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Post by Deleted on Dec 10, 2012 0:03:16 GMT
Alan I presume you are keeping the original or the one you built for family ? Don't forget the OPA134s and the 2n2 caps there too,or just the cheap additional 2n2s , as the S/N is measurably better,* and low level detail and ambience cleaner and more natural sounding. Kind Regards Alex.
* I had to build a low noise battery operated preamp in a die cast case for my CRO to see it, though.
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Post by Deleted on Dec 10, 2012 1:02:28 GMT
Hi Alex, #2 build is for my elder son and all mods will be done before he gets it also on my own #1 build. I have the OPAs just the 2n2s to get. The worst part of this new build is going to be the HA/Pre.................might have to go into rehab after or should that be respite? Regards, Alan
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Post by jeffc on Dec 12, 2012 4:16:16 GMT
Hi Alan, Thanks for this useful info, I've been wondering about just how far away the transformers need to be from the amp PCBs to ensure low distortion is preserved, particularly as my amp and PSU boxes will be timber except for the side heat sinks and 3 mm-thick aluminium top plates. Like you, I'll have to sit the amp and PSU boxes on shelves of my audio rack, which will separate them by ~30 cm vertically, with the PSU box below the amp. cheers.. jeffc
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Post by Deleted on Dec 13, 2012 10:58:10 GMT
I've started building up the boards and I'm first using up the bits I already have before ordering the rest. C5, C7 etc on Will's (essential, lifesaver) BOM don't mention the voltage. Can someone help? A more technical question now - which end of the SF12 goes through the PCB? Thanks guys Syd
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Post by Deleted on Dec 13, 2012 11:26:05 GMT
I've started building up the boards and I'm first using up the bits I already have before ordering the rest. C5, C7 etc on Will's (essential, lifesaver) BOM don't mention the voltage. Can someone help? A more technical question now - which end of the SF12 goes through the PCB? Thanks guys Syd Hi Syd I think they are the 100uF electrolytic caps near the -20 and +20V input terminals ? They should be 25V mininum , and 35V would be a little better if easy to obtain. The "bar" side of the SF12 goes to the trimpot,and is closer to the LS313 and LS352. Regards Alex
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Post by Deleted on Dec 13, 2012 11:51:48 GMT
Thanks Alex, that's great, I have the right caps here then. SF12s duly planted. Very much appreciated, hoped you hadn't gone to bed Syd
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Post by Deleted on Dec 13, 2012 16:15:19 GMT
Hi Syd, knew you couldn't keep your hands off Will's great boards. If I can help with anything just ask, do you have the SPKR PRO board? Were on a bit of a downer here at the moment and I'm finding it hard to concentrate on anything. Our six year old Granddaughter is having a hard time in hospital she went in on Tuesday and has been diagnosed with GBS, it affects about 1 in 100000 children in the UK, it has really upset us all. Regards, Alan
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Post by Deleted on Dec 13, 2012 16:36:01 GMT
Hi Alan, I had to look up what GBS stands for and it does not sound very nice. I hope your Grandaughter recovers well but you'll have a very worrying few weeks I guess. At that age they do seem to bounce back very well and hopefully they identified the problem early. Good luck with it all. Cheers, Dave.
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Post by Deleted on Dec 13, 2012 18:05:23 GMT
Hi Alan, I had to look up what GBS stands for and it does not sound very nice. I hope your Grandaughter recovers well but you'll have a very worrying few weeks I guess. At that age they do seem to bounce back very well and hopefully they identified the problem early. Good luck with it all. Cheers, Dave. Hi Alan sorry to hear about your grandaughter and hope she makes a good recovery. all the best from this end take care
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Post by Deleted on Dec 13, 2012 18:21:04 GMT
Thanks Lads, the prognosis via the consultant specialists treating her is good but you can't help but feel her pain. Alan
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Crispy
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Post by Crispy on Dec 13, 2012 21:00:35 GMT
Hi Alan, I had to look up what GBS stands for and it does not sound very nice. I hope your Grandaughter recovers well but you'll have a very worrying few weeks I guess. At that age they do seem to bounce back very well and hopefully they identified the problem early. Good luck with it all. Cheers, Dave. Alan, I also had to look it up, it does sound really nasty. It did say that most people fully recover and I am sure that this will be the case for your granddaughter (fingers crossed). It must be very worrying especially at such a young age, anyway I hope she makes a full recovery. All the best. Chris
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Will
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Post by Will on Dec 13, 2012 23:25:37 GMT
Hi Syd, Haven't checked, but think that the BOM only list parts that are suitable to be used (both physically and electrically) so Alex's remarks stand. I'll have a look and comment when I in full control (posting this after my companies Xmas do - and I may have had a drink or two looking forward to my IOSH HSE exam tomorrow ) Alan, really hope your grand-daughter is OK, we've had our share of hospital related worries with our youngest (asthma) and can imagine worrying about your children worrying about their children is as bad, if not worse. As Chris and Dave have mentioned, she's sure to bounce back!
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Will
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Post by Will on Dec 13, 2012 23:28:58 GMT
Syd,
on the SF12 installation, click the link in my signature for the AK Class A info - Chris made a great picture detailing how to fit this diode (was a 1N5xxx back then) this info still stands, as I modified the HA pcb for the amp pcb.
