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reduce power to reduce heat from UPC1342V kit
reduce power to reduce heat from UPC1342V kit
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Old 24th November 2020, 05:40 PM   #31
zergxia is offline zergxia  China
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Location: SiChuan
There may be "the lowest available gain of upc1342" in the manual
It may not work properly at 11x magnification. Friends, you have to be careful.

I think the 12-22pf capacitor is suitable. It can adjust SR according to specific needs. There may be these contents in the manual. Maybe you can try more complicated compensation methods, such as double pole compensation.
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Old 24th November 2020, 06:09 PM   #32
kozard is offline kozard
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Join Date: Mar 2012
Quote:
Originally Posted by zergxia View Post
There may be "the lowest available gain of upc1342" in the manual
It may not work properly at 11x magnification. Friends, you have to be careful.

I think the 12-22pf capacitor is suitable. It can adjust SR according to specific needs. There may be these contents in the manual. Maybe you can try more complicated compensation methods, such as double pole compensation.

I will look at the datasheet again. I asked the question because I am concerned that it might not be stable if I lower it. I was hoping someone else had lowered the gain successfully. If not I might need to leave it alone.
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Old 24th November 2020, 06:48 PM   #33
kozard is offline kozard
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Join Date: Mar 2012
Quote:
Originally Posted by zergxia View Post
There may be "the lowest available gain of upc1342" in the manual
It may not work properly at 11x magnification. Friends, you have to be careful.

I think the 12-22pf capacitor is suitable. It can adjust SR according to specific needs. There may be these contents in the manual. Maybe you can try more complicated compensation methods, such as double pole compensation.
Unfortunately the datasheet I have does not give information on compensation or gain options.

Perhaps I will try all my other experiments first and leave the gain and compensation as a last experiment. (With a DBT and small fast fuse.)

I have adjusted the gain of amplifiers like the MX50SE successfully but this driver IC is a little bit more of a black box. I have attached the equivalent circuit. The compensation capacitor is connected to pins 6 and 7.
Attached Images
File Type: png Equivalent Circuit.png (37.7 KB, 31 views)
File Type: png Datasheet Page 1.png (173.2 KB, 31 views)
File Type: png Datasheet Page 2.png (133.8 KB, 30 views)
File Type: png Datasheet Page 3.png (74.0 KB, 29 views)
File Type: png Datasheet Page 4.png (86.7 KB, 31 views)
File Type: png Datasheet Page 5.png (85.1 KB, 11 views)
File Type: png Datasheet Page 6.png (76.4 KB, 8 views)
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Old 25th November 2020, 01:35 AM   #34
zergxia is offline zergxia  China
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Unfortunately, there is nothing in the manual that we need.
The capacitors between pins 6 to 7 are Maitreya capacitors. Refer to LM4702, LME49810 and other similar ICs, and their value may be between 10-25pf. When the gain is 30 times, we can try to input a 20kHz square wave, and then gradually reduce the 15pf capacitor. If the rising edge of the square wave begins to overshoot, the capacitance value at this time is the smallest usable value. For safety, we can appropriately increase the minimum usable value of the Maitreya capacitor in actual use.

The manual does not provide the minimum usable gain or open-loop phase frequency diagram. But refer to the typical examples in the manual, and the situation of similar ICs such as LM4702 and LME49810. Similarly, we can gradually reduce the gain and observe whether the amplifier oscillates, and then leave a proper safe space. I think using 30x magnification is safe and applicable.

The smaller the resistance, the lower the noise. If you use a magnification of about 30 times, I suggest using 500R and 14k resistors. At the same time, you must also adjust the value of the coupling capacitor and the negative feedback capacitor. Capacitors are not expensive, and it is not difficult for modern audio sources to drive 10k resistance loads, so I think these costs are worthwhile.

After all the above are done, we can try to add more complicated compensation methods such as double pole compensation to further reduce the distortion.

Looking forward to your good news.:p
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Old 25th November 2020, 02:01 AM   #35
kozard is offline kozard
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The input low pass filter and the compensation capacitors appear to be tiny ceramic capacitors. I don't know the manufacturer, dielectric type or rated voltage. (Picture enclosed.) Hopefully they are NP0 but I don't know what the board was built with.

Does anyone have any comments on suitable types of capacitors for both purposes?

I was thinking of putting a small (10-15 pF) cap across the 56k feedback resistor and/or increasing the compensation capacitor prior to experimenting with reducing the gain.


In the future I would like to add a real oscilloscope to my bench. Right now I have a couple (slow) home made oscilloscopes (STM and Arduino based) and the common DSO138.
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File Type: jpg LPF and Compensation Capacitors.jpg (393.9 KB, 14 views)
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Old 25th November 2020, 02:22 AM   #36
bansuri is offline bansuri  Italy
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Quote:
Originally Posted by kozard View Post
Unfortunately the datasheet I have does not give information on compensation or gain options.
Well it gives the recommended value from 26 to 30dB.
I wouldn't go above 3k
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Old 25th November 2020, 02:38 AM   #37
kozard is offline kozard
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Yes, the reason I am asking is because I am concerned that it will become unstable.

Perhaps I will only go as far as 26 dB and see what difference that makes. From there perhaps I will increase the compensation cap and/or try a small cap across the feedback resistor to see if that helps at all. Perhaps that will be the limit for this board until I have more suitable equipment.

Right now I am listening to how the changes affect impulsive percussion sounds like splash cymbals. When I get a better scope at home I can look at 20 kHz square waves.


Perhaps I can make use of REW to make quantitative evaluations of the changes?
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Old 25th November 2020, 02:43 AM   #38
zergxia is offline zergxia  China
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Oscilloscopes are essential, and there are many options on the second-hand market. The year before last, I bought RIGOL's dual-channel digital oscilloscope for $70, and the bandwidth was upgraded to 100MHz after cracking. It is very affordable.
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Old 25th November 2020, 03:03 AM   #39
kozard is offline kozard
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I agree oscilloscopes are essential. I just don't have a "real" one at home yet.


Which RIGOL model is that affordable?
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Old 20th December 2020, 06:28 PM   #40
kozard is offline kozard
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I have attached a photo of my uPC1342V where I used an external rectifier and filter board to make sure that the rectifier and noise/interference from the rectification of the large signal AC power would not be a problem (so close to the input components/stage).

I did my first distortion measurements up to 8Vrms into a 4Ohm test load. The load is getting pretty hot so I might get a larger one before going higher.

I would appreciate expert comments and interpretation of the distortion measurements. (Keeping in mind it is a 4Ohm load not 8Ohm, and keeping in mind that I only went up to 8Vrms.)
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