the resistors are in the wrong place.SuperKris said:
The resistors are only to load the caps at startup. They will be bridged by the relay after 1.5 - 2 seconds. Their only purpose is to not pop the house fuses or wear down the on/of switch and/or regulator. Im never hreard about a CRC filter before actualy
The soft start resistor (about 10r to 20r for 110/120vac) should be in the Live lead to the primary of the transformer.
If you think you require slow charge then a NTC thermistor does the job better in the secondary feed to the smoothing caps.
This ground switch and the incorrectly wired Audio Ground to Safety Earth is very risky if there is a catastophic failure of the mains wiring. It could kill a user.SuperKris said:
Try to imagine how a 500A pulse will get from the Audio Ground or speaker terminal to the protective earth pin. That is what the ground switch must pass without the voltage on the chassis rising above ~ 50Vac. It must do this effectively to ensure that the T rated mains fuse ruptures very quickly.
AndrewT said:
I gues that would work too. Is there a real advantage in puting the resistor before the transformer? I ordered the wrong resistors anyway (4.7K, not 4.7r.... Argh...s tupid) so i could still change it. the relay will do 230V too, so i could still change it is there is a real advantage.
I did no think of a NTC thermistor because of the huge currents. Were talking 63V into 50.000 of caps here. Im not sure what what current will actual be, but it could be somwhere between 100 and 50 amps i gues. The rectifier is rated at 25 amps. The reason i choose 5 Ohm is that 63/5 gives 12.6 amps of current max. That should be a save number for all the parts. The wattage dissipated in the resistor will be huge. Somewhere around 800 watts max in theory, but that will drop down to around 100-150 watts within a few 100ms, and the total time the resistors are being used is less than 2 seconds. these are rated 50W so i gues they will survice that power for those 2 secs.
If you think here is a much beter way tell me. I can still change it now.
Are you saying that this is the wrong way to wire the ground? If so how should this be wired? Should the audio ground always be connected to the PE and chassis? All the amps i have ever owned (quite a lot) dont even have a PE connection, so how does that work??? And should the chassis always be connected to the audio ground? I think this is the case with most amps i ever owned.
I and many other users have 45mF, 60mF and 75mF of smoothing on power rails. I have never blown a bridge rectifier, for any reason and certainly not due to charging capacitors. 50mF should not cause a reliability problem.
The real reason for a soft start (different from slow charge) is to prevent the mains fuse rupturing when the transformer is trying to start itself from the off state. This start up takes just a few cycles of the mains, <=50ms. The initial current surge at switch on can approach 100A, but is very short term.
The real reason for a soft start (different from slow charge) is to prevent the mains fuse rupturing when the transformer is trying to start itself from the off state. This start up takes just a few cycles of the mains, <=50ms. The initial current surge at switch on can approach 100A, but is very short term.
AndrewT said:
Its not really that i fear the rectifier will die. But the amp was already blowing the house fuses sometimes when it still had 15.000uF of caps. So the only think im trying to achive is that stuff like that wont hapen anymore, and that the on/off switch wont die. If you think there is a beter way to do it than i thought off, i would love a few suggestions.
AndrewT said:
So what should i try to achive?
- There should be no connection between the PE and any mechanical or electrical parts of the amp. The middel pin should not be used or connected at all.
- The chassis should be connected to the ground of all the electronics.
If i understand this right i gues the question is, should i use a cap and/or resistor to connect the electronics ground to the chasis, or should it be a simple wire?
Also when you look at the picture of the back of the amp it looks like the swithc has something to do with the XLR inputs. Should that ground switch be connected to a pin of those XLR sockeds with or without a resistor and/or cap?
To me this sounds much more plausible.
Like i said... some retard has been rewirering the amp and probaly did some damage.
Good news! i finaly got the schematics!!! I put right values in there, so it should be complete. Check it out
So that solves the question of the grounding issue. Its supposed to be wired the way i got it. I also asked around a bit, and it seems more amps are wired this way, so lets drop this subject and leave it the way it is now.
I also i now have the current settings. P1 seems to controll it. short service manual says the current should be between 5 an 15 mA. The other 2 pots are for current limmiting. Will current limmiting have a negative effect on the sound (when not clipping)? If so, is there any reason i should set current limmiting a bit higher, so more current can flow When needed?
There are no pots for controling DC offset. If there is a noticable offset, should i change some resistors? and if so, what resistors should i be looking at?
