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Kerry

High Rollers
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Posts posted by Kerry

  1. The ultimate DIY? A Stax SRM-T2!

    in Do It Yourself

    Posted

    Don't worry. I've got a build that I've got most of the parts for and am just getting started. I think there are a few others that haven't finished their builds yet. But yeah, I have to believe that most are blissfully listening to their T2s.

    Regarding the angle brackets, they are currently boxed up, but I can get exact measurements next week. I think they were 1.5" x .73" and approximately .33" from the edge. They are not typically tapped and the hole size I use is approximately .132". Sorry I can't be more precise at the moment.

    Is that 5" horizontal per heatsink or for two? Sounds massive :D

  4. The ultimate DIY? A Stax SRM-T2!

    in Do It Yourself

    Posted

    I was just about to pull together the requirements for the transformers. I'd be looking for a significantly lower temperature rise. The last transfomer I ordered from SumR, we were able to get them made with a 22°C rise at full load.

    For the three transformers what were you thinking (power wise) for each winding? I think the most significant power is pulled by the Neg. 500V supply at about 33mA (per channel per LTSpice). I'd like to keep them as cool as possible so 4x seemed reasonable, which would put it around 133mA (assuming LTSpice is right).

    Here's the specs that Kevin gave so it's pretty close.

    craig asked that i publish the info on the transformers, should you decide to have them made elsewhere...

    high voltage transformer 2 are needed

    diameter 3.5 inches height 1.7 inches you can actually go up to 2.5 inches high, and slightly wider

    full load voltage---- regulation--- Iac--- off load

    475 --- 15.04 --- .13 --- 546.4

    285 --- 10.53 --- .06 --- 315

    75 --- 10.6 --- .06 --- 82.9

    filament transformer

    diameter 3.5 height 1.6

    30 --- 13 --- .5 --- 33.9 Center tapped

    6.3 --- 14.29 --- 1.5 --- 7.2

    6.3 --- 14.29 --- 1.5 --- 7.2

    6.3 --- 14.29 --- 4.0 --- 7.2

    6.3 --- 14.29 --- 4.0 --- 7.2

    Richard at SumR can take these and beef up the windings to accomodate the lower temp rise, but we need to make sure the size doesn't exceed 2.5" tall by about 3.5" wide (not sure on max width). I'd like to try to get the same specs as you if you are reordering.

  8. The ultimate DIY? A Stax SRM-T2!

    in Do It Yourself

    Posted · Edited by Kerry

    The amp / PSU can be built however you'd like. Stacking is definitely an option. :) I may do one this way - it could be a very small foot print.

    I'm using DipTrace to do all the design work. I've got the not-for-profit version that supports 1,000 pins.

    I'll see about elongating the pad size. I know what you are saying. Given some of the issues around bad semi's rework is a real possibility.

  9. The ultimate DIY? A Stax SRM-T2!

    in Do It Yourself

    Posted · Edited by Kerry

    Glad you're up and running again Craig.

    I've been having my own fun on another layout. I wanted do a layout for the BHT2E.

    Here's where I'm at...

    bht2ev06.gif

    I wanted the board small enough so that I can do a single chassis for the PS and amp boards. It can be done as two units (PS & Amp) with the depth being about 8" or 200mm and the boards being 12" wide.

    Since the 100V (BH) supply is not on the amp board and the bias for the tubes was reduced from 25mA to 12mA, this should produce a lot less heat than the BH. I'll want to play with the current to see / hear the difference. It models nicely at 10mA - 12mA which is only slightly more than the T2 at 10mA.

    I'm using the T2 output stage and servo and have added a servo to the BH front end. Again, it models well but I've also kept the adjustment POT to keep the servo's job to a minimum. If it affects the sound, I can just pop the opamp out and go manual.

    Who knows if it will actually work, but it's worth a try :D

  13. i'm on a roll... the kgsshv

    in Do It Yourself

    Posted

    Surprising how often transformers are underrated in professionally designed equipment. The calculation is simple for something like a heater transformer, since the secondary rms current rating is just the heater current. But with capacitor-filtered DC, there is a factor to be taken into account as a result of the short pulse-like nature of the charging current. This was originally analyzed by Schade in 1943 ("Analysis of Rectifier Operation", Proc IRE July 1943, 341-361) and resulted in a series of normalised graphical relations, which are still useful to this day. But whatever method of calculation you use (for example freeware PSU Designer II from PSUD2 ), the rms current rating of the transformer needs to be typically 2 to 4 times higher than the dc current drain. The exact factor depends on the capacitor size, the transformer effective DC resistance, the DC current, and the mains frequency.

