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Post by Deleted on Jun 14, 2012 23:38:35 GMT
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Post by Deleted on Jun 14, 2012 23:50:36 GMT
Hi Dave You can't do that as it is A.C. in at that point . You can either break into the +VE supply at the output of the bridge rectifier, or if you have a suitable voltage + and - supply, you could break in at that point, as well as the same point of the other transformer winding, and also connect 0 volts/earth to the appropiate point, and then feed that ALREADY DC + and - supply into the regulating stages. The bridge rectifier will then steer the DC inputs correctly to the appropiate regulators. Regards Alex
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Post by Deleted on Jun 15, 2012 0:07:22 GMT
Hi Alex, have you been at the Scotch?
The question is............................. not to do with breaking in Alex but simply operating the PSU with that trace broken at the junction of D2/D3 and the secondary positive out of the transformer. Alan
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Post by Deleted on Jun 15, 2012 0:22:01 GMT
No. Perhaps I should have been ? It's been far too long in between decent 12yo aged (or older) bottles. I asumed the question came from Dave because of the wording. I will re read your question to try and see what you are trying to accomplish. Alex P.S. The previous explanation still stands, but as to your present question, there will no longer be sufficient A.C. going in for the circuit to work.In other words , unless I am missing something here, (quite possible at the moment ) the output at the bridge rectifier will be far too low due to 1/2 the A.C. voltage in.
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Post by Deleted on Jun 15, 2012 4:58:21 GMT
The effects would be:
A: the unregulated DC voltage (+ and -) would be slightly lower. If the unregulated supply voltage is still higher than the regulated value (in other words if the lowest voltage of the ripple is still higher than the minimum dropout voltage of the regulator OR the JLH can 'sink' you won't notice in the regulated voltage. B: The ripple on the reservoir caps would become somewhat higher in amplitude. C: the ripple on the reservoir caps would become 50Hz instead of 100Hz D: the bridge rectifier diodes that are still working may get slightly warmer E: the trafo would be loaded improperly and might hum slightly louder
As long as the regulator still can do it's job you probably won't even notice.
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Post by Deleted on Jun 15, 2012 5:39:03 GMT
I meant that the circuit as designed would no longer work as intended. The JLH would be hunting all over the place due to the high ripple, possibly overheating and failing. The original JLH Current Limiter is a P.I.T.A. at the best of times, and is really only suitable for lower currents and normally not with larger than 2 x 2,200uF Low ESR in parallel in the JLH. There is also the possibility of it taking the LT1085 along with it, especially as it doesn't have protective diodes.
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Post by Deleted on Jun 15, 2012 23:40:12 GMT
Okay here's what actually took place............................... First off thanks Alex and Frans your input is always welcome. The question was posed after my build of the 'AK Mods' SC Class A 15W Amplifier went belly-up via the PSU. I'd had it working away nicely since early April just lying open on the bench waiting for it's case. Well eventually built the case and installed the beast that'd be about 4th June and it was working fine if a bit hotter than I liked at only 100mv................beefed up the heat sinking and still hot but now working at a full 240mv bias. Sound quality.....the best............I've ever heard. I'd used two IEC sockets for power in from the transformers double pole switched and fused on the positive line. So cased up it worked away fine for about four days then I lost the left channel. Checked power in ok voltage on negative line after reg ok and after JLH ok. Checked power in on positive side that was strange no ac out of the IEC socket checked fuse...............bloody hell! who pulled the fuse...............thought don't tell me MGLW's got pissed off at the time I'm spending up here and removed the fuse. Nah! that's daft but I was sure I'd put a 3amp fuse in..............checked the other IEC.......no fuse installed. Then I realised I'd forgotten that the IEC sockets were supplied without fuses installed and I'd been running the amp without them effectively breaking the positive line. I then checked the positive voltage after the LT1085 Reg it was 3.6 volts whilst before the Reg it was 44 volts. At this point I pulled the broken left PSU and replaced it with a new module built but not tested. Modified the IEC sockets on both lines doing away with the switch and fuse. Powered up all working fine, that lasted less than a day before the other PSU module went the same way as the first. Pulled that one replaced it with the another untested new module and the amps been playing away all day. Sounds great again.......................perhaps I should stick to making boxes. Regards Alan
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Post by Deleted on Jun 16, 2012 0:15:14 GMT
Hi Alan Looks like I wasn't that far out.I didn't bother going into 1/2 wave rectification vs. full wave, ( I was still half asleep ) but I am not surprised that the regulator was unable to function. You are lucky that the very high ripple didn't bugger the JLH. Kind Regards Alex P.S. Shit happens. We all have iour moments like that.
