End-game DHT Headphone Amp


This is a high end, 300B low power headphone amplifier with a 32 ohms output at max 6.75W. It has also 8 ohms speaker output which makes it a versatile amplifier.

The amplifier is uses all Hashimoto transformers and chokes, and it is assembled on a sturdy, high quality, 1/8″ aluminum made by Dave at LandFallSystems, and wrapped on walnut front and sides.

 The amplifier has a vintage look which it is emphasized by a large Bakelite knob and an aircraft dimmable Dialight red panel indicator.

This amplifier was designed with TLC in order to provide best out of the 300B tubes. It is a single ended design and consequently the sound is pleasant, detailed and easy to listen for long hours, with a predominant second harmonic.

The power supply has a powerful 5AR4 or GZ34 rectifier, followed by a CLCLC filtering using two Hashimoto 10H chokes, and two 4 poles Mundorf HV+ high fidelity capacitors. There are 3 separate 6.3Vdc regulated supplies for the 300Bs and C3g tubes, an excellent choice for zero hum. The filament supply for the 300Bs is using super regulators from Belleson.

The audio section of the amplifier uses the C3g pentodes in triode mode loaded on a cascode CCS for minimal distortions. The C3g is used as gain stage/ driver and it is capacitor coupled to the 300B, using two excellent MiFlex KPCU copper foil Poly/Paper in oil capacitors. The final/power stage is using the 300B self-biased using Mills resistors and Mundorf Mcaps capacitors. The 300B is loaded on a specialized Hashimoto headphone transformer.

All the small parts are audio grade and tested for the best sound. I used Takman Rex, Takman Rey, Mills, AMRG, Vishay Milspec and 5W Kiwame for the supply bleeders.

The amplifier is integrated with one RCA and one XLR input, and the volume control is a ladder type TKD CP2511 potentiometer, which is very smooth and clean sounding.

The XLR is transformer coupled to the RCA, using a high quality Jensen JT_11P-1 line input transformers. There is a switch provided to allow using either the RCA or XLR input. The XLR inputs have a ground lift switch which is recommended by Jensen technical stuff to keep it on lift position.

The bottom plate has over 100 holes for natural convection and 4 custom feet using wood and vibration isolators.

The amplifier delivers 6.75 maximum on 32 ohms (14.7Vrms), 4.3W on 50 ohms, and 1.8W on 120 ohms and 0.86W on 250 ohms headphones.

The amplifier will also deliver maximum 6.75W on 8 ohms speakers. There is a switch provided to use either speakers or headphones. However, depending on the grounding scheme of the audio chain it might have no audible effect.

Specifications and measurements

The following measurements are only to give you a sense of the approximate performance. I used a computer software and interface and this comes with some artifacts and noise that are not present when the amp is connected in an audio path. One, if owns high quality audio analyzer, can take more precise measurements

  • Input impedance RCA : 50kohms, unbalanced
  • Input impedance XLR : 13kohms, balanced
  • Frequency response: 20Hz-20kHz @ –0.5dB
  • Input sensitivity: 0.44Vrms at 1.1W power output
  • Max Input sensitivity: 1.12Vrms at 6.75W power output on 32 ohms
  • Gain max 22.5dB (13.3x)
  • AC voltage 120V, 50/60Hz
  • Dimensions: 19.25″x14″x10″ (W x D x H)
  • Weight: 55 lbs.
  • Main fuse 3A slow blow

Price: $7000 ( not including the EML300B tubes )

Lead time: 3-4 months ( could be shorter depending on the time to procure parts).

Please email me to discuss details at : simplepleasuretubeampsRCT@gmail.com

Shiny Eyes EML20A Preamplifier

The EML20A is an excellent choice for a single stage preamplifier that can satisfy the most exigent audiophile. This DHT has enough gain to use it with line output transformer and it is indeed, as stated by Emission Labs, one of the lowest distortion tube ever built.

The preamplifier has a separate power supply, which is a great practice inn order to make a quiet DHT preamp.

The power supply uses all Lundahl power transformers and chokes for the high voltage section. It is a CLC  supply with the Ludahl chokes in common mode for lower noise. The rectification is hybrid, using two TV dampers 6CJ3 on the positive and SiC 1200V on the negative.

The power supply is connected to the main preamp chassis through a 6 feet umbilical cord using a MIL spec Amphenol connector. The umbilical cord is carrying only DC and it is screened with copper mesh, which a good practice to have a good S/N ratio.

The low voltage supply for the filaments of the EML20As is on a separate board with its own transformer. There is a third DC supply for the Volume remote control and shunt output delay circuit.

