Headphone amplifier on ECC88 and 6N6P that is "FARELKA"

Pltin74 23 Jan 2025 21:04 14 4140 Cool? (+22)

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TL;DR

A headphone amplifier called FARELKA uses ECC88 and 6N6P tubes to drive Beyerdynamic DT990 Pro headphones.
The ECC88 forms a standard control stage, while the 6N6P output stage uses cathode followers with MJE340 transistor current sources and a 40 V heater elevation.
The power supply adds a gyrator filter and a capacitance multiplier, and the separate current-source supply delays turn-on by 15 seconds.
It stays silent in headphones and is described as sounding brilliant.
The design is not universal: the output stage should not be used below 250 Ω, and the transformer is rated at 200 V AC and 100 mA.

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Hello to all enthusiasts of home tube designs! I come today with a headphone amplifier project using ECC88 and 6N6P tubes. This amplifier was created to drive the Beyerdynamic DT990 Pro headphones, which, as befits studio headphones, have a sizable impedance (250 Ω). It was one of the longer projects, due to the fact that I am still a beginner when it comes to electronics, and also because I was implementing solutions that were completely new to me at the time. It is not a perfect design, and unfortunately it is not universal either, because the impedance that this amplifier can handle should not be lower than 250 Ω (due to the design of the output stage), but for my applications it is ideal.

I built the amplifier using components I had in store, i.e. transformer, tubes (although initially there was going to be a second 6N6P or 6N1P in the control stage, but I got a couple of ECC88s from a friend). As the power transformer had limited capabilities (200 V AC and 100 mA), it fell to a 'simple' cathode secondary for the output. Had I had a transformer with higher maximum currents and voltages, I probably would have opted for a White's secondary, but alas

.

There was a lot of news in the power supply, as I decided to implement active filtering with a gyrator (which in the end was not particularly necessary) and a capacitance multiplier. The control stage on the ECC88 is a typical circuit, without any miracles, except that it has a balance potentiometer in the cathodes of both tubes (not the best solution, but it works). Much more (in my opinion) happens in the final stage. The 6N6P tube acts as a cathode secondary, however it is not a typical secondary as the cathode resistor has been replaced by a current source on an NPN MJE340 transistor (now I would do it on a MOSFET). The current sources are powered by a separate power supply with a built-in base voltage turn-on delay (set to 15 seconds from what I remember). Each source has a precision potentiometer in the emitter to set the current, so that the current of both halves of the tube can be set perfectly. Because the voltage at the 6N6P cathodes exceeds the maximum heater-cathode voltage, I used an elevation voltage that is 40 V. I took a lot of information and inspiration from Mr Merlin Blencowe's books. I attached the MJE340s to the chassis because they heat up a lot, and that's why the name "FARELKA" came about, because the amplifier can get

(but of course within the norm).

I made the enclosure from walnut wood and aluminium, which I cut out using CNC. The screw mounts, the transformer 'cage' and some other parts were printed on a 3D printer. I placed the amplifier parts on a turret board, as I am a fan of this technique. I have tried to keep the interior as neat as possible, but that is for you to judge. I like it.

As for the sound - in my opinion it sounds brilliant. You can't hear any noises (when I first fired it up during testing and heard nothing in the headphones, I was sure it wasn't working. All I had to do was turn up the volume control). I'm not an audiophile or anything like that, but the amplifier continues to impress me, as well as my friends who have had the opportunity to test it.

What do you guys think? ;D

About Author

Pltin74 wrote 143 posts with rating 132 . Live in city Tęgoborze. Been with us since 2019 year.

