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  1. Old Comment
    miklos's Avatar

    HP 339A Mods & Upgrades

    Thanks for summing it up, much easier this way.
    The Dick Moore page link is unresponsive.
    Miklos
    permalink
    Posted Today at 08:25 AM by miklos miklos is offline
  2. Old Comment
    SyncTronX's Avatar

    HP 339A Mods & Upgrades

    Thanks for dropping in Ski. Maybe it will live a bit longer than the wiki did. Hopefully it will be
    easier to access for everyone too. That is the goal any how.
    permalink
    Posted Yesterday at 11:58 PM by SyncTronX SyncTronX is offline
  3. Old Comment
    skidave's Avatar

    HP 339A Mods & Upgrades

    Good work and great place to bring it all together.
    permalink
    Posted Yesterday at 12:29 PM by skidave skidave is offline
  4. Old Comment
    SyncTronX's Avatar

    HP 339A Mods & Upgrades

    HP339A Mods Blog

    You are most welcome. The gentlemen listed at
    the end of the blog are those who put in the real
    effort and the research and development. The
    least that I could do it summarize their work.

    Where I feel it important I'll try and link back
    to the original discusson, trail, error, and debate.
    permalink
    Posted Yesterday at 06:32 AM by SyncTronX SyncTronX is offline
  5. Old Comment
    anatech's Avatar

    HP 339A Mods & Upgrades

    Spike! Really great project! Many thanks for doing this.

    -Chris
    permalink
    Posted 4th December 2016 at 09:01 PM by anatech anatech is online now
  6. Old Comment
    abraxalito's Avatar

    My latest infatuation - transformers

    Yeah, passive ps beats active any day in my experience.
    permalink
    Posted 2nd December 2016 at 01:04 AM by abraxalito abraxalito is offline
  7. Old Comment

    My latest infatuation - transformers

    i have two amps the lifepo4 one and its predecessor which is very similar a dual mono version audiosector with a shunt supplied buffer dcb1
    actually was the point of the experiment to build a battery version of it for a more apples to apples comparison
    but there is no comparison the lifepo4 version is miles ahead
    sure you could pick flaws all day long with both
    but still remains a reasonable comparison for ps i think
    permalink
    Posted 2nd December 2016 at 12:53 AM by nige2000 nige2000 is online now
  8. Old Comment
    abraxalito's Avatar

    My latest infatuation - transformers

    Those cells have ESRs in the region of a few milliohms. So with six of them in series you'll be into say 20milliohm. Then with output currents peaking at say 2A that's 40millivolts peak of signal-correlated noise on your rails. Whereas for regulators they put out in the region of tens to a hundred uV of noise.
    permalink
    Posted 1st December 2016 at 11:37 PM by abraxalito abraxalito is offline
  9. Old Comment

    My latest infatuation - transformers

    yes tapped of the batteries at +/-19.8v
    i tried other supplies for the buffer for comparison at the time, and prefered the taps of the cells by quite a margin, i had assumed they were able to mostly absorb whatever noise the amp made
    i think the only way to figure it out is to build an amp/dac your way for comparison
    permalink
    Posted 1st December 2016 at 05:20 PM by nige2000 nige2000 is online now
  10. Old Comment
    abraxalito's Avatar

    Goosebumping headphone DAC-amp

    Lower signal-induced ripple on the power supply by virtue of having lower impedance. The aim is to reduce signal induced noise.
    permalink
    Posted 1st December 2016 at 10:30 AM by abraxalito abraxalito is offline
  11. Old Comment

    Goosebumping headphone DAC-amp

    Quote:
    Originally Posted by abraxalito
    Nice find, thanks a lot - I've been most curious as to how the level shifting is done to the output FETs as I'd like to explore raising the supply voltage...

