Hello Everybody,
I changed a normal concertina input stage to the attached schema.
Problem is, now it's arcing on shutdown of the amp for a few seconds.
It doesnt do it every time, but much to often.
I suspect its the voltage in the capacitors, in combination with the constant current source, who tries to keep the set current going, and raises the voltage on the plate.
It also happened on switch on, but I fixed that already by increasing the power-on delay from 15 to 30 seconds.
Anyone a solution?
A second question:
Does a CCS need some break-in time before it sounds best?
Because at first it sounded like
, and now, after about 3 days it sounds already better than without CCS.
greetings and thanks already,
Paul
I changed a normal concertina input stage to the attached schema.
Problem is, now it's arcing on shutdown of the amp for a few seconds.
It doesnt do it every time, but much to often.
I suspect its the voltage in the capacitors, in combination with the constant current source, who tries to keep the set current going, and raises the voltage on the plate.
It also happened on switch on, but I fixed that already by increasing the power-on delay from 15 to 30 seconds.
Anyone a solution?
A second question:
Does a CCS need some break-in time before it sounds best?
Because at first it sounded like
, and now, after about 3 days it sounds already better than without CCS. greetings and thanks already,
Paul
Attachments
Hello Everybody,
A second question:
Does a CCS need some break-in time before it sounds best?
Because at first it sounded like
greetings and thanks already,
Paul
No. Your ears have got used to it.
I was thinking about that too, but... Focus and soundfield/depth was about completely gone.
Maybe it were the old ecc88's. They weren't used for about 15 years... could it be that they need a re-break-in?
Sorry - asking the wrong guy. Break-in occurs in items that undergo significant physical change in the first period of life - car engines, speakers, girlfriends, that sort of thing.
Electronic components (including cables) don't "break in". Some may undergo some rapid changes in the first few (milli)seconds of operation (caps and the like...) but other than that the only thing breaking in is your hearing. This process takes as long as it takes to talk your brain into liking the new sounds it thinks it is hearing.
Others will disagree.
I'm really sorry, I dont have a clue to wat you're saying.
The amplifier without the ccs is in use for about a month or two without problems. So I dont think there's aything wrong with the caps.
The arcing is in the tube...if it happens I can see light coming out of the internal structure, and hear a crackling noise out of the speaker.
Pauldune, my guess is...
at turn off the first tube stops conducting...
the constant current source continues to pull current from the charged power supply capacitors...
it *forces* current into the grid of the second tube...
the curent flows in the second tube from the grid to the cathode to ground...
not good!
I have seen a forward biased diode placed from grid to cathode of the second tube to stop this problem. When the amp is operating normally the diode is reverse biased and not conducting.
at turn off the first tube stops conducting...
the constant current source continues to pull current from the charged power supply capacitors...
it *forces* current into the grid of the second tube...
the curent flows in the second tube from the grid to the cathode to ground...
not good!
I have seen a forward biased diode placed from grid to cathode of the second tube to stop this problem. When the amp is operating normally the diode is reverse biased and not conducting.
Ooops, a tad fast off the mark there Mr. aardvarkash10. Although I do not have references to hand, I understand that metal film resistors, electrolytic capacitors and vacuum tube cathodes all undergo small physical changes during the initial period of use. In other words, they do undergo some form of limited but real 'break in'.
We must differentiate this from the 'hype and bull' marketing used by the namby-pamby audiophile companies who use 'extended break in' to cover up simple psychoacoustic aclimatisation. Indeed their lies are shameful.
Example of protection diode: More cathode follower stuff
Credit: J Broskie / TubeCad
The same can be used in your amp.
Credit: J Broskie / TubeCad
The same can be used in your amp.
Attachments
True on all counts gordy, but the most important words being "small" and "limited" ie not enough to cause any discernable change. Apart from the 'lytics which have well documented learning curves.
Thanks! I'm gonna look into that. But there's only a 3v difference between the cathode and the plate. Doesn't that mean that al ac signals larger than 2.3v (3-0.7) get their tops shaven off?
Does it make any sense at all to place a resistor before the ccs, so that drops already some voltage? (and functions as a limiter in power off)
I really dont understand the fine workings of the dc coupled concertina with gain stage. Especially the bias-setting of the actual phase splitter eludes me. With ecc81 or ecc88 and the same resistors, still the same 7 mA, and same voltage.
Ive searched, but never found any good reads about it. Any tips?
Strange thing is, i'm really shure the amp started sounding better... with the ecc81, i just had bought new supermatched 6201 (sq) And they sounded really good.
Then I put in the ccs and the ecc88's. Now about the "color" of the sound, i find that very difficult, and mostly my own mood is involved in how good it sounds. But the sound field, (focus/ depth/ imaging) thats another thing. With the ecc81 it was pretty good, but right after the change, it sounded just like my pioneer receiver; bad soundfield. Almost difficult to hear the "voice in the middle", and very clouded. instruments were not "loose" and not easy to differentiate.
And that, you can imagine, was a great dissapointment. especially because the THD in the concertina dropped 90%. (from about 0.5 to 0.05) Still have some spectrum analyzer shots of that.
I was already looking into changing the splitter to a LTP with CCS in the tail, when the sound cleared up. And now after 4 days, im going to order some Dale resistors, to replace the temp cheap metal film R's I put in, because the sound is now better than ever.
lol - you just described a move from relatively high distortion to relatively low. Your ears LIKE the high distortion spectrum they were hearing. Thats so common its a truism. We like distortion in moderate quantities. So it sounds "worse" because of the drop in distortion, not in spite of it. The effect is not helped by your expectation that things would sound "better" instead of "different".
In the interim, you have retrained your ears to like what you now hear.
Welcome to a brief and personal introduction to psycho-acoustics.
In the interim, you have retrained your ears to like what you now hear.
Welcome to a brief and personal introduction to psycho-acoustics.
I really value your opinion, and maybe your right.
But I like to keep an open mind to things which are a bit mysterious, and dont want to prentend we know everything about sound/ amplifiers and related stuff.
And I like to think that the truth is somewere in the middle... I changed tubes, resistors and put some molten sand in the circuit. Maybe I had too high hopes. But the change is too much to just say "your ears got used to it"
Whatever... As long as i'm happy with the amplifiers, i guess it doesnt really matter.
whatever... As long as i'm happy with the amplifiers, i guess it doesnt really matter.
exactly!!!!
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