Aegis DIY Tube Headphone Amplifier
Nov 3, 2022 at 8:42 AM Thread Starter Post #1 of 1,958

L0rdGwyn

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I'm creating a thread for an upcoming DIY project I am working on, a tube headphone amplifier called the Aegis (pronounced EE-jis). This is a true DIY project, anyone taking on this project would assume full responsibility for acquiring parts, building, and testing the amplifier, although I will be available for questions and guidance if need be. I've placed a very high priority on making this design easy to build with a large portion of the circuitry on a PCB.

At a high level, the power supply is tube rectified, CLCRCRC filtered. The circuit features a choke-loaded 6SL7 input stage, capacitor-coupled to a triode-strapped pentode output stage. The output topology is a transformer-coupled cathode follower, which at this time is the only headphone amplifier of this topology that I am aware of. There is no silicon in this circuit, it is an "old school" tube amplifier design featuring Lundahl transformers and chokes. The amplifier includes a high and low output impedance switch for the purpose of matching high and low impedance headphones.

Tubes for the amp:
-Rectifier - 5V / 2A types; GZ34/5AR4, 5V4/GZ32, 5R4, 274B. 5Y3 can also be used with lower current output tubes like 6V6.
-Inputs - pair 6SL7
-Output - pair power pentodes; 6V6, 6L6, EL34, EL37, KT66, KT77, KT88, 6550. Others as well, compatibility list in progress.

I am currently putting together materials for the project which will include the following:
-Full build of materials (BOM) document with part numbers, prices, and where to source
-Information on ordering the chassis
-PCB gerber files and information on how to order (for those located in the CONUS, I may hold a stock of these PCBs and ship them to individuals on request, more to come on that)
-Project build document that will include amplifier schematics, information on sourcing parts, step-by-step build instructions, testing procedures

This is a relatively expensive design! Pricing of all of the parts is approximately $2,000 USD. However, this is meant to be a TOTL tube headphone amplifier, an equivalent design on the commercial market would be at least 3x the price. Regardless, the project should not be taken on by those who are not willing to commit the time and cost. This amplifier was recently at CanJam SoCal in the ZMF room and there are some forthcoming reviews. Hopefully Head-Fiers will then be able to determine if this is something they'd like to pursue.

At the time of my writing this, I am waiting to receive a second chassis and set of Lundahl components to build a second Aegis for the sake of creating the build document. I anticipate I will have the project posted in its entirety by the end of January at the latest. I will update here as the project develops, it is likely the major documentation and files will be hosted on a thread at diyAudio.com, which will be linked here.

PXL_20220825_013940963.NIGHT-2.jpg
 
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Nov 3, 2022 at 8:43 AM Post #2 of 1,958
The project is up on diyAudio. Note that you will need to make an account there to download the gerber files (accounts are free).

Aegis DIY Tube Headphone Amplifier: https://www.diyaudio.com/community/threads/aegis-diy-tube-headphone-amplifier.399473/post-7354944

Please read the document carefully, there is a LOT of information. Reviewing all of the steps may help you decide whether or not you are capable of building the amplifier.

I've notified Holger at Erhard Audio, Dave at Landfall Systems, and Brian at ELMA that the project is being released. Please be patient with Dave at Landfall, there may be a lead time on getting the chassis if he gets slammed with orders.
 
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Nov 3, 2022 at 11:58 AM Post #3 of 1,958
My Aegis review

 
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Nov 3, 2022 at 2:39 PM Post #4 of 1,958
L0RDGWYN’S AEGIS TUBE AMP REVIEW



First I’d like to thank L0rdGwyn for letting me borrow this amp for a lengthy testing. Second, I apologize for taking so long to get this done. I know how much everyone is interested in what I have to say… or rather what I have to say about the Aegis. I also would like it made known that the unit I demoed was a prototype and not the final spec’d DIY build.


BUILD and DESIGN

Straight from L0rdGwyn, here’s a quick explanation of the Aegis’ design:

It is a transformer coupled design. Input stage is choke loaded. Output stage is unique amongst headphone amplifiers as it is a cathode follower power stage (as far as I'm aware, this is the only headphone amp doing this at the moment). This achieves lower distortion and a low output impedance, good for driving low impedance and planars. This topology also removes a bypass capacitor from the output stage, which is a large contributor to the clarity and soundstage the amp achieves.

