Another awesome video! I know it’s an old one but I haven’t seen it in a while. I and I’m sure plenty others would love somebody like you to do an oscilloscope video. I have that Siglent you’re talking about and I think it’s great but I hardly know how to use it lol. I’m trying to learn in my spare time. I have had an interest in electronics since I was a kid. It started when I took the back off my black and white tv and took the speaker output and put it into the input of my stereo. I was probably 11 or 13 years old when I thought I invented surround sound and nothing blew up! But anyway it would really be great if you could do that because you explain stuff very good and speak right at my level. Thanks Tony!! I actually asked you this on a different video and forgot to check my notifications before I asked this. If you answered I apologize for asking again.
For us mere mortals, us non-Electronics Engineers, what is the purpose of this video? I've built a few dummy loads in the past for my tube amps. I am currently in the process of upgrading those dummy loads to reactive loads that more closely mimic the dynamic resistance of a real speaker moving real air. How do you apply this circuitry ... this device in creating resistive load boxes or in testing the output of tube amps?
Grate video! Just a simple question:- did the 100W dummy load distorted the sin wave of 150W or 200W and leads to wrong early clipping on the oscilloscope ?
Very well done. I never thought of incorporating the x10 (10:1) part in the load itself. I have actually built your voltage divider network and tested it on my crude 8 ohm load, and, so far, works great. Can I ask what was your reason for the choice of values (mainly the 8k2 resistor as this seems an odd value)? Is it for keeping a fairly high input impedance to the scope?
Wow, I was thinking to build a load from 2x200w per resistor, but this is a big step up, mostly I repair normal receivers with max power output from 25 to 30w RMS bigger amps, that's for higher classified technicians. Because my budget is not that big. I'm glad I can build stuff for myself for monitoring gear.
Thanks for the detailed video, i was looking exactly that because I was looking to safely measure the outputs of my amps and to troubleshoot a couple of issues they have Do you sell the boards for the dummy loads? Thanks a lot again and Happy holidays
Since the oscilloscopes became relatively cheap it started to be fun with measurements for everyone. But few have knowledge weather picture and circuitry show something useful. that they were looking for. .
Very nice... For my own curiosity (still learning)-- why not just use a 9M resistor in series with the output to the scope and a trimmer cap across that? Wouldn't that be exactly the same as a 10:1 probe? The 9M forming a 10:1 voltage divider with the 1M scope input.
I wanted to respond to Charlie’s post about a monitor speaker. I have been repairing high power amplifiers for many years and have used a trick for monitoring them on the bench, especially when I have to run them into dummy loads for a while. I use a 70V speaker transformer between the amp under test and my monitor speaker(s), along with the dummy loads.The transformer allows you to drop the level to the speaker(s) by a great margin, even when the amp is putting out hundreds of watts into the dummy load(s). The idea behind it is that if you were to use the 1 watt tap on the transformer, for instance, with an 8 ohm speaker connected to the secondary of the transformer, the primary impedance of the transformer would reflect 5000 ohms and as such would not change the load on the amplifier significantly. Also, at that tap, if the output voltage of the amp across the dummy loads was 70V, there would only be 1 watt of audio power presented to the monitor speaker. If you used the 1/2 watt tap, you would have 1/2 watt at the speaker, and the primary impedance of the transformer would be 10,000 ohms. BTW, 70V RMS at the output of the amplifier would represent 612.5 watts into 8 ohms. At lower output powers, you could use higher wattage taps on the transformer to obtain a comfortable listening level. Maybe Tony could do a video outlining the principles involved. Incidentally, 10 watt 70V transformers are really cheap. You can also get 5 watt transformers, and of course, higher power rated transformers. The only thing to watch out for is that the cheap transformers are quite reactive, especially at low frequencies, and will reflect a much lower impedance to the amp than expected. There are 70 V transformers that are rated for the full audio bandwidth, but they are, of course, more expensive. Also, if desired, you could still use a volume control between the transformer secondary and the speaker for fine volume adjustment. Hope this helps.
Regarding bridged amplifier testing, even if you only test one channel at a time, the scope ground connection will still short one amp channel to ground. One method would be to use both channels of the scope with only the test probe tips connected to the speaker terminals, and the ground of the scope tied to the amp chassis. Then invert one channel of the scope and use the add function. Of course, if you have a true differential probe, that the best way.
Been following the dummy load iterations.....I would like to see a volume pot and a monitor speaker so you could hear a little audio while hooked to the dummy load....keep up the interesting videos...
Nice piece of work. One concern I have is your use of the pot and the series resistor. Both would have a different thermal characteristic which could through your alignment out of wack as the resistor and pot change temperature. I would have scraped the series resistor in favor of using the pot alone to set up the 10:1 ratio, using the center tap to go to the scope probe. As the thermal resistance changes with temperature, the ratio would remain the same across both sides of the pot.
Nice build. I have a suggestion for the 3.1 version. Instead of using a 2 resistor voltage divider, with minor modifications in the existing circuit, you can use 3 resistors so that the ground lead of the scope will be somewhat "isolated" from the AMP's "ground" and still make a 10 to 1 divider. This would be handy for those rare beasts that do not share the earth connection between channels.
