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  1. Old Comment
    rjm's Avatar

    Headphone amplifier ground. Where to make the chassis connection?

    I did consider snubbers, but caps in various places were to no avail. I realized later it isn't actually switching noise that is the problem here but instead The culprit is the 500 mA, 1 ms current pulses flowing in the secondary windings seen twice a cycle charging the filter capacitors. The diodes are just doing their job.
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    Posted 8th February 2016 at 09:35 AM by rjm rjm is offline
    Updated 8th February 2016 at 09:37 AM by rjm
  2. Old Comment
    abraxalito's Avatar

    Headphone amplifier ground. Where to make the chassis connection?

    I love the copper cummerbunds. Looking at your eye candy made me wonder something - your bridges are really looking quite 'heavy duty' for the application - have you considered snubbering them? Or swapping them for (discrete) soft recovery diodes?
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    Posted 8th February 2016 at 01:04 AM by abraxalito abraxalito is offline
  3. Old Comment

    Headphone amplifier ground. Where to make the chassis connection?

    For a tiny bit of help, rotate the bridges 45 degrees to get the secondary's AC parallel to the PWBs, and a just a bit further away from the PWBs.
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    Posted 5th February 2016 at 04:19 PM by disfunctionalshadow disfunctionalshadow is offline
  4. Old Comment
    rjm's Avatar

    Szekeres 2015

    That looks promising! I was thinking that split supplies could be sued to good effect, if care was taken to ensure the output coupling cap couldn't be reverse biased...

    Unfortunately the text on your posted image is too small to read clearly, but I get the general idea.
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    Posted 4th February 2016 at 12:55 AM by rjm rjm is offline
  5. Old Comment
    rjm's Avatar

    Headphone amplifier ground. Where to make the chassis connection?

    One bridge rectifier for each of the dual secondary winding, so four in total. I've added a photo of the amp so you can see the details.

    I always try to keep the conductance angle under control by using moderate amounts of filter capacitance following the rectifiers. 2000 uF per rail in this instance, it sims out to about 10:1, or a quite modest 500 mA peak for 50 mA load.

    Magnetic coupling. I hadn't thought of that until you mentioned it, but, yes, it seems quite possible that the noise coupling mechanism is magnetic rather than electrostatic. That would explain why it is insensitive to the input wires and volume position. I'll try that trick rotating the transformer, but likely we'll have to rig up some flux containment. Pity there are no scraps of mu-metal about the place.
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    Posted 3rd February 2016 at 02:35 AM by rjm rjm is offline
    Updated 3rd February 2016 at 06:14 AM by rjm
  6. Old Comment
    abraxalito's Avatar

    Headphone amplifier ground. Where to make the chassis connection?

    Having unshielded trafos does rather complicate the matter of getting the optimum grounding. Are you using a pair of full-wave rectified windings or is there a CT?

    Looking at your FFT I rather do suspect that the current loops when the diodes conduct are coupling magnetically to other circuit loops. As the harmonics don't go down very fast with frequency - tends to be indicative of haversine-shaped pulses getting in. Reducing the first res capacitor size and then having a series L normally works to increase the conduction angle and hopefully that would attenuate the higher harmonics somewhat.

    <edit> Nice pic which answers my question, thanks! I'd turn the top trafo through 60degrees (clockwise) so the lead-outs aren't facing towards your input wiring. Toroids have lowish leakage flux but its always highest where the wires come out, as that's a point where symmetry breaks down.
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    Posted 3rd February 2016 at 02:09 AM by abraxalito abraxalito is offline
    Updated 3rd February 2016 at 02:38 AM by abraxalito
  7. Old Comment
    rjm's Avatar

    Headphone amplifier ground. Where to make the chassis connection?

    Thanks. Actually what I think I'm looking at here is noise from the transformers coupling to the boards. It all happens within the chassis (the transformers and diodes are right next to the boards) which explains why I get noise regardless of where I connect the chassis to the circuit ground.

    My transformers are unshielded, with no screen. (Talema 62062)
    permalink
    Posted 3rd February 2016 at 01:25 AM by rjm rjm is offline
  8. Old Comment
    abraxalito's Avatar

    Headphone amplifier ground. Where to make the chassis connection?

    My choice would be at the input GND, so long as your trafo has an interwinding screen which also goes to chassis. Then CM noise doesn't need to flow through PCB 0V tracks. Headphone CM noise will only be RF pick up so that's probably less severe than noise from the source component, unless that's battery powered.
    permalink
    Posted 2nd February 2016 at 02:42 PM by abraxalito abraxalito is offline
  9. Old Comment
    permalink
    Posted 31st January 2016 at 08:49 PM by wintermute wintermute is offline
  10. Old Comment
    rjm's Avatar

    What are "Ground Boxes"?

    "Earth" is a charge bucket, in essence, something you can safely dump however many Farads into without generating any potential. When you put a copper rod into the ground to act as an earth, I don't think you need a whole planet's worth of mass for this to operate effectively... but I have no idea how much mass you would need.

    This "Ground Box" is meant to act in a similar way but only for small amounts of high frequency, AC electrical noise that might be hard to bleed off to the safety earth due to the inductance of the ground wires.

    The idea is to put something that acts like a small capacity earth connection close the the equipment.

    Now that logic might be totally bogus, and why anyway this should be effective I don't know, but I'm curious as to what a "small capacity earth" could physically be and how it would operate.
    permalink
    Posted 25th January 2016 at 04:58 AM by rjm rjm is offline
    Updated 25th January 2016 at 05:01 AM by rjm
  11. Old Comment
    noSmoking's Avatar

    What are "Ground Boxes"?

