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

[silasmellor]

so when is it hitting the store?

 

[6L6]

Working on it, but in the meantime just get the boards from Mark and build.

 

[6L6]

Some photos of my build

Top view PCB

Back view PCB

PSU section of PCB

PSU components

Ferrite core with wire installed

PSU section stuffed

Custom tool for raising the power resistors.

Power switch

DC power jack

 

[6L6]

Continued

LED wiring

Board ready to test PSU section

Attach black to the panel ground point, read DC volts at cathode of D72. Proper reading will be -22 to -23VDC. Remember that the PSU is "upside down" in this project.

 

[Mark Johnson]

Standoff [specified in the T2 bill of materials] is M3, metric. I plan to use 4-40 standoffs because I have lots of 4-40 hardware around, but very little metric.

Sure, that'll work. One shade tree mechanic's trick for synthesizing a standoff, is simply to stack two or three 4-40 hex nuts instead. Now the distance between the PCB bottom surface and the chassis floor, equals the thickness of two or three hex nuts. Crude but effective and, thanks to the PCB overhead, invisible.

The diyAudio Universal Mounting Specification (link), used for lots of First Watt Nelson Pass power amps in the diyAudio store, has metric M3 tapped holes for board and transistor mounting on the heatsinks. So if you're thinking of doing a power amp one of these days, it might be a good investment to get an M3 bolt and nut assortment from Amazon or elsewhere. These will go into your T2 headphone amp build and they'll also go into your First Watt / diyAudio store power amp.

Sutemribor 320Pcs M3 Stainless Steel Button Head Hex Socket Head Cap Bolts Screws Nuts Assortment Kit + Wrench - - Amazon.com

Amazon.com: VIGRUE 810Pcs M3 Screw Assortment Kit 304 Stainless Steel Phillips Pan Head Machine Screws Bolts Nuts Lock Flat Washers with Storage Box: Home Improvement

You may also decide you want to replace the M4 bolts which come with the 1U Galaxy chassis, and use either black oxide or stainless steel socket cap M4 screws as mentioned in post #44. Both of the Beta Testers chose stainless steel, member adydula chose black oxide.

 

[6L6]

Building continued

 

[6L6]

T2 continued

 

[randytsuch]

Sure, that'll work. One shade tree mechanic's trick for synthesizing a standoff, is simply to stack two or three 4-40 hex nuts instead. Now the distance between the PCB bottom surface and the chassis floor, equals the thickness of two or three hex nuts. Crude but effective and, thanks to the PCB overhead, invisible.

The diyAudio Universal Mounting Specification (link), used for lots of First Watt Nelson Pass power amps in the diyAudio store, has metric M3 tapped holes for board and transistor mounting on the heatsinks. So if you're thinking of doing a power amp one of these days, it might be a good investment to get an M3 bolt and nut assortment from Amazon or elsewhere. These will go into your T2 headphone amp build and they'll also go into your First Watt / diyAudio store power amp.

Sutemribor 320Pcs M3 Stainless Steel Button Head Hex Socket Head Cap Bolts Screws Nuts Assortment Kit + Wrench - - Amazon.com

Amazon.com: VIGRUE 810Pcs M3 Screw Assortment Kit 304 Stainless Steel Phillips Pan Head Machine Screws Bolts Nuts Lock Flat Washers with Storage Box: Home Improvement

You may also decide you want to replace the M4 bolts which come with the 1U Galaxy chassis, and use either black oxide or stainless steel socket cap M4 screws as mentioned in post #44. Both of the Beta Testers chose stainless steel, member adydula chose black oxide.

Thanks, I've used the nut for standoff trick in the past, but I have a number of standoffs now, and Frys is down the street from work and they stock some standoffs.

I'm sticking with English units for now, will worry about m3 if I build a pass amp kit that uses m3. Didn't know it was the standard.

Pretty sure I can pick up some M4 bolts at the local big box store, will need to see what they have. There is also an independent HW store by work here that I like to support, and they have a pretty good assortment of nuts and bolts. Unfortunately, good HW stores are harder to find these days.

Randy

 

[adydula]

I would build it with the caps in the bom, and listen to it, then try the others..this way you become the resident expert!!

Then we can try your caps depending on how well it goes?

 

[randytsuch]

I would build it with the caps in the bom, and listen to it, then try the others..this way you become the resident expert!!

Then we can try your caps depending on how well it goes?

I ordered the BOM caps and some oscons. Pretty sure I have other suitable caps in my junk drawer, but I can be lazy so not sure how much actual cap rolling I'll do.

Thanks for all the pics 6l6. Makes a nice guide.

Randy

 

[blackdod]

I'm having trouble getting AWG28 cable. The best I have found is AWG27.

Any recommendation? How could I calculate the number of turns around the center?

 

[adydula]

I used some ethernet cable I had here that is 24 ga and got 12 loops easily.

Alex

 

[Mark Johnson]

If the number of turns is 8 or 9 or 10 or 11 or 12, you'll be fine. Don't be scared, use whatever wire you've got. 26 AWG solid core insulated "telephone wire" would be fine. Grab some wire, wind it on the core, and find out how many turns you're able to get. It might be adequate and plenty.

Post #60 shows the CAT-6 ethernet cable that I bought from amazon, then cut open to harvest the 28-AWG stranded wires used in my build of T2, and also used in both Beta Testers' T2 builds.

One builder told me he purchased "magnet wire" (wire whose insulation is an enamel coating) in 28-AWG, something resembling this. It is difficult to strip off enamel insulation, his plan is to use a chemical etch. Owww!

 

[6L6]

I bet if you use the smallest wire you have and get at least 3 turns on it, you’ll be fine.

More turns will probably be a little better.

 

[abraxalito]

More turns will probably be a little better.

More than three turns will likely saturate the core, assuming 400mA supply current.

 

[avtech]

Hi Mark, do you have any boards available or a GB?

 

[blackdod]

Thanks guys!!!.


I also have CAT6 cable (AWG24).

If both (AWG27 or 24) work correctly, I´ll use the one that is most comfortable for me to turn.

 

[blackdod]

Ready for check

 

[Mark Johnson]

Hi Mark, do you have any boards available or a GB?

Yes, I sent you a PM.

 

[Mark Johnson]

Blackdod, that picture in #98 is beautiful! Not even a wisp of flux visible anywhere, and a very pretty build. Congratulations.