all the caps in a standard Naimpreamp) should be replaced, ultimately with film caps. Resistors and transistors have only a minor affect on the sound.
EARTHING is nice as it is cheap to do and simple and reaps big rewards in terms of musical accessibility. Everything becomes bigger, bolder more realistic and textured.



Most of these mods are based on working on a NAC32.5 which is extremely easy to mod because it is made up of boards that can be pulled and is extremely cheap (roughtly half the price of the Nac72 which is its closest cousin. However, from reports these mods seem pretty effective in all the preamps in one form or another though i wouldn't do them on anything more than a NAC72 or Nac102 if you want remote, as beyond that you get more value by selling up, buying the cheaper preamp and using the surplus money to mod.

If you intend to mod preamps such as the Nac62 which has a mother board it may be worth doing them all in one go. Each and every one is a tested improvement and the hassle of getting the motherboard in and out again may not be worth it.


Mod Comments and information approx cost Bang for buck
DROP IN MODS The following mods all involve simple component changes and can be performed without any drilling- the new components just slip into the holes of the old. A few minutes with a soldering iron and a few pounds will give you a stunning whole new preamp and can be unequivocally recommended. They will take a NAC 32.5 to roughly NAC 82 level (IMO) having owned both. I recommend give it a try, you will notice the improvement from cold and full burn in will take a few days. You WILL be happy and may think about going further.    

1 upgrade gain boards Upgrade old NA321 gain boards to current (Nac82) status

There are 4 basic component changes that need to be made to upgrade the gain boards on all preamps prior to the Nac72 (I believe) to Nac 82 (and probably all current preamps that use this circuit) status. These are drop in replacements.

On figs 4 or 5
a) change R15 to 100K
b) change R10 to 10K
C) Add C6- Solder a 5.6pf cog ceramic cap across the base and collector of TR5 (actually this is easier if you drill pilot holes).
d) Change C3 from a 470pf to a 100pf polystyrene cap.

Makes sound leaner and clearer, tightens up the bass which can be a bit overblown on the 32.5.

£2 6/10

Powerrail decoupling capacitors

upgrade with oscon SP series

Upgrade to all boards. A Drop in replacement.

On the main gain boards there are two 47uf caps. C1 in figs 4 & 5 is the 47uf powerrail decoupling cap and the one you want. Replace this with a 56uf, 25V Oscon SP gives a good increase in dynamics, clarity and groove or 'boogy factor'.
On all other boards there is only a single 47uf cap which should also be replaced.
I wouldn't bother with the relay board cap though as it doesn't affect the signal, so you will need 6 to do the whole preamp (or 8 if you do phono boards too).
Thanks to Neil McBride and Andy Weekes

Note 1: Note you really want oscon SP series not SH or any other type as they are by far the highest specced 'audio grade' oscons.
Note 2: I probably wouldn't bother with 47uf, 50V elna silmics in this position as general reports are negative. If you wish to run the powerrails at 30V (see psu mods page as to why) dont use oscon SPs as they are only rated up to 25V. I don't know what might work well in this case but rubycon ZA or ZLs would be a good bet as they are very low impedance.
Note 3: DONT use Black gates here. I tried and they were undynamic and 'mushy'. waste of time.

6 caps @£2.50 each = £15 8/10

Feedback decoupling capacitor

Replace with Elna Silmic

This is a must do mod. Only on the gain board. Drop in replacement.

Replace C5 on the gain boards with 47uf, 35V or 50V Elna Silmic caps. Big increase in detail, smoothness, openness and instrumental seperation and just gets to the heart of the music somehow. This single change gets you 80% of the way from a 72 to an 82! Basically the feedback path would seem to be the most sensitive part of the preamp so upgrades here have a disproportionately huge effect.

