New Headphone Amp Project - Single ended class-A 2 Transistors Head Amp! "DIY"

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adydula

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I just got these in the mail today!
Have to order the parts and with my "life" issues it may be a few weeks before I start the build.

This is a relatively "easy" build, no small hard to solder parts...simple discrete parts and assembly.
The hard part is ordering the parts IMO!




Over at DIY there is a fellow Mark Johnsonm who out this one together...and being a DIY nut and addicted to the smell of solder....and always wanting to build that neat amp or
device that will get me closer to audi nirvana...here is what John says about this design:

"Headphone amps are very popular as DIY projects, and quite a large number are available. To name a few: Beta22, Objective-2, the famous CMOY amp, Sjöström QRV01-09, Butte, and many more. In addition to those, the diyAudio store right here on this very site also offers the (vacuum tube) Starving Student II headphone amp, and the (ICs + discretes) WHAMMY headphone amp. So why build yet another headphone amp? How is this one different from all the others?

I think the answer is, T2 has a unique combination of features that are not found together in other headphone amp designs:
All-discrete, solid state: no ICs, no vacuum tubes
Single ended, Class A circuit operating at 150 mA bias current (exceptionally high for a headphone amp)
No mains voltage inside the DIY chassis. Power supply is a commercial, safety rated, DC wall wart followed by a 2 stage supply filter on the PCB
100% thru-hole parts, mounted on a single PCB with plenty of spacing between components. Very easy to stuff and solder, suitable for first time DIYers.
Designed to be a comfortable and uncrowded fit within typical headphone amp chassis, including the "Galaxy 1U" chassis from the diyAudio store. Board is 182 x 112 mm
Headphone output (6.35mm TRS) on front panel, plus linestage preamp output (RCA jacks) on rear panel
Pre-made front and rear panel with silkscreened logos and control labels, for those DIYers who prefer not to drill + label the panels themselves. These are black PCBs, 2.0mm thick, cut to match the 1U Galaxy front & rear panels. PCB silkscreen labels.

T2 is powered by a 24V DC wall wart. With 150 mA of bias in each of 2 channels, that's 7.2 watts of power dissipation, just in the output stages (!). And it is housed in a chassis with no heatsink fins at all (Galaxy)? True. Figure 1 shows an infrared photo of T2 after it has reached final operating temperature. 90 minutes after turning T2's power on, I took this picture with a thermal imaging camera, using its High-Low mode. The camera automatically marks the positions of the highest temperature (37C) and the lowest temperature (27C). To prevent heat transfer between T2 and the tabletop during this experiment, a large wooden board, 1m X 1m, was used as a thermal insulator. The board laid on the tabletop and T2 sat upon the board. The exterior metal was slightly warm to the touch, not hot at all.

Here is the link to it: https://www.diyaudio.com/forums/headphone-systems/338435-single-class-headphone-amp-using-transistors-t2.html'
(rather than cutting and pasting a ton of stuff)...



Here is what its "going" to look like:



Alex








timind

Yep, ordering all the parts is the biggest pain. Keep us updated on the build.

adydula

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Parts on order...

The guys over at DIY made this one easy....they put together a Mouser link with the BOM!!

All parts except the 10K pot were in stock....and the pot I found at Parts Express...

So all in all its about $100 in parts, the board was $16 with engraved panels...

The case will be about $50 unless I build one myself..

Alex

poseidonsvoice

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Parts on order...

The guys over at DIY made this one easy....they put together a Mouser link with the BOM!!

All parts except the 10K pot were in stock....and the pot I found at Parts Express...

So all in all its about $100 in parts, the board was $16 with engraved panels...

The case will be about $50 unless I build one myself..

Alex

Enjoy the build! The pics on the linked thread in your 1st post should help as well, hopefully.

Some here:













Best,
Anand.
« Last Edit: 7 Jun 2019, 08:12 pm by poseidonsvoice »

adydula

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Hi Anand!

Hey i did get your PM and its neat that your in North Carolina as well as a few others!!

Maybe one day we will meet.

I have done a dozen or so DIY headphone amps and most work first time and perform vey well...this one is a relatively easy build.
The parts are whai I call "normal" size and easy to work with.

Compared to the 806 and smd parts these are like "giant" size!

