Dual La2a - [silent:arts] version

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Postby [silent:arts] » Fri Jan 25, 2008 7:43 pm

Yes, the heater goes to ground via the 100r (but you used the holes right after the terminal block, before the 100r resistors ?)
or wait, maybe you did not know you have to wire the heaters like in Drips v1 ?

should look something like this, or better (the silicon cable I used is not good drilled together:
Image

Take the tubes out and measure each heater terminal block input to ground if you actually have 100r. the PCB Billex made for me had a short at one side to ground (I checked the PCB Bernd send me for this, and it was right - but you never know).
[edit: with no power transformer connected of course]

the neon lamp is on the HV rail, if it shines it has more than 65V - that's good.

the best place to measure the HV (High Voltage) is the left side (looking from the front) of R129 or R229.
Last edited by [silent:arts] on Fri Feb 11, 2011 7:23 am, edited 3 times in total.
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Postby bernbrue » Fri Jan 25, 2008 7:48 pm

Hi,
Heater voltage is AC and after a closer look to the solder side of the pcb it seems, that the heaters (H1L, H2L, H1R, H2R) have to be wired by hand. Is that right Volker?
regards
Bernd
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Postby bernbrue » Fri Jan 25, 2008 7:50 pm

Volker, you are too fast :lol:
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Postby waldorfcave » Fri Jan 25, 2008 7:51 pm

damm, sure now erverything is clear :P
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Postby [silent:arts] » Fri Jan 25, 2008 7:54 pm

:D I hate this undocumented projects :lol:
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Postby waldorfcave » Fri Jan 25, 2008 8:30 pm

yes volker you are the man :P

after all my questions this projekt is very well documented :roll:


thx
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Postby waldorfcave » Sat Jan 26, 2008 2:03 pm

ok...this thing is running and compressing. :lol:

gain ratio have to be tuned like volker said (i use sowters) i do it later....

one problem is, that my unit hums a bit. more then it is ok for me :-(

it comes not from the powertransformer, i can move it from side to side and nothing happens.

maybe the ac heaters under the pcb?

i have measured the heater against ground, and i only have around 60 ohms
resistance between ground, but volker said it have to 100R?

maybe this is the fault?

maybe someone has an idea where to look first....

i will try and try :P
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Postby [silent:arts] » Sat Jan 26, 2008 2:09 pm

mhm, no hum here.
is it on both channels ?
can you do a photo of your ground pattern ?
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Postby waldorfcave » Sat Jan 26, 2008 2:12 pm

yes on both channels, exact the same

in the motherforum someone changed the rectifiers , and then his hum disapeares

Image
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Postby waldorfcave » Sat Jan 26, 2008 3:03 pm

...change the retrifiers still hum
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Postby [silent:arts] » Sat Jan 26, 2008 3:29 pm

all looks good at the photo.
when you disconnect the heaters from one side, is there still hum on the other side ?
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Postby [silent:arts] » Sat Jan 26, 2008 3:34 pm

waldorfcave wrote:gain ratio have to be tuned like volker said (i use sowters) i do it later....

one problem is, that my unit hums a bit. more then it is ok for me :-(


how much is "a bit" ? (LA2As are not famous for low noise)
is the hum constant or gain depended ?
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Postby waldorfcave » Sat Jan 26, 2008 3:39 pm

hum is to loud, not normal

hum is constant not gain depended.

rewire my ac heaters and check in one minute
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Postby Harpo » Sat Jan 26, 2008 4:04 pm

Did you mount the 7805 isolated from heatsink and caseground? Doppelkühlung :) You may have a ground loop. Is hum frequency pre (mains side) or post rectifier (double mains frequency)?

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Postby bernbrue » Sat Jan 26, 2008 4:05 pm

Lars,
did you use shielded wires for pots, output tranny and XLR? The HT wiring is a real pita. :x :) :) :) :)
Never mind, Volker
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