• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

My experience building a DRD d3A/300B amp

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Hello all,

This my first post on this forum, although I’ve been a long time reader here.

First of all I would like to thank to everybody that contributes to these forums. I still find that is amazing to be able to have a direct window to such variety of views, thoughts and ideas. I would specially like to thank Thorsten, who took the time and patience to privately guide me on the design of the amplifier that I’d like to present here. I know that he can get on the nerves of some people but I think that he just tries to spoil people to do their homework. He is an opinionated fellow and he sometimes like to present his knowledge in a mysterious and challenging manner but the wealth of info that he has shared with dummies like myself here is been of great help and the dude deserves my respect.

First a little background. I’m a classical musician. I got my Master in performance at USC in Los Angeles before coming back to Barcelona, were I teach and perform. As a musician I’ve been lucky enough to play with some great groups, like the LA Phil, for some great conductors and also in some nice places, like a few years playing at the Aspen Music Festival.

The first time I heard a tube amp was at the house of a Japanese student whose husband worked for Nakamichi in LA. It was somehow like love at first sight. I had no electronics background whatsoever…quite the opposite indeed but ever since then I started to read and read trying hard to understand the most I can, although I have to say that the wealth of info is sometimes overwhelming for someone like me. Still it’s pretty amazing what one can learn here and there.

After listening to some friends systems and from I gather in the forums, I started to have a pretty good idea of what would be the reproducing system that I would like to build myself.

To make a long story short and after a few small “experiments” I decided to build my first serious amp. It was going to be a 300B. Never heard one before but there would have to be something about it after all the buzz that there is around. For a moment I though of going with a kit like the Welborne DRD or the Lady day, which I’m sure it would have been much easier in terms of planning, building and parts collecting…but I decided to build it from scratch. What the hell, I though, do it ALL yourself.

As I said before, I got in touch with Thorsten who very patiently helped me out to adjust the values of his original 437a/300B DRD amp to use a d3A tube in the input stage instead. After a few months of parts collecting and finding the right time to build the this, it was finally done.

The chassis is pretty big, really oversized. I didn’t want to have layout problems. The aluminum top plates are from Schaeffer in Germany. All resistors on the amp side are Dale, except the 47k input resistor an the 60R4 grid stopper which are Caddocks and the 100R potentiometer which is a Vishay. I might change the grid stopper with a carbon type like a Kiwame or Riken soon. The capacitors on the B+ are Ducati motor-run. Yeap, I can brag about that with my motorcycling friends…electrolytic on the filament supply are Panasonic low ESR. I used Lundahl iron everywhere except the power transformers. I also got a pair of filament chokes from Jack Elliano, one of the guys that brought this type of design to the forefront. Wiring is 26AWG fine silver from Percy audio on Teflon sleeve. Ground bus is 12AWG silver. Input jack and speaker post are Neutrik. Tubes are Full Music 300B and 274A both “mesh” types. d3A are Siemens.

I have to say that due to my limited knowledge of electronics I had a TV repair man friend of mine help me out with the building and testing of these amps. A good idea if you’re are a newbie dealing with potentially deadly voltages.

The Volume control is a pair of copper TX-102s and the speakers were first a pair of Supravox signature bicones that were later upgraded to the field-coil 215-2000 adapted for open baffle.

Sources will need to be upgraded but for now they are primarily a MOTU 896 firewire interface that plays EAC extracted Ape or Flac files from the hard drive of my computer. Vinyl is played trough a Rega P3 with a Denon DL103R and a crappy phono box riaa stage.

Now for the sound of this thing. I mostly hear Jazz and Classical together with some 60s and 70s pop once in a while. A musician I sometimes find hard to believe how some people is so damn “accurate” while describing the sound of this and that component, specially giving the fact that there are sooooo many variables that could influence on the overall sound of a given system, starting with the quality of the recording itself. Well, this amp sound great, really amazing. Trust me guys, I heard not many other amps but enough to know that this is really a special design. First of all there is almost no noise coming out the speakers. Then, when the sound starts happening you always have the impression that you are hearing something that is VERY close to the original; for good and for bad. Awful recording are almost unbearable to hear…a pity because I have to really concentrate on the performance in order to not get distracted by the sound. Why is that? Because the amps sounds so amazing when you feed them well recorded material that it makes the bad recorded stuff look really bad.

I also make my own recordings of my students and myself. Last one was made on a pair of Schoeps mics on a very spacious venue. Mastering the recording on the Supravox and the 300Bs is just a pleasure. Really pretty close to what it sounded like there. For me personally there is no better proof of worthiness. I’m obviously quite proud of these babies, specially considering that less than a couple years ago I didn’t even know what a capacitor was.

