Line amplifier – Morpheus


Morpheus, in Greek mythology is the god of  dreams. He has the ability to take any  vacuum tube form, and appear in our d.i.y. dreams.

This is my first tube project, which was inspired by a design of  Triode Dick. Actually, I was visually attracted by the retro look of the the mu-line project realized by another Dutch diy-er gydotron, which really impressed me at the time (unfortunately, is now only a commercial site ).The story is simple: I was fed up by the sound of my system, consisting at the time in a  Borbely Audio combo, line and final amplifiers mosfet class A. The A75 (75 watt class A mono-block, 3.25 A ) final amplifier designed by Herr Doktor Erno Borbely sounded amazing, but the preamplifier was not on my taste – after listening for a few hours you feel no pleasure but pain 🙁  .  I decided then for a tube design, thanks to triode dick.
Having two separate chassis was the first idea, one for the passive PSU (left in the image) and the other one for the line itself, on a totally separated dual mono topology. The diagram for the line itself could be fund in the image above. This is a file created by triode dick, and is here just for illustration, not intended to be used for a commercial purposes, just for DIY use.The  Tri-Pent Mu stage topology is used as deeply explained in the website of Alan Kimmel.
The reason of choosing this topology for my first project was that I wanted to avoid by any means
any kind of  non-tube components in my project, as much as possible. Sounds stupid, but at the time I was a follower of this pro tube/ non silicon religion!
Despite a blind decision based on believes, not on science, it was a lucky decision: this MU stage,
based on a direct heated triode an tube rectified passive PSU sounded better than any SRPP or CCS
loaded single triode I ever heard implemented as a line amplifier !
Let’s be straight: I was having no idea on what will happened, I was just dreaming at the perfect sound !
The vacuum tubes used for this project:
–    B406 – a triode made in 1938 by VALVO company, NOS tube
–    D3a – a pentode made by Siemens in 1968, with very good sonic qualities
–    AZ1 – dual rectifier diode made by Tesla factory in 1952
The transformers and chokes are proudly made in Holland by the master of wounding Will Blaaw of Automatic Electric Europe.

I will just mention that this small and honest Dutch company is a blessing for us, diy-ers! Because I was using a totally separated dual mono configuration on a double chassis, I was ordering from AE two main EI transformers and four 10mA chokes, together with ‘hammer paint’ lacquer trafo covers, which are beautiful. The transformers came within the specified needs, well packed, treated with nitro-lacquer, assembled carefully and they perform quite well over time (10 years) without overheating or buzzing.
The capacitors:
I struggle at the time to build an old style passive PSU, but the main problem was that I could not find any PIO (Paper In Oil) capacitors available. After struggling for months, the faith was smiling to me: I have found some used PIO caps in one of the ancient UPS made in the 90’s for an IBM computer machine. I took the capacitors (General Electric made in Mexico in 60’s),  and after testing them (they measured perfect) I cleaned and painted them. They are still working!
One word: I will not recommend this kind of PSU except you can feel a difference or you want to build a really high voltage B+ single ended triode amplifier! They sound different, but with this kind of PSU it’s not easy to reach the noise floor of the modern PSU. Except the sound, of coarse ;]   The other capacitors used for Morpheus are: ELNA Cerafine for cathodes decoupling (from  Diy Paradiso),  Rubycon 400 Volt – 105*C for the anodes decoupling (you could try Balckgate WKZ if affording),  AUDYN for Csc and Cp ( from Alan Kimmel’s article), and AURICAP for the signal capacitor. I tried all kind of capacitors at the time, but the Auricap was giving so far the best sonic results, on my taste. As for Resistors, I was deciding to use DALE resistors (from aquablue) due to the good price/quality ratio. I have used in some other projects Caddock high performance film resistors, and I could tell that you should have a hell of a system to feel the difference made by good resistors in a blind test! Anyway, Caddock film ones could not survive the high voltages feeding the mu-stage. For the volume control, the Panasonic plastic potentiometer seemed to be the perfect choice at the time, but the high voltages make life harder for this device, which I could not say about the blue ALPS ones. Still, we manage to recover it and the volume is still working, Being one of the finest sounding volume control I used (good balance between R and L channel –
less than 2 percent in measured resistance at different angles of rotation, good vibration control due to the cast used for the outer box, little fingerprint on the sound for the given cost, nice feeling on hand while rotating the volume knob).
As you could see from the inside view picture of Morpheus line box, the project was soldered in a
Point-to-Point manner with WBT silver solder, and the wiring used for all the signal path, as well for the B+ and ground bus, was 0.6mm silver wire bought fro AE as well. I cannot recommend for sure the silver wire (depends on the system and the sound you are looking for), but I will highly recommend you to use a good solder like the WBT silver one (or any other silver containing solder with a lower melting point – the new rohs complying ones does not sound that good like the old ones ? ).The passive PSU was build in a simple manner, on a separate chassis. The rectifier valve used is AZ1 by TESLA, and the B+ filtering is totally passive CLCL. The second L choke was positioned on the signal chassis, solution dictated by the size of the PSU chassis and the big scale of the paper in oil capacitors. As for the filaments supplies, silicon was heavily used! The filament regulating chips (LM337) were mounted directly on the copper chassis with electrical isolation (see morpheus_inside_01)

The chassis was made from an wooden frame with a 3mm copper sheet on top. The spikes were turned from aluminum (not very good choice) the volume knob from brass.The rest of the hardware:
–    I was using an IEC 220 Volt connector with incorporate filter and  surge protection
–    For the valves sockets, were used some ceramic ones from ask jan first .
The problems
I have only one problem with this line stage: whatever I was trying, there was a terrible hum that disappear only when I was putting big screens over the B406 triodes. There was no other way, despite the big values for the grid resistors, clean bus grounding (no ground loops), anti RF ring stoppers on anode, grids and cathodes, stabilized and highly filtered filament supply for this particular direct heated triode. The ‘cure’ was providentially performed by an old ham radio buddy (niki), who just drop a kitchen shredder – linked to the ground bus potential – over the old VALVO tride! It was one of the happiest days ever from my tube DIY journey :]   .
The sound
Well, this was the most pretentious tube project I’ve done so far; after this one (which was done in a cost no object manner) I approached the so called ZEN manner – less is more! Still, the sound of this preamplifier maybe was closed to perfection, good enough to taste the valve nirvana !
Compared to the TL5.5 Line Stage Preamplifier 12AT7/ 12AT7 based preamplifier, the soundstage of Morpheus was huge and awesome. The timbre was close to perfection for voices and acoustic instruments; As well as the decay. Everything sounds pure, natural and effortless, with no strain. Micro-dynamics were thrilling, breath taking: a very good French recording of an ancient church organ was revealed as ‘imperfect’, and you could hear the background noises outside the hall, as well as the in-hall reverberance of the building.
What can I say, the only think which wasn’t perfect was the bass reproduction: it was deep enough, but not so controlled, and this was the only minus of this beautiful preamplifier.
The sound Morpheus produced was addictive; when turning up the volume you feel like jumping in hyperspace regarding the soundstage, depth of field and tone refinement.
I must to recognize that direct heated has its own advantage, especially if you are eager for big scale orchestra, voices or acoustic recordings.

Here we have posted a gallery with all the images available regarding the construction of Morpheus line amplifier

sweet dreams !

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