Help understanding Monster Power Filter design - Page 1
Forum section: electronics / beginners

author: lunarfox
author_rank: Newbie
timestamp: November 28, 2022, 04:19:52 am
content: First off, I hope this is the right area for this, please inform me if it should be put somewhere else. I kinda considered "Dodgy Technology" 'cause of all the marketing wank that Monster loves to push with these things and the ridiculous MSRP, but alas, I'm looking to learn more than anything!Anyways, I recently got a couple Monster Power HTS-5000 power filters for practically nothing. I mostly want it for the delayed turn on feature, but a line filter won't go astray either as fridges cutting on and off sometimes make my sound system pop softly. But as the saying goes, don't turn it on, take it apart! Build quality seems reasonable for what's essentially a glorified power strip and line filter, but for the MSRP I'd certainly hope so. Everything looks fine, so I plugged it in and noticed significant line frequency hum from a couple of the X2 filter caps.Long story short, there's 5 separate line filters with 4 different designs. There's 2 "digital" filters, one "video" filter, one "Audio" filter and one "High Power" filter. I traced it down to 2 caps at the end of the digital filter after removing and testing every single one and slowly adding them back in and power testing it. But here's the kicker; all caps test good and only the two caps at the end of the 'digital filter' hum. And it doesn't matter if I swap them with different caps. Even tried hooking them up to mains voltage directly (spicy) and they're dead quiet. They only hum in circuit.(Sorry, attaching pictures to the post in line didn't seem to work; they're all named below though!)First off, here's what the top of the PCB looks like with the main parts of the different filters labeled:Cue reverse engineering of filters! Looks like it should just be a pretty normal AC line filter from above... but in actuality, they have one of the coils on the toroid wired backwards? What's going on here? Do forgive the crudity of the pen-cad sketch.This prompted me to look at the other filters. The video filter is the only one that looks 'normal' to my eyes:Then there's something strange again in the audio filter; one of the coils is literally shorted:The high power filter is just a single 1uf X2 capacitor. This thing has A LOT of capacitors essentially just hooked up to the mains. 13 1uf caps to be exact. The power factor is atrocious, pulling almost a half amp at 120v while only using 4 to 7 watts depending on how many relays are active. I'm likely going to slim it down to just 1 or 2 filters so I can remove a lot of the caps and lower the idle current draw, but this brings me to what I want to know...What's the point of the design between the different filters? Particularly the "digital" filters? Why wire one of the coils 'backwards' like that? And why does the cap after it buzz so bad? Why's the audio filter short out one of the coils; why not just make it the same as the "video" filter? Trying to learn here more than anything! I would be happy to take high res pics of the top and bottom of the board if anyone's curious. Thanks for your time!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 28, 2022, 08:51:42 am
content: So what, they're all the same (ferrite?) CMC core and they've shorted one and reversed another (on the respective channels)?Your circuits are incomplete as they're at least a discharge resistor, or what looks like it, plus the relays and I guess two-turn CMCs before the terminal block, and maybe something else too, I don't know.Possibly the buzzing ones are resonating with the high differential inductance of the unloaded one-flipped CMC. This will go away under load (>20mA?), as will the DM filtering effect. Ferrite CMCs saturate readily with unbalanced DC bias.Why did they do this? Who knows. It's audio, it's woo, it's not supposed to make sense. They almost certainly didn't do any kind of EMC testing to prove the effectiveness of the design. There's probably no standard for what they're trying to achieve, so, no testing procedure to prove the design.Tim

