New API 525 build thread.

[901]

Peter,
thanks a lot for the info!

Are you sure you are talking about a three-coloured LED (RGB)? If so, how does it work? anti-parallel two of the three? Can you point me to a part number?

 

[peter purpose]

Two colours become a third when both sides are fed.
Just get any 3mm jobbie.

 

[901]

Peter, you are too funny!  ;D

Well, I already drilled the bigger hole. And now that I took a closer look to this part of the PCB I eventually got that this LED is nothing more than displaying the state of the IN switch.

From the prescription of a RGB LED I assumed you would be doing something really cool with this LED. E.g. a coloured level meter for the input. Nevermind.

 

[901]

Now that I got the missing parts I finished my build. 
But I have big difficulties to dial it in using the test procedure you posted.

• I supplied 0dBm (0.775V) 1kHz to the input and could easily dial in the -5dB at the output of A1. That´s 4. (A), (B) and (C).
• Then I switched it on (topmost push button) and also engaged compress mode (2nd push button) and adjusted the out pot to 0dBm at the output (after the tranny). This is at 2 o´clock in my case. 4.(D)
• Turning up ceiling control indeed does 2dB steps. 4.(E)
• I let the ceiling control sit on its last position and try to dial in the input pot so that the output is again 0dB. Turning up the input lowers the out to +2.8dB at 12 o´clock of the pot and past that increases again in level. I keep it at the lowest value for the further checks. ??? 4.(F)
• Turning down the ceiling control results in output jumps of up to +-0.6 dB. 4.(G)
• Adjusting R55 to fully CW the meter still has 2 LEDs off with the ceiling at 20 ??? 4.(H)
• 4.(I) talks about depressing the Limit button. So I assumed I´d switch off the Compress button and switch on the Limit button and adjust for no difference between the two levels using R75. Am I right in this? However I can´t get closer than -0.5dB for the Limit mode.  ???
• For 5.(A) I switch the signal generator to 10kHz and don´t touch any other controls. The output is now -2dB different from the input (limit mode). 
• Then I switch off limit mode and switch on compress mode. The level drops anoth 0.8dB. After that I switch on D-S and can see a drop by 7.3dB instead of -12dB.  5.(B)
• I switch on limit mode while leaving on compress and D-S, I get a drop by -1dB instead of -3.5dB  ??? 5.(C)
• For 50Hz with the same settings (compress on, limit on, D-S on) I get +14dB on the output!  5.(D)
• Switchin D-S on and off doesn´t do anything to the output level  ??? 5.(E)
• For -10dBm in the THD is way less than .1% in compress mode 5.(F)
• At -10dBm input I cannot dial R52 to clipping the signal.  5.(G)

I stopped the test there. The unit is kind of working, but not completely as it should. I tried some music through it and it sounds really bad.  :'(

There is a very obvious distortion on the lower frequencies. Sounding like a broken speaker.

What am I missing? Do I interpret the test procedure correctly? Where does the distortion come from?

 

[peter purpose]

I'm going to need a week to decypher that lot.

 

[901]

In short: the unit I tested fails some of the tests given and sounds horrible. And both units I have built expose this problem (values varying slightly).

I already spent the whole week with trying to figure out what´s wrong and can´t find anything.  :-[

So I´d like to know whether I just misinterpret the test procedure and screw it up by dialling in the wrong things (R75 and maybe R52) or there is another systematic mistake (used wrong components, assumed wrong pinouts, etc.). I don´t think I failed in the built itself, since both units are the same.

I hoped that other people reading this thread have gone through it and can comment on the test procedure and my interpretation. I cannot believe I´m the only one who attempted it???  :-\

BTW here is a picture of the sisters:

 

[peter purpose]

Let me build one of these new pcbs over the weekend and I'll see if there is something wrong.

 

[peter purpose]

Sorry 901, but I haven't had a chance to put one together yet.
I'll get to it as soon as I can.

peter

 

[901]

Any news?

 

[peter purpose]

Any news?

As yet no... haven't had the chance.
Have any that have built one experienced the same symptoms, or is it just 901?

 

[901]

Looks like I´m all alone here...  :'(

 

[zayance]

No you're not, i'll finish it this week.

 

[901]

Great! Happy Easter!

 

[peter purpose]

And I'm out of prison, so I'll get busy.

 

[peter purpose]

Almost there.... cough.

 

[peter purpose]

Slightly more almost there.

 

[peter purpose]

Finally got one built..... sorry for the delay chaps.
Waveforms are looking spot on.
Give me another few hours for listenning tests.

 

[peter purpose]

OK..... listening shows all working hunky dory and as it should, so you can rule out any pcb mistake.
901... take another look at your work.

 

[901]

Peter, thanks for the effort and the info.

I guess you also went through the API test procedure? How does the input behave at 4 (F)? Could you reach 0 dBm? Does it go down and up again when turning up the input?

 

[peter purpose]

I guess you also went through the API test procedure?
Yes, but as I don't have a distortion meter, I leave out that part and just leave the R52 trimmer in the middle.
How does the input behave at 4 (F)?
As it should.
Could you reach 0 dBm?
I could.
Does it go down and up again when turning up the input?
It does.