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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 30th May 2019, 09:49 AM   #21
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by abraxalito View Post
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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Old 30th May 2019, 12:59 PM   #22
Mark Johnson is offline Mark Johnson  United States
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Single ended class-A headphone amp using two transistors: T2
Quote:
Originally Posted by mercedese63 View Post
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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Old 30th May 2019, 01:07 PM   #23
Mark Johnson is offline Mark Johnson  United States
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Single ended class-A headphone amp using two transistors: T2
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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Last edited by Mark Johnson; 30th May 2019 at 01:20 PM.
 
Old 30th May 2019, 01:12 PM   #24
Mark Johnson is offline Mark Johnson  United States
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Single ended class-A headphone amp using two transistors: T2
Quote:
Originally Posted by Elvee View Post
Nice project BTW, it easily scores 8~9 on the N.P. scale...
Thank you, Elvee!
 
Old 30th May 2019, 01:25 PM   #25
6L6 is offline 6L6  United States
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Single ended class-A headphone amp using two transistors: T2
Quote:
Originally Posted by mercedese63 View Post
Why would anyone want to design/construct an amplifier that uses a big ole' nasty 3300uF output coupling capacitor??
Well, you certainly wouldn't want to ever listen to this --

Click the image to open in full size.


Or this -




Click the image to open in full size.

Click the image to open in full size.

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...)





.

Last edited by 6L6; 30th May 2019 at 01:28 PM.
 
Old 30th May 2019, 05:41 PM   #26
Mark Johnson is offline Mark Johnson  United States
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Single ended class-A headphone amp using two transistors: T2
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.
 
Old 30th May 2019, 05:49 PM   #27
6L6 is offline 6L6  United States
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Single ended class-A headphone amp using two transistors: T2
BOM updated to include the washers.
 
Old 2nd June 2019, 12:20 AM   #28
adydula is offline adydula  United States
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Got the pcb board and panels today!!

Thanks Mark...looking forward to putting this together soon!!

Alex
 
Old 2nd June 2019, 07:02 AM   #29
mercedese63 is offline mercedese63  United States
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Quote:
Originally Posted by Mark Johnson View Post
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).
 
Old 2nd June 2019, 04:15 PM   #30
Mark Johnson is offline Mark Johnson  United States
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Single ended class-A headphone amp using two transistors: T2
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!
 

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