[Builder Brad]

Hello,

I have a couple, or three questionsjavascript:emoticon('')
Confused

I am probably going to use two DL36-2 signal transformers in the 25 watt AKSAs and I would like to know if this is a good choice for use in the UK. The primary coil is OK in the UK and the secondary gives 18-0-18, however I really want to be confident that I am selecting a transformer that will work well in the AKSA. details on this unit can be found on the following site. http://www.belfuse.com/signaltransformer/SuppMag.asp

using the same supplier for the 55 watt AKSA is going to be more difficult because they do not make transformers with the required 25-0-25 secondaries, so I have a plan, but would like to know if i am going to be better off with a toroid.

My idea is to use four transformers in the 55 watt amp, two for each chanel. I would use 115v single primary and 12 volt dual secondaries with the primaries wired in series and the secondaries wired parallel in each transformer but wired in series together with the connection between both secondaries providing the -0-, thus creating two individual 24-0-24 transformers. I think that the ideal choice for this would be four DL-24-4 which provive 24VCT @ 4Amps when the secondaries are wired in series. Anyone care to comment? have I chosen the correct current version of this transformer? am I wasting my money by using four transformers?Should I just go and get toroids?  ect ect ect.

any ideas, sugestions, experiences would be gratefully appreciated.

[ginger]

Signal Transformers are a US brand and the dual primary versions are designed for 2 x 115 = 230V. That means that for UK mains (220V 50Hz) secondary voltages will be a smidge (technical term!!!) low - better to bit a bit low than a bit high.

If you haven't already spent your pounds/euros then its probably better to get something which is made in the UK and NOT try to patch up a solution from multiple transformers, BTW I think there was a problem with your proposed method of connecting the secondaries of 4 trannies for the 55). Wiring, particularly mains wiring will be simplified and will be much easier to make SAFELY.

Toroids are better than EI Cores with respect to magnetic field leakage and so using toroids MAY avoid some induced hum problems in a tight layout.

There are a number of UK AKSA owners. Why not email one or more of them for advice as to what they used and where they got them. Otherwise the RadioSpares and Farnell WILL have something suitable although they may charge 10 or 20% more.

Cheers,
Ginger

Edit:
Just looked through the RS Catalog.
They have Toroidal trannies from Nuvotem-Talema with 230V AC Primaries as follows:

120VA 2 x 18V @ 3.3A Stock No 223-8730 (suit the 25)
160VA 2 x 18V @ 4.4A Stock No 223-8774 (probably an overkill for the 25)
160VA 2 x 25V @ 3.2A Stock No 223-8780 (suit the 55)
225VA 2 x 25V @ 4.5A Stock No 223-8831 (suit the 55 hard use)
300VA 2 x 35V @ 4.28A Stock No 223-8881 (suit the 100)
May well be cheaper options BUT these would certainly suit.

[Builder Brad]

Thank you Ginger,

I really wanted to try to avoid using Toroids, it would just be too easy for me.  
Toroids seem to be in every piece of audio kit, with only a few exceptions.

poit taken re the primary power specs

Brad

[ginger]

No problem - so I looked in the Farnell catalogue:

EI Core Options
100VA 2 x 18V @ 2.75A Cat No 696-810 (suit 25)
150VA 2 x 18V @ 4.17A Cat No 696-900 (suit 25 hard use)
150VA 2 x 24V @ 3.12A Cat No 696-912 (suit 55)
200VA 2 x 24V @ 4.17A Cat No 696-997 (suit 55 hard use)

Yeh it should be 2 x 25V for the 55 but you won't notice the difference and the 200VA rated tranny would probably give you 2 x 25 V anyway since your lightly loading it - PLUS mains voltage fluctuates by 10% and transformer regulation is only about 10% - so its close enough.

And back to the RS Catalogue for EI Core trannies
100VA 2 x 18V @ 2.75A Cat No 805-293
150VA 2 x 24V @ 3.12A Cat No 805-394
200VA 2 x 24V @ 4.17A Cat No 805-473

I would recommend the 200VA for the 55N+ if money is no problem BUT the 150VA will handle it. There is a DIY theory widely cicrculating in the Valve DIY world that using overspecified trannies (EI in particular) gives sonic gains. I don't know how true it is from personal experience BUT the opinion was offered by some of the accepted Gurus like Allen Wright for example.

As you may have gathered its 15 minutes to home time Friday arvo here in OZ - looking up catalogues made me at least look as if I was busy.

Cheers,
Ginger

[andyr]

... There is a DIY theory widely circulating in the Valve DIY world that using overspecified trannies (EI in particular) gives sonic gains.  ...

Hi, Ginger,

The version of this theory which I came across was written by a Pommie, Neil McBride, who has a web site about modding/tweaking (ss) Naim gear.  For source components, anyway, he says use an overspecified VA - ie. if 15-0-15v, 30VA would be adequate ... go for 160VA!  I think he was talking about toroids but, of course, this would also be true of EIs.

