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Old 6th January 2013, 01:27 AM   #891
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Does anyone here build DiyAB Honey Badger amp with out stability issues?
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Old 6th January 2013, 02:42 AM   #892
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If you have more than 40V rails BC560C couldn't be used for Q9. Q5/6 never see more than a volt barring lightning strikes or cometary impact so they don't need high Vcemax. Q9 doesn't have low Vce so KSA992 here is no problem. You want a very high-gain fast transistor in this position.
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Old 6th January 2013, 03:29 AM   #893
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Quote:
Does anyone here build DiyAB Honey Badger amp with out stability issues?
Was this said in humor ? Of ALL the amps I built ... this one actually was put together without a miller cap using a mje340 VAS. Just a warm Zobel .. . Of ALL my prototypes , .. this one is the most "forgiving" ,.. and the best documented (Self and Cordell). So if this was a "trolling" attempt , wrong place-wrong amp!! .

PS ... amp is nearly idiot proof and burn proof - me and Jojo have experienced
this. I even use this amp while I type this (below-awesome source). Nothing but the best for my fellow DIY'ers .. .

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Old 6th January 2013, 03:43 AM   #894
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Quote:
barring lightning strikes or cometary impact
Well said , Keen .. . goes the same for the badger !!

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Old 6th January 2013, 04:39 AM   #895
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thank kean/os , gonna replace ksa992 with bc560c in Q5/Q6.
do i have to hfe match of this transisitor?.
thank you.

my build of this amp is rock stable! i follow all build guide by jojo and only change ksa1381 with 2sa1209.
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Old 6th January 2013, 04:51 AM   #896
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do i have to hfe match of this transistor?.
Not required , but the audiophile in you might WANT to ..
PS - Q1 and 2 are also candidates for matching , this will result in less offset.
The ideal is at least a close DMM match of 1-2 and 5/6, but the amp will still be
better than most with even recycled parts.

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Last edited by ostripper; 6th January 2013 at 04:55 AM.
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Old 6th January 2013, 04:55 AM   #897
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Originally Posted by ostripper View Post
Not required , but the audiophile in you might WANT to ..

OS
thank you OS , i'll hfe match of this transistor.

naf
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Old 6th January 2013, 05:10 AM   #898
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of course i match q1/q2 and guess what offset i got?... my dmm read 0.00mv
i gain knowledge from your thread... from frugal to mongrel ...
my deepest thank you
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Old 6th January 2013, 05:14 AM   #899
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By Tsip - if Q5-Q6 can be replaced by BC560 i guess that BC550C would be ok as well what about Q9? Can we replace with BC560 or BC550?
thanks
Q9 sees nearly the full rail voltage , might want to keep a high Vce device (2sa992) here.

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Old 6th January 2013, 05:30 AM   #900
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Hfe matching won't help. Vbe matching is what's important for a current mirror. Most BC5x0C I've measured are matched to 300uV. That's a just over a 1% mismatch. 1% at 3mA is 30uA. And this is without degeneration! Now lets consider temperature to make sure.

Q5 has about 1V Vce whereas Q6 has .66V. This corresponds to 3mW and 2mW respectively. The thermal resistance from junction to ambient of the average TO92 is 200, so this calculates to a temperature difference of .2C. The tempco of silicon is about 2.1mV/C, so we have a 420uV mismatch. So this leaves us with a 720uV total mismatch. This is 2.8%, corresponding to a mismatch of 84uA. If the cases are thermally coupled, differential thermal resistance is about 160 corresponding to a mismatch of 336uV.

And this is still without any degeneration.

Assuming an Hfe of 500 for the BC560C, mismatch caused by Hfe will be roughly 12uA. So improving matching by a factor of 8 with equal Vce and degeneration is the point of diminishing returns. BUT there is 220R degeneration in the original design. So lets factor this in. 720uV mismatch across 440R total degeneration means our Vbe-induced mismatch is reduced to 1.6uA - .005%! Despite mismatch and temperature variations, the biggest flaw with our current mirror is not a transistor mismatch. Of course, the degeneration tolerances will directly affect matching, so they are in fact the weakest link. Two 5% tolerance resistors have a potential mismatch of 10% - almost 4 times the max mismatch without any degeneration at all!

So, match R20/R21 first and only then worry about Vbe mismatching with the BC5x0C. You can check Vbe matching with your multimeter at the diode setting by placing the probes across the B-E junction and making sure they both match to 1mV (4%) or so. Let them sit a while and don't touch them with your fingers when you do this.

If you have matched R20/R21, you can verify transistor matching by probing across the emitters of Q5/6 with your DMM. It should be less than 1mV; short your DMM leads to make sure it can read DC below 1mV. Don't have a speaker connected while probing around in the amp. Even if you don't slip or drop a probe, touching the sensitive signal nodes may cause oscillation which could be dangerous for your speakers. A good idea is to use 10k-100k resistors in series with both probe leads, as this will block the shunt parasitics of the DMM.
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