OPA2 said:
That's what made it sound worse with bias below 10ma !
Above 10ma i did not detect any audible problems.
I am still investigating and looking for a simple cure... I might have already found something, but needs to test !
Mike
There is an optimum biasing current for class B amplifiers, as decribed by Douglas Self (I do not agree with some of his thoughts, but this one is correct). For this optimum Iq, there is the lowest crossover distortion. Underbiasing and overbiasing both lead to increase of high order harmonics content, whis is totally unpleasing. Underbiasing is worse. Overbiasing leads to Gm doubling (higher /doubled/ transconductance of output stage in class A part of transfer characteristics, more OLG gain), for this amp (I mean my sample) oscillations occur due to Gm doubling. I believe that correct class B biasing is a right step for this amp.
I am searching for a blonde long hair... to produce the "Charlotte" appearance...oh!
Oh! destiny.... now i am glad that mum already gone!...not to watch my shame!
regards,
Carlos
Oh! destiny.... now i am glad that mum already gone!...not to watch my shame!
regards,
Carlos
Re: I am searching for a blonde long hair... to produce the "Charlotte" appearance...oh!
Hi Carlos
if You will ask me : I prefer black! 😀
Heinz!
destroyer X said:
Hi Carlos
if You will ask me : I prefer black! 😀
Heinz!
Grrrrrrr!....ahahahaha!...that's rigth, the color do not matter
But i already have chances, as i have 2 working samples, and also many guys have.
hehe....the guilty can be:
The transformer
The wire
The resistor
The board
The weather
The neighboor
Or space invaders ....aahahahahah!
Will be hard to use those hairs and lipstick, first i will try my best to scape.
I can blame even those electrons having strange tendence to shake because of cold in Eastern Europe....hehe
regards,
Carlos
But i already have chances, as i have 2 working samples, and also many guys have.
hehe....the guilty can be:
The transformer
The wire
The resistor
The board
The weather
The neighboor
Or space invaders ....aahahahahah!
Will be hard to use those hairs and lipstick, first i will try my best to scape.
I can blame even those electrons having strange tendence to shake because of cold in Eastern Europe....hehe
regards,
Carlos
Carlos - we are in a close connection with Michael, and we have several similar results. I belive that you might better like to wait for them. Standard circuit tools will fix possible premises of instability, that might but need not necessarily happen. It is all about Bode plots.
May i sent music and pictures of Rio de Janeiro to you!
My heart is asking me to do that.
My brain is asking too.... be good to Charlie...oh!...Charllote is a tragedy!
5 pictures of my home town, Rio de Janeiro
I pretty music of Copacabana beach with my text translation
A brazilian making rithm using only hands and legs...have you seen that...ahahahaha!.
Send me adress...want to take care o Epupa too....he is a very good Enginneer too, not only my heart is asking...good sense too!
Can you imagine, my 72 old girl friends, watching me return to my home town using lipstick and long blond hairs...with a lot of black hairs in my leg...enormous stomach too!....what a shame...me good guys...be good with Charlie!
ahahahaha....joking, kidding...i do not mind...i want my friends happy as i am, as many guys constructed, and there are many very happy...and Doctor Pavel, Doctor Epupa and other big Doctors already assembled and said nice things to me (not that is perfect, but good!)
regards,
Carlos
My heart is asking me to do that.
My brain is asking too.... be good to Charlie...oh!...Charllote is a tragedy!
5 pictures of my home town, Rio de Janeiro
I pretty music of Copacabana beach with my text translation
A brazilian making rithm using only hands and legs...have you seen that...ahahahaha!.
Send me adress...want to take care o Epupa too....he is a very good Enginneer too, not only my heart is asking...good sense too!
Can you imagine, my 72 old girl friends, watching me return to my home town using lipstick and long blond hairs...with a lot of black hairs in my leg...enormous stomach too!....what a shame...me good guys...be good with Charlie!
ahahahaha....joking, kidding...i do not mind...i want my friends happy as i am, as many guys constructed, and there are many very happy...and Doctor Pavel, Doctor Epupa and other big Doctors already assembled and said nice things to me (not that is perfect, but good!)
regards,
Carlos
Attachments
What!!!! have i heard that!!!!.... that i am polishing Pavel's shoes!!!
