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Thread: M4 sounds REALLY hit or miss....

  1. #21
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    Ya sounds like we're two birds of a feather. Sounds like mickz has found somewhat of a solution. Where is that thread of yours mickz?
    Ya my screen is fine too, you'd think if one had that much crap coming through the audio it would translate to visual as well..

  2. #22
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    yeah really hoping its not the m4 making noise even though it is being fed filtered 12v. Im running the msi 965gm with a dell mini lcd via the lvds connection. have some china made multi touch bonded to the screen connected usb via the motherboard header. only thing on the rear usb is the bluetooth dongle for my mini keyboard/ mouse. haven't even connected the xm radio adapter and getting noise through the rear audio jack to the powered computer speakers.

    might end up running the atx wires through some sheilded wrap and maybe a ferrite bead. any info would be greatfull.

  3. #23
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    Mickz's stuff was in power supplies with minimal radio interferance? (page 16) with feed through capacitor pics on page 21, though he may have other stuff elsewhere.



    Quote Originally Posted by slociviccoupe View Post
    .... the m4 making noise even though it is being fed filtered 12v.
    It has nothing to do with its supply...



    And having a read thru this thread I noticed:
    Quote Originally Posted by Mickz View Post
    ... to keep voltage drop to a minimum for correct AUX battery charging – standard current calculators V wire gauge usually don’t take system noise and correct voltage drop for AUX recharging in to account (to many variables).
    Exactly!
    I NEVER use current calculators or gauge tables UNLESS they state the voltage drop they are based on. And with "industry acceptable"(sic)" voltage drops for 12V systems being up to 3 Volts, it's easy to see why I don't used them.
    For normal high current wiring I consider 0.5V a maximum for any single feed (GND or +ve).
    For batteries, even 0.1V can be a substantial difference(**).

    Instead I work from fundamentals , or reverse-engineer what the tables and calculators do - namely decide my max voltage drop, measure the length required and using Ohm's Law V = IR, plug in the current.
    Hence from R = V/I I know the maximum resistance for that length of cable.
    Divide that R by the cable length to get a max resistance-per-length, and the find the appropriate gauge.
    If that gauge is too uneconomical or large, I might reconsider.
    And the only time I look at gauge-current tables is to confirm I'm not exceeding the gauge's capability. (Though with Industry using 1V to 3V drops, my 0.5V etc drop will be fine (ie, by a factor of 2 to 6), but it's a nice calc or sanity check & confirmation.)



    ** Gauges required for battery charging can be tricky due to high initial charge currents.
    Note however that as the battery charges, its current reduces, hence reducing the voltage drop. (Also that a battery does charge at "low" voltages even below 12.6V, but...)
    So as long as the battery eventually sees a high enough voltage for long enough, it should be fine.
    More detail:
    High enough means (say) 13.8V to fully charge the battery, or higher (eg, 14.4V) to blow away soft sulfates after any discharge or non-float charged storage.
    With even big batteries "only" having up to 2A float currents, a relatively small gauge is required if charged long enough.
    But remember that the load's gauge for that same voltage drop (V=IR where I = load current & R = cable resistance) must be ADDED to the battery's required gauge.
    My observation - many (IMO gullible) people with intermittent 2nd/aux battery loads buy expensive dc-dc converters to keep the aux load & battery at 14.4V etc. If the wiring can keep the load powered without a substantial voltage drop, then with the load off, chances are that the battery will get its required voltage, keeping in mind that it may substantially recharge even at 13.xV with the load running.
    Tip:
    Protection is required at each battery end of the inter-battery link. (That's not a tip, that's mandatory.)
    Since initial battery charge currents can far exceed the normal battery charge current, fuses can blow. Hence I recommend self-resetting circuit breakers which are cheap up to 50A (or 30A for ATS type fuses) else a blown-fuse alarm for >50A installations and where auto-resetting protection is NOT used. Nothing worse than relying on an aux circuit which has unknowingly disconnected and is discharging the aux battery...

    FYI - the float current is the current that a battery absorbs at float voltage which is the voltage a battery's charge voltage should be reduced to once it is fully charged - typically ~13.2V for a 12V battery normally charged at 13.8-14.4V. That "fully charge current" will be a bit higher at 13.8 or 14.4 than at its float voltage.

    There is more, but it's again repeating what I've written so many times before...
    Last edited by OldSpark; 03-31-2012 at 06:32 PM. Reason: Added noise has nothing to do with filtered supply.