Some of the other questions i did not find awnsers for.
I still would love some ideas on the filter that filters out everything below 20hz and above 20k. Should this filter be removed, or maybe be ajusted so the amp can work with higher and lower feqenties too?
Also, im still a bit of a noob with this stuff, so i would love some ideas to improve the sound quality. I now have the schematics, so maybe someone can see if there is room for some improvement!
An externally hosted image should be here but it was not working when we last tested it.
So that solves the question of the grounding issue. Its supposed to be wired the way i got it. I also asked around a bit, and it seems more amps are wired this way, so lets drop this subject and leave it the way it is now.
I also i now have the current settings. P1 seems to controll it. short service manual says the current should be between 5 an 15 mA. The other 2 pots are for current limmiting. Will current limmiting have a negative effect on the sound (when not clipping)? If so, is there any reason i should set current limmiting a bit higher, so more current can flow When needed?
There are no pots for controling DC offset. If there is a noticable offset, should i change some resistors? and if so, what resistors should i be looking at?
Some of the other questions i did not find awnsers for.
I still would love some ideas on the filter that filters out everything below 20hz and above 20k. Should this filter be removed, or maybe be ajusted so the amp can work with higher and lower feqenties too?
Also, im still a bit of a noob with this stuff, so i would love some ideas to improve the sound quality. I now have the schematics, so maybe someone can see if there is room for some improvement!
I'm not an expert (closer to newb), but it looks like P1 (the VBE multiplier) should be wired differently to protect the output devices in case the pot's wiper goes open (gets dirty). Andrew (and others) can elaborate on how it should be modified, if that is correct.
If that trim pot is an open-case type, you should probably replace it with a sealed type trimmer so the wiper cannot get dirty. But if you do, make sure it is set to EXACTLY the same resistance.
For the current limiting circuit, if you raise the threshold, you may defeat its purpose and not be protected. It's probably not a good idea to adjust it without a lot of expertise and some good equipment. If you're not protected, one frayed speaker wire could ruin your whole day.
And replacing those current limiter trimmers with sealed ones (or even just static resistors) is probably also a good idea. But if you do, make sure they are set to EXACTLY the same resistances.
And I think you're misunderstanding the reason why the breakers are blowing during startup. As Andrew mentioned, it's due to the toroidal transformer drawing huge current, not the big capacitors, which is why Andrew recommends to move the soft-start circuit resistors to the primary side of the power transformer and reduce their on-time.
..Todd
If that trim pot is an open-case type, you should probably replace it with a sealed type trimmer so the wiper cannot get dirty. But if you do, make sure it is set to EXACTLY the same resistance.
For the current limiting circuit, if you raise the threshold, you may defeat its purpose and not be protected. It's probably not a good idea to adjust it without a lot of expertise and some good equipment. If you're not protected, one frayed speaker wire could ruin your whole day.
And replacing those current limiter trimmers with sealed ones (or even just static resistors) is probably also a good idea. But if you do, make sure they are set to EXACTLY the same resistances.
And I think you're misunderstanding the reason why the breakers are blowing during startup. As Andrew mentioned, it's due to the toroidal transformer drawing huge current, not the big capacitors, which is why Andrew recommends to move the soft-start circuit resistors to the primary side of the power transformer and reduce their on-time.
..Todd
taj said:
I replaced all the pots by closed 10 turn models. I also replaced all the caps btw, made some connections thicker, and removed a lot of connectors.
I have the equipment... I have a nice scopemeter and im building a nice dummy load. Also i know enough about electronics. Just no experience with amps.
Yeah, im thinking about doing that. It would also save me some difficult wiring. whats the best way to do it? would i be able to use those 4.7 Ohm 50 watt resistors? the relay im using can switch 4x 20A, so that should be enough. Sould i use one 4.7 ohm, or should i put those in serie to get 9.6?
taj said:
I have no idea what that means
There's a proper soft-start circuit here:
http://www.adam.com.au/cgpap/QuasiWeb/index.htm
Actually, I think there are a few of these circuits floating around if you Google for it.
Maybe Miller caps are called Heineken caps in Holland. No wonder I couldn't find one.
..Todd
http://www.adam.com.au/cgpap/QuasiWeb/index.htm
Actually, I think there are a few of these circuits floating around if you Google for it.
Maybe Miller caps are called Heineken caps in Holland. No wonder I couldn't find one.
..Todd
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