Single ended class-A headphone amp using two transistors: T2

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In the catalogue you linked, they do say this :

WHEN POSSIBLE, INSTALL A CABLE CORE OVER WIRES IN A COMMON MODE CONFIGURATION
(Out and back lines inside the same ferrite cable core). A differential cable pair inside the same core will make the ferrite core a
common mode choke that is not susceptible to saturation from very high currents.


So they're at least admitting the possibility, right?

I couldn't find any data in there about where the core might saturate but its possible to go back to first principles to work it out.
From the scarce information available from the datasheet, it is possible to infer the saturation limit: <130mA (@B=0.4T), but it does not really matter...

Nice project BTW, it easily scores 8~9 on the N.P. scale...
 
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If it's not a DC-coupled output design, I'm not personally interested in it

Here is another that you won't be personally interested in:

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Hi wrenchone, I remember writing post #38 in your thread. After you decided not to pursue it, I did. That's when I began looking for previous 2-transistor amplifier designs, and found a great many of them, including the ones I attached to post #1 here (copied below). You are right, the 2T amplifier topology did not originate in 2018 or 2019, it is much, much older. Turning it upside down to use an NMOS output xitor with a positive ground is a slightly new wrinkle. Frequency compensation at the 2nd stage, including cancellation of the right halfplane zero, seems to be another.

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6L6

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Why would anyone want to design/construct an amplifier that uses a big ole' nasty 3300uF output coupling capacitor??:confused:

Well, you certainly wouldn't want to ever listen to this -- :D

JS-F3Schematic_zps531955c7.jpg



Or this -




An externally hosted image should be here but it was not working when we last tested it.


1.png


6moons audio reviews: FirstWatt SIT-1









Or heavens above, perhaps measure the cap and see what horrible, evil, and just un-civilized distortions it imparts -

SYclotron Audio | Why are people obsessed with coupling caps?

SYclotron Audio | Capacitor Obsessions- The Zombie Awakes (edited to add data 2/21/18) (The intermodulation measurements are particularly interesting...)





.
 
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Oops, I just found a part which was omitted from the BOM. It's the "shoulder washer" (insulated bushing) which mounts the TO-220 power transistor to the heatsink, without letting the mounting bolt make electrical contact with the transistor's metal tab.

The part number at Mouser.com is 532-7721-7PPS and you need qty=2 of them, one for the left channel and one for the right channel. Mouser sells them for $0.74 each.

BUT WAIT

I just bought 2000 (two thousand) of them on eBay and paid a total of $10.27. I bought 1000 of the white, standard temperature range, bushings. I also bought 1000 of the brown, extended temperature range, bushings. These are the listings I used:

1000PCS Insulating Tablets Insulation Bushing Transistor Pads Circle TO-220 CYN | eBay

1000PCS TO-220 High Temperature Insulation Nylon Washer Bushing Brown Beige RoHS | eBay

Since I plan to do lots of DIY projects using TO-220 packaged devices, I think it makes sense to buy 2000 of them at $0.0051 per piece, rather than two of them at $0.74 per piece.

I'll work with 6L6 to update the BOM here on this thread. Meanwhile, I've included two bushings in every set of T2 PCBoards I've shipped out, just in case those folks bought the whole BOM already.
 
Here is another that you won't be personally interested in:

_

You're absolutely 100% correct with your assumption...LOL.

I'll stick with DC-coupled designs any day of the week whether they're a op-amp based designs using the wonderful sounding LT-1363/64 or discrete designs such as those as offered from Schiit Audio.


Good luck with your AC-coupled design(s).:rolleyes:
 
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Hmmm, if you want a Do It Yourself headphone amp project that's DC coupled from input to output, with zero capacitors anywhere in the signal path, unfortunately that means both of the DiyAudio Store headphone amp DIY projects are disqualified. WHAMMY has an AC coupled input, and Starving Student II has an AC coupled output.

