xrk971 Pocket Class A Headamp GB

[xrk971]

Aksa has a great explanation of why capacitive coupling on the input and output of an amp like this works so well. Besides guaranteeing that the cans never see DC from the rails - the caps are always polarized. The inputs at about 4v and outputs at about 8v. This pushes them into the linear crossoverless region where they sound better (sort of like Class A for caps).

http://www.diyaudio.com/forums/head...lass-headamp-without-heat-29.html#post4998397

 

[xrk971]

Just a note to those of you who may want to run this amp with 30ohm cans. You might want to increase R4 up one notch from 33R to 47R, or even 68R for higher bias and more slam but with the same great musicality. Just check the bias current ti make sure you are not running too hot to keep battery life reasonable. But listen to it "stock" first - it may be just fine.

So a note to Morde, if using with your 30ohm cans, try adjusting R4 and see if you can get a little more oomph for the bass authority. Please try and let us know how it sounds.

 

[wanfai]

pcgab - 2 boards - SHIPMENT RECEIVED
zman01 - 1 board
stellarelephant - 2 boards - SHIPMENT RECEIVED
samoloko - 1 pcb
Morde - 2 board - SHIPMENT RECEIVED
cyteen - 2 boards
funch - 2 boards - SHIPMENT RECEIVED
syyma - 2 boards - SHIPMENT RECEIVED
av-trouvaille - 2 boards - SHIPMENT RECEIVED
Mituisho - 2 boards
bogde - 2 boards - SHIPMENT RECEIVED
faltinsen - 2 boards
vanofmonks - 1 board
M_Balou - 2 boards - SHIPMENT RECEIVED
dwpeterson - 2 boards - SHIPMENT RECEIVED
agdr - 1 board
walangalam - 2 boards SHIPMENT RECEIVED
gwrskien - 2 boards - SHIPMENT RECEIVED
redarc12- 2 boards
dw1narso - 2 boards
zimmer64 - 2 boards
shambala - 2 boards - SHIPMENT RECEIVED
HaroldHill - 2 boards - SHIPMENT RECEIVED
gig - 2 boards
hui13 - 2 boards - SHIPMENT RECEIVED
pranavkr -1 board - SHIPMENT RECEIVED
JimS- 1 board
Kumori - 1 board
tubediy - Shipment received
AKSA - 1 board

 

[xrk971]

Wanfai,
Sorry I had you listed as tubediy - glad it made it to HK safely! That is still pretty fast. Happy building.
X

 

[faltinsen]

pcgab - 2 boards - SHIPMENT RECEIVED
zman01 - 1 board
stellarelephant - 2 boards - SHIPMENT RECEIVED
samoloko - 1 pcb
Morde - 2 board - SHIPMENT RECEIVED
cyteen - 2 boards
funch - 2 boards - SHIPMENT RECEIVED
syyma - 2 boards - SHIPMENT RECEIVED
av-trouvaille - 2 boards - SHIPMENT RECEIVED
Mituisho - 2 boards
bogde - 2 boards - SHIPMENT RECEIVED
faltinsen - 2 boards - SHIPMENT RECEIVED
vanofmonks - 1 board
M_Balou - 2 boards - SHIPMENT RECEIVED
dwpeterson - 2 boards - SHIPMENT RECEIVED
agdr - 1 board
walangalam - 2 boards SHIPMENT RECEIVED
gwrskien - 2 boards - SHIPMENT RECEIVED
redarc12- 2 boards
dw1narso - 2 boards
zimmer64 - 2 boards
shambala - 2 boards - SHIPMENT RECEIVED
HaroldHill - 2 boards - SHIPMENT RECEIVED
gig - 2 boards
hui13 - 2 boards - SHIPMENT RECEIVED
pranavkr -1 board - SHIPMENT RECEIVED
JimS- 1 board
Kumori - 1 board
tubediy - Shipment received
AKSA - 1 board

 

[xrk971]

