The battery was a bit weak, so I changed to a fresh one.
Re-did the measurements, but they came out exactly the same..
Re-did the measurements, but they came out exactly the same..
So, the next step is obviously to get some well-matched transistors in place and see if that improves the behaviour of the amp..
The process for matching transistors has been described to me, so its just to get going ..or..?
My first concern is that I have 6 amplifier cards all in all, so its going to take quite some time I guess..
My second concern is how many transistors I'll actually have to go through and how many I will have to discard. I have some left over and those allready installed, but how many more will I have to get??
I came across this thing called dual matched transistors, i.e. two matched transistors in one housing..
From what I read, some of these transistors were very finely matched, and there is allso the benefit of both transistors being thermally coupled within the same housing.
The reasons I find this appealing is because it could elliminate my worries of going through heaps of transistors, the match would probably be better than I could acheive my self, and I could buy exactly the quantity of transistors needed and not end up with a heap of discarded out-of spec transistors.
Has anybody used such dual transistors?
Are there any commonly available types wich could be suitable for replacing my BC546 nd BC556 pairs??
The process for matching transistors has been described to me, so its just to get going ..or..?
My first concern is that I have 6 amplifier cards all in all, so its going to take quite some time I guess..
My second concern is how many transistors I'll actually have to go through and how many I will have to discard. I have some left over and those allready installed, but how many more will I have to get??
I came across this thing called dual matched transistors, i.e. two matched transistors in one housing..
From what I read, some of these transistors were very finely matched, and there is allso the benefit of both transistors being thermally coupled within the same housing.
The reasons I find this appealing is because it could elliminate my worries of going through heaps of transistors, the match would probably be better than I could acheive my self, and I could buy exactly the quantity of transistors needed and not end up with a heap of discarded out-of spec transistors.
Has anybody used such dual transistors?
Are there any commonly available types wich could be suitable for replacing my BC546 nd BC556 pairs??
Yes, they are not expensive, the ones I allreadey bought were certainly not expensive but it seems the price corresponded with the quality and consistency!
And in all honesty, a "quick and easy" solution, if it can be had in the form of matched double transistors, has an appeal. Not from laziness or reluctance to undertake the effort of matching, but more so for the sake of moving hte project forward so that I can enjoy music with some good sounding amplifiers, which was the target from the outset of the project..🙂
And in all honesty, a "quick and easy" solution, if it can be had in the form of matched double transistors, has an appeal. Not from laziness or reluctance to undertake the effort of matching, but more so for the sake of moving hte project forward so that I can enjoy music with some good sounding amplifiers, which was the target from the outset of the project..🙂
well, doesn't seem to be too manny double transistors out there, its either SMD stuff or obsolete and expensive stuff with too low breakdown voltage..
I'll simply take my best shot at matching some transistors and solder them back on the amp board, fire up and se what happens!
I did some superficial reading up on differential pair input stages, and I was a bit surprised to learn exactly how critical matching was for distortion! Considering this, I'm quite surprised the elektor article didn't say anything at all about matching these transistors!
I'll simply take my best shot at matching some transistors and solder them back on the amp board, fire up and se what happens!
I did some superficial reading up on differential pair input stages, and I was a bit surprised to learn exactly how critical matching was for distortion! Considering this, I'm quite surprised the elektor article didn't say anything at all about matching these transistors!
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HI Elbert
I told you the transistors should be matched. 1.7 volts when I said this value is without the transistor is matched. Although it is not matched the dc servo works well and do not hear any big difference. From policy Elektor am especially disappointed in the amplifiers especially in the Titan 2000 many times I wrote the problem I had I never got an answer from the T. G
Nikos
I told you the transistors should be matched. 1.7 volts when I said this value is without the transistor is matched. Although it is not matched the dc servo works well and do not hear any big difference. From policy Elektor am especially disappointed in the amplifiers especially in the Titan 2000 many times I wrote the problem I had I never got an answer from the T. G
Nikos
I don't think beta mismatches in the input devices will give you an offset problem this big. I really think this amp is oscillating, which would give all the symptoms you have mentioned. The Crescendo, and the Crecendo Millenium, both sail very close to the wind in terms of stability. The original Crescendo compensation relied on the gate capacitance for compensation. Both these designs used lots of feedback to try to get low distortion, at the expense of stability margin.