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TechEkspert 24 Jan 2025 00:15

The design looks interesting, the wooden parts came out very professional. Perhaps a metal knob would be useful? Why do studio headphones have a higher impedance? You've described the listening experience... [Read more]

Olkus 24 Jan 2025 15:37

Pretty neat. It's nice that something audio and tube-based has appeared in the DIY section :) Wooden parts brilliantly done, the fit of the whole is also flawless. In my opinion, this black cage is a... [Read more]

Pltin74 24 Jan 2025 16:52

. I just like this knob for what it is, but maybe I'll think of something! I asked chatgpt because I didn't know myself, here is the answer: 1. precision and sound quality - Better driver control:... [Read more]

Olkus 24 Jan 2025 17:03

If you like it then OK. After all, it is you where this amplifier will stand and play, the most important thing is that you like it :) . . Anode voltages (if constant) are less of a problem than... [Read more]

PiotrPitucha 24 Jan 2025 19:36

Hello I disagree with ChatGPT's answers :) , a total crock. Reading this text, I feel like I am at an exhibition of paintings where instead of pictures in frames there are descriptions of them. Analysing... [Read more]

Pltin74 24 Jan 2025 20:19

don't want to publish the schematic as I plan to try and monetise my creations in the future :) . [Read more]

TechEkspert 24 Jan 2025 21:22

GPT sounds a bit like an audiophile with this analysis, I found another thing that GPT completely fails to do - write code in Bascom 8051 ;) What kind of woodworking is needed for such an effect?... [Read more]

Pltin74 24 Jan 2025 22:05

the wood has been sanded (at the carpenter's) and oiled with wood oil. after oiling nothing else :) . Added after 24 [minutes]: coding is better handled by claude, I recommend :) . [Read more]

jackfinch 25 Jan 2025 00:01

Hello What are the approximate costs of building such an amplifier and from which devices will this amplifier amplify the audio signal? Greetings [Read more]

Pltin74 25 Jan 2025 08:23

What costs are involved? About building it yourself or having it built by me? :D If it's the 2nd, then please priv :d As for sound sources, I've plugged everything I have into it: phone, computer and... [Read more]

tytka 26 Jan 2025 17:12

The interior aesthetics are undoubtedly an asset to this project. And I have to admit it, even though I am not a fan of the old style of mounting tube equipment. On the electronic side, it's hard to... [Read more]

Tremolo 26 Jan 2025 20:11

250ohm a 50ohm mentioned by kol titka is also OK. Maybe even 32ohm would do. The power will be reduced a little. As for size..the dedicated designs for the Sennheisers are huge. Too bad you can't see... [Read more]

Pltin74 16 Feb 2025 18:20

. The amp was designed to drive 250ohm headphones (which I have) to the maximum. You could plug 50ohm headphones into it, the music would "play", but the power would be drastically reduced (and it would... [Read more]

tytka 16 Feb 2025 21:24

. Well that opinion was probably a bit over the top though. Besides, note that in the 1960s of the previous century, it was even the Japanese who had inferior technical conditions to those to which... [Read more]

FAQ

TL;DR: For DIY builders using 250 Ω headphones, this ECC88 + 6N6P OTL amp solves one core problem: clean drive from a tube design. The builder reports "you can't hear any noises" and designed it specifically for Beyerdynamic DT990 Pro 250 Ω headphones, not universal low-impedance loads. [#21406898]

Why it matters: This thread shows the practical trade-offs that make a quiet, good-sounding tube headphone amp work with high-impedance headphones while limiting flexibility with 50 Ω or 32 Ω loads.

Option	What was discussed	Practical result
Simple cathode follower	Chosen because the transformer offered 200 V AC and 100 mA	Fits the available PSU limits and the final build
White cathode follower	Considered, but not used	Would need a transformer with higher current and voltage capability
250 Ω headphones	Target load for the build	Full intended operation with DT990 Pro
50 Ω or 32 Ω headphones	Mentioned as possible but suboptimal	Music will play, but power drops and tube operating points shift

Key insight: The amp succeeds because every major choice serves one target: a quiet OTL output for 250 Ω headphones. Its biggest strength and biggest limitation are the same design focus.

