I won’t be able to get to it till next week, but will double check that as soon as I can (although it worked before with same source and cable). Thanks for helping me with this.
I have a question about the output voltage. What will be the normal output voltage if i feed it with 0.5V input? My simulations shows +-4.4V, but osciloscope measures only +-2.5V without volume pot and load
^ If built to spec (I'm not sure what you're simulating), you should have 20dB gain => 10X => 5V. Your simulation is closer.
If the load is only the scope, that's a very high impedance. I am not sure what affect that may have. I'd assume you'd still get a proper output voltage, but put in your load and see.
BTW - Always use units, please. I am assuming you mean that your input was 0.5Vp and your output was 2.5Vp => 5X. If your input was 0.5Vrms, that changes things, but you're still off, just a bit further off.
Were you using a differential input? Did you short In- to GND? You typically get 0dB gain (or even slightly negative gain) without that jumper when using a SE input.
If the load is only the scope, that's a very high impedance. I am not sure what affect that may have. I'd assume you'd still get a proper output voltage, but put in your load and see.
BTW - Always use units, please. I am assuming you mean that your input was 0.5Vp and your output was 2.5Vp => 5X. If your input was 0.5Vrms, that changes things, but you're still off, just a bit further off.
Were you using a differential input? Did you short In- to GND? You typically get 0dB gain (or even slightly negative gain) without that jumper when using a SE input.
Thank you very much for the explonation. I've figured out that my signal source was producing full wave, but i considered it as a half-amplitude wave. Now the simulation results perfectly match the real ones
if you're using same Drek to measure both input and output, no need even to think about units, if goal is to get ratio/gain measured
though, when writing about test, good to at least say what's used for measurement, and stay aware of actual units (rms, p, pp)
though, when writing about test, good to at least say what's used for measurement, and stay aware of actual units (rms, p, pp)
Okay, I am back in town and tried out the cord with a different amplifier. No hum, clear, detailed, my iPhone sounds pretty good on my Martin Logan speakers. Back to the amp, is there something else I should try? I thought that a faulty JFET seemed like a likely culprit. Before I goofed up by turning the bias pot when I thought I was setting dc offset (thereby cranking the bias up to heaven knows what), there was no hum and it sounded great.
it's really that simple as pulling out all semis from pcb, and either trying them (easiest in small chinese testitall gizmo) or simply replacing
proper troubleshooting based on measurements in cold and live usually demands some mileage, and when one lacks that (or schematic, so no big picture), you measure for shorts, and then rest is exactly as I wrote - pull out, test, put back same or replacement part
proper troubleshooting based on measurements in cold and live usually demands some mileage, and when one lacks that (or schematic, so no big picture), you measure for shorts, and then rest is exactly as I wrote - pull out, test, put back same or replacement part
Thank you, Zen Mod. With respect to the jfets, I have a matched quadruple. If I use the other matched pair, will that pose a problem when I build the other channel (i.e., is having a matched pair in each channel good enough or do I need 4 matched devices)?
Thanks, it just occurred to me, should I desoldar the mosfets and leave them on the heatsink or remove them from the heatsink before removing the board?
Hey All, Day 1 complete of the build. I got all the boards put together, the case assembled and laid out, and will start wiring things together tomorrow. This was my first time doing a project like this. I really enjoyed it. A digitally controlled soldering iron with a variety of tips really made a difference compared to my DIY cable soldering with a basic iron. Also this website was invaluable. https://diyalephj.blogspot.com/
Before I start the wiring does anyone see any issues with my layout of the power supply parts, or any suggestions on how I could make it better?
Also the 400va 18v Antek transformer only came with 1 rubber piece, does that go on the bottom or top? or do I need to find a 2nd one?
Before I start the wiring does anyone see any issues with my layout of the power supply parts, or any suggestions on how I could make it better?
Also the 400va 18v Antek transformer only came with 1 rubber piece, does that go on the bottom or top? or do I need to find a 2nd one?
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The toroids should come with 2 metal plates and 2 round rubber insulators to prevent damage to secondary windings when mounted.
I have already posted on many occasions an Aleph J layout that minimises both the mains wiring length and the DC wiring length. Please use the advanced search feature in this thread to find posts with my username. You'll see some other pointers I posted to improve the sound. However, get the basic build going okay first, ensure it's all good, and then consider suggested modifications.
People who hear this amp go absolutely ballistic about its sound.... and I'm talking serious high-enders who I've known for a long time.
Good luck.
I have already posted on many occasions an Aleph J layout that minimises both the mains wiring length and the DC wiring length. Please use the advanced search feature in this thread to find posts with my username. You'll see some other pointers I posted to improve the sound. However, get the basic build going okay first, ensure it's all good, and then consider suggested modifications.
People who hear this amp go absolutely ballistic about its sound.... and I'm talking serious high-enders who I've known for a long time.
Good luck.
Looking good from what I see, I too followed that post for my build. The only thing I will call out is when you do all the other wiring, start LONG, like 18-24", because by the time you twist the wires and route them, you gobble up a ton of length. There are a few I wish were a few inches longer. You can always test fit before soldering, and cut them down a bit. It is also like to have extra slack in case you want to open things up later.
Progress! All I had time for tonight was to mount the mosfets and wire up the power supply and test it, and it passed the dim bulb tester perfectly. A solid 25.4/-25.4 volts coming off the V+ and V-. Slowly this week I will wire up and test the amp boards and let everyone know how it goes!