Another awesome video! I know it’s an old one but I haven’t seen it in a while. I and I’m sure plenty others would love somebody like you to do an oscilloscope video. I have that Siglent you’re talking about and I think it’s great but I hardly know how to use it lol. I’m trying to learn in my spare time. I have had an interest in electronics since I was a kid. It started when I took the back off my black and white tv and took the speaker output and put it into the input of my stereo. I was probably 11 or 13 years old when I thought I invented surround sound and nothing blew up! But anyway it would really be great if you could do that because you explain stuff very good and speak right at my level. Thanks Tony!! I actually asked you this on a different video and forgot to check my notifications before I asked this. If you answered I apologize for asking again.
For us mere mortals, us non-Electronics Engineers, what is the purpose of this video? I've built a few dummy loads in the past for my tube amps. I am currently in the process of upgrading those dummy loads to reactive loads that more closely mimic the dynamic resistance of a real speaker moving real air. How do you apply this circuitry ... this device in creating resistive load boxes or in testing the output of tube amps?
Thank you for this Video. Do you have a template to build the circuit board?
Grate video! Just a simple question:- did the 100W dummy load distorted the sin wave of 150W or 200W and leads to wrong early clipping on the oscilloscope ?
Very well done. I never thought of incorporating the x10 (10:1) part in the load itself. I have actually built your voltage divider network and tested it on my crude 8 ohm load, and, so far, works great. Can I ask what was your reason for the choice of values (mainly the 8k2 resistor as this seems an odd value)? Is it for keeping a fairly high input impedance to the scope?
Great. Now I have to spend the next six months trying to program my scope. 🙃😛
Great !!! Thank you very much, you explained very well!
Wow, I was thinking to build a load from 2x200w per resistor, but this is a big step up, mostly I repair normal receivers with max power output from 25 to 30w RMS bigger amps, that's for higher classified technicians. Because my budget is not that big. I'm glad I can build stuff for myself for monitoring gear.
Thanks for the detailed video, i was looking exactly that because I was looking to safely measure the outputs of my amps and to troubleshoot a couple of issues they have Do you sell the boards for the dummy loads? Thanks a lot again and Happy holidays
Thanks for the video. I have 2 dummy loads of 4.2 and 8.4 ohms, can I use for load testing of 4 and 8 Ohms? What's the maximum tolerance? Thanks.
Since the oscilloscopes became relatively cheap it started to be fun with measurements for everyone. But few have knowledge weather picture and circuitry show something useful. that they were looking for. .
great to learn from you.
Very nice... For my own curiosity (still learning)-- why not just use a 9M resistor in series with the output to the scope and a trimmer cap across that? Wouldn't that be exactly the same as a 10:1 probe? The 9M forming a 10:1 voltage divider with the 1M scope input.
I wanted to respond to Charlie’s post about a monitor speaker. I have been repairing high power amplifiers for many years and have used a trick for monitoring them on the bench, especially when I have to run them into dummy loads for a while. I use a 70V speaker transformer between the amp under test and my monitor speaker(s), along with the dummy loads.The transformer allows you to drop the level to the speaker(s) by a great margin, even when the amp is putting out hundreds of watts into the dummy load(s). The idea behind it is that if you were to use the 1 watt tap on the transformer, for instance, with an 8 ohm speaker connected to the secondary of the transformer, the primary impedance of the transformer would reflect 5000 ohms and as such would not change the load on the amplifier significantly. Also, at that tap, if the output voltage of the amp across the dummy loads was 70V, there would only be 1 watt of audio power presented to the monitor speaker. If you used the 1/2 watt tap, you would have 1/2 watt at the speaker, and the primary impedance of the transformer would be 10,000 ohms. BTW, 70V RMS at the output of the amplifier would represent 612.5 watts into 8 ohms. At lower output powers, you could use higher wattage taps on the transformer to obtain a comfortable listening level. Maybe Tony could do a video outlining the principles involved. Incidentally, 10 watt 70V transformers are really cheap. You can also get 5 watt transformers, and of course, higher power rated transformers. The only thing to watch out for is that the cheap transformers are quite reactive, especially at low frequencies, and will reflect a much lower impedance to the amp than expected. There are 70 V transformers that are rated for the full audio bandwidth, but they are, of course, more expensive. Also, if desired, you could still use a volume control between the transformer secondary and the speaker for fine volume adjustment. Hope this helps.
Regarding bridged amplifier testing, even if you only test one channel at a time, the scope ground connection will still short one amp channel to ground. One method would be to use both channels of the scope with only the test probe tips connected to the speaker terminals, and the ground of the scope tied to the amp chassis. Then invert one channel of the scope and use the add function. Of course, if you have a true differential probe, that the best way.
Been following the dummy load iterations.....I would like to see a volume pot and a monitor speaker so you could hear a little audio while hooked to the dummy load....keep up the interesting videos...
Nice piece of work. One concern I have is your use of the pot and the series resistor. Both would have a different thermal characteristic which could through your alignment out of wack as the resistor and pot change temperature. I would have scraped the series resistor in favor of using the pot alone to set up the 10:1 ratio, using the center tap to go to the scope probe. As the thermal resistance changes with temperature, the ratio would remain the same across both sides of the pot.
Nice build. I have a suggestion for the 3.1 version. Instead of using a 2 resistor voltage divider, with minor modifications in the existing circuit, you can use 3 resistors so that the ground lead of the scope will be somewhat "isolated" from the AMP's "ground" and still make a 10 to 1 divider. This would be handy for those rare beasts that do not share the earth connection between channels.
Wow, thanks for taking the time to explain setting up the watts math, I will definitely be setting it up on my scope.
How do you plan to accommodate bridged output amplifiers?