Acoustica 7 1 15 Amp

Overview

The psus on naim amps are always tempting to mod or diy as they appear simple but are actually a bugger to get right . Its easy to spend hundreds on making one that sounds no better than the powerrail off a Naim poweramp- I have several toroids and dozens of regulators and reservoir caps to prove the point.
Once you know what to look for however, its not difficult to make a better one for a fraction of the cost of a naim psu. Probably also why they are so attractive to the modder.
Essentially they consist of transformer, reservoir caps, rectifiers and regualtors.
IMO the regualtors are the dominant factor affecting sound quality of the psu but transformers also have a part to play as does getting the earthing right. I have found reservoir caps and the rectifiers to be of minor importance as long as they are of good industrial quality.
Bear also in mind that Julian Vereker once stated that for power transmission low impedance is critical and for signal transmission low capacitance.

Obviously see the recommended components and suppliers pages for links and information on these parts

TRANSFORMERS
Getting the transformer right can be a pit for the unwary. This is principally because off the shelf toroids are useless from an audio point of view and unless you know how to specify a custom one you'll probably get nothing better. However a good transformer can make a significant contribution to sound quality, giving a bolder, more vibrant and solid presention with 'darker' backgrounds and more instrumental seperation.
In the hicap Naim use a twin winding, centertapped toroid giving around 37Vdc at the reservoir caps which works out at around 27/28VAC. Size is around 500VA. My advice is to get a C-core from avondale or R-core from Hifi tuning (see components page). Otherwise custom specify but then you're sort of on your own. So anything you can look for?
1) I recommend avoiding toroids completely and going instead for R core, E/I core or C core transformers. These allow a lot less ultrasonic grunge from the mains through as they are quite low bandwidth compared to toroids.
To quote Les Wolstenholme again: 'Big 'C' Cores, I love 'em to bits. They embody all that's so right when it comes to the reproduction of music. The sound is big, powerful, rounded, blacker than black. Toroids - never quite came to terms with them - dry, nasal almost, noisy and somehow capable of constricting the sound.Why.?? We can only guess that the extra metal in stacked or C cores acts in two ways: It behaves as a 'built in' filter and stores quite a lot of energy as hysteresis effects. 'C' core disadvantages.?? Big, expensive, some external hum field. Experiment: Change any toroidal transformer in any amplifier/pre-amp for an equivalent stacked component, sit back and be amazed.'
Another quote by Martin Clark: Toroidal: A toroidal core is essentially 'gapless' leading to higher permeability (toroidals are still laminated but it's a continuous spiral of thin sheet). Close coupling of windings makes for low external field (low interference) and higher efficiency (lower iron and copper losses). This leads directly to much lower impedance over a wider bandwidth. Less core material can be used, leading to slightly better power: weight ratio (cost benefits). Cons, apart from how to manufacture, include the fact that the core is more easily saturated by DC components on the mains, due to higher core permeability and smaller cross-section. Leads to the infamous 'hum' problem. Laminated, A.K.A 'E-I' / 'Frame' transformers: Easy to make - the bobbins are wound separately, then the laminations interleaved, leading to gaps in core. Lower total flux and higher external field results; not as tightly-coupled (magnetic and capacitative) as toroidal types - special techniques required to achieve wideband coupling. Converse is that frame-type power transformers provide greater immunity to HF line noise than toroids, so they can be very good in pre-amp supplies. Split-bobbins also good for EHT safety.
I suspect the main reason frame-types are used for valve transformers is cost. Valve amps imply low production volumes and odd winding voltage requirements. Also significant is the fact that the advanced techniques to achieve wideband coupling (bi- and trifilar windings) are much easier to implement winding a bobbin, around which the transformer core is assembled subsequently. Note also that many valve and signal transformers rely on trick core materials (high-nickel-content) which can be too expensive/too brittle to wind into a toroid for high production volumes.

2) you want at least 2 centertapped windings. In practice I have found seperate windings for analogue circuits give a major boost to sound quality (see the ultra preamp build notes on the preamp page) so have 2 as a minimum. You must have centertapped configuration too so that you can use half bridge rectification. This sounds better than full bridge rectification and I surmise this is because it avoids diodes in the ground line so giving low impedance to ground. Who knows though.

