♫♪ My little cheap Circlophone© ♫♪

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#2,281
Hi @minek123

I am building my own board and want to use the Cascode implementation for the BJT Circlophone. I know you posted a schematic for the same in one of the previous posts.

1) How does it work, with reference to distortions compared to using 2 Zeners?
1667662652507.png


2) Also is there a difference in working for the CCS shown in the schematic vs the one below this line.
1667662717352.jpeg


Could you or Elvee guide me to the correct one? The idea is to be independent of the supply changes if needed due to some unforeseen reason one being output power transistor availability.

Could Elvee or You explain how the Cascode transistor works? Does it work like a variable voltage-blocking Zener diode? I am pretty new in this discrete amplifier side.
 
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#2,282
How does it work, with reference to distortions compared to using 2 Zeners?
Click to expand...
The same. Theoretically it should be slightly better, but you not gonna see any difference in real life or in a sim.

Also is there a difference in working for the CCS shown in the schematic vs the one below this line.
Click to expand...

The 2nd CCS (more complex one) is better - according to Elvee's sims - but I doubt there will be any difference
in real life.
 
#2,283
minek123 said:
The same. Theoretically it should be slightly better, but you not gonna see any difference in real life or in a sim.



The 2nd CCS (more complex one) is better - according to Elvee's sims - but I doubt there will be any difference
in real life.
Click to expand...
Hi @minek123

Thank you for the update on my query. 😊

Is the cascade modification voltage range dependent?

I will be running the circlophone via a 24-0-24 transformer

My configuration :
Output device is MJL21194 and VAS is 3503 also the current sense section is 2N5551.
 
#2,285
I second Minek: all of these improvements should bring tangible benefits, but the measured differences are completely insignificant.
If you are patient enough, you can probably locate these results somewhere in thread, but it isn't worth the trouble.
The cascode and CCS have a practical advantage: they make the C completely supply-independent.
 
#2,289
Hi @Elvee

I am facng some difficulty in using the attached ASC file with the input voltage set at 2VPP, the distortion are as displayed.
Also R9 and R12 ( R20 and R21 in ASC ) Rrespective values has been changed to 39 as per minek's asc changes, it seems that the simulation does not start with Cascode and 56 ohm.

along with R2 as 1k on the LTP common emittor resistor as per Minek's drawing

and some times it will not run only just keep re-iterating....
1668934889421.png


the below screenshot is when the input voltage is 2 volts and supply voltage is + / - 32volts,
something is making it break
1668939767703.png


there is something i am missing out ie way to operate and what should be value of

Below is with VIN as 1.5v set in the source module.
1668940360872.png
 

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#2,291
Here is my sim (50V rails) with simpler CCS.
My values (especially gain) were adjusted to 50V rails; not 25V rails.
With lower rails, you need to lower the gain, or Vin to make sim work.
In your sim I see Vin=2V - that's way too much, especially for 25V rails, obviously the amp will be clipping.

I quickly run a sim of the almost-original circlophone (with zeners) and 50V rails, and it's clipping in much nicer way.
 

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#2,292
minek123 said:
Here is my sim (50V rails) with simpler CCS. It works fine.
My values (especially gain) were adjusted to 50V rails; not 25V rails.
With lower rails, you need to lower the gain, or Vin to make sim work.
Click to expand...
I intend to run from 30 to 35 volts (0-24 0-24 Transformer) and i observered that making 56ohms as 39 and reducing the FB to near half , starts the simulation instantaniously but if FB is at 10k and R9 and R10 at 56 ohms than the sim does not start.
 
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#2,294
minek123 said:
Which ones are R9/R10 ? on which schematic?
To lower the gain, leave 10k resistor alone, and increase the value of the 470 Ohm resistor..
Click to expand...

From the Below Screenshot - I had reduced R23 ( FB ) to around 5K and R20 and R21 to 39ohm (which orginally are 56 Ohm) after which i was able to use input signal upto 2v ( atleast the simulation ran )

so as per your suggestion i have now reverted R23 to 10k and increased R36 to 1K from 470. I hope it is R36 as the below screen shot you were suggesting to increase.
1668962804808.png
 
#2,299
Elvee said:
The value of R20 and 21 is linked to all the rest of the circuit, changing them in isolation could bring problems. At the very least, you should modify R12 in the same proportion
Click to expand...
Hi @Elvee thank you, experimented with R12 from 22 to 33 and R to around 680 does allow me to have 2vpp, below is the screen grab @20kHz. If somehtin off please let me know, Also @minek and @rajesh thank you very much for the support.
1668965177234.png
 
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