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

Pltin74 4137 14

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

    Headphone amplifier built with ECC88 and 6N6P tubes, featuring a wooden and aluminum enclosure. .
    Homemade headphone amplifier with ECC88 and 6N6P tubes in a wooden and aluminum case.
    Handmade vacuum tube headphone amplifier with wooden casing
    Interior of a headphone amplifier with electronic components. .
    DIY headphone amplifier with tubes in a walnut wood and aluminum housing. .

    Cool? Ranking DIY
    About Author
    Pltin74
    Level 8  
    Offline 
    Pltin74 wrote 143 posts with rating 132. Live in city Tęgoborze. Been with us since 2019 year.
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  • #2 21407135
    TechEkspert
    Editor  
    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 quite succinctly, and it looks like the noise level and overtones are at a low level.

    How do you rate the bandwidth and frequency response?
  • #3 21407817
    Olkus
    Level 32  
    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 bit incompatible with the silver parts of the amplifier. Nothing else is black so in my opinion it would be better if either the grille was silver or the rest was also black. The white knob doesn't fit very well either, but I suspect it's a temporary solution ;) And the RCA sockets on the front - not very convincing to me, I think it would be better if they were on the back, there's plenty of space there.
    These black PCBs are some kind of "ready-made" or just ordered?

    Regards,
    A.
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  • #4 21407894
    Pltin74
    Level 8  
    TechEkspert wrote:
    Interesting looking design, the wooden parts came out very professional. Perhaps a metal knob would be useful?
    .
    I just like this knob for what it is, but maybe I'll think of something!
    TechEkspert wrote:
    Why do studio headphones have a higher impedance?

    I asked chatgpt because I didn't know myself, here is the answer:
    1. precision and sound quality
    - Better driver control: The higher impedance allows for more precise diaphragm control in the headphone drivers. This results in more accurate sound reproduction, which is crucial during mixing and mastering.
    - Reduced distortion: In headphones with higher impedance, the current flowing through the transducers is lower. This reduces the risk of electrical distortion and produces a cleaner sound.

    2 Appropriate adaptation to professional equipment
    - High-impedance amplifiers: studio equipment such as audio interfaces and headphone amplifiers are designed to work with high-impedance equipment. This combination guarantees optimum sound quality.
    - Greater power tolerance: High-impedance headphones can operate at higher power levels without the risk of damaging the transducers. This makes them more reliable in studio environments where high signal levels are worked with.

    3. versatility in studio environments
    - Works with a variety of audio sources: high impedance headphones are less sensitive to the quality of output from different devices, meaning they work better with a wide range of studio equipment.
    - Better noise isolation: Higher impedance allows for more effective noise suppression from external equipment, which is particularly important in an environment full of different electronic devices.

    4 Longevity and stability
    - The high impedance reduces the risk of overloading the transducers, which increases the durability of the headphones in intensive studio use.

    5. tonal balance at high volume levels
    - Higher impedance headphones can better maintain tonal balance at high volume levels, avoiding overly boosted lows or highs.
    ps. please someone knowledgeable on this subject to confirm or deny the words of the bot.

    TechEkspert wrote:
    You have described the listening experience quite succinctly and it looks like the noise and overtones are at a low level.

    How do you rate the bandwidth and response characteristics?
    .

    I haven't measured the noise and hum levels, nor the characteristics, but I plan to do so at some point.

    From a design point of view: at the input of the ECC88 there is a low-pass filter built from a 100pF capacitor(plus tube capacitance) and a 10k grid resistor. In front of the grid stopper there is a 50k potentiometer, which in the middle position (i.e. with the highest resistance in series with the grid stopper 10k + 25k = 35k) passes the bandwidth up to about 25kHz which is a little more than the audio frequency. At the output of the amplifier (cathode secondary) there is a high-pass filter made up of a 100uF capacitor and a 10k resistor which, with 250ohm headphones connected, passes frequencies from about 6.5Hz at a load value of about 244 ohms (10kII250ohm).

    as far as the subjective aspect is concerned: the bandwidth is wide, clear, there is no lack of bottom, and the treble is pleasant, not exaggerated. in my opinion the amplifier sounds great :) .

