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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. 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.
  2. *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...
  3. 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)
  4. 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 talk 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
  5. 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...
  6. 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...
  7. 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.
  8. 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.
  9. REQUIRED blue led is the blue ring around the power button on the power supply....
  10. 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.
  11. I would not want to speak for Joamat, but the impression I got was that the mini T2 was an attempt to simplify the complex design and make it as small as possible by going surface mount whenever possible. Ther is not a lot of space around Q17n but I think a 13mm by 4mm 1KV 2200pF (10mm lead spacing) film cap like a wima MKP1O112203C00JSSD will fit and there are film caps of the same size and rating ranging from 1000pF to 6800pF. The area around Q17p is more problematic due to an extra track which results in one tracking having to be rerouted. Channel 1: channel 2:
  12. Nice work, its always good to see progress and new ideas for the T2. Just to clarify. I did not design the mostly modern T2 or its battery. I simply created a series of posts on my build and posted my modified gerbers and updated and clarified schematics. I have been trying to collate the information scattered over years and years of posts into one or two long posts to provide a detailed starting point for new builders. I would not want to take credit away from the people who actually did the hard work of designing and testing. Your battery looks promising. If I could suggest, PTFE caps of sufficient voltage are quite large and not easily available new. I think it would be possible to find a place on the amp pcb for 1KV film caps e.g. wima. I would also be interested in the effect on the existing mostly modern T2 battery if just the cap is fitted - since such a modification would be very cost effective for existing mostly modern T2s. If the cap mod is shown to be stable and reliable I would be happy to update my existing post to include it in the schematic as a option and update the gerbers to make a place for adding the cap. regards James P.S independently of your effort MLA and I think Joamat have been working on a variant of the mostly modern T2 amp board that replaces the unavailable new 79 and 216 transistors with tta004 and ttc004, which if they prove stable, could result in a T2 only using current production components. (the pinout of the tta/ttc is different to the originals but they have not so far had to make any other changes).
  13. Things are looking up again... I just took delivery of some 6mm single flute DLC coated end mills, selling says they are designed to cut aluminium without liquid lubrication. Initial testing looks very good, absolutely throws chips out of the cut into near earth orbit when doing a full width slot. Zero chip welding. Surface finish as good if not slightly better than the 2mm end mill (So far got the speeds and feeds for the 6mm up to 400mm/min feed rate, 1.5mm DOC and 11K rpm). Cutting is very quiet and almost silent at 1mm DOC... The vfd and control box fans are louder than the cutting noises. I am sure there is much more to be got out of this end mill, but I'm progressing conservatively because these 6mm end mills are not cheap and I don't want to push it to destruction. The biggest take away for me is that buying cheap end mills from the manufacturer of the cncs website is not the best move and that end mill quality absolutely radically effects what you can do. I also think i'm going to invest in a oil/air mist system... (the hideous grey mess is the 3.175mm POC (piece of crap) end mill WITH cutting fluid dripped onto the cut... .) middle slot is 6mm end mill 1.5DOC 3mm total depth 11Krpm 400mm/min no cutting fluid no finishing pass no deburring... front slot same settings as middle slot but 1mm DOC and 10Krpm.
  14. i have no idea of the type of aluminium, its a disapante case I purchased some time ago from modshop. The fact I got such good results with a 2mm end mill, especially on chip removal and surface finish on it makes me suspect the 3mm end mill is just crap (the 3mm comes from a different supplier and is a different brand to the 2mm). So I have ordered some 3mm end mills of the same brand as the 2mm. The spindle does not seem to be slowing down, vibration was low, cutting noise was low and I did not use any coolant with the 2mm... as far as I can see if I can go 300mm/min 1.6mm depth of cut on a 2mm end mill with zero issues, low cutting noise and no lubrication, (I managed to break it at 500mm/min 1.6mm DOC but I was deliberately seeing how fast I could go), I should be able to do similar with a 3mm end mill of similar geometry (both single flute and both DLC coated)... but the best result I got with the 3mm was 0.2mm DOC, poor top edge and much reduced rpm compared to the 2mm. Any time I tried to increase the rpm chip welding became worse and chip evacuation did not improve, any DOC above 0.2mm I got lots of vibration and nasty noises.... looking carefully at the cutting the 3mm was not pushing material up the flute instead material was wrapping itself around the outside of the cutter and then welding itself to the top edges of the slot. I did not seem to be cutting so much as ploughing. Slower feeds resulted in the chips becoming like power and welding themselves all over the cut like fur... I tried cutting oil with the 3mm and this did not stop the welding. Feeling the edge of the flutes the 2mm feels super sharp all the way up whereas the flute the 3mm only feels sharp right at the bottom tip of the flute and the rest of the flute all the way up does not feel more than moderately sharp. I suspect this is why I cant get any sort of depth of cut. Even plunge cuts at the beginning of the slotting sounded much nicer on the 2mm than the 3mm end mill. (plunges straight down at 25mm/min)
  15. Short answer: in almost all cases high accuracy is not required unless specified otherwise in the bill of materials or schematic. Most builders are using 1% tolerance resistors up to about 1W, except in the most critical of uses, and high wattage resistors are usually 5% or so. Longer answer: There are several factors to consider. A "7K" 1% resistor could actually be between 7.07K and about 6.93K and still be in spec. Similarly 4.2K could be between about 4.24K and 4.16K and still be labelled as 4.2K 1% resistor. So if you are lucky with your 4.22K and 6.98K resistors they could fall within the specs of the 7K and 4.2K anyway. If you have a good LCR meter or multimeter you could buy multiple resistors, measure and hand select the closest match to the values you want. But this is usually not necessary and requires a highly accurate measuring device. If you need accuracy without measurement you can go for 0.1% parts but they cost more, typically don't come is as wide variety of wattages and often have lower voltage ratings. Also consider that all resistors heat up when current passes through them and the heat changes their resistance. The amount the resistance changes depends on the materials and manufacturing of the resistor and is usually specified in ppm per degree of temp rise (lower is better i.e. more stable but also more costly). Unless the use of the resistor in the circuit is critical, around 50 to 200ppm is fine for low wattage resistors and multiple hundred ppm is common for higher wattage... So in circuit, depending upon the power the resistor is dissipating, its resistance will vary from that measured when cold anyway... It is vital you don't exceed the voltage or wattage rating of a resistor and it is good practice to operate them bellow their ratings for safety and long term reliability. When looking at the voltage rating look for working voltage - this is the maximum voltage it can handle continuously. Some specs don't tell you working voltage but rather the maximum voltage just before failure which is a lot less useful. Some specs don't tell you if the voltage rating is maximum or working... so assume its maximum and the working voltage will be a lot lower.
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