pedefede

Hi All My experience: I had a LOT of trouble with noise, and replace a lot of parts. Changing my Shinkohs to Xicons helped a bit, but the trouble/noise came back. This made me think, that Xicons were better because of the 50ppm, but that 50ppm is still way too high. So i re-replaced some of the resistors with only small benifit. Finally the one thing that did the job was replacing the 10K pots in the four battery-sections, with a super-low ppm resistor: 5ppm (!!) in the series ptf56 from vishay, that had the same value as what i adjusted the 10K-pot to (6K in my case). Then i could do all the final tuning with the 2K pot. http://dk.mouser.com/ProductDetail/Vishay-Dale/PTF566K0400BZEK/?qs=V4kc8PiwqSBAoWKdj%2fYdnMPewyQYMP1WCgstHSwEDSg%3d THIS thing made the amp TOTALLY stable, and dead silent. So for 6 month i have enjoy'd the fantastic sound from this beast of an amp Happy new year to you all!! Peter

jep ok, i'll wait till my balanced DAC is finished ....

Just measured my output voltage, and it was slightly out of balance: (which corresponds to R-channel having a very small weight) L+ 100% L- 110% R+105% R- 110% (Switching input channels produces same result, so it wasnt the signal source) What primarily controls the gain? EL34? K216?, ecc88?

I am starting to build an ackodac, and will use twistedpears IVY-iii as an IV (as well as a "new take D1" later on). http://www.twistedpearaudio.com/docs/linestages/ivy3_schematic_1_0.pdf IVY-iii has 22R resistors on the balanced output from opa1632, to "help drive capacitive loads". Does T2 count as a capacitive loads?? (due to C10/11) peter

hmm ... since the mere sound of the 009 bass is nice, you might get away with using some software equalizer. But maybe the PC processing will mess up the sound quality Another route could be choosing an IV-stage for DAC, or a preamp, that has slightly more bass - but this seems even more dangerous - because you arent shure, weather the 2 frequency-characteristics match ... To buy - or not to buy - that is the question ......

This week i have been listening to some 009s (and 007) on my T2, that i might spend $$$ on. As you all know, the transparency of the 009 is insane ... However, i dont feel that they are linear at the bottum/bass ... the volume of the bass is too low. (The mere sound of the bass though, is very nice - articulate, good impact etc). So drums etc. sounds nice, but fade a bit behind in the soundstage. As i am only started with a new DAC-project, - i am playing on a "lousy" emu0404. But doing quick A/B-switch ... the 007 do play bass! - and seems a bit more compressed (not nessecarily bad!) and controlled - and sounds a lot more overall linear. It's like: - if i want classic or Jazz - go 009. If i want rock - go 007. (i will be satisfied with either i think) So: Am i the only one having this experience on T2 Peter (To buy - or not buy - that is the question...)

You are evil Voltron ... as if the T2 wasn't expensive on its own ... (Otherwise i need to 1. get broke 2. send my sister in law to fetch me a "cheap" pair from HongKong, )

Black sheep has been finished (almost): http://dl.dropbox.co...phone%20326.jpg (quick iphone pic in the dark) Noise issue solved - Replaced shinkohs 390K, 820K, 100R in one of the batteries for xicons. There is NO noise now, even at full volumen. Feels a bit wierd actually, to put the beast to full volumen, and to be unsure wether it has been turned on ... (I allmost blew my ears, when i accidently left the volumen at 100%, and put on a 1 KHz sinus signal ... ) You can measure the 50Hz noise from the unregulated heaters on the batteries ... but during to the balanced nature of the beast - it is canceled at output It plays fantastic ... I still have some to-do stuff (balanced volumen attenuater with fixed resistors, optimizing balance by switching tubes, trying with current-stock.tubes, eventually replacing more resistors for Xicons) (During measuring - i discoverd a small volumen-dependent oscillation (200KHz, 30mV pp at 100% volumen) . Too small to cure for now. - but that can wait ... now i really just wanna listen to the sweet, sweet music - and improve my signal sources, to match this thing ....! peter

Lifted all resistors (shinkoh) in the batteries on left channel 2+ mm. HUGE difference - noise is almost gone, and voltage is now stable. So no replacement seems to be needed. There is still some small scratching noises, and very small white noise. I'll poke around with a scope - and probably do INU-fix on pots. Right channel was born dead quiet, without any mods.

