Deathbringer 211 Tube Amplifier

Deathbringer 211 Tube Amplifier

Where it all began…

Our core business is not amplifiers, but manufacturing and selling various transformers. Amplifier design is just our passion, and it is rare to find such good matching combination where a transformer manufacturers actually loves designing amplifiers. We have been looking for a higher power tube amplifier to demo our transformers for quite some time but we just do not have the time to do so due to the busy schedule of satisfying our customers’ orders. Our little demo room (not our main priority) has been displaying a very old prototype 6B4G S.E.T. for years, and that was made and modified many times since the early 2000. It is getting uglier with more screw holes drilled, and time to be refreshed. With the publishing of this article, hope we have the time to finally make one proper demo amplifier to showcase our transformers. 

National Union 6B4G - clear and smoke glass

What to build?

What could be the last amplifier that you want to own? I know everyone wants AN Ongaku but not everyone can afford the price tag, although they do have such money, but it could be used better on some other priorities in life. What we aim to design here is something that everyone can own, sounds excellent and yet does not break the bank account.

We name this amplifier – DeathBringer 211, reason being that it will draw away the listener’s soul, even if they are the pickiest and the most perfectionist audiophiles when music being presented to them with this amplifier.

In order to achieve this, all aspects of the amplifier must be investigated and made perfect, right down to the screws and nuts being used, to bring out the absolute best of vacuum tube technology, with the perfect blending of old school engineering and modern technology. It is created for the ultimate goal – music delivery, direct to the person’s soul.

The Deathbringer 211 amplifier is for you to stop the quest for perfect amplifier, and focus on the music (or on other gears or aspects of HIFI) until end of life brings you and Deathbringer apart.

Preface

We have been having a 2A3 / 6B4G single ended direct heated triode tube amplifier in our demo room for ages, mated with a pair of Zu Audio Soul Superfly high efficiency loudspeakers. Although 2A3 / 6B4G is a very sweet and warm sounding tube, at times, more output power are called for to support the more dynamic pieces for various music pieces at certain passages even when paired with the 100dB/w/m Zu, which is considered very high efficiency loudspeakers. 

 

Zu Audio Soul Superfly Loudspeakers

We have thought of building the legendary and venerable giant 212 direct heated triode. That is for perhaps 2017 or so because we have had almost all the parts for 211 ready – the 16K output transformers, interstages, 2-coil chokes, single coil chokes, parts and etc. If we were to build 212, we would have to start all over on the parts collection. The price of new 212 tubes are still quite expensive, in addition. Wait it out and perhaps the price will drop with more and more companies building the new 212 tubes. From the sharing of our beloved customers, PSVANE 212 tube seems to be the leading 212 tube for new releases. 

Note: if customers want to build 212 now, we will be delighted to help you with it. 

212-D Vacuum Tube

NOS 212-D Valve

Anyhow, let’s go back to 211 SE DHT amplifier design now. It shall be designed a pair of mono-block power amplifiers, to be matched with our WE 417A and WE 418A compatible tube preamp with output transformers. More about that preamp later. For those interested to order a pair of this 211 SE DHT baby, please drop us a mail and we shall include you a pair too, which is a chance of a lifetime to get this delicately designed (J&K Signature) tube power amplifier. 

WE 418A Tube

WE 417A Tube

Overall features

When it comes to design, there is no right or wrong, but what’s best for you and your system. What we focus on is – tonality, resolution, clarity, dynamics and warmth.

Single Ended Triode – no push-pull, no Ultra Linear mode, no Pentode mode

Single Ended Triode operation – is still the best to our ears. We have built and tried other topologies, and yet we still come back to this. Others might yield better measured performance, higher power and etc but still, what is most important at the end, is the sound.

Direct Heated Triode is another crucial determining factor for good sound. Direct heated tubes are using the filament/heater as the cathode. Indirect heated tubes are having separate filament and cathode element in a tube and therefore is slightly more complex in build.

