• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Augustica Technologies DIY Headphone Amp Kit: Looking For EE Advice

L0rdGwyn

Active Member
Forum Donor
Joined
Jan 15, 2018
Messages
292
Likes
674
Hey ASR! I apologize in advance for being a bit of a knowledge mooch, but I am hoping some of my EE friends on the forum can lend a hand to a layperson on the soundness of a specific amplifier design :)

Backstory: I am primarily a headphone guy and current owner of a Schiit Lyr 2 hybrid-tube headphone amp (among others). Since recently building my Bottlehead Crack OTL head-amp, I feel the Lyr 2 really under-performs at its price-point. And given the recent Schiit that has come to light, I am not all that keen on keeping their products in my audio arsenal. So, the Lyr 2 has to go, which leaves me with my proud collection of 2c51/5670 tubes (a 6922 alternate) and no amp to put them in. Hence, I am in the market for an affordable amp capable of taking 2c51/5670 type tubes, preferably OTL. Enter Augustica Technologies.

They are a small telecommunications/electronics distributor based in Barrie, ON Canada offering three different DIY headphone amplifier kits available for purchase, either fully or self-assembled, one solid state, the other two OTL. Despite the fanatical nature of the headphone community these days, I was shocked to find there is no information/reviews/experiences with these amplifiers whatsoever on any forum. I am particularly interested in the Corvette model, as it is a 6922-based OTL circuit. After reviewing the information available on the site, a select few YouTube videos discussing the circuit design, the supporting documentation, and some correspondence with a member of Augustica Technologies, I am anticipating making a purchase in the hope of unearthing a true head-amp diamond in the rough :) the company rep I have been in contact with (who, based on our interactions, I assume is the designer of the amplifier) feels strongly that the amps are a better value that Schiit's products and will outperform them, given they use higher quality components and lack Schiit's minimalist design philosophy.

If the specs on the product page are to be trusted (given my cursory understanding of audio measurements), the Corvette amp offers impressive performance for the price. One particular spec that jumps out is the 230 Ohm output impedance, very high even for an OTL design. I will primarily be using the amp with the 300 Ohm Sennheiser HD 600 series and my 600 Ohm Sennheiser HD 250 Linear phones, so I don't anticipate the damping factor being an issue.

If anyone would be willing to humor me and comment on the soundness of the amplifier design/specifications, I would greatly appreciate it! Otherwise, feel free to ignore and/or chastise me, I understand it is a big ask to go through the documentation, let alone read the novel I wrote above :)

If/when I purchase the amp, I plan to do a subjective comparison to the Bottlehead Crack and Schiit Lyr 2. If the amp really lives up to my diamond-in-the-rough hopes, and members here are interested, I would be happy to send it to Amir to be measured.

Price for the unassembled kit is $300 CAD (~$240 USD), $500 CAD for the assembled kit (~$400 USD).

Thanks for reading! Below are links to resource materials:

Product page: http://www.augustica.com/corvette-c...fier-corvette-and-transformers-assembled-p-52

User manual, includes circuit operating theory:
http://www.augustica.com/Products/Amplifiers/Corvette/Headphone Amplifier Corvette User Manual.pdf

YouTube video, designer discussing components, specifications, operating theory:

YouTube video, designer displaying "fully assembled" DIY amplifier with expanded PCB (this is what I would be purchasing):
 

SpeedyRodent

Member
Joined
Jan 26, 2018
Messages
62
Likes
47
Location
Alberta, Canada
I have no experience with this particular headphone amplifier so I won't comment on the design or performance. The information is fairly limited on the website. Did not see schematics which I would expect for a diy project.

In general, the output impedance at 230 ohms is fairly high for headphone use. This will definitely affect the damping on the HD600 headphone. The calculated damping factor is 1.3 which is fairly low. Based on the HD 600 electrical impedance curve, the frequency response will be boosted in the 80 to 110Hz range. So expect additional bass in this range. Subjectively, some people might like this. Personally, I would not use this amp to drive the HD 600. At 230 ohms, it is too hard to predict how some headphones will react. Especially ones that have not been measured. No idea how the Sennheiser HD 250 Linear will respond.

Source: HD 600 electrical impedance
https://www.innerfidelity.com/images/SennheiserHD600.pdf
 
OP
L0rdGwyn

L0rdGwyn

Active Member
Forum Donor
Joined
Jan 15, 2018
Messages
292
Likes
674
I have no experience with this particular headphone amplifier so I won't comment on the design or performance. The information is fairly limited on the website. Did not see schematics which I would expect for a diy project.

In general, the output impedance at 230 ohms is fairly high for headphone use. This will definitely affect the damping on the HD600 headphone. The calculated damping factor is 1.3 which is fairly low. Based on the HD 600 electrical impedance curve, the frequency response will be boosted in the 80 to 110Hz range. So expect additional bass in this range. Subjectively, some people might like this. Personally, I would not use this amp to drive the HD 600. At 230 ohms, it is too hard to predict how some headphones will react. Especially ones that have not been measured. No idea how the Sennheiser HD 250 Linear will respond.

Source: HD 600 electrical impedance
https://www.innerfidelity.com/images/SennheiserHD600.pdf

Thanks for the feedback! Yes, the output impedance is...concerning. I think it's the highest I've seen on an OTL head-amp. However, I often use my Bottlehead Crack paired with the Sennheiser HD660S (damping factor of 1.25 with a Mullard 6080 as the cathode follower, 2.15 with a Tung Sol 5998) with what I feel are good results. Innerfidelity did an article a few years back discussing changes in frequency response based on output impedance, looks like I could expect around a +3 dB increase in mid-bass with a damping factor of 1.3. But your absolutely right, given the high impedance, it is something of a gamble.

Here's a link to the Innerfidelity article: https://www.innerfidelity.com/content/musings-headphone-amplifier-output-impedance

I'll see if I can get a copy of the schematic from the company rep :)
 
OP
L0rdGwyn

L0rdGwyn

Active Member
Forum Donor
Joined
Jan 15, 2018
Messages
292
Likes
674
I am told by my company representative that they do not publish schematics of their headphone amp designs.

Here are the step-by-step instructions for the assembly, published on their site: http://www.augustica.com/Tutorials/Corvette/corvette_tutorial.htm

They also include a "tutorials" section that discusses building various circuits within a 6922-based amplifier with schematics included, no doubt some of these are integrated into their Corvette amp: http://www.augustica.com/tutorials-ezp-7

Includes instruction on how to build a 6922 cathode follower, 6922 cascode circuit, 6922 operating point limits, parameters, cathode biasing, among others.
 
Last edited:

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
44,368
Likes
234,386
Location
Seattle Area
I am told by my company representative that they do not publish schematics of their headphone map designs.
That seems to be common for the fear of Chinese companies cloning them. Even Chinese companies are worried about that!

I watched the videos and the component choices are all pretty high quality. Other than that, I am not a tube guy so can't offer any other insight short of testing it. :)
 
OP
L0rdGwyn

L0rdGwyn

Active Member
Forum Donor
Joined
Jan 15, 2018
Messages
292
Likes
674
I've decided with the lack of information and high output impedance, this amp is too much of a risk. Also, the output impedance spec mysteriously changed to 90 Ohms on the product page. I inquired as to why and did not receive an answer. It then mysteriously changed back to 230 Ohms :rolleyes: not sure what is going on there. I will instead be purchasing the Arcam rHead for a good solid-state option and I am looking into purchasing the Feliks Audio Espressivo OTL, which takes 6922 driver tubes, and hence, 5670s :) after some play time, I can send one or both of these amps for measurements.

Thanks for your input gentlemen!
 
Top Bottom