Deepthought Posted March 23, 2021 Share Posted March 23, 2021 (edited) The step down transformer is non-isolating so it would seem that the reduction in noise was related to the reduction in voltage? Is 12-14V DC a common thing in the AC supply? That sounds alarming. I would have thought DC in the mains should be in the millivolts range. I believe the ATLHIFI units are designed in accordance with Elliots recommendations - https://sound-au.com/articles/xfmr-dc.htm Edited March 23, 2021 by deepthought Link to comment Share on other sites More sharing options...
andyr Posted March 23, 2021 Share Posted March 23, 2021 (edited) 2 hours ago, Monkeyboi said: In many cases a decently sized isolation transformer is better than trying to control d.c. offset in the mains with these d.c blocker devices because if it has sufficient capacity you can power all your gear through it, thus effectively solving the problem for all your gear with one device. Don't quite follow your logic, there, Alan? If a DC blocker is built to pass 10a ... then it can pass all that is supposed to be drawn from a ppt. You would have to be using a very large (at least 2400VA) isolation transformer to be able to pull 10a though it ... and I would suggest it would really have to be considerably larger (5KVA?) - in order for it to offer no constriction to 10a of current flow? 1 hour ago, deepthought said: I believe the ATLHIFI units are designed in accordance with Elliott's recommendations - https://sound-au.com/articles/xfmr-dc.htm If they're the "two electros are 2200uF" that LL posted ... I don't think so. Rod suggests 2x 4700uF caps. Andy Edited March 23, 2021 by andyr Link to comment Share on other sites More sharing options...
Deepthought Posted March 23, 2021 Share Posted March 23, 2021 1 hour ago, andyr said: If they're the "two electros are 2200uF" that LL posted ... I don't think so. Rod suggests 2x 4700uF caps. Andy " Larger electrolytics can be used if desired" Link to comment Share on other sites More sharing options...
andyr Posted March 23, 2021 Share Posted March 23, 2021 47 minutes ago, deepthought said: " Larger electrolytics can be used if desired" Sure - but: the basic - 2x 2200uF in series delivers just 1100uF ... so <1/2 what Rod recommends, and providing there's enough space on the PCB to accommodate larger caps. Andy Link to comment Share on other sites More sharing options...
Deepthought Posted March 23, 2021 Share Posted March 23, 2021 Not sure what point you are trying to make. Rod Elliot says "Larger electrolytics can be used if desired" and ATLHIFI has used 2X 47,000uf. So? 1 Link to comment Share on other sites More sharing options...
andyr Posted March 23, 2021 Share Posted March 23, 2021 7 minutes ago, deepthought said: Not sure what point you are trying to make. Rod Elliot says "Larger electrolytics can be used if desired" and ATLHIFI has used 2X 47,000uf. So? 47000uF is indeed great, dt. 6 hours ago, andyr said: If they're the "two electros are 2200uF" that LL posted ... I don't think so. Rod suggests 2x 4700uF caps. I assumed - mistakenly - as you can see from my earlier post that the ATL unit must use 2200uF caps. Andy 1 Link to comment Share on other sites More sharing options...
kukynas Posted March 23, 2021 Author Share Posted March 23, 2021 not sure where the confusion about Chinese vs ATL board came from but in any case larger cap for higher ripple values would be obviously better, I bought 25V/22000uf for my ATL board Link to comment Share on other sites More sharing options...
Monkeyboi Posted March 23, 2021 Share Posted March 23, 2021 5 minutes ago, andyr said: Don't quite follow your logic, there, Alan? If a DC blocker is built to pass 10a ... then it can pass all that is supposed to be drawn from a ppt. You would have to be using a very large (at least 2400VA) isolation transformer to be able to pull 10a though it ... and I would suggest it would really have to be considerably larger (5KVA?) - in order for it to offer no constriction to 10a of current flow? Andy Sure it can pass 10A if it is designed correctly and it will do this with minimal volt drop within the device. A d.c. blocker with piddly 2200uF caps won't pass 10A safely. Most 2200uF / 50V electrolytics aren't rated to pass 10A, more like under 2A even for low ESR electroytics. Just check the ripple current ratings of a typical 2200uF / 50V. Most are rated at about 1.7A maximum. Sustained currents exceeding the ripple current rating of the capacitors will eventually result in their failure due to inrush currents at switch on. Whilst the inrush current will be brief it will eventually destroy these capacitors. The other issue is the diodes. Those BYW76V diodes are only rated for 3A continuous. Given the diodes will be carrying the majority of the current the d.c. blocker @Leinster Lad has will get pretty hot under heavy loads so IMHO not a good choice of diode for the application. One needs to examine the current passing through the primary winding at no or low loads to see what actually happens. At switch on at the peak of the cycle the primary current is limited by the d.c. resistance of the primary winding. This can be significantly high depending on the applied voltage (let's assume 230 - 240 volts nominal here in Australia). Also there seems to be a preference with some DIYers of Chinese kit amplifiers and Chinese pre-built units to use transformers with 220v primary windings. These transformers not only are generally of a lower VA rating than would be ideal, the non-linear impedance nature of transformers under low load when voltages applied to the primary are above the specified can't be ignored as these conditions along with any d.c. present on the mains cause the transformers to run excessively hot and this can contribute to premature failure. In answer to your second question re 2400VA transformers. Yes to deliver 10A would require at least a 2400VA rating. The important thing is as I mentioned above is to ensure the primary is rated appropriately for the expected input voltage. The amount of iron in the core matters. Nothing wrong with slightly over engineering this transformer. Unfortunately most amplifier manufactures skimp on this and don't want to go to the expense of inrush current limiting circuitry as this increases production and design cost whilst lowering profits. Cheers, Alan R. Link to comment Share on other sites More sharing options...
