Power Supply Noise - Is this always a good solution?

[duck_arse]

perhaps you could try an R/C supply filter in-line with the digital pedal. if it cures your noise and still everything works, it could be a simple fix.

[Labaris]

perhaps you could try an R/C supply filter in-line with the digital pedal. if it cures your noise and still everything works, it could be a simple fix.

That sounds interesting. What would be the exact function of this filter? Thanks

[jblack547]

Yes, usually between 2 to 4 volts difference.

[duck_arse]

amz has a page on hum and supply r/c filtering.

http://www.muzique.com/lab/hum.htm

[PRR]

> 600 ohms is about the resistance of some distance (1mile? 2 miles?) of single twisted pair used for telephone communications.

600 Ohms comes from a specific, show-off, project. It is historically significant but rather outside the Bell Systems' day-to-day work. It did become Bell's major income for several decades.

Bell's original telephone could hardly get down the block. It needed an amplifier, and soon the carbon microphone was widely used. Interestingly in light of all the other patent litigation around the Bell System, it is not clear who really invented the carbon mike.

Now you could call across town. Getting to the next city required FAT wires so the still-weak signal wasn't lost along the way.

Bell expermented with carbon amplifiers. A receiver (earpiece) directly coupled to a HIGH-power carbon mike (no acoustics involved). Based on this they started stringing wires across the midwest then finally to San Francisco. FAT wires. They learned a lot about long-long lines and cascade amplifiers. You "could" talk across the country but the sound was almost unintelligible.

DeForrest put another bit of wire in the vacuum diode. It isn't clear he knew why, but the Bell System boys took the idea and ran. Bell did most of the useful vacuum tube work in the early 20th century.

They got the Transcontinental Line to work good. But unprofitable. Telegraph and telephone systems had long used "Phantom" connections to get more traffic through. If you have two pairs you can CT both and run another conversation between them. Bell also began work with carrier telephony. Modulating conversations to supersonic frequencies and back.

Then Radio really got hot. Central organizations distributed high-class programs from the big cities to the sticks.

Around the east Bell had lots of "cable", many twisted pairs in a jacket (today we say snake). They developed ways to get broadcast quality through cable. (Twisted-pair impedance always goes toward 100 ohms.)

But the hop from Chicago to San Francisco was tough. By this time Bell had strung #8 and even #6 (FAT to reduce inductance) as open pairs 8 inches apart (to reduce capacitance). Repeaters about every 150 miles.



Here's the open-end impedance of the open pairs, and the loss over several distances:



I quote: "Note that, except at low frequencies, the impedances of the various open-wire lines are quite uniform throughout the frequency range and do not depart greatly from 600 ohms."

Apparently they had already stacked carriers on these long lines, because when they extended the broadcast line bandwidth to 8KC in 1934 they had to remove the lowest carrier channel.

Does anyone remember the Red and Blue networks?

[tubegeek]

... the Bell System boys took the idea and ran. Bell did most of the useful vacuum tube work in the early 20th century.

PRR, I read something recently (I'll try to dig up more specific citation) that credited GE with moving from deForest's not-so-empty Audion towards the hard vacuum (which makes sense because of, you know, light bulb manufacture) which made a huge step forward at the early end of things, maybe 1912-ish?

One thing I wonder about  - the fact that all those lives were saved by the existence of radiotelegraph equipment on the Titanic and the Normandie (and the ham radio help of David Sarnoff - do I have that right?) - that must have been a hell of a PR boost for all the new technology, eh?

Does anyone remember the Red and Blue networks?

Very vaguely - more please?

[PRR]

> the ham radio help of David Sarnoff - do I have that right?

That's kinda what he said. It's probably untrue.

He later claimed to be the junior Marconi radio operator who "stayed at the key for three days". It is much more likely he was already in Marconi management and had the day off.

He was a self-promoter, but also promoted radio, including the idea of one-to-many, "broadcasting". Memorable was a live broadcast of a Dempsey boxing match.

There's several strands of vacuum tube advancement. Western Electric is one. GE bought American Marconi (the US seized it for WWI) and spun-out RCA; this gang was another major tube work group. RCA was supposed to be a patent-license office; it was Sarnoff who made RCA as big as it got.

He was involved with Rockefeller's massive NYC building project and became the prime tenant. Radio City Music Hall, Studio 8H, 30 Rock, etc.

Television had been floating around for a long time. Farnsworth worked alone, Zworykin pitched to Sarnoff, and in the end Sarnoff took all the credit. While some of this seems dastardly, development was VERY expensive and Sarnoff made TV a commercial proposition. And when color TV was born, CBS had a workable system and RCA fought it to death. NTSC Color is RCA's plan and served us (more or less well) for 50+ years.

NBC radio network was two networks, Red more commercial. NBC didn't call them red and blue at first. But Bell System was running 7 or 9 separate dedicated networks, and used color-tags to keep them straight. Much later NBC picked-up these colors as sub-brands.

The NBC chimes (G-E'-C') were incidentally a cue to telephone engineers to switch-over network lines at program changes.

NBC was so big it was ordered to split. After a fight, the Blue network was sold to a candy-man and was called ABC.

[jblack547]

Absolutely, You'll hear people mention power supply ripple. That is the rectified AC (100hz). I just looked at the data sheet and it says the input has to be 1.2v higher than the output.