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Post by Deleted on Jun 28, 2014 18:26:14 GMT
Hi Ed,
I have put together a few class 'a' designs over the years, and for me part CE is always in the for-front of your mind, the last unit idled at 290W and used around 320W at full chat, Stable down to 294Wrms @ 1 ohm around 54 @ 8ohms.
Though heat sinks were slightly more sizable lol.
I would agree that implementation is key with any design, and given the brief for not too much penny pinching!
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Post by MartinT on Jun 28, 2014 18:27:59 GMT
that particular amp(F4) is a buffer, it has a gain of 0.9. It can output upto 25w with the right pre Got it. So ideally you need a preamp which can swing big volts. |
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Post by Deleted on Jun 28, 2014 18:34:15 GMT
I think that's about it. I'm a bit out of touch with the firstwatt scene but I believe there is a recommended pre called pumpy(pumpkin) or similar which does about 10-12v RMS.
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Post by Deleted on Jun 29, 2014 3:30:04 GMT
I like Nelson's kit he really makes nice simply design "K.I.S.S." designs to be sure. But I thought his "A Class" amp were all Push-Pull with complementary FET,s from Silicon South (Nice FET,s)  Even is larger designs are Push-Pull very heavily biased.  But a wonderful K.I.S.S. design has I said. The F5 looks simular to the F4 except the F4 is a source follower design, using a TL431 to control the bias.  The simple Bootstrap Up voltage dynamic converter will over come the Vgs bias volts loss in the output FET,s but will limit its low frequency response. Acknowledgements: F5, F5 Turbo v3 are © Nelson Pass (FirstWatt), F-4 is © diyAudio. |
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Post by MartinT on Jun 29, 2014 8:19:29 GMT
As far as I am aware, all his Pass Labs products are fully balanced designs (not all designed by him, Wayne Colbourn knows his stuff). Certainly my XP-20 is. I love the way they drive power amps in such a controlled way and it's why I like balanced XLR connections.
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Post by Deleted on Jun 29, 2014 9:56:52 GMT
the Pass labs stuff is not the same as the firstwatt stuff... @colin AFAIK the semisouth chips were all JFET except the SITs that Nelson had made personally. I have 2 pairs of the semisouths which I managed to get before they went unobtanium after semisouth closed. the firstwatt range is fairly evenly spread across the the amp types..checkout the last column but 1 here: www.firstwatt.com/prod.htmlThe F5 to my ears does sound very close to the F4, Nelson has said there's not much in it, except personal preference. I believe the harmonic spread is slightly different. I rotate listening between my amps but every so often I stick with one for a bit longer. My personal favourite(it means nothing) of the firstwatts is the F2, which seems to stay longer than the F4. Unfortunately the F2 only really works with my single drive/full range speakers due to it being a transconductance/ current amp, but this doesn't detract in anyway. At the end of the day I always come back to my SV572, but thats another story. |
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Post by Deleted on Jun 29, 2014 10:01:25 GMT
Hi Ed, Thanks this is a design I have used in the past, it worked well but not as simple as Nelson,s work.
© Colin Wonfor
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Post by MikeMusic on Jun 30, 2014 9:19:11 GMT
Thanks Ed.
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Post by MartinT on Jun 30, 2014 9:23:21 GMT
the Pass labs stuff is not the same as the firstwatt stuff... I did know that. Sorry, I should have made it clear that I was being tangential  |
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Post by Deleted on Jun 30, 2014 9:32:17 GMT
wow, people spend years and loads of dosh trying to be tangential... you're gifted |
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Post by MartinT on Jun 30, 2014 10:38:18 GMT
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Post by ChrisB on Jun 30, 2014 15:31:43 GMT
the Pass labs stuff is not the same as the firstwatt stuff... I did know that. Sorry, I should have made it clear that I was being tangential ;) Tangenital? Have you been balancing little oranges on your willy again Martin? |
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Post by MartinT on Jun 30, 2014 17:05:21 GMT
Now I KNOW I spelled that very carefully  |
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Post by Sovereign on Oct 9, 2014 19:08:46 GMT
The shame is that Tube/Valve SECA designs are in the norm transformer coupled and this will lose top end and damping. The old designs by JLH and Noel Keywood and in the Mullard design books are all choke and or capacitor coupled, this does limit there damping factors and BW. With the latest beasts i.e. TOCA a large constant current load is used but the heat is high. The damping factor then can be increased to over 1000 as to 20-50 this sounds much better. The output is 5 FET's in parallel performing a Source follow output stage and the driver stage is only a single transistor with a high BW and high current capability. The control of the DC offset is another matter but no capacitor in the output or input path. 10Hz - 100KHz is now easily met. I to like Push-Pull FET designs but some can and do sound to harsh, one that come to mind was the Dr Thomas design and The Bryston. All of them sounded like the raw unrefined Maplin/Hitachi apps note design. Now the 300W MONO TOCA were in a class of there own, OK you did need you own substation but they did drive horrid loads, but at 1800W consumption each you would be broke after a good party. And big at the Penta Show people thought they were speakers at a 180KG each.  I have this man coming to my house in about 10 minutes, he is a bit of a legend in my books. I know my amp is new but he has modded it, and is dropping it off. I'm keen to hear the differences and I'm sure we will be winding up the wick a little tonight ;-) |
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Post by John on Oct 9, 2014 19:45:37 GMT
Please fedback was very impressed when I heard it James
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Post by Sovereign on Oct 9, 2014 20:30:37 GMT
I'm not hugely technical, but the Wonfor SECA A class TQ Iridium amp I have does not have any particular slant or strength in one area and weakness in another. I have had oodles of amps pass through my system and this is bar far the most comprehensively complete and satisfying amp I have heard. The bass is there is truck loads, with my 15 inch bass drivers coupled to the A class amp I'm sure I can hear the very lowest registers of the recorded music, the mid rage is very expressive and tangible, the treble sparkles but not harsh in any way and the overall presentation is bloody massive.
Colin replaced the output caps to something a wee bit more special, giving an even bigger and fuller sound, bass transients seem faster and the mid seems a wee bit more tangible. I've heard of speakers that are too big for a room, I honestly feel this amp is a little too big for my listening room.
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Post by John on Oct 10, 2014 4:33:18 GMT
Cheers for the update
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Post by MartinT on Oct 10, 2014 5:16:18 GMT
Pity Colin isn't around as he has lots of interesting things to say and I'd love a listen to his amp. The relatively low power scares me off, but I know class A can do things a bit special.
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Post by John on Oct 10, 2014 5:18:26 GMT
Not sure how it cope with your speakers Martin but it is a very musical amp
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Post by Sovereign on Oct 15, 2014 21:33:37 GMT
Pity Colin isn't around as he has lots of interesting things to say and I'd love a listen to his amp. The relatively low power scares me off, but I know class A can do things a bit special. Where are you Martin perhaps you could swing by Maidstone or I could see if I could pop up to you if I ever have a day free. I've had to pull the speakers out away from the wall about 250mm as the bas this amp produces was too much. With the repositioning of the speakers the bass is a little tighter and more defined, and less overpowering. I find that I tend to listen to music at around 10 - 15 db louder with this amp, I just love the way it, and the Croft Pre, reproduce music! Usually around 90db of pure musical pleasure. I would say I have really sensitive ears and hate stuff too loud TV, crowds, background noises etc. |
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