| jamesfeline |
Hello
My name is Nick from the UK and i have been making power amps for the last 20 years, this is my 1st response to this forum. Most of my amps have been designed by JLH. I was thinking of making the SC magazine 15w class a as described in this post. Any chance some of you could send me the CCT diagram and pics of your amps if you have constructed the amp in question ? also what are your views on this amp as regards sound quality ? would be helpfull before I start construction
best regards
Nick |
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| jamesfeline |
Hello again
Any body ?? surley some one must of construted this power amp ? or is it no good ?
best regards
Nick
:rolleyes: |
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| jamesfeline |
ok
what would you all go for ?
JLH 15w class A or the SC magazine 15w class A design ?
regards
Nick |
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| Netlist |
Nick,
I'm sure you will get more responce here in the Solid State forum. :)
/Hugo |
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| destroyer X |
Will be easier, and better for us, to watch it in advance, this may result in some comments from us.
20 years constructing is telling me that you may have a lot of things to comment too.
If you came from other forum section, chip amps or another...a transference (moved for good), post the schematic once more.
regards,
Carlos |
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| jamesfeline |
thanks for the feedback ... yes I am 42 these days a fully qualified electronics technician ,,, and I have had the audio bug since I was 14 years old. I have my own log cabin as a electronics workshop and dream of running my own company making audio gear ( all hand made ) at the highest quality possible ( well by me any way )
I will post some photos soon as I am still new new this site as I did not realise I was in the wrong section. I am a big fan of JLH as I have met the guy. I make highley modified JLH 80w mosfet power amps and a 250w bridged version .... you just need to see it also i have sold quite a few ... trying to get them CE approved
anyway
taking my wife out for a meal .... speak to you all when I get back
all the best
Nick |
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| destroyer X |
This forum is an enormous brotherhood..filled with knowledge till the top....bad folks are not more than 10 when we have thousands of nice educated folks.
I hope you enjoy and give us contributions telling things about your experience, and contributing in our threads too.
regards,
Carlos |
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| Greg Erskine |
hi jamesfeline,
I was just reading the May 2007 Silicon Chip magazine and guess what?.... they have just published an update to the old 15W ULD class-A amp. :D
Here's a quote from the front page, "All-new 20W Class-A Amp, the lowest distortion of any amplifier ever published...anywhere in the world!!"
Note 2 explanation marks.
regards |
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| sandyK |
I have been using this amplifier since shortly after publication.
The editor of Silicon Chip (as an engineer) was quite embarrassed about subjective quality of this amplifier when compared to a previous Class AB magazine project. He seemed to put most of the major audible improvements down to the superior channel separation of the Class A .
As good as the basic amplifier is, it is very accomodating of modifications to both the amplifier PCBs and Power Supply.
The output transistors , for example , may be replaced by 2SA1302/2SC3281 (or the latest Toshiba devices) for even better results. Using 2 regulator boards further improves the performance, as does replacing their series pass transistors with MJE15030/15031.Further benefit may be obtained by using a Harbuch PTT4639 transformer (dual secondaries) and 2 bridge rectifiers.
There are MANY other refinements also, that I won't go into at this stage.
sandyK |
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| smithy666 |
I think you hit the nail on the head regarding Silicon Chip projects. Sure, the design may be good, but they could have gone just that bit further to make it really great. I find in virtually all their projects that component selection is lowest common denominator stuff, ie whatever cheap parts are available from Jaycar/Dick Smith will do. They rarely give consideration to capacitor types, even in the signal path, which I doubt even the biggest sceptics would argue over the benefits of film vs electro.
One example is Silicon Chip's Oct 2005 "the best preamplifier ever" project, which features 4 non polarised electros (2x47uF and 2x22uF) in the signal path of each channel!! Arrrgh! They also use the same relay to switch the left and right channel and the distance between tracks for the left and right channel is about 0.5mm (one channel's track actually runs through the relay terminals of the other channel). Don't get me started on the carbon volume pots running back to terminal blocks. I'm not attacking their design, just the fact they put these up as the "best ever" published (do they read Elektor?) and of "audiophile" quality. Oh, please. |
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| Greg Erskine |
hey sandyK,
Have you been looking in my parts bin?
I'm building one of these amps but have been side tracked, well a couple of times. I'll have to talk to you more when I get back on it. I have the Toshiba 2SC5200/2SA1943, ON MJE15032/15033, 2 x Harbuch PTT4639 transformers and 2 x 2 regulator boards. I plan to build it standard first, though dual mono, then do the mods.
regards |
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| sandyK |
Smithy666
Don't forget that Silicon Chip requires the support of their major advertisers. If there wasn't liason with them, many of the projects would never get published.
Regarding the SC preamp, I did email them with constructive criticism.They replied , but didn't publish. I did connect an
"earth strip" of sorts between those close together tracks. It did improve things a little.SC agreed that they could have left some capacitors out of the signal path, as the DC out of the OPA2134 is usually much less than 2mV. In my preamp it was more like 0.2mV!
After those changes it became much closer sonically to my main preamp which uses 2 Class A PCBs ,and a modified version of the Class A design, but with 2SC5171/2SA1930 output devices. In other words, scaled down, but with even more bandwidth.
sandyK (Alex) |
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| jacco vermeulen |
Yeah, but any of you gents care to show what you're talking about ?
I've got the SC 100-watter schematic, i can pretty much imagine what the '98 Ultra-LD would be like, but a schematic beats a thousand of my insane thoughts any day of the week. |
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| sandyK |
Jacco
As a new member, I don't yet have full privileges as I am still under moderation. Perhaps, if you care to email me I can supply SOME additional information. (so long as I keep within forum guidelines, and the forum permits my email details at this stage)
sandyK |
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| ooops! |
| Has anyone had a chance to review to revised design yet? From what little I've seen so far it appears that they have addressed some of the concerns expressed here of the previous version. |
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| sandyK |
ooops
The new 20W version was only published this month.
It has approximately the same power dissipation as the original and no longer requires an external PSU. It is also claimed to have even lower distortion. Part 2 of this design should hit our newstands next Wednesday. I am currently using a highly modified version of the original 15W design.
SandyK |
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| srh |
Leo and co have been reading Doug Selfs book on poweramp design. Looks to me to be a high bias classic Self "Blameless" Class B with CFP output stage. Dunno why they just didn't pinch his Class A design with the rather nice bias regulator.
Steve. |
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| smithy666 |
| Same as when they copied the Elektor volume control - almost identical, but they managed to stuff it up with awful coupling caps and poor layout. Very ordinary magazine in my view, hence why I dropped my subscription recently...oh yeah, and Leo's stupid, baseless ramblings in his editorials (I think these annoyed me even more than the magazine's mediocrity) |
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| srh |
smithy666,
I have watched Leo evolve since he started with EA in the '70s. When it comes to audio design he is neither original nor adventurous IMO. I think he will be remembered for keeping electronic hobbyist publishing alive in Australasia and his tirades against valve amps.
Steve. |
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| sandyK |
They must have just got around to reading the D.Self book that they have been selling for years !
However, their projects are often highly modifiable. I have noticed recently, a reluctance, by at least one of their staff members to respond to suggestions and criticisms in the magazine itself e.g. The Studio Preamp recently had too many coupling capacitors. It was however conceded via email, that in hindsight, due to the low offset due to the OPA2134, that the number of capacitors could have been reduced. But, did they bother to tell their readers ? NO.
Having said that, have either of you two fellow Aussies constructed the original Class A design, and tried to improve it ?
You may be surprised just how good it can be, if you take the time to correct some of the deficiencies due to the cost cutting demanded by the kit suppliers. As far as I am concerned, these designs, whether borrowing on techniques pioneered by Douglas Self, or not ,should sound audibly better than many of the simplistic designs currently available in kit form.
How about what you guys would do to improve the basic magazine designs ? BTW, I have been using 3 Class A modules, 2 regulated PSU boards, AND a dual winding Harbuch low flux toroidal transformer, all in the same case, for surround sound use for several years . Without any hum problems.
If you feel that SC is letting the side down, why not tell them, and suggest some improvements?
NO! I have no connection with this magazine, except as a purchasing reader since it's inception.
SandyK |
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| sandyK |
O.K. So one of you is a K1W1.
SandyK |
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| srh |
SandyK,
And proud of it too!
No, I haven't built a SC Class A and don't intend doing so. Leo and co are besotted with low thd numbers and there is much more to reproduced music than that. I like FETs and Nelson Pass so an Aleph X is my next amp as soon as I can drag my fat lazy *** away from the pc and over to the soldering iron.
Steve. |
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| sandyK |
I have tried the FET route with designs such as the ETI5000, and AEM6000 by David Tilbrook. I found they had an artificial warmth
to the sound. Similar to the sound that so many people seem to like about valve amplifiers. I briefly revisited valves recently, with the SC valve preamp, but with a few minor mods to reduce PSU noise and increase separation. The soundstage was great and lovely sounding on DTV. When there was a lot happening at once, however,it exhibited exactly the same behaviour I heard at a HI-FI show many years ago in Melbourne with the >AU$100,000 Ongaku Valve amplifier , when someone slipped in a Madonna "Q Sound" recording. It sounded terrible. However, it's all about choosing whatever you get the most enjoyment from.
SandyK |
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| smithy666 |
Steve
I agree Leo will be seen as you say. Pity though, as in the days when EA, ETI and AEM were running, it was a much more exciting time for DIY electronics than it is today with just SC. Sure times have changed, but Elektor still manages to produce world class projects. Just compare the quality of the two. IMO AEM was a great magazine with some really innovative projects. SC just doesn't do it.
SandyK
No I haven't built it, as my speakers are too inefficient (Dynaudio Finale & Ellis 1801) for such a lower power amp. Even so, I doubt I would when there are more innovative designs out there (I use Giovanni Stochino amps published in Electronics World a few years back and am looking at doing a Borbely).
I think part of the problem is Leo's ego. If you dared to suggest a fault with the amp he would shout you down or say it was rubbish. Try telling him the benfits of better quality caps, for example (I doubt anyone on this forum would doubt the difference caps make). And it's not just audio projects - virtually every project they publish is aimed at the lowest common denominator. |
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| sandyK |
Smithy
Many years ago I modified the Studio 200 and told Leo Simpson what I had done. He didn't agree with my mods, but published a 4 page article showing both circuits and invited comments.
So, I don't agree with you. In the past I have found Leo does listen. On another occasion I mentioned that I had used a discrete version of the LH0002 buffer.Several months later SC published an AV switcher using similar, but different type transistors.
Perhaps he has changed over the years, but I think it's a newer team member that doesn't like suggestions.
SandyK |
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