We would wish to use more direct heated triodes in the design but due to complexity and adding too many variables to the equation and making it too complicated to manufacture, we stick to only having the power tubes as direct heated tube, whereas the gain and driver tubes are indirect heated tubes. We have made a no.31 driven no.45 SET previously and we loved the sound. The sound still lingers until today even if the amp was made in around 2003 or 2004. Perhaps we should build a no.31 driven no.45 driven 211 all DHT tube power amplifier! That would be really something to look forward to! If the gain of tube no.31 of 8 is too low, perhaps a NOS 4P1L direct heated tube can be deployed. This is a new rising star in the tube underground that boasts absolute linearity, and is designed by Telefunken for the military use. Unfortunately, application of this tube will limited the tube rolling variations – that is the only downside, which is tolerable since it is the best gain/driver tube available, why change / why roll?

Zero negative feedback

Too many authors have written about this. I will keep quiet and let the expert tell you why not, or why yes. We tried, and we can live with both. With feedback, sound character is more controlled, better behaving, better imaging, but a bit tensed. Without feedback, it is more open, lively and relaxed. You choose what you want. We are OK with zero negative feedback to get the more relax and open feeling, which is our preference. Music is for relaxation and enjoyment after all!

3 stage design

One may say that a 2-stage design is the purist way to go. Yes, we know. We can use a very high gain driver tube, employ step-up input transformers, step-up interstage transformers and various other methods. But, pulling off a 2-stage design with 211 SE DHT amplifier is no doubt possible but it would be stretching the design and/or operations too much and many not sound as relaxed and as comfortable in terms of operation as a 3-stage design. You push the design and the tubes will feel it -> you will hear it too!

An additional stage gives us the flexibility to tune the sound with different tubes too, to add more body and warmth to the overall sonic signature.

Design topology: Input transformer (optional) – 128 stepped volume control – 12SN7 gain stage – 1:1 IT coupled to EL803S driver stage – 1:1 IT or 2:1 IT coupled to 211 – 16K Output Transformer – 6AU4GT / 43IU separate tube rectification for gain/driver and power stages.

3 stage tube amplifier

Input transformer – provides impedance matching and isolation between the connected source and this amplifier, thus reducing noise picked up by the interconnects, isolates the ground noise coming from source, eliminates the chances of ground loop. Input transformers bring more body to the sound.

Stepped volume control – optional, if is used as pure power amplifier, this is not needed and should be bypassed. We use only the best – relay controlled constant impedance 128 or 256 steps attenuator. Relay control provides the flexibility to have more ladder steps compared to ordinary rotary mechanical based 23 – 44 steps attenuator, and therefore the right volume can be achieved instead of having 1 step too loud, 1 step too soft scenario. Relays are sealed too, with better (silver) contacts, and therefore better sound. Oxidation is not much of a problem for them. They are rated for hundreds of thousands of cycles too. 

Continuous carbon brush pots (bad channel matching, bad for stereo imaging, causes shifting of imaging and fuzziness) are ancient technology that should be discontinued usage for very high end amplifier like this. 

128 step volume control

Zero coupling capacitor – all interstage coupled design

Yes, no coupling capacitors. No grid leak resistor is needed. No grid choke is needed. No capacitors in the direct signal path to compress or color the amplifier. Absolute low impedance from grid to signal ground for driven tubes (good). Interstage has alll sort of goodness. 

A good interstage is efficient (>90% signal transfer rate) – having minimal signal loss, and isolates the stages from each other, and provide good DC current drive to the grid when it is needed, which capacitor coupled design could not do. 

Although direct coupling boast direct connection of the gain (which is superior in terms of transparency) - driver – power stages without any components but that is also prone to danger of bias runaway and damage the amplifier or tubes. We do not want that to happen – we want a VERY RELIABLE tube amplifier that can run for years of operation and abuse, without the need of servicing or repair. Imagine shit happens in the middle of a demo - I can foresee how our sales force face would be in such situation.

So, interstage is the only way to go, with active cathode bias to lock the tube at their designated operating point until end of life.

