CCS in power supplies

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:

01a Preamp by Nash

It’s always satisfying to see someone else enjoying the end result of their build work. Here’s a great example of Nash building his take on the 01a low gain DHT pre-amp:

Hi Ale,

Its now over two months since I have been listening to your low gain version of the 01A preamp in concert with a Slagle AVC after it.

Over a span of a few years I have built several preamps and I can honestly say that this one is substantially better than any of the others. As a classical music fan I value attributes like clarity, timbre, body, weight and speed and your design delivers! I would like to use the analogy of a superb cake with icing- the cake is the 01A pre and the icing is the AVC. Thank you for a great design!

I have recently replaced RMu and the divider resistors with the TT Electronics PFC series SMD resistors mounted on a 1206 adapter. These are tantalum nitride resistors and they sound wonderful in this application. 

Further, I am getting interested in your 300B SE builds. Are you using a preamp before these? Please send me a link to your latest work in this area which you feel I should consider.

Regards,
Nash Bapasola  in NJ

Continue reading “01a Preamp by Nash”

UV-201a final version – finished!

After doing all the soldering part (which I enjoy much), the preamp is now finished. It sounds as good as the original breadboard:

For the curious ones, here you have a picture of the inside:

The teflon sockets are bolted straight into the 4mm top aluminium plate. No microphonic noise this way. Rod Coleman V7 regulators set to 200mA. A pair of Russian Military NOS wire-wound resistors in parallel provides the filament bias. The gyrator PCB is set as per original circuit and each valve at 3mA. These are DC coupled to the MOSFET follower PCB set at 10mA each. The output is then taken out from a pair of FT-3 teflon caps.

Now to enjoy this beauty!

Gyrator PCB board updated (Rev06)

After some further testing and prototyping, I’ve updated the gyrator board PCB to provide additional protection to the lower FET device with:

Protection Zener (D3) between drain and source (through-hole)
Back to back protection Zeners (D1 and D2) between gate and source to ensure positive gate bias for higher currents on jFETs and use of enhancement MOSFET

Layout was carefully adapted to ensure track separation due to HV in place. Result is that the new gyrator board provides all protection needed on the lower device and simplifies the build process

Here is an example of a completed board tested:

01a Preamp Gen2: New Build

Yet, another 01a preamp. This time with a beautiful machined top plate and wooden frame:

Will try the Russian filament resistor which we tested at Andy Evans’ and sounded amazing. Just need to build a new pair of Rod Coleman Boards and do the wiring:

01a Preamp (Gen2) Universal HT Supply

Introduction

I received many requests throughout this year of folks building the 01a preamp (Gen2) asking for advice on the HT supply design. Well, I have my own incarnation which serves multiple purposes as is a shared supply, therefore isn’t useful to anyone.

My friend Andy Evans came up with a supply using available components. This is exactly what you are looking for the HT supply. I made some tweaks to Andy’s design, so all credit should go to him.

Design

The HT supply design is very simple. It’s mainly a choke-input valve rectifier supply. It has an additional LC smoothing stage. Here is the high-level circuit, see some notes

The transformer is a 250-0-250V / 50VA with an output current of 60mA. It has two windings for 6.3V AC heaters, but you only need one. Here is a great choice from a recommended seller.

The valve rectifier is a double-diode damper. Of course you can use some other options, but I like the sound of them. Here are some you might want to consider in your build:

6BY5G: a nice double-diode damper with lower filament requirements than the commonly used. This is my first choice
EZ-80: the famous rectifier. This is what Andy used.
EY-91: you will need 2 valves as there is one diode per bottle.
6C4P-EV: a nice Russian small double kenotron rectifier. Very cheap alternative for European builders
AZ1 / AZ11 mesh valves. Their sound is unique, however they are very expensive these days. You will have to add a pair of voltage dropping resistors to accommodate the lower filament voltage requirement.

For the indirectly heated diodes, it will be better to connect one end of the filaments to the cathode.

The chokes are commonly available. These are from Hammond (155J) and have 15H @ 30mA. The downside is the high resistance, over 1kΩ. This isn’t an issue here as the current consumption is low so the voltage drop is minimal. With a choke input supply you need a minimum current to operate. In this case is about 15-16mA so a bleeder resistor is needed (29kΩ 5W wire wound) .

C1 serves to equalise the output voltage. It pushes the supply to operate a bit more like cap-input (hybrid) by increasing the output voltage. I use it to tune the output voltage to 200V.

C2 and C3 are classic motor run capacitors. I personally use ASC Oil ones 450VAC rated. You can choose what you can get hold. You can use any good quality film capacitors. I like the WIMA DC-LINK ones, they are great.

The output ripple is about 7mV. This isn’t a problem as the gyrator load has a very high supply rejection (PSRR) so no need to go crazy on this. If you

The design is so simple that anyone should be able to build this easily.

Hope it works for you.

Merry Christmas!