  4. #24
    Maximum Bitrate Mickz's Avatar
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    Quote Originally Posted by bossman137 View Post
    but i now have a sure fire guide if I start making my setup as complicated and as current sucking as yours seems to be.
    I'm about ready to take pictures and show off, today was my first official bootup, SOO gratifying, however two small issues and one is directed expecially at you again mickz lol.
    1. UGLY UGLY, LOUD, static audio. And i started a different thread explaining all my trouble shooting, and basically it comes down to my M4 being the culprite, and I keep being pointed to you already covering this, but i can't find the specific thread where you cover a solution?
    Complicated is relative, simple systems can be just as unreliable as complex systems, this system is proving to be 100% reliable and totally glitch free.

    Power hungry? The system averages 3A to 4A (36 to 48 watts) total depending on the web cams that may be running. The complexity with the power and the AUX battery is to allow up to 10 hours of sleep time with a guaranteed fail save protection of the Vehicle battery.

    With the noise, the main reason I placed the M4 in a faraday shield is to eliminate RF interference from the M4 in the VHF, UHF region from killing and desensitising FM, DAB digital radio and GPS signals.

    However the M4 and most SMPS will set you up for what everyone refers to as the dreaded ground loop. If there is a noise voltage being developed between (and therefore across) the ground connections of interconnected audio devices then you will have noise.

    Any audio lead between any devices in the system should be double shielded, foil inner and quality heavy braid outer shields will help bring the ground difference to a minimum. I think we already talked about the need for heavy earth interconnecting cables and short thick chassis ground straps.

    If I use over the counter RCA leads to connect the DSP output to the Amplifier inputs (3 feet in length) I can hear a noise in the background, I made my own leads at a fraction of the cost of store junk and there is absolutely no noise through the entire system with everything wound up full and the DAB signal muted in the DAB module (all audio signal paths running).

    Quote Originally Posted by slociviccoupe View Post
    just got my m4 and experiancing noise problems. nothing connected to the motherboard but a small set of computer speakers through the rear audio out port and getting a hissing sounds through the speakers with the motherboard powered with the m4. the m4 is being fed regulated 12v via an old atx power supply. kind of bummed if this is going to be the first of many problems of interfearance with the m4. Im not getting any noise through the screen though. but then again it is a straight lvds connection to the motherboard. only thing the m4 is powering is the motherboard, sata laptop drive, and the 12v rail usually used for a p4 connection will be powering the mp3 car usb xm controller. but not connected at this time.

    if anyone can help really dont want to have noise problems this early. I do plan on using a usb soundcard to feed the rca pre outs to mu amps. but wanted to hear some audio just to try some things and encountering noise already.
    I had no noise from the output ports of the motherboard with the M4 even before the interference mods. I assume that you tried the system with a standard PSU and that the hiss noise was gone?

    Quote Originally Posted by slociviccoupe View Post
    might end up running the atx wires through some sheilded wrap and maybe a ferrite bead. any info would be greatfull.
    That will not work, because RF noise will just travel along the outer shield connection. Sometimes you can get lucky with ferrite beads but again the noise couples straight across. All of these solutions were tested on the M4 with a spectrum analyser, all failed.

    Let me apologize if Iím miss-understanding anything here guys. This is a complex subject, Iím sure some will think itís simple but RF noise suppression is complex. Furthermore some of the audio noise you hear can also be caused by RF mixing products producing signals down into the audio spectrum, there are a number of SMPS on the motherboard and in the M4 producing Audio and RF signals that can mix/beat/interact in various ways. Audio interference and ground loop elimination can be almost as complex, some people never have a problem in their installation and many factors make each installation different even with the same hardware. A lot resort to ground loop breakers (isolating transformers) personally I hate them for a number of technical reasons but thatís just my opinion.

    Thanks OldSpark for the links, I've been away since yesterday morning.
    GA-Z77N-WIFI, i5-2400S, 8GB, Intel 520 128GB SSD, M4-ATX Modified, 2 Rev Cams, 2 Web Cams
    8" 16:9 TRANSFLECTIVE, Win8-64, Dual GPS RX and Garmin PC + Odyssey Nav, FM-DAB+, BB-Rec
    T-Screen HVAC control, custom microcontrollers, code and FE. CarPC Project

  5. #25
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    No i don't have GPS, FM, or any other frequency depentand devices i need to worry about. I'll put ol faraday on the shelf then til those problems arrise, if they arrise. It's purely a AUDIO noise issue.
    I re read over your posts in this thread. What gets me is i've never had and issue to this extend with audio in my years of messing around with cars with much cheaper wire, equipement, and older cars. So add to my list of things to try.

    1. Use a little extra of my extra 8 guage to run a ground cable from the negative input of my M4 to a clean sanded bolt under one of my seats right?
    (what exactly do you mean by a short thick chasey ground strap?)
    ... what else while i run out to try number 1 lol

  6. #26
    Maximum Bitrate Mickz's Avatar
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    Basic short thick chassis ground strap = 4G cable or 2 x 8G in parallel and less than 12 inches in length.

    Then heavy shielded audio connecting leads to reduce ground path noise difference between the two audio devices.

