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Ess9018, Diff. Pair and your CCS...will this work ?

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Posted on February 11, 2017 at 08:31:55
multiblitz
Audiophile

Posts: 9
Joined: April 29, 2012
I have to admitt that I am using your CCS already in a differential pair for my power amp amd it works very nicely.

I am now think how could I upgrade my unbalancer with your ccs as well:

http://www.tubecad.com/2011/03/22/Unbalancer%20DAC%20Schematic.png

Currently A lm334 is used as current source. I guess your cascode current aources will do better ?

I am a bit careful now how to apply your ccs as

- the ess9018 has a current output and a voltage offset of 1.6V at its pins.
- currently, the lm334 simply makes the tube sink 5mA, no matter how positive the dac already is charging the geid of the tube.
- now your ccs use as well a negative voltage of -20V to work...

...I am not completly sure, if this nebative voltage influences the absolute grid voltage which normally will be set by the dac plus the tube....I dont want to destroy my dac...maybe a bit to cautious, bit I thoight I ask you first.

 

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RE: Ess9018, Diff. Pair and your CCS...will this work ?, posted on February 11, 2017 at 12:18:27
JKT
Audiophile

Posts: 469
Location: Midwest
Joined: November 26, 2002
Looking at the schematic you would need to build a negative PS (about -20V to -30V) to provide enough voltage margin to operate a cascode MOSFET current source. Although these CCSs will operate at 5mA current they perform better at currents greater than 10mA. In my experience a BJT cascode using BC549C transistors will give greater performance at currents less than 10mA. This would still entail building a negative PS.


"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln

 

RE: Ess9018, Diff. Pair and your CCS...will this work ?, posted on February 11, 2017 at 16:04:04
multiblitz
Audiophile

Posts: 9
Joined: April 29, 2012
I know that I need a negative supply of approc. -25V...my issue was if this negative supply changes the grid-voltage ? Or will still the Dac and the tube automatically sum up the offset of the dac with the negative cathode-grid voltage needs to allow for the bias the ccs has defined ? Maybe my thinking is twisted...

...I try to explain:

- The CCS has only two connections: Positive and negative. On th Negative we apply -25V. On the positive we have the connected cathodes of both tubes, right ?

- the tube will now develop a difference of voltage between cathode and grid which is equivalent to the current, let's say grid will become now -4V if cathode would be 0V.

-Now the Dac is connected with its +1,6V positive voltage offset to the grid.

- So which voltage will we now have at the grid ? Are the -25V completely consumed by the ccs ? Or is the negative supply influencing the absolute voltage on the grid referenced to ground ? The lm334 works currently, but has as well no negative supply...

 

RE: Ess9018, Diff. Pair and your CCS...will this work ?, posted on February 11, 2017 at 16:55:38
JKT
Audiophile

Posts: 469
Location: Midwest
Joined: November 26, 2002
The CCS will set the grids to wherever they need to be so the tube conducts the current set by the current source. The positive side of the negative supply will need to be connected to ground.


"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln

 

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