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Single ended class-A headphone amp using two transistors: T2
Single ended class-A headphone amp using two transistors: T2
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Old 2nd June 2019, 05:12 PM   #31
EUVL is offline EUVL  Europe
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> 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 :
The Borberly EB602-200 Revisited
The REAL John Linsley Hood Headphone Amplifier
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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Old 2nd June 2019, 07:05 PM   #32
adydula is offline adydula  United States
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Mark,

What particular size 1U Galaxy Case works with this project?

There are several choices?

Thanks
Alex
 
Old 2nd June 2019, 07:48 PM   #33
Mark Johnson is offline Mark Johnson  United States
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Single ended class-A headphone amp using two transistors: T2
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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File Type: png chassis.png (50.9 KB, 572 views)
 
Old 2nd June 2019, 08:04 PM   #34
adydula is offline adydula  United States
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Thanks!!

Alex
 
Old 2nd June 2019, 11:42 PM   #35
agdr is offline agdr  United States
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Single ended class-A headphone amp using two transistors: T2
Quote:
Originally Posted by mercedese63 View Post
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).
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

Last edited by agdr; 2nd June 2019 at 11:55 PM.
 
Old 2nd June 2019, 11:53 PM   #36
agdr is offline agdr  United States
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Single ended class-A headphone amp using two transistors: T2
Quote:
Originally Posted by 6L6 View Post

Here is a populated Mouser cart to build the T2 - Mouser Electronics
Ordered! That link is so slick. Thanks 6L6! Ordered the case just now from the diyaudio store, too. Mouser *almost* had everything in stock, too, which is rare. Only the pot on backorder. :P
 
Old 3rd June 2019, 01:32 AM   #37
Mark Johnson is offline Mark Johnson  United States
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Single ended class-A headphone amp using two transistors: T2
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.

_

Last edited by Mark Johnson; 3rd June 2019 at 01:35 AM.
 
Old 3rd June 2019, 03:26 AM   #38
adydula is offline adydula  United States
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Thanks just ordered the 10K pot from Parts Express....$15 + shipping...

Alex
 
Old 3rd June 2019, 07:45 PM   #39
adydula is offline adydula  United States
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Parts ordered less the (2) TO2 insulators and the pot, Total was $79 with shipping and tax.

Alex
 
Old 4th June 2019, 05:35 PM   #40
Mark Johnson is offline Mark Johnson  United States
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Single ended class-A headphone amp using two transistors: T2
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
Attached Files
File Type: pdf T2_bias_adjustment.pdf (636.4 KB, 112 views)
File Type: pdf T2_build_notes_part_1_of_2.pdf (672.5 KB, 95 views)
File Type: pdf T2_build_notes_part_2_of_2.pdf (455.8 KB, 102 views)
 

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