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.
Tag: Rod Coleman filament regulator
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:
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 🙂
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:
4P1L PSE Amp: assembling top plates
The additional machined top plates arrived yesterday. I assembled them this morning. Just need to assemble the chassis now before soldering!
HT and LT connectors
Rod Coleman’s boards
Filament resistors
Filament resistors
Speaker posts
Amorphous OPT and plate
DHT preamp “The Mule”
The birth of the Mule
The name I guess says it all. This is yet another DHT preamp with the gyrator PCB. So what’s different? Simply, a breadboard DHT preamp module ready to be abused. I’m planning to mod this to death and try a long list of other DHTs with the gyrator load.
I will only need to change the valve sockets (or build an adaptor) as well as the filament resistors and Rod Coleman filament regulators. Simple changes which can be done fast, will open the door to quick tests on my system.
In order to make this simple and a rapid build, I opted to use an IKEA chopping board. These are made of a laminated hardwood and are dirt cheap. A couple of hours are required to drill all the board like this:
Job done. You only need to do this once. Here is another look at the half-build Mule:
The initial sockets are NOS short pin UX-4/UV-4. I will play around with the 01a before I move to other DHTs. I still need to add the tag strips for filament resistors, output capacitors and the filament regulators.
Wiring will take a couple of hours and we should have another DHT amp to play with 🙂