Thank you so much J M Fahey, the aluminium extrusion seems a pretty cool idea :dbtu: I'm heading to local aluminium maker next weekend.
Thanks again...
Sajad
Thanks again...
Sajad
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Show posts MenuQuote from: phatt on October 01, 2017, 08:53:53 AMThank you Phil, Unfortunately that's the biggest heatsink I could find in stores here! Anyway I have a CPU heatsink laying around and I might give it a shot.Untill then I have to keep the volume down :cheesy:
Agree,,, a Very good effort, thanks for the pictures. :dbtu: :dbtu:
Obviously a lot of thought went into that project.
I take it you cut and bent the metal out by hand?
I know how hard that is,, because I've done it many times. :duh
Just note, You might need a bigger heat sink if you run it at full power for a long time.
Phil.
Quote from: J M Fahey on October 01, 2017, 07:16:23 AMThanks man, glad you liked it.
Cool project, congratulations :tu:
By the way, nice carpets, where are you from?
Always fill Country/City information in your user profile ... sometimes we are surprised
Quote from: J M Fahey on September 30, 2017, 09:39:05 AMThanks man, here are some pics:
Thanks Sajy :dbtu:
Now we need some pictures of the completed build and the cherry on the cake would be some tasty guitar playing demo :dbtu:
Quote from: J M Fahey on July 06, 2017, 07:25:00 AMThank you so much, I get your point quitely. What I was mistaking about was that I tought gain will reduce exactly by this proportion (Load R/R sense). In the mixed feedback mode, the current feedback is diffinitely reducing the gain but not by that simple proportion. I need to finally read Teemuk's book I guess...Quote from: sajy_ho on July 01, 2017, 10:56:39 AMEDIT: There is somethin I don't understand; why negative current feedback reduces the gain? PS I'm using 16 ohm guitar speaker!To drive amp you must match NFB signal.
You have two NFB voltages there, which are in series, one coming from resistive attenuator 39k/470 , call it "X", the other from [speaker impedance]/0.2 ohms , call it "Y"
So you need to match "X" voltage , which would be 84X as calculated before, PLUS "Y" voltage.
So if you have to match a higher voltage, you need a higher signal to do it, so net gain is lower.
In a simple example, suppose conventional NFB is 10k/1k , so gain is 10X
To get 10V RMS out you need 1V RMS in. That´s the conventional way.
Now suppose you have a 4 ohm speaker and a 0.4 ohm resistor.
NFB *there* will be again 1V RMS if amp is putting out 10V RMS
Now connect the 1k resistor, not straight to ground as usual but to the Speaker/0.4 ohm junction.
Hey !!! 0.4 ohms is almost zero ohms!!! It´s nothing compared to 1k!!!! It´s practically the same as connecting straight to ground !!!! Nothing should change!!!!
Think again: that junction is not ground at all, since it does not have ZERO volts on it (as true ground would) but 1V RMS ... which so is in series and summed to the standard 1V RMS.
Now you need 2 V RMS to drive that amp to 10V RMS out ... so now effective gain was reduced to 5X
That´s why I said earlier that even if going from 39k to 22k "looked" safe on its own ... in practice it might not ... specially with Peavey sanctioned 4 ohm (nominal) speaker .
Quote from: phatt on July 03, 2017, 08:53:44 AMI checked and it gets gradually hot after 10 minutes of running with input connected to ground!
I just looked at the picture of your build,, your heat sink needs to be larger. 8|
Having said that I've opened a lot of small amps that use the same/similar power chip and they have less than ideal heat sink so yes they run hot and would likely last longer if the heat sink was larger.
With no signal after 10~15 minutes the chip should stay at room temp if not there is a problem.
As *J M Fahey* has already mentioned it could be an oscillation above your ability to hear and hence heating up even at idle.
These small amp chips will reach their limit quite fast and early distortion is common
Phil.