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Topics - shinychrome0

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Preamps and Effects / Custom LPF build is distorted
« on: August 05, 2010, 07:33:51 PM »
I've been working on designing and building a 5 cascaded stage low pass filter , and it doesn't exactly do what i want it to.  The schematic is attached.  There is some output, but it is sputtery and badly distorted.  Is there something in the schematic that shows a design problem?  I've been staring at this thing and prodding with my meter all over to make sure its built exactly to the schematic, and nothing is touching or shorted where it shouldn't be.  The schematic is attached.

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Amplifier Discussion / Audio power meters
« on: June 05, 2010, 08:13:35 PM »
I'm looking for something to monitor the wattage that my amp is sending to my speakers.  Its very hard to find anything that's suitable, and doesn't have a bunch of extra features.  I play a digital Line 6 preamp into a 300 watt tech 21 amp, which powers 90 watts of speakers.  So i would really like to be able to tell how much power the speakers are getting.  I would love to be able to turn up more, but i'm afraid to blow my speakers.  Tone tubby's aren't cheap, and neither are celestion century's.  I've seen a few units like the radio shack APM units from the 70's, but is there anything in current production that does the same thing?  I prefer buying new rather than used for stuff like this.

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Amplifier Discussion / Crate PA-8 repairs
« on: May 17, 2010, 10:17:53 PM »
I have a Crate PA-8 8 channel powered mixer that is having some problems.  It was given to me for free because it needs repairs.  AT any volume, and on any of the eight channels, the output distorts.  I don't think the output transistors are blown or else there would probable be no sound coming out.  Two diodes in the power supply section have burnt the board, but they test fine.  But obviously something caused them to overheat.  I'm not entirely sure what to check next.  i can send a schematic to anyone who needs to look at it, but i'm not supposed to post it per crate's terms of use.  They were kind enough to provide it so i think i'll respect their rules.  Thanks guys!

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Preamps and Effects / cascading low pass filter sections
« on: May 06, 2010, 04:45:17 PM »
I'm attempting to make a high-order low-pass filter that i run after all my effects in my signal chain.  I'm trying to figure out how to cascade several single pole filters. I know you can't just slap one after the other, but what if i stick a simple op amp buffer between each stage?  would that cascade correctly and give the desired effect?

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Amplifier Discussion / high quality power cables and the skin effect
« on: February 11, 2010, 10:56:48 AM »
I'm doing some research to try and build my own high quality power cable.  I always like DIY projects, and the good cables are all way to expensive for me.  $1800 for a power cable?  Yeah, i'll pass on those.  In my research i came across a property of wires called the skin effect.  Its a little complicated, but i think i get the idea, which is that heavy gauge wire has a very low resistance to DC and low frequency AC signals (like the mains power frequency)  but they actually have a higher resistance to higher frequencies.  Correct me if i'm wrong.  The way i see it, a very heavy gauge cable could be used to filter out the type of high frequency noise on the AC line that expensive cables claim to get rid of. 

Is this a decent theory?  If so, what are the benefits of using different materials?  Is silver really any better than copper?  It sounds like silver is better at high frequncies, so would i actually be better off with something cheap like really heavy gauge copper?

Also, what kind of frequncy range is the noise on a power line usually at?  Mega of giga hertz?  Or much lower?

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Amplifier Discussion / Help repairing crate xt65r
« on: January 21, 2010, 05:10:19 PM »
Hey guys. A buddy of mine asked me for help trying to repair or at least diagnose the cause of his xt65 dying.  Its not actually dead, per se, as it still makes some noise.  But the noise it makes is only a loud buzz, and the guitar signal cannot be heard. 

This all started hen he played a gig and had the thing at max volume for an hour or two.  He said smoke started coming out of it and its been worthless ever since.  I hooked it up to a test speaker to measure the transformer voltages under load to see if the transformer itself was the problem.  as soon as i turned it on, the cone on the speaker moved forward as far as it could, and began to smell like it was burning after only a few seconds. Obviously something is placing a high DC potential on the speaker. 

So i have two questions

1. What could cause DC on the speaker like that?
2. Is it safe to test a transformer with just the primaries connected, and measure the voltages at the secondary side? 

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