Hi Nordic,
For re-biasing, the input needs to be zero (shorted) and you *must* use a dummy load 8 to 10 ohm resistor.
If there is not a dummy load then bias adjustments can make the offset flip-flop, as will rail current, this because there is no realistic load with output terminal imbalance.
Set the bias pre-set for no quiescent current.
Adjust the differential pre-set for minimum output offset.
Increase the bias to 25mA.
Re-trim output offset.
Set bias current to say 60mA (or whatever is recommended)
Re-trim output offset.
Give it a blast with a real LS.
After 30 mins recheck offset and bias.
( I set bias here by measuring voltage accross a 0.22R resistor, so that when these are taken out the settings will not change. )
If bias not stable at the next switch-on then something strange is happening, because this behaviour has not been reported with other DX amplifiers, nor indeed others using similar circuitry.
Cheers ......... Graham.
For re-biasing, the input needs to be zero (shorted) and you *must* use a dummy load 8 to 10 ohm resistor.
If there is not a dummy load then bias adjustments can make the offset flip-flop, as will rail current, this because there is no realistic load with output terminal imbalance.
Set the bias pre-set for no quiescent current.
Adjust the differential pre-set for minimum output offset.
Increase the bias to 25mA.
Re-trim output offset.
Set bias current to say 60mA (or whatever is recommended)
Re-trim output offset.
Give it a blast with a real LS.
After 30 mins recheck offset and bias.
( I set bias here by measuring voltage accross a 0.22R resistor, so that when these are taken out the settings will not change. )
If bias not stable at the next switch-on then something strange is happening, because this behaviour has not been reported with other DX amplifiers, nor indeed others using similar circuitry.
Cheers ......... Graham.
Yes Loek..... fine image...the Mill.
I do not know Loek, i think Klaas did not informed him pickup....but for sure your observation is important.
regards,
Carlos
..........................................................................................................
Mr. GEM
Thank you Graham...you are giving a very nice support to Nordic...very good that.
Have you perceived that your great sonics amplifier will be constructed in Nedherland?
Enjoy.... your wonderfull sound unit will be there...Klass will feel extremelly happy... i hope he did not kicked my poor Dx simple unit out!
hehe.... hard competition.... product from Doctor Graham Maynard...oh pain!...oh!...oh!
But, as you belong to the club, this will make Dx unit shine too!
regards,
Carlos
I do not know Loek, i think Klaas did not informed him pickup....but for sure your observation is important.
regards,
Carlos
..........................................................................................................
Mr. GEM
Thank you Graham...you are giving a very nice support to Nordic...very good that.
Have you perceived that your great sonics amplifier will be constructed in Nedherland?
Enjoy.... your wonderfull sound unit will be there...Klass will feel extremelly happy... i hope he did not kicked my poor Dx simple unit out!
hehe.... hard competition.... product from Doctor Graham Maynard...oh pain!...oh!...oh!
But, as you belong to the club, this will make Dx unit shine too!
regards,
Carlos
Hi Carlos,
The DX and the GEM are such different conceptions, made to do the same thing - enjoy music.
Once you acheive a good level, as with the DX, the returns diminish for the costs involved.
Yet both designs were built out of listening tests.
The DX should run at first switch-on, though there have been probs.
The GEM needs very careful construction and could go pop in a big way due to wiring mistakes, or oscillate and go pop if rules are not followed.
I would not dare open a thread myself for fear of constructors failure and cost,
and I am sure you can understand this.
Besides, I have been slowly developing my own home loudspeaker through which to enjoy my GEMs, for even here there are different aspects to listening.
A good amp and good LS can 'take you there' (to the performance) from one special seat in a listening room.
But that is not my scene.
I want to bring the music into my room in a way which I can enjoy from the rug, the sofa, the table and even the hall and kitchen with doors open.
My new cabinet has developed fine, though I have no workshop or carpentry skills with which to finish it; yet.
Of course I shall help/follow Klaas with his construction, which I am about to do now.
Cheers ........ Graham.
The DX and the GEM are such different conceptions, made to do the same thing - enjoy music.
Once you acheive a good level, as with the DX, the returns diminish for the costs involved.
Yet both designs were built out of listening tests.
The DX should run at first switch-on, though there have been probs.
The GEM needs very careful construction and could go pop in a big way due to wiring mistakes, or oscillate and go pop if rules are not followed.
I would not dare open a thread myself for fear of constructors failure and cost,
and I am sure you can understand this.Besides, I have been slowly developing my own home loudspeaker through which to enjoy my GEMs, for even here there are different aspects to listening.