Onto the build, visually the Aegis is not going to knock your socks off and has a fairly pedestrian tube amp look to it. As far as amps go, looks are far from the most important thing to most enthusiasts. The Aegis is a beast of a unit, with the row of triple Lundahl transformers contributing greatly to its heft. The chassis for this unit is powder coated black and has a very nice finish (although it’s quite the dust magnet). The front panel of the Aegis features a power switch, volume knob and 6.35mm headphone jack. On the back of the amp you have the IEC, an output impedance selector knob (5ohm for headphones up to 150ohm and 17ohm for 150ohm headphones and above) and two RCA ins. There’s not a lot of bells and whistles on the Aegis, but there doesn’t necessarily need to be.

This might sound a little strange, but one of my favorite features of the Aegis is the unit’s toggle power switch. It provides a hefty and satisfying “chunk” when turning on/off. I’m also quite happy that it’s on the front of the unit instead of the rear (like on the DNA Stratus). This Aegis has a stepped attenuator installed, although the final DIY version will have a non-stepped Alps pot. I’m personally not a big fan of stepped attenuators, but that’s more of a personal choice. The only thing I really missed from the Aegis was a 4-pin XLR connector. I guess having to use a 6.35mm adapter with my balanced XLR cables isn’t exactly the end of the world though…


SOUND, PERFORMANCE and TUBES

I’m not one to beat around the bush, so I’m just going to go ahead and say that the Aegis sounds simply amazing. Similar to other high end Class A SET amps that I’ve heard, the Aegis provides ample power, fantastic clarity and a well balanced tube sound. While the tube selection will alter its sonic output somewhat (more on this later), the results won’t be nearly as dramatic as most OTL amps. If I had to boil down the Aegis’ sound overall, I’d say it’s detailed, spacious and engrossing.

I threw a large range of headphones at the Aegis including a Sennheiser HD540 (600ohm) HD650, HD800, Fostex TH-900, multiple ZMF models and a HiFiman Susvara. It performed exceptionally well with all of them. As I anticipated, the Sennheiser and ZMF headphones had great synergy with the Aegis. More impressive was how well the Aegis handled the orthodynamic headphones that I used with it. In particular, I was worried that it would struggle powering the Susvara, but surprisingly it didn’t. Even though the volume pot was around 5 o’clock, the Aegis was able to drive the Susvara pretty well. While it wasn’t quite as good as from my Cavalli Liquid Gold, it was more than adequate and greatly benefited from the Aegis’ expansive staging.

While I didn’t delve extensively into tube rolling, I did spend a few days trying different combinations of the tubes Keenan provided. My favorite combo that I used was the Mullard EL37’s with RCA 5916’s (or Tung Sol 6SUGTY for a little more energy). This pairing provided a large, yet detailed sound that still retained enough tube magic to make everything sound very organic. I also quite liked the EL34 tubes, which have a beefier midrange and a bit more heft in the lows compared to the EL37’s. These paired well with the planars I tried with the Aegis,most notably the ZMF Caldera. The trade off of these tubes is a very noticeable reduction in staging. The Fivre 6V6G’s were a nice middle ground between the EL37’s and EL34’s. As far as rectifiers, I didn’t notice a huge difference between the two provided, but also didn’t really focus on them that extensively.


DNA STRATUS COMPARISON

To give you an idea of how the Aegis stacks up against a well respected SET amp, I directly A/B’d it to my longstanding workhorse, the DNA Stratus v3. I’ve never really tube rolled my Stratus much, so I stuck with my standard loadout: Ken Rad 2A3’s, Ruby Tiger select 6N1P and a Marconi U52. For the Aegis I used the tube combo of Mullard EL37’s, TS 6SUGTY’s and RCA 5R4G. The headphones I used for this comparison were a ZMF Verite Open (Ziricote) and HiFiman Susvara.

Comparing two different tube amps is always a little problematic due to what tubes add to the amp’s overall sound. In this case, I felt pretty comfortable having spent so much time with both tube rolls. With that in mind, it came as no surprise that the Aegis had noticeably larger staging compared to the Stratus. However, that didn’t necessarily make it better in every regard. I actually preferred the smaller staging with my Verite Open as vocals were pushed closer and the presentation overall felt more cohesive. On the Susvara, I leaned more towards the Aegis, although this could be track dependent.