The only thing about most DIY is they dont necessairly look like hogh dollar retail gear, mainly due to the case...but the performance is as good as many other higher dollar retail stuff....

...and then their is the satisfaction of you built it, and they are more of a "rare" thing...etc...

My ODA is a perfect example of that....the desktop O2 that NWavguy might have made had he stuck around a few years back...and its a really great SS amp with enough power to drive almost anything...

ok over and out
Alex

adydula

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Well here is my build 99% complete....all parts soldered in except for the ferrite bead choke, waiting on some 28 ga wire to make it and install..its help reduce any noise coming from the 24vdc switching power adapter.
The case will be here tomorrow and we should be able to finish wiring up the panles, test, and intstall in the case.

Alex












poseidonsvoice

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Looking good. And don’t forget R3-R6, the RCA output loading resistors.

Best,
Anand.

adydula

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Thanks for reminding me!!

I actually did not see these in the schematics?

Mark also left me a note at DIY as well..

I just popped them in!

Appreciate your "eyes"!

Alex

mresseguie

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Learning how to competently solder is on my 'do to' list. Until then, I have to be satisfied with watching you build this.

I'm  :green: with envy!

Michael

adydula

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Learning to solder is not that hard. It does take some practice which you can get by buying a bunch of cheap comonents and a pc board and having at it.
I am self taught...and its like electcical plumbing!

You need to use the correct solder, have a decent soldering iron and understand that too much heat for too long could damage semiconductor components.

The hard part would be to learn how to handle the components and which ones need a little more attention than others.

Having a clean soldering iron tip, all the time makes maximum heat transfer and easy soldering.

Handling the iron and accurately placing the tip on the area needed is something you get used to after awhile.

The "mass" your soldering sometimes comes into play, and the thicker componemt lead or connections with several items require more heat at a longet time.

But its really pretty easy and easy to tell if your solder joints are good or not with careful inspection!..

If you want to start some DIY project, let me know, I would suggest some projects that are fairly simple...

Alex
« Last Edit: 8 Jun 2019, 03:04 pm by adydula »

adydula

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Well its completed and working!!

Worked first time and thats a really good feeling!

Mark Johnson is one of those electrical engineering wizards that has a real winner with this one.

Such a simple amp and really easy to build, old school for sure.

No op amps, nothing exotic, just two transistors and bunch of caps, resistors, diodes etc...and it runs from a small
24vdc 500ma switching walwort...very small in size.

I still need to get a knob for the volume but its in the case, calibrated etc..



There is even a small pot to adjust the brightness of the LED!! lol...

How does it sound or work...

After 90 minutes of running the case is barely warm to the touch. Class A , 2 watts..those big resistors present the load and they are elevated
off the board and do get very warm.

First impressions are very very positive...the new'itis thing we get with new stuff has to be taken into account but

I am hearing stuff like I have never heard before...this amp is very special to me.

Usually swapping from one amp to another the changes are rather minimal not like getting a new or different set of headphones.

With this amp its like I have new headphones its that good.

Gosh its a simple 2 transistor amp with all discrete components and shouldnt work this good..its like I am here and I am good...hear me roar!! lol

The sound is extremely open and clear. Transparent. Holographic soundstage. Tonality great...makes everything new again.

The signature of this amp makes listening to live performances a real leasure...its the closest thing to being there with cans I have experienced.

Channel seperation is great, vocals are real.....I cant stop gushing on this one.

I would have to say this is the best SS amp I have ever heard....thats a giant statement.

For the cost of this amp, time spent building etc...its a STEAL for performance...

More than enough power to drive my T1's, HD 600s extremely loud.

Mark shared his secret:

I'll tell you the secret formula for designing an amp that sounds like T2:

1. Make it Class A

2. Run it at a ridiculously high bias current

3. Don't fark up the rest of the circuitry too badly

That's what I did, and the result seems decent.


I have a dozen head amps here, half tube, half SS, many of them are great...this little amp humbles them all!

It goes to show old designs with slight twists can work very very well....the cost of this was approx $160 bucks or so.

If your looking to get into DIY this is a great amp to start with.

Its going to be hard to listen to anything else right now!

Life is Good!