Monkeyboi Posted March 23, 2021 Share Posted March 23, 2021 2 hours ago, deepthought said: Not sure what point you are trying to make. Rod Elliot says "Larger electrolytics can be used if desired" and ATLHIFI has used 2X 47,000uf. So? This unit is more like the business. Beefy diodes with a 10A continuous current rating. Personally I would have mounted them with a bit of clearance above the PCB as they will get hot with a full 10A load. The electrolytics are rated at 15.1A @ 60 deg C. Aluminum electrolytic capacitors - Snap-in capacitors - B41231 (tdk.com) Cheers, Alan R. Link to comment Share on other sites More sharing options...
Leinster Lad Posted March 23, 2021 Share Posted March 23, 2021 10 hours ago, Monkeyboi said: Those BYW76V diodes are only rated for 3A continuous In the DC blocker that I have , the diodes are in parallel pairs, (there are 8 in total) so that should be a bit better. Also looks like the caps are series positive to negative ( + - + - ) instead of the recommended +--+ Link to comment Share on other sites More sharing options...
Monkeyboi Posted March 24, 2021 Share Posted March 24, 2021 (edited) 4 hours ago, Leinster Lad said: In the DC blocker that I have , the diodes are in parallel pairs, (there are 8 in total) so that should be a bit better. Also looks like the caps are series positive to negative ( + - + - ) instead of the recommended +--+ #1 rule of diodes. Same way connected parallel diodes don't share the current equally. The one with the slightly lower forward voltage drop will start conducting more than the other and eventually sink most if not all of the current. If the maximum sustained current through the conducting diode is exceeds its rating it will fail. This same rule applies to zener diodes for the same reason except in a zener we are referencing the reverse avalanche breakdown voltage (the zener voltage in layman's terms). Now when the first diode fails due to excessive current it will most probably fail to an open circuit (the most common failure mode for this condition), leaving the remaining parallel connected diode(s) to carry the load. Of the remaining diodes, one will almost certainly have a slightly lower forward conduction voltage than the remaining diode(s) left in circuit, so the cycle of failure is perpetuated. There are workarounds to attempt to mitigate the problem - Thermally bond the diodes to improve thermal tracking (doesn't always work well) Wire a low ohmic value resistor in series with each diode to promote current sharing similar to what is done with parallel transistors. (doesn't always work 100%) Use diode arrays in the same package with the presumption that because the diodes are likely to be closer matched on the same die. (hit and miss) and finally, what should have been done in the first place is to use a diode suited to the application. This is by far the best option and not only increases reliability but lowers component count. IMHO, those 3A glassified diodes were probably the buy of the day at the Shenzhen electronics markets. IME, some Chinese designers have NFI what they are doing. Kinda like shades of the el cheapo Japanese electronics back in the 1950s. IME, anything made in China by no-name manufacturers should be de-rated by at least 50% of the claimed specifications. IOW, but with this particular product don't attempt to draw more than 3A continuously through it based on the diode specs alone. I could expand on the consequences of the diodes failing but I'm running out of time today to elaborate more. Post later. Cheers, Alan R. Edited March 24, 2021 by Monkeyboi 1 Link to comment Share on other sites More sharing options...
Leinster Lad Posted March 24, 2021 Share Posted March 24, 2021 Here is my circuit as far as I can tell ? Link to comment Share on other sites More sharing options...
Leinster Lad Posted March 24, 2021 Share Posted March 24, 2021 Okay, a couple of things. The two caps are wired + - + - NOT as suggested in the article as + - - +. I will have to change this. It is a bit hard to work out the exact circuit because the board is double sided and black lacquered, making it really hard to see the tracks. So, I've bitten the bullet and ordered a couple of low ESR caps and some suitable diodes. 8 x https://au.mouser.com/ProductDetail/512-RHRG3060 2 x https://au.mouser.com/ProductDetail/647-UXY1V732MHW The rest of my board is for filtering and it looks fine to me. Link to comment Share on other sites More sharing options...
Leinster Lad Posted March 24, 2021 Share Posted March 24, 2021 Link to comment Share on other sites More sharing options...
andyr Posted March 24, 2021 Share Posted March 24, 2021 18 hours ago, Monkeyboi said: IME, anything made in China by no-name manufacturers should be de-rated by at least 50% of the claimed specifications. IOW, but with this particular product don't attempt to draw more than 3A continuously through it based on the diode specs alone. What you say is all true, Alan ... but not many people are going to listen to you - coz, after all, stuff "made in China by no-name manufacturers" costs a lot less than stuff made in Oz. (Perhaps you should change your SNA-name to "Cassandra"? ) Andy 1 Link to comment Share on other sites More sharing options...