The other noticeable difference between these amps was the Stratus sounded a little more dynamic, while the Aegis was slightly more delicate and refined. I’m not sure how much to contribute this to the tube rolls on each amp, but in this case I’m leaning towards a little bit of both. Either way, both amps are very impressive and on par with each other as far as sound quality and technical ability. I think anyone would be happy to own either of these amps, although there are caveats of purchasing each. The latest Stratus v4 is a bit pricey at around $4.5k and currently has at least a year wait. While the Aegis’ parts will run you around $2k, it is only DIY at this time. So you will either have to assemble it yourself or pay someone to build it. The good news is that L0rdGwyn says the Aegis is easy to build and should be achievable by someone with basic soldering skills.


FINAL THOUGHTS

L0rdGwyn’s Aegis amplifier is incredibly impressive, and it certainly belongs right up there with some of the best TOTL tube amps on the market. It can drive a large range of headphones, the availability and cost of tubes is excellent, and the overall sound quality is simply fantastic. I could easily see someone having this as their only amp and being completely content. If you have the time, money and skill to build your own Aegis, I can’t recommend it enough.

PXL_20221109_193102401 (1).jpg
 
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Nov 4, 2022 at 1:07 AM Post #5 of 1,958
good one.... any spec on the transformers?
 
Nov 4, 2022 at 7:32 AM Post #8 of 1,958
This is such a cool and great idea to do this amp DIY....kudos Keenan. :)
 
Nov 4, 2022 at 2:44 PM Post #11 of 1,958
Hello,

Are you also planning a Eu version or just a sole Us version?

If so, would there be a plan where you know what should be soldered where, or would it be better to have someone professionally build it for me?
Personally, I'm not too well versed in this.
My soldering skills depend on the day, to put it kindly.
I can read a plan but not everything.
Measuring the current flow is also always such a thing as a beginner, of course I don't know what needs to be measured as a setpoint.
For example, I always find it very important when you do something like this before you switch it on and see 2000$ go up in smoke 😭😂😭😂.

Apart from that, I think you've come up with a good idea.
It will keep the circle small where you will probably have such an amplifier.
 
Nov 4, 2022 at 3:17 PM Post #12 of 1,958
Hello,

Are you also planning a Eu version or just a sole Us version?

If so, would there be a plan where you know what should be soldered where, or would it be better to have someone professionally build it for me?
Personally, I'm not too well versed in this.
My soldering skills depend on the day, to put it kindly.
I can read a plan but not everything.
Measuring the current flow is also always such a thing as a beginner, of course I don't know what needs to be measured as a setpoint.
For example, I always find it very important when you do something like this before you switch it on and see 2000$ go up in smoke 😭😂😭😂.

Apart from that, I think you've come up with a good idea.
It will keep the circle small where you will probably have such an amplifier.

The mains transformers can be wired for 115V or 230V, which will work with other mains voltages in that region, just slight variations in operating voltage but all within tolerance of the tubes' specifications.

As I said in my first post, there will be step by step instructions with testing procedures with photos. I would encourage anyone considering the build to read the document when it is posted in a few months to get a feel for whether or not they feel they can perform the required tasks, if not it might be a good idea to ask a friend with soldering skills to build it or commission someone else to build it. However, there is very minimal point-to-point wiring, less than even a Bottlehead kit.

Here is a picture of the PCB.

PXL_20221029_134205003-2.jpg

Here is the interior of the prototype that was reviewed by @Monsterzero . Some modifications have been made in the final circuit, test points added to the PCB for example, but the majority of the circuit is the same.

PXL_20220904_174416297.jpg

As you can see, there is very little in the way of point-to-point wiring, most of the circuitry has been accounted for on PCBs. Populating the PCBs is very easy, as simple as placing the parts in the designated positions of the PCB, soldering them, and clipping the leads.

Obviously I come from a place of experience, but with all of the parts in front of me, I can build this amplifier from scratch in 6 hours.
 
Nov 4, 2022 at 3:31 PM Post #13 of 1,958
My Aegis review


Awesome review @Monsterzero !
The mains transformers can be wired for 115V or 230V, which will work with other mains voltages in that region, just slight variations in operating voltage but all within tolerance of the tubes' specifications.

As I said in my first post, there will be step by step instructions with testing procedures with photos. I would encourage anyone considering the build to read the document when it is posted in a few months to get a feel for whether or not they feel they can perform the required tasks, if not it might be a good idea to ask a friend with soldering skills to build it or commission someone else to build it. However, there is very minimal point-to-point wiring, less than even a Bottlehead kit.

Here is a picture of the PCB.



Here is the interior of the prototype that was reviewed by @Monsterzero . Some modifications have been made in the final circuit, test points added to the PCB for example, but the majority of the circuit is the same.



