Some other Source Follower COnfigurations

[EUVL]

Different devices, different characteristics, different bias points, .....

If you put in enough effort to optimise, and are prepared to live with more heat, you might be able to change the harmonic spectrum of the DAO TCS as well.

But why bother ? It soiunds good as is.
Build one first, and then modify to improve.
More fun so than first time ultimo.




Patrick

[ljfont]

Patrick,

Could you comment on the attached drawing. It's an excerpt from "The Art Of Electronics" Horowitz and Hill. 2nd Edition. Pg 135

It talks about a source follower with source resistors R1=R2. Which guarantees Vo = Vi , if Q1 = Q2. This circuit has greater linearity when operated below IDSS. Compared to a circuit without source resistors.

Thanks,

Leo

[EUVL]

See post#1, Borbely's article Fig.15.

This is the circuit everyone knows, everyone uses in one form or another (Curl Follower, Pass B1, and my original DAO Follower, ....).
There are many detailed descriptions of this circuit on the inet. Please refer to the original B1 thread from Nelson.

B1 Buffer Preamp
http://www.analogzone.com/col_01302004.pdf

The purpose of my article was to show something different, and hopefully also somewhat better.


Patrick

[EUVL]

Someone asked me by PM for the low power version of the DAO with 100mA bias. I have to disappoint him because it was ages ago and I had so many versions that I did not document everything to a state that I can publish. But here is a slightly lower power version with 200mA bias, and only the top cell is shown. But it is easy to figure out how to copy and paste that to the bottom to form the current source I think.

And no, I don't have a TCS version that I can publish from my drawer. I probably have the calculation done somewhere in my archive, but I did not build one and am therefore not going to publish one. Perhaps one day when I retire and have more time, then I shall make them all available. In the meatime, please bear with me and build the high bias version that everyone who took the trouble seems to be extremely happy with.


Cheers,
Patrick

The original DAO follower circuit and its development history can be found here :

http://www.diyaudio.com/forums/pass-...ml#post1130743
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[TheShaman]

I was thinking of building an M2 or a PPAv2 headamp (for those AKG 701's Santa will leave at my fireplace!) but this looks interesting..
It seems the Taylor version is..."taylored" (pun intended!) for the 701s.

Is there a PCB for us DIY newbies? Are there any parts that are hard to source?

[juma]

Patrick, what do you think of lowering Pd by lowering supply voltage ?
+/-24V is too inefficient for just 2 or 3 volts of output signal. Cascoding MOSFETs won't feel well with lower Vds, so I thought to use BJTs instead (they don't mind). Cascoding devices don't have noticeable sound impact anyway, and with +/-12V we could keep original Id and still have half of Pd.

[EUVL]

> Is there a PCB for us DIY newbies? Are there any parts that are hard to source?

Simple answer is no & no. There is a layout published that you can copy, or you just hard wire P2P, which is easy enough.

> with +/-12V we could keep original Id and still have half of Pd

If you argue that you only need 2V swing, then you hardly need more than 30mA current, which means that 200mA bias is a hell of a lot. I would still stick to 16V rail and 200mA bias, as I always want some voltage headroom. But by all means try it and let us know.


Patrick

[juma]

Originally Posted by EUVL

....
If you argue that you only need 2V swing, then you hardly need more than 30mA current, which means that 200mA bias is a hell of a lot. I would still stick to 16V rail and 200mA bias, as I always want some voltage headroom. But by all means try it and let us know.
Patrick

Since this is single ended class A headamp I'd like some current headroom too - you are right about current for 50 Ohms headphones, but 16 Ohms devices are getting more and more popular.
That will be my next project, right now I'm busy with this circlotron (you'll remember the idea from F5 thread), and I have 1 channel working nicely:

[njepitt]

Hi Everyone,

I'm thinking about building the DAO follower headphone amp, maybe with the Taylor mod, and I have a couple of questions. (I'm not sure whether this is the right thread for them, really, since info about the DAO seems to be spread over a few threads.)

1. Somewhere I read the total draw is about 15W, I presume per channel. So a 60VA or 100VA toroidal trafo would be adequate, right? Toroidals down here in Brazil are pricy and hard to get - would there be much difference if I used a normal EI?

2. The photos of Steenoe's build show pretty big heatsinks, but if total draw is only 15W per channel it should be OK to use much smaller ones, right? Anyone have some kind of size estimate?

3. Has anyone put a crossfeed circuit in one of these? Not quite sure whether I want one, but I'd be interested to hear suggestions.

4. For a PSU circuit I'll probably use a version of Salas' regulator, and maybe put a B1-style buffer in to make the whole thing an integrated. Any thoughts?

Thanks for any help, and if all this is in the wrong thread let me know and I'll repost. (Or the mods can move it, I guess..)

Cheers

Nigel

[EUVL]

1. The bias is about 200-250mA. If you use +/-20V rails, you will dissipate about 10W per channel.
So 20W for stereo, and 60VA will be fine. 100VA is plenty. But you will find little price difference between the two.

You can of course use normal EI, or even batteries.
If using EI, it is better to mount the transformer away from the amplifier to minimise magnetic disturbances.

2. You need a heat sink of say minimum 1W/°C.

3. Not me.

4. If you want to put a buffer upfront, you might as well add a proper line stage with gain instead.
But this depends on what headphone impedance you intend to drive with.


Hope this helps,
Patrick