2 caps @ £1.50 = £3 10/10
  Replace with Black gate N series

People have also used these with reported good results though not tried them myself in this position. My personal tastes based on experience of black gates as coupling caps would be 'nah' but you never know- I might be totally wrong. Note the burn in with black gates is also 2 weeks as an absolute minimum (they sound terrible at the start) which is a pain and they revert to their unburned-in state if left unpowered for a while. Personally I don't like what black gates do but some people swear by them. If in doubt a silmic is quintessential Naim.

2 caps @ £7.50=£15 ?
4 signal path capacitors Upgrade these capacitors

This is complicated. There are several possibilities here that can be used to replace the blue 10uf, 35V tantalum input and output caps on all the boards.

Sizewise, the BC128s, elna silmics and black gates are all drop in replacements so are simple to install. The 2.2uf SMRs require drilling new pilot holes (easy) but are definitely worth it and (in my opinion) the best caps available so far though you can get away with 1uf too with barely noticable loss in bass.

However, signal path caps, among many positive attrirbutes, also seem to affect the subjective sense of brightness balance and presentation of the music a certain amount so taste can become an issue, whereas good powerrail and feedback caps don't seem finiky in the same way. Generally the BC128s and Evox smrs do give a sense of brightness but this is not intrinsic, rather down to the fact that they are revealing in the treble region- This is down to system quality issues. Your CD player needs to be top notch or these caps will reveal the edginess of uncontrolled distortion in the treble region that lesser CD players have. With a good source (or probably vinyl) they are superb and not at all bright but rather revealing. Be warned. If in doubt stick with the tants. They are actually not bad caps in that they have good musical qualities and are very forgiving of dodgy treble if ultimately limiting.
I've compared tantalums, silmics, solid aluminium, oscon, BG Ns, ansar supersound polyprop and PPS caps.
Heres a little summary (IMO of course): Tantalum are nice though not great on clarity or high frequency extension, nor 3D; musically involving though. Solid aluminium (BC128) are very musically involving though a tad bright. Oscons are very 'funky' and have good bouncy bass though a tad confused and a bit 2D. I reckon tants are better. BG Ns are very smooth, clear and detailed with a lovely silky 3D sound though I find they have the yawn factor- not very involving somehow and mush instruments together musically. Polyphynl sulphide (Evox SMR) have a very tight puchy bass, involving mid; musically involving though revealing in the treble. Your source better be up to scratch or they can be too much. Can sound a bit grey. Silmics are nice and organic, involving though not the last word in clarity but easy on the ear. Ansar polyprop I found relentless and overbright. No like. Get the impression that electrolytics are easier on the ear though not so revealing or 3D


a) 10uf, 25V BC128 solid aluminium caps. These are very musical, with more detail, punchyness and muscial involvement.. Bass is a bit Flabby initially but burns in within a week or so becoming tight and groovy.They can sound slightly bright or revealing in the treble.
Thanks to Les Worstenholm

£0.70 each 6/10

b) 2.2uf Evox Rifa SMR polyphynelsulphide caps. Use only on the INPUTS ONLY of every board (board output caps do need to be 10uf or bass dissapears). With them Bass become exceptionally tight and punchy, dynamics increase, the whole soundstage opens out more and you get greater transparency and clarity. Things sound more realistic or' in your livingroom'. In my opinion the best signal path caps. Some have found the sound a little 'grey' which I acknowledge so again your whole system needs to be up to scratch.
Expensive and values above 3.3uf are difficult to get hold of- only at ELFA to my knowledge sell up to 10uf. don't seem to really burn in noticably- what you hear is what you get.
Thanks to Les Worstenholm

£2 each  
      c) 10uf, 35V elna silmics. Musical, warm and detailed caps. Possibly not quite the tightest bass but a nice alternative to tantalums and no hint of brightness.
0.95 each  

d) 10uf, 50V black gate N series caps. expensive with very open and seductive sound, but ultimately unmusical caps IMO. Bass and dynamcs leave somewhat to be desired and does not seperate out musical strands well- instruments seem to mush together in the midle of the soundstage in a very un-naimlike manner. Some swear by them but personally find them 'hi-fi' and boring.

