Rather than create another "beginner question" thread, I'm adding another question here. Thanks in advance for any help.
It appears that one of the trimpots (KT2) on my Chinese JLH69 board isn't working correctly. With 24V going into the board, I am unable to get the current below about 1.6 amps. I tried another 202 trimpot and got the same issue - both trimpots bottom out at about 1.6 amps. Would simply increasing the resistance value of KT2 get the current down to 1.2 amps?
If increasing the resistance value of KT2 is the way to go, would a fixed-value resistor work in place of the KT2 trimpot? Is the substitution a simple as inserting the fixed resistor into the outer holes of the trimpot's PCB location? I'm thinking of simply swapping fixed resistors until I get the current amount that I'm looking for.
Some pictures to help with my issue. The first is the amp (which I'm sure is quite familiar). The second is a schematic drawn by a YouTube source based on my amp's circuit - I've added basic notes to help my understanding of the situation.
It appears that one of the trimpots (KT2) on my Chinese JLH69 board isn't working correctly. With 24V going into the board, I am unable to get the current below about 1.6 amps. I tried another 202 trimpot and got the same issue - both trimpots bottom out at about 1.6 amps. Would simply increasing the resistance value of KT2 get the current down to 1.2 amps?
If increasing the resistance value of KT2 is the way to go, would a fixed-value resistor work in place of the KT2 trimpot? Is the substitution a simple as inserting the fixed resistor into the outer holes of the trimpot's PCB location? I'm thinking of simply swapping fixed resistors until I get the current amount that I'm looking for.
Some pictures to help with my issue. The first is the amp (which I'm sure is quite familiar). The second is a schematic drawn by a YouTube source based on my amp's circuit - I've added basic notes to help my understanding of the situation.
The easiest way would be to increase what seems to be R8 in your drawing. If 220 ohm is fitted then try 270 or 330 ohm.
This one:
This one:
Thank you, Mooly!
For giggles, I tried the amp @ 24V with 1.3 amps. I was surprised at how cool the amp was after driving a pair of 4 ohm speakers for an hour.
My new 24V power supply is a Mean Well LRS-100-24 with an adjustable voltage output. If you're willing to make a recommendation, what voltage/amperage would you suggest for driving 4 ohm speakers?
Here's the spec sheet for the power supply:
Mean Well LRS power supply info
Here's the speaker if you're curious:
Parts Express "Samba"
Samba impedance graph (sorry that it's a bit dark) -- and thanks again for any help.
For giggles, I tried the amp @ 24V with 1.3 amps. I was surprised at how cool the amp was after driving a pair of 4 ohm speakers for an hour.
My new 24V power supply is a Mean Well LRS-100-24 with an adjustable voltage output. If you're willing to make a recommendation, what voltage/amperage would you suggest for driving 4 ohm speakers?
Here's the spec sheet for the power supply:
Mean Well LRS power supply info
Here's the speaker if you're curious:
Parts Express "Samba"
Samba impedance graph (sorry that it's a bit dark) -- and thanks again for any help.
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Class A behaves a bit differently to the more usual Class B and AB. Heat dissipation is worst at no signal and decreases as you drive it harder into low impedance loads as an ever greater part of the bias current is 'diverted' to the load.
Heat dissipation is the big problem in deciding what voltage and current to use. I wouldn't really go much over 24 volts with the transistors so close together on that bracket, even if the main heatsink is large. We also listen at mostly low levels:
https://www.diyaudio.com/community/...h-voltage-power-do-your-speakers-need.204857/
So I would suggest you see what actual sort of output you really need and work to that.
You can also experiment empirically and see how low a bias current you can use for the levels you listen at. You might be surprised.
only 02 days after power on original JLH . I ready modified it become like this and feel more better.