CCS as anode load.

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pre65
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#1 CCS as anode load.

Post by pre65 »

As some of you might know, on my GK71 amp I use an Ixys 10M45s CCS device as the anode load on the 12HG7 driver valve. This was because I had no anode chokes at the time.

There have been "mutterings" ( :wink: ) as to the desirability of this approach, but it sounds good to me. :)

Anyway, I've just found some data about this method from P Millett, and thought I would share it with my chums. 8)

http://www.pmillett.com/current_source.htm
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#2

Post by little eddy »

I to used this approach as a temp solution on my 41MPs but also sounds good to me. I'll be absolutely chuffed if the inter stage txs are an improvement.
TD-125/RB250/MC25FL & 'Snail' phono, NAS/SBT with CS4398 DAC, 41MP pre & MoFo Power, still messing with OBs.
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andrew Ivimey
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#3

Post by andrew Ivimey »

i.m.h.o. that a choke load sounds better as will an interstage transformer but the ccs is simple and of course it works too!
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#4

Post by IslandPink »

I would tend to agree, although the CCS will sound better in the low bass as it has no time constant down there ( chokes always have limited inductance in practice ) . I haven't heard that particular CCS though ....
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#5

Post by pre65 »

They say a cascode CCS sounds better. :wink:
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#6

Post by andrew Ivimey »

'They...' who are these mysterious, shady and altogether the sort of types who hide in dark places !?!?
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#7

Post by IslandPink »

The Cascode CCS Mafia, Andrew :shock:
Most CCS's these days are cascodes or more complex. The cascode bit increases the impedance of the CCS and reduces the capacitance seen by the valve - which improves the sound. You can build a simple CCS with one transistor, but it sounds sh]te .
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#8

Post by little eddy »

pre65 wrote:They say a cascode CCS sounds better. :wink:
I tried this with my phono stage as they say the load goes up significantly thus further reducing distortion.

But when I tried various 'set' resistor values, unless I'd wired them up wrong, found that the normal resistor/current relationship didn't apply and it was difficult to adjust for larger currents, 8.5ma being the highest I could reasonably manage.
TD-125/RB250/MC25FL & 'Snail' phono, NAS/SBT with CS4398 DAC, 41MP pre & MoFo Power, still messing with OBs.
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#9

Post by pre65 »

I spent some time on Google looking for information on how to set the current on a cascode CCS, but found nothing I could understand. :( :?
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#10

Post by pre65 »

I've ordered 4 X Supertex DN2540N5 mosfets to try a cascode configuration.

Hopefully I will find some info on how to configure them. :)
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#11

Post by pre65 »

Found this diagram. It's for 38ma but that's probably near enough for me.

http://i869.photobucket.com/albums/ab25 ... 53d5ec.jpg
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#12

Post by IslandPink »

You didn't buy some of the K&K Audio PCBs for them, then ?
:D
I built some up recently. I have the circuit somewhere ...
Watch out for static - Nick warned me they are very sensitive to that . I got them in & working OK for the small 6N6P pre-amp unit I built ( CCS-loaded ) .
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#13

Post by Paul Barker »

Phil in the link you found current set by R1 and adjust trimmer parallel resistance. result would be the same current with just a single mosfet stage.

You don't need a formula, just put a 150 ohm pot in R 1 position remove tha existing adjust pot, and adjust it to set the current you desire. Change out for a fixed resistor of impeccable credentials afterwards. Or perhaps have a choke wound with the correct dc resistance in place of R1 for a possible added benefit and at least no anticipated detriment.

Don't touch the mosfet package with your fingers, don't let static anywhere near it, if it doesn't kill it in one it will precipitate a short life.
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#14

Post by simon »

This link might help Philip? SY discusses the cascode CCS and shows how to test it for the required current. As Paul says, just replace R5 in fig 5 with a pot/trimmer and set the current.

http://syclotron.com/ImPassePreamplifier.pdf
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#15

Post by thomas »

simon wrote:This link might help Philip? SY discusses the cascode CCS and shows how to test it for the required current. As Paul says, just replace R5 in fig 5 with a pot/trimmer and set the current.

http://syclotron.com/ImPassePreamplifier.pdf
That's a good article- wish I'd seen it before I put mine together!

This might be a case of the blind leading the sighted but here's my effort. Two ccs's on one perf board. Both DN2540's share a heatsink as I didn't really know what I was doing (!) and the variable resistor is a 0-200r multiturn jobbie. Carbon stoppers as close as I could. The extra resistor is for optional mu out.
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