Both Channels are working, and playing music. There is still no more sign of oscillation. I do have noise in left channel (very same sympoms as Kerry, Bubliss), and 1 battery there is adjustable, but voltage is drifting a lot - so keeps having to being re-adjusted. - So i will try lift my resistors - and if that doesnt change, ill replace. What resistors are reported as "noise-curing" as of now? - Gilmore: Xicon - Inu: Takman - chinsettawong = 1% Royal resistors (Thai brand)

Does anyone have a working link to Craigs excelsheet from post 1830, about RV1 and RV2 ?

Well, oscillations killed pretty easily. I only had one C12/13 = 2,2pF (per channel), like Gilmore. So i added 1 more for the other side, and the oscillation died. (It MIGHT have been caused by pickup noise etc, from all the test leads for the 8 multimeters (i borrowed from work). These were remove in the second test. ) I will go to sleep with such a happy smile on my face, that my wife will think I had sex elsewhere ....

YESSS!!! first channel has a LIFT OFF!! All leds light up nicely (Replaced the other J79, that was only "slightly" dead, so it took my quite a long time to find the bugged part) anyway - battery adjustable and fine at 740 - and all voltages measures fine. However, i have oscillation problem: There is a 860KHz (i think) oscillation around 14V peak-peak at each output (though in phase - so V-out-difference is only at 1,5 V peak-peak). The V across R42 in battery - minus-side: is adjustable through 2K pot, to 6,55V (like kerry). (A humming can be heard somewhere, while measureing) - plus-side: is not adjustable through 2K pot (?!?), sits steady at 5,3V (No humming). Oscillations sounds somehow like Craigs problem. (I do have 5pF caps across each 100K feedbackresistor ... gotta read/check, weather the resistor it has to be moved) - Its the non-adjustability of the one side R42 that puzzles me ...

Gratz Kerry!! I finally have another day off, so I hope to soon be finished debugging mine.

I used the LEDs from the Mouser-BOM: 859-LTL-4213 In the datasheet: http://datasheet.octopart.com/LTL-4213-Lite-On-datasheet-125834.pdf they are indeed specified at 2,1V at 20mA, but the operating voltage in T2, they work at 0,5mA - where Vf is down to around 1,82V (see page 4 on datasheet)

Replaced the D10 and "rebooted". Same problem, battery adjustable to 740V, but out-minus can only be adjusted up to -320V Everything lights - except now D24 doesnt (but it does work, and have correct Vf). So it seems, that the problem is the CCS around Q30 and Q31. I tried to test it, and it behaves a bit wierd. I put 0,5mA through top of D24 (as R60-61 will do), - but then you only get 1,5mA though Q31. And the voltagedrop across D24 is only around 0,7v instead of 1,8V The other side (Q30) and other channel (not yet powerd up) behaves similar. Any ideas?

This week i finally had some time, so i did the last checks - and powerd on the amp!! At first instance, some LEDS didnt wanna light ... and it looked much like Inu's problems described in post 1131. And while debugging, a spark went off ... so it seems like I also failed to face Mekka ... Anyway - checked all semiconducters, - most seemed OK. Replaced a J79, and D6,7,10,11 I fired (the left channel of) the beast up again this evening - and all LEDS light now - except D10 (which is shorted again). - minus side is adjustable - battery adjustable and ok - but plus side cant get above -320V, battery is adjustable and ok (wierd, since its the CCS for EL34 at plus-side thats bugged.) - FETS seems fine ... from a quick check - the 6dj8 cascode stage seems to works nice ok - Q24, J79 only has -485 V (instead of 450) - R56-at -462V and R57 at -307V Will check Qs around D10, - tomorrow.

