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jamesmking last won the day on July 27 2021

jamesmking had the most liked content!



  • Hobbies
    breaking 2mm carbide end mills
  • Headphones
    stax sr007a
  • Headphone Amps
    DIY T2, DIY joamat mini t2, DIY single box blue hawaii se, megatron, DIY hi-amp alpha centauri
  • Sources
    garrard 401, loricraft psu+plinth, hadcock 242 se, ortofon cadenza bronze, leema agena, mf v90 dac + golden reference LV psu + synchronous rectifier
  • Other Audio Gear
    quad esl 2805, leema hydra, townshend allegri, dcs 905 adc, ps audio p3, van den hul first cables, cardas golden reference mains cables, cardas golden reference speaker cable

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  1. mouser currently has ksa1156. radio spares has STN9360, FJPF2145TU and FQPF8N80C
  2. Stax headphones are designed to take hundreds of volts of audio signal , a small offset of a few volts are absolutely not an issue. The offset will change with temperature. ALL amplification devices are somewhat temperature sensitive - including valves and transistors. you can demonstrate this easily, just blow gently onto the valves and what the offset change... This is why you are getting different results with the cover on and off. So don't worry you are not going to hear any difference or cause any damage to the headphones or shorten their life...
  3. yes, for short term testing, e.g. for checking output voltages, voltage regulation etc. (P.S. its also possible to test the grlv with no heatsink with no load.)
  4. T2 psu back panel, design and cut. I wanted to have the pin outs of the sockets for the umbilical chords from the psu to amp to be on the psu back for future reference.. I decided to go for 10degree 0.1mm tip engraving bit for the lettering, 0.025mm depth of cut rather than laser. Screw holes done with 3.175 end mill and main cut outs 6mm end mill. Now I have a good collection of quality bits and little experience now. CNC machining is starting to become FUN 🙂. Its so much nicer and more satisfying watching a CNC cut than using a hand drill and Dremel... Tool changing is a bit of a hassle and then I have to use a Z block and Z probe command get the new Z height reference for the tool sickout. So I try to minimise the number of different tools used. Tape hold-down and CA glue works perfectly. I'm very happy with the surface finish, perhaps the text for the pinouts and lines could be a little narrower, but its certainly not a disaster. Cut still currently in progress: The nice thing about symmetrical panels is that you can always adjust your settings and have another go with the other side... I decided to decrease the line width by half, nock 20% off the size of the socket decals, decrease the socket decal font size, change the style of the lines and reduce the engraving depth from 0.025 to 0.02mm... I think the new version should look a little less blocky and a bit more refined... The 0.02mm engraving depth is slightly too little, other than that I think its an improvement.
  5. I completely agree that if you have T2 pcbs already its not worth getting new ones. I'm thinking gerbers with minimal changes for new builders who want a build and forget solution only using available transistors. Serial/habitual/continual modifiers can always edit the gerbers of my or others T2 pcbs.
  6. *Sigh* why can't we have nice transistors?... I have updated the schematic to show both KSA/KSC and TTA/TTC series transistors. I'm working on changing the gerbers so that leg twists will not be needed 🙂 One channel done, I think, needs checking...
  7. So if my brain is not totally scrambled (which is possible its my first week back lecturing). KSC2690 or TTC004 NPN replaces 2SK216 N channel. Base-> Gate, Emitter -> Source, Collector -> Drain and Ksa1220 or TTA004 PNP replaces 2SJ79 P channel, Base-> Gate, Emitter -> Source, Collector -> Drain which gives modern T2 circuit (green replacements original moved to the side)
  8. This depends on what DC output voltage you are building for which depends on the input AC voltage to the GRHV which depends on the AC rms output of the transformer you are using... for example if you are building for 400V DC output to power for example a blue hawaii then you need about 360VAC rms input to the golden reference. (360VAC rms is about 509 peak when full wave rectified by the diode bridge before the input cap (DC voltage * square root of 2) which is enough for the internal voltage drops inside the GRHV and gives you some margin so the GRHV can actually regulate). Mains voltage typically varies by about +-10% so that is factored in to. But if you mains voltage is high then the input filter cap will see additional voltage so 550 rated cap should be fine for 400VDC output... If you are going for 450VDC output (about the maximum a GRHV can do) then your cap is going to be marginal and a 600V rated cap would be better.... The output cap should only see the output DC voltage, so if your GRHV is outputting 400V DC a 450VDC or 500VDC rated output cap should be fine. Dont forget many high voltage caps especially the 680uF are 80mm tall and so too tall to fit into a 2U case.... Kemet make some nice high voltage caps with life time ratings of around 15000 hours. https://www.mouser.co.uk/c/passive-components/capacitors/aluminum-electrolytic-capacitors/?q=kemet 550V&life=10000 Hour~~20000 Hour&voltage rating dc=550 VDC&rp=passive-components%2Fcapacitors%2Faluminum-electrolytic-capacitors|~Life
  9. CRCW2512475KFKEG which is same series as the original and so is 500V 1W and 475K should be fine in this application and is in stock at mouser.... lets say the resistor has the full 500V across it - which is worst possible case, V/R = I so the current through the bleed resistor would be 500/475000 = 0.00105A power dissipation in the bleed resistor would be W = I * V = 0.00105 * 500 = 0.53W and so well within the 1W capacity of the resistor... if the resistor has less than the full 500V across it the power dissipation will be less...
  10. Thanks for the photos R30 and R31 are in series and look to be the bleed resistors for the high voltage input smoothing cap so the voltage is shared between R30 and R31 but the input cap has the highest voltage across it. 200V working voltage is probably not enough here since the input is probably rectified to more than 400VDC R28 is the single bleed resistor for the output cap and so has the entire output dc voltage across it. So unless your psu is only outputting 200V or less, then a 200V working voltage resistor will definitely not be enough by a large margin. Since its a bleed resistor the exact value is not critical, a higher value would simply mean the high voltage would bleed to 0V at a bit slower speed and a bit lower value would very slightly increase power consumption when the power supply is on...
  11. I don't have a layout or schematic for the golden reference HV SMD but if it is similar to the through hole. The only places resistors with 250K+ resistance are used is in 1. bleed resistors for the high voltage smoothing caps - and so subject to high dc voltage. My best guess would be they are using a single resistor for the bleed unlike the through hole which uses two 250K 1/2W. So a single 1W 500V 510K would be about right here 2. output sense resistors - and so subject to high dc voltage 3. in the 580V bias circuit and so again subject to high dc voltage But this is only a guess based on looking at the through hole schematic... I have never built a golden reference hv SMD version.
  12. mostly modern T2 or possibly fully modern if the tta/ttc substitution for the 79 and 216 proves to be reliable. I don't think I will ever build an original.
  13. REQUIRED blue led is the blue ring around the power button on the power supply....
  14. First attempt at a complete front panel. Single flute 6mm end mill and 0.1mm V bit used. Depth of cut 0.02mm on the engraving. I also used tape and CA glue as the hold down method for the first time - I really like it. Much less vibration and far quieter when cutting in the middle of the work piece compared to just clamping the corners. As usual no deburring or finishing pass. The surface finish on the volume pot pocket is silky smooth - the photo does not do it justice. Very happy with the results. Not so happy that I have zero artistic talent for cool looking front panel designs.... Another go at a Stax socket with the better quality end mills. Much better surface finish than my previous attempt cheapo mills and I'm using faster feeds and speeds this time. Just shows that a crap end mill gives inferior results even on soft plastics. There are no burs around the edges of the cuts and the surface is smooth.
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