    Added after 5 [minutes]:

    Olkus wrote:
    In my opinion this black cage is a bit out of keeping with the silver components of the amp. Nothing else is black so in my opinion it would be better if either the grille was silver or the rest was also black. The white knob doesn't fit very well either, but I suspect it's a temporary solution. And the RCA sockets on the front - not very convincing, I think it would be better if they were on the back, there's plenty of space there.
    These black PCBs are some kind of "off-the-shelf" or just ordered?

    Thank you for sharing your feelings! I personally like the effect of a kind of colour 'dissonance' in the form of the black cage, and as for the knob, I personally like that too, however your responses are prompting me to see what the other knobs will look like. The RCA sockets are at the front because there are more wires at the back with AC and anode voltages (with high current) so if they were located there, it could affect some interference. But really thanks for the feedback !

    Olkus wrote:
    These black PCBs are some "off-the-shelf" or just ordered ?
    .
    The PCBs are also of my design, they were ordered from the JLCPCB website. Greetings!
  • #5 21407919
    Olkus
    Level 32  
    Pltin74 wrote:
    Thanks for sharing your feelings! I personally like the effect of a kind of colour "dissonance" in the form of the black cage, and as for the knob, I also personally like it, however your responses make me want to see what other knobs will look like.


    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 :) .

    Pltin74 wrote:
    The RCA sockets are at the front because at the back there are more wires with AC and anode voltages (with high current) so if they were placed there, it could affect some interference. But really thanks for the feedback !
    .

    Anode voltages (if constant) are less of a problem than AC. I would just be afraid that the RCA wires at the front will spoil the aesthetics of the amplifier, there will be a preamp, DAC or whatever added after some time and it will make a "noodle" at the front.

    Pltin74 wrote:
    PCBs are also of my design, they were ordered from the JLCPCB website.


    This is also what I suspected ;) However, I personally would not want to order such small PCBs and would make at home, even much larger ones I make at home, comes out cheaper overall.

    Regards,
    A.
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  • #6 21408196
    PiotrPitucha
    Level 34  
    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 an amplifier without a schematic diagram is like tuning the drive of a car
    without an engine.
    It is a great pity, because there are few tube designs now and it would be interesting to
    to learn about new (or old) solutions of such constructions.
    designs.
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  • #7 21408290
    Pltin74
    Level 8  
    >>21408196 don't want to publish the schematic as I plan to try and monetise my creations in the future :) .
  • #8 21408387
    TechEkspert
    Editor  
    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? Sanding/varnishing/staining?
  • #9 21408414
    Pltin74
    Level 8  
    >>21408387 the wood has been sanded (at the carpenter's) and oiled with wood oil. after oiling nothing else :) .

    Added after 24 [minutes]:

    TechEkspert wrote:
    cannot-write code in Bascom 8051
    coding is better handled by claude, I recommend :) .
  • #10 21408573
    jackfinch
    Level 19  
    Hello

    What are the approximate costs of building such an amplifier and from which devices will this amplifier amplify the audio signal?

    Greetings
  • #11 21408688
    Pltin74
    Level 8  
    >>21408573 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 turntable - all flawless.
  • #12 21411100
    tytka
    Level 23  
    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 say, because we don't know anything. But I perfectly understand my colleague not wanting to reveal his secrets. (I am increasingly thinking the same thing myself.)

    As for the impedance of the headphones, it's clear that when you're doing an OTL tube design, you're not going to power low-impedance headphones with it. Although those stated 250 ohms are a bit puzzling. I use my OTL myself to power 50 ohm headphones with no problems.

    To be honest, even for a tube headphone amplifier, I find your project quite large. Personally, I would prefer something smaller. I know, everything is a matter of taste. And apparently we do not discuss about taste. But since you have presented your project, let me express my own opinion.
    At first glance, visually, the design gives the impression of neat refinement. But when I looked at it a little longer, apart from the aforementioned large dimensions, I could see a lack of style here, as if it were a total misfit. (I don't mean the combination of wood and metal. This, done well, I like very much.) For me, too many colours of wood, aluminium would be enough. And here additionally black of the transformer grille, grey/white volume control knob. On top of that, I would prefer a solid rather than split aluminium insert on the front. Other than that, though, for me, the RCA inputs on the front are a poor idea. They spoil the aesthetics a bit (especially when something is plugged in, rather than standing as in the pictures, unconnected). And while I'm on the subject of sockets, the headphone jack you used isn't one of the prettiest either. Yes I know, it allows for easy mounting in the faceplate, but it also disfigures it a bit.

