Author Topic: BJT doubler, I am going mad ... am I??? hihi haha  (Read 262 times)

Steben

BJT doubler, I am going mad ... am I??? hihi haha
« on: October 23, 2020, 01:47:23 PM »
Ok, so my thoughts dwelled into class C amplifier stages. The classic cathodyne is used again.
As you can see the voltages at the emitters are nicely cut at the center voltage of the input, being zero.


Now one would think.... wow if we sum those voltages, we have a somewhat full wave rectifier, right?
Well... no...



What the?


« Last Edit: October 23, 2020, 01:51:08 PM by Steben »
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rutgerv

Re: BJT doubler, I am going mad ... am I??? hihi haha
« Reply #1 on: October 23, 2020, 02:06:12 PM »
Without knowing anything about cathodynes, I would guess perhaps the phase shift of the capacitors is in practice slightly different between positive and negative half.

anotherjim

Re: BJT doubler, I am going mad ... am I??? hihi haha
« Reply #2 on: October 23, 2020, 02:37:26 PM »
What's the output directly at the mixer amp output like? If you have an assymetric wave and it's filtered, it gets bent due to altered harmonic amplitudes?
My name is Fudd. F, f, f, f, Fudd.

amptramp

Re: BJT doubler, I am going mad ... am I??? hihi haha
« Reply #3 on: October 23, 2020, 03:00:02 PM »
You have nowhere for the base current to flow in the first image, not even to ground (which would be a good choice).  You pull a positive pulse that charges up the base capacitor and then what?  The base charge has to wait for leakage to remove it and it stays positive until then.  It would be similar to blocking or gulp distortion in an amplifier.

Steben

Re: BJT doubler, I am going mad ... am I??? hihi haha
« Reply #4 on: October 23, 2020, 03:33:16 PM »
You have nowhere for the base current to flow in the first image, not even to ground (which would be a good choice).  You pull a positive pulse that charges up the base capacitor and then what?  The base charge has to wait for leakage to remove it and it stays positive until then.  It would be similar to blocking or gulp distortion in an amplifier.

If I add resistors to ground at the bases of the C transistors, output at emitters becomes a fundamental sine wave of 0,5mV. Probably because the coupling cap charges just a little as in a clamp.
Rules apply only for those who are not allowed to break them

Steben

Re: BJT doubler, I am going mad ... am I??? hihi haha
« Reply #5 on: October 23, 2020, 03:54:26 PM »
Lol, with a discrete BJT mixer stage, it works  ;D



Rules apply only for those who are not allowed to break them

iainpunk

Re: BJT doubler, I am going mad ... am I??? hihi haha
« Reply #6 on: October 23, 2020, 05:29:12 PM »
was the voltage at the non inverting side of the opamp actually clean?? or was it contaminated? how about a big capacitor to ground from there?
why use drugs when you can just hold your breath for like a minute and then stand up from your seat really quickly.

Steben

Re: BJT doubler, I am going mad ... am I??? hihi haha
« Reply #7 on: October 25, 2020, 07:04:46 AM »
was the voltage at the non inverting side of the opamp actually clean?? or was it contaminated? how about a big capacitor to ground from there?

I'll get into that, since I use a BJT stage it works great (in sim).




Output with pre drive: https://sndup.net/9d5w/bjt+double+nil.wav
Output with low drive: https://sndup.net/9tr3/bjt+double+nil+2.wav   (sounds gated, no?)
« Last Edit: October 25, 2020, 07:07:52 AM by Steben »
Rules apply only for those who are not allowed to break them

iainpunk

Re: BJT doubler, I am going mad ... am I??? hihi haha
« Reply #8 on: October 25, 2020, 10:58:39 AM »
that sounds great! fairly clean!

i think that 2nd one sounds slightly gated indeed
why use drugs when you can just hold your breath for like a minute and then stand up from your seat really quickly.