That looks like the fix, just remember to set the pots back to zero. You could probably use <500R values. Use what you have in your parts stash.
My FQP Fairchild Version is now biasing correctly and is actually playing music. As I cannot switch for and back, it is hard to tell if its the better amp than the Harris Version.
Actually I am a little bit in doubt, as the Piano in the Köln Concert from Keith Jarrett does not completely convince me. I will check the Harris amp later with this concert.
Actually I am a little bit in doubt, as the Piano in the Köln Concert from Keith Jarrett does not completely convince me. I will check the Harris amp later with this concert.
The ACA mini powered by a lipo has become one of the best amps I’ve ever heard. The biggest difference over the brick power (with filter) is that the sound stage is larger and the LF is just incredible: it certainly doesn’t not have greater LF extension but has tremendous slam in comparison.
Hey all!
My little ACA mini is rather impressive! Bias has been stable for the last 18 hrs (297 mV, 11.45 V left, 299 mV, 11.52 V right), and it is valiantly right now pushing a pair of 1973 Large Advent (with brand new original specs woofers from Simply Speakers). Bass is very good too!
Sorry if this has been discussed before, the search engine is not very good, but I noticed a strange issue:
One MOSFET's heat sink is significantly cooler than the other 3 (which are around 45-50 degrees Celsius)! Left front one (IRF520). Barely above body temperature. And that was after over 18 hrs being ON. I used only a very small amount of white paste from a CPU cooler kit, properly smeared. The MOSFET itself is also not very hot.
Music is fine, at least by ear--both channels appera to be performing similarly. What gives? Cheers!
--Christian
My little ACA mini is rather impressive! Bias has been stable for the last 18 hrs (297 mV, 11.45 V left, 299 mV, 11.52 V right), and it is valiantly right now pushing a pair of 1973 Large Advent (with brand new original specs woofers from Simply Speakers). Bass is very good too!
Sorry if this has been discussed before, the search engine is not very good, but I noticed a strange issue:
One MOSFET's heat sink is significantly cooler than the other 3 (which are around 45-50 degrees Celsius)! Left front one (IRF520). Barely above body temperature. And that was after over 18 hrs being ON. I used only a very small amount of white paste from a CPU cooler kit, properly smeared. The MOSFET itself is also not very hot.
Music is fine, at least by ear--both channels appera to be performing similarly. What gives? Cheers!
--Christian
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They should feel even, and certainly not be cold. That usually happens when devices not balanced during bias. Did you measure offset?
Thank you guys! After another 12 hrs or so, they are now close to each others in temperature. And yes I had measured all voltages properly ("Bias has been stable for the last 18 hrs (297 mV, 11.45 V left, 299 mV, 11.52 V right)"). I am listening to it right now--wow!
Thank you Mr. Pass for another great gift!
--Christian
Thank you Mr. Pass for another great gift!
--Christian
Indeed, all outputs should come to temperature evenly in less than 20 minutes.
@christiang
Try cycling the amp off/on giving it time to cool, then see if it comes comes back up to temperature evenly and quickly.
It does get warm to the touch, but not hot. I did notice some interesting behavior as it powers up from a discharged condition, it does take a bit to come to life and it sounds pretty distorted until then. Ideally, you should let the LED come on full before turning up the preamp into it. Give it a minute -less, but no hurry- on mine. Likely wise, turn down the preamp BEFORE turning off the amp. Otherwise it will sound like i's breaking.
BTW- I just got gifted one of these.... (*), built, beautiful, beyond perfect craftsmanship. Thanks...
The amp is sitting on top of an F5 and F4. I put the jumpers because I'm still stuck on the sound of Aleph. Plus I lost them jumpers at first, so I figured I wouldn't lose them if they were installed.
Let's say I've been on the rampage lately listening to these amps.
I think this amp is in between both the F5 and F4. It really has no right to sound so good, but it does. Tomorrow I'll listen without the jumpers.
It feels like the very low noise floor of the F4 meets the dynamics of the F5. With the noise floor so low, you don't have to play music very loud to still hear dynamic range. Mind you, this is going into an 85 db/w mini monitor, 3 way, coax. So, its not gonna do a Spinal Tap at 11. (**)
Audio nirvana starts when your system can fully soundstage, flesh out the voices and instruments, yield some real bass.... at 90 db peaks. (**)
I'm very happy.
BTW- Nelson, this one is simply awesome. Thanks. Physics is indeed a fun talent to have, eh? :-D
(*) THANK YOU, THANK YOU, THANK YOU, THANK YOU!!!... I need to put you in contact with my wife so you can teach her the kind of gifts I really like. ;-)
(**) Actually, if we think about it, it's not the actual level of the peaks but the dynamic range of the system. If the noise floor is very low, then you can still get "loud" dynamics at much lower absolute level peaks.
(***) Do note that I am the guy who posits the First Hundred Watts matter (with Maggies).
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Same here. Then I realized you can leave them "installed" by plugging the jumper to only one pin of the header. It'll then be there when you want to switch back!
Ahh, the old Angel Food Donuts in Long Beach were the best!