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Post by Deleted on Jun 16, 2012 6:53:30 GMT
Hi Alan,
It seems like you have been running the amp on halfwave rectifiers from the day it was built in a case (using the IEC sockets to connect the secondary of the AC trafo) As I suspected you wouldn't even have noticed this as the unregulated voltage might still be high enough for proper operation. My point 'D' above is probably the reason for 1 side of the PS failing (check the bridge diodes I suspect just 1 to be faulty) as the needed current (you also increased the idle current) was now only supplied by 1 diode instead of spread over 2 of them. replace all 4 diodes with better suited types and this might very well bring it back to life unless other parts were destroyed in the process depending on how the diode failed (open circuit or fused to 0 Ohm)
remember my PM about diodes and me questioning if they were able to stand the PEAK currents that exist when using high wattage trafo's and large (low ESR ?) smoothing caps ?
Even with full bridge rectifiers the peak currents will be nearing it's limits which in turn will limit it's lifespan. Not into days but you can expect the PS to fail within 10 years or so... suddenly.. unexpected.
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Post by Deleted on Jun 16, 2012 7:40:44 GMT
SBYV28
IF(AV) 3.5 A VRRM 50 V to 200 V IFSM 90 A trr 20 ns VF 0.89 V TJ max. 150 °C
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Post by Deleted on Jun 16, 2012 9:51:28 GMT
Exactly.. my point, more suitable diodes are available ! Like those intended for 50Hz rectifiers for instance... but these tend to deteriorate the sound though so beware.
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Post by Deleted on Jun 16, 2012 20:02:55 GMT
Alex, That's for another day when I get round to bringing those defunct modules back to life for my elder sons' AK MODS SC CLass A Pre/and Power Amps as I'm now using the ones I built for his Mark II. Fortunately having two spares to hand gave me a quick out.
Frans,
yes that looks like what I did when the beast was cased up. In a way it was possibly fortunate that I did fail to insert the fuses since it brought my "Numptieness" to the fore sooner rather than later.
Yes you are right everything seemed OK when cased up except that I didn't check voltages but then why would I it had been working OK for weeks uncased ............ lesson learned..........check, check, check.
I did take on board your PM point about more suitable diodes but surely the point of this mod is to push the boundaries a bit in our quest for higher SQ and Alex's suggestion of the SBYV28 series possibly does that. Given a ten year life of higher SQ against a longer one allied to deterioration in SQ using more suitable (longer life) 50Hz rectifiers I guess I'd always go for the former. As always I am indebted to both of you knowledgeable guys for your valued input. Amp sounds great as I type. Regards, Alan
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XTRProf
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Pssst ! Got any spare capacitors ?
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Post by XTRProf on Jun 17, 2012 23:36:53 GMT
The diodes can be changed to even better Schottky if those are already not Schottky.
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Post by Deleted on Jun 17, 2012 23:56:45 GMT
The diodes can be changed to even better Schottky if those are already not Schottky. The diodes are fast,ultrafast reverse recovery types. Even you will be unlikely to hear any difference between both types. As for slow types with snubbers, while this may virtually eliminate switching noise artifacts, I have a gut feeling that it may assist higher level RF getting in to the amplifier via this route, even when the diode is not conducting. Alex
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XTRProf
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Pssst ! Got any spare capacitors ?
