Aegis DIY Tube Headphone Amplifier
Nov 3, 2022 at 8:42 AM Thread Starter Post #1 of 103

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 11:58 AM Post #3 of 103

Monsterzero

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My Aegis review

 
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Nov 4, 2022 at 1:07 AM Post #5 of 103

Fatdoi

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good one.... any spec on the transformers?
 
Nov 4, 2022 at 7:32 AM Post #8 of 103

whirlwind

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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 103

Deleeh

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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 103

L0rdGwyn

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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 103

raindownthunda

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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 103

L0rdGwyn

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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 103

Deleeh

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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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