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Author Topic: USB Oscilloscope for Audio Work  (Read 1324 times)

Ike Zimbel

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Re: USB Oscilloscope for Audio Work
« Reply #20 on: April 27, 2021, 03:28:27 pm »

Thank's Mark.  Definitely didn't start with this type of gear.

Here's the first audio load I have, built it in the early 80's - new 1000W 8 ohm resistors sit atop the old 240W Heathkit.  It sported 4 x 60W wire wound resistors and would get quite warm running up a Phase Linear 700.  Today's amps would incinerate it in seconds.
I'm jealous! My furnace has been out of action for a week...could have used some heaters like that! New furnace coming tomorrow. That'll keep me off the o'scope market for a while  :'(
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~Ike Zimbel~
Wireless frequency coordination specialist and educator.
Manufacturer's Representative (Canada)
Radio Active Designs
Pro Audio equipment repair and upgrades.
~416-720-0887~
ca.linkedin.com/pub/ike-zimbel/48/aa1/266

Steve-White

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Re: USB Oscilloscope for Audio Work
« Reply #21 on: May 07, 2021, 01:38:03 pm »

I'm jealous! My furnace has been out of action for a week...could have used some heaters like that! New furnace coming tomorrow. That'll keep me off the o'scope market for a while  :'(

:)  That's something I need to do at my place in the next year or so - replace furnace/air handler simply because it's 25 yrs old now.

Yeah, these things should pump out plenty of heat.  Not sure where the resistors are used, but appear to be some kind of industrial application as they are referred to a "Braking Resistors".

Scope and Function Generator arrived.  Unpacked and put on the bench, fired 'em up last night to have a look at the screen.  Display doesn't have the contrast or sharpness I'm used to looking at on ancient Tektronics scopes of the past.  Not a problem, just an observation - footprint of the gear is fantastic as is the energy efficiency.  I do like the the full color display over the monochromatic stuff of the past.

Looks like some gear I'll be happy with for the duration.  Need to figure out how to setup the Function Generator for various modes, continuous sine wave output is simple to get going.  I ordered some 1/8" & 1/4" aluminum plate and a couple of 120V 120mm box fans.  As well a couple of large heat sinks.  I'm probably going to mount the load resistors up into a cheap blow molded SKB 4U road case for versatility in use and just overall packaging as well as functional airflow aspects.

First thing the Crown rep asked me was what power source I would be using.  He also said the amps could handle full RMS rated power output at 4 ohms for 2-3 minutes duration just fine.  Not sure at this point if I ever would want to do that - maybe for a short duration blast.  In which case it's going to take 240V supply.  Will probably end up doing amp testing in the main shop, use the welder plug and a generator extension cable for power when running the large racks up.  L14-30R twist lock for the welder plug in the shop, which is what I am going to use for the large racks anyway.
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Ike Zimbel

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Re: USB Oscilloscope for Audio Work
« Reply #22 on: May 07, 2021, 03:06:09 pm »

:)  That's something I need to do at my place in the next year or so - replace furnace/air handler simply because it's 25 yrs old now.

Yeah, these things should pump out plenty of heat.  Not sure where the resistors are used, but appear to be some kind of industrial application as they are referred to a "Braking Resistors".



Diesel-electric locomotives are often equipped with "dynamic braking". The actual propulsion in these units is via electric motors in the trucks (bogies, running gear) and when these are not providing traction (ie when the train is coasting, or decelerating) they effectively turn into generators. The current they generate can be routed to resistor grids, which provide a load, which provides dynamic braking to the wheels. And, yes, they have big fans to cool the resistor grids.
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~Ike Zimbel~
Wireless frequency coordination specialist and educator.
Manufacturer's Representative (Canada)
Radio Active Designs
Pro Audio equipment repair and upgrades.
~416-720-0887~
ca.linkedin.com/pub/ike-zimbel/48/aa1/266

Russell Ault

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Re: USB Oscilloscope for Audio Work
« Reply #23 on: May 07, 2021, 03:37:54 pm »

Diesel-electric locomotives are often equipped with "dynamic braking". The actual propulsion in these units is via electric motors in the trucks (bogies, running gear) and when these are not providing traction (ie when the train is coasting, or decelerating) they effectively turn into generators. The current they generate can be routed to resistor grids, which provide a load, which provides dynamic braking to the wheels. And, yes, they have big fans to cool the resistor grids.

It's not just locomotives; almost any electric motor can be effectively (and cheaply) braked using an electrical load (although, depending on how much momentum is involved, actually stopping using only dynamic braking can be a challenge). One close-to-home example is the auto-stop function when you release the handle on an electric lawnmower (which is often accomplished using nothing more complicated than a long piece of wire).

I would guess your resistors are designed for an application that falls in between these two extremes (probably, as you guessed, in an industrial automation setting).

(As a total aside, if your train is electrically powered you can use voltage converters instead of resistors to produce "regenerative braking", which effectively uses other trains as your train's braking load. Needless to say this represents a significant efficiency gain, especially on rapid transit systems where stopping is frequent, or on mountainous systems where a descending train can produce a decent portion of the electricity been consumed by an ascending train.)

-Russ
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Steve-White

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Re: USB Oscilloscope for Audio Work
« Reply #24 on: May 07, 2021, 05:17:12 pm »

^^^ Yeah it seems I've seen some of that as it applies to hybrid automobiles.  The coast down and braking recirculated to battery charging.

These resistors are built, very solid and large, but the wire size is right at what would be rated power in terms of core area or gauge size.  For the usage in my case is fine, just an observation.  I did the math, 250W RMS is 25A @ 100V RMS so each 8 ohm resistor will be carrying 12.5A RMS at rated power.  That's just for awareness, so I don't get any surprises.

I plan on milling the bottoms of the resistor cases flat and using thermal paste at the interface with 1/4" aluminum plate - with large heat sink on the other side.  May not be needed, I don't know yet.  But, when using the old Heathkit it got hot - I only held the amps full tilt for about 30 seconds and that will likely be a protocol that's followed today.  Probably  a bit longer duty cycle for burst testing.  Overbuild, and you only build once.  :)

I'm only interested in giving the amps a clean bill of health for field operation.  A basic checkup, gain, low power signal, high power signal, output RMS & burst and make sure the cooling system is operating as it should.

The resistors are intended for use in a similar environment to amp testing.  No huge voltage/current spikes as judged by the wire size on them.
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Steve-White

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Re: USB Oscilloscope for Audio Work
« Reply #25 on: May 07, 2021, 05:18:48 pm »

Diesel-electric locomotives are often equipped with "dynamic braking". The actual propulsion in these units is via electric motors in the trucks (bogies, running gear) and when these are not providing traction (ie when the train is coasting, or decelerating) they effectively turn into generators. The current they generate can be routed to resistor grids, which provide a load, which provides dynamic braking to the wheels. And, yes, they have big fans to cool the resistor grids.

I was thinking train braking when I looked at them.
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Re: USB Oscilloscope for Audio Work
« Reply #25 on: May 07, 2021, 05:18:48 pm »


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