Tag: Fixed Bias PCB

300B SE Amp: build part VI (Fixed Bias Board)

And the fixed bias PCB is completed. All individual PCBs mounted over a ground plane PCB. It will be a stacked build. On top of this PCB, another one will hold the driver. Firstly the D3a in a hybrid mu-follower configuration:

PCB mounted, now to wire them
Nice dim glow from the HV LED array. Boards are working properly and the heatsinks good enough for 20mA idle per channel.

Tested and bandwidth of these source followers is nearly 10MHz with plenty of current drive at 20mA idle.

300B SE Amp: build part V (Fixed Bias)

Last year I developed a voltage reference using an HV LED. Unfortunately these devices from OSRAM seem to be discontinued. I managed to buy enough parts for my own use though. What is interesting from these LEDs is that the dynamic resistance is low. About 150Ω with good current, or between 300Ω to 500Ω.  Tempco is very low and with such a low dynamic resistance, they are great for creating a voltage reference with a stable CCS:

The LEDs are extremely bright and found that with a 1mA current are dim enough whilst retaining the stability needed. I have a cap multiplier arrangement and the LED array is fed by a stable CCS. Jumpers on the board allow bypassing LEDs and there is also the option to use a trimmer for variable voltage adjustment. Very handy for screen grid supply and phono stages. The reference voltage is extremely quiet with more than 100dB PSR.

OSRAN 67V LED curves

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