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Canterbury Windings transformer for Naim shoebox cases

misterc6

misterc6

Wasted and wounded, it ain’t what the moon did
Some years ago I asked Terry at Canterbury Windings to design a 200VA audio grade transformer for the Avondale NCC200 amplifiers (mono and stereo) I was building at that time. This was highly successful and I guess they can still be obtained quoting type number TM363A.

More recently I built a pair of NAP110 mono amplifiers using the original Naim NAPA boards but have now replaced these with the new Avondale Qudos amplifier boards. These sound great running with the standard Naim +/- 39v power rails but I suspect that, like the NCC200 boards, they will perform even better with higher voltage rails.

I gave Terry some rough design figures for a 120VA, 35 - 0 - 35 V transformer that would fit in the same space as the H & F 110 transformer. He came up with this:

Quotation no: 040817-1 Connah
Power rating: 120VA
Primary: 0-240V @ 50Hz
Electrostatic screen
Secondary: 35-0-35V @ 1.7A rms
GOSS band
Regulation: approx 6.3%
Estimated dimensions: 104mm diameter away from leadouts x 53mm high
Mounting: M6 insert in a potted centre
Leadouts: approx 200mm long flexible (stranded)
Audio grade construction

The price for two or more transformers is £58.05 each plus carriage at cost and I'm putting two on order today with a lead time of four weeks.

I don't think a group buy is feasible due to the cost of re-shipping.

I've posted this in case anyone else is interested. The NCC200 and Qudos boards certainly benefit from the higher voltage rails as do the original NAPA boards. If you plan to use these new transformers with NAPA boards I would advise changing TR1, TR2 & TR3 to BC546Bs and the power supply electrolytic capacitors to ones with a 63v rating.

Here's a photo of the earlier 200 VA version (which won't fit in the shoebox cases!):

DSCF0438 by Malcolm Connah, on Flickr
 
Further to the above, Terry use to offer a very nice discount for those paying with cash. Although I'm not currently starting any new builds myself, it would be good to see these excellent transformers being used in as many PFM builds as possible. As I still pass Terry's place fairly frequently, I'd be more than happy to 'help out' in order to make these available at the best possible price.

Also, I don't think a group buy 'middle man' would be required for re-shipping, as Terry has been happy to ship directly to individuals in the past. Given the price and rarity of copper, I'm surprised the price of these haven't gone through the roof.

Obviously, this would need confirmation from Terry.
 
grazie said:
Further to the above, Terry use to offer a very nice discount for those paying with cash. Although I'm not currently starting any new builds myself, it would be good to see these excellent transformers being used in as many PFM builds as possible. As I still pass Terry's place fairly frequently, I'd be more than happy to 'help out' in order to make these available at the best possible price.

Also, I don't think a group buy 'middle man' would be required for re-shipping, as Terry has been happy to ship directly to individuals in the past. Given the price and rarity of copper, I'm surprised the price of these haven't gone through the roof.

Obviously, this would need confirmation from Terry.
Click to expand...

Thanks for that. I was very pleased with the quality of the 200 VA transformers I had from him and am expecting nothing less from these.

I had a 250v primary on the 200 VA and have gone for 240v on these; my mains is always high and typically 248v.

I imagine Terry could also make a direct replacement for the 110 transformer with a 27.5 - 0 - 27.5 v secondary and ~ 2A current.
 
With apologies for the delay this pair of identical twins just arrived:

IMG_0011 by Malcolm Connah, on Flickr

and here's one of the babies nestled in a Qudos mono amplifier:

IMG_0013 by Malcolm Connah, on Flickr

The initial impressions are very good with the higher voltage rails giving the amp more room to breathe.
 
Looks excellent Malcolm, nice neat job
Agree that terry's transformers are also superb quality

Alan
 
Funnily enough I was casually looking at possible transformer uprate choices for my recently completed 110 monoblocks now fitted with Qudos and minicap 6 boards. Looks like I'll be opening them up again soon, these look just what I need!
 
I am curious I don't get the idea of chucking all the internals out of the 110, why not just sell them on and get a slightly bigger box and fit a bigger transformer.
Thats what I did have a nice 350VA job from Terry,better still got an even bigger box and went Voyager,building up some Qudos boards now.
 
GWM said:
I am curious I don't get the idea of chucking all the internals out of the 110, why not just sell them on and get a slightly bigger box and fit a bigger transformer.
Thats what I did have a nice 350VA job from Terry,better still got an even bigger box and went Voyager,building up some Qudos boards now.
Click to expand...

