I intend to use this thread to document my F5m build and serve as a build guide for others.
UPDATE Nov 30 2024:
I have finished my F5m build and it powered up without issue so I'm ready to post a document for anyone who may find it useful.
It's actually not a Guide, but more of a cookbook for my own build. I will leave the official guide to experts who are much more knowledgeable than I am.
The document contains notes I initially made for myself so there could be typos and other errors. I made it available rough instead of waiting for a fully edited copy since it could help new builders as-is.
UPDATE Dec 2 2024: I created a simulation for F5m if anyone wants to take a look:
F5m Simulation
UPDATE Nov 30 2024:
I have finished my F5m build and it powered up without issue so I'm ready to post a document for anyone who may find it useful.
It's actually not a Guide, but more of a cookbook for my own build. I will leave the official guide to experts who are much more knowledgeable than I am.
The document contains notes I initially made for myself so there could be typos and other errors. I made it available rough instead of waiting for a fully edited copy since it could help new builders as-is.
UPDATE Dec 2 2024: I created a simulation for F5m if anyone wants to take a look:
F5m Simulation
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Hi Guys,
I am utterly perplexed with a problem with the bipolar power supply. I assembled the PSU and wired it according to the schematic. I am 100% certain I did this correctly. Got the thermistor in series, the capacitor in parallel. Check. The rectifiers are oriented correctly. Check. On the PSU, the caps are oriented correctly. Check. The ground thermistor is connected to the chassis through the metal standoff. Check. Everything is done correctly, as far as I can see. I checked the output voltage of the transformer and found 18.5VAC and 18.6VAC. Check. No problems to this point.
So, I turn on the power, expecting to see 24VDC output voltages, but instead I get a blown fuse. After trying a few times to get a different result (the definition of insanity) I disconnected the PSU and measured the resistance across RECT 1 (no resistance) and RECT 2 (no resistance either). Huh? That would seem to explain my blown fuses, but why would there be no resistance?
It seems I have a short circuit, but I have no idea what's going on here. What am I missing? I still haven't wired the amplifier boards yet, pending resolution of this problem. I sure would appreciate any help in resolving this problem. I don't have the first clue what to do. Feel free to berate my ignorance if necessary.
Thanks,
Dave Chorney
I am utterly perplexed with a problem with the bipolar power supply. I assembled the PSU and wired it according to the schematic. I am 100% certain I did this correctly. Got the thermistor in series, the capacitor in parallel. Check. The rectifiers are oriented correctly. Check. On the PSU, the caps are oriented correctly. Check. The ground thermistor is connected to the chassis through the metal standoff. Check. Everything is done correctly, as far as I can see. I checked the output voltage of the transformer and found 18.5VAC and 18.6VAC. Check. No problems to this point.
So, I turn on the power, expecting to see 24VDC output voltages, but instead I get a blown fuse. After trying a few times to get a different result (the definition of insanity) I disconnected the PSU and measured the resistance across RECT 1 (no resistance) and RECT 2 (no resistance either). Huh? That would seem to explain my blown fuses, but why would there be no resistance?
It seems I have a short circuit, but I have no idea what's going on here. What am I missing? I still haven't wired the amplifier boards yet, pending resolution of this problem. I sure would appreciate any help in resolving this problem. I don't have the first clue what to do. Feel free to berate my ignorance if necessary.
Thanks,
Dave Chorney
Hi Dave -
Take a few nice photos of the PSU in its current state, and please ensure that you include all wiring from the PEM through to the filter boards. We should be able to get it sorted. Do you have a dim bulb tester and/or a variable transformer?
Take a few nice photos of the PSU in its current state, and please ensure that you include all wiring from the PEM through to the filter boards. We should be able to get it sorted. Do you have a dim bulb tester and/or a variable transformer?
Is it possible to remove these posts from this thread? It's not relevant to my guide and is confusing for someone who may think it is related and have to read it to know it's not... I don't see a way to flag the authors.. just a 'report' link... not sure how this works.
I look forward to your build guide RoboDNA. I have my kit with power supply and I have received my antec transformer, an AS2218. I am now shopping for a proper chassis. I will be ready to begin building hopefully by March. Life is pretty busy right now. There is a great deal of information on the 109 pages of the other thread, much of it meaningless to me.
