Hello,
Is this a suitable scope to troubleshoot Wurlitzer amplifiers? Would a signal injector be required as well?
https://www.amazon.com/Oscilloscope-Persistence-Measurement-Bandwidth-Genera...
I have only done a few basic repairs and servicing, so am still a novice.
If it can be helpful, would appreciate early response; there is time constraint to ask a friend to assist with the purchase.
Many thanks 🙏
SHANKAR SINGH
Hard to say how good a square wave will look on it. I didn't look but does it have a square wave test output?
And yes, you need a signal generator that can put out a 1Khz square wave. If using a sine wave you may as well skip the generator and the scope. I made a short video to show how much distortion an amp can have without seeing it with a sine wave, then switch it to a square wave and the distortion jumps off the screen at you. If I can find that video I'll upload it to youtube and post a link. Square wave or nothing.
Oops, just noticed that it also has a signal generator in it. It's probably good for amp work which is about as basic as it gets. I've been thinking of getting a newer cheap one since all I use mine for is amps. The Techtronics is around 45 years old and the control pots are going bad.
If working on Cobra amps, you will need to input the signal after the oscillator. Just yesterday I found my misplaced worn out Cobra Cartridge that is soldered to an RCA jack. Rub my finger over the needle to make sure the oscillator circuit is working.
Tony
On 11/25/2023 6:56 AM, Shankar Singh via Jukebox-list wrote:
Hello,
Is this a suitable scope to troubleshoot Wurlitzer amplifiers? Would a signal injector be required as well?
https://www.amazon.com/Oscilloscope-Persistence-Measurement-Bandwidth-Genera...
I have only done a few basic repairs and servicing, so am still a novice.
If it can be helpful, would appreciate early response; there is time constraint to ask a friend to assist with the purchase.
Many thanks 🙏
SHANKAR SINGH _______________________________________________ Jukebox-list mailing list --jukebox-list@lists.netlojix.com To unsubscribe send an email tojukebox-list-leave@lists.netlojix.com %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s Searchable Archives:http://jukebox.markmail.org/
This scope appears similar to the JYE Tech offerings, of which I have the "DSO Shell." My tech friends laugh at me, but I thought it was cute, it was fun to put together, and I have found it reasonably useful. I haven't used it for amp servicing yet, though. I am not sure the one I have is suitable for tube amp usage due to the input voltage rating. I also have an old Sencore 60MHz CRT analog scope I can bring out if I feel like manipulating its weight; the JYETech "toy" gets used more...
I will point out that the scope you list doesn't have a real case, looks like it's 3 layers of pc boards kept together by stand offs. Part of the info on the page mentions "DIY oscilloscope kit" so there may be some assembly required on your part. The fact that it's battery operated and won't be referenced to ground is possibly a positive thing in my book, though.
Info says it "can withstand up to +/- 400V AC/DC voltage signal". I can't decide whether that's what can be displayed, or only what the protection circuit will keep from destroying the rest of the scope, though.
If similar to mine, it's just above the level of a toy, but enough to be useful. Do be sure to check out the prices of low end "real" digital scopes, I think they're in the $200-$300 range. Ask yourself if you'll be happy with the limitations, or wish you'd saved the money to apply to a more complete unit.
You might not be able to take certifiable measurements with it, but you can probably get a good picture of what's going on in your circuit.
Tony: I would love to see your video if you can find it!
--> Steve
On Sat, Nov 25, 2023 at 07:19:25AM -0500, Tony Miklos via Jukebox-list wrote:
Hard to say how good a square wave will look on it. I didn't look but does it have a square wave test output?
And yes, you need a signal generator that can put out a 1Khz square wave. If using a sine wave you may as well skip the generator and the scope. I made a short video to show how much distortion an amp can have without seeing it with a sine wave, then switch it to a square wave and the distortion jumps off the screen at you. If I can find that video I'll upload it to youtube and post a link. Square wave or nothing.
Oops, just noticed that it also has a signal generator in it. It's probably good for amp work which is about as basic as it gets. I've been thinking of getting a newer cheap one since all I use mine for is amps. The Techtronics is around 45 years old and the control pots are going bad.
If working on Cobra amps, you will need to input the signal after the oscillator. Just yesterday I found my misplaced worn out Cobra Cartridge that is soldered to an RCA jack. Rub my finger over the needle to make sure the oscillator circuit is working.
Tony
On 11/25/2023 6:56 AM, Shankar Singh via Jukebox-list wrote:
Hello,
Is this a suitable scope to troubleshoot Wurlitzer amplifiers? Would a signal injector be required as well?
https://www.amazon.com/Oscilloscope-Persistence-Measurement-Bandwidth-Genera...