3) Beyond this it gets hazy. However useful key words if you intend to specify yourself would probably be: split bobbins, electrostatic shields, extremely low impedance secondaries, low core saturation, low capacitative coupling.

To put things into perspective: I've tried several large toroids including a huge 630VA custom toroid from Antrim Transformers, all of which were completely blown away by a small 160VA twin centertapped R-core from Hi-Fi Tuning. Night and days stuff.

RESERVOIR CAPS
In my limited experience these are not too critical as long as they are good quality. Use Kendeils or BHC aerovox ALS30A. I've tried various sizes from 10,000uf to 33,000uf and found no great difference. ALW on the other hand has found the capacitance important (hmm?) however and would stick with around 15,000 a side for a hicap type transformer. Maybe there is a sweet spot but I've not found it so can't say. Currently use 22,000uf Kendeils from Avondale which are a tad cleaner though lighter than the BHCs. I still like the 'darker' presentation of the BHCs though. Look for low ESR and ESL though. Generally physically large size caps are considered to sound better, probably because they generally have these low values. The now discontinued Elna cerafine 63V, 10 000uf caps are also reputed to be superb possibly the best out there and also the discontinued simens sikorel though physically huge and extremely expensive.

RECTIFIERS
Again not particularly critical IME. Have used normal silicon bridge rectifiers, ultra fast soft recovery diodes and also made up shottky bridges (see below). Shottkys sound probably the best, but silicon bridges are easiest to mount and theres no great gulf between them. Ultrafast soft recovery are perhaps a tad cleaner but more clinical than silicon bridges IMO.

REGULATORS
These are by far the most critical in PSUs IMO. Don't bother with monolithic regulators e.g LM317, LT1086, LT317. They are all pretty much of a muchness and not that great. The best available by a mile are the discreet ALW superregulators based on the design by Walt Jung- see Low Noise Power for Analog Circuits (ED Analog Special 6 23 1997) . and also http://home.comcast.net/~walt-jung/wsb/PDFs/Improved_PN_Regs.pdf.See below for build details. These are stunning and will give your preamp a huge boost in absolutely everthing. Rhythm, timing, texture, involvement the works. These really are the magic bullet for audio. Even with a lousy raw psu upstream you will still hear huge gains using these regulators. The same cannot be said of LM317s etc.
Possible alternatives are the Avondale APX boards which reportedly (ta Ron) are also very good though have a different presentation to the ALW superregulators. Not heard them personally though.

A couple of points to bear in mind are also:

Low impedance- wiring: as regards the Julian Vereker comments above, keep impedance low by using low gauge hookup wire. I use 2.5mm2 stuff from maplins but probably anything 1.5mm2 upwards will be fine. You can even strip apart 3 core mains cable with these gauges from B&Q for example.

Low impedance- connectors: Again regarding the Vereker comments, its worth noting that your DIN sockets have approx. 5mOhms impedance, Bundy sockets about 3mOhms and my preferred Neutriks also about 3mOhm. I would therefore solder the umbilical cord from the psu directly and use a cable gland so eliminating one socket. For comparison, 1m of 2.5mm2 copper wire will have an impedance of around 7mohms and a good reservoir cap around 8mohms ESR.

Keep the rectifiers near the reservoir caps. There are big currents involved as the rectifiers switch on and off so keep them near the caps. There have been reports this makes a sonic difference and indeed some respected audio designers e.g. Jonathan Carr of connosieur audio mount the rectifiers directly on the reservoir caps with a pcb. The avondale Mcaps also use this principle.

Earthing: See simple mods 1 below. This is critical and can make a HUGE difference to sound quality. Essentially the two supplies (+ve AND ground) should be kept completely seperate and only joined at the star earth in the preamp, not at the -ve terminals of the 2 reservoir caps. See the psu project schematics below for a clear idea of this.
Thanks to Mr Tibbs for this one

Signal routing: See simple mods 2 below. Naim amps route the signal from poweramp to preamp via the pre psu. There are many reasons why this is technically illogical and listening backs this up. The solution is to route both psu and poweramp direct to the pre. This gives a shorter signal path and keeps power and signal lines seperate. In itself this gives a small difference though its not night and day but worth doing. However it allows you to use big cable for power umbilicals.

