Keantoken, about the noise, you might be right... But the noise is typically caused by the components itself. To be honest, i don't know why symasym is that silent. It might be because of the balanced use of the 1st LTP output.
The thermal tracking is indeed done on its own by each channel, but as the outputdevices would also be warmed up by the heatsink, the differences should be minimal.
I typically program in C/C++, not in Java, my programs have to run realtime and as fast as possible.
I indeed have some plans for a simple distortion analyzer, a bit like spectralab.
Any recommendations about a lower priced dmm ? Would this mastech be a bad choice ? In fact, i mainly want to replace my 20 years old cheaper dmm...
Mike
The thermal tracking is indeed done on its own by each channel, but as the outputdevices would also be warmed up by the heatsink, the differences should be minimal.
I typically program in C/C++, not in Java, my programs have to run realtime and as fast as possible.
I indeed have some plans for a simple distortion analyzer, a bit like spectralab.
Any recommendations about a lower priced dmm ? Would this mastech be a bad choice ? In fact, i mainly want to replace my 20 years old cheaper dmm...
Mike
Hi Clem,
Take the switch apart and clean with 99% alcohol if you can. Nothing else.
Do yourself a favour and test your meter's AC response if you have the time. On each range. This is really easily done on a Fluke 5500A (or better) calibrator. An audio oscillator and a 'scope will do in a pinch, or another known good meter such as an HP 34401A
-Chris
Take the switch apart and clean with 99% alcohol if you can. Nothing else.
Do yourself a favour and test your meter's AC response if you have the time. On each range. This is really easily done on a Fluke 5500A (or better) calibrator. An audio oscillator and a 'scope will do in a pinch, or another known good meter such as an HP 34401A
-Chris
Hi Chris, (MikeB, some inputs for your Mastech)
Thanks for the inputs. Actually I already cleaned out the selector contacts some time ago. Fixed it for a few months, then it's back. If you look at the contact patterns, there are scratches and pits near the edges, so I guess there really isn't much that can be done anymore (well, I could give it another cleaning of course).
Oh, I forgot - the other problem that I found with it, conductive pattern migration. The selector's pads are soooo close to each other that sometimes the wiper contact just drags this really thin filament of material, shorting pads together... You know when this happens because the digits on the display show funn (i.e. two decimal points turned on)...
AC Freq test - well, it's an everyday meter, something I use only for fixing electrical stuff (60Hz) / simple electronics. I know its limits - I have the HP bench unit when it comes to servicing amps and other "nice" things, remember?
Cheers
Clem
edit: oops - one other thing about the Mastech unit I have- the "battery low" indicator comes on LATE. If you find yourself reading consistently higher than normal voltages, it's time to replace the battery (9V), even if the meter isn't saying the battery is weak...
Thanks for the inputs. Actually I already cleaned out the selector contacts some time ago. Fixed it for a few months, then it's back. If you look at the contact patterns, there are scratches and pits near the edges, so I guess there really isn't much that can be done anymore (well, I could give it another cleaning of course).
Oh, I forgot - the other problem that I found with it, conductive pattern migration. The selector's pads are soooo close to each other that sometimes the wiper contact just drags this really thin filament of material, shorting pads together... You know when this happens because the digits on the display show funn (i.e. two decimal points turned on)...
AC Freq test - well, it's an everyday meter, something I use only for fixing electrical stuff (60Hz) / simple electronics. I know its limits - I have the HP bench unit when it comes to servicing amps and other "nice" things, remember?
Cheers
Clem
edit: oops - one other thing about the Mastech unit I have- the "battery low" indicator comes on LATE. If you find yourself reading consistently higher than normal voltages, it's time to replace the battery (9V), even if the meter isn't saying the battery is weak...
Hi Clem,
Sorry.
Scrubbing with the alcohol will remove the tracking. That's a terminal fault though because the material is disappearing from where it belongs, as you've noticed.
I just wanted to make a point about AC accuracy on a low cost meter. I wanted someone else to do my dirty work.
Now we are seriously OT. Mike's amps await!
-Chris
Nope, I forgot.I have the HP bench unit when it comes to servicing amps and other "nice" things, remember?
Sorry.Scrubbing with the alcohol will remove the tracking. That's a terminal fault though because the material is disappearing from where it belongs, as you've noticed.
I just wanted to make a point about AC accuracy on a low cost meter. I wanted someone else to do my dirty work.
Now we are seriously OT. Mike's amps await!
-Chris
roender said:
Okay, i have my new dmm...
Just made hfe readings of the outputdevices: (50ma bias)
left channel: 24%
MJL0281: 98
MJL0302: 79
right channel: 10%
MJL0281: 86
MJL0302: 95
I did not match these resistors, they are rated 5%. (according to measure inboard they are matched < 1%)
By swapping transistors i would get 9% to 3%.
I think, not too bad for just taking the devices out of their bag...
Mike
MikeB said:
Yes Mike, mje15030/15031 drivers are from stoneage.
I just have mesured hfe in real life (in symasym, see attached photo) for 5 peers of this drivers and 3 peers of mje15034/35.
This is what i found:
hfe(15030): 134, 139, 99, 122, 132. Production date (PD): w27 y06
hfe(15031): 237, 220, 245, 310, 229. PD: w33 y06
Now, take a look at this:
hfe(15034): 185, 185, 189. PD: w28 y06
hfe(15035): 200, 204, 202. PD: w34 y06
All mesurements was made at Ic=71mA, R26 = 15ohm
If you look at ONsemy specs for mje15030/31, you will see that DC gain is linear only after Ic >= 200mA at 25grdC. Also, dc gain is linear at higher temperature.