The main preamplifier  uses the excellent high gain EML20A mesh in a self biased setup and loaded on a Monolith Amorphous Core LTA 01/25mA line output transformer (wired 4:1).

The cathode bias resistors are Mills MRA-5 and the decoupling capacitor is Elna Cerafine.

The input is DC coupled and the output is transformer coupled. There are no coupling caps for input or output, an no negative feedback ( global or local).

The volume control is ePOT V3 mini by Tortuga Audio using either LDR module or 60k discrete steeped attenuator module. The display is Oled and remote by Apple.

This is one of the simplest one stage preamps that is using an excellent sounding DHT and extremely low distortions, second harmonic being dominant. The gain is 14dB ( 5x) and with a 2Vrms source will provide 10Vrms at a Zout of 375 ohms. Measured THD was 0.02% at 10Vrms output ( 50Vrms on the plate).

“Shiny Eyes” Supreme 300B Headphone SET Amplifier

This  headphone amp was due for many years. It was many years ago when I start fiddling with the idea.

After many experiments and measurements, I concluded  that a SET 300B headphone amp is best fit to my sound taste and design preference.

With few things left over or repurposed from previous projects, I’ve managed to finish a C3m – 300B headphone amplifier. It is a one enclosure amplifier using all Lundahl transformers and choke and the long lasting EML300B. If you don’t recognize the C3m in the pictures is because I cut out the aluminum screening can.

The power supply is using a Lundahl power transformer and choke and a hybrid bridge. The rectifier bridge is using SiC 1200V diodes for the negative and two 6CJ3 TV dampers for the positive. The vacuum tube rectifiers are ramping the B+ in a very slow manner ( about 20 seconds). The filtering is C-L-C with 50uF first cap and 220uF second. I am using a Neurochrome Maida 21st Century regulator which provides 385V with extremely low ripple, and protection at 300mA. This accomplished two of many requirements : a super quiet amplifier and the 300B/output transformers are protected. The filaments of the 300Bs are DC powered from a separate supply using its own transformer and it is regulated. Also the C3m filaments are DC powered from a separate supply using its own transformer and it is regulated. I am very careful about the design of the power supply which is a key to a good sounding SET amplifier.

The main amplifier is using the LL2765AM/70mA wired as 12:1 step down. The 300B is biased at Ua=310-320 V and Ia=65-70 mA, dissipating about 22W on the plate. This gives a lot of headroom for this amp and also a long life for the power triodes. The driver/gain stage C3m is loaded on a cascode CCS and it is capacitor coupled to the 300B using very good sounding Miflex caps. Both tubes are self biased and there no NFB applied.

The enclosure is a excellent built and sturdy by Landfall Systems. I used blood wood hardwood for the front and sides. The top plate was redone, CNC at Front Panel Express for a more professional/pleasant  look.

The amplifier frequency response is 25Hz-25kHz at -1dB, the overall gain is 14-15dB and THD with 1Vrms input is 0.02%, delivering 1W on 32 ohms or 100mW on 300 ohms. The FFT, at a 2Vrms output shows only the 2nd harmonic, all other harmonics are hidden bellow the noise floor. This gives this amplifier an extreme SET DHT sound, very clear, pleasant and clean.

The Zout is 8 ohms. The headphone amplifier can also be used as a preamplifier delivering very clean signal to a lower gain input sensitivity amplifier. Given the very low output impedance, it can drive heavy capacitive loads ( long cables/lines) and amplifier low input impedances.

Radu’s Ultimate 300B Amplifier: Shiny Eyes 10Y/20A – 300B SET Amplifier

Ultimate 300B front overview

There is no greater satisfaction for a music lover than having an ideal audio chain. This is a 300B amplifier that will not disappoint. It is the result of many years of experimentation and R&D with DHTs ( direct heated triodes).

Why 300B?

  • Because it is one of the most praised DHTs of the past.
  • Because it can deliver enough power to drive speakers that are not super sensitive and therefore more available.
  • Because it is available as new production in many brands and “flavors”
  • Because, if well designed, an amp using 300B can satisfy an exigent audiophile

I am publishing this build after the 71A sub-watt amplifier. I love the sound of both amps, as well as few other amazing DHTs such as the 45. Each amp can offer rewarding sound experience as long as it is paired with an appropriate speaker. I want to emphasize that one can’t go wrong when using these old design vacuum tubes.

I’ve always liked the sound of a 2 stage amplifier. The best sounding of 2 stage amps have a DHT for both the final stage and the driver.  In many cases these amps have low input sensitivity and therefore need a preamp with medium or high gain. If the preamp is using a DHT then the whole audio amplification  is DHT. The great advantage of having all DHT amplification is the low distortion where the 2nd harmonic is predominant. There is no need for global negative feedback. The sound will be amplified in a way that is not loosing detail and will be extremely pleasant.