This might also be useful:

This is critical and makes a HUGE difference to sound quality with a far more coherent and musical sound which just sucks you into the music in a wonderful fashion. simply everything is better.
The Naim earthing scheme as seen on the hicap (fig 1) is NOT optimal and is probably still maintained for historical reasons. One can see the psu has a star earth bus bar type arrangement between the 2 reservoir caps -ve terminals and everything is grounded there.
Much much better is this: The two channels should be kept completely seperate and only joined at the star earth in the preamp. This means DO NOT connect all the grounds to the busbar connecting the two 0V terminal of the reservoir caps as Naim do. Rather there should be no bus bar at all and TWO ground wires as well as two positive power rails going from the psu to the preamp. https://truepup271.weebly.com/casino-gambling-for-dummies.html. Both ground wires are then soldered to the star ground in the preamp. This will require modifying the wiring to the dins going to the preamp but requires only minor effort. See the raw psu project schematic (project no1 below) for a clear idea of this and compare to how naim do it in picture of hicap (fig 1 above). However as said, doing the earthing correctly makes a huge difference to sound quality.

Thanks to Mr Tibbs

Rerouting the signal path

You can only do if you have an external PSU for the preamp. Use your 4 pin snaic to connect from preamp direct to poweramp. However you must desolder the +ve line on the din socket within the preamp (see poweramp din socket diagram below) as you don't want 24V coming into the preamp from the poweramp (if you use a nap90/140/150/160/180 etc). Then use your 5pin hicap snaic to connect directly between preamp and psu. See the avondale audio site for a diagram of this.

However this then allows you to build an ALW power umbilical (see below) to transfer power which is nice. If you use 1mm 4 core you can then wire it up for the MR Tibbs earthing mod (no1) above with 2 +ve rails and 2 ground rails. Though I suspect using 2 of the 1.5mm 3 core cables with thicker gauges would sound much better.

upgrading the regulators

An ALW superreg

Replace the LM317s in your (DIY) hi-cap, flatcap, snaps etc. with ALW superregs. These are utterly brilliant and will transform just about anything they power. They are a bit costly in DIY terms and take a couple of hours or more to build but worth every single penny without doubt. The absolute must do.

PCBs are purchased directly from ALW audio, see http://www.alw.audio.dsl.pipex.com/

For Walt Jung orginal articles see see Low Noise Power for Analog Circuits (ED Analog Special 6 23 1997) . and also http://home.comcast.net/~walt-jung/wsb/PDFs/Improved_PN_Regs.pdf.
sample farnell parts list here.
stuffing guide and manual can be downloaded here.
some useful datasheets here if you need:
AD825
AD817
LM329
LM317T
TL 431
D45H11
D44H11

Note: Remote sensing: The superregs have both ground and output remote sensing facilities. To be honest I'm not sure wether using remote sense make a huge amount of difference. The main importance in this is to provide low impedance and although significant, low impedance is not critical to good regulator performance- the difference between suppling a premap with 27ohm powerrail resistors and without is clearly to be heard and positive but not huge.
However remote sensing can make the regs unstable (if its bad, you'll clearly hear this as you move the remote and power lines around as a buzzing from the speakers and your poweramp will get hot) but it may also be at a low level and detectable only by scope. For this reason I'd recommend only using remote sense with onboard regulators where the power and sense lines are not more than about 5-10cm long. I've had bad instability with even 6 inches of wiring. If remote sensing I'd also use some form of shielding. I use a core and shield wire for my remote sensing with the remote lines in the center core shielded by the outer braid which carries the power or earth connection and I've never had any problems this way.
Twisting the wires together is another possiblity. The original Walt jung article illustrates that you can also shield the remote sense lines using core and shield wire with the outer shield connected to the reg ground.

Alternatives which have had good reviews are the Avondale tracking regulators and the Avondale APX boards. Not tried them personally but a report is they have a different presentation to the ALW superregs though are also good.

DIY rectifier bridges

Bearing in mind comments regarding rectifiers above, here are pdfs for etching your own shottky full and half bridges. The diodes these are designed for are MBR20200CT. The bridges are designed to work to 20A, 200V. Parts available from farnell; see components page.