Interstage Coupled Tube Amp

Direct Coupled Tube Amp

Tubes selection

12SN7 / 12SX7 double triode in gain stage – NOS, good sounding, and inexpensive. Medium high RP but still decent and manageable to be IT loaded. Users can substitute with 6SN7 with a flip of toggle switch (can be installed) to change the filament voltage from 12V to 6V. We chose that because of the sound quality it offers. There are plenty of new and NOS 12SN7 / 12SX7 / 6SN7 for rolling to match different personal tastes. The 12SX7 is military grade and offers better resolution and stability compared to other tubes (more rigid though, 12SN7 is more analogue). The flexibility (to roll) it offers is really valuable.

12SN7GTA Tube

12SX7 Tube

EL83 / EL803s in driver stage – power pentode, NOS, good sounding, and inexpensive. Used at triode strapped, has low Rp, very linear, high current / high drive strength (capable of large V-swing (about 150Vpp) needed to drive 211 to full power and beyond), is a small power tube, can be considered high gain as a driver tube. 

There are plenty of NOS Telefunken EL803s is available, with some variants of more normal EL83 and EL803 in the market. If EL803s was a commercially used tubes with big name tube amplifiers, it would have cost over U$500-1K per pair. You are getting absolute premium quality NOS Telefunken EL803s at a very decent price. Cheaper than a brand new driver tube from recent tube manufacturers.

Telefunken EL803S with Falcon logo

***Notice the “Falcon” mark on the right tube that indicates specially selected tubes for the German elite forces. If you have that mark on your Telefunken ECC803s, it would be fetching over U$1K or more. Here, is only maybe U$10-20 a piece, at the time this article is written.

211 – Direct Heated Transmitting Triode - NOS is our choice but new versions from various manufacturers are readily available. Brightly lit(!), inexpensive (NOS GE VT4C is still available at decent price), the power tube used in legendary AN Ongaku amplifier, capable of 19W class A output power and slightly more if biased into class A2 (drawing grid current, into +ve grid bias region). We do not like class A2 and therefore will bias it at class A only. 

Still, with our 16K high impedance OPT and unique operating point, class A2 comes as a bonus, and valued reserves when power is called for, and can deliver as high as 31W. 845 is another good candidate, with higher output power and lower Rp, but NOS 845 is almost impossible to find, and with much higher price than the 211. 845 has more power and authority (darker sounding) compared to 211. 211 wins in terms of resolution and finesse, and has a more balanced and livelier character. 

Note: for those that requires class A2 operation constantly, a bigger driver tube, such as EL84, 6L6 or EL34 would be recommended to deliver even MORE current drive to the grid of 211. This would require a bigger interstage though, and the specifications (soundwise will be slightly inferior for the golden ears, for tin ears like mine, these 2 would sound the same) may not be as good as a small interstage. You get some, you loose some. The world is fair.

RCA 845 Tube

GE VT4C - 211 Tube

6AU4GTA – TV Damper Diode -  NOS, plenty of choices, low Vdrop (25V, lower impedance), high voltage damper diode for tube rectified power supply for 211 power stage. It is far superior to 5R4 that has very high Vdrop, and good ones (5R4) are getting expensive. 5R4 is working near the maximum too if used for 1.3K B+ used in this amplifier. 6AU4GTA still have plenty of spares and is working comfortably at this voltage. The slower warm up time is beneficial to protect the power tube too and prevent turn on surge.  

Sylvania 6AU4GTA

43IU / 45IU / RGN2004 – 4V tube rectifier - Europeon tube rectifiers, NOS, visually absolutely stunningly beautiful, fully of body and rich in tonality. This is the ideal tube rectifiers to be used on the gain and driver stage that will dictate how the amplifier will sound. Time for some color palette to tune the amplifier! The driver / gain stage has lesser demand and these tubes will be perfect for this task.

The filament is 4V 2A, and therefore have plenty of choices around for tube rolling due to the low voltage and low current B+ demand for these stages.

Cossor 43IU Tube

RGN2004 Tube

Telefunken RGN2004 Rectifier

Telefunken Logo

Tube rolling will not be an issue at all with this design. There are plenty of NOS tubes to choose from, from gain, driver, power and tube rectification stages. 

Biasing

Bias method: 12SN7, EL803S, 211, selectable active assisted or passive cathode (self) biased.

