Official LYNX Power Amp builder’s thread

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#441
It is difficult for me to comment, as I have very very good relationship with Jan.
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Dear Pavel. Please feel free to comment all you want 😉

Bo;
I'm glad to hear that you are back on track 😉

All;
As I have stated many times in emails and on internet forums, the LYNX was from the very beginning ment as a "replacement" Amp for the good old 70-80s very dynamic Studio Power Amps.

Quite a lot have over the years asked for the LYNX to have "supernatural" specs like BW up to 1 MHz etc., which I always has dissuaded. Please tread the design for what it is; A replacement clone for the 30-40 years old Amps.

The original LYNX was from the very beginning fitted with the LF356 opamp, which works great in this design. This opamp is a bit slow and noisy for todays standard, but it was the standard opamp many years back.......

Over the past years, many have build the LYNX (either using original or home made PCBs) with succes, even though I never thought that the LYNX would be so popular in the DIY world as it has become.
Also the LYNX may be quite a big mouthful for some first time diy'ers due to the high power involved.

And last. Thanks to all who participate in this thread, as it is impossible for me to get time to reply to every question asked 😉
 
#444
Some modifications for stability...C4 is most important (local NFB around OPA)..You can find it in all QSC amps.
 

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#450
I could really use some help here. I thought everything was ok, but as I slowly raised the bias go get 1.4V tpA-tpC the 0.5A fuse blew. I bought new ones, but the -DC fuse blows immediately. It turns out that Q111 was blown, measuring short between all three pins BCE.

I switched the Q111 (MJE15033) and put in another fuse. This time everyting was ok and I measured 124V over the rails.

Then I was going to measure tpA-tpC again, but as soon as I touched tpC with the scope-probe GND-clamp, the fuse blew and the Q111 is also blown again.

The scope is on safety shield (ground) and so is the GND connection on the amp.

What could be wrong?? Help!

Best regards,

/Bo
 
#456
I have now built the replacement card for the one that went into flames. The base resistors burst so bad that the conductive paths on the card were burnt off.

If there is anyone out there with extra 15032/3, some 2W 33R resistors and 8 2.2R base resistors for sale, please let me know.

Best regards,

/Bo
 
#457
Yesterday I tried the OPA827 from TI, but oscillations reappeared. I really have to learn how to tune these bastards.

Is there any good documentation online on bandwidth limiting etc?

I bought P-A's adapters from svalander.se and soldered the surface mount OP onto those, together with the 100nF caps. The other caps were the original ones though, 100pF and 2 x 33pF.

I'm awaiting my OPA627's. If those work I will not touch a thing...

Also: Thank you Jan for helping me out, component-wise!

Best regards,

/Bo
 
#459
One of my card is up and running, but the other all of a sudden has started to draw some power on the input side. 0.5A fast fuses as well as 1A fast fuses blow on the +DC side. Everything seems to be ok when measuring the trasistors etc. Anyone has any tips on what could be the problem?

Best regards,

/Bo
 
#460
This really puzzles me. If someone can explain, I'd be grateful.

It seems, if I connect power to the output stage, but leave the fuseholders empty, the input stage draws a lot of power. Is this true, and if so, why? Looking at the schematic, I can see no way of current flowing from the input +DC and -DC through to GND on the output stage.

My working card did the same (input stage fuses blew), but when I added the fuses, it worked fine again.

Best regards,

/Bo
 
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