This amplifier is using either the 10Y/VT25 or the EML20A as driver. The driver is loaded on an interstage transformer Lundahl LL2756/25mA. The driver is powered through a CCS ( cascode depletion mode mosfet) that is adjusted to 25mA. Both the driver and the final stage ( EML300B) are self-biased.

The 300B is loaded on a excellent sounding output transformer Monolith Etude1. The output is switchable between 4 and 8 ohms.

Each tube filament is powered by a Coleman regulator that has individual multi-turn potentiometer for fine adjustment. As always there is no “free lunch”. The excellent sounding Coleman regulator needs re-adjustment every time one will replace a tube. Believe me, it is worth the trouble…

The power supply was built in a separate enclosure ( using a Modushop ( Italy) Pesante enclosure placed sideways to minimize footprint). It has 4 separate raw DC supplies for the filaments of the 4 DHTs. The high voltage supply is in a quasi choke input mode and it uses all film caps ASC. The rectifiers are 6CJ3 TV dampers.

The umbilical cord is permanently attached to the power supply enclosure and has a military grade Amphenol 11 pins connector at the amp end. Few years ago I found a nice 1000V NOS large Simpson panel meter on eBay. I am using it to show the B+ high voltage of about 480V. The power supply has two main switches: one for the filament supplies and the other one for the high voltage supply. They are in series and therefore one can’t turn on the high voltage before turning on the filament supply. In the past I’ve used a relay to delay the high voltage. In this case, I prefer manual switching because of the slow warm up caused by the Coleman regulators. Some of the 300B need few minutes to reach steady state on the filaments, such as the EML300B. Turning on the filament supply switch will allow the user to wait a desired amount of time before switching on the high voltage. The high voltage will slowly ( takes about 20 seconds) ramp up. This is beneficial for the life of these expensive vacuum tubes.

The input sensitivity is about 3Vrms for 8W output with the EML20A driver and about 8Vrms with the 10Y driver. I am using a switchable 01A-26 full gain  ( x8  or 18dB)  preamplifier that provides sufficient signal level for both drivers.

I will always refrain to describe how any of my builds will influence the sound. That should be a personal preference. However, the synergy amp -speaker/room is the most important. It definitely sounded noticeable better using Rullit’s field coil speakers in cabinets designed by my audiophile friend Rich, compared to my TangBand tower speakers.

Here are some pictures that will give you an idea of how this amplifier is built:


And here is the power supply:

A marvelous low power 71A DHT amplifier

C3g-71A amplifier 2019

Iphone May 2019 299

Seeing an amp delivering such a low power, one might ask the question: ” How low can you go? “. Believe me, I can go even lower.

Here is a 750mW DHT amplifier using the amazingly good sounding 71A. Last year I’ve been asked by Kevin at Glow In The Dark Audio to build such an amp and here is the link to the description and his impressions about it: http://www.glowinthedarkaudio.com/radu-tarta-71a.html.

At that time I was not thinking to build one for myself, but after listening to the amp I’ve built for Kevin I’ve decided to make my own. It is almost the same design with the exception that I’ve used the C3g as driver. The reason I needed a bit more gain was to be able to use it without a preamp.

I’ve used same Sony power transformer and Tamura 5k/8/600 output transformers. I am impressed with the sound of these small output transformers: very detailed and balanced.

The enclosures are made with Cherry hardwood and the top plates are 12×12” sanded aluminum.

The power supply uses the 80 rectifier in a choke input LCLC filter, and separate raw DC supply for the filaments of the 71A and C3g. The umbilical cord is screened and carries only DC and it is terminated on a Mil spec Amphenol connector. I found two vintage Westinghouse panel meter that show the B+ voltage and the total current in mA.

The amplifier is using an active load for the C3g ( DN2540  CCS) and it is capacitor coupled to the 71As. Both stages of the amp are self biased and are using high quality components. The amplifier has a very smooth TKD CP2511 stereo attenuator.

The filaments of the 71A are powered by two Coleman regulators that bring the sound of this little power amp to a next level. There are two multi-turn potentiometers and a panel meter that allow the user to adjust the voltage to 5V for each 71A filaments.

The amplifier can also be used as a high gain ( 30dB) line stage due to a 600 secondary on these little Tamura transformers. This comes handy when one has a very low input sensitivity amplifier. It can also be used to drive a First Watt F4 ( which has unity gain) to its full power.

