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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 29th May 2019, 03:43 AM   #11
agdr is offline agdr  United States
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Single ended class-A headphone amp using two transistors: T2
Very good work, Mark!
 
Old 29th May 2019, 04:52 AM   #12
abraxalito is offline abraxalito  United Kingdom
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Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
With so many turns through your L2 I can't help but think you're saturating it. How much current is the circuit taking (I see you said its under 400mA but how much under) ?
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Old 29th May 2019, 06:32 AM   #13
Mark Johnson is offline Mark Johnson  United States
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Single ended class-A headphone amp using two transistors: T2
Here is the full line catalog from Laird Performance Materials pdf link. The exact Laird part used in the T2 circuit is listed (a) on the schematic; and also (b) in the Bill Of Materials.

The curves and graphs and explanations in the catalog, may help you decide whether any ferrite bead designed for EMI suppression, might ever undergo "saturation" when subject to DC current flow {as in the second stage of the T2 power supply filter}. If saturation can occur, at what number of amp-turns does saturation become a problem for EMI suppression beads? Surely Laird customers would want to know, and surely Laird would provide this information.
 
Old 29th May 2019, 06:38 AM   #14
abraxalito is offline abraxalito  United Kingdom
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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.
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Old 29th May 2019, 05:56 PM   #15
Mark Johnson is offline Mark Johnson  United States
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Single ended class-A headphone amp using two transistors: T2
Default 28 Gauge wire stripping / sourcing

The AWG-28 wire which I sent to the two Beta Testers, to wind T2's power supply choke "L2", was taken from CAT-6 ethernet cables. It's teflon insulated, silver plated, stranded wire. Very high quality stuff!

But, not so easy to strip off the insulation. Teflon outside + stranded inside == difficulty for many $15 wire stripper tools. Sometimes these tools cut the wire instead of stripping it. Sometimes they cut 30% of the strands while removing the insulation. Sometimes they stretch and deform, but don't actually remove, the insulation.

Old baxtards like me, who use plain ordinary diagonal cutting pliers to strip wires manually "by feel" (i.e. after lots of practice and lots of mistakes), will have no special difficulty with stranded CAT-6 wire. And anyone can get pretty good at it by a bit of practice. Strip one of these wires 20-30 times, and notice what works & what doesn't. What gives nice clean strips with no cut strands? How does it feel in your hands, when you're doing it right? Remember that feeling.

Another way to go, of course, is to use solid core AWG-28 wire. Low cost wire stripping tools perform beautifully on this stuff. Remember that hobbyists used to build their prototypes with Wire Wrap (30-AWG solid core wire) and they had no trouble stripping it, at all. So, if you don't want to learn Wire Stripping By Feel, solid core AWG-28 is a viable option. Plus it makes excellent hookup wire for preamps, line stages, headphone amps, and other projects that don't pump ten watts into eight ohms. I bought this kit of ten different colored spools of 28 gauge solid core wire, from Remington Industries. Its insulation is a little thicker than the stranded CAT-6 wire, so you may not be able to not get a full eleven turns through the L2 core. But that's the tradeoff you make in order to have easy wire stripping.

https://www.remingtonindustries.com/...ors-25-length/

Shipping inside the US was very quick, I received it 3 days after ordering. If you live somewhere else in the world, scout around for a local source. I hope you are able to find similar quality at similar prices. If not, you still have the option to learn Wire Stripping By Feel. Then buy CAT-6 ethernet cables locally, they're cheap everywhere.

Finally, I should mention that it only takes 3 minutes to wind eleven turns around the L2 core. If you wind the choke and then have a mishap when stripping the ends, so what? You've lost $0.01 worth of wire and 3 minutes of your life. Unwind and discard the old wire, and try it again. 3 more minutes. Then strip it again and have better success!
 
Old 29th May 2019, 08:36 PM   #16
agdr is offline agdr  United States
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Single ended class-A headphone amp using two transistors: T2
Quote:
Originally Posted by Mark Johnson View Post
I bought this kit of ten different colored spools of 28 gauge solid core wire, from Remington Industries. Its insulation is a little thicker than the stranded CAT-6 wire, so you may not be able to not get a full eleven turns through the L2 core. But that's the tradeoff you make in order to have easy wire stripping.

https://www.remingtonindustries.com/...ors-25-length/
Good stuff! Here is another similar possibility, on Amazon:

28 AWG silicon stranded

28 AWG (and they also have 26 and 30 AWG available, it appears) 5-color silicon-insulated wire for $16, with the "free" prime shipping. I use 26 AWG silicon wire for hookup in one of my projects here and just love the stuff. Flexible as a wet noodle.

The silicon insulation cuts well too with standard (well, Greenlee stainless 1917-SS cutters, a little better than Walmart :P) wire cutters. The silicon is often fairly high temp too, won't shrink back when soldered. I've never bought this brand before. I wonder how the thickness of the insulation stacks up to the PVC though - would 11 turns still fit in the core? Hmmm.

Also - click on the "compare with similar items" below the description, that brings of several more brands of similar.

Just a thought! Going to be a fun project.

Last edited by agdr; 29th May 2019 at 08:41 PM.
 
Old 29th May 2019, 08:43 PM   #17
xrk971 is offline xrk971  United States
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Single ended class-A headphone amp using two transistors: T2
That silicone insulation wire is great stuff. It is used for super high current (tens of amps) DC motors in RC cars and helicopters. The flexibility is provided by the very small diameter strands of wire and the soft silicone which is heat resistant. I use it for flying leads to off board mounted power MOSFETs and BJTs. Usually 16ga or 18ga for the multi amp applications. This allows flexibility in mounting transistors on a heatsink at a different location than the PCB.
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Old 30th May 2019, 01:40 AM   #18
adydula is offline adydula  United States
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Mark,

I sent you a PM for a set of boards!!

Alex
 
Old 30th May 2019, 06:02 AM   #19
mercedese63 is offline mercedese63  United States
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Quote:
Originally Posted by agdr View Post
Very good work, Mark!
Why would anyone want to design/construct an amplifier that uses a big ole' nasty 3300uF output coupling capacitor??
If it's not a DC-coupled output design, I'm not personally interested in it, but other members here may not give it any consideration whatsoever.

I see you have heatsinks on the TO-92 devices.
I assume this is because your are operating them near their maximum dissipation and potentially helps keep them from self-destructing?

Last edited by mercedese63; 30th May 2019 at 06:13 AM. Reason: Spelling error.
 
Old 30th May 2019, 07:07 AM   #20
wrenchone is online now wrenchone  United States
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Gee-gosh golly - what a blindingly original concept. I don't think I've seen anything remotely like this...

Except perhaps here...

Simple Single-Ended Headphone Amp
 

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