Well I guess you get what you pay for with free sites huh? Sorry about that. I didn't want to use up the space here, but I'll post a couple of the pics.
Here's one of the chips, LM1875, 220k feedback, 10k input resistors, .1uF across ps pins, 47uF input cap all from the Shack.
Here's one of the chips, LM1875, 220k feedback, 10k input resistors, .1uF across ps pins, 47uF input cap all from the Shack.
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Here's the inside of the chassis, transformer is from ApexJr. It's a Torroid Tech 1010VA I wired the primaries in series to get half the usual secondary voltage, after recifiers (MUR860) and ps caps (1000uF Panasonic FC) I have +/-22.5DC rails. The chassis is from a broken RCA tape deck I got at the Radioshack outlet here in Charleston for $5.
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Dustin,
Very nice.
But...
You need some PSU bypass caps on the chip's pins, because the caps are very far away.
100uf will do.
The way you have it I don't see another choice.
Solder the caps direcly to the LM1875s (+ and -), and join the grounds of the two channels (you can do it with the caps' legs).
From a midle point of that, make it the power ground.
No more hummmmmmm.
Very nice.
But...
You need some PSU bypass caps on the chip's pins, because the caps are very far away.
100uf will do.
The way you have it I don't see another choice.
Solder the caps direcly to the LM1875s (+ and -), and join the grounds of the two channels (you can do it with the caps' legs).
From a midle point of that, make it the power ground.
No more hummmmmmm.
I just did as suggested and put a pair of 1000uF caps right on the pins of one channel of my amp to see try and get rid of the hum. It didn't work. It still has the same hum as without the cap right on the pins. I'm thinking either the noise is radiated from the torroid, or maybe I'm getting some noise injected from how I have the LED's wired. Right now the wires to connect the LEDs to the power supply cross the AC lines, so maybe some noise is being induced. Anybody got any other ideas? I really thought the caps would take care of it for sure.
i am not an expert!!!!!
however when it comes to hum I have had my share !!!!!
Something that has ALWAYS been the source of humm in my gc's (3 so far) is a bad ground loop or an bad iec receptacle that let not ground go through ..... You might wanna check that
and one last thing, you wrote that the toroid is more than 1000 VA
wow..... so it is more that 50 Ampères ????
I would suggest trying a smaller toroid for that matter, but you dan't need to take my word for it, check it out with other participants here.
J-P
however when it comes to hum I have had my share !!!!!
Something that has ALWAYS been the source of humm in my gc's (3 so far) is a bad ground loop or an bad iec receptacle that let not ground go through ..... You might wanna check that
and one last thing, you wrote that the toroid is more than 1000 VA
wow..... so it is more that 50 Ampères ????
I would suggest trying a smaller toroid for that matter, but you dan't need to take my word for it, check it out with other participants here.
J-P
Hi Dustin;
Nice work! On the hum issue, did you use shielded cable on both the inputs and the outputs? I've found that to be the key to reducing hum over here....sorry to ask a dumb question if you are using shields, but my middle aged eyes couldn't tell from your pics if you were....
Good luck and all the best!
Morse
Nice work! On the hum issue, did you use shielded cable on both the inputs and the outputs? I've found that to be the key to reducing hum over here....sorry to ask a dumb question if you are using shields, but my middle aged eyes couldn't tell from your pics if you were....
Good luck and all the best!
Morse
uvodee --Thanks for the suggestions, I'll be sure to check the IEC and my star grounds again. I'll try bypassing the IEC and see if it helps.
Morse-- No shielded cable, just a couple strands of regular CAT5 twisted together.
bonsai171-- The torroid is way oversized for this amp, but I'm probably going to add more channels to it. Each LM1875 is only good for ~20W. But that's plenty for my use. I'm not using any active preamp. Just a pot and the input cap between the amp and my CD player. Check out Nuuk's site some folks made some awesome GC's with valve buffers.
Morse-- No shielded cable, just a couple strands of regular CAT5 twisted together.
bonsai171-- The torroid is way oversized for this amp, but I'm probably going to add more channels to it. Each LM1875 is only good for ~20W. But that's plenty for my use. I'm not using any active preamp. Just a pot and the input cap between the amp and my CD player. Check out Nuuk's site some folks made some awesome GC's with valve buffers.
Well, I'm quite embarassed to admit this but at least I found out why my amp was humming. It wasn't even the fault of the amp. The RCA cable coming from my volume pot to the amp was picking up noise. I realized it wasn't the amp when I unplugged the input and the hum went away. I can't believe I didn't try that earlier, but at least I know now. Thanks for all the suggestions everybody, I appreciate the help!
Hi Dustin;
Glad to read that you've got the hum issue pinned down! Finding the source for that kind of thing can be a genuine pain....
>>>...RCA cable coming from my volume pot to the amp was picking up noise...<<<
You might want to check both the cables and the volume control independently.
Don't know if you've built your own IC cables before, so please take no offence if you already know this, but you can build some cheap but good ones that are good at noise rejection by using shielded microphone cable. Just connect the shield to the cables ground lead at the source end and leave it floating at the amp end. It works.
Just my 2 pence here, but here's my recipe for "cheap but good." Go on over to Parts Express and get some of their 39 cent a foot "Professional Microphone Cable" (I bought a 100 foot reel of it - I use it that much....) and their "Dayton" brand gold plated RCA connections. Maybe not "high end audio", but it marginally outperforms Monster IL400 MK II's IMHO (I've got several pair of those...) for about 1/4 the price.
Good luck and all the best,
Morse
Glad to read that you've got the hum issue pinned down! Finding the source for that kind of thing can be a genuine pain....
>>>...RCA cable coming from my volume pot to the amp was picking up noise...<<<
You might want to check both the cables and the volume control independently.
Don't know if you've built your own IC cables before, so please take no offence if you already know this, but you can build some cheap but good ones that are good at noise rejection by using shielded microphone cable. Just connect the shield to the cables ground lead at the source end and leave it floating at the amp end. It works.
Just my 2 pence here, but here's my recipe for "cheap but good." Go on over to Parts Express and get some of their 39 cent a foot "Professional Microphone Cable" (I bought a 100 foot reel of it - I use it that much....) and their "Dayton" brand gold plated RCA connections. Maybe not "high end audio", but it marginally outperforms Monster IL400 MK II's IMHO (I've got several pair of those...) for about 1/4 the price.
Good luck and all the best,
Morse
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