thuytn
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Posts posted by thuytn
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While waiting for the delivery of the heatsinks, I built 2 short DC umbilical cables using 18awg wires. I experimented with new cable sleeve and the result is just great, very soft and flexible.
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The large cap version seems to take 35mm power caps. Would suit your need if you want to use large ones.
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It’s great to see more people working on the CFA-3, it should get more attention!
Regarding the GRLV, this is the one I have been using in the Dynalo, Dynahi and forthcoming CFA-3. It’s version .47, dated 2018 with small caps (25mm diameter). I’m not so sure about the name because I downloaded it and renamed to something easier to remember.
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I also had the protector powered off the GRLV in my Dynahi. It worked fine but the Dynahi itself is very stable. I'm not sure with stock parts on the silkscreen, what's the dc offset trigger value? I know amb's e12 will do at 80mV.
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There are still missing parts but so far so good, transistors will be all mounted directly on the heatsinks. This is gonna be a dual chassis setup with custom cut heatsinks. I have some balanced headphone protector boards, not sure it’s worth adding the extra wirings... still waiting for Kevin’s ZF/SS switch board anyway.
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I suppose we still have the same transformers specs like the full-sized GRHV? 330vac for 400vdc and 360vac for 450vdc outputs?
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3 hours ago, MASantos said:
I have about 160mA bias atm and the heatsink is about 34 Celsius. Transistors are about 10 C higher. I'll push it a bit closer to 180-200 once it is all done to see if it makes any difference.
Thank you. Seems much cooler than I thought.
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How hot does the heatsink get? Seems to me it's like 220-250mm long?
That power hole seems to be meant for the 12mm Bulgin-like switch...
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With my own machined aluminum buttons, they are quite smooth. You need to press a bit harder than the illuminated switches though. They also sell plastic buttons but the feeling was not so great.
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You meant this? The button diameter is either 5mm or 10mm. I got bored of the illuminated switches after using so many of them and changed to this simple switch a while ago.
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@RudeWolf How did you adjust the input trimpot? Also, what’s the part number of the 47uf ceramic cap on the CFA3 are you using?
Great looking build, btw. I’m thinking of building the CFA3 with shorter heatsinks (300mm).
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Great guide, thanks!
What's the value of C1,C2 are you using?
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The resistors sparked to the ground plane. I spent a good whole day elevating all of them. Also fixed the PSU, all voltages are ok now. (*wheww)
Now back the amp section, the same thing happened. I couldn’t get the trimmers as low as 6.55V. Same as 740V.
The LED at +500V didn’t lit.
I wonder if the sparkling to ground plane affected the board itself?
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So I swapped out the parts and fooled around with the trimmers, got all the batteries dialed correctly, offset was ~10V. Plugging the headphones and got sound! My Carbon definitely felt threatened. This was at 2am and I was both excited and sleepy, listened to it for a bit and turned off the amp.
Next morning when I got it up again, some resistors in the amp sparked. Looks like I didn’t elevate them high enough 😕 Also the +250v rail went bad and couldn’t regulate, outputting +320v now. Been checking around but still couldn’t find the culprit.
I wonder what would be the root of this?
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Yes, I couldn’t get them down any lower... Will remeasure the points when I power it up again, for now I’m kissing goodbye the K216s... these rare and expensive sands.. damn
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So I have been working on the T2 for a couple months. Yesterday I got the PSU up and running on first power up, no issue.
Now moving on to the amp section, I got stuck at the usual place, batteries. Using Kerry’s adjustment, on one of the batteries, I could only get down to 7.43V on the 22K resistor, 784V on battery, 13V offset. Another one got stuck at 806V but with 470V offset! 😕
Nothing smokes. What should I do first to check?
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For something a little better than the RK27, the TKD 2CP-601 is a good one.
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5 hours ago, JoaMat said:
There are only a few modern npn alternatives to c3675. One is fjpf2145 which I’ve used since several years. In my modified T2 the fjpf2145 work alright with its batteries. The battery I’m trying now drives c3675 but not fjpf2145 without stn0214 in a Darlington pair. With stn0214 in the battery you can use whatever npn you like c3675, c4686, ksc5026 or fjpf2145. So for time being I don’t consider stp03d200, but it will certainly work.
Joachim,
Is the FJPF2145 a direct replacement for the 2SC3675 in the original T2? My stock on the 2SC3675 has been running low, would love to have some alternatives.
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1 hour ago, Pars said:
One could ask why you are building a hi-powered amp for an easy to drive phone? Maybe an SS Dynalo would have been a better choice?
Agreed. I actually much prefer the Dynalo than the Dynahi with “medium” headphones like the Utopia and HD800S. Way more relaxing.
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I used 50K/5pf for 7x gain which is very suitable for my Utopia. Don’t think I ever need a higher gain.
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10 hours ago, MASantos said:
need to go and find a better DAC with balanced out that doesn't break the bank.
I use the el cheapo iFi Zen DAC ($129) to feed my Dynalo/Dynahi/Megatron/Carbon with satisfactory result. Providing a healthy 4Vrms, it can also works as a preamp. You need to build a custom 4.4mm-XLR cable though. It’s hard to believe I can get that many features from a commercial product for such a low price.
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Sounds like out of phase problem. Check wiring.
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Michael,
Could you revise my order to just 5x mini-T2 and no psu? My friend backed out so I think 5 is enough for me.
Thanks again!
DIY mini T2 Build Thread
in Do It Yourself
Posted
^ Yes, I also noticed that. I thought my Epcos caps’ leads were large but they fit all Kevin’s boards.