ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Hi all,
I had a cracked PCB exactly where craig had his (https://archivedforum2.beoworld.org/forums/t/22490.aspx)
And the weirdness of the artifacts before i read his adventure and found it made me think there was issues with the output darligtons in my left channel, as that was the only explanation i could find.
So i decided to change them all out, they were an old mishmash of originals and replacement BDV series from old repairs anyways, smeared paste all over...
So I got myself new Tip147's and TIP142's from a reputable swedish place.... adjusted idlecurrent.
Sound is clean and nice, plays loud, stays cool....perfect! BUT.. they sound awful... gone is that round warm 70ties sound.. now it sounds cold, modern, bas is all over the place and mids are gone...llike any modern asian amp.
Can this really be? or is it in my head... everything else in the setup is the same...
Im seriously thinking in putting the old stuff back... this is awfull
Or do Darlingtons require "burn in"???? never heard of it before...
Any Tip's ? :=)
BM 2000 *1974, 2x BM 1200, BM 1001, BG 1200, BG CD X, BC9500,BM3300,Bcord 3300, BG CD3300, Beovox Cona, Beovox CX100, Beovox 1200, Beovox RL60.2
I haven't had this problem when replacing the old texas instrument darlingtons for TIP's....or at least not that I have noticed. But I have read some comments by Dillen where he advocates the use of good old stock transistors if one can get them.....
Craig
Idle current set correctly?
Martin
Yupp 5,8 mV or there abouts across top of output resistor pairs, just like before, stable
Hmmm.....will need to check, but I think the setting should be 5,5mv from the top of one resistor to ground, 12-15mv across the top of both.....Martin?
Just checked back on my previous posts and 5.5mv across the topd of the emitter resistors is good (the 12-15 refers to the mA measurement)
After all of the BM4400 I have set up one would think I should know this by now! 10-15 mV across both resistors, 5.5mV across the tops of both (which is one resistor)
Yepp on the tops, just like Beolover :=)
https://beolover.blogspot.com/2015/05/beomaster-4400-full-recap-and-output-trimmer-replacement.html
Everything works, and works wonderfully.. it just sounds incredibly dull and not at all like before..
Is it in my head or shall i realy try switching back...? I can't find any scientific facts on Darlingtons needing burn in or sounding differently after 30years etc.. etc..
Forget about the burning in of semiconductors.I still have to see any scientific proof of any difference, and I have never in my several decades with electronics in general and B&O audio inparticular experienced anything to that effect myself.Are the new output stage darlingtons chinese counterfeits? Sorry for asking, but even "trusted suppliers" can't safely say, that they are sellling genuine parts. Hence the above reference to my saying that I would very often prefer to fit good used original output stage transistors rather than buy new of unknown origin.Did you fit low-ESR capacitors in the output stage? If you did I suggest you replace them with standard types.
Dillen: Forget about the burning in of semiconductors.I still have to see any scientific proof of any difference, and I have never in my several decades with electronics in general and B&O audio inparticular experienced anything to that effect myself.Are the new output stage darlingtons chinese counterfeits? Sorry for asking, but even "trusted suppliers" can't safely say, that they are sellling genuine parts. Hence the above reference to my saying that I would very often prefer to fit good used original output stage transistors rather than buy new of unknown origin.Did you fit low-ESR capacitors in the output stage? If you did I suggest you replace them with standard types. Martin
I'm with Martin about this. Is your BM4400 was recapped?... with what?
I feel pretty safe they are correct and good caps, I recaped it myself using a kit from Martin in 2016! :=)
And it has sounded beutiful eversince.. i actually think som of that adventure is here i the forums somewhere... steep learningcurve.
No... the change in sound came came a few weks ago when i fixed the cracked PCB and changed out all the Darlingtons.
I noticed a crack in the ceramic coating in one of the emitter resistors, so perhaps change them out and also replcae the trimpots for 25 turn ones to get even more exact on the idle current..but i feel this small deviations now are still within the range, so shouldn't effect sound that much..
Found this while googling, does the idle current realy chnage sound this much?
https://www.tnt-audio.com/clinica/bias_e.html
The idle current is important, mainly to avoid crossover distortion.If set to low, the distortion will cause a shrill and harsh sound and the tweeters will easily be overloaded due to the amount of higher harmonics.If set to high, the output stage will heat up and the bottom figure on your electric bill will increase unnecesarily.If you can set the idle current the emitter resistors are fine.And since the capacitors apparently can be ruled out :-) and I take it your repairs to the board are fine and double-checked, I would suspect the darlingtons.Can we see a photo or two?
Here they come, new TIP147 and TIP142 in situ and the old bunch
If the old ones are still good, I suggest you fit them back.
...so the old lady is back sounding like before....
Here are the new TIP's upclose.... realy bizzare if they are fake, or just "new".. but i guess I just proved that they absolutely made a difference.
Thanks all for the help, as the saying goes, if it ain't broke don't fix it!
Those darlingtons look nothing like the real thing.Wrong lettering, no date code, - even the housing is wrong.
Good job!
Very interesting thread, I would like to see how the fakes measure up on a transistor tester 😏
craig
I have one of these https://youtu.be/9sbfdtYDPCM
Its mostly very accurate, for the right applications...never tried darlingtons before on it..
So it identfies them as regular NPN or PNP tranistors with a hfe of 24-50 (!) quite uneaven between the units...and ofcourse i was expecting more like 1000
and forward voltage between 900-1100mV so atleast that sounds normal?