I am planning on a "stock" as designed build. I have already built my nu-tube preamp and I think the F5m will be great match. Good luck with this guide. I, and I am sure many other beginners like me will benefit from it!
I am planning on a "stock" as designed build. I have already built my nu-tube preamp and I think the F5m will be great match. Good luck with this guide. I, and I am sure many other beginners like me will benefit from it!
I'm working on my build. Now that I have more info. and am further along, I realize the board builds are very simple and you really don't need a guide for that part of the project. Take a look at the pictures @birdbox recently posted and that should be all you need to get components soldered. I've spent most of my time on wiring and I do think that is the most difficult part. What I did is laid out all the components on my work bench, outside of the case so I could visualize how they all connected together.
I'm trying to take pictures along the way so I can post them in a 'F5m Guide' but it will be more of a documentation of my own build and not a suggested 'guide' for anyone else since it is my first build and am making mistakes as I go. I am learning about safe A/C design and I have little previous experience in that area. ( I'm a low-voltage microcontroller/software guy ) I know one builder recently discovered their transformer was shorting out to the bottom of the case and the only thing saving him when touching it was earth ground. I'm trying to go over-and-beyond with safety on my build, including running a grounding wire to each panel/heatsink so they are grounded when screws are removed or when panel is being removed ( dropped into case while holding or when setting offsets ).
For the case, I have the build guide done for the Modushop's Deluxe and it is the one I would get.
I'm trying to take pictures along the way so I can post them in a 'F5m Guide' but it will be more of a documentation of my own build and not a suggested 'guide' for anyone else since it is my first build and am making mistakes as I go. I am learning about safe A/C design and I have little previous experience in that area. ( I'm a low-voltage microcontroller/software guy ) I know one builder recently discovered their transformer was shorting out to the bottom of the case and the only thing saving him when touching it was earth ground. I'm trying to go over-and-beyond with safety on my build, including running a grounding wire to each panel/heatsink so they are grounded when screws are removed or when panel is being removed ( dropped into case while holding or when setting offsets ).
For the case, I have the build guide done for the Modushop's Deluxe and it is the one I would get.
Thank you for this PDF roboDNA. I will print it and find it helpful. Happy for you in that your amp is up and running. My goal is for mine to be finished by second half of 2025. I tend not to be in a rush with things.
APO
APO
I just updated the simulation with bias set to 26mV which is the 'default' setting recommended in the F5m Documentation. ( half of the 1.1Amp to 1.4Amp max bias )
I also changed the input signal to 3volts. You can play with the resistor settings to get a good visual on how each one affects the output signal. Adjusting a trim resistor's value ( right panel ) also changes the 2nd trim's bias value so if R8 is increased for Q3's bias, so does Q4's bias. R8 seems to pull the signal up and R9 down. You can also hear the audio and hear distortion but that can also bee seen in the bottom graph. I'm sure the component parameters are not an exact match for the MOSFETS/JFETS but it seems close enough to get values that match the F5m documentation. I can now see how to adjust DC offset as well.
I also changed the input signal to 3volts. You can play with the resistor settings to get a good visual on how each one affects the output signal. Adjusting a trim resistor's value ( right panel ) also changes the 2nd trim's bias value so if R8 is increased for Q3's bias, so does Q4's bias. R8 seems to pull the signal up and R9 down. You can also hear the audio and hear distortion but that can also bee seen in the bottom graph. I'm sure the component parameters are not an exact match for the MOSFETS/JFETS but it seems close enough to get values that match the F5m documentation. I can now see how to adjust DC offset as well.
Simulations are a good tool to understanding the operation of an electronic circuit. Simulations can be very educational. I use LTSpice all the time. 🤓
By the way, your bias is off by a factor of 10:
26mV/0.47R = 55mA
By the way, your bias is off by a factor of 10:
26mV/0.47R = 55mA
I use a bit of LTSpice in Kicad 😉 I have big parts of the Moog Model D simulated in Falstad to understand it.
Good eye on the factor of 10. I now see the docs state 520mV as default so my bias should be 260mV in my simulation ( half ). I'll have to take a fresh look tomorrow, but for some reason I can't get the simulation to get to 500mV bias.
Good eye on the factor of 10. I now see the docs state 520mV as default so my bias should be 260mV in my simulation ( half ). I'll have to take a fresh look tomorrow, but for some reason I can't get the simulation to get to 500mV bias.