PowerPad and the ultra extreme headphone amp TPA

Upupa Epops · 2004-08-27 6:05 pm

Carlos, peranders is professional, not amateur

- by soldering with paste and hot air by big hole paste flow away.

carlosfm · 2004-08-27 8:02 pm

I meant a big via almost the size of the pad, and fill it up with solder with... the soldering iron.

Of course P-A is doing it the recommended way, but I just gave a suggestion to do it simple.

peranders · 2004-08-27 9:58 pm

I understand what you mean Carlos but I want to keep the pcb solderable for wave soldering... just in case. Big plated holes aren't so good when it comes to wave soldering. I think it possible to solder by hand with those 18 small vias. Reports about this will come :nod:

carlosfm · 2004-08-27 10:32 pm

peranders said:
Reports about this will come

Indeed.
I'm making a prototype on veroboard.

Listening tests when finished.
I've just started.
Let's see (listen) if :up:

or

.

Upupa Epops · 2004-08-27 10:37 pm

If resuts will be not OK, is here big field for shifting this chip to class A

.

carlosfm · 2004-08-27 11:23 pm

Upupa Epops said:
If resuts will be not OK, is here big field for shifting this chip to class A .

With a switch to turn biasing on and off.

Mmmmm... 100ma? :hot:

peranders · 2004-08-28 10:10 am

The layout is ready now. Notice that the groundplane isn't shown, which are on both sides.

http://www.sjostromaudio.com/hifi_files/qrv/qrv07r0layout_cp.pdf
http://www.sjostromaudio.com/hifi_files/qrv/qrv07r0layout_cl.pdf
http://www.sjostromaudio.com/hifi_files/qrv/qrv07r0layout_sl.pdf

http://www.sjostromaudio.com/hifi_files/qrv/qrv07r0schema_p1.pdf
http://www.sjostromaudio.com/hifi_files/qrv/qrv07r0schema_p2.pdf
http://www.sjostromaudio.com/hifi_files/qrv/qrv07r0schema_p3.pdf
http://www.sjostromaudio.com/hifi_files/qrv/qrv07r0schema_p4.pdf

A group buy? Anybody interested? This question was put already at head-fi.org but noone seems to dare to build it

fit · 2004-08-28 10:34 am

I am currently doing similar project but as buffer I am planning use OPA627 as e buffer - and no caps in signal path... I just wonder why are you using two resistors in PS Reg ?

Upupa Epops · 2004-08-28 11:17 am

Precision PCB - I am applauding

! Probably it will give too high sound quality, so you must give in front off some " glass " for humanize of sound

.

Upupa Epops · 2004-08-28 1:39 pm

627 on output ?

carlmart · 2004-08-28 1:53 pm

peranders said:
The layout is ready now. Notice that the groundplane isn't shown, which are on both sides.

That means the so much discussed copper heatsink is part of the groundplane?

A very very minor comment on the regulator output capacitor. It's been some years since I have been using smaller caps at the output of 3X7 and similar regulators, like 100uF or so. Sometimes split 47uF and 47uF between reg output and chip input. Audio quality seems to improve with small caps there, but I am not quite sure why.

So perhaps it might be interesting trying a smaller cap than 470uF at your reg outputs. Instead it pays off putting a larger cap between adj pin and earth.

This is certainly a project to try with batteries too.

A group buy? Anybody interested? This question was put already at head-fi.org but noone seems to dare to build it

Soldering the heatsink is certainly a concern on this DIY project. But Upupa Epops said pins 6 to 15 might be heat-sinking pins, so maybe joining all those pins and the copper surface below the chip, pre-covering it with a thin solder layer and when applying heat with a solder pen on the pins to solder them that would also solder the IC below pad. Just a thought.

Interesting: I was also curious about the gain you used, but it seems TI indirectly seems to recommend no gain on this stage. It looks like a buffer, as the gain is set by the previous stage. Perhaps I should say a differential buffer, as that is what the TA seems to be. Pity TI rarely includes an equivalent schematic on their datasheets, as National usually does.