I think the "Butte" DIY headphone amp does meet your requirements, it has direct coupled input and direct coupled output. Bare PCBs available so DIYers don't have to lay out a circuit board themselves. Google will help you find it.

The O2 / Objective2 DIY headphone amp is disqualified, and so is the original CMOY "headphone amp in an Altoids tin". Most headphone amp projects seem to have at least one capacitor in the signal path! T2, in this thread, has two.

Good luck with your DIY projects!
 
> Most headphone amp projects seem to have at least one capacitor in the signal path! T2, in this thread, has two.

Oh, I can name a few which are DC coupled through the signal path.
Where should we start ?

Let's name a few which are not mine :
https://www.diyaudio.com/forums/hea...borberly-eb602-200-revisited.html#post5492307
https://www.diyaudio.com/forums/hea...ley-hood-headphone-amplifier.html#post5402030
The Pioneer Super Linear Circuit

None DIYA links :
the Headphone amplifier
The Cavalli-Kan Kumisa III stereo headphone amplifier

And a couple of my own :
The DAO SE all-FET Class-A ZGF Headphone Amplifier
UTHAiM -- Just for Fun
Current Drive for Headphones & The Super Linear Transconductance Amplifier

A few of them have Gerber files or PCB layouts in the public domain.


Best,
Patrick
 
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Hi Alex, I bought the Galaxy 1U chassis with steel covers, in the "230 x 170mm" size. I will try to make a LINK to that sales page on the diyAudio Store website.

The PCB for T2 is 182 x 112mm, so it fits comfortably in the 230 x 170 chassis, with adequate room for the ALPS Blue Velvet (RK27) volume control in front, and the Rean gold plated RCA jacks in back. Have a look at the build photos attached to posts #1-5 (still growing), it's not packed tight or cramped at all.

In case my web link doesn't work, I attach a screen capture image below. If you have any reason at all to buy two chassis instead of one, the discount is fairly dramatic.

MJ
 

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You're absolutely 100% correct with your assumption...LOL.

I'll stick with DC-coupled designs any day of the week whether they're a op-amp based designs using the wonderful sounding LT-1363/64 or discrete designs such as those as offered from Schiit Audio.


Good luck with your AC-coupled design(s).:rolleyes:

Lol! DC voltage on source ---> straight through DC-coupled headamp ----> into expensive headphones ----> Amazon for new headphones. Good luck to you too, sir! :) I would never design or use a headphone amplifier that didn't have a DC blocking capacitor somewhere in the signal chain (a DC servo won't react fast enough, either, to save the headphones). Like Mark's neat little design here :)
 
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There are lots of dual gang, audio taper, 10K ohm, smooth (not knurled) shaft, ALPS RK27 "Blue Velvet" pots on eBay at pretty good prices. Dunno if they are counterfeit or not.

Parts Express and Parts Connexion also sell ALPS RK27 Blue Velvet pots, almost certainly NOT counterfeit, for about five dollars less than Mouser link

You can also consider using the smaller sugar cube sized ALPS RK097 pot, which Mouser has in stock, plus one of those adapter PCBoards from eBay which makes it easier to solder wires onto the (small!) pot.

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I've attached below a couple of documents in .pdf format.

One of them explains how to adjust the three trimmer potentiometers on the T2 circuit board. Two pots adjust the bias currents in the two amplifier channels, Left and Right. The third pot adjusts the brightness of the front panel LED.

The other document is a loose collection of Notes To Builders, with photographs and explanations of several steps in the construction process, especially the final "fly wires" which connect the PCB to the components on the front panel and rear panel.

I will ask the Moderators to please move these attachments to post #2 at the top of this thread, if that's technically feasible. That way, first-time readers of this thread will see them immediately. And old-timers will know where to go look if they want to read the pdfs again.

If that succeeds then this post (#40) becomes superfluous and unnecessary. So it can be deleted.

MJ
 

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