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HackerNap failed

337alant said:
Do not try the Avondale method with speakers connected:eek: phiz bang pop*

Alan
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Eh.!! Where did I recommend that?

The literature I publish clearly states that loudspeakers must NOT be connected during tests.

Kindly refer to your CD Alan.
 
I have over the last day increased the bias from 3.5mv to 5.6mV.
Blimey what a game, lid on / lid off / heating on / heating off / speaker connected / speaker disconnected / breathing / holding breath, it all alters the voltage.
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Yes it does ;)

The real point of that old article was to point out that, providing your NAP-alike shows at least 4mV across an emitter resistor, you're into the 'diminishing -returns' ballpark, and about 6mV is 'enough'. NAP250s are set to 7.2mV IIRC, and even my humble graph shows why. But 5mV or so gets you close enough, and since the quasi-comp stage is not thermally-compensated by the Vbe 'base=spreader' it will drift/hold low when tested with the lid off. Expect it to rise 1 or 2mV when closed-up for 20mins+. So you're quite close enough. Mild or even drastic overbias does not improve distortion performance at all ( I really need to follow this up some more one day for the NAP)

Definitely set your amps up with speakers disconnected - only to save the speakers in case of a probe slip. It makes no difference to the amp of course, which will maintain dc offset and bias whether or not a load is connected (the very definition of a feedback-controlled amp)

16mV offset is in the 'trivial, don't care' bracket'; under 50mV is fine; and 100mV is about my own upper limit of acceptable. That said, as PD has pointed-out here before, even 100mV makes for a very trivial cone offset and thermal loading in the bass unit (<10mW for a nominal '8ohm' bass driver)

Hope this sets minds at rest.
 
I have had a look at Martin Clarks notes again on bias setting and also a few threads on here, it sure can give you a headache...

I have over the last day increased the bias from 3.5mv to 5.6mV.
Blimey what a game, lid on / lid off / heating on / heating off / speaker connected / speaker disconnected / breathing / holding breath, it all alters the voltage.

Source and pre connected, volume set to zero and source stopped, speakers connected.
There is 16mV on the output terminals which is pushing 0.16mA into the speaker.

I will try and table some voltages below
Upper_______________________Lower
5.6____Speaker connected_____3.2
4.8____Speaker disconnected___3.7

Does this make any sense?

I think I will try Johns current method next.
Should the speakers be connected during the test or not?[/
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LesW said:
Eh.!! Where did I recommend that?

The literature I publish clearly states that loudspeakers must NOT be connected during tests.

Kindly refer to your CD Alan.
Click to expand...

Les 100% agree, You never recommended that you clearly state dont do it on your Diag, I was just warning Tony as he has been experimenting with his bias with and without speakers attached.
Alan
 
Thanks to you all for you considered response.

I actually feel as though I know what I am doing now, last night I set the bias to 27mA using the series current method in the power rails.

Listening was curtailed by a power cut crapping the squeeze server data base and nas raid sync error, should all be ready for a listen tonight.

Tony
 
So some listening done after almost doubling the standing current to 27mA, got to be dramatic after all this fiddling around surely.

Well unfortunately not really, effect on low bass, mid bass, mid range - absolutely none, sounds just the same to me. Top end, well maybe an imagined improvement as its so slight, I think some instruments can be located a little more precisely in the room (imagined space) and then its only the delicate instruments within a well recorded piece.

Compared to fiddling with capacitors or getting the 0v feeds and internal cable its not worth a lot of time, Carl was right, so long as you have at least 3.5mV or 15mA don't worry and don't bother cracking it up to the upper levels unless your a little anal like myself.

Tony
 
john.luckins said:
If 11 mA goes to the front end that leaves 27mA for the output stage, all of which goes through the 0.22 ohm resistors, which gives us 5.9mV across each of these. To my mind this is a good way to set the bias up without poking around a live circuit. I believe it is what LesW recommends.
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I'll have to check what I've set my Voyager clones at. I think I ignored the front end supply, but 11mA is nearly a third.

Thanks
 
6mv across 0r22 is 27mA idle bias in the output stage; 7.2mV across 0r22 is 32mA; and the 'ballpark minimum' of 4mV is still 18mA.

Close enough is probably...close enough.
 
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