BTW, you guys are talking about Rb, the base resistors on the output trannies. You may actually also use a jumper there. Rb is only needed if you have some instability. Does everything work if you disconnect the output boards? You do know that you can test the main + driver boards into an actual load? Once that is proven, connect the outputs and bias.
Also, I see from the picture that you only take your feedback from the one output board. I think you must get that from both. Connect the output point from both output boards together and then take the FB from there.
PS: Sorry, I see you did. I missed that orange wire. Early morning and not quite awake.
PS: Sorry, I see you did. I missed that orange wire. Early morning and not quite awake.
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My suggestion: Disconnect the wires to the output boards from the driver board. Then check to see that you have around 0mV on the FB point, -550mV to -600mV on the negative drive point and 550mV to 600mV on the positive drive point. Make sure that the values vary correctly when you adjust the offset pot and bias pot. You can connect a speaker between the FB point and Ground and listen to music at quite respectable levels.
Hi all, I am building my KSA50 using a layout the same as the original KSA100 with two heatsink towers, with the PCB's attached to the towers. I am using Jan's PCB's and I have quite limited space between the filter capacitors and the heatsink towers making it very difficult to adjust offset and bias pots.
Will there be a problem if I remove the pots from the board and position them where they can be easily adjusted, this will probably mean that they are connected to the boards with about 100mm of wire.
Will this lead to any detrement in performance?
Thanks
Alan
Will there be a problem if I remove the pots from the board and position them where they can be easily adjusted, this will probably mean that they are connected to the boards with about 100mm of wire.
Will this lead to any detrement in performance?
Thanks
Alan
Thanks for the help, disconnected the output boards, running at 1/4 rail around 10v using a variac, I am getting close to rail voltage off the FB, D+ and D- relative go ground (around 7-8v), is something seriesly wrong here? Did I fry a mosfet or one of the little transistors?
Also make sure all of your ground connections are correct. I had a similar type of result the first time I powered the board up, just because my signal ground was not connected. Also, short the signal input to signal ground when you do this. And crank that variac up else you will get strange results as the bias voltages might not be high enough to switch them small critters on.
Don't know if you prefer not to deal with eBay vendors, but I did a search yesterday and found the following.
High Power Pure Class A Amplifier PCB KSA50 | eBay
New DIY Class A KSA50 150W Mono Amplifier Board | eBay
High Power Pure Class A Amplifier PCB KSA50 | eBay
New DIY Class A KSA50 150W Mono Amplifier Board | eBay
I have purchase the PCB of the first link, the quality is quite good. For more info go to the following link, one of us built his KSA-100 clone with these PCB's.
Eric
http://www.diyaudio.com/forums/solid-state/183562-ksa-100-jims-audio-ebay-new-post.html
Stupid question.
I am trying to bias this sucker. Do one need to attach a load when biasing the outputs? All my voltages looks OK up to the point after the the drivers. I start off biasing with 520mV on the driver output, but when I measure the voltage over Re, I never get more than around 150mV, no matter how much I open the trimmer.
I am trying to bias this sucker. Do one need to attach a load when biasing the outputs? All my voltages looks OK up to the point after the the drivers. I start off biasing with 520mV on the driver output, but when I measure the voltage over Re, I never get more than around 150mV, no matter how much I open the trimmer.
OK, my left hand channel seems to work perfectly. I biased it to 325mV on Re, and heatsink temps seem fair since the Ta = 36 deg C here at the moment (16h00). I also checked the voltages of Re 1 to 6 and all the voltages are 325mV. The offset is 0.5mV. BTW, Re = .5R.
The right hand channel is not so fine. I can't get it to bias. Also, the voltages on the driver output seems strange so I will have some debugging to do. I get 550mV on the +ve drive while I get -660mV on the -ve drive but with on offset on the FB point of 2mV.
The right hand channel is not so fine. I can't get it to bias. Also, the voltages on the driver output seems strange so I will have some debugging to do. I get 550mV on the +ve drive while I get -660mV on the -ve drive but with on offset on the FB point of 2mV.
Found my problem. Forgot to solder the output transistors on the bottom layer of the negative output board.
However, this side doesn't seem to be matched so well as the left hand channel. Some of my transistors pull slightly more than the other.
Right Hand side +ve outputs:
Re1 = 303mV
Re2 = 310mV
Re3 = 333mV
Right Hand side -ve outputs:
Re4 = 312mV
Re5 = 320mV
Re6 = 322mV
Should I be worried? Also, my sinks takes a long time to get hot enough so that I can just hold my hands on them for 20 secs. Is this normal for the KSA50 clone?
However, this side doesn't seem to be matched so well as the left hand channel. Some of my transistors pull slightly more than the other.
Right Hand side +ve outputs:
Re1 = 303mV
Re2 = 310mV
Re3 = 333mV
Right Hand side -ve outputs:
Re4 = 312mV
Re5 = 320mV
Re6 = 322mV
Should I be worried? Also, my sinks takes a long time to get hot enough so that I can just hold my hands on them for 20 secs. Is this normal for the KSA50 clone?
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