Yes, there are other biasing methods available, and they have their pros and cons, and their sound signature. To name a few – fixed bias, ultra-path, battery bias, LED bias, and many more. We like the simplicity and therefore has chosen bypassed cathode bias or active biased (using 3-pin regulator such as LM317 (or TL783 - high voltage version) – we have used and published that in diy-audio-guide.com many, many years ago) for this design, which is very good sounding, safe and automatically biased when the tube ages. Active assisted bias locks the tube bias at designer designated point so that it stays the same until end of life of the tube. It eliminates the need for user to repeatedly bias the tubes when it ages over time. 

This also reduces the importance of matched tubes – tubes are not dynamically matched and it ages differently over time, which negates the effects of matching at the first place. Tube matching – a myth? Go figure. 

Constant Current Sink and Source

Cathode Bias / Fixed Bias

No point arguing which is better. It is just a matter of choice and preference.  Traditional cathode bias with bypassed resistor is warmer sounding compared to active bias with LM317 regulator, which is more HIFI and neutral. One can tune the sound slightly with different cathode bypass capacitors, and bypassing of cathode bypass capacitors to get what they want. We thought of adding a switch to switch between active bias and conventional cathode bias too... Why not?

We run the tubes conservatively too against the manufacturer specified absolute maximum values. This way, it has much longer service lifetime and produced much relaxed sound.

Operating points

This is a multiple-step processes for getting the operating point right. Calculate it on paper, implement it, measure it, compare it against theoretical results, and fine tune it for best output power and sound. The beauty of vacuum tubes is that it can be operated at infinite operating points and it will still work. Whether that point is optimum, providing good voltage swing, working below maximum permitted specifications, and etc, is another question. 

I have discussed the 211 operating points previously when I talk about our high primary impedance output transformer impact on amplifier design. You can use that as a starting point and go from there. There shall be tuning needed after actual implementation for fine performance tuning. 

Calculated and designed output power, when 211 tube Pd is at 72W (a very conservative operating point) 

Class A1 = 14.3W

  Class A2 = 31.3W  

Actual measured output power = to be determined when unit is built, and when different tubes are tested.

The 16K output transformer we made previously has frequency response of 20Hz – 20kHz @ -0.5dB (flat), 7Hz – 40kHz @ -3dB or better. It will get better over time as we fine tune the winding and improve our output transformer material technology and winding methodology.

http://jandkaudiodesign.blogspot.sg/2016/02/211-tube-loadline.html

http://jandkaudiodesign.blogspot.sg/2016/02/211-output-transformer.html

EL803S operating point – chosen at 70-80% Pd to provide enough current drive to manage the large 211 grid that will draw grid current when operated near 0V Vgrid, and with the widest Vswing that it can provide (~150Vpp) to drive 211 into full power (~80Vpp class A1, ~100Vpp class A2). If there are sufficient gain in the full system (has a preamp for example), the interstage transformer between EL803S and 211 can be set to a 2:1 step down to provide doubled the current sync capability for even more graceful transition between Class A1 and Class A2. 

  

211 Operating Point

6SN7 operating point

Components selection

Cathode bypass capacitor for pre (12SN7) and driver (EL803s) tube: Sanyo Oscon

Sanyo Oscon – solid capacitor with organic semi-conductive electrolyte or conductive polymer, very low ESR, excellent noise reduction capability and frequency characteristics (suitable as decoupling capacitor as the impedance has ideal frequency characteristics), large ripple current, long life span and most importantly, good sounding.

Sanyo Os-Con caps

Cathode bypass capacitor for 211: Siemens Sikorel®

Siemens Sikorel – extremely high reliability and long useful life, wide temperature range (up to 145 degC), outstanding parametric stability, high ripple current capability, low ESR and most importantly, good sounding.

Sikorel Capacitor in action

Siemen Sikorel Capacitor

Sikorel Specs

Sikorel Capacitor Specs

PSU capacitors 1 – Secret Metallized Polypropylene Film Capacitors. I’m going to keep a secret on what is to be used here, but it is definitely something really good. It is not audiophile branded and not being made especially for audio, but the quality far exceeds what the audiophile capacitors can achieve. 