Hey all. Progress and then fail tonight.
I got everything installed, passed the DIM bulb test again on the power supply, so I moved on to DIM bulb test and power up of the amp boards. They both were successful, so I pulled the DIM bulb tester to get the initial bias adjusted. I got R27 adjusted to where I was reading 0.35V across the resister on R18. Everything was going great, the readings were stable with R7 was adjusted and reading zero from the speaker terminals as well. After things warmed up for 25 mins (I was waiting for 30 mins to readjust) there was a pop and the fuse blew. In pulling it all apart to troubleshoot it looks like I have a blown transformer.
Any ideas why things would run fine for 25 mins then pop? When I pulled out the 3300pF safety capacity to test it one of the leads looked fatigued/broken, not sure if that happened with the pop or when I bent the lead to install it. Otherwise all the boards looks fine, nothing visually looks off. I double checked the mosfets were isolated from the heatsink, double checked all the wiring, grounds etc.
I went ahead and ordered a new transformer and safety capacitor and plan to invest in a variac. This is my first amp build to any tips are appreciated on where to start.
I got everything installed, passed the DIM bulb test again on the power supply, so I moved on to DIM bulb test and power up of the amp boards. They both were successful, so I pulled the DIM bulb tester to get the initial bias adjusted. I got R27 adjusted to where I was reading 0.35V across the resister on R18. Everything was going great, the readings were stable with R7 was adjusted and reading zero from the speaker terminals as well. After things warmed up for 25 mins (I was waiting for 30 mins to readjust) there was a pop and the fuse blew. In pulling it all apart to troubleshoot it looks like I have a blown transformer.
Any ideas why things would run fine for 25 mins then pop? When I pulled out the 3300pF safety capacity to test it one of the leads looked fatigued/broken, not sure if that happened with the pop or when I bent the lead to install it. Otherwise all the boards looks fine, nothing visually looks off. I double checked the mosfets were isolated from the heatsink, double checked all the wiring, grounds etc.
I went ahead and ordered a new transformer and safety capacitor and plan to invest in a variac. This is my first amp build to any tips are appreciated on where to start.
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^ First. Bummer! Getting so close and then having an issue isn't my idea of a good time, but it happens eventually to everyone.
I personally have never seen a transformer primary "separate". It looks like what you're trying to convey is that you've lost continuity between the ends of one of your primaries. Is that correct?
I have two guesses, but I'm sure others can come up with a few more ideas.
1 - Check to make sure one of your crimp connections didn't fail on either end of the primary. Cut them off and check the resistance of that primary again.
2 - The primary may be "cut". I am not sure for Antek transformers, and I've never unwrapped one, but I think it's typical for the transformer primaries to be wound onto the core first with the secondaries wound 'on top'. So, that would make it more challenging to 'cut' a primary within the actual wrapped 'package'. However, the only other plausible explanation (I can come up with) is that somehow the primary was severed due to friction / pressure / repeated bending.
Check to see if either end of that primary has a very low resistance to your perforated base plate.
That's about all I can think of at the moment.
I personally have never seen a transformer primary "separate". It looks like what you're trying to convey is that you've lost continuity between the ends of one of your primaries. Is that correct?
I have two guesses, but I'm sure others can come up with a few more ideas.
1 - Check to make sure one of your crimp connections didn't fail on either end of the primary. Cut them off and check the resistance of that primary again.
2 - The primary may be "cut". I am not sure for Antek transformers, and I've never unwrapped one, but I think it's typical for the transformer primaries to be wound onto the core first with the secondaries wound 'on top'. So, that would make it more challenging to 'cut' a primary within the actual wrapped 'package'. However, the only other plausible explanation (I can come up with) is that somehow the primary was severed due to friction / pressure / repeated bending.
Check to see if either end of that primary has a very low resistance to your perforated base plate.
That's about all I can think of at the moment.
I cut the ends off the primary side and sure enough I have continuity! I’m going to get some new connectors and put it back together tonight and see how it goes. Thanks!
The worst part is I prefer to solder but figured it would be ok following the "DIY Aleph J: A Build Guide". Lesson learned, listen to my inner voice.
I can't say I wasn't warned in this video on crimping:
I can't say I wasn't warned in this video on crimping:
Alright. After work today i pulled off all the connectors, wired it all back together and went to test the power supply (with the amp boards disconnected) and it fails the dim bulb test. I went through and while the transformer has continuity now it isn't transforming when I test it with the multimeter and has a dead short in it. I guess it fried itself somewhere in the failure. Next steps are to get a new transfomer and go from there. I might just build a new universal supply board and let the power supply burn in for a bit before restarting board testing.
I also pulled the amp boards off the heat sinks and visually inspected them again, they look fine.
I'm worried I have a bad component somewhere that might cause thermal runaway and if I build a new power supply the amp boards will cook it again, is this possible? I'm going to do some more research on this thread, but any help in how to test the amp boards to verify before I fry it all again would be helpful.
I also pulled the amp boards off the heat sinks and visually inspected them again, they look fine.
I'm worried I have a bad component somewhere that might cause thermal runaway and if I build a new power supply the amp boards will cook it again, is this possible? I'm going to do some more research on this thread, but any help in how to test the amp boards to verify before I fry it all again would be helpful.