author: lunarfox
author_rank: Newbie
timestamp: November 28, 2022, 09:39:39 am
content: The audio and video circuits have the same ferrite core, the hot side coil is shorted on the audio filter. The digital filter has smaller chokes (likely due to less expected load) and it's here that the second choke's windings flipped on the neutral.Each filter does indeed have one discharge resistor as well as the two turn CMCs after a relay switching the hot lead. I didn't bother drawing them as they're the same on each filter. I only noted the portions of the filter that seemed different. One of these days I'll get into doing proper cad schematics. This is a fairly small and simple circuit after-all.Either way, having one coil shorted (audio filter) and one coil flipped (digital filter) seems like it would render any potential line filtering useless in my eyes (as you seemed to elude to). Audio woo as you mentioned. I'm just trying to understand the circuitry before I poopoo on it and simplify it. I will load up the circuit tomorrow and report my findings, I feel a bit silly for not trying it before posting but I was caught up in the excitement of 'oooh, new electronic thingy to poke at'.I have looked far and wide and have yet to find scientific evidence that these Monster power filters actually do anything meaningful to equipment hooked up to them. It seems like, to me, one filter (capacitor, CMC, capacitor) should be adequate in reducing or eliminating common mode noise and the little surges on the mains (such as from inductive loads switching on and off; I personally know every time my room mate's mini fridge turns on/off if my stereo is on). That seems to be the basic goal of all these filters (at least after scraping away all the bull).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 28, 2022, 10:43:45 am
content: Keep some things in mind when doing the simulation:- Start with a proper four-port harness.- Don't know what a port is? Read up on RF theory; it's the most effective way to test these sorts of things. In short, a port is the end of a transmission line: a Thevenin or other equivalent source, where we are interested in not just transmitted power, but incident power as well. Because these are linear circuits, superposition is obeyed, and we can separate these easily.- Most often, anyway, we run the simulator with one source "hot", the rest at zero. Or maybe in pairs (see below). In that case we get the input impedance and output gain in one pass. Then swap active sources and get the same for the other pair(s), etc..- Of particular interest here are CM and DM performance. So, both sources (say H and N on the left side) in phase (CM) or opposite (DM), and measure the average (CM) or difference (DM) on the other side of the filter.- You will need a figure for the coupling factor or leakage inductance. These are NOT ideal transformers. In fact they are wound that way for two specific reasons: the sectoral windings maximize leakage inductance and isolation voltage. The leakage of course makes the X caps effective, but they still need to be quite large values.- You will need a nonlinear core model for the one-swapped case. I use this, myself,https://www.seventransistorlabs.com/Modeling/SPICE/INDSAT.cktbut you may find built-in library elements more handy, I don't know. Notice nonlinear models ONLY apply to Transient analysis. The linear signal analyses can be done with AC Steady State analysis.Technically, CM may be both lines in parallel to a 50 ohm source, not 50 ohms per line (which is 25 ohms parallel equivalent!). Depends on exactly how things are tested; CMC datasheets typically show both lines in parallel, then testing attenuation in a 50-ohm system, so, attenuation is relative to 100 ohms total series resistance (i.e., 20dB attenuation means the choke has ~1kohm impedance). Modules may be tested differently, I don't know offhand. There is also an asymmetrical impedance test (1/100 ohm I think?) which can be more informative at low frequencies, or for DM where the impedance (Zo = sqrt(L/C)) is lower to begin with.Oh yeah, there's no Y caps in there, huh? That's not a great sign. That means CM attenuation is limited to the CMC impedance and load resistance alone. And real equipment need not have 50 ohm CM impedance, for... fairly obvious reasons I guess?Tim

author: strawberry
author_rank: Super Contributor
timestamp: November 28, 2022, 11:44:11 am
content: these cheap capacitors spoil after ~4y of usage.anyway, highly doubt that some filter will stop your fridge from spoiling audio equipment. proper audio signal shielding maybe

author: Equipmonk
author_rank: Newbie
timestamp: December 16, 2023, 12:37:51 am
content: Sorry to start up an old thread. Recently stumbled across a non-working Monster HTS5000 power conditioner. Opened it up, and the transformer (with the red tape / banding) was loose in the chassis. Board is undamaged, but transformer pins are broken off and it's not salvageable. The transformer has no markings, and Monster does not provide any schematics from what I can find. The other transformer inside the chassis has some markings, so not sure why this one does not. I know it's a long shot, but I saw in one of your pictures the same transformer with the red tape over the windings that I'm trying to find any information on. I thought maybe you might have noted it on your troubleshooting. Thanks for any help.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 16, 2023, 07:01:28 am
content: FWIW, that looks to be a split-bobbin style mains-frequency power transformer, probably in the 10VA capacity range. What voltage(s), you'd have to trace the circuit some more. Or find the broken ends of the windings (what was attached to the broken-off pins) and try to connect to them, even if not to patch it up then just to get a measurement. Assuming you have the means to do so.Tim

author: Equipmonk
author_rank: Newbie
timestamp: December 16, 2023, 07:20:33 pm
content: Thanks Tim. I appreciate the insight and suggestions.

author: 5U4GB
author_rank: Super Contributor
timestamp: December 17, 2023, 01:45:36 pm
content: Quote from: lunarfox on November 28, 2022, 04:19:52 amWell there's your problem right away, a proper audio power filter needs tolook like thisin order to be effective. Everyone knows you need at least four different colours of capacitors to handle the different colours of frequency response.