About the wirering. Are everybody using the "setup" that i saw in post 1497/1498 ?? I was kinda worried about having +500V sitting right next to -560V. I'm considering "grouping" the plus and minus rails - but then again - if there has been some kind of standard evolved ...

The Bakelit sockets wasnt choosen because of the price! (which anyway is roughly the same as the Teflon ones). And they seem to have the exact similar shape - so i didnt do something stupid there. (The displacement issue is due to how the PCB are mounted to the alu L-brackets (where i only premounted the side+front/back - but left out the top plate). I guess the default solution is to re-mount the L-brackets ... But I came up with another solution. If I dont start to assemble first the sides to the front/back, and then top/bottum; - but instead first the sides to the top/buttom - and then the front/back, there is room for the sockets in the holes (2 of the sockets touch the top plate, but without much tension). There will then be half a millimeter space between the front and the sides. The cabinet seems pretty stable. (The back and sides are in firm contact). (If i tighten the screws, i guess i can get the sides and front to touch, but i think it will put some stress on the solderings of the sockets. ) [EDIT:] And today i loosened the 2x7 screws, that holds the L-brackets to the sides/heatsinks. I was then able to push the PCB+Brackets a bit a way from the front, (because of the space between the screws in the holes) before fastening again. This gave another 0,3mm, and things looks nice now. The sides, of 2 of the sockets just touch the top panel, but i dont think that will be a problem now.

While mounting the amp (almost done), I am having trouble with the tube sockets, that fits the holes in toppanel rather tight. 2 of the EL34 sockets are "dis-placed" about 1 mm too close to the front. I did choose Bakelit sockets (with same dimensions as the teflon ones), so i cant really cut in them. Any ideas? Melt a bit away with a soldering iron?

Returned from hollidays, and today i finished the powersupply My LM7912 also gave -15V like Gilmore ... but actually a spare TS7912 worked instead I also had quite some trouble with the +250 rail (i gave only 90V). After some searching, it turned out that i switched the direction on the zener on the FET. Luckily i didnt fry any other parts, so now its working Readings: +576 +496 +246 -260 -495 -557 +11,87 -12,07 Now on, to quite a lot of wire-work ....

Build myself a rough curvetracer, for testing/matching and the K216 seemed rather similar. And alle the J79 was ok - but the one from the different batch was quite different. However just as i finished, i somehow burned one of the good quad - and the dealer doesnt have any more from that batch So i need buy 2 new "low gain" types, to put in one of the channels peter

Assembling the mosfets 2sk216 and 2sj79 now is there any way to match them? (since there are a lot of parameters etc., and I dont know the operating mode/conditions). I allready did the simple test: http://www.4qdtec.com/mostest.html all K216 turned out fine. But got trouble with J79: I have 5 (1 extra - but from a different production batch. The 4 reads "6 G5" and 1 "0 J15 5yx"). Now one of the 4 cant be turned permanently on by the diode-tester (or my finger). the internal diode reads about 450 when off. Which suggests "some issue" with the internal capacitance. But i have no clue wether this is relevant. The extra from another batch works, but reads 425 when off. Which one to discard? Or better: what other test to perform? peter

Hi All Just wanted to share my (slow!) progress: PS Amp Seems i keep find small new components, i forgot to order ... peter

Build my own tubetester (out of a cheap PC-scope). Lot of fun - and it seems to work So for testing input tubes, i deducted the following from the amp-schematic - please comment: operating points, where i need to measure: U2: Vgrid = -2 V I = 5mA Vplate = ?? cant see U1: Vgrid = -1 V I = 5mA Vplate = 69V What is the most important parameter? Gain/mu or transductance?