Tag: bartola pcb

DHT Supply PCB

I took me a couple of years but eventually found the time to build the BOM and a simple documentation guide for the DHT LT supply PCB. I’ve been using this PCB for a long time on most of my DHT preamps and in my current 300B SE Amplifier.

It’s a 16 x 8 cm board which can be stacked for a stereo DHT stage. Enough flexible is provided for all sort of filtering combinations (either choke to cap input supplies).

Some may say is a killer, but I add a common-mode choke to suppress HF noise from mains. I design my supplies with a no-compromise thinking and best possible components (e.g. including split-bobbin main transformers), chokes and capacitors to deliver the lowest noise possible to the filament supply.

This board doesn’t replace the filament regulator (e.g. Rod Coleman regulator), it’s just the raw supply circuit needed before them.

I will sell the remainder of my stock of these lovely ENIG finished PCBs. You can order them here.

LL1943 / LL1933 SUT PCB V02 – Balanced option

After a long time, decided to update the PCB of the LL1943 SUT to provide extra flexibility on the grounding connection. This is in essence to ensure no ground loops and noise when either using balanced or un-balanced cabling from the cartridge into the PCB:

LL1943: note the additional jumpers added

The additional jumpers are in line with the recommendations from the Datasheet. Here is the diagram:

For a fixed connection (like in most of the cases once preamp has been tuned/optimised) you can replace the jumpers by solid core wire jumpers soldered to the pad for best connection and performance.

This PCB is also for the LL1933. Basically is the same SUT but with 1+1:8+8 instead of 1+1:16+16 windings.

I made a small batch (I won’t need more than 2 or 4! myself) so the remaining will go on first-come-first-serve basis.

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 filament supply

In the process of rebuilding my old 300B amplifier, I decided to make a new filament power supply. It all came up around the components I had at hand, so it could’ve been improved but that meant extra cost:

I have a pair of custom-made JMS transformers with multi-taps secondaries. This helps me tweaking the right output voltage. Anyhow, any 15V transformer would do. Perhaps you want 14V to ensure you don’t dissipate too much on the filament regulators (e.g. Rod Coleman regulators)

I used my flexible LT supply PCB which allowed me to build this in less than 1 hour. I also used some existing chokes made in the UK by “Spirit” which are ok for this purpose. The Lundahls are in use, so can’t reuse them:

300B filament board ready

I used some SOT-128-2 schottky rectifiers but any other should work as well. Resistors are wirewound and the CMR choke is what I had in stock as well. A simple 15mH/3A should do fine.

The output measured well at 9V with a 6R load which dragged 1.5A. A bit more than the 300B but should be a good indication of performance. Also ripple level is good at 2.5mVrms. The rest will be cleaned up by the regulator itself 🙂

 

DHT Folded Cascode Experiments

Here we are on holidays and surprisingly I struggle to find any free time in which I can sit down in front of a tablet and write this blog entry. This is actually quite good as it’s a sign of me being disconnected and looking after my daughters. Life is good.

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Tail CCS PCB test

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.

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Cap Multiplier test

I managed to find the time this weekend and do a quick test on the Cap Multiplier PCB. It turned out that I missed a thermal pad on the PCB so had to add a short jumper. Nothing major, but the PCB needs adjustment.

Below is the diagram of one of the ways the PCB can be used. This is the most complex circuit, a basic one can be wired instead. The CCS (M1 and M3) provides better PSRR as well as regulation. A stable current is fed to R4 and P1 to set the voltage. C2 is the cap multiplier and the M5 used can be any suitable MOSFET. T4 provides current surge protection to the MOSFET as well as short circuit. R7 sets the current limit.

The boards fits various film caps, I have some WIMA DC Link which are great and fit perfectly:


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