Monkeyboi Posted March 25, 2021 Share Posted March 25, 2021 1 hour ago, andyr said: What you say is all true, Alan ... but not many people are going to listen to you - coz, after all, stuff "made in China by no-name manufacturers" costs a lot less than stuff made in Oz. (Perhaps you should change your SNA-name to "Cassandra"? ) Andy What people spend their money on is of no concern to me mate. I just have a low level of sympathy for them when they get scammed with an amplifier that delivers half the output power the maker claims it's supposed to or is equipped with a transformer that's well below the required VA rating and with a 220v primary instead of a 240v primary which experiences a meltdown or blows up. Likewise for other bits of kit with outrageous claims We live in a disposable society Andy. People aren't interested in real quality. What they want is lots of "gold" plated plastic bling. Things aren't built to last because in order maximise profits most manufacturers aren't going to use high quality parts, instead opting for components that hopefully last just beyond the warranty period (if even any warranty is offered). The difference between the layperson and someone working in the electronics industry is those working in the industry know the difference between the quality of components and can generally spot a fake Nichicon electrolytic capacitor by sight alone. Unfortunately there will always be a faction of people who will dismiss well established scientific evidence and facts in favour of pseudo science because it serves their narrative. Cheers, Alan R. Link to comment Share on other sites More sharing options...
Monkeyboi Posted March 25, 2021 Share Posted March 25, 2021 18 hours ago, Leinster Lad said: Here is my circuit as far as I can tell ? I think there's an error in the reverse engineering. The two 2200uF capacitors appear to be effectively across the mains and not in parallel with the diode arrays in a series configuration with the output, that is in series with the load . Also they are in aiding (+-+-) not opposing (+--+) polarities. Cheers, Alan R. Link to comment Share on other sites More sharing options...
Leinster Lad Posted March 25, 2021 Share Posted March 25, 2021 O I've mentioned the polarity of the caps a couple of times now. The two electros, near as I can tell, (which is a bit hard because of the double sided board and black lacquered tracks) , both visually and metered, are wired as per my mud map diagram. Pretty sure. One leg of the cap bank is direct to the input active trace. The other end of the cap bank is connected to neutral input leg via one bank of diodes. The X2 cap is connected the same but opposite. (to neutral input trace and then to active thru the diode bank on the active input trace) So it is a bit more complex than the very simple circuit reference earlier. Whether it works or not I have no idea, and after all, it is not going to be powering the Queens pacemaker! Link to comment Share on other sites More sharing options...
Monkeyboi Posted March 25, 2021 Share Posted March 25, 2021 1 hour ago, Leinster Lad said: O I've mentioned the polarity of the caps a couple of times now. The two electros, near as I can tell, (which is a bit hard because of the double sided board and black lacquered tracks) , both visually and metered, are wired as per my mud map diagram. Pretty sure. One leg of the cap bank is direct to the input active trace. The other end of the cap bank is connected to neutral input leg via one bank of diodes. The X2 cap is connected the same but opposite. (to neutral input trace and then to active thru the diode bank on the active input trace) So it is a bit more complex than the very simple circuit reference earlier. Whether it works or not I have no idea, and after all, it is not going to be powering the Queens pacemaker! I'm not doubting you mate. Just the circuit makes no sense whatsoever. Cheers, Alan R. Link to comment Share on other sites More sharing options...
Leinster Lad Posted March 25, 2021 Share Posted March 25, 2021 Looks to me that it is like 2 DC blockers, cross connected utilising different cap values. Link to comment Share on other sites More sharing options...
kukynas Posted March 25, 2021 Author Share Posted March 25, 2021 I can't see how it's connected on top of the board but below how it's connected at the bottom of the board (at least what I can see from the picture), each pair of diodes is connected in opposite direction with joint in the middle (square) LL, can you confirm and maybe mark how are the caps connected from the top? Link to comment Share on other sites More sharing options...
Leinster Lad Posted March 25, 2021 Share Posted March 25, 2021 Link to comment Share on other sites More sharing options...
Leinster Lad Posted March 25, 2021 Share Posted March 25, 2021 I've added the connections on the top of the board and drew in the X2 cap Link to comment Share on other sites More sharing options...
Leinster Lad Posted March 25, 2021 Share Posted March 25, 2021 (edited) As you can see from the pics, the top layer is really difficult to see. Cannot see where the tracks for the electros are on top of the board. As i've ordered replacement caps and diodes, i'll pop them out later. Should make the top tracks more visible. Edited March 25, 2021 by Leinster Lad Link to comment Share on other sites More sharing options...
kukynas Posted March 25, 2021 Author Share Posted March 25, 2021 4 minutes ago, Leinster Lad said: As i've ordered replacement caps and diodes, i'll pop them out later. Should make the top tracks more visible. yeah, I think we need to see how it's connected otherwise it would be kind of weird Link to comment Share on other sites More sharing options...
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