This is not the first post to discuss problems with these designs and will not be the last.
Best thing here is to take a close look at the compensation and make sure the amp is stable.
Good Luck.
This is not the first post to discuss problems with these designs and will not be the last.
Best thing here is to take a close look at the compensation and make sure the amp is stable.
Good Luck.
Nikosokey,
Matching is on the schedule, so it will be interresting to see what it brings..
In a way, it is "good" to hear that Elektor amplifier projects are not allways solder-and-play, allthogut that is the impression I sort of got from the magazine article...
Bonsai,
I hooked my scope up to the output of the amp, and could not identify any ac signals, or anything other than the DC offeset. I swept through the whole time/ div range, yet found nothing.
or is there something particular about identifying oscilation that I have missed??
From what has allready been posted, I understand that beta missmatch is not a primary concern with regards to offsett, but that Vbe is, and I did have a Veb missmatch of 4 mV and 5 mV in each of the input pairs.
Verification of theoretical explanation through practical testing is now the next step..
Matching is on the schedule, so it will be interresting to see what it brings..
In a way, it is "good" to hear that Elektor amplifier projects are not allways solder-and-play, allthogut that is the impression I sort of got from the magazine article...
Bonsai,
I hooked my scope up to the output of the amp, and could not identify any ac signals, or anything other than the DC offeset. I swept through the whole time/ div range, yet found nothing.
or is there something particular about identifying oscilation that I have missed??
From what has allready been posted, I understand that beta missmatch is not a primary concern with regards to offsett, but that Vbe is, and I did have a Veb missmatch of 4 mV and 5 mV in each of the input pairs.
Verification of theoretical explanation through practical testing is now the next step..
You can identify that your amp has oscilation problems without a scope.If some transistors are very hot or amp consume very much current then you have oscillations.Sometimes also the resistor in the zobel network is very hot.
I remember as I had oscillations in my amp it has consumed 5 amps of current and this was in idle.
I remember as I had oscillations in my amp it has consumed 5 amps of current and this was in idle.
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Well,
I havenæt actually measurted current consumption, but after leaving the amp on for about 30 min, the average temperature on transistors was around 36 degrees C, and none of them seemed to be particularly warmer than the others.
But yes, That's one of the things I've heard abourt, oscilations causing transistors to get very hot very quickly, possibly followed by more or less spectacular catastrophic failures..
I havenæt actually measurted current consumption, but after leaving the amp on for about 30 min, the average temperature on transistors was around 36 degrees C, and none of them seemed to be particularly warmer than the others.
But yes, That's one of the things I've heard abourt, oscilations causing transistors to get very hot very quickly, possibly followed by more or less spectacular catastrophic failures..
but you did when you powered it up through the bulb tester.
The bulb going out tells you that power consumption is very low.
something strange going on with this amp. Having said that, you do seem to have quite big Vbe deltas - 4-5mV is a lot
I think it's a problem with output mosfets.Maybe they are not from the same batch or have to big spread in specs. Mosfets generally have this problem.Or maybe they are faked or otherwise damaged.
You can try if it works with other mosfets or bipolar transistors and if it works then you know what was the problem.
You can try if it works with other mosfets or bipolar transistors and if it works then you know what was the problem.
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Been quite bussy lately, so not much progress so far... 🙁
Anyway, contemplating how to set up for some measurements as described by Andrew, i.e. "long tail pair".
Seems obvious that I should get one of those experimentation boards and some other stuff in order to rig something where voltages can be easily adjusted and transistors easily swapped..
But why won't HFE and Vbe matching with the multimeter be good enough?
I understand that I can not controll the current when using a multimeter, but will the values change in a non-linear fashin with variation in current??
Anyway, contemplating how to set up for some measurements as described by Andrew, i.e. "long tail pair".
Seems obvious that I should get one of those experimentation boards and some other stuff in order to rig something where voltages can be easily adjusted and transistors easily swapped..
But why won't HFE and Vbe matching with the multimeter be good enough?
I understand that I can not controll the current when using a multimeter, but will the values change in a non-linear fashin with variation in current??
well, now I've bought a breadboard and I'm ready to attempt some transistor matching.
