Official LYNX Power Amp builder’s thread

Status
Not open for further replies.
Jump to Latest
#404
bomellberg said:
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
Click to expand...


I changed PCB and compensations. My version runs great with LME49710.
 
#406
masteramp:
OK, great. Then I know it should work with my setup.

With the input grounded, I get 0V tpA - tpC. I also get -0.27V on tpB, which could be a clue perhaps, since the offset should't be this big, right? If I turn the bias pot I can get it down to 160mV, but not lower. Also, the adjusting does not give any change on tpA - tpC, that's still 0V.

Best regards,

/Bo
 
#408
Idefixes said:


Could you explain more. Are modification due to use of LME49710.

Marc
Click to expand...

I used different value of C102 and C103 - 100pF. My Lynx (OP27/37, LME49710) is stable with C102/103 from 82pF to 120pF.
Lynx can be tuned by changing value of C102,103 and 109 for most of OPAs.
Is it truth, Jan?
:trapper:
_____________________________________________
Base-Emitter voltages should be around 0,6V
 
#409
OK, here are the results of the Swedish jury:

All measurements are in order B C E
Code: 
        B     C     E
Q103:  60.2  0.47  61.0
Q104: -59.6 -0.69 -60.3
Q106:  0.38  62.3   0.0
Q107: -0.72 -62.1   0.0

Q105: -40m  0.36  0.74


Also, since the amp was on for some time, I noticed the only thing getting warm at all was the zener resistors.

Best regards,

/Bo
 
#410
I used different value of C102 and C103 - 100pF. My Lynx (OP27/37, LME49710) is stable with C102/103 from 82pF to 120pF.
Lynx can be tuned by changing value of C102,103 and 109 for most of OPAs.
Is it truth, Jan?
Click to expand...

No. C102 and C103 are miller caps. I found that a value of app. 33pF provides the best square wave respons.
C109 is there to prevent oscillation. 100pF works fine in most cases.

Also, since the amp was on for some time, I noticed the only thing getting warm at all was the zener resistors.
Click to expand...

Not sitting at my usual working PC with all informations, this is from my head.
Q103 and Q104 seems ok. Drawing app. 4 mA through R111/R112. Voltages at Q106 and Q107 seems low, but this could be caused by the bias setting.....
Drivers Q110 and Q111 should get warm if on, so they must be off. I will look more into it, when I sit at my normal working PC.
 
#415
bomellberg said:

I guess the million dollar question is: why is it oscillating?



/Bo
Click to expand...

This topology is difficult to keep stable.

You may try very slow opamp at first, like OP27, or probably uA741. If you get stable, you can try faster opamp, and tune frequency compensation.

To take the scope was the 1st reasonable thing you have done. No one should work without scope!!!
 
#416
Dammit Ragnwald! Are you trying to get me broke? :bawling:

Jokes apart, it would be really interesting to try another OP. Perhaps the cheaper OPA134 or what it's called. But an even more satisfying solution would be to solve it with the LM49710, as mastermind has clearly shown is possible.

Tuning some caps perhaps? I just don't have a clue... 😕

Best regards,

/Bo
 
#418
PMA said:
To take the scope was the 1st reasonable thing you have done. No one should work without scope!!!
Click to expand...

Oh, I thought the 1:st reasonable thing was to start this DIY-project in the first place! I actually think I have done some reasonable things before this, but I admit I have made some stupid mistakes, now in afterthought. :smash:

Thanks for you suggestions, PMA, I'll try to see if I can get my hands on a slower OP.

Best regards,

/Bo
 
#419
Ragnwald:
Yes, I know, I re-read the whole thread yesterday. The pictures that PMA has taken is speaking for themselves. But since I already had the LM49710's that's what I went for. If I can't fix the oscillations I will offcourse swap them for something else, perhaps the OPA627.

Best regards,

/Bo
 
Status
Not open for further replies.
Top Bottom