Quick Facts

The amplifier was built around ECC88 in the control stage and 6N6P as the cathode-follower output stage, with a transformer limited to 200 V AC and 100 mA. [#21406898]
The 6N6P stage uses NPN MJE340 constant-current sources, a delayed turn-on for base voltage of about 15 seconds, and heater elevation of 40 V. [#21406898]
The stated input-side HF limit is about 25 kHz at the volume pot midpoint, using 100 pF, 10 kΩ, and an effective 35 kΩ series resistance. [#21407894]
The output high-pass network uses 100 µF and 10 kΩ; with 250 Ω headphones connected, the builder estimates a low cutoff near 6.5 Hz at about 244 Ω effective load. [#21407894]
The enclosure combines walnut wood, aluminium, CNC-cut parts, 3D-printed details, sanding, and oil finishing; the PCBs were custom-designed and ordered from JLCPCB. [#21406898]

How does an ECC88 + 6N6P OTL headphone amplifier like "FARELKA" work with 250 Ω Beyerdynamic DT990 Pro headphones?

It works well because the amp was designed specifically around 250 Ω headphones, namely the Beyerdynamic DT990 Pro. The ECC88 handles voltage gain, and the 6N6P works as a cathode-follower output stage, which suits higher-impedance loads in an OTL design. The builder describes the result as quiet enough that initial testing sounded like silence until the volume was raised. He also states the amp should not handle loads below 250 Ω as its intended operating condition. [#21406898]

Why was a simple cathode follower chosen instead of a White cathode follower in this ECC88/6N6P headphone amp?

A simple cathode follower was chosen because the available transformer was limited to 200 V AC and 100 mA. The builder states that with a transformer offering higher voltage and current capability, he would have preferred a White cathode follower. That makes this a supply-driven decision, not a purely sonic one. In practice, the simpler output stage let the project fit the parts already on hand and stay within PSU limits. [#21406898]

What is a gyrator in a tube amplifier power supply, and what does active filtering with a gyrator actually do?

"Gyrator" is an active PSU filter stage that imitates choke-like smoothing electronically, a key characteristic being ripple reduction without using a large physical inductor. Here, the builder added active filtering with a gyrator in the power supply as one of the project’s new elements. He later says it was "not particularly necessary," which implies it was used mainly to improve supply cleanliness rather than to solve a proven fault. In this build, it was one of two extra PSU-cleanup measures alongside the capacitance multiplier. [#21406898]

What is a capacitance multiplier, and why would you add one to a tube headphone amplifier PSU?

"Capacitance multiplier" is an active PSU smoothing circuit that makes a supply behave as if it had much larger capacitance, a key characteristic being reduced ripple and noise without huge capacitor values. This amp includes one in the power supply as part of the builder’s effort to keep the amplifier quiet. That matches his listening report: he says no noise was audible in the headphones during startup testing. In a tube headphone amp, that makes the PSU quieter under real listening conditions. [#21406898]

How do you set up and bias a 6N6P cathode follower with an MJE340 constant-current source and emitter trimmer?

You bias it by setting each half of the 6N6P with its own MJE340 current source and emitter trimmer. 1. Power the output stage from the dedicated current-source supply with the delayed base-voltage turn-on. 2. Adjust the precision trimmer in each emitter. 3. Match both tube halves so their currents are set as accurately as possible. The builder used separate sources for each half and says the delay was about 15 seconds. He mounted the MJE340 devices to the chassis because they run hot. [#21406898]

Why is heater elevation around 40 V needed in a 6N6P output stage when the cathode voltage gets too high?

Heater elevation around 40 V is needed because the 6N6P cathode voltage exceeds the tube’s maximum heater-cathode voltage if the heater stays near ground. The builder explicitly states that he added an elevation voltage of 40 V for this reason. In a cathode follower, the cathode sits high, so raising the heater reference protects the heater-cathode insulation. Without that shift, the tube can operate outside its safe heater-cathode limit. [#21406898]

What bandwidth and frequency response should you expect from an ECC88 input stage with a 100 pF capacitor, 10 kΩ grid stopper, and 50 kΩ volume pot?

You should expect a top-end bandwidth of about 25 kHz at the volume pot midpoint. The builder explains that the ECC88 input uses a 100 pF capacitor plus tube capacitance and a 10 kΩ grid resistor, with a 50 kΩ pot ahead of the stopper. At the midpoint, the effective series resistance becomes 35 kΩ from 10 kΩ + 25 kΩ, and he estimates that passes bandwidth to about 25 kHz. Subjectively, he describes the sound as wide, clear, and not lacking bass. [#21407894]

How do you calculate the low-frequency cutoff of a headphone amp output that uses a 100 µF coupling capacitor with 250 Ω headphones?

