Burns B3 Guts

Posted: 10/9/2019 11:25:08 AM
H3rv3

Joined: 10/9/2019

Hello,

Any progress on the schematic of the volume plate?
Could the second IC not be a gate IC? using only one inverter gate cannot make the oscilator, the frequency of which should match the resonance of the LC circuit that would pull the signal to 0 through the diodes at resonance and less so when the resonance is affected by the hand, that means the antena is not connected where it is shown.

Posted: 10/9/2019 3:04:18 PM
edavid

Joined: 9/2/2019

Hello,Any progress on the schematic of the volume plate?Could the second IC not be a gate IC? using only one inverter gate cannot make the oscilator, the frequency of which should match the resonance of the LC circuit that would pull the signal to 0 through the diodes at resonance and less so when the resonance is affected by the hand, that means the antena is not connected where it is shown.

1. The volume circuit IC is definitely a 74C14

2. Of course you can make an oscillator out of one Schmitt trigger gate: http://electronics-course.com/schmitt-trigger-oscillator

3. I don't understand your comment about LC circuits - there are no inductors used in the Burns circuit   OK, I will take another look

Posted: 10/9/2019 7:17:25 PM
H3rv3

Joined: 10/9/2019

Thanks for the confirmations.
1. Good to be sure, i could not find one in my local shop though
2. Right, i was wondering why the same circuit as the pitch oscilator was not used. Any idea?
3. In the schematic proposed by Goño, there is a 100uH inductor. This is not the case? I though that would form a band pass filter. Other circuits seem to modify the center frequency of the filter with the antena rather than changing the oscilator frequency. Just wondering how this one works.

I will be building as per the latest diagram from Practical Electronics (06-07-08/2019), waiting for the boards, but also interested in building with the B3 method.

Would like to hear if anyone has tested it.
Thanks

Posted: 10/9/2019 7:29:25 PM
Thierry

From: Colmar, France

Joined: 12/31/2007

@edavid: Why do you tell wrong things here? There is one fixed inductor in the B3’s volume demodulator circuit.
I’d suggest that we let guessing and speculations outside and apply scientific criteria to such analytical discussions: Tell only what had been proven and verified!

Posted: 10/9/2019 7:40:35 PM
edavid

Joined: 9/2/2019

@Thierry, if you have the volume side schematic, please post it instead of just sniping.

Posted: 10/9/2019 8:41:40 PM
Goño

From: Guadalajara, Jalisco, Mexico.

Joined: 7/5/2019

Thanks for the confirmations.1. Good to be sure, i could not find one in my local shop though2. Right, i was wondering why the same circuit as the pitch oscilator was not used. Any idea?3. In the schematic proposed by Goño, there is a 100uH inductor. This is not the case? I though that would form a band pass filter. Other circuits seem to modify the center frequency of the filter with the antena rather than changing the oscilator frequency. Just wondering how this one works.I will be building as per the latest diagram from Practical Electronics (06-07-08/2019), waiting for the boards, but also interested in building with the B3 method.Would like to hear if anyone has tested it.Thanks

Puedes probar CD40106 o CD4584 incluso alguna compuerta NAND como el CD4093.
Por lo que veo en el lado del volumen hay un oscilador un filtro pasa banda y un rectificador, si tuviera uno ya estaría el esquema verificado aqui.
Saludos.

Edit by moderator: You are not the only member here who is not a native English speaker. But this is a forum in English language, thus I ask you kindly to do the same as I do and to write in English, as a matter of respect and courtesy for other readers. You and I, we may like it or not, but English has established as a standard for international exchange, especially in the technical and scientific domain. Even the international medical science has switched over from Latin to English, long time ago.

Posted: 10/9/2019 8:48:17 PM
Thierry

From: Colmar, France

Joined: 12/31/2007

I don’t have a drawn schematic and I do not need one. The circuit is simple, self-explaining and very easy to understand as I could find out while repairing about 12 of these beasts over the last 10 years.

In case someone wants a deeper understanding: There is a single CMOS inverter based volume oscillator whose frequency is fix. That frequency is coupled onto a parallel resonant LC circuit whose amplitude varies with the parallel volume antenna capacitance. A simple diode rectifier gets a control voltage from this which is then used to modify the bias (and thus the amplification factor) of the output transistor. All that can be tracked down within 2 minutes with an oscilloscope. No black magic.

Basically, the volume circuit has the same principle of operation as the well known Jaycar, Enkelaar, and Subscope theremins. The differences are just that these use LC instead of RC oscillators and that they have discriminator stages with fixed frequency while the volume antenna varies the oscillator frequency. But the principle is the same, the so called Foster-Seeley discriminator, one of the first and simples FM demodulators.

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