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Post by Deleted on Dec 14, 2012 0:03:04 GMT
Syd, on the SF12 installation, click the link in my signature for the AK Class A info - Chris made a great picture detailing how to fit this diode (was a 1N5xxx back then) this info still stands, as I modified the HA pcb for the amp pcb. Will I read that daily, I think literally for weeks, back then. Then, in my usual way I forgot it had uses here too So far fingers crossed I have got further along than I expected by now. Mind you my Farnell list should keep them happy Best of luck with your exam, bad timing just after a Chritmas 'do' though! Syd
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Post by Deleted on Dec 17, 2012 22:41:42 GMT
Hi Alex Back last year there was some talk about 4 ohm speakers and this build. Is there any problem or anything different I need to do, because I just checked today and guess who has 4 ohm speakers? Thanks Syd
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Post by Deleted on Dec 17, 2012 23:02:14 GMT
Hi Alex Back last year there was some talk about 4 ohm speakers and this build. Is there any problem or anything different I need to do, because I just checked today and guess who has 4 ohm speakers? Thanks Syd Hi Syd The amplifier will supply only about half it's rated power in pure Class A into 4 ohms, and then crosses over into Class AB , albeit at lower than typical distortion. Doubling up on the PSU area with both transformers and PSU PCBs as we are doing will also assist with 4 ohm operation.It is also possible to increase the supply rail voltages and bias a little more, provided that heatsinking is adequate. Bear in mind though, that in a typical domestic situation, that we rarely go much above 1watt . I tried an older 15W Class A version in to Geoff B's big 4ohm Ohm Walsh speakers several years ago, and it still had power in reserve for home theatre use.The fact that is direct coupled, and doesn't have a rolloff at the LF end seems to give it more punch at the very low end despite it's modest power ratings. Regards Alex P.S. Don't forget that most of the valve amps that some seem to love, despite their technical shortcomings, rarely go much higher than 15W per channel.
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Post by Deleted on Dec 17, 2012 23:57:50 GMT
Hi Alex
So I don't need to do anything different to using the parts set out on the BOM?
Its 20V traffos this time? - getting a bit punch drunk trying to get up to speed again!
Thanks again Alex
Syd
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Post by Deleted on Dec 18, 2012 0:34:37 GMT
Hi Syd Readily available toroidal transformers go 12,15,18,25. Mine uses a special Harbuch dual winding 21-0-21 transformer. As we are using 2 simpler PSU PCBs instead of a single PSU PCB with higher current capabilities, we are able to dispense with the series pass transistor. This means we don't need as high a voltage to start with.This allows us to use 2 of the more readily available 18-0-18 toroidal transformers. They should be a minimum of 80VA each. We are also using the lower voltage drop Schottky diodes to rectify the A.C. This also helps to ensure that the voltage regulators have adequate voltage headroom for proper operation.If someone obtained a couple of 20-0-20 transformers to special order, they would be able to turn the voltage up a little higher and get a few more watts.Not that you would be likely to notice the difference though. Kind Regards Alex
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Post by Deleted on Dec 18, 2012 1:15:42 GMT
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Post by Deleted on Dec 18, 2012 1:18:26 GMT
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Post by Deleted on Dec 18, 2012 2:21:11 GMT
And you are still running at only 15W with 1A bias ? They sound ideal if the PSU case will take them as well as 2 x 18-0-18 30VA s for the preamp too.
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Post by Deleted on Dec 18, 2012 10:03:10 GMT
Thanks Alex, Alan & Shaun Express speed replies as usual Those Airtronic look ideal, I'll get some ordered up. Just need to do a final check through of my order for the bits I don't have and no doubt a few more queries addressed to you guys and then hopefully onward and upward Regards Syd
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Post by Deleted on Dec 18, 2012 10:16:02 GMT
And you are still running at only 15W with 1A bias ? They sound ideal if the PSU case will take them as well as 2 x 18-0-18 30VA s for the preamp too. Hi Alex yes i still have your amp running at 15W 1A and found no need for trying to squeeze more out. I would say that I've been surprised how far 15W can go but I've had 1.5W tube amps so no big surprise. just super SQ Hi Syd here is my PSU unit the upside down Monkey ;D ;D not the only way of doing things but gives you some idea of the transformer size. BTW i had great service from Airlink and nice transformers which arrived a few days after ordering. pretty impressive any questions just ask away take care
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Post by Deleted on Dec 18, 2012 10:35:55 GMT
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Post by Deleted on Dec 18, 2012 11:27:04 GMT
And you are still running at only 15W with 1A bias ? They sound ideal if the PSU case will take them as well as 2 x 18-0-18 30VA s for the preamp too. Hi Alex yes i still have your amp running at 15W 1A and found no need for trying to squeeze more out. I would say that I've been surprised how far 15W can go but I've had 1.5W tube amps so no big surprise. just super SQ Hi Syd here is my PSU unit the upside down Monkey ;D ;D not the only way of doing things but gives you some idea of the transformer size. BTW i had great service from Airlink and nice transformers which arrived a few days after ordering. pretty impressive any questions just ask away take care Hi Shaun Makes the original SC PSU look a little puny ! Don't forget that their PSU may have dissipated a tiny bit more heat than yours due to 21-0-21V toroidal. That means your PSU has quite a bit more heatsinking than necessary. Perhaps you did intend upping the power ? ;D Kind regards Alex
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