Maybe it is a good ideea to increase drivers temperature by increasing bias current at 70mA for mje15030/31 (R26=15ohm).
This is not a problem for mje15034/35. This drivers have linear dc gain starting from 10mA to 1A at 25 to 150grdC.
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Yes, it's "nice" that onsemi improved their manufacturing, resulting in devices having hfe-variations of only ~6% in the same batch.
I have mje15030/31 each within one batch.
All mje15030 measure hfe = ~90. (+/- 2%) Batch: CQ502
All mje15031 measure hfe = ~250. (+/- 6%) Batch: CQ501
How am i supposed to match these ?
Gladly, i had an older batch where hfe's were all around...
It's nice to see that mje15034/35 are at least within 10%.
My MJLs were from identical batch (npn/pnp)
Mike
I have mje15030/31 each within one batch.
All mje15030 measure hfe = ~90. (+/- 2%) Batch: CQ502
All mje15031 measure hfe = ~250. (+/- 6%) Batch: CQ501
How am i supposed to match these ?
Gladly, i had an older batch where hfe's were all around...
It's nice to see that mje15034/35 are at least within 10%.
My MJLs were from identical batch (npn/pnp)
Mike
Devilish devices (666). 
Not the most linear drivers, the same money buys 20 watt flat liners with twice as high Ft.
Average hFe difference at different Vce and Ic levels is wicked good. With a small difference of the average hFe between npn and pnp, finding a pair with comparable hFe doesn't require a large selection quantity.
Not the most linear drivers, the same money buys 20 watt flat liners with twice as high Ft.
Average hFe difference at different Vce and Ic levels is wicked good. With a small difference of the average hFe between npn and pnp, finding a pair with comparable hFe doesn't require a large selection quantity.
Mike,
I have an idea. I don't know how much it pertains to the Hfe war, but I will post it nonetheless.
I was thinking that you could put a resistor on the left side of the output LTP (if you know what I mean), say a trimmer POT, and adjust it until the output is closest to 0 when there is no input. I acknowledge that some people would not like the idea of purposely imbalancing an LTP, but I was just wondering if this will cause more problems than it solves. It may be a 'cheap' solution, but who cares about cheap if it works well?
BTW, since my input is distorted in LTSpice, couldn't I plot output/input on the FFT to get a better distortion idea?
I have an idea. I don't know how much it pertains to the Hfe war, but I will post it nonetheless.
I was thinking that you could put a resistor on the left side of the output LTP (if you know what I mean), say a trimmer POT, and adjust it until the output is closest to 0 when there is no input. I acknowledge that some people would not like the idea of purposely imbalancing an LTP, but I was just wondering if this will cause more problems than it solves. It may be a 'cheap' solution, but who cares about cheap if it works well?
BTW, since my input is distorted in LTSpice, couldn't I plot output/input on the FFT to get a better distortion idea?
To be honest, i don't know what you mean...
But, as i said earlier, i do not like the idea of using an extra unbalance to compensate another.
As to the hfe-war, the problem with unmatched drivers is that as this amp is ClassAB, the outputdevices beeing open (while the other closes) they put different loads to the vas, creating half-waves distortions.
I attached the currents delivered by the outputdevices to give you an understanding of halfwaves.
Mike
But, as i said earlier, i do not like the idea of using an extra unbalance to compensate another.
As to the hfe-war, the problem with unmatched drivers is that as this amp is ClassAB, the outputdevices beeing open (while the other closes) they put different loads to the vas, creating half-waves distortions.
I attached the currents delivered by the outputdevices to give you an understanding of halfwaves.
Mike
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You just answered a question I was wondering for a long time, Mike!
Now I know that each transistor outputs a 'rectified' version of the input. I didn't know if each transistor was supposed to be open or if one was supposed to be closed while the other one open. Now I know. BTW, does this mean that one transistor acts as a CCS while the other one amplifies?
I was talking about this:
Now I know that each transistor outputs a 'rectified' version of the input. I didn't know if each transistor was supposed to be open or if one was supposed to be closed while the other one open. Now I know. BTW, does this mean that one transistor acts as a CCS while the other one amplifies?
I was talking about this:
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This balancing resistor will only reduce the thermal load to the above upper transistor, and stop functionality of amp when supply voltage drops.
Yes, each transistor outputs a 'rectified' version of the input, while the one is open, the other one is simply dead, doing nothing. Only in a ClassA amp both devices are working simultaneously.
Mike
Yes, each transistor outputs a 'rectified' version of the input, while the one is open, the other one is simply dead, doing nothing. Only in a ClassA amp both devices are working simultaneously.
Mike
Finally... I know the difference between operating mode of a transistor and the operating mode of an amplifier!
Could someone give me a copy of their LTSpice SymAsym file?
I have attached a graph of the output for my am running at 5mV input. Are the bumps on the off cycle of the blue trace parasitic oscillations? Also, The bumps at the ends of the waves are different than the ones on your pic. Are these bumps a result of the capacitors between the output pairs and drivers? I am using MJL0281a/0302a for outputs and MJE15034/35 as drivers.
Could someone give me a copy of their LTSpice SymAsym file?
I have attached a graph of the output for my am running at 5mV input. Are the bumps on the off cycle of the blue trace parasitic oscillations? Also, The bumps at the ends of the waves are different than the ones on your pic. Are these bumps a result of the capacitors between the output pairs and drivers? I am using MJL0281a/0302a for outputs and MJE15034/35 as drivers.
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