Imagine having these parameters for a 40UF/900V capacitor: Ipeak = 800A, Irms = 17A, ESR = 5m Ohm, response 40V/us. Below is a snippet of the general features. This capacitor will be deployed on the 1^st 2 stages of the CLCLC filter to filter all the gremlins (ripple/noise) after the tube rectification. The high voltage tolerance makes it easy for not needing to series too many capacitors to meet the Vdc requirements.

B+ = 1290Vdc. Vcap = 900V x2 = 1800Vdc.  Still plenty of headroom left. 900Vdc rating is when used at high temperature (85 degC). 1100Vdc is the rating when it is used at low temperature tolerance (70 degC - still pretty high for us, we aim for only 50degC at nominal operations). So, at cold start, the turn-on spike will be fully absorbed and is within tolerance of this ultimate B+ capacitor. 

The highest temperature it can tolerate is 105 degC and still, the DC tolerance is 650Vdc, which when put in series, is still over the B+ of 1290Vdc (1300Vdc). Did I mention that the useful life is 100,000 hours at 70 degC?

Secret 211 B+ PSU Capacitor

PSU capacitors 2 – Philips / Vishay / BC Electrolytics. Although we wish to use full polypropylene film or paper in oil capacitors all over the power supply, the last stage requires something with larger capacitance to achieve the critically damped response to reduce ringing (causing sibilance) and provide the best response to current draw. 

These are no normal electrolytics too. Look at their specs. We like them for the sound, but they themselves are no ordinary peasants. Ultra long life, low ESR, high durability, high temperature tolerance, and etc. Look at the specs below! Did I see 90,000 hours of useful life? That is 63 years of use if you play it for 4 hours a day.

Vishay Electrolytic Capacitor

Philips BC Electrolytic Capacitor

Tube sockets: Teflon tube socket with gold plated copper pins for 12SN7 and EL803S. High quality ceramic with thick aluminum mounting and gold plated copper pins for 211. – low stray capacitance, high temperature tolerance, good damping, good contacts and high reliability. Nothing much to shout about. For those more ambitious, a separate plate to mount the tube sockets, coupled with rubber or spring dampers to the main chassis will be perfect. VT4C.com sells some very nice copper and aluminum plates for mounting tube sockets. Yamamoto sockets will be a good but slightly expensive option.

211 Tube Socket

High quality 211 tube socket

Teflon 8 pin socket

Teflon 5 pin socket

RGN2004 Tube Socket

8 pin teflon socket

Resistors
We take special care in selecting the resistors use - one is for safety reasons where right voltage and wattage tolerance are strictly observed for SAFETY (most importantly), and sound, and lastly - long life operation. We design the gear to work for a very long, long service life. Let's take a look below: 

Signal / cathode bias / low voltage power supply resistors – Riken RM carbon film resistors, for tone and body. Carbon film resistors are noisy no doubt but they produce the tone and body that other resistors could not do. Open up those legendary vintage amplifiers and you will find carbon film resistors all over them, on top of the oil capacitors that are very famous in the older days. With the right usage/applications and over-sizing, carbon film is an excellent choice for tube amplifier building, especially used in the signal section.

Grid stopper resistors – Grid stopper is used to prevent high frequency oscillations. Solder one with the shortest resistor leads to the grid of the tubes. Any carbon film capacitors in the range of 10 – 1K Ohm will be ideal, depend on the tubes used. Too much and it shall reduce the high frequency response of the amplifier. Too less and it shall oscillate. I will go without first, measure, and insert as necessary. Matching of the values are not important as long as they are nearby. Carbon film resistors are famous for their large tolerances.

Kamaya Carbon Film resistor

Carbon Film Resistor

High wattage / high voltage / signal and power resistors

Riken carbon film resistors (hand matched for a large pool of resistors) are used for signal related sections (cathode, load, and etc) – for tonality and body. These carbon film resistors do not have very close tolerances and therefore matching and burning in is required before being applied. We will take special care to match and burn them in before any usages. They are also used in places with low power dissipation to prevent temperature drive. We used 2W parts for a 0.25W requirement to reduce the drive and prolong the lifespan of these resistors.

