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Post by Deleted on May 22, 2018 17:56:26 GMT
There are many kinds and sizes. Toroid, EI, C core, R core and maybe others. Do you prefer gear with any one type or does it not matter ?
Toroids cant be beaten for lower stray field and are the ultimate choice for power amp output stages. But in other places i like a GOOD EI frame jobbie. I just prefer the sound of these on cdp, phono stages, preamps and power amp input stages. Have to be more careful with stray field from these things but distance is king here. I have some on the input stages of my nva amp boards and in my cdp.
They are supposed to filter out more mains related crap than toroids but i have no way of proving it. Also higher winding resistance but again i wouldn't know.
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Bigman80
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Post by Bigman80 on May 22, 2018 18:55:33 GMT
Good choice for a thread. Some of my absolute favourite amps have had frame transformers. Bolt down Naim 250 is more musical than the later one IMO. I had an ancient Exposure IV with a big frame transformer too, it was the best Exposure amp I've ever heard. Better than the later Dual transformer ones by a clear margin. Lots of valve amps I've owned with frame transformers have been epic, Oh, my Bedidi 100/100 upgraded to 2 spec was another beauty with a big frame transformer.
I know nothing about electronics but there is a string correlation for me.
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Post by dsjr on May 22, 2018 19:21:19 GMT
Bolt up Naim 250's had a totally different circuit layout to the radically re-done CB and Olive models and this early 250 and the 120 were to me the best amps they ever made for musical involvement and should be regarded as valve amps for matching to speakers...
I can get my head round toroids (I kind of have to don't I?) but not sure about frame types as I've never used them. I suppose the wiring of twin secondary's wouldn't be any different though.
I think there's an electronics sub-science about transformers, how to use them and in audio coupling needs, how they saturate and at what frequency. Not sure the *type* is relevant though, but *size* in terms of VA rating certainly is. Naim did a NAP200 once (I think it was) which was a clone of the amps made for Capital radio in their earliest days. Supposed to fit between the 160 and 250 and using a big frame transformer. Not a pleasant sounding product I recall...
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Post by Deleted on May 22, 2018 19:37:36 GMT
I'm no electronics expert. I do slightly favour the noratel toroidal transformers. Always found them to have good clean bass. I like the 500va one, seen in the Roksan Kandy series.
S.
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Post by Deleted on May 22, 2018 19:39:43 GMT
True enough, a frame transformer cant make a bad sounding amplifier circuit sound good. I have compared toroid and frame in amps and my cdp and for certain roles i do prefer the frame transformers. You do need taller enclosures though or no enclosures ! Or do what naim did and hammer them flatter.
I spoke to Terry at canterbury windings when i got my power amp toroids designed and made. He said that with toroids the best thing you can do is make them as tall as possible rather than wide. So i got him to make them as tall as his winding machine was able (80mm). Over sizing the core is also beneficial i am led to believe so he built my 340 va toroids on 500va cores. Added an electrostatic shield between primary and secondary windings to reduce capacative coupling and a external shield (belly band) to reduce electromagnetic stray field.
May be all bollocks though........
Not all frame transformers are created equally either. I got some rather nice ones from Les at Avondale audio.
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Post by dsjr on May 22, 2018 20:12:23 GMT
Can't be arsed with fancy foo trannies. I'm amazed how much powerful music comes from an NVA amp with relatively tiny transformer and supply. My AP70-based NVA power amp went as loud into 'normal' speakers as the Krell KSA50S with a humungous (in comparison) toroid? transformer, sounded at least as good and didn't get as hot either... I liked the Krell though, but I didn't fully realise it was designed for balanced preamp sources only (converting it to phonos was a botch of the input circuit* and not really recommended)
* Unless I'm mistaken, the Krell was balanced straight from the input with banks of (very warm) transistors at each stage to be a current amp right from the beginning. The amps I usually use have a single ended input and it' turned into a plus and minus signal further in I think...
