Generating square waves for audio amplifier testing

[@isoguy.]

Hey, R&R is allowed. Dedicated viewers are greatful for anything you produce, when ever you have time and you feel like making them. Thanks for sharing

[@theblowncapacitor4418]

Hope everything is well. Still my favorite content on the tube. Thank you sir!

[@SuburbanDon]

Hang in there John. We can wait for you.

[@rrangana11]

Years back when I tried with siple Hex inverter but the Schmitt trigger inverter worked the best.

[@markanderson8066]

Might have been interesting to try a cap from signal output to ground (As you did) but ALSO from signal output to Vcc (power) of the micro. The output stage has two transisitors - one to pull the signal high and one to pull it low... So a from output to power and one to ground may have helped balance the capacitive loading. Interesting to see the effect, in any case. Love your videos John!

[@JohnAudioTech]

There is the capacitor across the supply and ground that make the rails low impedance to high frequencies, so I'd expect the same result whether putting the cap from out to Vcc or out to ground. Thanks for watching my channel.

[@pliedtka]

Other than 555, how about clock using Schmitt trigger and some 74xx to clean the edges, but I didn't try it, so can't tell about quality of the rising edge - no fast scope at my place. The freq would be easily adjustable. If the amp input imp would be say 10k, them 500ohm out impedance should be OK. If you need lower impedance then there are some very fast CFT buffers, with high slew rate - Cordell probably mentions them in his book. Just an idea to try.

[@adamp9553]

If the low part of the wave is ground, the low overshoot may have to do with a lack of conductance on that leg of the switching process to ground versus some inductance. Maybe a high speed inverter/buffer could fix that?

[@johnyang799]

What I use is the one from the oscilloscope. Most oscilloscopes have the calibration square wave. Imo, that square wave is good enough.

[@johnneybot9542]

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[@slap_my_hand]

6:11 Why don't you use C? Compilers for AVR and Cortex M produce quite good results. Your code will also be more readable and (mostly) protable between architectures.

[@JohnAudioTech]

I'd like to at some point. It's not a priority with everything I've got going on now.

[@DAVIDGREGORYKERR]

What about a Royer Oscillator.

[@1pcfred]

No 555 timer?

[@JohnAudioTech]

I didn't think of that. From past tinkering, I don't think the 555s slew rate is as fast as the microcontroller's.

[@1pcfred]

@@JohnAudioTech then you want Burr Brown. Personally I wouldn't trust the output of your scope at its peak bandwidth. Perhaps DSO scopes are different than CROs though?

[@JohnAudioTech]

I'm thinking one of those PWM mosfet driver chips would have fast output. My scope is 1Gig samples/sec but it will depend on how they limit the signal. This scope can be made into 100Mhz with hacked firmware.

[@1pcfred]

@@JohnAudioTech the rise time seemed to increase so much when you changed the time base. I'm curious if it aligns with any spec the hardware may have. Though what that is I can't say. I'm trying to look at the data sheet for that chip too. It is dense stuff. A downside to complex hardware is it is complicated. At least with a 555 timer they come right out and say 100 ns rise and fall times.

[@Bencarelle]

Not the 1980s anymore...

[@chrisg6597]

How do you know that some of that ringing wasn't the Scope or the Probe, when you were looking at the output from the microcontroller and that adding the capacitor wasn't the equivalent of high frequency compensation? High quality Scope Probes usually have 2 trimmers for both low and high frequency compensation.

[@JohnAudioTech]

It is possible the scope and probes contributed some. I'd expect similar results if it were mainly the scope and probes. The Feeltech leads could be responsible for the ringing since the ucontroller had none.

[@johnyang799]

It's true. That's a thing to consider. Also just because you can calibrate with scope or the probe using built in square wave in the scope it can be considered as sort of the limit of the scope.Using the calibration signal for square wave is pretty good from my experience.

[@johnneybot9542]

FEEEEEEEEEEEEEEEEEEL TECH !

[@lcarliner]

What about using sawtooth waves as an alternative?

[@jg97873]

Usually a square wave is the worst case scenario, since the high frequency content is higher than other waveforms like the sawtooth. With the rising edge you can see in the time domain the relative stability of the system you're testing (with the overshoot and ringing).

[@johnyang799]

It's usable. One of the edge is essentially the same as square wave. But in general, square wave is to show the step response which is a pretty useful information when you design.

[@lcarliner]

The reason for suggesting use of the sawtooth wave is that the rise agrees more with the amount of rise needed is more likely to approximate what is just needed for accurate reproduction in the hearing range, even at 15000 hertz the necessary frequency range to produce a perfect square wave shape would be far in excess of what is needed. The beauty of the sawtooth wave is that it would reveal the actual transfer (not frequency) linearity of the amplifier. The closer line slope of its rise would quickly reveal why the triode tube sounds most pleasing, then in decreasing rank, the pentode or tetrode tube and the FET (which is equivalent to the pentode, and the worst, the bipolar transistor.

[@isettech]

LOL. Audiophiles. Just because the scope can display a 100 MHZ signal does not mean the amp can reproduce it. 10KHZ from the scope looks square on the scope, and if you put it through an audio amplifier, the amp may have some response out to maybe 50KHZ, but not make 1 MHZ. Use the fast rise time signals for TDR cable measurements instead of testing an amplifier. PWM from the uP is suitable for driving PWN motor control, class D amps, and SMPS drive signals. Are you trying to use an audio amp for a TV antenna amplifier?

[@JohnAudioTech]

Nothing to do with audiophiles. To have low distortion figures at the top of the audio spectrum (20Khz), the amplifier must retain a large amount of open loop gain at 20Khz so that there is headroom for negative feedback to function properly in closed loop. This means the amplifier will have response out to several hundred KHz. I hope to explain this better in a future video.

[@CasualR1der]

If you want actually fast edges look into avalanche pulse generators.

[@ejlockpix]

Hi John!

[@JohnAudioTech]

Hey, what's up?

[@Zentron]

Just play a little Hardstyle through it, Square Waves are common in that music!

[@TONY-gj3jl]

La traccia quadra brucia gli altoparlanti alti