I have a STK4141-II based receiver that I've been tweaking. It's now a power-amp only. Thanks to advice from this forum (thanks!), I recently uprated the smoothing caps (tripled). Wow!
The amp seems to run from 26-0-26 (the app note for the chip recommends up to 32v). I can get old 12v Lead Acid batts for free. So, I was thinking about four batts in two banks: '+'24V--0--'-'24V.
Then I read about offset problems that might occur if the battery banks are not equally charged, or if one bank depletes more rapidly than the other.
Can anyone comment on this?
The amp seems to run from 26-0-26 (the app note for the chip recommends up to 32v). I can get old 12v Lead Acid batts for free. So, I was thinking about four batts in two banks: '+'24V--0--'-'24V.
Then I read about offset problems that might occur if the battery banks are not equally charged, or if one bank depletes more rapidly than the other.
Can anyone comment on this?
Safety first ! If using lead acid batteries ensure they are fused at the terminals. Never underestimate the amount of current that can flow.
Any normal DC coupled configuration of opamp (the STK's are really just power opamps) is unaffected by unequal rails. The output zero point is determined by the ground referenced inputs and internal offset imbalances... nothing to do with the rails.
Any normal DC coupled configuration of opamp (the STK's are really just power opamps) is unaffected by unequal rails. The output zero point is determined by the ground referenced inputs and internal offset imbalances... nothing to do with the rails.
Mooly,
Thanks. Yes, fuses at the batt end! Good reminder.
Analog_sa,
I'd read that different batteries have different noise levels, so it makes sense that old will sound different to new. Fortunately, I have a good choice of batts, some better than others.
Sakis,
You might be right, but the STK (which I found on the street) is the best I can afford at the moment. Besides, I enjoy turning 'junk' into something useful.
Thanks. Yes, fuses at the batt end! Good reminder.
Analog_sa,
I'd read that different batteries have different noise levels, so it makes sense that old will sound different to new. Fortunately, I have a good choice of batts, some better than others.
Sakis,
You might be right, but the STK (which I found on the street) is the best I can afford at the moment. Besides, I enjoy turning 'junk' into something useful.
Zoodle said:
..... hmmm yes you must be right stk is junk !!! but then the good thing is that you might get something out of it by learning the benefits of the batery issue or by simpli working arround in this circuit ....
carry on .... let us know about ""before and after"""
keep an eye on the "dynamics" play demanding things to be able to see the diference
try to notice the briliance of the high
let us know
Re: may be it has a point
You are probably right, the STKs i've heard did not sound too good. There is at least one diyaudio member who really liked some of the STKs though and he seemed to know what he was talking about
http://www.diyaudio.com/forums/showthread.php?postid=29669#post29669
sakis said:
You are probably right, the STKs i've heard did not sound too good. There is at least one diyaudio member who really liked some of the STKs though and he seemed to know what he was talking about
http://www.diyaudio.com/forums/showthread.php?postid=29669#post29669
If your worried about offset issues just try it, with no speakers connected and say 24-0-12 or 12-0-24 and measure.Untill one or other rail drops below a value that causes internal constant current sources and voltage references to function correctly, the STK will "behave" as a normal op amp.
Lead acid batteries won't give much imbalance anyway. Fully charged say 12.5volts on load, totally discharged say 11volts. It's a non issue.
Lead acid batteries won't give much imbalance anyway. Fully charged say 12.5volts on load, totally discharged say 11volts. It's a non issue.
hipanni said:
i have nothing to say against what you wrote
proper protect is a n outside thing and there is no point talking about here
cheap yes available yes ...any country yes ....very easy design double yes pcb also triple yes !!!!
but the diference from a descrete amp tha will play 1000 times better and is going to be more of an excersize more dofocult to design and make pcb
but it will play alot better than any stk ....and if the bias is too litle you can crunk it up any time you like ...and so on and on and on
Watch that chip, Sanyo stopped production a decade ago and the only replacements are fake, as most chips in my country are today. I have two 12-year old STK4191s still in active service and though they're tough chips, the sonics are terrible. Good enough for cheap compact stereo, but I agree that a proper discrete circuit will be way better, or even a more modern chip like the LM3886.
24/0/24 would be fine for the 4141, these chips are essentially discrete amplifiers (hybrid construction, so they use actual semiconductor dies inside the package). They are openable and repairable, though a very hot iron is required. I remember someone here used to do that, and mentioned that the substrate sucked up heat very fast.