Alex
 :D :D :D







timind

Excellent work there Alex. I'll try and keep this in mind this fall when it's time for nifty projects.

adydula

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Just got the knob this am....so here it is working!
Also just found out that the yellow led thats adjustable wired this way is yellow,
Reverse the wiring and it glows green!! LOL





Alex

randytsuch

I just bought a board set, shipped yesterday.

Need to order the rest of the parts now, but with the Mouser BOM uploaded it won't be too bad.

Randy

adydula

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Great Randy...

The bom makes thing easier for sure. They might not have the volume pot...parts express has it.
Standoffs for the pcb are in the bom but u need screws etc and small screws for the TO2 transistors..keep us posted on the build. Oh the case at diystore comes from Italy took five days..quick.

Alex

randytsuch

Great Randy...

The bom makes thing easier for sure. They might not have the volume pot...parts express has it.
Standoffs for the pcb are in the bom but u need screws etc and small screws for the TO2 transistors..keep us posted on the build. Oh the case at diystore comes from Italy took five days..quick.

Alex

I'm pretty sure I have either a blue velvet or dact laying around that I can use for the pot.
I also have a bunch of screws and stuff for hw, so not worried about that part. 

Randy

adydula

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Looks like your all set then...the BOM includes the insulating "spacers or washers" for the TO2 devices.

Alex

poseidonsvoice

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Nice to see others attempt the build.

Enjoy. It’s rather straightforward.

Best,
Anand.

adydula

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yes straight forward fir sure..

Mark wanted to make a simple but yet good amp to entice beginners and folks that think DIY is too hard to jump in and try this part of the hobby.

Hoping to help keep this part of the audio journey from going extinct.

...and for the bucks here and how well it works its indeed a great first time amo ...and a great amp period.

If someone sees this is a full CLASS A amp, etc they might want to really know what that is or means...

Science and math is a great subject and this is a neat way to get your kids or yourself invoived...

Alex

poseidonsvoice

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yes straight forward fir sure..

Mark wanted to make a simple but yet good amp to entice beginners and folks that think DIY is too hard to jump in and try this part of the hobby.

Hoping to help keep this part of the audio journey from going extinct.

...and for the bucks here and how well it works its indeed a great first time amo ...and a great amp period.

If someone sees this is a full CLASS A amp, etc they might want to really know what that is or means...

Science and math is a great subject and this is a neat way to get your kids or yourself invoived...

Alex

Alex,

I don't know about you, but I have little concern that this aspect of audio is going to go extinct. It might not be as profitable for manufacturers but it certainly doesn't look like it is going extinct, especially with the power of the internet.

On May 26, 2019, there were 10,051 users of diyaudio.com simultaneously. Most of the threads there are dedicated to some aspect of diy, whether it be speakers, solid state electronics, or tube electronics.

Well over 1000 of Pass's ACA amplifier kits have been sold, and most of the time, when they have a sale, it's gone in 3 days. Many of the partial and full kits have backlogs, and waiting times, with people whining about when the diyaudiostore is going to have replenished stock.

And there are over 1/2 million registered users of diyaudio.com forum now. They may not all be active, but it far exceeds most audio forums in my experience. Many of the members donate to diyaudio directly.  And the yearly Burning Amp festival in San Francisco is rumored to become a 2 day event from 1 day due to the increase in participation.

What is going on today makes the era of Dynaco, Heathkits, Scott, etc...a thing of the past and the level of sophistication of the circuits rivals some very high end designs. Whether you want ultralow distortion Class AB or Class D or play with Class A designs, there is something for everyone.

And we haven't even talked about Bottlehead, Transcendent Sound, Neurochrome, AMB, Hypex, etc...

If you know how to solder, the audio world is your oyster. Most projects are thru hole. Some of the best and most advanced projects are SMD. All you expend is time. For some, time is serious money, for others, it's a journey. You be the judge. You be the boss. Nobody is forcing you however, cause there will be somebody else to take your place  :wink:

And from what I have seen (even though I am not a die hard headphone enthusiast in any shape or form), headphones are here to stay. Just look at the turnout for RMAF, AXPONA, etc...

There are enough diyaudio projects (particularly if you look outside of headphone amplifiers), to keep you busy for years.

Best,
Anand.