universal chip pre-amp project

[cancerkazoo]

how does BOM look?

Any suggestions? Tried to find a film for Ci since it is in the audio path.

[cancerkazoo]

..also how much current do I need? would 2 * 115v in /9v out be enough @ 2.8VA a piece?

9 * 1.404 = 12.636v ....so that should be enough voltage.

ready to order parts, just want to confirm.

thanks
Steve

[tent]

Originally Posted by digi01

You said you use a 12V(AC) toroid,then you have 14.2V unregulated DC.the zener is used to get a fixed voltage.you should have 12VDC on output.
sounds like the zener is not in gear.you need check if the zener is connected in reverse.

Hi Digi!
I'm back from holidays.. Well I double checked the Zener's connection and it seems to me correct: but I still get a couple of volts more on the output.. maybe they are defect or not enough powerful (1A-12V).. I'm connecting them referring to the black stripe pointing exactly like the >| symbol (so the stripe points towards the upper of the schematic in + direction)..

will try to change and see..

tent:wq

[digi01]

Originally Posted by cancerkazoo

how does BOM look?
Any suggestions? Tried to find a film for Ci since it is in the audio path.

the BOM is great.
i think the part number 505-MKP20.33/100/5 MKP is good for Ci.
for the power supply,a 2.8VA transformer with 2 x 9VAC is good.

[digi01]

Originally Posted by tent

Hi Digi!
I'm back from holidays.. Well I double checked the Zener's connection and it seems to me correct: but I still get a couple of volts more on the output.. maybe they are defect or not enough powerful (1A-12V).. I'm connecting them referring to the black stripe pointing exactly like the >| symbol (so the stripe points towards the upper of the schematic in + direction)..
will try to change and see..
tent:wq

1A-12V zener is enough powerful for this preamp.
the black stripe connect to + is correct.can you take a photo?

[tent]

Originally Posted by digi01

1A-12V zener is enough powerful for this preamp.
the black stripe connect to + is correct.can you take a photo?

Hi Digi01,
sorry for the late answer.. I tried to change the two diodes with a couple of ones with more wattage, but still no change: I read 13.2V on the output, I can smell something nasty over the diodes, and they get hot, even the last two caps 100uF, 64V get hot! What is going on? Anyway the sound is great and the thing is correctly powering your small pre-amps, but I do not dare to keep them powered on more than a minute.. I also am using a test bulb before the trafo, just to make sure nothing is cabled wrong.. no light in it.. cluesome..
This time I attach you also a picture of the PSU.. I assembled it all straight.. so there are three straight lines on the bottom side of the PCB (interrupted at the two 0.5w resistances.. )..

Thanks,
tent:wq

[mjf]

hello.
can you measure the voltage drop across the 10 ohm res?
probably the current is too high so you will have to use a bigger resistor (perhaps 22 ohm or bigger).
greetings...........

[digi01]

to tent,
mjf suggestion is great.
look the photo i think your connection is correct.
the read 13.2v on the output is normal.my psu is 13.1v on the output.
i still have no idea why the 100uf 64v cap is getting hot.i wonder if the zeners and caps is getting hot without laod?

Zang

[tent]

Originally Posted by digi01

to tent,
mjf suggestion is great.
look the photo i think your connection is correct.
the read 13.2v on the output is normal.my psu is 13.1v on the output.
i still have no idea why the 100uf 64v cap is getting hot.i wonder if the zeners and caps is getting hot without laod?

Zang

Hi all,
good idea yeah.. I'll try with a 22ohm (or maybe the important is to upgrade it from 0.5W to some 1 or 2W ?). Anyway the voltage drop I measure is: 31.1V before and 26.6V after the res (I'm measuring between upper and lower rail instead of with gnd for practicity.. )
Anyway I was thinking that after the zeners the voltage on the output should have been 12V anyway, or no? not 13V...
And yes.. they seem to get hot also without load.. I just tiread without load.. maybe it gets some more time to get hot.. but can be an impression..

tent:wq

[tent]

ok, shouldn't have been so lazy.. -> the voltage drop is 2.3V between the 10ohm res (15.5V before and 13.2V after).. does it say something to you?

tent:wq