    I see 0.12ohm resistors for current sensing, going to live dangerously and short those out.....
    What is the advantage of removing the 0.12ohm?
    permalink
    Posted 1st December 2016 at 09:17 AM by ChuckT ChuckT is offline
  12. Old Comment
    abraxalito's Avatar

    My latest infatuation - transformers

    You mean you'd use the amp's power supply to feed a buffer? 32V either side? Or you have another one? If you tap off from your batteries that'll have a fair bit of load-dependent noise on it, wouldn't want to feed that into a line stage.
    Yeah you either want a trafo or a cap to ensure no DC on your pot, preferably replace it with TVC.
    permalink
    Posted 1st December 2016 at 02:12 AM by abraxalito abraxalito is offline
  13. Old Comment

    My latest infatuation - transformers

    There's loads of 2sk208 FETs about though
    Been ps sensitive isn't much of an issue for me in this instance as the power supply is already there in my amp
    I think I'll have to try both

    I think the pot needs to be after buffer not before as it is now
    If the pot is DC sensitive it would either need a traffo or DC blocking cap before signal enters a pot?
    I'll definetly try a tvc on amp out too as I think it would be nice not to use a pot
    permalink
    Posted 1st December 2016 at 01:56 AM by nige2000 nige2000 is online now
  14. Old Comment
    abraxalito's Avatar

    My latest infatuation - transformers

    Don't those FETs have rather tricky availability? Do a similar thing but using bipolars, its easier and cheaper. But it makes no sense to put the load across the current source, the load should be across the active transistor. Putting the load across the current source makes the circuit ps sensitive.
    If you use bipolar transistors then you can make a buffer which can handle 1VRMS with two LiIon batteries for supply (7.2V).

    Notice the JFET is needed to get zero input offset voltage because its fed by a pot (pots are very DC sensitive), but with no pot the input offset isn't very important. The FET needs an output cap all the same as its Vgs is not going to be zero.
    permalink
    Posted 1st December 2016 at 01:24 AM by abraxalito abraxalito is offline
    Updated 1st December 2016 at 01:36 AM by abraxalito
  15. Old Comment

    My latest infatuation - transformers

    Ah OK

    Like this only I used 2sk208 gr
    Click the image to open in full size.
    permalink
    Posted 1st December 2016 at 01:20 AM by nige2000 nige2000 is online now
  16. Old Comment
    abraxalito's Avatar

    My latest infatuation - transformers

    EF buffer needs supply voltage about 1V more than the signal its handling in both directions. So suppose its handling 1VRMS that's 2.8V peak to peak, you'd need a 5V supply as minimum. You'd also need to control the DC offset tightly if you used the minimum supply voltage. Do you have a link to the pass b1 schematic, I'm not familiar with it?
    permalink
    Posted 1st December 2016 at 12:41 AM by abraxalito abraxalito is offline
  17. Old Comment
    abraxalito's Avatar

    Flattening the NOS droop

    The transistor is just a current conveyor in that situation - it reduces the ps sensitivity of the DAC but does nothing to reduce the output impedance. Hence still needs buffering.
    permalink
    Posted 1st December 2016 at 12:37 AM by abraxalito abraxalito is offline
  18. Old Comment

    Flattening the NOS droop

    what if i had the bc807 for i/v and feed 3.3v from float charged lifepo4 cell into base?
    permalink
    Posted 1st December 2016 at 12:12 AM by nige2000 nige2000 is online now
  19. Old Comment

    My latest infatuation - transformers

    so no ignoring the elephant then so eh..
    have to rearrange some stuff then so
    how would pass b1 type buffer fair out instead of ef's in such situations?
    what voltages are required for the class a ef buffer?
    permalink
    Posted 1st December 2016 at 12:07 AM by nige2000 nige2000 is online now
  20. Old Comment
    abraxalito's Avatar

    Flattening the NOS droop

    You'd want a buffer first - Matt Garman sketched up a schematic of I/V followed by buffer and filter on the 8 * TDA1387 thread.

    Output impedance can be measured yeah - you need a test source i.e. signal gen or for DAC, test waveform. You can create test waveforms in Audacity. Say you want to measure at 440Hz, create a sine at this frequency then with an AC voltmeter (should be sensitive, 4 digit DMM should work) measure the output voltage. Then put a load on say 1k, measure again. Math on those two voltages gives the output impedance.
    permalink
    Posted 30th November 2016 at 11:39 PM by abraxalito abraxalito is offline
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