Never assume or overlook the simple things - LONG Rant

[John_P_WI]

I've been out of the "big amp" building cycle for the last several years due to "life" (a very, very bad divorce - with kids, remarriage to another gal ending in divorce (I blame ex1 for this), health issues and finances). These factors knocked me out, I basically said effit to everything that took effort and melted into my couch every day after work with a few beers. I did continue to develop new circuit ideas during this time - but this is not a sob story....

Fast forward, New Year's resolution - I decided to get away from the TV and forget the problems of my first 50 years of life and focus on positives. I think it was smokebreak who posted about the little lm386 chip amp and I thought what the hell, it's small, fun and I don't need to work at my big bench which has a gutted bassman 10 converted to a 2203 sitting on it - I could never get rid of a buzz in the amp. Brought an o'scope, power supply and a few other items including a 4x12 cab from the basement up and set up a temporary work table in front of the window in my now empty dining room. Forget working in the man cave, it's now the "man house".

Long story short, the little lm386 chips are a blast, I built and tried cascaded jfet front ends, ala a JCM 800, used buffer inputs and built TL072 front ends - similar to a Zen drive. Everything that applies to big amps, applies to these small amps. I highly recommend anyone interested in learning amps to start with one of these chips and discrete components. Followed immaculate decoupling and grounding schemes. Arghhh, still had a buzz that I could not get rid of - same buzz that caused me to gut the bassman 10 2203. Hooked a battery am radio up to the scope tuned in between stations, sure enough 60 Hz spikes blasting through the air. I tried chokes, isolation transformers, snubbers, turning off computers, lights, dimmers, bench supplies, 12v batteries - you name it lil battery amp still buzzed. Didn't sound right with the volume rolled back either. Shit.

Add to the story, I work with a brilliant analog EE. He brought over an express inspired amp that he built and I just couldn't get it to give it up. Same thing, funky when rolling the volume back and noise. This guy makes his living in medical instrumentation, believe me he knows his discipline.

Fast forward, out of frustration I grabbed a piece of 2 conductor shielded wire ran the hot lead to the lil amp input resistor, the 2nd wire to the bottom of the input "leak resistor" and the shield (not connected to the guitar) grounded at the first filter cap. Pure Silence! Strat heaven, oh the tones, absolutely no buzzzz.

The common factor in all was the %$*)&^ "gold standard" guitar cable from my amp bench that I assumed was good. Never overlook anything in a system - I'm sure the buzz in the converted 2203 and my buddies anemic express are all directly related to the same cable. Sorry for the rant, I hope it can be a learning lesson - no matter how good your building chops are - a faulty $30, 10 foot cable can ruin your fun. It's not always the amp or guitar - IT can be what is in between.

This now concludes a 2 week lesson of frustration, but game on, game on. Time to build in silence....

Hope all of you guys and gals are well. I'm sure all of you can share a similar frustration. Let's hear 'em.

[xtian]

Well, John, I appreciate the word about troubleshooting systems, but what I like best is that you've lived thru the poo pile, and are back up and punching. Man House! Yes! You go, guy.

[boots]

Yes, instrument cables and alligator clip leads are truly evil.

I also discovered that you can't get rid of the hum if you sit at your bench playing your guitar through the amp that is sitting right in front of you on the bench. Turns out that guitar pickups are really good at picking up transformer magnetic fields (fluorescent work lights, too).

Simple things like that can drive you crazy.

[matt h]

(deleted)

[Bob S]

We've probably all had something along these lines.
For me something like this happens every time I think I'm starting to know what I'm doing. Humbling.
Welcome back John - hopefully the tough times are over.

[John_P_WI]

Thanks Guys, the next few years will be rough but the lil amp has given me focus again and you would never believe how loud 1/2 watt is through a 4x12.

BTW, I have 7+ full sets of complete iron from champ to kt88 to 4x6l6 mocking me to build them up, one set is an original Hoffman 50w from early-mid 90's I'm thinking something along the line of Friedman's Marsha / HBE - with a few twists. This one will be for you Bob (and Miles and Colossal Dave).

Yes, good to have focus again.

Take care my friends.

[Colossal]

I'm thinking something along the line of Friedman's Marsha / HBE - with a few twists. This one will be for you Bob (and Miles and Colossal Dave).

Yes, good to have focus again.

Take care my friends.

Good to hear you are on the mend John. I knew you were getting through some rough times. Welcome back.

Looking forward to HRM build, hot rodded Marshall, not rubber monkey Mr. Dumble!

[boots]

Time to get back on the ham bands, John.

[John_P_WI]

Time to get back on the ham bands, John.

Yeah, funny thing you say that. I stumbled across my keyer and manual key the other day... almost pulled out a receiver too as I was digging around for my ARRL handbook for some advice on the buzz issues. I need to downsize some pics of the o'scope buzz and post a few for your humor.

It truly is amazing how the fundamental basis of electronics glues all of the hobbies together.

Similarly is the very close approximation of operation between the common 12AX7 and the gain stage set up of a discrete jfet (except that the jfets will oscillate at crazy high frequencies) - although I haven't figured out yet how to get the Marshall notch or scooped shark fin waveform yet from jfets....

[John_P_WI]

Not trying to be pedantic, but IF any of you who are struggling to understand gain stages, grab a few jfets, resistors and a battery... Best part, unless you are playing with LND150's the voltage is safe and harmless.

Set it up like a tube, in the most simplistic terms:

Drain = Plate, Gate = Grid and Source = Cathode

In this pic I am dropping 3.6v across the Drain resistor and one can see the inverted gain:

https://www.dropbox.com/s/geatyii5t5224 ... l.jpg?dl=0

[John_P_WI]

Here is a link to the noise that I was fighting, the noise on the sine was coupled in via the bad cable - notice the "diode" spikes riding along the sine wave. IF I recall, this was taken at "speaker jack" with no signal injected.

https://www.dropbox.com/s/11ctm7lpmmeep ... s.jpg?dl=0

Finally, the scope hooked up to the speaker out of an am radio tuned between stations. Notice how the spikes were magnitudes above noise floor of the radio and at 8.3 ms apart (120 hz "scr noise"). These are spikes from a dimmer in the room that I set up in temporarily during a blizzard. Don't let RFI ruin your day.

https://www.dropbox.com/s/lf8b9k3b66j2c ... z.jpg?dl=0

Get a scope and a few parts and learn - been away for too long, good to be back...

[John_P_WI]

Xtian,

Thanks for the kind words, It has been hell for me, but am looking forward. There is truth to the "nice guys finish last"...

[Reeltarded]

John all that sucks up until the part where it sounds like you are stepping out.

That is fantastic.

[Structo]

Hi John, I'm glad you were able to pull yourself up from those awful circumstances.

Since my health problems started several years ago, it's hard not to be depressed.
No job, no money.....

I suppose it is some kind of mid life crisis accented with potential mortality issues.

I still try to see a glass half full but it is a struggle to do so.

I'm glad you are feeling better, it ain't easy.