I have only done a few basic repairs and servicing, so am still a novice.
If it can be helpful, would appreciate early response; there is time constraint to ask a friend to assist with the purchase.
Many thanks 🙏
SHANKAR SINGH _______________________________________________ Jukebox-list mailing list --jukebox-list@lists.netlojix.com To unsubscribe send an email tojukebox-list-leave@lists.netlojix.com %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s Searchable Archives:http://jukebox.markmail.org/
Jukebox-list mailing list -- jukebox-list@lists.netlojix.com To unsubscribe send an email to jukebox-list-leave@lists.netlojix.com %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s Searchable Archives: http://jukebox.markmail.org/
On 11/27/2023 6:55 PM, Steve Wahl wrote:
Tony: I would love to see your video if you can find it!
--> Steve
Square wave audio amplifier test vs a sine wave.
Tony,
Thanks for sharing.
What would have been some of the problems with the amplifier that caused the distorted square wave signal?
When you feed a small square wave at the input, what should you expect at the output? - about how much increase in amplitude? change in frequency? inverted?
With the Wurlitzer transistor and tube amplifiers, should speakers be connected at the output while injecting the square wave?
Would the test points to trace the square wave with an oscilloscope be the same as the ac test points in the amplifier schematic?
Many thanks
Shankar Singh
On Nov 28, 2023, at 09:16, Tony Miklos via Jukebox-list jukebox-list@lists.netlojix.com wrote:
On 11/27/2023 6:55 PM, Steve Wahl wrote:
Tony: I would love to see your video if you can find it!
--> Steve
Square wave audio amplifier test vs a sine wave.
https://www.youtube.com/shorts/etiVH11iyrk _______________________________________________ Jukebox-list mailing list -- jukebox-list@lists.netlojix.com To unsubscribe send an email to jukebox-list-leave@lists.netlojix.com %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s Searchable Archives: http://jukebox.markmail.org/
On Tue, Nov 28, 2023 at 08:16:28AM -0500, Tony Miklos wrote:
On 11/27/2023 6:55 PM, Steve Wahl wrote:
Tony: I would love to see your video if you can find it!
--> Steve
Square wave audio amplifier test vs a sine wave.
Ah, I think I get it.
The square wave has all the odd harmonics, so your 300Hz square is like simultaneously putting sine waves at 300, 900, 1500, 2100, 2700, 3300, ... (at decreasing amplitudes) through the amp.
So you're testing the amp over a wide range of frequencies at once, but also seeing if there's interferences / interactions between those frequencies within the amp.
Is that right?
--> Steve
On 11/28/23 08:47, Steve Wahl via Jukebox-list wrote:
Ah, I think I get it.
The square wave has all the odd harmonics, so your 300Hz square is like simultaneously putting sine waves at 300, 900, 1500, 2100, 2700, 3300, ... (at decreasing amplitudes) through the amp.
Correct. Don't expect the output to be perfect, especially if your amplifier has a magnetic RIAA equalized input. Tone controls will also affect it. Rounded corners show poor high-frequency response. Peaked leading edges show poor low-frequency response.
So you're testing the amp over a wide range of frequencies at once, but also seeing if there's interferences / interactions between those frequencies within the amp.
Is that right?
Yes, also any instabilities. In the case shown in the video there is leading edge ringing which shows a tendency to oscillate or unwanted resonance.
On 11/28/2023 11:47 AM, Steve Wahl wrote:
On Tue, Nov 28, 2023 at 08:16:28AM -0500, Tony Miklos wrote:
On 11/27/2023 6:55 PM, Steve Wahl wrote:
Tony: I would love to see your video if you can find it!
--> Steve
Square wave audio amplifier test vs a sine wave.
Ah, I think I get it.
The square wave has all the odd harmonics, so your 300Hz square is like simultaneously putting sine waves at 300, 900, 1500, 2100, 2700, 3300, ... (at decreasing amplitudes) through the amp.
So you're testing the amp over a wide range of frequencies at once, but also seeing if there's interferences / interactions between those frequencies within the amp.
Is that right?
--> Steve
No, the square wave input is a perfect square wave. The problems arise when you see the ringing (up AND down in the circuit/output. This is not to be confused with a single spike which is sometimes normal with the treble turned up to max. Maybe I'll try testing an amp before rebuilding it and get a good picture of a distorted signal. Even a good signal will show different looking output than the input do to the frequency response of the amp. I had later noticed that I had the input at 300hz instead of 1K. While trouble shooting I often turn the frequency down so it doesn't make my tinnitus a lot worse than normal. (I have the tinnitus all the time but a 1K square wave will make it really bad.) I have the speakers on 100 watt L pads to turn the volume either down all the way or just very quiet so I can make the speakers quiet while the volume of the amp is turned way up.
