Guys,
PLEASE! Lets keep this thread about the project at hand. If you want to start another thread about the ZAP please do it.... but add a link from this thread to it I'm interested in it too but it deserves a whole thread of its own and this thread needs to stay on track. Wading through all the BS thats been posted here makes it alot more difficult for those that want to or are building the KSA-50 clone.
Thanks,
Mark
PLEASE! Lets keep this thread about the project at hand. If you want to start another thread about the ZAP please do it.... but add a link from this thread to it I'm interested in it too but it deserves a whole thread of its own and this thread needs to stay on track. Wading through all the BS thats been posted here makes it alot more difficult for those that want to or are building the KSA-50 clone.
Thanks,
Mark
Testing Questions
Thanks stewart, you are always there for me buddy!
OK, I fired up the Krell softstart, power supply and input stage (separately, and now together). I feed in a 10 KHz sinewave and get out a 10KHz sinewave, amplified, from the pos and neg outputs. Whew!
Hey, what now?
I suspect that I should set the bias in the middle-- do I want to set this now?
I suspect that I adjust dc offset-- how do I do that?
should I take a difference signal between pos and neg output?
should I be looking for or adjusting anything in particular?
Thanks stewart, you are always there for me buddy!
OK, I fired up the Krell softstart, power supply and input stage (separately, and now together). I feed in a 10 KHz sinewave and get out a 10KHz sinewave, amplified, from the pos and neg outputs. Whew!
Hey, what now?
I suspect that I should set the bias in the middle-- do I want to set this now?
I suspect that I adjust dc offset-- how do I do that?
should I take a difference signal between pos and neg output?
should I be looking for or adjusting anything in particular?
your board seemm to be working fine so what I reccomend is to set the bias at its lowest point when you add the output stage. Also run it at lower voltage, say +/- 20 volts if possible in case of wiring error... may save things. When its all working ok then bring up the rails and then increase the bias to where you want it set..... do this over about an hours time.
Mark
Mark
bias
I would set the bias if only I knew how. Never did it before but I'm sure its one of those blue thingies with the screw top. Haha, I'm only half kidding.
I am unable to bring it up halfway, had to go whole hog. + and - 36.8V
What is the actual output? There is a pos and neg for the output stage... should I look at each separately or subtract one from the other?
Should the pos output have a nice clean sinewave or should it have only the positive half and be missing some of the neg half? I get entire waves as far as I can tell so far.
I would set the bias if only I knew how. Never did it before but I'm sure its one of those blue thingies with the screw top. Haha, I'm only half kidding.
I am unable to bring it up halfway, had to go whole hog. + and - 36.8V
What is the actual output? There is a pos and neg for the output stage... should I look at each separately or subtract one from the other?
Should the pos output have a nice clean sinewave or should it have only the positive half and be missing some of the neg half? I get entire waves as far as I can tell so far.
Both halves should be out of phase from each other and not necessarily clean looking. Running the main board by itself is just to make sure its functioning ok and that you don't destroy the output devices by accident.. The output stage is everything not on the main board if you're using jan's board and everything after the driver board on Al's board. Use K-AMPS class A calculator to find what your bias should be set too. Just plug in your output devices and a few other parameters... its easy and works really good.
Mark
Mark
output is...
...from the junction of the output emitter resistors, the same place from where the feedback wire runs to the main board...
Setting the bias is easy...turn the pot so the DC you measure across both the driver emitter resistors is at a minimum. Connect the driver board to the outputs, then if you can, slowly apply power to the whole shooting match, monitoring current draw, anything more than a few 10's of milliamps is bad, you'd want to turn everything off and check your wiring......If you can't do it slowly, then just turn it on...from a distance?
Anyway once you have all the parts connected, power applied and no smoke issuing from anything, attach a meter to measure the voltage across one of the 0r68 output emitter resistors (say Re1), and another to measure the output voltage relative to ground, and if you have 3 meters (and who doesn't?) attach another one to measure the total voltage across the driver emitter resistors r127/128...
Slowly turn the bias pot to increase the output idle current, you can also measure this as the voltage across the 25ohm driver emitter resistors, nothing happens at first, basically until the board output voltage reaches about 1.2v across r127 & 128, then the outputs start to turn on and you will read a voltage across Re1...keep increasing until you have about 0.2 volts across Re1...with 3 output pairs this corresponds to ~1A total idle current, you'd probably want to allow this to sit for a little while check temps, make sure the voltages across all the output emitter resistors are nearly the same, any big discrepancy should be investigated. Once you are satisfied that everything is OK, start increasing the bias until you see ~0.4v on Re1...as the temperatures on the sinks change this is going to move around, once it seems to have settled, adjust the other pot to reduce the DC offset to the lowest possible value (<50mv was easy to achive on all the boards I've made). This will wander as the temps change, so repeat the process a few times over the course of an hour or two...
