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After playing very nicely for about a week my homebuilt pre/phono pre has developed a cyclic buzz. Every few seonds it goes Bzzz for a half a second. Can't find anything external causing it Got me stumped. Anyone run into anything like this before?
Vince
Follow Ups:
Thanks for all the tips folks. For the time being at least, it seems to have gone away on it's own. If it does come back I and if I find the cause I will let everyone know what it was.
Thanks
Vince
Sounds like it could be a cold solder joint, especially to ground. One way to check (with the power off) is to wiggle every wire and component lead including ground wires gently with a needle nose pliers and see if anything breaks free.
Vinnie,If you are still reading this, go check all your ground connections. I had a similar buzz when I built my Aikido preamp board. Turned out that I forgot to solder the ground end on one of the resistors. The resistor lead was touching the hole on the circuit board but was not soldered in.
Tonight I unplugged both ups units, made sure the cell phones were turned off (they were off last night too)and turned on the system. No buzz at all. Aha, says I, I have found the problem. Just to be sure I turned the ups units back on one at a time. Still no buzz. This has definite potential for making me crazy.
Ideas anyone?
Humid/rainy weather sometimes encourages arcing in outside HT lines and such. I've also experienced EMI from airport radar that sounds very much like your description of the noise. Is your preamp totally shielded?
I do get a buzz when my cell phone rings or receives a text message. I used to have a UPS for the computer and it didn't affect the system......like I said before the passive EQ circuit is more sensitive to RFI and perhaps AC induced noises from the immediate environment. Are you using a separate power supply? Through the years I've learned that the best way to keep a preamp quiet is by by building the PS on another chassis.
Hey Joseph
Yep, using a separate ps chassis. The thing that makes me crazy is for it to be there last night and not tonight. I can't think of anything that could have done it unless it was coming from outside the house. I have never heard this particular buzz and pattern before, so maybe you are right about the EQ circuit picking up something. I'll just have to wait and see if it happens again. Any way to shield the EQ circuit?
Vince
> Any way to shield the EQ circuit?
Faraday cage?btw - Put a small HF cap (100MHz something) across the input from the PSU as well.
mvh /Pär
I don't think it is possible, it is the circuit topology that makes it more vulnerable. Kinda' similar to amps that employ negative feedback are quieter than those without.
I had a similar problem a few years ago and it turned out to be the APC UPS battery backup box for my computer.
Did it start after you had been using the UPS for awhile without any problems? We have had two new UPS's in the house for several months and I have never noticed a problem before.
Vinnie,I can't remember. I do remember it took a while to track it down to the UPS.
Unplug the two units from the wall and see if your problem goes away...
The cyclical noise got onto the powerline, and into my system even though the stereo was on a dedicated line and the APC box was in another part of the house.
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Hi Vince,Do you live in an RFI infested area? I have a friend who built the circuit and lives practically under a TV/radio tower and has no problems but another who lives half a mile away who can't get rid of RFI on any preamp he tried. I ocassionally hear a cops as they pass by for a few seconds.....sometimes this is the price to pay for passive RIAA EQ, so I guess YMMV. other than that it can be a cold solder connection....
Regards,
nt
Had something simular , turned out to be the doorbell transformer in the attic was going bad . Hardest case of trouble to find , ever .
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