    WOW!
    Well if you put a wire in a bucket of dirt ,I don't think it will conduct into the ground.
    I do know that soil charts provide info on soil resistance and that should be a basis to the size of a hole depth and circumference size in the ground.
    The bigger the hole the better or more conduction,When CB was a big hobby ,It was a know fact to dig 3 holes 12" and 4 feet in red clay/sandy soils about 10 feet apart layed out as a triangle ,a solid copper ground rod 3/4" and 8 feet long was driven into the center of the hole and as you filled in around the rod, salt was poured around the rod and saturated with water.
    This did improve transmitting distance and resulted in less squelch (noise).
    I do know that bonding electrical boxes to ground is a NEC requirement for code and it makes conductor for static and a return path for electrics on neutral conductors.
    You can put in a ground rod OR use a water pipe it must be copper not pvc and take a VOM and see if you can read any resistance between them,if yes then a current could flow,so ground your equipment,
    Sigbee's and several other devices have gone down this road already google it and see what you think,I don't see how boxes with dirt in them can make a return to earth ground ,maybe magic dirt?
    Regards,
    NS
    permalink
    Posted 24th January 2016 at 02:40 AM by noSmoking noSmoking is offline
  12. Old Comment
    abraxalito's Avatar

    High-end chipamp build project

    I tried higher voltage - it has overvoltage protection but mine didn't blow up, just muted. Bring the voltage back down again and it's fine. That's automotive stuff for you, very rugged.
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    Posted 21st January 2016 at 02:26 AM by abraxalito abraxalito is offline
  13. Old Comment

    High-end chipamp build project

    Lol no need to answer that found out the hard way
    On with version 2
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    Posted 20th January 2016 at 06:52 PM by nige2000 nige2000 is offline
  14. Old Comment

    High-end chipamp build project

    Sounds good
    have you tried higher voltage than 19v?
    or whats the upper limit?
    permalink
    Posted 20th January 2016 at 05:55 PM by nige2000 nige2000 is offline
  15. Old Comment

    Ground loop noise, why it is and what you might do about it

    The use of a 10R resistance in parallel with a diode bridge to shunt fault voltage/current directly is pretty commonly used as part of the amplifier audio ground to earth connection. This is not the same as putting resistance in series with the shield, but is in the ground loop path.

    The nature of the problem is this: when you have TWO paths (cable shield AND earth ground) you form a loop that is available for inductive coupling to AC fields, e.g. from the mains, that are all around us. This is shown by the dashed line in Figure 1 at the first link below, and the text in the section "What Causes Earth (Ground) Loops?" further down that page.

    Another great way to form ground loops is when you have MULTIPLE shielded cables running between two pieces of equipment (even if they are NOT earthed!). If you separate the cables, you again are forming a loop with their shields and hum pickup ensues. I learned this from my own experiences. I could pick up and move the cables farther apart or closer together, and this would change the amount of hum present in the system. In that case adding small (e.g 4.7R) resistors to each shield was effective.

    You need to break at least all but one of the paths (e.g. N-1 of the N paths) to avoid forming the loop.

    For more info, see:
    Earthing (Grounding) Your Hi-Fi - Tricks and Techniques

    See the PS schematic on p11 of the pdf at link, below. An NTC thermistor is used instead of a resistor, but the concept is the same.
    http://www.firstwatt.com/pdf/art_f5_turbo.pdf
    permalink
    Posted 19th January 2016 at 05:25 PM by CharlieLaub CharlieLaub is online now
    Updated 21st January 2016 at 04:21 AM by CharlieLaub
  16. Old Comment

    45watts Class B

    It has an interesting current-dump output stage. In theory it should work fine, but don't expect super-high-fidelity performance. Do you know the component values for this circuit?
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    Posted 19th January 2016 at 01:42 PM by ojg ojg is offline
  17. Old Comment
    critofur's Avatar

    Radio Shack Linaeum measurements

    " it was quite easy to discern the difference between different types of cables"

    Sound quality is irrelevant when discussing cables - the only possible way a cable can be "better" ["sounding"] than a generic copper cable is if it has some flaw which colors the sound, which should not happen with any properly designed cable.
    permalink
    Posted 16th January 2016 at 11:43 PM by critofur critofur is offline
  18. Old Comment

    Szekeres 2015

    Here's what happens to PSRR if you re-reverse the Reverso:
    Click the image to open in full size.
    You could improve things again (plus general performance) by reducing the value of R1, the input series resistor, but it would still remain a fair bit worse, and maximum PSRR obviously remains limited by the MOSFET's gain.
    permalink
    Posted 15th January 2016 at 09:58 PM by sgrossklass sgrossklass is offline
  19. Old Comment
    abraxalito's Avatar

    High-end chipamp build project

    I've heard there are Taobao agents who will place the order for you, for a smallish fee. Guess try Googling for 'Taobao agent' and see what shows up.

    I did a quick Yahoo and there's a website 'www.howtotao.com' which has reviews of agents. But it wouldn't load quick enough here....
    permalink
    Posted 14th January 2016 at 01:02 AM by abraxalito abraxalito is offline
  20. Old Comment

    High-end chipamp build project

    is there a simple way for western europe to order from taobao often seen stuff id like to try
    permalink
    Posted 13th January 2016 at 07:39 PM by nige2000 nige2000 is offline
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