Tony
On Tue, Dec 12, 2023 at 06:55:39AM -0500, Tony Miklos via Jukebox-list wrote:
On 11/28/2023 11:47 AM, Steve Wahl wrote:
On Tue, Nov 28, 2023 at 08:16:28AM -0500, Tony Miklos wrote:
On 11/27/2023 6:55 PM, Steve Wahl wrote:
Tony: I would love to see your video if you can find it!
--> Steve
Square wave audio amplifier test vs a sine wave.
Ah, I think I get it.
The square wave has all the odd harmonics, so your 300Hz square is like simultaneously putting sine waves at 300, 900, 1500, 2100, 2700, 3300, ... (at decreasing amplitudes) through the amp.
So you're testing the amp over a wide range of frequencies at once, but also seeing if there's interferences / interactions between those frequencies within the amp.
Is that right?
--> Steve
No, the square wave input is a perfect square wave.
I think we're actually agreeing here.
I never took signals theory, but I've read about it and have played with square waves and filters, and adding sine waves together on synthesizers. Acording to theory, a square wave contains the fundamental plus all the odd harmonics. See for instance this wiki page:
https://en.wikipedia.org/wiki/Square_wave#Fourier_analysis
So, with a square wave, you would be exercising the amp's ability to operate over a wide range of frequencies simultaneously, at the fundamental frequency and all of the overtones present in the square wave. Any oddities (e.g. deficiencies in frequency response) will distort the resulting waveform, as you have said.
The problems arise when you see the ringing (up AND down in the circuit/output. This is not to be confused with a single spike which is sometimes normal with the treble turned up to max. Maybe I'll try testing an amp before rebuilding it and get a good picture of a distorted signal. Even a good signal will show different looking output than the input do to the frequency response of the amp. I had later noticed that I had the input at 300hz instead of 1K. While trouble shooting I often turn the frequency down so it doesn't make my tinnitus a lot worse than normal. (I have the tinnitus all the time but a 1K square wave will make it really bad.) I have the speakers on 100 watt L pads to turn the volume either down all the way or just very quiet so I can make the speakers quiet while the volume of the amp is turned way up.
I don't have diagnosed tinnitis, though maybe a light case of ringing that I can ignore when I'm not thinking about it. I have friends who do have it bad, and I don't envy any of you! Putting Lpads on your test speakers is a very smart thing to do, IMHO.
--> Steve
On 12/12/2023 6:50 PM, Steve Wahl via Jukebox-list wrote:
On Tue, Dec 12, 2023 at 06:55:39AM -0500, Tony Miklos via Jukebox-list wrote:
No, the square wave input is a perfect square wave.
I think we're actually agreeing here.
I never took signals theory, but I've read about it and have played with square waves and filters, and adding sine waves together on synthesizers. Acording to theory, a square wave contains the fundamental plus all the odd harmonics. See for instance this wiki page:
https://en.wikipedia.org/wiki/Square_wave#Fourier_analysis
So, with a square wave, you would be exercising the amp's ability to operate over a wide range of frequencies simultaneously, at the fundamental frequency and all of the overtones present in the square wave. Any oddities (e.g. deficiencies in frequency response) will distort the resulting waveform, as you have said.
Oh OK, that makes sense after giving it a little thought.
I don't have diagnosed tinnitis, though maybe a light case of ringing that I can ignore when I'm not thinking about it. I have friends who do have it bad, and I don't envy any of you! Putting Lpads on your test speakers is a very smart thing to do, IMHO.
--> Steve
Although I have tinnitus all the time, it is usually very mild in the morning and I seldom notice it. Later in the day it gets very noticeable. Things like chocolate can make it a lot worse, same for aspirin or other NSAIDS. (and of course a 1K square wave)
I've played around a little with the signal generator trying to match it to the tinnitus, it's up somewhere near 1Khz but different than a square wave and far from a sine wave. To me a triangle wave sounds almost the same as a square wave.
I was sort of stunned that it isn't always a high pitch with everyone. From what my wife tells me, hers is a "whooshing" sound. I sort of didn't believe hers is tinnitus but read up on it and found that it indeed isn't always a high pitch.
I don't know why my text keeps going a step larger than normal, I'm not fixing it here just to see if it comes through the list this way.
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