£3.20 each  

e)Mix and match. A good mix is 2.2uf SMRs on the input of all boards, 10uf BC128s on the output of the buffer boards and 10uf Elna Silmics on the output of the main gain board.
The Elna smooths the brightness of the other caps and adds a little magic which makes for a tight, musical and involving listen.


Feedback path Resistor upgrades


Welwyn RC55Y

Upgrade to Welwyn RC55 resistors

Naim use the BC componets SFR25 resistors everywhere which can be improved on.
Replace R1 and R2 on the gain boards (Fig 5) with Welwyn RC55y resistors. Minor cleaning up of the sound with a slightly sharper presentation but not greatly noticable. My thoughts are that the returns from replacing these resistors are not huge.
Thanks to Les Worstenholm

£4 2/10
Vishay S102J
VishayS102J bulk foils

Not tried them but reports are that they are somewhat soft in sound. Also stupidly expensive. and you can't get the 12K value so would need to parallel 2.

£12 ?
    vishay dale cmf55

These are nice alternatives. Smooth, detailed with good bass and my favourite

0.20 each 2/10
6 Transistors  

This is not a mod as far as I'm concerned but BC550/560 are perfectly fine replacements for the ztx214/384 transistors. Can't really hear any difference between em anyway.

More fiddley mods These mods all bring further improvements from the medium to the huge but now you start rebuilding the preamp to a certain extent. It is possible to cram the parts in though you may need to look at rebuilding- see below    

On board regulators

regulating the preamp variously

A huge upgrade. Fundamental improvement to the sound. There are various regulators and regulator systems you can use use but the ALW (Jung) superregulators beat any monolithic regulator eg lm317, lt1086 etc. I've heard by an absolute mile. Just bags more detail, dynamics, rythmically tighter, more pitch perfect, faster, textured, more open soundstage, more involving, the works. Truly fabulous.

1/2 regs: the easiest option is to replace the lm317 regulators with superregs in your psu. See the psu page for information on this or does a very indepth write up on modding a snaps and the oscap hicap clone.

1/2 regs: Another option, if you don't have a psu, is to place them directly in the preamp and use the powerline from the poweramp for voltage feed. This means delving into your poweramp which has an internal lm317t regulator and changing the resistor to give a minimum of 30V going to the pre (an ALW regulator needs 5V headroom. However a bonus is that regulators ideally work best closest to the circuit they are regulating. For calculating these resistor values see the lm317t datasheet which you can pull off the internet. Finding space for 2 superregs in a NAC 32.5 or similar case is no problem at all.

6 regs: Using 6 onboard superregs is also possible so you can regulate each board (4 buffers and 2 gain boards) independently which is an optimum solution. This is easiest with a wide case amp e.g the Nac102. However you get a fair proportion of the gains just using two regs. Be warned that there have been a couple of reports of increased hiss if using the superregs onboard. Never had ANY problem with this personally in all the various iterations I've tried though.
It is possible to do this with the shoebox sized cases also, but you have to either remove the phono cards, cut out the phono card pins and be a bit clever in how you glue the boards in. Its inelegant and I wouldn't trust it to be moved around much without bits shifting.
More sensible is to rebuild with the motherboard project below. This allows you to mount the superregs to the bottom of the tray and fit the motherboard on standoffs just above

For more information on superregs and how to build them see the psu page or go to ALWaudio website at and download the manual.
Many thanks to Andy Weekes for this one. Respect.