Good luck
Stuart
(I buy DMMs from harbor freight for $3.95 each, they seem accurate enough, and when I screw up and dump a couple hundred volts into the thing on the ohms setting I don't care much)
...from the junction of the output emitter resistors, the same place from where the feedback wire runs to the main board...
Setting the bias is easy...turn the pot so the DC you measure across both the driver emitter resistors is at a minimum. Connect the driver board to the outputs, then if you can, slowly apply power to the whole shooting match, monitoring current draw, anything more than a few 10's of milliamps is bad, you'd want to turn everything off and check your wiring......If you can't do it slowly, then just turn it on...from a distance?
Anyway once you have all the parts connected, power applied and no smoke issuing from anything, attach a meter to measure the voltage across one of the 0r68 output emitter resistors (say Re1), and another to measure the output voltage relative to ground, and if you have 3 meters (and who doesn't?) attach another one to measure the total voltage across the driver emitter resistors r127/128...
Slowly turn the bias pot to increase the output idle current, you can also measure this as the voltage across the 25ohm driver emitter resistors, nothing happens at first, basically until the board output voltage reaches about 1.2v across r127 & 128, then the outputs start to turn on and you will read a voltage across Re1...keep increasing until you have about 0.2 volts across Re1...with 3 output pairs this corresponds to ~1A total idle current, you'd probably want to allow this to sit for a little while check temps, make sure the voltages across all the output emitter resistors are nearly the same, any big discrepancy should be investigated. Once you are satisfied that everything is OK, start increasing the bias until you see ~0.4v on Re1...as the temperatures on the sinks change this is going to move around, once it seems to have settled, adjust the other pot to reduce the DC offset to the lowest possible value (<50mv was easy to achive on all the boards I've made). This will wander as the temps change, so repeat the process a few times over the course of an hour or two...
Good luck
Stuart
(I buy DMMs from harbor freight for $3.95 each, they seem accurate enough, and when I screw up and dump a couple hundred volts into the thing on the ohms setting I don't care much)
Dc
I see that I am getting the same DC voltages as Stewart posted. Almost had a heart attack until I realized that his voltages are measured across the resistor, NOT measured from a point to ground. Whew.
Resistor __ Stewart ___ Me
R113 _____ 2.2 ____ 2.15
R121 ____ 1.59 ____ 1.52
R122 ____ 1.0 ____ 0.92
R120 ____ 1.59 ____ 1.51
R108 ____ VDC-27 ___ VDC-27.3
This has really helped.
I see that I am getting the same DC voltages as Stewart posted. Almost had a heart attack until I realized that his voltages are measured across the resistor, NOT measured from a point to ground. Whew.
Resistor __ Stewart ___ Me
R113 _____ 2.2 ____ 2.15
R121 ____ 1.59 ____ 1.52
R122 ____ 1.0 ____ 0.92
R120 ____ 1.59 ____ 1.51
R108 ____ VDC-27 ___ VDC-27.3
This has really helped.
more changes...
While the changes discussed (VI limiter, CCS for LTP, Vas protection, DC servo), are all technically worthwhile, it's hard to call the result a ksa50 when you are done...and it's not immediately clear it will make any useful difference to the sound...
I installed current sources in the LTP for a reason other than sonic quality, it simply makes the front end of the amp insensitive to rail voltage. I'll be happy to share the trivial circuit I used, but it is at first sight an unneccesary complication of a 'normal' ksa50. The big krell is not primarily class A, so there are benefits, PSRR improves etc.
If you have a massively oversized power supply and wish to drive unknown loads to maximum possible output then the addition of a properly designed limiter could be a real asset...or you could just use a line fuse of the correct value...though replacing it can be a hassle...
Depending on the intended use of the amp, there are definitely good reasons to add some or all the features discussed, but we, collectively, haven't really provided good guidance as to why an average builder would care to...
my 2c
Stuart
While the changes discussed (VI limiter, CCS for LTP, Vas protection, DC servo), are all technically worthwhile, it's hard to call the result a ksa50 when you are done...and it's not immediately clear it will make any useful difference to the sound...
I installed current sources in the LTP for a reason other than sonic quality, it simply makes the front end of the amp insensitive to rail voltage. I'll be happy to share the trivial circuit I used, but it is at first sight an unneccesary complication of a 'normal' ksa50. The big krell is not primarily class A, so there are benefits, PSRR improves etc.
If you have a massively oversized power supply and wish to drive unknown loads to maximum possible output then the addition of a properly designed limiter could be a real asset...or you could just use a line fuse of the correct value...though replacing it can be a hassle...