Carbon Film Resistor

Riken RM-2 Resistor

Riken Carbon Comp Resistor

Vishay Sfernice RLP and RWM milspec enameled wire wound power resistors, and KOA metallized oxide resistors (only used as bleeder for capacitors) are used at place that requires high power dissipation. They are fire proof, have excellent endurance and low drift (~5% after 1000 h) at high dissipation, with silver / gold / copper termination and tin plated copper leads.

Usually these are used in professional equipment such as test & measurement industries, medical appliances and aerospace industries. They are surprisingly good sounding ultra-reliable. You shall hardly see them in commercial audio equipment due to the cost involved in purchasing these resistors, perhaps in some VERY high end equipment only.

Panasonic 561 Resistor

Vishay Sfernice

Vishay Sfernice Resistor

Sprague Resistors

Vishay Enamelled Wirewound Power Resistors

Koa Metal Oxide Film Resistors - high voltage

KOA metal oxide film resistors

Precision Wirewound Resistors

What you often saw in cheap tube amps - the blue metal film resistors, we try not to use them. Metal film has a sharp sound character that we try to avoid. They lack of the body and "noise" that carbon film resistors produce.

Transformers (Z11, Super Hi-B, NanoCrystalline, Hybrid Permalloy)

Types of core materials are very important for transformers making, be it a power transformer, choke, interstage or output transformer. If you have not used any high quality cores for your transformers, it is your great loss. They run more efficiently, saving you tonnes of energy (energy bills), they produce less heat, they last many times longer, and they sound much better! 

What comes next will be the winding method. Safety and sound come first. Rubbish (you know what I mean) winding method will fail in a very short service time, and is unsafe - fire and electric hazard. With the correct winding method, safety is given, and transformer performance will be optimized and sound or power quality will be a sure thing. We have talked a lot in our blog on transformers and shall not touch so much here.

J&K Interstage Transformers – interstage transformer is one of the best methods for signal coupling and have the option (step-down to lower output impedance) of provide better drive strength for the driven stage (better bandwidth). The secondary also provides a low impedance path for the grid current as opposed to a grid leak resistor of 50K and above. The quality and bandwidth of the interstage transformers will be crucial to the sound. Use one lousy unit and all hell break loose. Fortunately, J&K is expert in transformer making, and we will be using our own interstages for this purposes. It is recommended that the gain to driver stage interstage uses NanoCrystalline core to unearth, retain and amplifier the smallest signal / nuances for the consequent stages. The driver to power stage interstage can see NanoCrystalline core too, but EI Z11, Super Hi-B or hybrid (Z11 + Permalloy) are acceptable.

J&K inductors / chokes – 2 coil chokes (differential) and single coil chokes, with decent Rdc and inductance are required in Deathbringer design to produce the quietest B+ PSU. Some likes to use tube regulated B+ PSU, either shunt or series regulated. All have their pros and cons, but we still prefer old school traditional chokes with proper tuning of accompanying capacitors to obtain critically damped power supply for the best transient response, low B+ impedance, and low ripple voltage. 3mV – 5mV remaining ripple is the minimum requirement for this design. 2 coil choke are used too to reduce the differential noise, and isolate the analog circuit from transformer/rectifier return current.

Every component in the power supply are analyzed individually and collectively, and selected for the best possible combination to obtain the results mentioned above – capacitance, capacitor ESR, inductance, inductor DCR, capacitor voltage rating, inductor design, reaction of capacitance, inductance, topology (CLC/LCLC), DCR, current draw and etc will determine the output of this filter. Nothing is left out in the design to obtain the best possible B+ power supply.

This is no cut and paste job from past designs. This PSU is specially made for Deathbringer 211 amplifier. Cut and paste, even from famous designs and you are destined to fail. We have repaired and seen the horror stories even with famous designs. Some schematics online are modified (to fail) by evil folks that try to sabotage your creations - beware and be warned! They do not match your designs anyway, why copy theirs? Tailor made it for your amp!

