Hey guys.
So, at long last I have completed all the metal work and have started the final assembly of my 6 channel LM4780 amp. I am writing to bounce/check some wiring with people mainly because this is my first amp build and I really don't have a clue what I'm doing.
To start, I have 3x400VA toroidal's, each powering 2xLM4780 boards from AudioSector. This is his recommended specs so all good there.
Now for the stupid questions:
1. The 'blue & brown' wires coming into the transformers are AC so I can connect them either way to the 'red and black' from the transformers?
2. The transformers have dual 22v secondaries (green+blue/green+blue) and the boards have pads marked AC1(+,-) AC2(+,-) before the rectifiers. So as long as I connect a winding to AC1 and the other to AC2 I should be good?
3. I have a some CL60's to limit current inrush that I will wire in parallel with the transformers, I have heard of people on this forum use multiple CL60's, is there any advantage to this?
I hope this all makes sense to somebody
and am excited to finally finish the project.
Cheers all.
Dean
PS. Included a pic of my workshop mono OB, made with spare/free parts just for a laugh.
So, at long last I have completed all the metal work and have started the final assembly of my 6 channel LM4780 amp. I am writing to bounce/check some wiring with people mainly because this is my first amp build and I really don't have a clue what I'm doing.
To start, I have 3x400VA toroidal's, each powering 2xLM4780 boards from AudioSector. This is his recommended specs so all good there.
Now for the stupid questions:
1. The 'blue & brown' wires coming into the transformers are AC so I can connect them either way to the 'red and black' from the transformers?
2. The transformers have dual 22v secondaries (green+blue/green+blue) and the boards have pads marked AC1(+,-) AC2(+,-) before the rectifiers. So as long as I connect a winding to AC1 and the other to AC2 I should be good?
3. I have a some CL60's to limit current inrush that I will wire in parallel with the transformers, I have heard of people on this forum use multiple CL60's, is there any advantage to this?
I hope this all makes sense to somebody
and am excited to finally finish the project.Cheers all.
Dean
PS. Included a pic of my workshop mono OB, made with spare/free parts just for a laugh.
Attachments
Nice neat build.
1) Yes, but make sure they're all the same way round. However, I'd put a fuse in line with each traffo, rather than relying on just one.
2) Yes. I assume you'll be linking the AC rails between pairs of amps?
3) You should be fine with just the one CL60 per traffo, but better practice is to disconnect the CL60 after warm up with a relay. Search on "soft start circuit" for some examples.
And finally, I hope you don't have any metal running through the middle of that transformer bracket, that would created a shorted turn which would be very bad news indeed.
1) Yes, but make sure they're all the same way round. However, I'd put a fuse in line with each traffo, rather than relying on just one.
2) Yes. I assume you'll be linking the AC rails between pairs of amps?
3) You should be fine with just the one CL60 per traffo, but better practice is to disconnect the CL60 after warm up with a relay. Search on "soft start circuit" for some examples.
And finally, I hope you don't have any metal running through the middle of that transformer bracket, that would created a shorted turn which would be very bad news indeed.
I meant parallel but will now be wiring them in series, cheers Tecchy.
Answers
1. They will all be wired the same way, I have a fuse & DPDT for each traffo.
2. I will be linking them between pairs using terminal blocks.
3. The 4 long bolts are clamping the traffo's in place, the center is hollow and I have rubber/alloy/rubber clamped between each one for mechanical/electrical isolation.
Questions
3. Will I be safe using only the CL60 for the moment and getting a 'soft start circuit' later on? (read 'broke')
4. Is there an electrical/audible cost to using CL60's?
5. The traffo has 2x115V primaries, I connect them is series by connecting the black from primary 1 to the red of primary 2, then soldering and heat shrinking them, was this correct?
Cheers
Dean
Answers
1. They will all be wired the same way, I have a fuse & DPDT for each traffo.
2. I will be linking them between pairs using terminal blocks.
3. The 4 long bolts are clamping the traffo's in place, the center is hollow and I have rubber/alloy/rubber clamped between each one for mechanical/electrical isolation.
Questions
3. Will I be safe using only the CL60 for the moment and getting a 'soft start circuit' later on? (read 'broke')
4. Is there an electrical/audible cost to using CL60's?
5. The traffo has 2x115V primaries, I connect them is series by connecting the black from primary 1 to the red of primary 2, then soldering and heat shrinking them, was this correct?
Cheers
Dean
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Questions
3. Will I be safe using only the CL60 for the moment and getting a 'soft start circuit' later on? (read 'broke')
4. Is there an electrical/audible cost to using CL60's?
5. The traffo has 2x115V primaries, I connect them is series by connecting the black from primary 1 to the red of primary 2, then soldering and heat shrinking them, was this correct?