For details on superregs, see the PSU page.
SEE also powerrail decoupling (mod 9) below if using superregs


~£30 each 10/10

feedback capacitor


replace with polyester cap

As the feedback cap is the most sensitive part of the preamp, upgrading this cap from an elna silmic to a film cap should reap greater rewards.... and it does. Replacing C5 on the gain boards with a 47uf, 63v evox rifa MMK polyester cap brings further gains. From cold these caps are a whisker better than fully warmed up silmics and over a couple of days they burn in subltly to provide what can only be desribed as a bit of magic. Its subtle but it strips away distortion so everything becomes more relaxed but at the same time more intense, less harsh, more musical. It is hard to describe but it allows you deeper access to the music with more emotion, intensity and less effort. You'll have to cram this in but use extension leads to the cap and afix the cap conviently as close as possible to the circuit. Use hotmelt glue or something to hold the cap in place.
Oddly enough a technically better 47uf mundorf Mcap polypropylene sounded worse- more detail but breaks the music apart and ruins the enjoyableness of the preamp so stick with the polyester which is very coherent.


£15 9/10

power rail decoupling capacitor

prototype phase showing some evox smrs and MMKs being tested

replace with film caps

This is brilliant but apparently only works if you are using supperregulators. normal LM317 type regs won't work.
Replace the powerrail decoupling caps (C1 on the gain and buffer boards), with film caps in the 3.3uf-5.6uf range. Apparently the supperregulators are happiest driving small capacitive loads and 47uf is large so reducing the capacitance lets them work better. And it shows. Also being a film cap they decouple to highter frequencies and are lower impedance so its a win all round. The result? it almost isn't possible but dynamics and bass tightness increase yet again, speed also increases- music fairly hurtles along its so tight, but the 2 points I most noticed were rythmic and textural changes. Rythmically it is so accurate that subtle instrumental thrums reveal themselves as actual rythms instead and everything just become more pitch accurate. Texturally instruments also sound more lifelike and some bass instruments sound like kodo drummers just set up shop in your living room- this is seriously good stuff!
what caps to use? 5.6uf Mundorf polypropylene Mcaps
are the best by far I've tried. The bass is just so funky and groovy. Evox SMRs also work, maybe slightly more subtle but not as much fun. Audycap plus 3.3uf, though top quality audio caps and very expensive, are terrible with soggy bass and a 'weird' if detailed sound. andy Weekes says even 3.3uf polyesters are ok.
Many thanks to Andy Weekes for this one. Respect.


£2 each 9/10
9 Coupling caps replace all signal path caps with smr caps

Replace the OUTPUT coupling caps with 10uf Evox SMRs. They're big so you really need to either hot glue them to the mother board and run flying leads to the pcb holes or do somehting of this nature. lenth of flying leads is not an issue. An upgrades motherboard is another possibility. They increase the effect of input SMR caps with yet more transparency and tighter bass but see the caveats in mod 4 above regarding their sound balance.


£7 each 5/10
10 removing the balance pot

remove the balance pot and replace with 2 welwyn rc 55y or any good quality resistors e.g vishay dale cmf55s. Try values around 2k67. Not tried this yet but apparently cleans up the sound a bit.
Thanks to Les Worstenholm

£2 ?
11 Upgrading the volume pot

Replace the volume potentiometer with a nobel or panasonic pot. Panasonic pots are apparently very detailed. Nobel slightly smoother. Possibly the best may be a stepped attenuator stuffed with vishay dale cmf55 resistors. These are sold for a rediculously low prices on ebay from malaysia (you have to search) but seem to get universal good reveiws. apparently they need to burn in significantly and being a stepped type this is difficult so you need to connect all the resistors up and burn them in before installing is the advice. Not tried these myself yet.

see recommended components page for info.


£30-£60 ?
Rebuilds 1- The Motherboard This involves rebuilding your preamp with a motherboard but brings further gains and allows the higher level mods to be incorporated into a narrow shoebos preamp case.    

get overlay here (pdf)

This motherboard is based on the NAC82 layout though oddly enough the Nac252 has a similar board. However it has been redesigned to allow space for large film caps for ultimate performance. Also being very compact it allows for placing 6 superregs in a shoebox sized case though there is probably insufficient space for phono cards so its a line stage only solution. Additionally it has the time aligned filter section on not just the buffer boards of earlier models.