You calculate it from the output high-pass network formed by the 100 µF coupling capacitor and the effective load seen at the output. In this build, the builder treats the output as 10 kΩ || 250 Ω, giving about 244 Ω effective load. Using that value, he estimates the cutoff at about 6.5 Hz. That means bass extension should comfortably cover the audio band when 250 Ω headphones are connected. [#21407894]

What happens to power output, operating points, and tube stress when you connect 50 Ω or 32 Ω headphones to an amp designed for 250 Ω loads?

Power output drops, operating points shift, and tube stress increases when you connect 50 Ω or 32 Ω headphones to this amp. One commenter says even 50 Ω or maybe 32 Ω may still play, but the builder clarifies that the amp was designed to drive 250 Ω loads "to the maximum." He adds that 50 Ω headphones will produce sound, yet power is drastically reduced and the change is unhealthy for the tube because operating points move. That is the thread’s clearest failure case and limit. [#21442307]

ECC88 vs 6N1P in the driver stage of a tube headphone amplifier — which is better and why?

This thread does not prove one tube is better; it shows why ECC88 was used in this specific build. The builder says he first considered another 6N6P or a 6N1P in the control stage, but finally used ECC88 because he received a matched pair from a friend. He also describes the ECC88 stage as a typical circuit without exotic tricks, aside from a balance potentiometer in the cathodes. So the choice here was driven by parts availability, not by posted measurements or a formal tube comparison. [#21406898]

Where is the best place to mount RCA inputs in a tube amplifier to minimize hum and interference: front panel or rear panel?

In this build, the front panel was chosen to reduce interference risk from rear wiring that carries AC and anode voltages. The builder explains that the back of the enclosure already has more wires with AC and high-current anode supply present, so moving RCA inputs there could worsen interference. Another commenter argues rear placement would look cleaner, especially after adding a DAC or preamp. The thread therefore favors front placement for noise control in this exact layout, not as a universal rule. [#21407894]

How do you build a neat turret-board tube amplifier layout and keep the internal wiring quiet and organized?

You keep it neat by separating functions, using a turret board, and planning the chassis around heat and noise. The builder says he mounted the amplifier parts on a turret board, kept the interior as tidy as possible, and fixed the hot MJE340 devices to the chassis. He also kept RCA inputs away from the rear area with AC and anode wiring. A commenter later says the inside makes a better impression than the outside and praises the interior workmanship as very good for DIY. [#21442636]

What woodworking steps were used to get the walnut-and-aluminium enclosure finish — CNC cutting, sanding, and oiling?

The enclosure used CNC-cut walnut and aluminium, then sanding and oiling. The builder says he made the case from walnut wood and aluminium, cut the parts on a CNC machine, and printed mounts, the transformer cage, and other parts on a 3D printer. When asked about finishing, he explains the wood was sanded by a carpenter and then oiled with wood oil. He adds that nothing else was applied after oiling. [#21408414]

How much does it cost to build a DIY ECC88 and 6N6P headphone amplifier like this, and which parts usually dominate the budget?

This thread does not give a build total, so no exact DIY cost can be quoted from the source. The builder avoids posting a price and instead jokes that anyone wanting one built by him should contact him privately. Even without a number, the thread shows where complexity sits: a custom wood-and-aluminium enclosure, CNC work, 3D-printed parts, custom PCBs from JLCPCB, a transformer, and multiple tube-stage PSU features. Those are the most likely budget drivers mentioned here. [#21408688]

Which audio sources can feed this type of tube headphone amplifier properly, and how does a turntable with or without a built-in RIAA preamp change things?

A phone, computer, and line-level turntable source can feed it properly, but a turntable without RIAA preamplification cannot. The builder says he connected a phone, computer, and turntable and that all worked fine. A later correction adds the key condition: this amplifier does not include an RIAA preamp, so the turntable must have one built in, or an external phono stage must be used. That makes line-level sources straightforward and raw phono cartridges unsuitable on their own. [#21411100]

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