Cheers again
Dean
3. Will I be safe using only the CL60 for the moment and getting a 'soft start circuit' later on? (read 'broke')
4. Is there an electrical/audible cost to using CL60's?
5. The traffo has 2x115V primaries, I connect them is series by connecting the black from primary 1 to the red of primary 2, then soldering and heat shrinking them, was this correct?
Cheers again
Dean
For 220/240Vac I suggest a pair of series connected CL60 for the transformer Primary.
This pair could reliably start up a 1200VA transformer, or three 400VA transformers, but will run hot some of the time.
Bypass those CL60 soon after they have achieved their soft start purpose.
I also agree that every transformer has it's own close rated fuse.
This pair could reliably start up a 1200VA transformer, or three 400VA transformers, but will run hot some of the time.
Bypass those CL60 soon after they have achieved their soft start purpose.
I also agree that every transformer has it's own close rated fuse.
G'day Andrew.
I didn't even think to post this under AudioSector, perhaps a moderator can move it? Thanks in advance.
So, Each transformer has its own fuse and switch so I can use/disable 2/4/6 channels depending on whats connected.
This also allows/requires me to use a separate CL60 for each transformer. If 2 in series is enough for all 3 400VA traffo's then would 1 each work well?
I will have to do some research on the soft start idea and implement it later, money is very tight at the moment. Do you have any suggestions on where to start looking and what to look for?
Cheers
Dean
I didn't even think to post this under AudioSector, perhaps a moderator can move it? Thanks in advance.
So, Each transformer has its own fuse and switch so I can use/disable 2/4/6 channels depending on whats connected.
This also allows/requires me to use a separate CL60 for each transformer. If 2 in series is enough for all 3 400VA traffo's then would 1 each work well?
I will have to do some research on the soft start idea and implement it later, money is very tight at the moment. Do you have any suggestions on where to start looking and what to look for?
Cheers
Dean
Does this look any good?
Would I need one for each Traffo?
Soft starting switch full kit for power amplifier ! | eBay
Would I need one for each Traffo?
Soft starting switch full kit for power amplifier ! | eBay
Hi Dean, looks nice! I've moved to AudioSector as suggested/requested
edit: It looks like there is 1500uF smoothing capacitance per rail, however it is implemented on the amp board rather than on the ps board (none on the PS board as far as I can see). I ran my LM3886 with 1,00uF / rail for over a year without any problem. I recently added an additional 4,700uF per rail (total 5,700uF) this reduced the hum on the output a little (it was very low to start with, virtually inaudible literally had to put my ear up to the speaker cone to hear it at full volume) other than that I didn't really notice any difference. I think 1500uF per rail should be fine.
Tony.
edit: It looks like there is 1500uF smoothing capacitance per rail, however it is implemented on the amp board rather than on the ps board (none on the PS board as far as I can see). I ran my LM3886 with 1,00uF / rail for over a year without any problem. I recently added an additional 4,700uF per rail (total 5,700uF) this reduced the hum on the output a little (it was very low to start with, virtually inaudible literally had to put my ear up to the speaker cone to hear it at full volume) other than that I didn't really notice any difference. I think 1500uF per rail should be fine.
Tony.
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not necessary. One mains switch, one mains fuse, one mains chassis connected to PE. Then 3 fuses supplying three transformers.
only if that is what you can use.
NO !!! a pair @ ~30r will behave very differently starting 1200VA than a single @ ~15r will do for 400VA. Completely differently.
15r seems to work for medium size transformers on 110/120Vac, but not well enough on 220/240Vac. Too little current limiting at the higher voltage supply.
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I love it when Andrew gets excited 
Thank you Tony for the move, and thanks for the input on the caps.
So, just to clear things up...
1. The back panel has already been built, so each transformer has its own switch and its own fuse, I don't want to change that. Which means that when i implement inrush limiting I need to deal with each transformer separately.
2. I am not sure what you mean by 'only if that is what you can use'? I can switch any one of the three pairs on separately with this setup?
3. I always appreciate your technical experience/input Andrew but telling me what 'not to do' is only half the answer. Hopefully I have explained what I have and would love to find out what I 'do" need to do with that to limit current inrush. Are you saying the CL60 is underrated or overrated? Are you saying I should use 2 in series for each transformers with 240v input?
Please read this with the respect intended.
Cheers
Dean
Thank you Tony for the move, and thanks for the input on the caps.
So, just to clear things up...
1. The back panel has already been built, so each transformer has its own switch and its own fuse, I don't want to change that. Which means that when i implement inrush limiting I need to deal with each transformer separately.
2. I am not sure what you mean by 'only if that is what you can use'? I can switch any one of the three pairs on separately with this setup?
3. I always appreciate your technical experience/input Andrew but telling me what 'not to do' is only half the answer. Hopefully I have explained what I have and would love to find out what I 'do" need to do with that to limit current inrush. Are you saying the CL60 is underrated or overrated? Are you saying I should use 2 in series for each transformers with 240v input?
Please read this with the respect intended.
Cheers
Dean
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