With Q2 and Q3 on the line amp board, I'm just checking orientation, followed the schematic but want to double check
Hi Andrew, should have put this all in one message, on the remote board R18 says 1k but this isn't in the BOM R26 on the board says 1k but in the BOM it says 10k which one is correct?
Nearly a new year now so progress made on this year's project, here's some photos of the boards which there doesn't seem to many of in the thread. If anyone sees any mistakes, these are unintentional so please let me know!
Phono board
Line stage
Balanced line out
Input select board
Phono board
Line stage
Balanced line out
Input select board
It may just be an artifact of the resolution when one zooms in, but you might want to check the solder joints under magnification. Insure that the filets cover the end caps. One end of C4 as an example could be a problem. The labs I have worked in all use binocular microscopes cranked to a high power to check surface mount work. Fascinating world down there when you zoom in: cars, trucks, little people waiting for busses...
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Thanks for pointing that out, I have a loop on order from Amazon for this, when youvsay C4 which board do you mean?
Yes - to ensure you have no major issues, just apply power and measure the test voltages. If that's ok, I would recommend applying a test signal and then check that the boards work correctly. you really don't want to be assembling the preamp only to find it has problems because then you might have disassembly etc.
(Neat solder jobs BTW 👍 👍 👍 👍 👍 )
(Neat solder jobs BTW 👍 👍 👍 👍 👍 )
That sounds like my wife 'what are those little gas storage tank things doing?' 😆
Makes sense.
Just one more question for now, remote board R18 says 1k but this isn't in the BOM R26 on the board says 1k but in the BOM it says 10k which one is correct?
I didn't find the soldering too difficult to do by hand, time and patience was the hardest part!
I've finally applied power to the line stage pcb and have a few voltages that don't line up with the schematic,
The voltage over R21/22 is 33.5mv should be 35mv
The voltage at U4 pins 1 and 5 is 0.4V should be 0.77V
The voltage over R20 is 0.68V should be 0.62
The voltage over R21/22 is 33.5mv should be 35mv
The voltage at U4 pins 1 and 5 is 0.4V should be 0.77V
The voltage over R20 is 0.68V should be 0.62
Chris, those voltages are all within tolerance. Can you adjust the output offset for 0 mV?
Sorry about your previous question that I did not answer- I will do it tomorrow.
Sorry about your previous question that I did not answer- I will do it tomorrow.
Thanks @Bonsai
All those voltages are measured without signal wires attached, any issues here?
Yes I can adjust the output offset to 0.03mv on both channels, could probably adjust further but I don't thinks its needed?
With the Balanced line amp is it easier to measure the opamp voltage at R1/2 and R11/23 also R13/14?
All those voltages are measured without signal wires attached, any issues here?
Yes I can adjust the output offset to 0.03mv on both channels, could probably adjust further but I don't thinks its needed?
With the Balanced line amp is it easier to measure the opamp voltage at R1/2 and R11/23 also R13/14?
You should short the inputs when you check for offsets because if you are picking up any noise (hum etc), the meter may dance around a bit.
0.03mV is excellent - so that's good.
On the PCB above, if you measure at R1 and R2 wrt 0V, you should get +-2~3mV max, but because the output is AC coupled through C3 and C4 , that offset will not go through to the next stage. The output offset measured at J4 and J5 of + and - wrt 0V should be a few mV max and measuring from + to - on J4 and J5 (so not wrt 0V this time) should at most be 4mV, but probably a lot less than this.
0.03mV is excellent - so that's good.
On the PCB above, if you measure at R1 and R2 wrt 0V, you should get +-2~3mV max, but because the output is AC coupled through C3 and C4 , that offset will not go through to the next stage. The output offset measured at J4 and J5 of + and - wrt 0V should be a few mV max and measuring from + to - on J4 and J5 (so not wrt 0V this time) should at most be 4mV, but probably a lot less than this.
Chris,
R18 must be 10k and R26 must be 10k
I will update the documentation this coming week.
Any more questions, don't hesitate to ask.
Hi @Bonsai
Measured this today, voltages as follows all dc volts and inputs shorted.
R2 2.4 mv
R1 6.34 mv
J5 + is 0.03mv
J5 - is 0.04mv
J4 + is 0.027mv
J4 - is 0.036mv
- to - on J5 is 0.008mv
- to - on J4 is 0.009mv
I think these are good? Only question is voltage on R1