As you can see, there is very little in the way of point-to-point wiring, most of the circuitry has been accounted for on PCBs. Populating the PCBs is very easy, as simple as placing the parts in the designated positions of the PCB, soldering them, and clipping the leads.

Obviously I come from a place of experience, but with all of the parts in front of me, I can build this amplifier from scratch in 6 hours.
I had dreamed of the day you would produce a DIY kit (pretty sure I nudged you several times that this would be of high interest:)) so it's super cool to see that you're realizing this dream! Amazing that you're giving the plans away for free! What a contribution to the community. As others have said, thank you so much for doing this.

I know you haven't published the parts list yet, but I'm curious how much customization you're thinking there would be depending on the individual builder's preferences. For example, could a builder try different brand caps, volume POT/attenuator, RCA plugs, or other components as long as the values stay within spec? Assuming things like the chassis color/finish could be customized by working with the chassis manufacturer. I'm also guessing there would be things more difficult to change (like different power switches or larger components that don't fit on the PCB) that would require bigger modifications i.e. modifying CAD files probably beyond the comfort/skill level of most casual builders. Would there be the ability to easily tweak any specs like output impedance by changing parts to different values?
 
Nov 4, 2022 at 4:07 PM Post #14 of 1,958
Awesome review @Monsterzero !

I had dreamed of the day you would produce a DIY kit (pretty sure I nudged you several times that this would be of high interest:)) so it's super cool to see that you're realizing this dream! Amazing that you're giving the plans away for free! What a contribution to the community. As others have said, thank you so much for doing this.

I know you haven't published the parts list yet, but I'm curious how much customization you're thinking there would be depending on the individual builder's preferences. For example, could a builder try different brand caps, volume POT/attenuator, RCA plugs, or other components as long as the values stay within spec? Assuming things like the chassis color/finish could be customized by working with the chassis manufacturer. I'm also guessing there would be things more difficult to change (like different power switches or larger components that don't fit on the PCB) that would require bigger modifications i.e. modifying CAD files probably beyond the comfort/skill level of most casual builders. Would there be the ability to easily tweak any specs like output impedance by changing parts to different values?

I'm excited about it, but also nervous to a certain extent, I'll feel better when a few people have built it successfully :)

Yeah there is some flexibility to change parts, depending on the part.

I used a chassis cutout for the RCAs that should fit quite a few different brands, so the builder could choose what they like there assuming their chosen RCA fits.

The potentiometer is a little bit tricky - it has to be a 20-25K pot maximum given the high Miller capacitance of the input stage, otherwise there will be high frequency rolloff. The source impedance of the pot must remain low, 20-25K max ensures that it is. HOWEVER, some ladder type pots, like a TKD, have a higher source impedance than your typical log taper potentiometer, even if they are 20-25K, so I would not recommend using them.

The input stage bypass and coupling capacitors could be changed assuming they fit on the board. But, IMO, I would not recommend changing the bypass caps. I did extensive A-B testing of audio grade electrolytics for the input stage, the Jupiter Cosmos caps were far and away the best, I think using something else in that position would be a step down in performance. I designed the PCB around Jupiter copper foil 0.22uF 400VDC coupling caps, but you could certainly use a different cap in that position as long as it meets the spec and fits.

Dave at Landfall, who makes the chassis, can do different powder coating finishes, so that could be coordinated with him. I will say though that I cannot guarantee how any specific coating will turn out, some powders coat better than others in my experience.

Any change that would require altering a mounting hole in the chassis would need to have the CAD files modified. I'm sorry but I am not likely to volunteer my time to do that for each individual request, but someone could ask Dave at Landfall if he is willing to make the changes for them.

There is a switch to change taps on the output transformer for changing the output impedance to suit different headphones, also using different output tubes will change the output impedance to a minor degree. In general, higher transconductance outputs will result in a lower output impedance and vice versa.
 
Nov 4, 2022 at 4:58 PM Post #15 of 1,958
Hey,
Thanks for your great feedback.
Yes, now that you see a picture, I would dare to build it myself.
I'm sure I could get it soldered cleanly in 2-3 quiet Saturday afternoons.

Nothing against the Jupiter condenser, it is certainly very well chosen.is more a question.
What do you think of the Vcap Odam?
Unfortunately it is not available in a 400v version, only in a 630v version, and the new CuTf is only available in 630v.
I have installed the Odam and the TFTF in the Feliks Euforia and found it to be a great added value compared to the standard Mundorf capacitors that are installed.
But I would still be surprised by the Jupiter, which is also supposed to be very good and I think fits very well to the sound tuning.
 

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