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Topics - cbg Rick

#1
Preamps and Effects / noisy preamp
February 14, 2019, 02:33:45 PM
A little background, I've been messing around with building chip amps for a few years now. (Guitar amps) Mostly battery powered lm386 amps and a couple tda 2030 amps from kits. I did take a 2 year electronics course about 30 years ago and do remember bits and pieces of what was taught.
Over the last few years I have wanted to build an amp of my own. Nothing outrageous just a simple 20 watt amp. After a couple false starts and becoming overwelmed because I bit off more than I can chew I have a new plan.
I have a TDA 2030 power amp built from a kit that works now I want to put a pre amp in front of it. I have a simple 2 transistor preamp built and according to LTSpice it works.
When I wired it up on the breadboard it does indead work but I get alot of what sounds like 60 cycle hum. The power amp is dead quiet until I put the preamp output into it. I added 2 2200uf caps across the power rails on the breadboard and it does get quieter but is still too noisy.
I scaned a copy of the circuit and attached it since I couldn't figure out how to attach a file from LTSpice.
edit; the resistor values are as calculated in spice, I used the closest values I could.
This is not the finished preamp, just the starting block to build on. I am curious as to why it is so noisy. I'm looking for input on what changes to make and where to go from here.
#2
Amplifier Discussion / Etching your own boards
January 01, 2019, 08:03:01 PM
I'm looking for input on how you guys make your "one off" circuit boards.
I've been messing with a chip amp. I built it on a breadboard then on perfboard, now I want to etch my own circuit board. Back in the  day I used the rub on stencils from Radio Shack to etch my own boards. Searching the internet I see the stencils are still available but the reviews are less than stellar and I could only find 2 different suppliers of the rub on style stencils (both with bad reviews) I did a quick search and found a "how to" on using a printer, transfer paper and heat to put the circuit layout on the copper clad board. Just wondering what options are out there to make a "one off" circuit board. 
#3
I found the plans for this amp in the December 1967 Popular electronics. It is rated at 22 watts with a 45 volt power supply. I'm sure the transistors are long out of production and I plan on using a 24 volt power supply. I'm using this amp as a project to dust off 30 years of cobwebs that accumulated on the knowledge I used to have.
I did build this amp on a breadboard using 2n3904 and 2n3906 for the first two stages and I used TIP 31 and TIP 32 as the output transistors. I used the resistor values called for in the schematic. I powered it up with 12 volts and it sort of worked with a very distorted output. Next step, I built a 24 volt power supply and powered it up again and the magic smoke escaped from a couple transistors  :o I had rebuilt the circuit and may have made a mistake in wiring.
I decided to regroup and start over fresh. Since this is a learning project I'm going to recalculate the bias resistor values and see what I come up with.
#4
The Newcomer's Forum / Old newbee
April 29, 2015, 07:44:01 PM
Hello everyone,
Getting back into guitars and amps after 30 years. I discovered Cigar Box Guitars about a year ago and this new hobby has renewed my interest in guitars and electronics. I've been collecting components and information for a while now and and getting ready to build my own amp. I still remember some of the electronics theory I learned in college 30 years ago and am trying to relearn some of what I've forgotten.
I've built a couple lm386 based amps and I am happy with them, now I'm ready to bump it up a notch. I found a 1967 issue of Popular Electronics with plans for a 22 watt amp and would like to work up to building it.
The pic is of one of my later builds along with my amp.