ad8610 class a bias +v rail or-v rail? - diyAudio
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Old 24th April 2004, 07:12 PM   #1
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Default ad8610 class a bias +v rail or-v rail?

i've seen it on another forum where it was said the ad chips should be biased to the +v rail anyone tried this? i have mine biased to the -v rail right now. thanks, crippledchicken
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Old 25th April 2004, 11:38 AM   #2
cdl is offline cdl  Denmark
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As far as I have understood, it shouldn't make a big difference, which rail you use - both should force output into class A.
So unless you think that your + rail is more quiet thant your - rail, I would just leave it the way it is.

By the ways, I have had my ad8610 biased to the negative rail for some time, but I recently removed the biasing resistors. I had a suspicion that a slight hum I was hearing was PS ripple coming through the resistor... I was wrong though; the hum actually is caused by the way the single-ended input of my power amp is wired.

But what I'm getting at, is that I haven't noticed all that much of a difference in the sound. This is not because I am deaf, the effect of adding the biasing resistors was quite pronounced with OP37...
So if you are uncomfortable with the biasing resistors, try removing them...

I think I will bias my AD8610's again eventually, though - makes me feel good. But I will use a constant current source and not a resistor. And THAT will have to wait until some other important things (hmm, such as an input selector and other comfy gimmicks) have been built...

cheers,

cdl
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Old 25th April 2004, 03:34 PM   #3
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hi cdl, thanks for the reply,the poster on the other site said he had been biasing them to the-v. rail several times, and wondered why he never really noticed much difference. he said looking at the data sheets, which i'm not that good at interpreting, seemed to show a slight positive bias already present in the chip it's self. so his explaination was, by adding bias to the-v. rail he wasn't gaining anything. he also said when he changed to+v bias he got better sound, and noticed what he had been missing all along. then a couple of other posters tried, and claimed the same results. so i thought i would check this forum, for more opinions/experiences before i went to the trouble of reversing my jfet cascodes. i might just give it a try if i do, i'll post the results and let you know what the differences are if any. thanks again, crippledchicken
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Old 25th April 2004, 03:41 PM   #4
cdl is offline cdl  Denmark
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Thank you - sounds interesting. I will be very curious as to your results with positive-rail cascodes, when you get there!

/cdl
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Old 26th April 2004, 06:44 AM   #5
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hi cdl, changed the ad8610s to +v. class a bias and they don't even sound like the same op amps! they sounded thin with too much tizz in the upper end before but now, the mid range is much smoother, tizz is gone, the lows have the sound of more power but tight bass.i had to reduce my subwoofer level a little after the change it's just more naturnal sounding.i thinki've found out what i've been missing. i 've not tried the resistor but, it might be worth trying when you have some spare time. i know what sounds good in one component, or system might not sound good in another but, the curiosity, was too much i just had to try it and glad i did. good luck, crippledchicken
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Old 26th April 2004, 07:06 AM   #6
sonnya is offline sonnya  Denmark
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mmhhh sound more like oscillation to me...

I use them too. Both in my CFB power amp for servo, and also in my test/prototype preamp.

And they does not have to change that much, when biasing them.
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Old 26th April 2004, 07:19 AM   #7
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oscillation? you mean now, or before? sounds great now chips don't run hot. sure hear alot more details and the vocals are alot smoother in my familiar cds. thanks for your reply crippledchicken
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Old 26th April 2004, 07:23 AM   #8
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Very interesting. I briefly tried CCS at 2mA from negative and either didn't hear a difference or prefered the sound without the biasing.
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Old 26th April 2004, 07:36 AM   #9
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high there analog, i never thought about it till i saw the posts on the audio asylum about it. so i removed my cascodes, from the negative biasing and noticed no difference but when applied to the positive rail the whole sound just seemed more balanced. beats me why it sounds so much better! i'll just keep a close check on chip temperatures and if no problems, i guess i'll leave them as is. reguards crippledchicken
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Old 28th April 2004, 07:17 PM   #10
cdl is offline cdl  Denmark
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Quote:
Originally posted by crippledchicken
...they sounded thin with too much tizz in the upper end before but now, the mid range is much smoother, tizz is gone, the lows have the sound of more power but tight bass.i had to reduce my subwoofer level a little after the change
Hmmm ... well I actually like the sound of mine as they are now without bias ... preferred them over opa627 for their nice reproduction of voices, while preserving a little more detail than AD825. I believe the rest of my listening chain should have quite linear freq. response and I'm puzzled over your report of lacking bass...

So I'm really curious now - must try pos bias as soon as I can.

Would you by any chance be willing to share the circiut you use for the opamps with us / me, crippledchicken?
And oh, maybe your cascodes as well? That would be really nice of you

cheers!!

/cdl
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