pcgab - 2 boards - SHIPMENT RECEIVED
zman01 - 1 board
stellarelephant - 2 boards - SHIPMENT RECEIVED
samoloko - 1 pcb
Morde - 2 board - SHIPMENT RECEIVED
cyteen - 2 boards
funch - 2 boards - SHIPMENT RECEIVED
syyma - 2 boards - SHIPMENT RECEIVED
av-trouvaille - 2 boards - SHIPMENT RECEIVED
Mituisho - 2 boards
bogde - 2 boards - SHIPMENT RECEIVED
faltinsen - 2 boards - SHIPMENT RECEIVED
vanofmonks - 1 board
M_Balou - 2 boards - SHIPMENT RECEIVED
dwpeterson - 2 boards - SHIPMENT RECEIVED
agdr - 1 board
walangalam - 2 boards SHIPMENT RECEIVED
gwrskien - 2 boards - SHIPMENT RECEIVED
redarc12- 2 boards - SHIPMENT RECEIVED
dw1narso - 2 boards
zimmer64 - 2 boards
shambala - 2 boards - SHIPMENT RECEIVED
HaroldHill - 2 boards - SHIPMENT RECEIVED
gig - 2 boards
hui13 - 2 boards - SHIPMENT RECEIVED
pranavkr -1 board - SHIPMENT RECEIVED
JimS- 1 board
Kumori - 1 board
tubediy (Wanfai) - Shipment received
AKSA - 1 board

You guys in the US must have received your boards now but are asleep at the wheel and have not updated the list.

 

[Morde]

...
So a note to Morde, if using with your 30ohm cans, try adjusting R4 and see if you can get a little more oomph for the bass authority. Please try and let us know how it sounds.

My LCD-2 cans are 70ohm and I just tried it briefly with iPad plugs to see everything works before plugging in more expensive cans. But I actually do have one pair of AKG K845BT phones that have - beside the Bluetooth - a possibility to feed by wire and the impedance is 32ohm. So maybe I'll build another version with different resistor values and give it a try.

Anyway I'm really happy with the results as it is with this tiny one. Just waiting to get my Altoids tin box and the batteries to get it finished.

 

[xrk971]

The LCD-2's look like awesome headphones. In some ways, reminds me of an AMT but without the pleats. My AMT tweeters have some of the best resolution ever for speakers so I can only imagine what similar technology does for headphones.

So glad it paired up nicely with the LCD-2 planar magnetics.

https://www.audeze.com/products/lcd-collection/lcd2

 

[vanofmonks]

pcgab - 2 boards - SHIPMENT RECEIVED
zman01 - 1 board
stellarelephant - 2 boards - SHIPMENT RECEIVED
samoloko - 1 pcb
Morde - 2 board - SHIPMENT RECEIVED
cyteen - 2 boards
funch - 2 boards - SHIPMENT RECEIVED
syyma - 2 boards - SHIPMENT RECEIVED
av-trouvaille - 2 boards - SHIPMENT RECEIVED
Mituisho - 2 boards
bogde - 2 boards - SHIPMENT RECEIVED
faltinsen - 2 boards - SHIPMENT RECEIVED
vanofmonks - 1 board - SHIPMENT RECEIVED
M_Balou - 2 boards - SHIPMENT RECEIVED
dwpeterson - 2 boards - SHIPMENT RECEIVED
agdr - 1 board
walangalam - 2 boards SHIPMENT RECEIVED
gwrskien - 2 boards - SHIPMENT RECEIVED
redarc12- 2 boards
dw1narso - 2 boards
zimmer64 - 2 boards
shambala - 2 boards - SHIPMENT RECEIVED
HaroldHill - 2 boards - SHIPMENT RECEIVED
gig - 2 boards
hui13 - 2 boards - SHIPMENT RECEIVED
pranavkr -1 board - SHIPMENT RECEIVED
JimS- 1 board
Kumori - 1 board
tubediy - Shipment received
AKSA - 1 board

 

[xrk971]

My bet is Pcgab will be the next to have a build with first sound.
Although Agdr is pretty handy as well as this amp has his Super CMOY footprint.

pcgab - 2 boards - SHIPMENT RECEIVED
zman01 - 1 board
stellarelephant - 2 boards - SHIPMENT RECEIVED
samoloko - 1 pcb
Morde - 2 board - SHIPMENT RECEIVED
cyteen - 2 boards
funch - 2 boards - SHIPMENT RECEIVED
syyma - 2 boards - SHIPMENT RECEIVED
av-trouvaille - 2 boards - SHIPMENT RECEIVED
Mituisho - 2 boards
bogde - 2 boards - SHIPMENT RECEIVED
faltinsen - 2 boards - SHIPMENT RECEIVED
vanofmonks - 1 board - SHIPMENT RECEIVED
M_Balou - 2 boards - SHIPMENT RECEIVED
dwpeterson - 2 boards - SHIPMENT RECEIVED
agdr - 1 board - SHIPMENT RECEIVED
walangalam - 2 boards SHIPMENT RECEIVED
gwrskien - 2 boards - SHIPMENT RECEIVED
redarc12- 2 boards
dw1narso - 2 boards
zimmer64 - 2 boards
shambala - 2 boards - SHIPMENT RECEIVED
HaroldHill - 2 boards - SHIPMENT RECEIVED
gig - 2 boards
hui13 - 2 boards - SHIPMENT RECEIVED
pranavkr -1 board - SHIPMENT RECEIVED
JimS- 1 board
Kumori - 1 board
tubediy - Shipment received
AKSA - 1 board

 

[syyma]

xrk971,

The schematic and board shown C1 input cap value 1uF but the BOM stated with 2.2uF. Please verify the discrepancy.