As for asymmetric rails, difficult to tell. The STKs expose some of the current mirror stages to external components, and the bootstrap as well. There are quite a few resistors that hang off the pins apart from the usual input/output/mute, and those have internal connections to the input and output stages. I don't really know if it'll cause an issue, and I'm not too keen to experiment as I only have these last two chips (and a project they need to go into).
You'll have to try it on a dummy load or open circuit (STKs have no problem with open circuit).
24/0/24 would be fine for the 4141, these chips are essentially discrete amplifiers (hybrid construction, so they use actual semiconductor dies inside the package). They are openable and repairable, though a very hot iron is required. I remember someone here used to do that, and mentioned that the substrate sucked up heat very fast.
As for asymmetric rails, difficult to tell. The STKs expose some of the current mirror stages to external components, and the bootstrap as well. There are quite a few resistors that hang off the pins apart from the usual input/output/mute, and those have internal connections to the input and output stages. I don't really know if it'll cause an issue, and I'm not too keen to experiment as I only have these last two chips (and a project they need to go into).
You'll have to try it on a dummy load or open circuit (STKs have no problem with open circuit).
Hi sakis,
yes your thought is 100% right . But during experiment other ic is not use because it's circuit is veri sensitive in small variation ic failiur. But stk series ic stands while small variation. Me also use stk ic past 5 years i done experiment using tone control with stk ic. To still its working. But other ic's not stand.please reply me .
BY
kannan
yes your thought is 100% right . But during experiment other ic is not use because it's circuit is veri sensitive in small variation ic failiur. But stk series ic stands while small variation. Me also use stk ic past 5 years i done experiment using tone control with stk ic. To still its working. But other ic's not stand.please reply me .
BY
kannan
Hi Sangram. I was hoping you would post.
I might postpone the battery experiment, despite Mooly's reassurance; although my STK cost me $0, I can't afford to replace it at the moment.
Instead, I'll move the transformer into a separate case (an old ATX P/S case). The transformer is currently positioned directly beneath the amp board, which can't be ideal.
BTW
Should I be adding 'bypass caps' across my smoothing caps? If yes, what type should I be looking for? I recently added extra capacitance -- some old "6800"mF caps added to the existing "3800"s (the aggregate measures just over 9,000mF each side). I've read that you're supposed to 'bypass' them. I admit I don't really understand it. Again, my priority is safety of the chip.
Contentious, the 'snubber' theory is. But I kind of just add them in, I don't see any harm and they cost nothing. It's more important to add some bypass at the chips. The STK reference PCBs don't have any bypassing closer than 4 inches near the pins, and the pinout means it's not possible to get too close, specially to the negative pins, but I manage a few caps an inch away or so. Not optimal, but helps a lot.
For the 'snubbers' I use 100nF ceramics, or 33nF polyester caps with a 1 ohm, 1 watt metal film resistor. For chip bypass it's usually a 10uF Panasonic FC, or a 100uF FM, and a 100nF X7R ceramic SMD soldered directly on the power pins.
All the 'snubber'/bypass do is reduce the inductance of the large caps, or the PCB tracks bringing in the supply respectively. this is supposed to improve HF performance but in truth I haven't been able to spot much difference wit or without them.
Don't worry about your chips, mine have proved that one can abuse the STKs and get away with it. I have had mine oscillating due to poor layout, and have run them bridged into 4 ohm loads, an impossible task for most amps. Now I respect their age, and they only do light and occasional duty, till my active line arrays get going with them performing most of the heavy lifting...
For the 'snubbers' I use 100nF ceramics, or 33nF polyester caps with a 1 ohm, 1 watt metal film resistor. For chip bypass it's usually a 10uF Panasonic FC, or a 100uF FM, and a 100nF X7R ceramic SMD soldered directly on the power pins.
All the 'snubber'/bypass do is reduce the inductance of the large caps, or the PCB tracks bringing in the supply respectively. this is supposed to improve HF performance but in truth I haven't been able to spot much difference wit or without them.
Don't worry about your chips, mine have proved that one can abuse the STKs and get away with it. I have had mine oscillating due to poor layout, and have run them bridged into 4 ohm loads, an impossible task for most amps. Now I respect their age, and they only do light and occasional duty, till my active line arrays get going with them performing most of the heavy lifting...
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