High Voltage Full Wave Rectification

Choke Input Full Wave Rectification

Note: Above design utilizes 2-coil choke in differential mode to reduce noise further. The effects are much better than normal single coil choke alone. 

J&K Output Transformers – output transformer is the heart of a tube amplifier. Nothing is truer than that, so are the input transformers, and interstage transformers. The form a chain and the strength of the amplifier with be the weakest link of them all. Do not skimp on any of them. Output transformer design is even more difficult as it will be faced with an unknown and varying low impedance load – the loudspeaker, millions of them with hundreds or even thousands of different designs, not to mention the crossover types and designs. Unlike interstages where the driven stage is basically limited to a confined parameters – small – medium – big power tubes with almost known capacitance and circuit topologies.  

Therefore, choosing a high quality pair of output transformers is crucial to the good sound of this amplifier. And, we know what we are going for in this case. Do you?

People often like the idea of having multiple secondary impedance taps to match different loudspeakers, such as having 0-4-8 Ohm, or 0-8-16 Ohm, or worst 0-4-8-16 Ohm taps. Go lock down what speaker impedance you are going to have, and limit it to 1 single impedance tap, or worse, 2 impedance taps. Having a single impedance tap at secondary will reduce the design complexity of multiple impedance taps at secondary. The design of an output transformer is already complicated enough, please do not make it worse. If you want the best, have only 1 single tap. If you want the best of both worlds, buy 2 pairs of output transformers, 1 with 8 Ohm, the other with 16 Ohm, or 4 Ohm to match what you have, using a switch to switch between the output transformers.

J&K Power transformers – power transformers selection seems trivial but is very important. That is where all the energy comes from. Use high quality power transformers with high quality cores will reward you in several aspects – low operating temperature, low electric bill, long lifespan, high quality sound, dark background, safety, money saving from damaged amplifiers (all that hard work gone down the drain) and many more. I have seen transformers caught on fire and yet the fuse did not blow and that is something that you truly do not want to see.

Other things such as configurable multiple mains input, multiple electrostatic shields, 24/7 rated operation, balanced winding method for balance output voltage at both arms for center-tapped winding, use of high grade cores, high quality OFC copper wires, low noise, low mechanical vibration, high efficiency design, high accuracy design (5% tolerance), and etc are by default standard features. 

Power Supply

Power supply makes or breaks an amplifier. Wimpy power supply = wimpy amplifier. We are looking for stability, no ringing, critically damped, fast response rate, low ripple, and most importantly tube rectified (for tonality and warmth). We are listening to power supply sound.

Ripple wise, we aim for 10mV-30mV on B+ for power stage, and <5mV for B+ for gain and driver stage. Stabilization rate, we aim for <0.5s for all stages. There shall not be any ringing on the power supply ramp up as this is an indicator how well it will behave during actual operation. Ripple is sinusoidal and voltage is flat after it stabilizes at ~0.2s-0.5s. Current is drawn according to the music passages, and the recharge rate of the power supply determines how well it can keep up with the music. The nearby bypass capacitors take charge of the high frequency needs, and the power supply, as a whole, manages the low frequency energy draws to supply to the amplifier stage and to replenish the energy drawn to 

Ultra Responsive High Voltage B+ PSU

B+ PSU for gain / driver stage

Take a look at the power supply response at the attached picture. They are the result of actual current draw at actual B+ voltage required by the 211 amplifier. The high voltage B+ is with capacitor input topology, and the medium voltage supply is with choke input topology. Both are tube rectified, with only 2 chokes as filters. There are chokes at the return path too, to reduce the noises at the ground return path, and isolate them from polluting the analog ground.

5/30/2016 - added additional graphs on the PSU. I doubled the load at 2s and you can see that the power supply recovered to the steady state in <0.5s. That's what a real dynamic PSU should behave. If it takes >1s to recover, you know it is going to be sloppy. Using the most expensive audiophile capacitor will not help you here if it is fundamentally wrongly designed.

Active regulation with tubes, shunt or series, some may ask. They are not for power amplifiers. They are based on feedback and we aim for zero feedback. You WILL hear them since we are listening to "power supplies".

