germanium transistor makes square wave round on my digital scope.....

[darron]

i had a germanium booster circuit and had the gain/level knob set so that gain sounded about unity. i fed it a weak square wave signal of less than 1V peak-to-peak which comes through perfectly square on my digital velleman scope. activate the unit and the square wave starts to round off its edges very slightly. I fed it around 5000 Hz and a signal so weak that it is way before the point where you hit the headroom limit. the knob on the boost adjusts actual gain like the SHO, not volume, so it wasn't pushed to its limits then just voltage divided down.


so it made me start thinking about what 'smoother' results germanium may have from mojo (audible, not just mental) to explanation. it was an AC128 so t wouldn't have radio frequency sort of response, but would it just be a frequency response thing for the transistor? you may expect rounded clipping, converting a sine wave to square for sure, but i wasn't expecting this. usually we test with sine waves, but they are already so round that we might not be able to see the change in shape being this small of a difference.

anybody have some facts/readups to follow this? (: 

photos are nice too.

[aziltz]

its probably less to do with the Ge Mojo juice, and more to do with filtering.

Square Waves involve a lot of strong harmonics to do what they do.  Think about it.   You need very fast frequencies to make out the detail in a sharp corner.  The sharper the corner, the higher the frequency.  We're talking 7th, 9th, 13th and upwards.  Run a square wave through any low pass filter, even with a higher cutoff that the ear might not detect and you'll see some rounding.

[darron]

its probably less to do with the Ge Mojo juice, and more to do with filtering.

Square Waves involve a lot of strong harmonics to do what they do.  Think about it.   You need very fast frequencies to make out the detail in a sharp corner.  The sharper the corner, the higher the frequency.  We're talking 7th, 9th, 13th and upwards.  Run a square wave through any low pass filter, even with a higher cutoff that the ear might not detect and you'll see some rounding.

so the good point to observe may be frequency response of the coupling capacitors as much as anything else.. hmmm... (:

[earthtonesaudio]

If your boost is wired like a Rangemaster the only low pass filtering is invisible, in the form of the collector-base capacitance and the bandwidth of the transistor.

If you have it wired like a SHO with output-input feedback, then you also have the capacitance across that feedback resistor.


But in principle, I agree with Aziltz.  Clipping by itself should make the wave squarer, not rounder.

[darron]

If your boost is wired like a Rangemaster the only low pass filtering is invisible, in the form of the collector-base capacitance and the bandwidth of the transistor.

If you have it wired like a SHO with output-input feedback, then you also have the capacitance across that feedback resistor.


But in principle, I agree with Aziltz.  Clipping by itself should make the wave squarer, not rounder.

very much like a SHO. and i agree, clipping would normally make things look more square. i thought i'd jump in and cover that the circuit shouldn't be self-distorting because everyone may then think that's what i meant.


thanks for your responses guys (: