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Seeing as Kevin sells both current sources and plate chokes, I was wondering if he could elucidate about his experiences designing and advising with both.
Specifically, I'm curious if there's certain topologies, technical situations or signal chain considerations (phono pre-amp, linestage, etc.) that would cause one to be preferred over the other. Also, any descriptions of schemes where the difference between the two was more audible would be helpful.
I've googled this a bit over the last couple days but felt asking Kevin directly would be the best.
Thanks.
A plate choke presents a high, but varying, impedance. A CCS presents a much higher and much more constant impedance. In general, a CCS isolates from the power supply and controls the signal current path better. It also keeps a tube operating in the most linear way. So, for input and small signal tubes, and places where voltage swing is modest, a CCS is generally a better choice.
But, when you need a large signal swing, a choke is better. A choke can swing above B+. So, for a 300B output tube, for instance, to get full power with a CCS load, you'd need a PS that was hundreds of volts higher than B+ and a CCS that can dissipate tens of watts. Instead, a choke can come close in performance without the overhead.
Thank you so much for the information.
I have three projects I'm working on that could potentially benefit from either chokes or CCSs. My current power amp is a K&K audio modified ST-70 that I'm pretty happy with, but I wanted to make sure the pre amps I'm building didn't impart too much of their own signature on whatever I played.
My observations having used both is that use of an audio choke (experience limited to Lundahl) in the plate instead of a cascode CCS (with IXYS depletion mode MOSFETs) results in a slightly "softer" sound. By "softer" I mean that the CCS is perhaps more precise about transients and gives things a slightly brighter sheen, but nothing is really lost with choke loading by comparison. In my view the choice is guided by overall voicing needs and by cost for medium and low Rp tubes ( <15K). For higher Rp tubes (extreme example = 12AX7), the CCS is the only choice of the two that will really give extended high frequency performance.
So if I have a design that needs a bit more air on the top end, I would choose a cascode CCS, but if the choke hits it just right, the sound with the choke tends to accommodate tipped up recordings a bit better.
Kevin Carter
K&K Audio
www.kandkaudio.com
Thanks Kevin!
Would you say both are superior alternatives to a plate resistor? Do you prefer a simple resistor in some applications?
Your insights are helpful.
I've never had a case where I preferred a resistor to either. Often the difference is large enough to be surprising at first.
Kevin Carter
K&K Audio
www.kandkaudio.com
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