lm1875 fizzing away probelm - Page 6 - diyAudio
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View Poll Results: Was a good idea to use two lm1875 or a big stk chip
Use stk 8 27.59%
use lm1875 21 72.41%
Voters: 29. You may not vote on this poll

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Old 8th January 2013, 01:16 PM   #51
PetruV is offline PetruV  Romania
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I would like some pics
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Old 8th January 2013, 04:03 PM   #52
PetruV is offline PetruV  Romania
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added output cap and it does not go down but whe i touch the input i hear just a pop not a continous buzz it is ok?
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Old 8th January 2013, 05:54 PM   #53
blu_glo is offline blu_glo  England
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Quote:
Originally Posted by PetruV View Post
I would like some pics
1. Front view of my LM1875 laboratory amplifier. designed really for listening tests it features bootstrapped input to give 1M ohm input impedance, so it can be used with high output impedance valve preamplifiers!
2. Rear View of unit there are two phono sockets connected together internally and go to the input on the amplifier pcb. This allows any source connected to be routed on to another place if necessary. The Silver 3 pin plug is a future uprade to allow a regulated power supply upgrade. the speaker terminals are cheapo sprung ones but could also be gold plated 4mm banana sockets if preferred. The mains lead is a 2M length of molded cable/mains plug permanently wired in to the unit.
3. Front view with front lifted away, transformer and secondary fuses (to the right) visible. these fuses are wired before the bridge rectifier (small black block type - not visible - but just behind the fuses)
4. Top view a common mode HF choke comes from the rectifier to the reservoir capacitors 4700uF 35V then go on to the board supply connections. The two fat diodes are the regulated supply upgrade path. A diamond earth keeps charging currents out of the amplifier ground. The orange capacitor has a 47R resistor (value is arbitrary, just a few 10s of ohms will do!) in parralell and these connect oV to the chassis which is of course earthed.
5. Closeup of the Maplin PCB LM1875. to repeat this project any suitable PCB can be used and the following devices and their PCBs are interchangeable (taking care not to exceed max supply rails for each device and any electrolytic capacitors!): LM1875, TDA2030, TDA2040, TDA2050.

The outer case is extruded aluminium and has sufficient surface area to act as a heatsink. The LM1875 in standing or operation raises the temperature and the box runs slightly warm to the touch which is to be expected. Heavy loads 4 ohms etc cause more heating but I've not had these shut down on me yet (4 years and counting). The enclosure is available from outlets supplying Hammond enclosures and should be approx. UKŁ10.00

That's about it. Oh ,and they sound great. I've still got to get matching boxes for the regulated power supplies but Maplin (UK) have stopped stocking them so I'm going to have to do a MOQ order from Farnell who are cheaper in the long run anyway!
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Last edited by blu_glo; 8th January 2013 at 06:03 PM.
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Old 8th January 2013, 06:46 PM   #54
PetruV is offline PetruV  Romania
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Very cool design and look
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Old 8th January 2013, 07:24 PM   #55
PetruV is offline PetruV  Romania
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I tested this amp with an steper motor as input,when i turn it slowly i can quietly her it in the speaker,if i turn it just alittle faster is very loud,is that normal,after a certain input level the amp fully kicks in,because the input sensitivity not amplifing too quiet signals
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Old 8th January 2013, 07:38 PM   #56
blu_glo is offline blu_glo  England
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The faster you turn a motor the more efficient it gets, so yes, thats what I'd expect....
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Old 8th January 2013, 08:25 PM   #57
PetruV is offline PetruV  Romania
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Quote:
Originally Posted by blu_glo View Post
The faster you turn a motor the more efficient it gets, so yes, thats what I'd expect....
I know that but just a tiny bit faster makes a very large diference,but i think thats normal, anyways is it now safe to plug into a computer
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Old 8th January 2013, 08:38 PM   #58
blu_glo is offline blu_glo  England
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If you're not sure if it's OK you might try plugging it into something somewhat cheaper than your computer, e.g. old walkman from headphone out will do!!
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Old 8th January 2013, 08:42 PM   #59
PetruV is offline PetruV  Romania
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Originally Posted by blu_glo View Post
If you're not sure if it's OK you might try plugging it into something somewhat cheaper than your computer, e.g. old walkman from headphone out will do!!
Like the kind of stuff i dont have?,someone from here needs to post a simple oscilator scematic using any pnp,npn transistors
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Old 8th January 2013, 08:43 PM   #60
PetruV is offline PetruV  Romania
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Any more info on why that tda 1517 isn behaving?
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