A good amp and good LS can 'take you there' (to the performance) from one special seat in a listening room.
But that is not my scene.
I want to bring the music into my room in a way which I can enjoy from the rug, the sofa, the table and even the hall and kitchen with doors open.
My new cabinet has developed fine, though I have no workshop or carpentry skills with which to finish it; yet.
Of course I shall help/follow Klaas with his construction, which I am about to do now.
Cheers ........ Graham.
Yep something certainly is fried... blew both fuses, just now... I have spares of everything, except I'd have to look for tip41s and bd139... think I have some bd135... will that do?
Luckily I use 17W rail resistors...
The construction bit was the fun part certainly.... my first metalwork.... well.... hybrid. And today after I figured out it would assemble more straight if I first clamp it before screwing, I am even more impressed with the build... Its not perfect, but you'd have to look damn close to notice. Especialy the second heatsink side came perfect... Learned working with new medium and new drill press by then...
Luckily I use 17W rail resistors...
The construction bit was the fun part certainly.... my first metalwork.... well.... hybrid. And today after I figured out it would assemble more straight if I first clamp it before screwing, I am even more impressed with the build... Its not perfect, but you'd have to look damn close to notice. Especialy the second heatsink side came perfect... Learned working with new medium and new drill press by then...
Oh Nordic !
So it is out with all semiconductors, test/replace as necessary, rebuild, and fire up all over again.
From memory BD135 has much higher capacitance and has lower voltage rating.
Hi Carlos,
We saw pictures here of that very serious plane crash in your country.
News says the runway had just been resurfaced and opened before the drainage grooves could be cut.
Apparently another 200 poor souls were killed in a near identical crash some years ago. So sad
Cheers ....... Graham.
So it is out with all semiconductors, test/replace as necessary, rebuild, and fire up all over again.
From memory BD135 has much higher capacitance and has lower voltage rating.
Hi Carlos,
We saw pictures here of that very serious plane crash in your country.
News says the runway had just been resurfaced and opened before the drainage grooves could be cut.
Apparently another 200 poor souls were killed in a near identical crash some years ago. So sad
Cheers ....... Graham.
Senators are still discussing that last accident...over the jungle...the Legacy and
the Boeing.... this novel did not finished yet.... too much talk and no decisions.
Unfortunately dear Graham...we already pay because undeveloped...there are problems that we have to overcome.
thank you,
regards,
Carlos
the Boeing.... this novel did not finished yet.... too much talk and no decisions.
Unfortunately dear Graham...we already pay because undeveloped...there are problems that we have to overcome.
thank you,
regards,
Carlos
Sound much like the way things go here...
So far the sa1943 measured fine...diode test the from BE, BC and passed only one way... CE, no conduction, hFE corresponds with no. I wrote on back of transistor before installation...
2sc5200 is a paperweight... conducting just about between all pins.
I dont mind takeing out the large components, but do I need to test the input transistors too?
This is my first solidstate "repair" as this channel worked weeks ago....I suppose it has just been bashed aruond too much in my crazy workshop/office...
I'll go get some bd139 to stock my drawers from RS then, they still have the 10uf input caps I ordered to try as well there, for pickup... oh and the snubbing diodes for the bridges...
So far the sa1943 measured fine...diode test the from BE, BC and passed only one way... CE, no conduction, hFE corresponds with no. I wrote on back of transistor before installation...
2sc5200 is a paperweight... conducting just about between all pins.
I dont mind takeing out the large components, but do I need to test the input transistors too?
This is my first solidstate "repair" as this channel worked weeks ago....I suppose it has just been bashed aruond too much in my crazy workshop/office...
I'll go get some bd139 to stock my drawers from RS then, they still have the 10uf input caps I ordered to try as well there, for pickup... oh and the snubbing diodes for the bridges...
Hi Nordic,
Is it worth taking a CHANCE on the new outputs you fit, IF one of the lesser devices has already failed too ???
When you get shorts and burnouts of output devices you cannot have any idea what voltage that device applied to the one in front at the instant before it failed.
Five minutes checking time for each semiconductor could save five days of re-order waiting time.
Simply not worth worth the risk, and I write from experience !!!
Cheers ........ Graham.
Is it worth taking a CHANCE on the new outputs you fit, IF one of the lesser devices has already failed too ???
When you get shorts and burnouts of output devices you cannot have any idea what voltage that device applied to the one in front at the instant before it failed.
Five minutes checking time for each semiconductor could save five days of re-order waiting time.
Simply not worth worth the risk, and I write from experience !!!
