The load that sees 16.9V 4.1A are not MPC74s, but 4ohm power resistors on heatsink as shown in his photo (gold anodised ones on the RHS).
The MPC74 1R resistors that he mentioned were those for the CRC power supply (white ones on the LHS).
And they are hot to 150 degC at the case, as on our own example of the CRC.
Ambient air next to them are in our own example about 80 degC.
The rest I already explained (why it is OK to have 150degC at the case).
Or anything else that you want to know that I have not answered ?
Cheers,
Patrick
The MPC74 1R resistors that he mentioned were those for the CRC power supply (white ones on the LHS).
And they are hot to 150 degC at the case, as on our own example of the CRC.
Ambient air next to them are in our own example about 80 degC.
The rest I already explained (why it is OK to have 150degC at the case).
Or anything else that you want to know that I have not answered ?
Cheers,
Patrick
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Andrew, my initial odd results were simply due to my improper measurements. I was simply measuring across the wrong points, and I did not need to change anything with the wiring shown in that photo to obtain useful +/- voltages.
On another note, what sort of ripple voltage (correct term?) should I be seeing when I scope the PS under load? If I have it setup correctly, I'm getting around 150mV peak to peak.
On another note, what sort of ripple voltage (correct term?) should I be seeing when I scope the PS under load? If I have it setup correctly, I'm getting around 150mV peak to peak.
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I found much lower ripple, but I will re-check next time I open up the amp.MS22 75004 thermistor and 3.15A slow-blow fuse. All OK.
5 mV ripple P2P (the scope say 100Hz! WhyI thought I was living in a 50Hz country).
Rectification and caps does not generate much heat. The R's in the CRC get very warm, but nothing to worry about.
I have not been following all of the details of this thread and the F5X design. What protection circuits (over-current, speaker, ...) if any, are being used or proposed for the F5X? I seem to recall one idea with worked in conjunction with a voltage regulated power supply, but I do not know whether that progressed to fruition.
Tested my first (of four) amp boards over the weekend. JFET bias were all within 1%, and I threw in the output FETs. The output FETs all tracked extremely closely as the channel warmed up, and were within 5mV at the stabilized state (with no adjustments). Great job to Gerhard and Nic on the matching!
I aimed for 1.5A bias per Dave's recommendations and setup the Vgs accordingly. I ended up with about 1.6A on these initial adjustments (my +/- rails are about a 1V higher so maybe the little extra heat pushed the bias up slightly). After reading Nic's comments about the cased amp bias drifting up, I think I may shoot for bias of 1.8A or so uncased.
I aimed for 1.5A bias per Dave's recommendations and setup the Vgs accordingly. I ended up with about 1.6A on these initial adjustments (my +/- rails are about a 1V higher so maybe the little extra heat pushed the bias up slightly). After reading Nic's comments about the cased amp bias drifting up, I think I may shoot for bias of 1.8A or so uncased.
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I think I will run some test signals and try playing a little one channel music before I float the X.
Speaking of bias, since my rails are a bit higher at 16.9V I'd expect the amp to run a bit warmer. In fact, I was measuring around 59 degrees C peak uncased at 1.6A bias. Connecting up the front and rear panels will add a little "heatsinking", but it still seems like my amp might run a little warmer than 62 degrees shown in the linear audio article. How hot would you feel comfortable running the heatsinks long term? 65 degrees?
Speaking of bias, since my rails are a bit higher at 16.9V I'd expect the amp to run a bit warmer. In fact, I was measuring around 59 degrees C peak uncased at 1.6A bias. Connecting up the front and rear panels will add a little "heatsinking", but it still seems like my amp might run a little warmer than 62 degrees shown in the linear audio article. How hot would you feel comfortable running the heatsinks long term? 65 degrees?
Me ? 65~70°C.
You should decide whether you want to go regulator eventually first.
If so you can set the regulator to 16V or even 15.5V.
And then you are free to choose.
16V 4A is optimised for 6R speakers.
So if your speaker impedance is lower, you don't want to reduce current.
If you have 8 ohm, then 1.6A per FET is plenty.
Patrick
You should decide whether you want to go regulator eventually first.
If so you can set the regulator to 16V or even 15.5V.
And then you are free to choose.
16V 4A is optimised for 6R speakers.
So if your speaker impedance is lower, you don't want to reduce current.
If you have 8 ohm, then 1.6A per FET is plenty.
Patrick
Thank you! I am indeed very happy to learn that our "in vitro" results are reproducible "in vivo" in your hands.
Hello all. I am making a brief post before I go offline again.
I have been horrendously buisy these last few months with more than I could handle. Not just study but other stuff too. I have sent Vitalica a refund and will send one to alazira shortly.
This is not me saying that you will not get your boards. Rather they are here ready for the first bit of testing to be done before more work is done soldering them. I want to make a testing video for them, however I do not have the time right now and do not know when I will (it could be a couple months). So please let me know which of the following options do you want:
1. I test the boards when I have the time and make up the documentation.
2. I send you them now and I still make documentation however I do it at a slightly later date and your boards and the boards have only had inspection and a cursory electrical check.
3. I send the boards and parts to the person that makes the documentation. They can keep the boards or send them on to you.
In all three cases you get to keep the refund. I will send you the only non standard part by express mail tomorrow. You should be able to sort out the rest at digikey. I have sent back more than the amount you sent me to compensate you in some way for your time.
I want to thank you for your patience so far and apologise for my lateness.
Alazira can you confirm for me how much I need to send you.
Bye for a little while. Alexis shaw.
I have been horrendously buisy these last few months with more than I could handle. Not just study but other stuff too. I have sent Vitalica a refund and will send one to alazira shortly.
This is not me saying that you will not get your boards. Rather they are here ready for the first bit of testing to be done before more work is done soldering them. I want to make a testing video for them, however I do not have the time right now and do not know when I will (it could be a couple months). So please let me know which of the following options do you want:
1. I test the boards when I have the time and make up the documentation.
2. I send you them now and I still make documentation however I do it at a slightly later date and your boards and the boards have only had inspection and a cursory electrical check.
3. I send the boards and parts to the person that makes the documentation. They can keep the boards or send them on to you.
In all three cases you get to keep the refund. I will send you the only non standard part by express mail tomorrow. You should be able to sort out the rest at digikey. I have sent back more than the amount you sent me to compensate you in some way for your time.
I want to thank you for your patience so far and apologise for my lateness.
Alazira can you confirm for me how much I need to send you.
Bye for a little while. Alexis shaw.
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So I'm getting down to the point where I need to start assembling the protection/control PCB. I know the protection/control board build article is in progress, but is it safe for me to start populating the boards per the latest BOM? Or would it be wiser/easier to wait for the build article for the fix?