    I am very sorry to have expressed my opinion so strongly. It's not my intention to belittle you or your actions. But since you mentioned your intentions to possibly sell, I simply expressed my opinion from the point of view of a potential customer.

    p.s.

    Pltin74 wrote:
    What about the sound sources, (...) and the turntable - all flawless.
    .
    Except that not every turntable. You don't have an RIAA preamp in this amp, so the connected turntable must have one built in.
  • #13 21411456
    Tremolo
    Level 43  
    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 that wonderful classic assembly through the sweeping enclosure. Like 1960s Japan but much more professional and qualitatively better.
    Helpful post? Buy me a coffee.
  • #14 21442307
    Pltin74
    Level 8  
    tytka wrote:
    With regard to headphone impedance, it's clear that when you're doing an OTL tube design, you're not going to power low-impedance headphones with it. Although those stated 250 ohms are a bit puzzling. I myself power 50 ohm headphones with my OTL without any problems.
    .
    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 also be unhealthy for the tube, as the operating points would shift etc).

    tytka wrote:
    I am very sorry to have expressed my opinion so strongly. It is not my intention to belittle you or your actions. But since you mentioned intentions of a possible sale, I simply expressed my opinion from the point of view of a potential customer.
    I am very happy for any constructive criticism because it allows me to learn a lot and as you say it allows me to know the opinion of a potential customer, also you have nothing to worry about and apologise! I am a person of the "younger generation" and I and my friends personally like the way it looks, I also know that not everyone has the same taste and not everyone will like it, but I find your opinion valuable and I will probably speak up when I actually design something to sell! The only thing is that I'm actually going to change the volume knob for a different one, because I can see that there's a lot of feedback about how it looks. Thanks!

    Added after 3 [minutes]:

    >>21411456 §
    Tremolo wrote:
    250ohm a 50ohm mentioned by kol titka is also OK. Maybe even 32ohm would do. The power will be reduced a little.
    .
    Exactly!
    Tremolo wrote:
    As for size..these dedicated designs for Sennheisers are huge
    .
    Yes, these are huge (and for me visually uninteresting) amps. Mcintosh also has a relatively large headphone amplifier

    Tremolo wrote:
    Like Japan from the 1960s but much more professional and qualitatively better.

    I never thought anyone would say my work looked more professional than the layout of the iconic Japanese amplifiers for which I sincerely thank you!
  • #15 21442636
    tytka
    Level 23  
    Pltin74 wrote:
    I never thought anyone would say my work looked more professional than the layout of the iconic Japanese amplifiers
    .

    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 we currently have access. Also, although many consider the Japanese designs of the time to be a benchmark; with all due respect to them, they were unfortunately not perfect. There were some not entirely well thought-out solutions and design flaws in them. On the other hand, however, with some minor or major problems, they often served their users much longer than their designers had planned.

    By the way, I will repeat what I suggested earlier. Your design, which you have presented here, makes a much better impression on me looking inside than when I look at it from the outside. And although the inside is not perfect (one could pick on some things), the fact is that, as a diy project, overall it makes a very good impression of the quality of the aesthetics of the interior workmanship.
    Of course, with the exterior aesthetics, it's no tragedy, but in my opinion the potential is there and you still have something to work on in this area.
    Of course, I realise that the current state may appeal to many people and in their opinion I am wrong, I am not right.
    Well, the truth is that I know perfectly well what I like and what I don't like. I don't have to look for my favourite style, because I know it perfectly well. And I actually pride myself on the fact that I am not at all impressed by, for example, the Tesla Cybertruck.
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Topic summary

✨ The discussion revolves around a DIY headphone amplifier project utilizing ECC88 and 6N6P tubes, specifically designed to drive Beyerdynamic DT990 Pro headphones with a 250 Ω impedance. The creator shares insights on the design process, challenges faced as a beginner in electronics, and the aesthetic choices made, including the use of wood and metal components. Participants provide feedback on the amplifier's design, questioning the choice of RCA socket placement and the overall aesthetics. The importance of high-impedance headphones in studio settings is discussed, highlighting their benefits in sound quality and compatibility with professional equipment. The creator expresses a desire to keep the schematic private for potential monetization of the design.
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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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