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I have developed a new hum from what I assume is the Project Phono Box MKII. I have only been back in vinyl for about a year and it has sure changed since the 70's. When I first hooked my turntable and phono into my system it had a hum. Not unexpected, but cured by connecting a ground from the turntable to the phono and on to the pre. Nothing has changed electrical in my house for ages. I do not have grounded plugs (joy of living in an old not updated house!) and have only once had a ground loop from the Vandersteen's and that was in a downstairs theater.Cured it by running a dedicated ground to an outside ground post.
Symptoms:
1. New problem that just happened, everything has been fine.
2. Noise increases as volume is increased.
3. Sounds like a loud ground loop hum
Tried So Far (none worked):
1. Isolating turntable from phono both from interconnects and AC do not cancel noise.
2. Unplugging one interconnect from phono to pre decreases noise but does not cancel.
3. Plugging system into a different wall socket on another floor of the house.
4. Trying different interconnects.
5. Ran a isolated ground to exterior ground post and connected grounds.
6. Unplugged the subs from the system.
7. Switched grounds from phono, turntable, and pre
8. Disconnected all grounds.
9. Isolated Phono Box power supply from the system.
10. This is my dedicated music system and is not connected to any other A/V equipment.
Any ideas? I think it is the Project Phono Box or it's power supply. I appreciate any help as I am a serial lurker and rarely post. My many thanks in advance.
Doug
Follow Ups:
I got the new caps in the mail and replaced the two 470uF 25v with 470uF 35v. The hum is a bit quieter but still prevalent. Any ideas. I was thinking a new power supply but this one seems to be hard to find. It is 120vac in and 16vac out. Any leads on where I can find this power supply. Have had no luck with google.
I just took one of these in for repair. Actually a Phono Box SE. It also hums. Upon opening it up I found two 470ufd capacitors badly bloated.
My guess would be you have the same problem
Dan Santoni
I just changed the two caps, and this preamp is now hum free.
One thing I discovered, besides being really cheap caps, there is 24V on each of them. The caps are rated for 25V. A little too close for comfort.
Dan Santoni
I have opened the box and the caps don't appear bloated but I will replace them anyway.
Blackdog,
what caps did you replace yours with?
Should I go with a 35V 470 uF?
It will take a bit of wire bending, but go with 35V.
Dan Santoni
Damn, I'll say. No wonder they bloated up. I generally prefer a 10 to 20% below spec margin, given voltage spikes at start up. I'm planning to change the old caps in a Marantz tuner I have. The first cap is rated at 50 V, and sees about 45 volts after warm-up. I'm going to up it to a 63 V cap, for the very reason you mentioned.
To get this back on the topic of phono (while still thread stealing. Sorry bewareofdoug) do you subscribe to electrolytics in the power supply having a "sound"? I need to re-cap a phono stage power supply. The objectivist in me is looking at low ESR, high ripple handling caps, specifically the Nichicon HE type.
The subjectivist in me is considering Elna Silmic II caps, which, while more difficult to fit, are recommended by the likes of Nelson Pass, among others, for their sound quality (although Pass didn't specify the power supply specifically).
Curious what you think about this.
"You won't come back from Fletcher-Munson curve"-Jan and Dean
I prefer to use the lowest ESR I can get on any given cap. Generally for two reasons. I find they sound better, and they also tend to last longer.
9 out 10 times the best are Panasonic or Nichicon
Dan Santoni
I suppose the only way I'll know if the low ESR Nichicon HE sound better than the RFS "magic silk" Elna is to try them for myself.
But I'll agree with you in advance regarding the "last longer" part. The Elnas in the values I need are rated at 1000 hours, the Nichicon HE @ 10,000 hours.
I've generally used Panasonic FM or FC in the past, but after reading the post linked below, I thought I'd try the Nichicon HE. The poster claims they measure better than the Panasonics. Or they did twelve years ago, anyway!
Thanks for your reply. Much appreciated!
"You won't come back from Fletcher-Munson curve"-Jan and Dean
Part of what he said there is true. The HE do have really low ESR. The part about FC's not meeting spec is bull. I've been using Panasonic for over 20 years and they generally measure much better than spec.
Blackgates on the other hand were some of the worst spec'd caps I've ever seen. The failure rate was pretty high too.
Dan Santoni
Spend $15 on the cheapest phono preamp you can buy online and see if it cures the noise issue. This will be well worth the money considering the time invested already.
That sounds like a good idea. I am going to replace the caps as Blackdog suggested and see if that works since it is cheap and easy. Thanks for the suggestion.
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