Due to its careful built and separate power supply this amp is perfectly quiet.

At this level of power output one needs ultra sensitive, easy to drive speakers of 106+ dB.


Shiny Eyes Turbo 45 SET Amplifier

Shiny Eyes Turbo 45 SET Amplifier


My latest 45 amplifier is a great candidate for a keeper. After a listening session to a Yamamoto 45 amplifier at Rich’s place, and following his thought about more power from a 45 amp that can better drive his Zu audio 99 dB speakers, I started a R&D and breadboarded many of driver choices. The final result was a switchable EML45/45B with 45 driver and 6SN7 gain stage. Despite the efforts to make it as compact as possible, in one enclosure, the final result was a 20.5x13x11″ and 55 lbs monster. The power supply contribute to a good portion of the weight. It has a custom made Heyboer power transformer used for HT with a 750V CT feeding a full wave tube rectifier ( 2x 6CJ3) followed by a 1.5/10uF-LL1673/10H CCMR mode-100uF/550V  Mlytic HV+–LL1673/10H CMMR mode – 220uF/550V Mlytic HV+–. All filaments are DC regulated using LD 1085/V. Separate dual bobbin 56W Triad transformers are used for all 4 of the 45/45B tubes. The 6SN7 filament is also fed from a regulated power supply.

The amplifier is using Electra print 7k/8 ohms low IMD custom transformers and LL2753/30mA as interstage. One can use different type of 45 for the driver such as old RCAs, old globes, EML45. The final tubes can be either any type of 45 or switchable to EML45B.

The wood case is made of exotic bocote wood sealed with 3 coats of shellac and two coats of urethane.

The amplifier sounds excellent using 45 globes for the driver and EML45 for the finals, but is really blooming when using EML45 as driver and EML45B for the final.

Shiny Eyes Mini SE 4P1L amplifier

miniSE4p1l closeup

A while ago I bought a pair of new Tango M705 and wanted to find a good use for it. I also had a small wood case made of oak and accent stained with chestnut. This was the beginning…

I always wanted to build a compact 4P1L amp and here it is my new “Shiny Eyes” Mini SE 4P1L amplifier.

This is a very nice sounding  1.7W amplifier that sounds way bigger that one might think. The secret is to match it with high sensitivity and easy to drive full range drivers., use it in small rooms or be fine with lower sound levels. It can also be used in multi system speakers when driving upper mids or highs when the level of power is sufficient when using high sensitivity drivers.

The amp is using top components and iron. The output transformers  are Tango M705 and the power transformer and choke are Lundahl. The amplifier has only two stages which is my most preferred setup.

The power tube is the 4P1L in triode mode and the driver/gain stage is the 6SN7 loaded on a mosfet CCS ( cascode DN2540). Both stages are worry free, self biased. The overall gain allowed a very small GNFB of -3dB that improved the THD and the bass frequency response. The 4P1L filaments are powered by voltage regulators, a solution required by the compact size.

The B+ power supply is full wave tube rectified and using a 6BY5GA rectifier and a CLC filter: 50uF PP, LL1673/20H common mode and 220uF Mlytic Mundorf. A really nice 150mA sealed Marion meter is showing the total current. This meter will show about 85mA. The frequency response is 30-40kHz at -0.5dB and THD of 0.7% at 1W with 2nd harmonic dominant.

The amp sounding very detailed, transparent and quite dynamic for its small size. I am very pleased with the sound of a small power compact amp. The amp weights 22 lbs and the size is  13x11x10″.


A Valve Phono-stage Cube


Radu RIAA top

How I’ve got to build this phono stage? My first phono stage build was Kevin’s “The Muscovite” using a nice sounding HF triode 6S3P. I was delighted with the sound of it, but never got beyond breadboard stage. The second build was Salas’s “Valve Itch” phono stage. I had a pleasant sound and dead quiet.

Few years later, I pushed myself to build a good phono stage for my Dual turntable and few records that I own. I had few items that determined the final shape of the preamp: many 6S3Ps bought when trying the Muscovite, a complete RIAA filter components, a readymade cherry box from a different project, and not only. I almost could say that I used most of the components from other projects leftovers.

The design is mostly influenced by Merlin Blencowe. I used the 6FY5/EC97 for the first stage and 6S3P for the second stage. The output is low impedance due to a Mosfet source follower DC coupled to the second stage.

Having a single tall box, imposed to a toroidal mains transformer and SiC rectifiers followed by a CLC filter. To ensure a very low ripple and low output impedance of the power supply, I’ve used an shunt regulator SSHV1.  As a must, I’ve used a regulated supply for the 6.3V filaments.

