A belated test of this simple, yet effective PCB. I made it as small as possible, however in order to provide flexible connections, it’s actually double the size. Still at 4 x 4 cm is small enough.
You can solder the 2mm PCB connector or alternatively you can use the 2-pole block connectors. It provides the full functionality for a cathode follower, however you can bypass some elements when using it as a tail CCS for a differential pair for example:
You can use either R2 or P1 to set the CCS current. T1 is any high hFE NPN you have at hand. I use BC547C because I have plenty. For the top device you have 2 options in order to accommodate different power requirements. I use the 2SC3503 as it has low capacitance and works up to 300V with 7W of PD. T2 is for TO-126 devices and T3 is for TO-92 ones. You can use a plethora of different NPNs here depending your voltage requirements.
If you want to self-bias the cathode follower you have R3 and R4. If not required, R3 should be replaced with a wire jumper and R4 ignored.
R1 set the current for the LED voltage reference array for both T2/3 and T1.
R11 is a build out resistor. Again if not needed, can be replaced with a wire jumper.
Cathode Follower Test
As per my previous test for the SLCF board, I used the 6J52P/6Z52P high-gm pentode in triode mode. Here is what I breadboarded quickly this morning:
Being lazy I didn’t play much with the operating point. I left the CCS set to 15mA, not 20mA as per previous example. The results of this stage are impressive. Here is the neat frequency response:
The stage is flat up to 4.2Mhz. Also the distortion is extremely low. Here is an example of the harmonics at 3Vrms:
You can see the level of harmonics is very low with a THD of 0.003%. It’s just down there.
Here’s a picture of the rat nest!
A bit less HF response due to the lack of bootstrapping in the anode and similar distortion performance to the SLCF in terms of distortion. Both stages are operating at different bias levels so can’t compare apples to apples.
PCB prototype was a success…
Looks great! I especially like all the connection options. I used the same style CCS as the tail load in a differential shunt cascode build (inspired by your articles). Although I haven’t tried it yet, the same board can be adapted as an anode load. Did you give any thought to that while designing yours?
Hi Tim, great to hear from you. I’m glad the shunt cascode worked for you. A great topology.
I didn’t think of this CCS as anode load as I do have another PCB which is for CCS using depletion FETs cascoded. That can be used also for tail, but is a bigger board.
The mirrored PNP version of this circuit is better fit for anode load. Problem with this one is the high output impedance gets compromised by the LED array impedance through R1.
Keep working on your stuff, I like it 🙂