Hi Andrew,
Thanks for your reply, explaination and formulas.
Everyone,
I assume it is better to find a BiPolar for C7 than Electrolytic type (assuming quality is same)? If so then better for a BiPolar then to make one by putting two Electroyltics in series?
My reading suggests two camps related to the Rubycon caps. One camp really swears by them. The other camp that is lukewarm to not impressed suggests one has to change the circuit topology a tad. I am working from memory on this Rubycon camp stuff from few months back when crossed some articles by chance about Rubycons. Some suggestion was made when using a Rubycon as a PCB PSU bypass cap that one did not need tjhe 0.1uF film bypass cap as well. I know C7 is not performing that function. I am not wishing to open up the debate on Rubycons here. I just mentioned Rubycons as seems they have some sort of special case considerations when getting "best" cap possible. Personally I am avoiding Rubycons as it just seems out of my leauge to know how to choose when and how to use Rubycons. Not to mention much harder to source.
I do not seem able to source a 100uF BiPolar. I can source 47uF Panasonic, Elna or Nichicon BiPolar types. To acheive the Time Constant I would parallel two of these 47uFs. I assume better to use two of same make/model as cause more problems than would offset of the endearing qualities. Would this be better than a single "high" quality Electrolytic? My choices for electrolytics are the same makes as BiPolar plus (skipping Rubycon) Cornell Dublier, Phillips, and Sprague. My hunch is to use Sprague electrolytic if I cannot use a BiPolar.
All that is left now is for me to figure out the lowest working voltage rating can use and the best voltage I can use for C7.
Regards,
John L. Males
Willowdale, Ontario
Canada
12 May 2006 16:17
Thanks for your reply, explaination and formulas.
Everyone,
I assume it is better to find a BiPolar for C7 than Electrolytic type (assuming quality is same)? If so then better for a BiPolar then to make one by putting two Electroyltics in series?
My reading suggests two camps related to the Rubycon caps. One camp really swears by them. The other camp that is lukewarm to not impressed suggests one has to change the circuit topology a tad. I am working from memory on this Rubycon camp stuff from few months back when crossed some articles by chance about Rubycons. Some suggestion was made when using a Rubycon as a PCB PSU bypass cap that one did not need tjhe 0.1uF film bypass cap as well. I know C7 is not performing that function. I am not wishing to open up the debate on Rubycons here. I just mentioned Rubycons as seems they have some sort of special case considerations when getting "best" cap possible. Personally I am avoiding Rubycons as it just seems out of my leauge to know how to choose when and how to use Rubycons. Not to mention much harder to source.
I do not seem able to source a 100uF BiPolar. I can source 47uF Panasonic, Elna or Nichicon BiPolar types. To acheive the Time Constant I would parallel two of these 47uFs. I assume better to use two of same make/model as cause more problems than would offset of the endearing qualities. Would this be better than a single "high" quality Electrolytic? My choices for electrolytics are the same makes as BiPolar plus (skipping Rubycon) Cornell Dublier, Phillips, and Sprague. My hunch is to use Sprague electrolytic if I cannot use a BiPolar.
All that is left now is for me to figure out the lowest working voltage rating can use and the best voltage I can use for C7.
Regards,
John L. Males
Willowdale, Ontario
Canada
12 May 2006 16:17
problem!?
Hi Quasi,
I power up my 2 amp modules and the sound is great, but something is wrong.
When I put sine wave (commputer sound card) at input (1khz) I only get about 8V in 10ohm resistor at output.
Also when I try to set bias current I could only get it to 60mA.
Interasting both of amp have indetical bias currents and output voltages.
Please Quasi and others give me some advice what to check or what could went wrong.
Hi Quasi,
I power up my 2 amp modules and the sound is great, but something is wrong.
When I put sine wave (commputer sound card) at input (1khz) I only get about 8V in 10ohm resistor at output.
Also when I try to set bias current I could only get it to 60mA.
Interasting both of amp have indetical bias currents and output voltages.
Please Quasi and others give me some advice what to check or what could went wrong.
Miodrag,
I may be way off here, but many a times it is suggested that the BCE's are checked on transistors to ensure are in correctly. When one uses a different transistor that too often the alternate has a different pinout than the original. As I recall you are using a BD139 for T8 and that has a different pinout than the BC546. I also recall the colouring of your wires from the PCB to BD139 were different in sense of you did not use the same colour to same pin or pad connection on PCB. Not matching the colours is not an issue of itself unless they were in fact supposed to match up the same way.
As it is same problem for both modlues my gut says either the same PCB error was made or the same error to a connection I suspect is transistor related has been made. Check the BD139's first. I suspect there is no shorting between heatsink and output devices/Vbe, but recheck just to make sure none of them are shorting to the heatsink case.
Did you set up the bias using the technique quasi suggests with resistors in place of the fuses?
I am am not an expert like many here, so I could be way off base in my suggestions.
Regards,
John L. Males
Willowdale, Ontario
Canada 12 May 2006 17:38
I may be way off here, but many a times it is suggested that the BCE's are checked on transistors to ensure are in correctly. When one uses a different transistor that too often the alternate has a different pinout than the original. As I recall you are using a BD139 for T8 and that has a different pinout than the BC546. I also recall the colouring of your wires from the PCB to BD139 were different in sense of you did not use the same colour to same pin or pad connection on PCB. Not matching the colours is not an issue of itself unless they were in fact supposed to match up the same way.
As it is same problem for both modlues my gut says either the same PCB error was made or the same error to a connection I suspect is transistor related has been made. Check the BD139's first. I suspect there is no shorting between heatsink and output devices/Vbe, but recheck just to make sure none of them are shorting to the heatsink case.
Did you set up the bias using the technique quasi suggests with resistors in place of the fuses?