You are entirelly rigth...i am doing that.... correct.
What's the problem!
I like him....what's problem man?
Want to figth?
I have two water pistols...ready?
So go back 10 steps turn and shot....hehe...i will be exactly behing you....watter over your nose!!!...aahahahahahahah!
regards,
Carlos
You are entirelly rigth...i am doing that.... correct.
What's the problem!
I like him....what's problem man?
Want to figth?
I have two water pistols...ready?
So go back 10 steps turn and shot....hehe...i will be exactly behing you....watter over your nose!!!...aahahahahahahah!
regards,
Carlos
But...
Everything seemed to work ok, power dissipation was normal, dc offset was about 2.5 mV, sound came out from the speakers, nothing seemed to get hot,...but...
From the first second music came out from these amps, one thing was
clear: THIS WAS NOT THE SYMASYM I HAD BUILT on a breadboard some time ago. It was another amplifier. A WORSE amplifier. Much worse. 😕
Why? I don't really know. It wasn't that it was a particular problem. It was rather that it gave me a flat sound. No dynamism, clean but poor treble, normal bass (as always, nothing like the super extended controlled bass I had with the previous version). Like something was between me and the speakers.
After 2 hours of listening and thinking if it was my imagination or not, suddenly one channel started to distort heavily. I unplugged it, replugged it, distortion continued. I'll check it perhaps tomorrow, too late now for something like this.🙁
Everything seemed to work ok, power dissipation was normal, dc offset was about 2.5 mV, sound came out from the speakers, nothing seemed to get hot,...but...
From the first second music came out from these amps, one thing was
clear: THIS WAS NOT THE SYMASYM I HAD BUILT on a breadboard some time ago. It was another amplifier. A WORSE amplifier. Much worse. 😕
Why? I don't really know. It wasn't that it was a particular problem. It was rather that it gave me a flat sound. No dynamism, clean but poor treble, normal bass (as always, nothing like the super extended controlled bass I had with the previous version). Like something was between me and the speakers.
After 2 hours of listening and thinking if it was my imagination or not, suddenly one channel started to distort heavily. I unplugged it, replugged it, distortion continued. I'll check it perhaps tomorrow, too late now for something like this.🙁
Pretty work with a bad luck my dear Dimitris...can you send me, by direct mail, a
maximum resolution possible, deeply focused image, this way i will have the chance to check all circuit to help you.
Sorry by the bad moments Dimitris, you had better sound with the first "fast assemble".... this is extremely deceptive to you, having produce a pretty work and having problems.
I had also...hehe..inverting BC639 transistors and missing connections, but your case...with the board, problem may be different.
I have been using otenet.gr...... are this one working?
Having not answer from you....this is sad to me...silence followed with bad news.
The most common that happen between our communications, the personal ones, is that i always receive informs that did not find your adress...but reaching you in the reality...in a matter of days you find time and answer....but now a days, not returning nothing, nor the informs that did not found you, nor your answer.
My mail continue to be nanabrother@yahoo.com and the pleasure to have news from you continue the same.
Please, let me try to help.
regards,
Carlos
maximum resolution possible, deeply focused image, this way i will have the chance to check all circuit to help you.
Sorry by the bad moments Dimitris, you had better sound with the first "fast assemble".... this is extremely deceptive to you, having produce a pretty work and having problems.
I had also...hehe..inverting BC639 transistors and missing connections, but your case...with the board, problem may be different.
I have been using otenet.gr...... are this one working?
Having not answer from you....this is sad to me...silence followed with bad news.
The most common that happen between our communications, the personal ones, is that i always receive informs that did not find your adress...but reaching you in the reality...in a matter of days you find time and answer....but now a days, not returning nothing, nor the informs that did not found you, nor your answer.
My mail continue to be nanabrother@yahoo.com and the pleasure to have news from you continue the same.
Please, let me try to help.
regards,
Carlos
Hi Dimitris !
First, excellent work ! Your PCBs are a beauty, and even perfectly drilled ! 🙂
Okay, flat sound, no basspunch, no dynamics, poor trebles, lifeless, no, that's not symasym !
What you are describing is the sound of an oscillating amp...