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Bigman80
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Post by Bigman80 on May 22, 2018 20:29:27 GMT
My 4 X A40s were great and they only had small transformers. I guess it will depend on the speaker and it's crossover, but 4 X A40 were light years ahead of 2 X A80. I think A80s use two larger transformers per side, so bigger and even more isn't necessarily better. Even the AP10PX made some great sounds with my Spicas.
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Post by Deleted on May 22, 2018 20:31:50 GMT
Hmmmmmm....Makes you wonder sometimes.
S.
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Bigman80
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Post by Bigman80 on May 22, 2018 20:52:05 GMT
I hesitate to say it, but the AP10px was a better amp than the A80s in my system. Maybe they were duds in some respect but they did little for me.
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Bigman80
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Post by Bigman80 on May 23, 2018 11:25:41 GMT
Can't be arsed with fancy foo trannies. I'm amazed how much powerful music comes from an NVA amp with relatively tiny transformer and supply. My AP70-based NVA power amp went as loud into 'normal' speakers as the Krell KSA50S with a humungous (in comparison) toroid? transformer, sounded at least as good and didn't get as hot either... I liked the Krell though, but I didn't fully realise it was designed for balanced preamp sources only (converting it to phonos was a botch of the input circuit* and not really recommended) * Unless I'm mistaken, the Krell was balanced straight from the input with banks of (very warm) transistors at each stage to be a current amp right from the beginning. The amps I usually use have a single ended input and it' turned into a plus and minus signal further in I think... I think you're right about the KSA-50S but were there balance and singe ended versions? I seem to recall seeimg both. My KSA-50 was probably my favourite amp. It sounded like it had bottomless power and was really sweet and groovy. The KSA-80 and KSA-100 I had were both technical,y capable but not special in anything like the same way. Edit: I was getting mixed up. The amp that was made in both balanced and single ended visions was the KSA-80. |
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Post by dsjr on May 23, 2018 15:54:34 GMT
The KSA 80 a colleague had was superb into his Apogee Duetta Signature panels and he kept these for years (the 80 was the pre-balanced version). I never heard it into conventional speakers so no idea how ott the delivery would have been. Simon (SQ) had a couple of ten-fifteen year plus old KSA250's I think it was, and at this age and regularly used, they were totally effed! he completely stripped and rebuilt them, serviced them to within an inch of their multi-capped lives, cleaned the leaky-cap residue from the cases and lovingly reassembled them (I saw the AOS logs of the second restoration). Having heard how horrible an un-serviced KSA250 sounded (made an off-tune Naim sound sweet!), I can see why he needed to do it.
www.stereophile.com/solidpoweramps/404/
Now to NVA... I know the AP10 in speaker as well as 'just' headphone form and can confirm how 'nice' it sounds if the speakers aren't too power hungry. The A20 takes this further, but I would say that, wouldn't I?... I've never had the A80's here, but regularly use the equivalent of an AP70 power amp section (twin transformers at higher secondary voltage than the smaller ones and supplies using 10,000uF caps). This amp has greater dynamic range and in my pov, less compression (I'll be told off as NVA's don't 'clip' as other amps do). I honestly think the smaller ones sound so airy and atmospheric because they're slightly bigging this side up to make up for slight breathlessness when pushed. The bigger amps reproduce the music with greater 'accuracy' in terms of dynamics (same bloody boards and output devices) and it's my opinion that the dynamic range is more truthful. My larger amp went easily as unburstably 'loud' as the Krell did and without a hint of distortion or a tweeter about to blow. I can't do this with the A20's for example, as they start to get 'breathless' if I abuse them on test (I can't describe it any better). it's a kind of superior 'control' I think, where the smaller amps are looser in feel. the more demanding the speaker, the more the larger NVA's come into their own, so maybe if you have a small or very efficient well damped speaker, the smaller ones may be all you need, so better spend the difference on one of their 'SA' preamps.