The grounding scheme is important to sound quality and using this tighter grounding layout and also star supplying the powerrails reaps considerable benefits compared to a nac32.5s when using identical parts. The effects are similar to going from standard caps to elna silmics in the feedback loop. More ease of access to the music, more texture more easy to listen too and adds some magic.

for this project you need to download the pcb schematic and etch onto a pcb, stuff using the parts list given then rewire the preamp cutting out the mother board. If you don't feel comfortable doing this or can't figure out how to you probably shouldn't attempt this project.

For details on superregs, see the PSU page.
I'd recomend you know a bit about preamps and modding as no backup can be given for this project.


  stuffing guide

get stuffing guide here (pdf)

These datasheets should come in useful but basically you need to turn around the bc parts 180o to the zetex parts as the pinouts are different

However as I feel this idea has been superseeded by the 'Air Guitar-iste' preamp project below I've not put together a parts list. The bits are all available by cannabalising from the 'Air Guitar-iste' bits, the recommended components web page and a bit of serching on farnell.





get pcb artwork here (pdf)

See the Air Guitar-iste preamp build notes below for how to etch your own pcb

Rebuilds 2- The 'Air Guitar-iste' preamp This is a stripped down and optimised version of the motherboard. Less functionality (a pure line stage only) but higher performance AND happily cheaper but it is the core naim circuit and has been rebuilt of the naim principles of optimising powersupplies and grounding though with top notch (I think) parts.    


The Air Guitar-iste preamp (gotta call the thing something) is' rather nice' or the best preamp soundwise I have been able to build in 6 years of fooling around and modding the naim pres and scrounging ideas from everywhere possible, primairily pink fish, avondale, It incorporates the very finest of all the psu, grounding and component upgrades I've managed to find and test and is actually extremely simple to build. In fact you can build it from scratch or hack a normal preamp and build it. Parts and timewise it is far simpler to build than the mother board. And nope, theres no 729 style time aligned filter boards and yep, read the build notes for an explanation of why not.

For an idea of whats involved and how it sounds read the build notes below. I would however confidently expect it to stomp a Nac52 like a bug and for a 'from scratch' build price of around £400 inc psu I reckon thats pretty good.

Again I'd recomend you know a bit about preamps and modding as no backup can be given and although I'm pretty sure I haven't made any mistakes in my write up notes and labelling, it will help to know how to check schematics and know your parts if I have.
Also Note: The Air Guitar-iste pre does require a raw dc psu. Build information on this is on the psu page.
For details on superregs, see the PSU page also.


stuffing overlay
Parts list and datasheets

Get the parts list here (microsoft excel document) with rough costings, order numbers etc.
Again you'll also need the parts list for the raw dc psu and superregs on the psu page.

However here are some datasheets for bits you might want to know more about:
alps blue pots
grayhill input selector
clare prma reed relay
mundorf caps
vishay dale resistors and the mouser values
J510 diode
Evox SMR
Evox MMK




stuffing guide

build notes

Get the build notes here (microsoft word document)

with details and pictures for hacking a naim pre or building from scratch. This gives you most of the info you'll need.



pcb artwork


get pcb artwork here (pdf)

stuffing guide here (pdf)

get stuffing overlay here (pdf)

See build notes above for all details on how to etch your own pcb

  Wiring schematic

get wiring schematic here (pdf)

This is enough to give you the idea. obviously each input socket has to be wired to the selector which is not shown to make it easier to see.
If you are hackin a naim pre then this is not an issue for you but if you're building from scratch then it is. Note how the input wires are shown to the opposite side of the case to the power lines. Might be worth wire training them with the ground lines though.
if you want to add a balance pot its all pretty self explanatory.

  Block diagram

get block diagram here (pdf)

just an overview of how a naim preamp runs. for the Air Guitar-iste the 729 buffer has been omited as explained in the build notes and the 32 and upward preamps also have a tape output buffer which is the same as fig7 above as far as I know (not the 729 boards buffer).