"Gladly" Pavel (PMA) built a symasym using same layout and transistors like you,
the bc550c in input and the Toshibas at output. His version also oscillated, but he was able
to get rid of it by simply turning down the biasing to ~30ma, reading 6mv over the 0.22ohms.
This should help for now, but is not the final solution. Pavel did not detect any instabilities
after having turned down the bias.
I suspect that increasing the 1.2ohm basestoppers to 4.7ohm might do the job, but this is not
verified or tested yet. It seems that symasym does not really like the Toshibas...
Or the bc550 is slower than the mpsa18, or has more gain ?
In theory symasym has plenty of phasemargin, but only ~4db margin for the gain...
Too bad that one channel is already blown, hopefully it will be easy to find the defect part
by measuring some biasings. If you're lucky, it's only a blown fuse. (positive side)
But it is most likely to be one the transistors in vas.
Do you have access to a scope ? Hopefully it will not be necessary to add parts, it would be
a shame to do that with these nice boards...
Have you verified that the 22pF is really 22pF, it's just on the photo they look like having
the same size/proportions as the 100pFs.
For a beginning i suggest that you turn down the biasing to ~30ma, and/or reduce the 22pF to 10pF.
Have you grounded the heatsinks ? Sometimes this already helps.
I am sure that we will get these 2 babys singing !
As both amps were playing music and everything was normal (except the sound) it is unlikely to
be a fault on your side. Your inputtransistors are bc550c ?
Did you run out of 500ohms ? I ask because of the 2 paralell resistors on the right board ?
regards,
Michael
First, excellent work ! Your PCBs are a beauty, and even perfectly drilled ! 🙂
Okay, flat sound, no basspunch, no dynamics, poor trebles, lifeless, no, that's not symasym !
What you are describing is the sound of an oscillating amp...
"Gladly" Pavel (PMA) built a symasym using same layout and transistors like you,
the bc550c in input and the Toshibas at output. His version also oscillated, but he was able
to get rid of it by simply turning down the biasing to ~30ma, reading 6mv over the 0.22ohms.
This should help for now, but is not the final solution. Pavel did not detect any instabilities
after having turned down the bias.
I suspect that increasing the 1.2ohm basestoppers to 4.7ohm might do the job, but this is not
verified or tested yet. It seems that symasym does not really like the Toshibas...
Or the bc550 is slower than the mpsa18, or has more gain ?
In theory symasym has plenty of phasemargin, but only ~4db margin for the gain...
Too bad that one channel is already blown, hopefully it will be easy to find the defect part
by measuring some biasings. If you're lucky, it's only a blown fuse. (positive side)
But it is most likely to be one the transistors in vas.
Do you have access to a scope ? Hopefully it will not be necessary to add parts, it would be
a shame to do that with these nice boards...
Have you verified that the 22pF is really 22pF, it's just on the photo they look like having
the same size/proportions as the 100pFs.
For a beginning i suggest that you turn down the biasing to ~30ma, and/or reduce the 22pF to 10pF.
Have you grounded the heatsinks ? Sometimes this already helps.
I am sure that we will get these 2 babys singing !
As both amps were playing music and everything was normal (except the sound) it is unlikely to
be a fault on your side. Your inputtransistors are bc550c ?
Did you run out of 500ohms ? I ask because of the 2 paralell resistors on the right board ?
regards,
Michael
Michael,
I had to decrease Iq of output pair even more. For those 25-30mA, the amp was unstable after turn-on, then stabilized in some 1 minute. This shows dependence on operating points of transistors. I had to go to 10 mA to make an amp uconditionally stable, even for 1500pF, even for my dummy speaker load. I am sure that the case is output stage Gm doubling together with high OLG and phase shifts. I do not believe in input pair influence, I went to BC547 without change. It is the 2SC5200/2SA1943, but excellent transistors. Iq = 10 mA is a little bit low value for me, I am afraid I go underbiased. I am sure to solve the problem after I recover, decreasing my temperature from 39°C 😉.