Secondly, if you can get this 160VA tranny wound on a core which is designed for a 1KVA tranny then it will sound unbelievable!!

However, I seem to remember Hugh commenting that he carefully sized the VA of the power transformers for the different AKSAs and, if you use a transformer designed for the 100 watt (in terms of VA) in a 55, it will lose some of its "nimbleness".

So mebbe the theory doesn't apply to power amplifiers - only source components??

Regards,

Andy

[SamL]

I can remember  Hugh mention about double c core that he souce from Oz sometime ago. Maybe they also avaialble in Euro.

[Builder Brad]

Ginger,

Cheers for the info, I had not considered using RS for the trannies as I did not think they would be able to offer units of sufficient quality for the "ultimate" DIY amp project. Are the lower power RS EI transformers good enough in the AKSA kits or should I just go for a high spec toroid from Antrim:

805-221 75VA 2x18 @ 2.08A 10% regulation  -- 25watt
805-394 150VA 2x24 @ 3.12A 10% regulation – 55watt

Has anyone had any experience with these transformers in AKSAs?

Andyr,

I would normally overspec everything that I do, applying lots of  “more is better” philosophy, however I had read Hughs cautionary comments regarding oversize transformers reducing the AKSAs performance. This is one of the reasons why I am building one 25 watt amp for my tweeters and a 55 for the mid range and will only use 100s on the woofer channels. When I first looked at the AKSAs I was going to use 2 x 100s for the tweeters and mids and continue to use the 300watt monoblocks in my system.

[andyr]

... Andyr,

I would normally overspec everything that I do, applying lots of “more is better” philosophy, however I had read Hugh's cautionary comments regarding oversize transformers reducing the AKSAs performance.  This is one of the reasons why I am building one 25 watt amp for my tweeters and a 55 for the mid range and will only use 100s on the woofer channels.  ...

Hi Brad,

That is exactly my setup ... 100w/55w/25w each side, except that I have implemented them as monoblocks.  Three AKSA modules in a case, with a separate case containing the transformers and PSes.

Good luck!!

Regards,

Andy

[Occam]

Brad,

Unless those high spec Antrim toroids contain an interwinding shield, I think you might prefer the RS EI core (or equivalents). Toroids that lack shielding have very high bandwidth (making adequate audio output trannys) and high capacitive coupling. Granted, they do have low em fields.
The low cost EI core trannys are typically dual bobbin transformers, which have low bandwidth and minimal capacitive noise coupling via the simple epediency of physical separation of primary from secondary. But the tradeoff is that the EM fields of EI cores can be problematic.
FWIW

[AKSA]

Brad,

Some fantastic advice here from other AKSAphiles;  thanks guys!

I have done some mixing and matching with transformers and found that there really isn't much sonic impact.  Most of the sonics come from the amp design, the power supply filter caps, and the power supply rectifier diodes, with the transformers probably chiming in below that.

Occam's comment about winding capacitance is absolutely true;  but then, such capacitance will be shorted to ground in the filter caps anyway, so the problem is actually transferred elsewhere in the chain.  Regulation of 7% on the 100W is adequate;  this can rise to 11% on the 160VA used for the 55W.

Hope this is useful information,

Cheers,

Hugh

[RonR]

Hi Brad,

If you're looking for the 'Ultimate', Avondale audio (famous Naim tweakers) have:

'AST Audio Grade transformers both Toroidals and 'C' Cores ranging from 120VA through 2KVA' at:

http://www.users.zetnet.co.uk/avondale/aaModnPcbsTransform2.htm

Usual disclaimer: I have no connection with them, I'm not even a customer, but I may just use their transformers when I build my next AKSA power amp.

Cheers,

Ron.

[Builder Brad]

Hugh,

Thank you for the feedback.

I am still considering the RS Components EI transformers for the 25 and 55 power amps. On your site you recomend checking b4 using any transformers that are not recomended are these RS units going to be Ok in the AKSA amps, or should I just go for high spec torods from Antrim with poted cores, varnish dipped, gos band and extra copper wire.

Maybe I could ask Antrim to wind the 80VA and 160VA componnts onto 500VA cores, as sugested earlier in this thread.

I have also just remembered that you also feel that the transformer makes a minimal  contribution to the overall sound of the AKSA. I think the problem is that I have been waiting for my kits to turn up and have spent too much time......................

Brad

[Builder Brad]

hello Ron,

I have sent a couple of e mails to Avondale with my requirents and they have  
not replied. They would have been a good choice being based in the UK and I liked the specs. I even talked to someone at their offices who confirmed that they had recived the e mail and were waiting on prices and details from their suppliers........sounds expensive.

Brad