Waveform Interpretation needed.

[laatsch55]

Ok Joe, at 15Khz I'm getting this out of the 700.

 

[jbeckva]

Notch/xover/IMD distortion? Does bumping the bias up a tad help any?

 

[laatsch55]

That was my next trick Jer. I've seen this before but not with the little curly Q in it.

 

[mlucitt]

Lee, is the distortion most obvious at 15kHz or does is occur across the frequency spectrum? If it is crossover distortion, you would think it would increase with power out but not change much across the spectrum.

This would be a good time to check the bias level and then look at the trace with 50mV higher and 50mV lower to see how that affects the trace. But you probably already thought of that...

Mark

 

[orange]

Where are you reading this at? I just jumped in but your 'notch' looks like a wall to me.

 

[Gepetto]

You have the 10 ohm resistor installed at R77 Lee?

 

[laatsch55]

Yes I do.

 

[Gepetto]

My next concern would be C11L/R then Lee.

 

[laatsch55]

As you said, "Every microfard has it's nanohenry"

 

[laatsch55]

Lee, is the distortion most obvious at 15kHz or does is occur across the frequency spectrum? If it is crossover distortion, you would think it would increase with power out but not change much across the spectrum.

This would be a good time to check the bias level and then look at the trace with 50mV higher and 50mV lower to see how that affects the trace. But you probably already thought of that...

Mark

Mark, I wasn't ignoring you Bud. I had tried differing frequencies, it got less extreme as the freq got lower, had not tried varying the bias.

 

[mlucitt]

No problem man, we are both very busy and that sure beats the alternative. This is moving week for me at work; same client, new building. Just adding drama to working with the government.

I figured that you saw the notch at 15kHz because that's where it was strongest. It will be interesting to see if turning on the transistors sooner/later with the bias moves the distortion or makes it better/worse.

Mark

 

[laatsch55]

I feel the same way Mark. Joe's comment about C11 got me to thinking ,---the changing distortion with freq would lead ya to believe a cap is involved because of an electro's instability with increasing frequency?????

 

[Gepetto]

C11 is also the bootstrap cap and affects the ability of the amp to transition from high side drive to low side drive.

I see the effect of the bootstrap cap on the high side waveform starting normally at about 27 KHz as distortion of the positive side peak starting to show up.

 

[laatsch55]

Hence your research to get rid of it via the new board hooks??

 

[laatsch55]

So, am I looking for higher ESR or drift from UF rating?

 

[Gepetto]

Hence my research Lee, correct. Not sure on your second question Lee. It probably has nothing to do with C11 in your case but just pointing out potential areas. Do you have the Zoebel network installed at the outputs?

 

[laatsch55]

Ahh.... that was my first thought Joe. It is one of those that is installed between the output rails on the back wall. Second question was what was I looking for with C11, as in it potetially being the problem and what was I looking for in it.

 

[laatsch55]

I changed all outputs and drivers also, so this may have affected it also.

 

[Gepetto]

Black Gates are new old stock generally so just something to check. They have usually been sitting around a long time.

 

[laatsch55]

Ok Joe.