    With regards to why you have a problem now: The way a certain mother boards has its ground layout designed, the design of the MB audio IO circuit and grounding, the type of case the MB is in, the construction of the mounting posts and the MB to chassis to vehicle ground paths. The type of PSU and the power it was designed to deliver. The lowest input voltage the PSU can work down too and the frequency, design, size, and cost compromises made in achieving that design. The layout of the input circuitry in the new amplifier and its internal earthing and low level input stage supply noise rejection is designed into same, the exact position of the Amplifier and the PC in relation to each other and how each is connected to the chassis, the type of steel or other metals used in the construction of the vehicle.

    Not trying to be a smart $%^ with the above but some pieces of equipment just wonít work together without major pain.

    With the above in mind, the M4 can deliver some real power and run down to around 6 or 7v and still supply full output current on the +5v and +12v rails , IMHO that combination and the design used to achieve it contribute greatly to the extra noise produced by some SMPS. Having said that I see many people with Audio PSU noise even in small systems with low power SMPS.

    It totally sucks, but at least it can be overcome, but again itís a PITA having to put in the extra effort and expense to do so
    GA-Z77N-WIFI, i5-2400S, 8GB, Intel 520 128GB SSD, M4-ATX Modified, 2 Rev Cams, 2 Web Cams
    8" 16:9 TRANSFLECTIVE, Win8-64, Dual GPS RX and Garmin PC + Odyssey Nav, FM-DAB+, BB-Rec
    T-Screen HVAC control, custom microcontrollers, code and FE. CarPC Project

  7. #27
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    I fully plan on overcoming this, and you give me hope thanks lol. I ran a single 8 guage a few like 2 ft (seput is in my glove compartment), and it didn't help at all. But tomorrow i'll give an honest go, cut it in half and find a real permant ground. But just to double check we're talking 3 wires coming from the negative lead of the M4 right, two to ground and one to the neg battery?
    Ya I mostly just jimmy rigged and cut up an old case to fit my mini itx (was sick of bleeding money for the time being just wanted it up and running). in a week or so i'm just going to draft up a custome case to fit my glove compartment then just cut it out with a water jet at my university out of some 1/8 in aluminum. Would it help to ground the pc case chassis to the car chassis.

  8. #28
    Maximum Bitrate Mickz's Avatar
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    The ideal would to be to mount the M4 case to a common aluminium panel that also has the Mother board mounting. The M4 PCB ground plane is common to the M4 Ground connector so going this way allows you to have a large single (or two smaller) cables connected from the aluminium mounting plate straight to a good clean vehicle chassis connection along with a cable from M4 NEG to battery NEG . Otherwise, what you are planning to do will be fine - one lead back to the NEG battery terminal and one (or two) to the vehicle chassis. If the MB is isolated from the M4 then a ground strap from the MB should be included.

    Iím sure your know the following but just in case, something to watch is any connection to the Line Input on the PC may suffer from a far greater noise ground difference connection than the Line out. Itís important to fix any noise from the PC to AMP connection first and not plug any device that shares the vehicle or M4 supply or ground connections into the line in, that means a battery powered portable MP3 player or something like that as the signal source, or nothing plugged in if the noise is present without any signal and line input gain to zero in that case, then tackle the input device noise/wiring once the Line out connection is clean.

    Itís difficult to cover every mounting condition on a forum where answers are short and generalised, so there are always exceptions to everything said and solution that donít appear to work may still help in other ways, and Iím skimming over the shbject. There are occasions where the analogue signal run to the AMP may be too long (amplifier is too far from the signal) and alternative solutions have to be used because of the noise from the PC-PSU.
    GA-Z77N-WIFI, i5-2400S, 8GB, Intel 520 128GB SSD, M4-ATX Modified, 2 Rev Cams, 2 Web Cams
    8" 16:9 TRANSFLECTIVE, Win8-64, Dual GPS RX and Garmin PC + Odyssey Nav, FM-DAB+, BB-Rec
    T-Screen HVAC control, custom microcontrollers, code and FE. CarPC Project

  9. #29
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    Ok so I have the aluminum going to waterjet it tomorrow, so either way I'm going to have a much better ground circuit. And I'm confident that will help a lot because out of curtuosity I took some 8 gauge touched it to my pc chassis to a bolt and three static was very much reduced. I'm curious if anyone thinks a optical to 3.5mm cable would work and help. Ps how does a little cable take digital to analog anyways, people say it works!

  10. #30
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    Optical cable in an electrical circuit? Not without converters.

    Unless I misunderstood, people will say that, especially a few days ago before noon (April 1st). Others say things like using mobile phones to open your car if you lose your fob; place a battery in series with speakers for more power; and satellites forward emergency calls when terrestrial mobiles are out of range.

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