    ...

    Craig - Thanks for this post.

    I'm still a bit unclear in the calculation. I downloaded the duncan amps PSU Designer. I basically got similar results in LTSpice. On an active battery regulator in LTSpice with a 425V output, DC current draw of about 50mA and front end 340uF capacitance I'm seeing spikes of about 2.5A. I thought maybe to divide by 1.414 to get an RMS value, but that is still 1.77A. You mentioned needing to use 2 - 4 times the DC requirements (which seems right to me). If this is a pure average then I can approximate it around 3x - 4x.

    I did a quick scan on the web (looking up schade curves), but didn't see what I was looking for yet. I thought I'd lazy and ask.

  14. The ultimate DIY? A Stax SRM-T2!

    in Do It Yourself

    Posted

    Marc's right. I haven't added holes for the standoffs just yet.

    Also, the AC on this will need 2x 330VAC CT, 1x 140VAC, 1x 28VAC, and 1x 28VAC CT (not counting the filiment windings). This uses less power than the original BH, so I was thinking of doing it in one transformer.

    For the bias, it uses a similar doubler to the orginal BH, with a bit more capacitance, and then the IXCP10M90S against some zeners (same as the T2). It supports two taps out, Stax Pro for the higher and it has an option for what the lower one is (500V - for HE 90 or 240V Stax Normal).

  16. The ultimate DIY? A Stax SRM-T2!

    in Do It Yourself

    Posted

    Here's some fun stuff. It's my draft for the BHT2E (per Inu :D) power supply. It's got +425V, +15V, -15V, -295V (via 160V against the -455V rail), -425V, and -455V (via 30V against the -425V rail). The dimensions are 12" x 5.5".

    abpowersupplyv10.gif

    Once, I have this built, I may take a BH board and hack it up a bit to test the design. Any thoughts are greatly appreciated.

  18. The ultimate DIY? A Stax SRM-T2!

    in Do It Yourself

    Posted

    kerry came up with this one... a BHSE with the servo's from a T2.

    http://gilmore.chem.northwestern.edu/BlueHawaii-T2-Servo-v1-2.zip

    opens with ltspice.

    I forgot to knock down the voltage going into the opamp servo, but it is the same as on the T2. Model still works, though I'm not sure what would happen in the real world. I just added it to my model. I would love to get feed back on this. It's actually the T2 output and the BH input with servo similar to the vendetta / T2 for the input section.

  20. The ultimate DIY? A Stax SRM-T2!

    in Do It Yourself

    Posted

    Just for the record, there were three mods to the power supply and amp:

    (1) The power supply mod developed by Kevin and Inu to make it stable

    (2) Adding precautionary 750 ohm resistors in series with the gates of all K216's

    (3) Adding 5pF 1kV caps (I used ceramic, Inu used mica) across the 100k feedback resistors. That was also an Inu mod.

    (1) and (3) are essential IMHO. (2) is discretionary - these resistors were not present in the original from examination of the photos.

    It has already been said - this sucker runs real hot. Once it has been on for a few hours the heatsinks, front panel and top plate are toasty.

    Thanks Craig for summarizing. Very glad you got everything working :)

  21. The ultimate DIY? A Stax SRM-T2!

    in Do It Yourself

    Posted

    I wish no word “2SC3675” or “2SK216” in his next post.

    Now I have two competing fantasy images of Craig: either he's in blissful audio Nirvana playing music nonstop and achieving new levels of awareness --or-- he's been electrocuted by the T2. I know the reality is more mundane, but whenever this happens that kind of thing runs through my head. :jacob:

    I think it may be as simple as he can't post anymore without breaking Inu's wishes :D

  23. Oscilloscopes

    in Do It Yourself

    Posted

    If I looked it up correctly, the max input voltage on the 2465 is the same as the 1052E (400V). I also saw somewhere mention 300V RMS for the 1052E. I think it's said that there should be a 10x correlation between GSa/s and bandwidth, so even if I hack it to 100MHz it should be good, right? But who knows just how much of a fall-off there is around the extreme frequencies, in comparison with the 3dB standard. Or if it'll throw everything off whack.

    Thanks, guys, I think I'll keep doing a bit more research.

    What was the result? Did you end up with a digital scope. Reason is I was thinking of getting the 1052E as well. Also wanted to check what the max voltage is with the 10x probe. Thx.

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