Depending on the intended use of the amp, there are definitely good reasons to add some or all the features discussed, but we, collectively, haven't really provided good guidance as to why an average builder would care to...
my 2c
Stuart
This post brought back the thought of me buying and installing fuses for my KSA-50 clone. Hey, what amperage are you using? I'm using either 5 or 7.5 A, bought everything from 2A up to 10A. Not sure. Have to check, but so far have not blown any......knock on wood.
Getting back to the original topic of Post 2393 et cetera
I don't think that there are any shoulder washers that can fit a TO-3 for a 6-32 screw. Am I right? If so need to go with live heatsinks.
If you have them, why not place small fuses in the rails when you hook up the output, Mr Green ?
With the way you've set up the output stage, a short could blow all the devices.
With the way you've set up the output stage, a short could blow all the devices.
That thought has not eluded me; I might do that.
But then again......You know, maybe I give myself too much credit. But I see myself as a person who will screw up the premade boards but not the output stage, for which there is a clean schematic and which I kind of understand and which I am hand wiring myself very carefully. But I am glad you all are out there watching over me. Mabye too little credit.
Where is the guy that made the original boards? Did you all make him mad? Have not seen nor heard anything from him. Did something bad happen or did we have poor form?
Here is a question- how many hours of DIY can you do before your eyes give out and can no longer focus on the small connections you are making? T
oday I got 1 hour in in the morning and 7 in the afternoon before I could no longer focus. Yes it took me 7 today to test all my wacky boards, after this I could not even read the schematics and layouts withhout staring stupidly. If is PM only I can't see after about 5 hours. No glasses or mag devices. When I can't focus I know its time to stop the DIY for that day.
Test Setup
OK, since I am up....here is how I tested everything tonight.
a big pic; terry is gonna be peeved!
hey, its still connected, if you want me to measure something, just let me know.
Ok FYI.
1. The board on the steel thingie on the left is my soft start delay circuit.
2. The board on the right on the steel thingie is the soft starting board containing two NTC thermisters that provide resistance to each power xformer primary when power is applied. After a few secs, they are bypassed as the 1st board (above) activates the 117V/ 15A relay (on the right board) to shunt the NTC components.
3. The tiny Toroid is for powering the delay circuit and other stuff.
4. You see a big toroid, just begging for another one to be put on top of it so the 7.5" x 5/8" bolt can hold them both.
5. You see some caps, these are supplementary to the main Computer Grade PS caps.
The other stuff is.....well....a mass of wires and test equip.
No garage pics tonight, this is the kitchen!
OK, since I am up....here is how I tested everything tonight.
An externally hosted image should be here but it was not working when we last tested it.
a big pic; terry is gonna be peeved!
hey, its still connected, if you want me to measure something, just let me know.
Ok FYI.
1. The board on the steel thingie on the left is my soft start delay circuit.
2. The board on the right on the steel thingie is the soft starting board containing two NTC thermisters that provide resistance to each power xformer primary when power is applied. After a few secs, they are bypassed as the 1st board (above) activates the 117V/ 15A relay (on the right board) to shunt the NTC components.
3. The tiny Toroid is for powering the delay circuit and other stuff.
4. You see a big toroid, just begging for another one to be put on top of it so the 7.5" x 5/8" bolt can hold them both.
5. You see some caps, these are supplementary to the main Computer Grade PS caps.
The other stuff is.....well....a mass of wires and test equip.
No garage pics tonight, this is the kitchen!
I'm sorry, dont mean to make you MrRed, i'll refrain.
(i knew which way to turn to adjust dc, yet i blew an entire side of non-insulated mosfets on a heatsink because of a short, took me 6 weeks to get new RCA Mosfets at the time)
Very nice looking chassis, MrGreen.
(i knew which way to turn to adjust dc, yet i blew an entire side of non-insulated mosfets on a heatsink because of a short, took me 6 weeks to get new RCA Mosfets at the time)
Very nice looking chassis, MrGreen.
No!
Jacco, I'm not mad. I need your advice, help with whatever you see that needs comment!
Hey, which way do you turn the bias R to adj. bias on this one? what about the other Trimpot, how does turning that have any affect?
The chassis will be very very nice when I am done...if I can get this to work. Do you see the 1.5" by 1" APEX JR. rubber feet? They will be "adjusted" in the final version. FYI, the chassis is from a surplus store, cost $5. No bottom though, had to make one. Long story.... Either way, the chassis looks more like a computer tower than an amp. It will have solid black walnut side panels just like my GC, here
If you want one, I can probably get one cheaply-- say $5-$20.00 and they will break down flat for shipping. Let me know by Tomorrow at noon CA time which is when I head to the surplus store- they had 5 of them a month ago at various stages of being scratched up....but in my case those will be covered up.