I'm not trying to shill up NVA FFS, but possibly trying to put what I've heard (as well as yourselves)into a kind of perspective - and my speakers range from complex BBC-Boomers which need all the help they can get to reproduce bass remotely well, to some rather good JBL Control 1's which continue to pleasantly surprise how clear they are in a small system situation and how well they 'time,' however you take that term, with my beloved old original IMF Compact in between (rather better than the Super Compacts for many smaller UK rooms and they have doped bass and mid units too  ) |
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Bigman80
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Post by Bigman80 on May 23, 2018 18:52:07 GMT
IMFs are reported to be power hungry, although I'm not sure if I've heard any. I can recall almost gettng to hear a giant pair in a guys attic room, and I recall chatting with another guy in his home and seeing his IMF compacts. We listened to quite. Few bits that evening and I'm not embarrassed to say I can't remember if we played them or not. Either way up, they are an unknown (or forgotten) quantity to me.
You're completely fine to talk about NVA as much as you like here, Dave. You know the stuff well and you like it. You also have a greater experience of the ranhe and how the cheaper and more expensive bits vary. All those daft debates about ahilling have spoiled forums for too long IMO.
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Post by dsjr on May 23, 2018 19:11:04 GMT
The baby IMF's I have are around 20 litres or so, are a simple three way stand mount with an easy load and they sound incredible for a 1971 design and pretty darned good for today too imo. Floor standing IMF's are different and the transmission lines can sound terrible today on a beefy amp an juicy vinyl source.
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Bigman80
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Post by Bigman80 on May 23, 2018 20:36:41 GMT
True enough, a frame transformer cant make a bad sounding amplifier circuit sound good. I have compared toroid and frame in amps and my cdp and for certain roles i do prefer the frame transformers. You do need taller enclosures though or no enclosures ! Or do what naim did and hammer them flatter. I spoke to Terry at canterbury windings when i got my power amp toroids designed and made. He said that with toroids the best thing you can do is make them as tall as possible rather than wide. So i got him to make them as tall as his winding machine was able (80mm). Over sizing the core is also beneficial i am led to believe so he built my 340 va toroids on 500va cores. Added an electrostatic shield between primary and secondary windings to reduce capacative coupling and a external shield (belly band) to reduce electromagnetic stray field. May be all bollocks though........ Not all frame transformers are created equally either. I got some rather nice ones from Les at Avondale audio. I missed somethig on first reading. The reference to taller toroids being better. The Exposure ones are double the height of Naim. They do sound mighty fine to me. |
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Post by Deleted on May 25, 2018 9:20:21 GMT
I can't say that I have compared the same transformer design with one being a lot taller than the other but Terry at Canterbury windings said it made a big difference, whether to stray emi or something else I do not know. There is an art to winding a transformer it is said and I am no way an expert so cant really say.
Big (VA) transformers do tend to be more "musical" though - the lower resistance of the windings must help with dynamics and the load does interact with the impedance of the thing (lower impedance being better). With more VA though the stray field becomes larger and so steps must be taken to minimise its effect on sensitive circuits. Distance is king here - I have proved it to myself countless times. Shielding is very hit and miss and mostly pointless. Material type has a bearing. Aluminium is next to useless. Steel is what you want and the thicker the better, but then things start to get very heavy and you don't know how the ferrous metal is compromising the circuits performance. Wood and plastic have no shielding properties at all but if transformers are kept well away from anything sensitive then there is no problem.
All IMO of course
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Bigman80
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Post by Bigman80 on May 28, 2018 8:23:10 GMT
I seem to recall Colin W using tall transformers in the Inca Designs amps.
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Post by dsjr on May 28, 2018 9:51:31 GMT
Big (VA) transformers do tend to be more "musical" though - All IMO of course Try telling that to an NVA AP10 or A20 |
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Post by Deleted on May 30, 2018 15:14:37 GMT
Hello Dave, I am just going to go ask my AP20 and see what it says  |
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Post by dsjr on May 30, 2018 17:10:08 GMT
Should tell you clearly enough  |
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