Future holds a new house that hopefully will be finished in March. I will finally have a decent space to listen to my system (right now I have it on my rather small living-room) I will then probably upgrade my analog rig to a Teres turntable. I’m also looking forward to build Steve Bench’s no C phono stage and I will probably have to add a set of open baffle subwoofers to go with the Supravox…but that will probably have to be covered on a different post.

I’m sure that the amps could probably be improved and so you know, I’m totally open to any kind of suggestions.

Thanks again to everyone and I hope that my experience serves a motivation to all of you undecided adventurers that are afraid of trying. Go for it! Is really worth it.

Best regards,

Luis Gascón.

Yes here they are, I tried the first time around but I didn´t get to do it right...


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ohh nice ... I like these wood/brass cabinets. And I like DRD as well, a very clever idea. I have read lots of positive reports on that topology and I would love listening to them.

From the schematics I see you did use the AM OPTs from Lundahl ... somewhere here on diyaudio a Jap guy (or was it somewhere else??) was saying that permalloy Tamura/Tango are way better than LL. An other great pick up would be a MQ iron. They are not exactly that cheap btw.


nice amp, that's more or less the same as I am going for. I think I will stick with a lower b+ though...... Thorsten has a nice schematic on his yahoo group.

I really like the look of the we717a, I'd like to use it just cause it looks cool!

Also I am thinking of having a universal power transformer, so that I can convert to 45 tube if necessary. That will mean buying an extra pair of opt's though........ All amorphous chokes and opt's. I have Pieter from Tribute winding me some amorphous opt's for my dac so I can get an idea of how good they really sound. I will see if Thorsten will oblige any info on 45 tube conversion when the time comes. I think it is best to start with, the 300b, plenty of power, should sound pretty detailed too in this topology.......

Unfortunatley I am also in the situation of not being able to hear the 300b in SE or 45 in SE before building. But sometimes a chance must be taken.......

In your case it seems to have paid off!


Congratulation for the assembly. I also wanted to carry out one and for what I see they are very satisfactory their results with the Supravox.


Enhorabuena por el montaje. Yo tambien queria realizar uno y por lo que veo son muy satisfactorios sus resultados con los Supravox.


Bas Horneman said:
Which schematic on the yahoo group?

I'm as puzzeled as you...

Bas Horneman said:
PS..yahoo groups suck...in the look and feel imo

I have been using Yahoo groups since before they where e-groups, a long time. So I keep the groups there.... I agree they have disimproved some and look dated nowadays....

Hi everyone,

Originally posted by Bas Horneman
Did you use the AM versions straight away? Or did you upgrade to them later?

I got them straight away. I think I know were you are going. No, sadly I didn't have a chance to compare the Lundahl amorphous core to any other output trannie so I had to go with intuition and faith. Still I'm quite happy with Lundahl. The construction quality is superb and there is many other builders that seem to be happy with the swedish iron.

Originally posted by Gluca
somewhere here on diyaudio a Jap guy (or was it somewhere else??) was saying that permalloy Tamura/Tango are way better than LL. An other great pick up would be a MQ iron. They are not exactly that cheap btw.

I'm sure that either Tamura, Tango or MQ are great also...and for sure that I'd love to compare the different sound of each one. On the other hand I want to believe that after a certain quality mark, the sound is not going to change THAT dramatricly from one to another...one hopes.

Originally posted by Gluca
what about a DC current regulated heater?

Do you mean Guido Tent's filament supply? I've heard about it...but as I said earlier, due to my limited knowledge of electronics, I wouldn't know if it would be preferable to the hefty stuff that I have now. I'll have to wait and see what the common wisdom of this and other groups have to say...

Originally posted by Bas Horneman
Would there be any chance of buying a cd or two from you?

Gee, I'm flattered. I primarily do recordings to spoil my students and to have memories of their performances so I won't try to sell anything, I'll be very happy to just send you some stuff when I get home...right now I'm away on vacation.

Originally posted by Bas Horneman
Luis.. I like the fact that you have incorporated an of the shelf product LL1667/15mA for your DRD. That makes it a lot easier for folks to build a copy of your amp.

Yeap, I figured that too. I hope I help some people that way. In fact, choosing what and what not to use was probably the most difficult bit building these things. Consider that I didn't really have any kind of bits and pieces at my place...I had to order everything.

Originally posted by Kuei Yang Wang
Hey, thanX for the flowers...

If you ever show up in Barcelona it won't be flowers but a good bottle of Rioja...

Thank you all. Regards,

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