I’ve also built a Lipshitz-Jung precision Inverse RIAA to test the phono stage. It showed a perfect flat frequency response and a 41-42dB total gain. The THD measured 0.04% at 1Vrms output.

Despite the simplicity of the circuit I’m very pleased with the sound result.


Shiny Eyes EML300B – C3g single ended amplifier

Here is my latest creation inspired by the beauty of a pair of EML300B that was lying unused.

front L

As always, I try to create 2 stage SE amps for many reasons. Hard to do 2 stages with low gain power DHTs. One of the few tubes that have the advantage of high gain, great linearity and still a bit of headroom to be able to let the 300B signature be predominant. The 300B starts clipping at 8W or so and that corresponds to a 1.65Vrms input. The C3g starts clipping at 2.3Vrms input. This allows a headroom of 2.9dB which is not a lot, but still way better than no headroom and better than many designs out-there with drivers that will go into clipping before the 300B.

Anyway, the 300B will distort above 2% at 4.5W and in my opinion the listening levels for a 300B amp should be at 2-3W and that allows a 6-4.2 dB power headroom and therefore creates a more realistic 7.4 dB signal headroom for the C3g.

I was a bit reluctant to built it in one case, but many audiophile are looking for single enclosure amps as more convenient use of space. It ended up weighting more than 50lbs.

The big challenge, when building a tube rectified DHT amp in one enclosure, is to keep it quiet. This amp is dead quiet on my 96dB speakers and my 100dB headphones.

The power supply uses the LL1651 and two LL1673 10H chokes in common mode. The B+ is around 475V. This time I didn’t use the famous Coleman regulators because of lack of space. The 300B filaments and the C3g filaments are powered using LD1085V regulators.

The amplifier is transformer coupled using the LL2753 and the output transformers are Jack Elliano’s Electra-Print 3.5K to 8Ohms low IMD. The tubes are self-biased and decoupled with Elna Cerafine. All the resistors for biasing the 300B are Mills MRA-12. The 300B is biased at 380V/-80V/75mA and the C3g at 225V/-3.5V/17mA.

The amp has an input sensitivity of 1Vrms for 3W output. The frequency response is 20Hz to 25kHz at -0.8 dB and the damping factor of 2.3 which calls for easy to drive, full range drivers.

This amp sounds great on my TangBand and Mark Audio speakers. The bass is well defined and under control, the mids are superb and the high are clean and crisp.


Shiny Eyes SE UL EL34-6SL7 tube amplifier

Shiny Eyes SE UL EL34-6SL7 tube amplifier

front L

Despite the fact that my love stays with DHTs, I’ve designed and built this amp to fill a gap that I thought it was worth the effort: making an amp in one enclosure, small enough but able to put out more power than a 45 or a 4P1L could do. I’ve also wanted to compare the sound with the 300B amp  I was building at the same time.

It all started while I was trying to figure out what amp to build with my last pair of James6123HS. I breadboard the EL34 and tried many drivers and configurations. I’ve ended up liking  the 6SL7 paralleled and using a small amount of global NFB, just enough to bring the distortions down, while widening the frequency response and increasing the damping factor.

This amp measure good as well as sounds very nice. It gives a max 8W at 1.7% ( 0.58% at 1W, 1% at 3W and 1.25% at 5W). The input sensitivity is 1Vrms for 5W output. The frequency response is 10Hz-40kHz @ +0.25dB for 3W output. The damping factor is about 7.

As expected this amp has a predominant 2nd harmonic and the sound is very pleasant. Dear reader, please remember this is still a low power, single ended amp and  will do the right thing if it is used with the right type of speaker ( easy to drive, preferably full range) and music.

I am very pleased with the sound of this amp and considering the cost of tube replacement, I am kindly recommend it for ever is looking for a decent cost SE tube amp that will sound as close to a DHT as possible.

I’ve used all good quality, audio grade components: James 6123HS output transformers, TungSol tubes, Heyboer custom order main transformer and choke, quality Made in Japan sockets, Cardas binding posts, Kimber RCAs, Obbligato Premium Gold coupling caps, Vishay and Takman resistors, Elna Cerafine decoupling caps. The power supply is using CREE Schottky diodes, CDE lytics  and DC regulated filament supply for the 6SL7.

This is a well build amp that will last for a long time and give a rewarding sound. It is self-biased so there is no need for any adjustments throughout the life time of the tubes.

All the equipment is attached to the 1/8″ top aluminum plate that sits on a hardwood wooden case made with the outstanding Brazilian cherry, light oil and urethane coated ( 4 coats).

The amp weights 37 lbs and measures 13x13x9″.