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Post by XTRProf on Jun 18, 2012 1:58:24 GMT
The diodes are already fast, slow recovery types. Even you will be unlikely to hear any difference between both types. Actually, it should be FAST BUT SOFT RECOVERY type so that it don't overshoot. Schottky is that. Even though may not be discernable, it's always best to build the best that it can be for peace of mind. Schottky is not that much more expensive, btw. As for slow types with snubbers Until now, I still don't understand why people put in snubbers when diode technology has already advanced to Schottky where it's already fast but don't overshoot. Snubbers are just to prevent overshoot and the resulting switching noise. If snubbers are put in, it will slow any fast diodes from being fast. So why put in the faster diodes but only to slow them down thru snubbers? Also, don't the circuit moving away from KISS with snubbers? The same for advance capacitors with bypass. Well, the same old building to the best mentality applies, I guess.
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Post by Deleted on Jun 18, 2012 2:39:06 GMT
The diodes are already fast, slow recovery types. Even you will be unlikely to hear any difference between both types. Actually, it should be FAST BUT SOFT RECOVERY type so that it don't overshoot. Schottky is that. Even though may not be discernable, it's always best to build the best that it can be for peace of mind. Schottky is not that much more expensive, btw. As for slow types with snubbers Until now, I still don't understand why people put in snubbers when diode technology has already advanced to Schottky where it's already fast but don't overshoot. Snubbers are just to prevent overshoot and the resulting switching noise. If snubbers are put in, it will slow any fast diodes from being fast. So why put in the faster diodes but only to slow them down thru snubbers? Also, don't the circuit moving away from KISS with snubbers? The same for advance capacitors with bypass. Well, the same old building to the best mentality applies, I guess. Chong Schottky diodes are not suitable here unless you use the larger TO220 style types , as the normal schottky diodes such as the 1N5822 have only 40V Peak Repetitive Reverse Voltage and are 3A average forward rectified current. Neither do I wish to use a diode with 2mA reverse current at it's rated voltage at 25C , and 20mA at 100C. Some of the TO220 style types are much better in this regard, but their reverse recovery time is slightly worse than the chosen SBYV28 -200 and they are much more expensive. Alex P.S. I should have said Ultrafast reverse recovery time
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Post by Deleted on Jun 19, 2012 6:24:10 GMT
a simple link will convey my sentiments. sound.westhost.com/power-supplies.htmselect: Rectifier Diodes Recommended for those that make their own power supplies. I encourage the DIY'ers to read the complete article about power supplies. Ofcourse, the guy has no clue what he is talking about, nor does N. Pass he quotes now and then.
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Post by Deleted on Jun 19, 2012 6:32:22 GMT
a simple link will convey my sentiments. sound.westhost.com/power-supplies.htmselect: Rectifier Diodes Recommended for those that make their own power supplies. I encourage the DIY'ers to read the complete article about power supplies. Of course, the guy has no clue what he is talking about, nor does N. Pass he quotes now and then. Rod is no doubt clued up, but like someone else we know, he is VERY anti subjectivity ! ;D I note that even an >80 year old member also hears differences between Headphone cables that are supposed to be impossible according to some.
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Post by Deleted on Jun 19, 2012 6:42:10 GMT
Nelson Pass is also very anti subjectivity ? He claims the very same.
I thought he was 'highly acclaimed' and 'highly regarded' and a role model in subjectively found differences ?
In any case... anyone making their own power supplies might want to check out the information over there. You are always free to know better, but at least you have the chance to learn a bit more about audio power supplies for power amplifiers.
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Post by Deleted on Jun 19, 2012 6:58:09 GMT
As I suggested to N.P. some time back, he should call his next amplifier FETucinne. ;D As far as I am concerned FETs add artificial warmth like most Vacuum Tube designs.However , like with those glowing relics from nearly 100 years ago, many people prefer colouration over a neutral presentation.
No wonder you like quoting Rod Elliot . His views are similar to yours, and at odds with what the vast majority of RG members report hearing ! ;D
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Post by Deleted on Jun 19, 2012 21:02:22 GMT
I guess this thread is well past it's sell by date EVEN A RIGHT NUMPTIE CAN SEE THAT FRANS & ALEX/ALEX&FRANS Alan
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Post by Deleted on Jun 19, 2012 21:28:10 GMT
As long as you got it working and are enjoying it again it has served it's purpose.
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