That's what we ended up doing for a short run of amps. I took the opportunity to make the cases a bit taller so we can fit a bigger transformer with a better aspect ratio (another of Terry's BTW - it was a 300VA 30-0-30)
 
Personally I think 35V secondaries are too high for a 120VA transformer, at clipping the transformer will saturate at max current before the amplifier gets close to the rail voltages even with a perfect 8 ohm load. With a reactive load and/or 4 ohm speakers it would be worse, and worse again if used to drive two channels:

35V secondaries -> approximate max of 30v rms into 8 ohms -> 3.75A current -> 112.5W
27.5V secondaries -> approximate max of 24V rms into 8 ohms -> 3A current -> 72W
 
GWM said:
I am curious I don't get the idea of chucking all the internals out of the 110, why not just sell them on and get a slightly bigger box and fit a bigger transformer.
Thats what I did have a nice 350VA job from Terry,better still got an even bigger box and went Voyager,building up some Qudos boards now.
Click to expand...

I can understand that point of view but my project grew like topsy. I don't like/am not much good at metal work. I don't see any point in going over a 120VA transformer for a NAPA/NCC200/Qudos mono amplifier but did want to increase the rail voltages from Naim's +/- 39v to +/- 50v based on my previous experience with NCC200 mono and stereo amplifiers.

I've built/modified many mono and stereo amplifiers over the last ten years with transformers up to 500VA per channel but I've found that the Law of Diminishing Returns definitely applies and 120VA per channel gives more than enough grunt for me.

I previously sold one pair of the original NAPA boards and expect there to be quite a bit of interest in the pair of Holden and Fisher 110 transformers if I offer those up for sale together with the remaining pair of NAPA boards.

Overall I'm more than happy with what I have now.
 
The question was really value for money,Naim amps still seem to command ridiculous prices for what is quite average performance these days,ready made box's from modshop for example are easy to use ,they make a shoe box version which is big enough to take a decent size transformer.Just make a few holes with drill.
I have to say a 300ish VA transformer seems the sweet spot for me tried smaller and not as good but I was using a pair of Gale 401 at the time which are a horrible load and low efficiency.
 
hmmm i'm considering ordering from Canterbury from California of all places ... the american transformer winding people are driving me nuts - I'm trying to get one wound (a modest 75-90 VA with four taps) - and i'm getting quoted USD 450 and UP!!! i guess they aren't interested in small fish ...
 
Well worth contacting Terry, but I do remember him telling me that his small transformers aren't cheap as of the amount of labour involved is comparable.
 
I've ordered several transformers from Terry shipped to the USA and he's done a fantastic job every time. Prices are reasonable, shipping is at cost, highly recommended.
 
misterc6 said:
These sound great running with the standard Naim +/- 39v power rails but I suspect that, like the NCC200 boards, they will perform even better with higher voltage rails.

I gave Terry some rough design figures for a 120VA, 35 - 0 - 35 V transformer that would fit in the same space as the H & F 110 transformer.
Click to expand...

For us knobbies that have not tinkered with Naim products I'm guessing there is a typo in there, original rail voltage +/- 29v?
 
cjarchez said:
For us knobbies that have not tinkered with Naim products I'm guessing there is a typo in there, original rail voltage +/- 29v?
Click to expand...

There's no typo. The rail voltage obviously varies slightly depending on the tolerance of the incoming mains supply but the early Naim power amplifiers (NAP) have rail voltages of around +/- 39 Vdc.
 
Ok, so what is the standard TX rated at to then run 39v rails? From your description and lack of my knowledge of Naim inner workings, it reads like you are either downgrading voltage or making the new TX run hard to achieve the required higher voltage rails, again at what voltage btw.

This is a genuine question, not a challenge.
 
There are plenty of tutorials on line to help you!

In its basic form the power supply in a NAP uses a transformer with a centre-tapped transformer, a bridge rectifier and two smoothing capacitors. The dc voltage on each rail is approximately 1.41 x the ac voltage on half the transformer secondary. A 27.5 - 0 - 27.5 Vac secondary would produce +/- 38.8 Vdc rails.

The 35 - 0 - 35 Vac transformer I specified from Canterbury Windings would produce +/- 49.35 Vdc rails.

HTH
 
Aha. I knew the theory but was missing the standard and target figures from your op.

So basically, in both cases the TX will be running at full tilt as far as vdc is concerned.
I've been told this was less than desirable for a power amp but acceptable for preamps and DACs. Preference being, ideally running at the same vdc as the rated vac or up to half way between.
However, it obviously worked for Naim in this design so why not.

I've upgraded power rails in a DIY headphone amp and an Aclass power amp, both were great successes with very pleasing results.
Your work is also much tidier than mine!
 
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