Sidney

 

[xrk971]

Please use BOM 2.2uF on input and 1uF on output bypass.

 

[pcgab]

My bet is Pcgab will be the next to have a build with first sound.

ha! maybe, I've got the jfets matched, need to solder them on then measure the mosfets.

I found a stash of 25v/470uF Panasonic FCs and got them to fit, a small piece of 3m extreme mounting tape under them to lift them off the board a bit.

 

[xrk971]

Nice work Pcgab! I had a good hunch about your progress.

The 470uF is nice but 2200uF really helps to increase stereo separation and reduce turn off thump to almost inaudible. Sadly you have to use 16v rated ones to do this. It's not a big risk with Li-ion batteries as they are 16.4v. Although it's on already so go with t and if you need to upgrade later.

Good luck matching MOSFETs. It's easy actually with the real deal jig.

Nice looking build btw, can we peek at the Class A business side?

 

[pcgab]

Nice work Pcgab! I had a good hunch about your progress.

The 470uF is nice but 2200uF really helps to increase stereo separation and reduce turn off thump to almost inaudible. Sadly you have to use 16v rated ones to do this. It's not a big risk with Li-ion batteries as they are 16.4v.

I think the batteries I got are li-ion as well. Maybe I'll order some 16v 2200uF caps.

I have some bigger value 25v caps, but they're pretty darn big. I would have to notch the tin to make room for them, and that might not even work!


I found some 2200uF 25v Nichicon's in my stash, but I don't think I can make them fit.

 

[pcgab]

Nice looking build btw, can we peek at the Class A business side?

Of course!

Missing a few components in this pic, and clearly I need to do some cleanup. I think there may be a resistor or two with a small bridge, I'll check those out again before power up.

I bought a hot air re-work station and am enjoying using it. There was no way I could solder these with just an iron.

http://a.co/gAwqJTg

For the price, I think it's a great deal. The solder paste I bought is lead free, and has ~3% silver iirc. It does seem to take a bit longer to start to flow than I would expect, but I haven't tried any solder paste with lead as yet.

Overall, the smd work has been much smoother than I initially thought it would be. I had some issues with measuring the BF862's initially, but after some practice and guidance it's smooth sailing now. 'Smooth sailing' considering I am measuring grains of sand

 

[pcgab]

and I forgot to attach the pictures, ha!

 

[xrk971]

Nice looking SMD joints there. I hate non lead solder. Stuff is the bane of reliable good looking clean solder joints. And it has cost the high reliability satellite electronics business billions of dollars in damages. How? When solder is lead free, the tin will grow whiskers out into free space over time. Guess what happens when they get long enough? Shorts. Big $600M Geocom Satellites are designed for 15year operational lifetime. Now in 5 to 7 years these tin whisker anomalies show up. Like gremlins appearing in the scene.

We know because we have identical ground equivalents of what is flying. So we can test and see cause of failures.

Anyhow rant over.

I love leaded solder

My leaded solder paste and hot plate trick works pretty well too. I will need to get a hot air gun for rework in the future.

So for hot air work just add paste first? Doesn't hot air blow parts not yet anchored around?

 

[bogde]

Of course!

Missing a few components in this pic, and clearly I need to do some cleanup. I think there may be a resistor or two with a small bridge, I'll check those out again before power up.

I bought a hot air re-work station and am enjoying using it. There was no way I could solder these with just an iron.

http://a.co/gAwqJTg

For the price, I think it's a great deal. The solder paste I bought is lead free, and has ~3% silver iirc. It does seem to take a bit longer to start to flow than I would expect, but I haven't tried any solder paste with lead as yet.

Overall, the smd work has been much smoother than I initially thought it would be. I had some issues with measuring the BF862's initially, but after some practice and guidance it's smooth sailing now. 'Smooth sailing' considering I am measuring grains of sand

nice station and great work! congrats!

 

[DontHertzMe]

When solder is lead free, the tin will grow whiskers out into free space over time. Guess what happens when they get long enough? Shorts.
.
.
.
I love leaded solder

Agreed. Lead-free solder is a pain in the backside. Plus the benefits of removing lead have been questionable.