Preamplifiers, maybe, but not necessary if you know what you are doing. One can hardly hear hum on our preamplifiers or power amplifiers with volume turned to maximum and ears next to the speaker drivers for our high end version. Some low end versions may sacrifice some to get decent sound over minimal acceptable hum (only audible when ears are next to the speaker drivers).  

It is no easy feat to get the right response for both the supplies. It is easy to dump in lots of capacitors, chokes and multiple stages of filters, but you won’t get such results as this. Too much capacitors and chokes will slow down the power supply too much and cause it to be slow and muddy. Bass will be loose and sloppy although there are tons of energy reserves when it is at steady state.

Try and you shall see.  

Chassis

Copper and aluminum plates, 3mm to 5mm thickness. Solid hardwood base. CNC cut holes. What could be nicer than that? It comes with a price but the return manifolds – you get a unique and living amplifier, much better than cold hard fully metal chassis. 

Usually our chassis will be made of Myanmar solid black ebony wood, which is one of the hardest and densest wood available for audio use. The usual wood thickness will be 20mm for the base, and thicker upon user request. For finishing, we usually do not use lacquer or paint, but with wood wax or oil to keep the wood alive and reduce chemical poisoning. 

Hardwood Tube Amp Chassis

 

Solid Wood Tube Amp Chassis

Wood Valve Amp Chassis

Layout

When it comes to layout, look and shortest signal path are always in conflict. If you want to look the nicest, it will not be with the shortest signal path. Therefore, we shall evaluate the importance and do the best fit of both worlds.

Point-to-point wiring with the short signal paths will be implemented, with the exception of filament supplies that will be mounted on PCB to enable neat wirings. Filament supplies are less critical and therefore are allowed to do so. For mounting of components, 5mm turret boards or thick 5mm-10mm is used to secure the components in the chassis for safety and stability. Partial star ground and bus ground methodology.

Solder

Solder – yes, solder is important. That is the most frequently used component in a tube amplifier! We use only high quality solders. WBT, Furutech, Almit, and Kester, these are the ones we use for soldering the amplifier. If one wants to use Nassau or WE solder, so be it. We use high quality solders only. Those with unknown sources and quality will not be used.  

Soldering iron – Hakko controlled temperature soldering station and Antec 25W solder irons are what we used to ensure each and every solder joints are property bonded to provide the best contact and connection possible. Joints are secured mechanically first before being soldered/sealed with solder.

Volume Control

23 steps, 64 steps, 128 steps, or 256 steps attenuator can be used, as long as it is not carbon brush pots. If you must use carbon brush pots, then go for Alps Black Beauty. Stepped attenuators are matched between channels and therefore provides better stereo imaging than carbon brush pots. Furthermore, precision resistors and sealed relays are used to provide better contacts, stability, and results. 

Relay 128 step volume control

There are still more to be discussed, such as the mechanical parts used, binding posts, RCAs, screws and nuts, switches, knobs and such, but this article has gone too long.

Till then, hope you enjoy this article. 

Notes: 

1. Shipping case is a must for overseas shipment. We have professionally made studio equipment cases, used for professional studio equipment, for purchase with the purchase of our gears. 
2. Some of you may not agree with what we practise, that we totally understand. It is a matter of taste and personal beliefs. Let's keep personal opinions to ourselves and do not argue over it. PEACE.
3. Our design methodology may change depending on usage and final goal of the designated gear.

J&K Audio Design

5/29/2016


Product Lists  
Level 0

Level 1: link 1, link 2, link 3

Level 2: link 1, link 2, link 3, link 4, link 5, link 6 

Level 3: depends on type, size and complexity. Email us for details.

Iso-trans: link 1, link 2

* Finished amplifiers, DACs, audio gadgets, upgrades and repairs - this is not our core business and we do it out of passion. We do not have fixed models, fixed price and we customize for each individuals. The sky is limit of creativity.  

* Our product lines are always improving and increasing. If you do not see what you want, contact us!  

* Please email for volume discounts, distributor and OEM pricing.