The use of CCS in HT power supplies is well known, however generally misunderstood why it can be a good addition to some circuits. There is an excellent article from Gary Pimm which has been lost and luckily I found it on my archive. Here it is in case you haven’t read it. Worth it as a refresher or for anyone who is new to the subject:
Continue reading “CCS in power supplies”Tag: SiC bias
The low gain DHT pre-amp library
For more than 10 years I’ve been experimenting, designing and enjoying DHT pre-amps. Without over-dwelling on this subject, to me DHT preamps bring the unique sound transparency and detail we all seek for. They can make night or day difference in any system. And is not about gain, hence I’m focusing on sharing this blog entry.
01a Low Gain DHT preamp
How many times I’ve been asked “how do I lower the gain of the DHT preamp?” many builders love the DHT sound and yet don’t really need that gain. Of course when you use a transformer load, step down is the obvious choice. And it works really well when you invest in a very good quality OPT.
However, when you use DHT with high rp, generally most of the low current ones, you face a tough challenge with regard to frequency response.
With the hybrid mu-follower topology (aka gyrator) we have the problem that the gain is fixed to nearly mu.
I’m in love with the DHT sound and in a preamp a 01a and the 801a/VT-25 DHT Preamp Update preamp cannot be beaten in my view. They all deliver a gain of 8 with a hybrid mu-follower topology.
This can be overcome in the following way: Continue reading “01a Low Gain DHT preamp”
300B SE Amplifier Finished!
When everything was going to plan…
This build became one of the quickest and eventually the most painful from all, perhaps not really. However, it was very challenging in the end. I will tell you why in more detail. Yet, it has been a fantastic learning experience.
6e6p-dr Headphone Amp – part 3
I’ve been running with this HP amplifier for a few weeks now and I have to say I’m delighted with it. I matched a pair of 6e6p-dr on my eTracer and after fiddling with the operating point a bit, I settled for Ia=25mA and Va=180V. Anode voltage will depend on the valve as said before, the Russian valve parameters tend to be all over the place. Anyhow, expect anode voltage to be around 170 to 185V. The beauty of the gyrator PCB is that you can adjust the anode voltage with the trimpot.
Continue reading “6e6p-dr Headphone Amp – part 3”Diode cathode bias
Playing with the semiconductor curve tracer I did a quick test of potential candidates for diode cathode bias:
The popular HLMP-6000 is a superb LED with its low impedance. The SiC diodes have proved to be a great match with an impedance lower than 2Ω. Bias voltages will be around 0.7-0.8V for low currents. The classic Schottky SB540 has a very low impedance, but its forward voltage is so low that is not practical for diode cathode bias. What surprised me was to see the 1N4007 to be a good match. The impedance is higher than the LEDs or SiCs, but good enough. The green LED on the opposite extent has a significant dynamic resistance over 10Ω.
Interesting to see that a minimum of 2mA should be run through with small signals to ensure the diode operates in the linear region. The higher the better. An arrangement with an extra source of diode current (e.g. LND150 or DN2540 CCS shunting current to the diode) can be used when dealing with lower cathode currents due to the valve being used.
Further tests are required….