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Old 16th September 2004, 05:18 PM   #1
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Default Noisy amplifier

I've just completed 2 Velleman amp kits and placed the two kits in an enclosure together. They're sharing a DC input of 15v and 1,000 mA. I've got them running my computer monitors. The problem is that I have a ton of noise and there are electrical anomalies when other electrical devices in the house are operating.

What have I done wrong and what can I do to fix it???

Ps: I think my gain is out of whack. I have to open the volume control panel and turn the wav volume all the way up to minimize the noise, and turn the master volume all the way down to keep it at respectable levels. Any suggestions?

Jonathan
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Old 16th September 2004, 06:29 PM   #2
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I assume that the kit circuits you are talking about do work and are assembled correctly and correctly biased. What does the output sound like with no input connected? If the noise persists, try using a seperate DC supply for each channel, commonly grounded though, as there may be some ground loops causing RF oscilations and noise. usually sounds like strange fuzzz or fffffiiiizzzzz.

One source of the noise could be the power supply. If someone on the same house circuit turns on a blender or vaccum cleaner, there will be transient voltage spikes on the power line due to energy built up in magnetic fields inside the motors. Monitors also create noise. FCC regulations require a limit to the inerference created for the sake of other electronic devices. This doesn't mean that there is no noise coming from it. Be sure to include a varactor or some other form of transient suppression.

Also the enclosure should be made of metal. This will shield RF from the circuit and create a "clean" space for the circut to operate. If the input impeadence is high with a good high frequency responce, the circuit may be prone to RF noise.

Are you sure the input impeadence is matched to the computer audio output??
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Old 16th September 2004, 07:48 PM   #3
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Default Re: Noisy amplifier

Quote:
Originally posted by jlandrum
I've just completed 2 Velleman amp kits and placed the two kits in an enclosure together. They're sharing a DC input of 15v and 1,000 mA. I've got them running my computer monitors. The problem is that I have a ton of noise and there are electrical anomalies when other electrical devices in the house are operating.

What have I done wrong and what can I do to fix it???

Ps: I think my gain is out of whack. I have to open the volume control panel and turn the wav volume all the way up to minimize the noise, and turn the master volume all the way down to keep it at respectable levels. Any suggestions?

Jonathan
15V @ 1 amp doesn't sound like much for 2 amps. Are you sure the supply holds up and isn't sagging. What nominal power are those amps?

Jan Didden
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Old 16th September 2004, 07:59 PM   #4
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They're like 2 watts at 8 ohm. They're stated in the manual as requiring 15vdc, 500 mA each. I thought it would be ok to run the power inputs in series and double the amperes. Was I right in assuming so?
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Old 16th September 2004, 08:13 PM   #5
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Uhh...power inputs in series?? You mean in parallel? The 1A seems OK, yes.

Jan Didden
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Old 16th September 2004, 08:27 PM   #6
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Quote:
Originally posted by cunningham
I assume that the kit circuits you are talking about do work and are assembled correctly and correctly biased.

They are assembled according to the directions, but what do you mean by biased? This is my first amplifier to build, and the Velleman directions are vague at best.

What does the output sound like with no input connected?

Worse. The speakers hit a 60hz hum with maximum excursion.

If the noise persists, try using a seperate DC supply for each channel, commonly grounded though, as there may be some ground loops causing RF oscilations and noise. usually sounds like strange fuzzz or fffffiiiizzzzz.

That's exactly what this sounds like. It's almost like the gain is too high. I was able to diminish this slightly by opening the master volume panel, muting everything except Wave and minimizing the system volume.

One source of the noise could be the power supply. If someone on the same house circuit turns on a blender or vaccum cleaner, there will be transient voltage spikes on the power line due to energy built up in magnetic fields inside the motors. Monitors also create noise. FCC regulations require a limit to the inerference created for the sake of other electronic devices. This doesn't mean that there is no noise coming from it. Be sure to include a varactor or some other form of transient suppression.

What's a varactor? I'm obviously novice, but I did feel like there was some kind of filter I could put in line with the power supply to solve this. The only problem is I don't know what it is.

Also the enclosure should be made of metal. This will shield RF from the circuit and create a "clean" space for the circut to operate. If the input impeadence is high with a good high frequency responce, the circuit may be prone to RF noise. Are you sure the input impeadence is matched to the computer audio output??

The enclosure is a two-part assembly of aluminum and steel. The aluminum chassis is where the amps are mounted, and there's a steel cap to go over the top. What do you mean by input impedance? I'm just using the 1/8" headphone jack as a source. I cut the cable off an old pair of headphones and wired that to the inputs.

Also, to install them to the metal chassis I squirted some silicon-based caulk on the bottom of the board and just stuck it on the aluminum. Was that ok?

Thank you for EVERYTHING,
Jonathan
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Old 16th September 2004, 08:53 PM   #7
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jlandrum, please check out how you use the "quote" function. If you want to comment more than once you have to do a little cut and paste plus editing. Please don't write your text WITHIN the QUOTE-tags.
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Old 17th September 2004, 02:02 AM   #8
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Default same problem

which velman kit did you use? if its the one based on the tda2003 chip its not designed for use with mains!!! its layout is for portable 12v batt. I had a similar problem with mine a few years ago when i started building amps. i ended up with 600,000uf woth of caps. on the power line. not good!! let me know how you get on coz ive got a few deigns for smaller chip amps. c ya soon, steve.. ..
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Old 17th September 2004, 02:20 AM   #9
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Default P.S. silicon caulk?

how well did you trim the leads on solder side of board? if you stuck them down with caulk, how thick? you may have a lead sticking through the caulk into the aluminium case. velman kits are quite good for mounting holes, use nylon stand offs, long plastic nuts with a screw in each end. see ya soon, steve.. ..
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Old 17th September 2004, 05:29 AM   #10
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Worse. The speakers hit a 60hz hum with maximum excursion.

This looks like a signal grounding or AC filtering issue

I think the modules aren't mounted and/or wired properly

Schematics and/or pictures of the actual system showing how the modules are wired and how the components are mounted on the boards may be very useful in finding the problem
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