Tunedguy57
New Member
I'm looking for someone that can tell me how to remove epoxy from boards of Audionics BT2 preamplifier.
-
Feeling lucky? Check out the AK 24th Anniversary Giveaway thread and join in the fun!
Audionics BT2
- Thread starter Tunedguy57
- Start date
-
- Tags
- audionivs bt2
Register to hide this ad
Tunedguy57
New Member
Thanks for reply, Dogwan.
Trust me: that black blocks are really hard as stone.
If it should be silicon, then it'd be a really unusual kind.
I guess they put it to hide what' s inside.
In early unit was mounted a really ancient OP, to be more precise, the FIRST commercial op-amp made by Fairchild about 1965: uA709.
Later they used TLO71, a much better part.
The problem with these black blocks consist of electrolitycs inside, whose aging condemn to be poor and poor with time.
Trust me: that black blocks are really hard as stone.
If it should be silicon, then it'd be a really unusual kind.
I guess they put it to hide what' s inside.
In early unit was mounted a really ancient OP, to be more precise, the FIRST commercial op-amp made by Fairchild about 1965: uA709.
Later they used TLO71, a much better part.
The problem with these black blocks consist of electrolitycs inside, whose aging condemn to be poor and poor with time.
Last edited:
dogwan
Dogwan
Got it. It's been a while since I messed with mine. Brain isn't what it used to be, LoL.
I believe the reason they potted the circuit was an early attempt at resonance control. I may be wrong about that though. Don't remember where I read that.
I've had good luck using a heat gun and scraper to remove excess epoxy. Though never tried it on a "block" of epoxy. And never tried it on electronics.
You could also try freezing it and try shattering the epoxy with a small rock hammer or such. That might get the bulk of it out of the way for a heat gun to beore effective. Or at least expose enough of the parts for replacement.
Just spit balling here with ya'.
BTW, here's my thread on modding my bt2 with a different phono stage.
https://audiokarma.org/forums/index.php?threads/help-w-rat-rodded-audionics-bt-2-preamp.959390/
I believe the reason they potted the circuit was an early attempt at resonance control. I may be wrong about that though. Don't remember where I read that.
I've had good luck using a heat gun and scraper to remove excess epoxy. Though never tried it on a "block" of epoxy. And never tried it on electronics.
You could also try freezing it and try shattering the epoxy with a small rock hammer or such. That might get the bulk of it out of the way for a heat gun to beore effective. Or at least expose enough of the parts for replacement.
Just spit balling here with ya'.
BTW, here's my thread on modding my bt2 with a different phono stage.
https://audiokarma.org/forums/index.php?threads/help-w-rat-rodded-audionics-bt-2-preamp.959390/
Tunedguy57
New Member
Yea, I considered the anti-resonance thing.
You could be right.
Anyway whoever not insane never could close electrolitycs in a black box.
And moreover the same result could have be obtained with wax, so common in front-end of radios.
Thanks for the link: I'll give a look later.
You could be right.
Anyway whoever not insane never could close electrolitycs in a black box.
And moreover the same result could have be obtained with wax, so common in front-end of radios.
Thanks for the link: I'll give a look later.
Tunedguy57
New Member
During my attempts to make the devices free from epoxy I could see some unusual things.
In input there is an obsolete uA709, non invert pin no.3.
On pin 2 a usual return of feedback with a 196k on 10k, and a 4,7uF to earth.
But the "thing" strange at me is a diode at output pin6 connecting to two transistor in a way I cannot get. (no push pull! No common emitter nor emitter follower)
After the two transistors there is a further one, whose base is common with that one of other channel, it could be a muter circuitry.
It' s really difficult to understand the schematic, since part of it remains hidden by epoxy.
Is there someone more lucky searching the circuitry of this preamp?
In input there is an obsolete uA709, non invert pin no.3.
On pin 2 a usual return of feedback with a 196k on 10k, and a 4,7uF to earth.
But the "thing" strange at me is a diode at output pin6 connecting to two transistor in a way I cannot get. (no push pull! No common emitter nor emitter follower)
After the two transistors there is a further one, whose base is common with that one of other channel, it could be a muter circuitry.
It' s really difficult to understand the schematic, since part of it remains hidden by epoxy.
Is there someone more lucky searching the circuitry of this preamp?
dogwan
Dogwan
The Potting should be in the center black box (linestage section) and only fill about half the metal case. In other words, if you remove that module you shouldn't be able to get the circuit board out of the metal shield case.
Tunedguy57
New Member
Yea, I am referring to line stage, that is in the black box near power supply board.
Inside there is a board for both channel and half of it is potted in epoxy.
It' s not so difficult getting out the board from metal black box but it has been really hard making free part of circuitry hidden in epoxy.
I can't believe there is no possibility to know smthng else on circuitry of this preamp....
Step by step I' ll do it.....human went on the moon....I will open this damn epoxy!
Inside there is a board for both channel and half of it is potted in epoxy.
It' s not so difficult getting out the board from metal black box but it has been really hard making free part of circuitry hidden in epoxy.
I can't believe there is no possibility to know smthng else on circuitry of this preamp....
Step by step I' ll do it.....human went on the moon....I will open this damn epoxy!