I have a 1k resistor in series with the collector, and a 10k + 25k potbetween + and base.
for a transistor pair, I have separate 1k (Rc) resistors for the collectors and the bases and emitters are connected together.
Emitter goes to ground.
This set-up is based on my best understanding of diagrams and descriptions for a measurement set-up so far.
So far, I've got 1 BC546 transistor (NPN) inn this circuit.
I have 14,35 V connected.
I adjusted the 25k pot so that I got a voltage across Rc corresponding to 10 mA. From the transistor data- sheet, the saturation current is 10 mA for this transistor.
Voltage across the 10k resistor corresponds to an Ib of 1,15 mA
Veb is 0,71V
but how do I go about from here??
I have a 1k resistor in series with the collector, and a 10k + 25k potbetween + and base.
for a transistor pair, I have separate 1k (Rc) resistors for the collectors and the bases and emitters are connected together.
Emitter goes to ground.
This set-up is based on my best understanding of diagrams and descriptions for a measurement set-up so far.
So far, I've got 1 BC546 transistor (NPN) inn this circuit.
I have 14,35 V connected.
I adjusted the 25k pot so that I got a voltage across Rc corresponding to 10 mA. From the transistor data- sheet, the saturation current is 10 mA for this transistor.
Voltage across the 10k resistor corresponds to an Ib of 1,15 mA
Veb is 0,71V
but how do I go about from here??
Well, I've made my first fumbling attempt at matching.
First, I used the multimeter to find a good HFE match and I ended up with a pair of BC 546 B's measuring 355 and 354.
I then went on to test them individually in the setup previosuly described.
I got an Ib of 1,1455 mA and 1,1445 mA and Ic of 11,5921 mA and 12,1610 mA respectively.
To me, this looks reasonably OK, but I lack the experience to judge the significance of the actual difference.
Could anybody say wether or not this is actually a usable match before I solder the transistors back on to the card?
First, I used the multimeter to find a good HFE match and I ended up with a pair of BC 546 B's measuring 355 and 354.
I then went on to test them individually in the setup previosuly described.
I got an Ib of 1,1455 mA and 1,1445 mA and Ic of 11,5921 mA and 12,1610 mA respectively.
To me, this looks reasonably OK, but I lack the experience to judge the significance of the actual difference.
Could anybody say wether or not this is actually a usable match before I solder the transistors back on to the card?
That's good match. I remember by Elektor was an article about a transistor tester, called SC-analyser.SC Analyser 2005 - ELEKTOR.com | Electronics: Microcontrollers Embedded Audio Digital Analogue Test Measurement
I build this one and it's very good for this purpose.
I build this one and it's very good for this purpose.
Thank you for your reply Leon!
Good to hear that I seem to be going in the right direction. as mentioned I have no practical experience with this, so second opinions are very valuable to me!
That SC analyzer sure looks like a helpfull tool, so that is definitively something I'll consider getting!
Now, I've just completed measuring out the BC556b PNP pair T3 and T4, and I got these results:
Hfe: 265 and 265 (again, with the multimeter)
Ib 1,1445 mA and 1,4436mA
Ic 14,507 mA and 14,507 mA
Looking at the results, this allso seems quite OK, but I get the same value for Ic on all four Transistors.. this seems to good to be true.. I have measured the voltage across the 1k (or 994 Ohm) collector resistor and divided the voltage with the resistance to get the collector current.
This requires me to use a voltage range on the multimeter with only 2 decimal places, perhaps lack of measurement resolution is the explanation??
Good to hear that I seem to be going in the right direction. as mentioned I have no practical experience with this, so second opinions are very valuable to me!
That SC analyzer sure looks like a helpfull tool, so that is definitively something I'll consider getting!
Now, I've just completed measuring out the BC556b PNP pair T3 and T4, and I got these results:
Hfe: 265 and 265 (again, with the multimeter)
Ib 1,1445 mA and 1,4436mA
Ic 14,507 mA and 14,507 mA
Looking at the results, this allso seems quite OK, but I get the same value for Ic on all four Transistors.. this seems to good to be true.. I have measured the voltage across the 1k (or 994 Ohm) collector resistor and divided the voltage with the resistance to get the collector current.
This requires me to use a voltage range on the multimeter with only 2 decimal places, perhaps lack of measurement resolution is the explanation??
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