Official LYNX Power Amp builder’s thread

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#501
Bo;

Nice looking amp you build 😉

Would disconnecting them both be a bad idea? It's a bit difficult to see in the schematics if the input ground is connected internally on the card to some other ground. Jan, for future versions of the schematic, perhaps you could have different symbols for the different grounds?
Click to expand...

The LYNX was from the beginning only intended to be build by me and a few friend, so the silk screen have some misguidings and the QAG could be more detailed.....

The input Gnd (signal Gnd), the VAS Gnd and the Output Gnd are separated on the PCB, and have no interconnections. The first version had one common Gnd on the PCB, however I (we) found it easier to remove possible hum, when having split Grounds.
On the new v3.01 PCBs I just have made, the Grounds are now labeled; SGnd, VGnd and Gnd.

Regarding Bias adjustment, you can replace the 5K pot with a 1-2K pot. This makes the Bias adjustment less sensitive.
 
#502
Hi Bom,

the main Audio Ground should not be at the midpoint of the caps.

Make the main audio ground floating connection near the PCB and on a route from RCA to PCB.

Connect the three PCB grounds to this floating main Audio Ground.
Connect the speaker return here.
Connect the RCA ground here.
Connect the PSU ground here.
Connect the Safety Earth disconnecting network to the PSU ground.

If this does not work then move the signal ground to my first post location.
i.e. PCB Sig grnd to RCA ground, then a common wire between the two RCA grounds back to the main Audio Ground.
It's just a pity that the RCAs are so far apart.
But, this could be used to make independent main Audio Grounds for each channel and use two disconnecting networks to connect the two PSU grounds to Safety Earth. A pseudo dual mono, with shared secondary windings. This cannot be done with centre tapped and single rectifiers for each channel.

Finally,
the Safety Earth disconnecting network cannot be 10r//C alone.
The fault current that could flow during catastrophic mains failure mode is kA.
The 10r will burn out just a quickly as the mains fuse. It will be chance which ruptures first.
You must parallel a Power Thermistor or a pair of inverse parallel high current diodes to pass the kA fault current.
 
#503
Yesterday, I realized that my power connections from the toroid was totally wrong connected. I had fed my rectifiers with 42Vac instead of 84Vac. For some reason I have still gotten 120V on each capacitor bank, which I can't really explain. :bigeyes:

Anyway, it is corrected now, and the amp works as before.

BUT, once again, I have had a problem with bias. For the third time, the bias has somehow changed, putting Vbe on the drivers to 1.2V. I heard a loud humming from the amp and then the T4A fuses on the output blew.

What would I sacrifice by going down a little in bias? I would like to know that I'm have some margin in case it decides to change itself again. Also, I'm thinking of replacing the potentiometers to smaller ones, as suggested by Jan, since the bias adjustment is very sensitive.

I also broke the RCA ground loop with two small 10R resistors. The humming is gone and just a nearly inaudiable "ssssssss" is heard if you listen really closely to the speakers. I think I'm running with this solution if I don't encounter any more trouble. If I do, then Andrew's suggestions will be implemented.

When I finished up last night, I sat for a long time listening to sweet music, which was really satisfactory and soothing. The amp is really great, when it doesn't blow drivers.

Best regards,

/Bo
 
#504
Hi Bo 😉

You have tamed the beast 😀
And I'm glad you like the sound.

The humming is NOT produced by a to high bias, but to either oscillation or ground loop.
Was this before or after you changed the RCA Ground loop?

If you where measuring the 1.2V Vbe with a DMM, the high reading could be caused by the same above mentioned reasons.

I also think you would be more comfortable if you change the bias pots, so you feel in better control over the amp 😉
 
#505
Non-Authorized LYNX clone on ebay

A kind fellow diy'er have justed my informed me, that a Hong Kong guy is selling non-authorized LYNX PCB clones on ebay;
http://cgi.ebay.com/Diy-LYNX-150-po...emQQ_trksidZp1742.m153.l1262#ebayphotohosting
even though following disclaimer is stated on my site;
The LYNX circuit and PCB layout provided here is only for non-commercial diy build and use! You are allowed to make your own PCBs for personal use, but please accept that in that case I do not provide any support! You are not allowed to make and sell copies of the PCBs!
Click to expand...
Direct link to my site with the LYNX disclaimer;
http://www.audio-circuit.dk/index.php?option=com_content&view=article&id=48

I know there are not much I can do about it, however in the future anyone who seeks support from me on LYNX matters has to provide documentation for, that their LYNX PCB's are the original from me.

😡
 
#506
Inevitable.

Sorry to hear about the "fake" Lynx pcb`s being made available on ebay. It was always going to be likely that someone would copy your amp pcb`s. In some ways it just proves that the Lynx is worth copying and by doing so they have given your amp design even more credibility.
Can ebay not do anything about this?
Cheers Jan
Best regards Jerry
 
#508
Fake OPAMPS

Just wanted to let you all know that the OPA627:s I bought and have used for the last weeks were fake.

I bought them from "Goodbuy711" on ebay. Searched thoroughly on the internet but missed some comments on him at head-fi.org.

It turns out they are not OPA627 at all, but some other OPA. I measure 5.8K between pin 1 and pin 5 (both ways), a reading which should be 58K-62K.

So, my advice to you all is, measure your OPA627 according to the above, and always buy your OPAMPs from a trustworthy source.

I still have LM49710's and OPA827's to play with, but it is very difficult to suppress those oscillations.

Best regards,

/Bo
 
#515
As it will be with the rest of all the good "thinking" around here

This will end up a dead place if we begin to think too much like that

If you sell boards, you will still need to supply schematic and BOM, so in that case it wont change much anyway
 
#516
Don't you see tinitus

The BOM, schematic PCB layout and how it is build is available for all to see!
It's fine for the people who are honest, like yourself and just want to build an excellent amplifier.
Believe me I am not having a go at Jan.
I have released a bucket load of my own designs over the years and have watched many others built them and I have been very pleased to see them now spread all over the internet, But I am not pleased to see others that have profited by my work and not even bothered to give me at least the credit of my name...
 
#518
I like to say the following:

Assume NOTHING is published and the project is a success, as this Lynx amp is, It will not, and I repeat: It will not make copying impossible.
They buy ONE unit and make as many copies as they want.

It will not keep them from copying, selling, making profit form someone else's work.

It is very frustrating to see them rob you.

I still have to finish mine (Lynx amp from Jan)
Only thing that can be done is not buying from them...

Cheers,
Tarzan
 
#520
I went on Ebay recently a looked at ALL the kits offered
within (at least 150 kits) ...all from CN and HK.
What I found was a full array of amps ranging from J curl
amps , ALL the most popular amps at DIYaudio (I dissected
any provided schemas) I found aussieamp clones .. everything.
But the parts quality (cheap caps , fake toshibas) was
horrible.
What was more amazing is that some are asking premium
prices for "audiophile" clones. I saw many "aspen" amp
wannabe kits , some venders asking $200 for a kit !
shameful but obviously cheap merchandise.
Stay away!
OS
 
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