Jacco, I'm not mad. I need your advice, help with whatever you see that needs comment!
Hey, which way do you turn the bias R to adj. bias on this one? what about the other Trimpot, how does turning that have any affect?
The chassis will be very very nice when I am done...if I can get this to work. Do you see the 1.5" by 1" APEX JR. rubber feet? They will be "adjusted" in the final version. FYI, the chassis is from a surplus store, cost $5. No bottom though, had to make one. Long story.... Either way, the chassis looks more like a computer tower than an amp. It will have solid black walnut side panels just like my GC, here
If you want one, I can probably get one cheaply-- say $5-$20.00 and they will break down flat for shipping. Let me know by Tomorrow at noon CA time which is when I head to the surplus store- they had 5 of them a month ago at various stages of being scratched up....but in my case those will be covered up.
Jacco- do you see where it says "C5" in the pic above (post #2514)? That is actually a package of fuseholders that I was thinking of using for the purpose you suggested. Really. You are good.
Hey, where did everyone go? Its only 1:26 am?
Hey, where did everyone go? Its only 1:26 am?
Re: No!
Depends whether you aquired positive or negative turn trimpots for the Krell.
Apex has really nice 1.5"x1.5" feet, i was droolin over my screen yesterday, a fat guy like me needs fat feet.
Nice GC, i like the table it sits on more.(making myself a 400lbs 4'x7.5' diningroom table at the moment)
A word of caution if i am permitted :
a safe procedure is to ground heatsinks.
Using live heatsinks may lead to oscillation, in some cases.
With the mega vented duct you have there is no need to install the TO3's without mica's.
I did it because the design i constructed was a class AB amplifier that used 75 watt TO220 RFP Mosfets, and i desired it to go class A, without mica's more than 0.50 C/W is saved.
Dont take my word for it : ask Nelson Pass or your astronaut/Dr/Amplifier designer Norman Thagard, read his words>>
lgreen said:
Depends whether you aquired positive or negative turn trimpots for the Krell.
Apex has really nice 1.5"x1.5" feet, i was droolin over my screen yesterday, a fat guy like me needs fat feet.
Nice GC, i like the table it sits on more.(making myself a 400lbs 4'x7.5' diningroom table at the moment)
A word of caution if i am permitted :
a safe procedure is to ground heatsinks.
Using live heatsinks may lead to oscillation, in some cases.
With the mega vented duct you have there is no need to install the TO3's without mica's.
I did it because the design i constructed was a class AB amplifier that used 75 watt TO220 RFP Mosfets, and i desired it to go class A, without mica's more than 0.50 C/W is saved.
Dont take my word for it : ask Nelson Pass or your astronaut/Dr/Amplifier designer Norman Thagard, read his words>>
Attachments
trimpots...
...one adjusts bias, the other adjusts the output offset. The output offset pot is closest to the input of the amp...
In the KSA50 I use a 4A fuse on the primary side of my ~400VA transformers, and 4A for the rails of each channel...should be enough for real world loads, and thus far has't given any 'false' failures...
You are doing well to last 5+ hours doing this sort of closeup, intense work. I rarely make it past two...even less working with 100v rails...
You can figure out which way to turn your bias pot by measuring the voltage across r127/128...see my other post. I twisted mine to insert the leads so that clockwise increased the bias current, seemed more intuitive. Other people have cut the traces etc...
Stuart
...one adjusts bias, the other adjusts the output offset. The output offset pot is closest to the input of the amp...
In the KSA50 I use a 4A fuse on the primary side of my ~400VA transformers, and 4A for the rails of each channel...should be enough for real world loads, and thus far has't given any 'false' failures...
You are doing well to last 5+ hours doing this sort of closeup, intense work. I rarely make it past two...even less working with 100v rails...
You can figure out which way to turn your bias pot by measuring the voltage across r127/128...see my other post. I twisted mine to insert the leads so that clockwise increased the bias current, seemed more intuitive. Other people have cut the traces etc...
Stuart
Re: trimpots...
Hi Stuart,
Are you saying that by twisting the leads on the turnpots can eliminate the need to cut the traces on the original boards? Could you explain that further please?
When I made that suggestion to reduce the size of you pics to fit the page, I was trying to be helpful. When you replied that you "didn't want to", I realized that you didn't want my help. This statement makes it even more clear. I'll stay out of your way from now on.
Blessings, Terry
Stuart Easson said:
Hi Stuart,
Are you saying that by twisting the leads on the turnpots can eliminate the need to cut the traces on the original boards? Could you explain that further please?
When I made that suggestion to reduce the size of you pics to fit the page, I was trying to be helpful. When you replied that you "didn't want to", I realized that you didn't want my help. This statement makes it even more clear. I'll stay out of your way from now on.
Blessings, Terry