Full bridge download here. (pdf)
Half bridge download here. (pdf)
MBR 20200CT datasheet here (pdf)

~£15 fullbridge,

£7 half bridge

This is the psu you want if you are going to use onboard regulators in the preamp or for the ultra preamp project (see the preamp page). It provides 2 seperate raw DC feeds to the preamp and forms the basis of your powersupply.
It is designed as a pure psu i.e. signal goes from pre straight to poweramp not via the preamp psu and incorporates the Mr Tibbs earthing mod and so uses a 4 pole neutrik speakon arrangement for the umbilical.
If you want to be traditional you can replace the cable gland with a 5 pin din socket and use a 4 core ALW power umbilical (see below for details). This will still sound damn good.

If you wish to supply 6 onboard regulators in your preamp then you have 2 options:
1) Use 8 pole neutrik plugs and sockets and an 8 core umibilical cord. You will then have to take 6 positive rails from the 2 reservoir caps along with 2 earths. I suspect this may be the optimal solution though not tried it. A variation on this theme is to have 2 din sockets at the back of the psu and use 2x 4 core ALW power umbilicals to get the requisite 8 lines into the preamp.

2) Make the raw dc supply exactly as above. Then take the power for the 6 superregs from the 2 positve terminals on the Neutrik socket within the preamp.
Note; This is slightly easier but i suspect there may be a sound quality penalty and it might be significant compared to option 1.

Get the buid notes here. (word document) this should give you all the information you need to get a supply up and running.
Get the parts list and costing here. (excel spreadsheet)
Get the schematic here (pdf)

This is basically the raw dc psu (see above for all details) but with 2 superregs IN the case as opposed to in the preamp similar to the naim hicap. The pink fish OS sauce cap as diagramed at ALW audio here basically shows how to do it.

If possible again I would use the Mr Tibbs earthing mod (no1 above) as well as the rerouting signal path mod (no2 above) and thus a 4 core ALW power lead.
If you are a fool to yourself and want to do things totally standard naim style with a heavy sound quality penalty, then you will want to use a 3 core ALW power umbilical (see below) and earth everything to a bus bar between the -ve terminals of the reservoir caps.

However you can see from here if you want to make a DIY supercap (fig 2 above), just shove more regulators into the case. i would note that in naim pre's in general the gain boards receive half the total regulation of a hicap for themselves and the buffers, tape buffers etc get the other regulator ( front to back regulation) i.e. the gain boards are the most sensitive and responsive part of the preamp. You'll then probably want to use an 8 pole speakon interconnect with 8 core interconnect (6 rails plus 2 grounds) or the multipin burndy sockets.

The Snaps is a small outboard supply that can be used to feed the digital circuits (switching, remote etc) in a NAC102/NAC82. Its essentially just a regulated supply that feeds 18V to the preamp which is then internally regulated within the pre to the required voltages.

To quote Les Wolstenholme of Avondale: 'Listen, just get yourself one of those 'wall warts' you know the little power unit used for a million and one things. 18 - 24 Volts of regulated DC at around 500mA (half an amp in real money), attach the appropriate 2 pin line socket (available from your local CB shop or Maplins) observing polarity of course and off you go. I've tried one on an 82 and listeners can't tell the difference between a £9.95 device and the NAPSC which costs 'ever so slightly more'. The secret of operation of this simple device is not that the digital circuits need sophisticated power (there are internal regs in the pre-amps to cater for that need), just power independent of the audio circuits.'
The socket is available from maplins: Lkg Line Skt 2-Way FK22Y 27 £1.39

Thanks to Les Wolstenholme

The Andy Weekes snaps

An alternative project, which is a bit more costly but does the same thing and looks great, is thanks to Andy Weeks, originally posted on the pink fish forum:

Left is the Lawtronics SLA1500 sealed lead-acid, current limited charger. It's basically a PCB containing toroid / rec / smoothng + an LM317K with heatsink (size: 44x100x160). They are available from Farnell, in a couple of flavours, the 12/24V being the one to go for. The farnell p.no. for the charger unit is 4271040, and they are £42.65 each.
In addition you'll need a case, and if you fancy something nice, it can be squeezed into a Hammond IP45. The largest sizes are the ones you want (farnel 427-3035 [53x103x160] or farnel 427-3047 [54x103x220] . The board slides into slots in the case - so no drilling to fix it in!
There's little room for an IEC inlet in the smaller one so a couple of cable glands to take the mains cable in and the DC out + an internal fuse holder (which you can attach to the PSU board) will save space. If you're careful you may be able to fit a single panel-mounted fuseholder, but things are tight and you'll need to plan carefully.
Finally you'll need a connector for the NAPSC supply. Again Maplins: Lkg Line Skt 2-Way FK22Y 27 £1.39
Don't forget to earth the metal enclosure, you'll have a unit that looks the business for a fraction of the new price and a piece of piss to build. I doubt it would be much cheaper if you built the raw PSU bit yourself.
The charger boards have an on-board current limit (designed for charging sealed lead-acid chargers) but this can be disabled easily if you want to. You can also upgrade caps etc as you see fit, and the output voltage is set with a pot - I'd remove it and fit fixed R's to give the correct output, to save future unreliability and additional noise. I'd also permanently link the 12/24 V selection jumpers too, for the same reasons.
You can obviously add an LED (a useful reminder of the presence of power in there, I use one of these for the purpose of keeping preamps warm, whilst swaping and evaluating

Thanks to Andy Weekes

Interconnects, Power umbilicals, Plugs and sockets

Naim use those as listed in the components page. Which pin does what can be read off the back of the naim gear as it is clearly indicated there but for reference its here below:
see components page for farnel numbers

Naim use these on their high end gear for interconnects between their psus and equipment i.e supercap to nac52, 500psu to Nap500 etc . They are the Metalok Bantam series now produced by FCI (formerly Burndy).

Apparently these require a special insertion tool to place the pins in the sockets and extract them. Bear in mind the pins take 1.5mm cable max. You will want to solder the cable to the pins not crimp them.
Use the machined pins also as they have an impedance of 3mOhms as opposed to the other pins which are greater.
Also use the basic hoods for strain relief.

This is the pin voltage and channel configuration for the NAC52 burndy

Invaders from planet moolah. My preference is to use the Neutrik 4 and 8 pole sockets/plugs for psu umbilicals. They also have an impedance of <3mohm but accept large diameter cable (over 2.5mm) so you can use very heavy gauge and therefore low impedance cables for psu power umbilicals: Also the pins are molded in the sockets so you don't have to fool around with insertion tools etc and they have screw terminals. This means its easy to screw in the cables into each pin socket to fix them into position and THEN solder them in for a low impedance connection. Use a good 40W soldering iron for this.

8 Pole neutrik for power on a CD3.5

get datasheet on neutrik 8 pole speakon sockets here

get datasheet on neutrik 8 pole speakon plugs here

see components page for ordering information.

Power Umbilical

ALW psu power lead

Snaic and ALW 3 core powerlead on a CD3.5 with red heatshrink.

This is basically for connecting the cd3/cd3.5/cd5 to an external psu or psu to preamp powerfeed if doing the 'rerouting signal path' mod no2 above.

Gives a noticeably more solid and dynamic sound and is just better all round.

Use 2 normal 5 pin din plugs as per components list and a meter of the flexible, 3 core 1.5mm mains cable available from B&Q. Solder as per the 5 pin din socket diagram above. Note it is a thick cable and a very tight fit so you will have to strip back 10cm or so of the outer sleeving at each end and reseal with heatshrink tubing to allow the wires to go through the plugs. Use 1.5 -2cm diameter heatshrink. This is how naim used to do it with grey powersnaics also.
The cables are also too thick to thread into the pin holes in the din sockets so you need to tin the pins and ends of the wires heavily, then touch together and heat to get a good join.
It is a slighly fiddly job but not difficult to do.

So you'll need 2 x 5pin, 240o din sockets and just over a meter of 3 core or 4 core wire.

If using 4 core cable (to make use of the Mr tibbs earthing mod) you will only be able to fit 4 core 1mm2 cable in a din plug.

see recommended parts page for order numbers etc.

Thanks to Andy Weekes