Cheers ........ Graham.
Vbe matching means that parallel pairs pass identical quiescent. If their betas vary, then providing they are driven from the same driver it is of no consequence, and in any event gnfb will equalise, precisely as Graham says.
I use 0.47R emitter resistors, rather large, so as to reduce quiescent to just 60mA or so and to force current sharing AT HIGH CURRENT. Also means you can leave my amps on all day and still feel green. These resistors are within the nfb loop anyway, so they have little impact on Zout. They do cost rail efficiency, but at high current help to iron out the non-ohmic Ic v. Vbe discrepancies, pushing the distortion spectrum lower by flattening the transfer function - if that makes any sense......
Don't try to 'pull off a Hugh Dean', Nordic, you'll be disappointed. Half the time I scarcely know what day it is....
I see NM just turned 89!! Wish him a Happy Birthday from me!
Cheers,
Hugh
I use 0.47R emitter resistors, rather large, so as to reduce quiescent to just 60mA or so and to force current sharing AT HIGH CURRENT. Also means you can leave my amps on all day and still feel green. These resistors are within the nfb loop anyway, so they have little impact on Zout. They do cost rail efficiency, but at high current help to iron out the non-ohmic Ic v. Vbe discrepancies, pushing the distortion spectrum lower by flattening the transfer function - if that makes any sense......
Don't try to 'pull off a Hugh Dean', Nordic, you'll be disappointed. Half the time I scarcely know what day it is....
I see NM just turned 89!! Wish him a Happy Birthday from me!
Cheers,
Hugh
Yep, him and my grandma.... Lol, did you know our flag is sometimes called MJs underpants... cause it looks like a Y-front...
Have one more diffirential transistor to test, and the one on the vbe board.... breaks my heart hurting the tracks and haveing to repair with wire.... next time I will drill bigger holes...
So far only the one output transistor was damaged...
That makes sense to me... I saw on a more practical level the voltage diffirences, metering all the spots, setting up the previous channel.
Lol maybe Graham can write us a article on how the darned thing actualy work... opamps... yep I know as much about setting up gain as I'm likely to ever need to... but sand.........
P.S. I normally only know when its Monday... but loose track after that... I have no need for dates and things in my current life.
Have one more diffirential transistor to test, and the one on the vbe board.... breaks my heart hurting the tracks and haveing to repair with wire.... next time I will drill bigger holes...
So far only the one output transistor was damaged...
That makes sense to me... I saw on a more practical level the voltage diffirences, metering all the spots, setting up the previous channel.
Lol maybe Graham can write us a article on how the darned thing actualy work... opamps... yep I know as much about setting up gain as I'm likely to ever need to... but sand.........
P.S. I normally only know when its Monday... but loose track after that... I have no need for dates and things in my current life.
Hi Hugh,
Mmm - Thursday. Is it ? You made me laugh.
We try so hard to make things just right, and then when we get 'there' we wonder what all the fuss was about.
After I finished my GEM design I deliberately fitted badly mismatched devices, and could not hear the difference !
Quite different to the old transformer coupled push-pull days when transistors were precious and NFB was limited !
Cheers ......... Graham.
Mmm - Thursday. Is it ? You made me laugh.
We try so hard to make things just right, and then when we get 'there' we wonder what all the fuss was about.
After I finished my GEM design I deliberately fitted badly mismatched devices, and could not hear the difference !
Quite different to the old transformer coupled push-pull days when transistors were precious and NFB was limited !
Cheers ......... Graham.
Hi Nordic,
You sound as if your are struggling without a Solder Sucker.
This sucks the solder off a pcb pad without damaging or lifting the track.
Or maybe your iron is too hot !
Service engineers use temperature controlled irons and solder suckers, then can lift a transistor out, check and have it back in or changed in less than two minutes.
Once an iron has reached temperature it does not need so much current. You could make a stand with a microswitch operated by the weight of the iron so that a diode is in series with the element when it is not actually being used for soldering. Makes the bit last so much longer too.
Cheers ........ Graham.
You sound as if your are struggling without a Solder Sucker.
This sucks the solder off a pcb pad without damaging or lifting the track.
Or maybe your iron is too hot !
Service engineers use temperature controlled irons and solder suckers, then can lift a transistor out, check and have it back in or changed in less than two minutes.
Once an iron has reached temperature it does not need so much current. You could make a stand with a microswitch operated by the weight of the iron so that a diode is in series with the element when it is not actually being used for soldering. Makes the bit last so much longer too.
Cheers ........ Graham.
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