Tchuss,
Pavel
I had to decrease Iq of output pair even more. For those 25-30mA, the amp was unstable after turn-on, then stabilized in some 1 minute. This shows dependence on operating points of transistors. I had to go to 10 mA to make an amp uconditionally stable, even for 1500pF, even for my dummy speaker load. I am sure that the case is output stage Gm doubling together with high OLG and phase shifts. I do not believe in input pair influence, I went to BC547 without change. It is the 2SC5200/2SA1943, but excellent transistors. Iq = 10 mA is a little bit low value for me, I am afraid I go underbiased. I am sure to solve the problem after I recover, decreasing my temperature from 39°C 😉.
Tchuss,
Pavel
The amplitude of those 6.6 MHz oscillations was Iq dependent, the higher Iq, the higher amplitude, up to 1V - 2V. For similar reasons I recommend supply rail series resistors for evaluation, see my web page.
Michael/Pavel,
I have been down this track with the Toshiba outputs as well.
I solved it by using 100R base stoppers on the drivers, 10R on the outputs, and going to 0R47 on the emitter resistors. I use a highish bias, 58mA, and find that with the larger emitter resistors this drifts very little with an optimised Vbe multiplier.
Instability is an issue with these very fast output devices in emitter follower configuration, and is just audible as a loss of resolution at high frequencies and a shrinking of the sound stage. And of course, they do get warmer........
I have no reason to imagine it's any different for any amp using the double EF output configuration, and I agree with you, Pavel, this is not strictly layout related (although a bad layout with long, parasitic tracks can worsen it) but rather a function of minority carriers in the base region of fast, large output devices.
Cheers,
Hugh
I have been down this track with the Toshiba outputs as well.
I solved it by using 100R base stoppers on the drivers, 10R on the outputs, and going to 0R47 on the emitter resistors. I use a highish bias, 58mA, and find that with the larger emitter resistors this drifts very little with an optimised Vbe multiplier.
Instability is an issue with these very fast output devices in emitter follower configuration, and is just audible as a loss of resolution at high frequencies and a shrinking of the sound stage. And of course, they do get warmer........
I have no reason to imagine it's any different for any amp using the double EF output configuration, and I agree with you, Pavel, this is not strictly layout related (although a bad layout with long, parasitic tracks can worsen it) but rather a function of minority carriers in the base region of fast, large output devices.
Cheers,
Hugh
Hello Carlos, Mike, Pavel, and Hugh.
Thank you all very much for the interest. Yes, I thought too about oscillating (after the final result, I must admit. Before it I thought I had make some mistake during assemble, or my ears were playing tricks on me). I read this thread regularly, so I knew that I had to bias down. My Iq is 30 mA for output (around 70 mA for the whole amp).
Unfortunately I have not access to an oscilloscope.
I will read carefully everything you wrote Mike, and try again. News coming soon, I am at work now. Have a nice day.
Carlos everyrthing ok with your computer? Private mail coming soon...😉
Thank you all very much for the interest. Yes, I thought too about oscillating (after the final result, I must admit. Before it I thought I had make some mistake during assemble, or my ears were playing tricks on me). I read this thread regularly, so I knew that I had to bias down. My Iq is 30 mA for output (around 70 mA for the whole amp).
Unfortunately I have not access to an oscilloscope.
I will read carefully everything you wrote Mike, and try again. News coming soon, I am at work now. Have a nice day.
Carlos everyrthing ok with your computer? Private mail coming soon...😉
Dimitris,
your problem were oscillations, that is for sure. All the symptoms you described confirmed it. As you have the same components as me, please follow my recommendation - make Iq of the output pair 10 mA and you will be safe for now. For future, we shall find better solution.
I am running longterm (several hours) half-power test (most dissipated power in output transistors) of symasym to dummy load, but I do not challenge the others to follow me, as I have pretty oversized heatsinks. For Iq = 10mA.
Regards,
Pavel
P.S. And please do not listen to much to voices of magicians, they will not cure for now 😉
your problem were oscillations, that is for sure. All the symptoms you described confirmed it. As you have the same components as me, please follow my recommendation - make Iq of the output pair 10 mA and you will be safe for now. For future, we shall find better solution.
I am running longterm (several hours) half-power test (most dissipated power in output transistors) of symasym to dummy load, but I do not challenge the others to follow me, as I have pretty oversized heatsinks. For Iq = 10mA.
Regards,
Pavel
P.S. And please do not listen to much to voices of magicians, they will not cure for now 😉