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Old 29th July 2010, 01:01 PM   #111
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j511, Nigel? Not sure, not so common anymore

I just used a jfet + resistor - the resistor is there to set the current thru the leds and not really reqd for a zener - the simpler way works okay, so ...

Not sure about the shunt reg details but it was pretty complete (if that helps!) I did go a bit nuts with the caps and used a few of those big rushian k73-16 foils caps on it - ended up running about 400mA thru CCS - got nice and HOT! The headamp cct is dependent on p/supply "sound", so it's easy to 'tweak' sound for different 'phones.

The protection/delay was a Rod Elliot thing - plenty kits around - used oversized relays, double contacts, wipers, etc - use them in power amps -

Tone controls - a few years ago, Pete Millet did a rather interesting design called the HA4 with input filters - well worth a look.

For travel, might be worth looking at some of the hybrid headamps and 'tweaking' them - as usual, most of their power supplies suffer from size constraints.

Ah, 'morning Patrick, this little design of yours is going to last forever! the B1 buffer in front seems to soften the sound a bit, and the JC seems 'not there'.
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Old 3rd August 2010, 01:52 PM   #112
njepitt is offline njepitt  United Kingdom
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Hi everyone,

Still thinking about how and if to build this, or do a different headphone amp. I'm ploughing through stuff here and on the other sites, but no clear ideas yet, except that sooner or later I'm going to do a DAO, whether before travelling or after.

As I mentioned above, my problem with doing a DAO to take on sabbatical is that it may be too big and heavy. Is anyone with a complete amp willing to measure and weigh it for me? (James? I'd love to see photos, too...)There may be things I can do to reduce weight, like choosing trafo and heatsinks with care, but it would help to see what other people have done. Also, juma posted a version above in post #96 with lower rail voltages and MJE243 in place of the IRFP240 - did anyone build it? (juma?) This would presumably have a slightly lower bias current (??) and therefore I could get away with smaller (and therefore lighter) heatsinks...

Well, thanks for any help.

Cheers

Nigel
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Old 3rd August 2010, 03:21 PM   #113
EUVL is offline EUVL  Europe
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If size and weight is important, you should not do Class A.

The circuit weighs nothing, as always.
But heat sinks and power supplies do.

Light weight, compact solution means Class D or Class AB to me.


Patrick

PS Class A means great sound. So you have to set priorities.
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Old 3rd August 2010, 04:38 PM   #114
njepitt is offline njepitt  United Kingdom
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Default Quote]

Quote:
Originally Posted by EUVL View Post
If size and weight is important, you should not do Class A.

The circuit weighs nothing, as always.
But heat sinks and power supplies do.

Light weight, compact solution means Class D or Class AB to me.


Patrick
Agreed, for sure, but in this case I'm just trying to figure out *how much* it'll weigh. I don't need anything portable-and-battery-powered, but I can't take something that weighs as much as my F5, for instance. (At least, not if my wife catches me...) My best guess so far is that the heatsinks will have to be about half the size of the heatsinks I used on the F5 and the trafo will be *much* lighter and smaller. In terms of size, if I can make it no larger than a shoebox that's probably OK. (My guess is that's doable, if not a little smaller.) If I can get it in around 3 kilos that's probably OK, if it's 10 kilos that's probably not...

Quote:
PS Class A means great sound. So you have to set priorities.
Again, I understand and agree - this is why I'm trying to find out what other people's experiences have been like.

Cheers

Nigel
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Old 3rd August 2010, 05:24 PM   #115
EUVL is offline EUVL  Europe
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Send a PM to Steenoe. He can tell you how much his excellent build weighs.
I use batteries, so no reference for you.


Patrick
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Old 3rd August 2010, 10:28 PM   #116
njepitt is offline njepitt  United Kingdom
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Quote:
Originally Posted by EUVL View Post
...I use batteries, so no reference for you...
I've only just remembered you mentioned batteries in an earlier post. You mean you are using batteries on the DAO with Taylor? How? At what rail voltages? I'd have thought it would run through them pretty quickly, but perhaps I have misunderstood something (again...)

This may be a convenient alternative for me - just ship the amp without any batteries in it, and buy rechargeables online to be delivered to where I'm going... In fact, with a little thought and care maybe it could be built with two power options- either batteries or a PSU in a separate case. Leaving the PSU at home would certainly help with weight...

Cheers

Nigel
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Old 4th August 2010, 03:51 AM   #117
EUVL is offline EUVL  Europe
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I use 24V truck batteries. No option for you.

Patrick
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Old 4th August 2010, 10:51 AM   #118
njepitt is offline njepitt  United Kingdom
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Hi Patrick,

Quote:
Originally Posted by EUVL View Post
I use 24V truck batteries. No option for you.

Patrick
I should have guessed it would be something like this because of the power draw... You're quite right - no option for me for any number of reasons...

I've been researching importing toroidal trafos, which will be pricier than an EI, but (it appears) a good deal lighter. (And better, anyway...) Mouser has what appear to be nice ones from Triad Magnetics with parallel 18V secondaries, at 600g for 50VA and 1kg for 100VA. Seems to me that either of these would do the job if I run 20V rails, or a little less, so the 50VA one seems a better choice, to save a little weight without compromising the sound too much. (At all?)

I'm still considering doing the version juma posted in #96, although maybe with the 16V rails Patrick suggested. Would there be any disadvantage?

Cheers, and thanks for any input.

Nigel
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Old 4th August 2010, 03:23 PM   #119
EUVL is offline EUVL  Europe
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The cascode device in the DAO circuit is an integral part that contributes to the triode characteristics of the LU1014.
By changing that device to say a BJT, the dynamic Vds of the 1014 will be different, and so will its triode characteristics.

I am by no means suggesting that it is better or worse, because I have not tried.
But I would suggest you try to measure the behaviour of that transistor group first.
Maybe you can change a few component values to get it to work.

Or maybe juma has already tried ??


Patrick
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Old 4th August 2010, 04:41 PM   #120
juma is offline juma  Serbia
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I made the circuit I proposed in post #96 and results are very pleasing, it sounds better with my HD555 (Z=50 Ohm) than any other popular unity gain headamp. It's that good that I didn't feel the need to compare it to original DAO circuit.

About triode characteristic of the JFET there are at least two aspects of it:
1. triode transfer characteristic (Id dependance from -Vgs) is intrinsic. It's there whatever you do.
2. triode output characteristic (Id dependance from Vds). It normally doesn't exist - output characteristic of JFET is pehthode by nature. The way to change its' character to triode is to induce feedback from drain to gate. Of course, LU1014 is known for its' a small triode region that we aim for: around -1V of Vgs and Vds less than 5V. That small region is also intrinsic - not dependant on cascoding device.

Since in DAO we have constant Vds (by means of tight cascoding - cascode's reference is tied to JFET's Source) there can not be any influence of that kind; so using a BJT or MOSFET as cascoding device doesn't make any difference to JFET's or resulting device's (complex sum of JFET and cascoding device) behavior.
There is an arangement with such an effect - Mr. Pass implemented it in F3, and it's very different from DAO - a modulated cascode, where resulting device exhibits aforementioned properties.

Last edited by juma; 4th August 2010 at 04:49 PM.
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