Official LYNX Power Amp builder’s thread

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#383
Robert GS said:
Well - IF bomellberg has a oscillation problem - this might do the trick if NOT then he really might have an even bigger problem... but which 😕
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Decoupling and filter are two different things. For power are there elyt capacitors and for preventing oscillations are there 100nF foil or ceramic capacitors. This value is defined by capacitance and inductance of wires etc.
 
#384
I can agree with the capacitance and inductance that's why I recommended to place the capacitors on the board and I must admit that I hadn't looked at the schematics before I posted. 🙁
Then again I use 2,2uF for decoupling at my amps and other higher power amps I have seen schematics of use 1uF or more - it doesn't harm you know 🙂
 
#385
OK, this is a long shot, but I really need to clarify something.

In the QAG, there is a nice picture of an assembled LYNX. The transistor closest to the camera is Q110. The text on that transistor is 15033, which is NOT what the schematic or the assembly guide states.

Are these interchanged?

Best regards,

/Bo

EDIT: The picture is the one on the web-page and not in the QAG.
 
#387
I know they're not interchangeable, I just don't know why there is an 15033 at Q110 in Jan's picture.

Here's another question:

There is an errata in the QAG, stating that the silk screen for the Q106 and Q107 is incorrect, and should read "ECB" instead of "EBC". Correct me if I'm wrong, but should't the errata be for Q106 and Q104??? In my opinion there is nothing wrong with Q107, reading "BCE" (as does Q103).

Best regards,

/Bo
 
#388
In the QAG, there is a nice picture of an assembled LYNX. The transistor closest to the camera is Q110. The text on that transistor is 15033, which is NOT what the schematic or the assembly guide states.
Click to expand...
You are right about the error in the website picture (which was corrected before power up (this just shows how easy it is to make mistakes), but no new pictures where taken.
Please see bottom of page 6 in QAG, where the MJE15030 is shown.

There is an errata in the QAG, stating that the silk screen for the Q106 and Q107 is incorrect, and should read "ECB" instead of "EBC". Correct me if I'm wrong, but should't the errata be for Q106 and Q104??? In my opinion there is nothing wrong with Q107, reading "BCE" (as does Q103).
Click to expand...
You are correct. The ECB correction goes for Q104 and Q106.

I will update the QAG when I get the time.
 
#389
Thanks Jan, for the clarification!

Well, the other board behaves exactly as it did earlier. 30-80mV reading between tpA and tpC and approx 0.3V between tpB and GND.

The 30-80mV is slowly fluctuating. I'll check it tonight with the oscilloscope from work.

masteramp:

You have used the LM49170 in your amp right? I mean, could it be the OP-amp? I have seen several issues earlier in this thread about OP-amp choices causing oscillations.

Best regards,

/Bo
 
#394
Here is a picture of the setup:

An externally hosted image should be here but it was not working when we last tested it.


Only the two smallest caps in the PSU are connected (2 x 2200 uF). Base resistors are lifted. Fuses on the Voltage Amplifier Power +DC and -DC. Note also the small blue cable between GND on the 3-pole connector to GND on the input, as per the pre-test instructions.

Best regards,

/Bo
 
#398
Yes. One problem is for sure your long wires from the PSU to the PCB. These should be kept as short as possible and twisted/braided as PMA describes.

If you check the power wires with an oscilloscope, I think you will see a lot of noise running in those unbraided wires.

I once had a neon type working lamp besides my workbench (app. 2 meter distance), and couldn't work out why I always measured a lot of noise and oscillations in my circuits, until one day the neon lamp died. Then all measured just nice 😉
 
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