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Everything posted by JoaMat
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Thanks, good to know what components that are at risk. I’m using a KGSShv style PSU and I’ve a small inventory of FQPF8N80C, 30V Zener and 15R power resistors and so far that has been enough. Also omitted current limiter since it hasn’t protected me. One other question, @jose. Do you have four separate 6.3 VAC for the tube heaters?
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Great, quick recovery. What parts in GRHV needed to be replaced?
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I’m sorry for your misfortune. Did it happen direct after you power up the amplifier for the first time?
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Nice! Interesting build indeed. Making generic boards satisfying all builders is not easy. Myself - I do like mirrored amp boards without terminal blocks. Until phase 3 – we wait for phase 2.🙂
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It’s some time since I disassembled the headphone and my memory isn’t the best, anyhow. Remove earpad fixed by double sided tape and remove the two screws now exposed. Gently remove the now loose inner ring one none ear side and all inner parts are accessible. It’s easy to detach earcup from headband, one screw only, and cable – then you have the earcup completely free. I believe it’s fairly easy to work on the headphone, but as always be careful. Personally I think Kaldas is an overall nice design. Good luck.
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Warning!!! I’ve tested sot 23 even a 500V/0.5W piece. Three times it started OK, but after some time (several power ON/OFF and hours) without a warning one of Q30/31 has popped and corresponding resistor totally destroyed. Furthermore two ksc2690 (k216 eq.), one fjpf2145 (c3675) blown and damages to PSU. If you don’t know what you are doing (I obviously haven’t a clue) don’t change Q30/31. Let them be 2sc3675 (or fjpf2145 - I used it for more then six years now).
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A faulty ksc2690 (2sk216 substitute) north of one of the batteries. It tested alright on transistor tester but at a much lower hFE than specified.
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Problem solved. No hum or noise that my old ears can detect.
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Thank you. Them pins looks very interesting indeed. Regarding my current project. Goal with it was to build a T2 on an original board with all modern components. After a visit in the ditch I returned to the narrow road. Rebuilt the batteries to original LED version on the board. Had to change some resistors as I reduced voltages - battery is 640V instead of the original 740V. Furthermore the change to fjpf2145 instead of 2sc3675 called for a Darlington par out of pair of fjpf2145 in batteries. Very easy to make a Darington pair on the original board. Yellow Teflon wire from base to a via on the board – perfect and the via has a perfect diameter. Some components (ksa1220, ksc2690,ksc1008 and j112) have different pin out as the original ones so I twisted their legs to fit the board. Thanks Michael (mwl168) for how to bend legs on the ksc1008. Bottom line: I believe I’ve built a decent version of DIY T2 with all modern components. I’m satisfied and am about to make myself not so sober (it’s Friday evening). P.S. some problem with one channel, unwanted noise and hum. Happens now and then if you have T2s…
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Nice balance servo. Here is an old T2 board with small boards with HN4C51J replacing 2SC3381. By the way Kerry, what kind of pins do you use with your small daughter boards?
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Yes, of course.
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No twisting they can't be at same side of the board due to pin layout of c3381.
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You use a board without 2sc3381 footprint?
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I’ve used mpsw06, big brother to mpsa06. Here in my modified T2 (mpsw06 in red circles). Here in a DIY T2. Both pieces on same side of board and held together by heat shrink tube. Than you have to twist legs so they look like a Dancing Fool. A lot easier just to stick a pair of TO92 from opposite sides. Want surface mount? HN4C51J.
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Now I’ve tried them. KSC1008, put them in like this, one from component side and the other from solder side. Save you a lot of money. J112, changed 22K resistor to 13.7K then able to adjust to 6.55V. Doesn’t save you so much money.
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Here is a T2 on original DIY T2 board with all modern components. High voltages decreased by 100 V to satisfy fjpf2145 and ksa1156. Batteries are on small daughter boards. There is annoying hum on left channel. Right channel is silent so hopefully it’s possible to get rid of the hum.
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Kerry Design mini GRHV\GRLV and JoaMat mini T2 Group Buy
JoaMat replied to mwl168's topic in Do It Yourself
I’ve been using 1.6mm/1oz boards for some years now and I believe they are sufficient in most cases. James (jamesmking) has built one mini T2 and I’ve built two with 1.6mm/1oz. -
So you have 7.43V with the 10K trimmer at endpoint? What is the voltage cross 22K resistor of the other battery?
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Power supply is back. Replaced a number of FQPF8N80C, 30V zeners, 15R power resistors, one 2sa1486 and one 2k resistor. What actually killed the power supple (except the guy that should be feeding ducks) has to be investigated…
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Today has been a nice and interesting day. I finished a mini T2 with active battery. The copper color board on right side in picture in previous post. Late afternoon I were ready for the first power on. One DMM to measure one side verses ground and another to measure the other side. High voltage clicked in – no explosion – on side showed a few volts verses ground while the other almost 400 volt verses ground. It took some time for me to realize that the 400 volt reading in fact was the BIAS. I’m getting to old for this. When I found the right measuring points I had very nice readings. Batteries are always interesting. Readings as follow. Left +194V and -443V, right +196and –443V. So they also seem to be alright. (using 640V instead of original 740V) Connecting headphone. Very noticeable hum but the music sounded good. After a while very annoying noise came. The noise almost disappeared when I approached the trimmer with the screwdriver but came back when I pulled back my hand. Turned power off and changed the small tubes, power up again, lower my guard and went for a cup of coffee and… it all exploded… So tomorrow I have to fix the power supply for the second time within a week. On amplifier board visible; burned traces, resistors and one popped transistor. Maybe I should feed ducks.
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Thanks, BUL216 added as c3675 substitute candidate. Here is a schematic of latest battery module if interested. R2 sets current through the voltage reference. R2 = 4.7K gives roughly 0.9mA. With 4.7K Q3 is needed if NPN is FJPF2145. If NPN is 2SC3675 Q3 is not needed. If R2 is 2K then roughly 2mA. Then Q3 is not needed for neither 2SC3675 nor FJPF2145. Purpose of R4 and R5 is to determine current through Q9,Q11 and Q10,Q12. With Q3 I measure roughly 0.05mA through both sides. Without Q3 almost all current goes through Q10/Q12 and if not enough the desired voltage can’t be regulated and that is what happens with FJPF2145 while 2SC3675 works but it’s very close…
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No, fjpf2145 is not a direct replacement for 2sc3675. 2sc3675 is a 900 V device while fjpf2145 is good for 800 V. I’ve used fjpf2145 in all c3675 positions on T2 except for Q8-10 and Q13-15 (output current sources). But if you decrease to +/-400V I guess you can replace c3675 with fjpf2145 here as well. I’ve also replaced c3675 with other transistors than fjpf2145. For instance Q30,31 with 2sc3324, a sot23 smd part. Might pop up in a future mini T2 with active battery...