Carlos

carlmart · 2004-08-28 2:01 pm

peranders said:
This question was put already at head-fi.org but noone seems to dare to build it

Perhaps because it's a project involving only SMD parts? And many of them?

If you re-design it using regular size parts, leaving only the audio ICs to deal with, there might be some more interest. It would be a more DIY version. That's what Pavel does.

Carlos

fit · 2004-08-28 2:15 pm

Upupa Epops said:
627 on output ?

no - at the first stage where Per is using AD8610 - OPA627 is stable at gain=1
(I have PCB with SOIC8 mask so I can use any opamp

)

carlosfm · 2004-08-28 2:57 pm

carlmart said:
It's been some years since I have been using smaller caps at the output of 3X7 and similar regulators, like 100uF or so. Sometimes split 47uF and 47uF between reg output and chip input. Audio quality seems to improve with small caps there, but I am not quite sure why.

Actually I would (and do) use just a 100nf cap. :att'n:

And electrolythics+ceramics on the chip.
Not big electrolythics on the reg's output and just 100nf on the chip.
I'm using 68uf+0.1uf on each voltage pin on the chip.

P-A, I'm makin' it, and I'm using small 470uH chokes (instead of resistors) on each voltage, for each pin, to isolate, because I have a LM317/337 PSU for both channels.

I will test this as a line pre, not a headphone amp.
The two applications have different implementation, mainly the feedback resitor has a different recommended value.
The recommended feedback resistor is even different for low or high impedance headphones! :att'n:

I'm becoming a specialist in decoding TI datasheets, one needs to read between the lines! :dodgy:

Almost done, but I have to go out now.
Gonna do a listening session with my phono pre and a Linn LP12.

Later,

carlosfm · 2004-08-28 8:44 pm

P-A, I've just noticed that you don't use the Cadj cap.
Any reason not to include it?

peranders · 2004-08-28 10:18 pm

fit said:
I am currently doing similar project but as buffer I am planning use OPA627 as e buffer - and no caps in signal path... I just wonder why are you using two resistors in PS Reg ?

You don't have to use caps in my design, just omit them if you don't want them.

You mean two resistors in parallel? This was just for convinience.

peranders · 2004-08-28 10:20 pm

carlosfm said:
P-A, I've just noticed that you don't use the Cadj cap.
Any reason not to include it?

No not really but a have larger output caps instead.

peranders · 2004-08-28 10:28 pm

carlmart said:
Perhaps because it's a project involving only SMD parts? And many of them?

If you re-design it using regular size parts, leaving only the audio ICs to deal with, there might be some more interest. It would be a more DIY version.

I like SMD simply and it's fun... and not so hard to solder either.

Anyway, anybody here interested in a group buy?

Devil_H@ck · 2004-08-28 10:35 pm

peranders said:
No not really but a have larger output caps instead.

Adding Cadj gives a lot beter regulation, try a 220µF cap.

carlosfm · 2004-08-28 11:24 pm

peranders said:
No not really but a have larger output caps instead.

It's not the same thing with these regs...

Devil_H@ck said:
Adding Cadj gives a lot beter regulation, try a 220µF cap.

That's it.
More than 80db PSRR.
But 220uf seams too much...
I normally use 47uf.
On this pre I'm using 68uf.
With more than 10uf the protection diode is needed.
I use both protection diodes.

Oh, btw, the board is just finished.
Gotta test it.
:att'n:

Advise: This is not really like some op-amps (627 included, and most fet-input op-amps), you need to use output coupling caps with this chip. :att'n:

I have around 60mv DC offset on the outputs.
Not much, but I decided to put the caps in.

Let's see what this delivers as a pre.
It's late now, so I can't crank up the volume.
More tests tomorrow.
I'll leave it :hot:

in' in.

PowerPad and the ultra extreme headphone amp TPA

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