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Topics - lapsteelman
« on: February 28, 2013, 11:01:25 AM »
I have a vague memory of an artical in Radio Electronics magazine in the early 90's about using an audio amplifer IC (I think it was the lm1875) and a low noise op amp in an unusual way. I seem to remember that the power amp was in the feedback loop of the op amp, but it was almost 20 years ago so I could be wrong. I think it would have been around 1993. If anyone has a scan of the original artical or can link me to more information on this circuit technique I would greatly appreciate it.
I was pretty new to electronics at the time, but I think the jist was that using this circuit topology you got all the noise specs and low THD of the op amp, ( which I believe was a ne5534) and the power amp IC was just acting as the muscle. (again.......20 years ago, forgive me if I got it wrong).
« on: March 24, 2012, 04:25:07 PM »
« on: December 09, 2011, 01:57:52 AM »
On a zobel network does it matter what order the resistor and cap go? I see it both ways in schematics.
(Resistor first, cap to ground or cap then resistor to ground).
« on: October 13, 2011, 09:22:30 AM »
OK, so last night I am playing around with a chipamp (LM1875). I got the circuit done and needed to hook it up to a power supply. I had a power supply done up with a bridge rectifier and caps, but I couldn't find the center taped transformer in the garage. I wanted to test it so I hooked up an non center tapped transformer to the power supply board and it worked. ( Although the voltage were not equal, the negative was about 1.5 volts lower than the positive)
I tried it with the amp and the amp worked fine. Is there a downside to doing this? Could I just put some equal, high value resistors across the caps to equal out the voltage?
« on: July 16, 2011, 05:06:28 PM »
Forgive a newby if this is a painfully basic question. I am wondering about zobel networks.
First off, How big does the resistor have to be? I am working with the National lm1875. In the databook it looks like they just use a 1/4 watt 1 ohm resistor. In a schematic in Make magazine they use a 1 or 2 watt resistor.
The other thing I am wondering. Is there a formula for calculating the resistor and capactor value of these. For example I have no 1 ohms in my box but I have plenty of 10 ohms. Can I change the cap value and make this work?
Thanks for your time.
« on: March 01, 2011, 11:31:34 PM »
Does anyone have a good 12 volt amplifier IC that they have had good luck with. I have used the LM383 in the past and it was OK but I am looking for something cleaner for my lap steel. I would like to get at least 8 watts out of it. Thanks
« on: January 18, 2011, 12:14:43 AM »
I have been checking out some chipamp sites and I noticed some of the builders use ultra fast diodes in the power supply. I think this is supposed to reduce noise. (not 100 % sure). Is this just hype or is there something there? I ask because I have been building and tearing apart guitar and hifi amps for years and they all seem to use pretty generic diodes in the power supply.
I am toying with the idea of putting a switch in the power supply to go back and forth between the two styles to see what kind of difference it makes. Has anyone ever done anything like this?
I am making this amp for my steel guitar and I want a CLEAN, CLEAN, CLEAN sound. A good steel amp is alot like a hifi amp. (with reverb!)
Thanks, this is a great forum.
« on: January 10, 2011, 12:00:22 AM »
I just wanted to say Hello, Name is Frank
I stumbled on this forum while looking for schematics, and finally decided to join up. Lots of good info here!!! I have been playing with audio amp IC's for almost 20 years, building effects pedals, etc. Its a lot of fun and really a pretty cheap hobby. I mostly play lap steel.
I am thinking about building an amp for my steel with the LM3875 or the LM3886 for my next project. Right now I am working on a theremin.
Hope to get to know you all better.
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