I am am not an expert like many here, so I could be way off base in my suggestions.
Regards,
John L. Males
Willowdale, Ontario
Canada 12 May 2006 17:38
Hi Pejinm,
Can you let me know what your voltage rails are and also your power supply configuration i.e, transformer size capacitor bank size.
Also how are you measuring the output? Is it with a meter or CRO. You need to be sure that you are measuring the output just before the amplifier clips and this needs to be observed on the CRO. Some meters will not give an accurate reading at 1kHz.
To test if T8 is working properly simply heat it up (gently). This will cause bias current to reduce.
If both modules show the same characteristics and they sound good then your amp is probably perfect.
Give me the above information and we'll go from there.
Cheers
Quasi
Can you let me know what your voltage rails are and also your power supply configuration i.e, transformer size capacitor bank size.
Also how are you measuring the output? Is it with a meter or CRO. You need to be sure that you are measuring the output just before the amplifier clips and this needs to be observed on the CRO. Some meters will not give an accurate reading at 1kHz.
To test if T8 is working properly simply heat it up (gently). This will cause bias current to reduce.
If both modules show the same characteristics and they sound good then your amp is probably perfect.
Give me the above information and we'll go from there.
Cheers
Quasi
The feedback capacitor thing;
In my amp I used a plain polarised electrolytic..... Please don't report me to any fanatical audio group....
In theory this junction is at 0v DC potential and so no reverse biasing will occur. Even if the output sat a 100mV or so (a really bad condition) the voltage would be divided by 30 (assuming the cap started to conduct)
Granted if the amp develops a fault and the output swings the right way (or wrong way depending on your point of view) and other components failed then this capacitor could meet it's maker. It would though only be one of several parts replaced.
So is a non-polar electrolytic better? Yes a good one is, but remember that non-polar electrolytics are the equivalent of two polarised electrolytics back to back (that's why they are bigger). This can mean a higher ESR and inductance.
Of course a non-electrolytic would be great but it would be too big.
So once more, the world is full of compromises.....
Now I'm gonna put my crash helmet on...
Cheers
In my amp I used a plain polarised electrolytic..... Please don't report me to any fanatical audio group....
In theory this junction is at 0v DC potential and so no reverse biasing will occur. Even if the output sat a 100mV or so (a really bad condition) the voltage would be divided by 30 (assuming the cap started to conduct)
Granted if the amp develops a fault and the output swings the right way (or wrong way depending on your point of view) and other components failed then this capacitor could meet it's maker. It would though only be one of several parts replaced.
So is a non-polar electrolytic better? Yes a good one is, but remember that non-polar electrolytics are the equivalent of two polarised electrolytics back to back (that's why they are bigger). This can mean a higher ESR and inductance.
Of course a non-electrolytic would be great but it would be too big.
So once more, the world is full of compromises.....
Now I'm gonna put my crash helmet on...
Cheers
Hi Quasi,
Thanks for reply,
I have 400VA transformer with 4x4700uF/100V (per module) the rails are +/-72V.
I measured the output with standard digital multimeter, but also the sound level on speakers was very low for 350W amp.
I already try to heat up T8 and response was good.
I'm little bit concerned because I expect a lot stronger amp. Something is probably wrong with the modules.
Is there a chance that I put a wrong value resistor somewhere?
I also measured the current on the rails and it was 370mA at full gain with sine wave signal and 10ohms at output!
Regards,
Miodrag Pejin
Thanks for reply,
I have 400VA transformer with 4x4700uF/100V (per module) the rails are +/-72V.
I measured the output with standard digital multimeter, but also the sound level on speakers was very low for 350W amp.
I already try to heat up T8 and response was good.
I'm little bit concerned because I expect a lot stronger amp. Something is probably wrong with the modules.
Is there a chance that I put a wrong value resistor somewhere?
I also measured the current on the rails and it was 370mA at full gain with sine wave signal and 10ohms at output!
Regards,
Miodrag Pejin
Hi Miodrag,
Do you have access to CRO to check if the waveform is clipping.
If you cannot turn the amp up enough to get some clipping then either you do not have enough signal input or the feedback components are incorrect.
Check the level of signal going into the amp. It needs to be at around 1.5v RMS to achieve full output. If you are using the line out from your sound card you may not be getting enough drive.
Do you have another pre-amp you can use?
With your power supply you should get about 195 watts into 8 ohms (one channel driven). Driving both channels you should get around 150 watts per channel into 8 ohms.
Cheers
Do you have access to CRO to check if the waveform is clipping.
If you cannot turn the amp up enough to get some clipping then either you do not have enough signal input or the feedback components are incorrect.
Check the level of signal going into the amp. It needs to be at around 1.5v RMS to achieve full output. If you are using the line out from your sound card you may not be getting enough drive.
Do you have another pre-amp you can use?
With your power supply you should get about 195 watts into 8 ohms (one channel driven). Driving both channels you should get around 150 watts per channel into 8 ohms.
Cheers
Re[02]: The feedback capacitor thing;
Your secret is safe with me quasi.
lol lol lol .... No need for the crash helmut Quasi. I already assumed a non-electrolytic would be better, but boat anchor I did not want.
I was unaware that Bi-Polars were really just two electrolytics in one package.
Am I to assume the 0V DC potential, at worse 100mV, means I am safe choosing a capacitor with a working voltage of even 6.3V for C7? When one uses a electrolytic the - side faces signal ground or the + side for C7?
From your comments I will source the best quality electrolytic I available without much difficulty. The new commerical receiver I happened to pick up for $80.00 a few months ago sadly uses electrolytics even where one could use non-electrolytics. Still it sounds very respectable with 2SC5200/2SA1943 ouput stage, the 2SB649A and 2SD669A drivers and a torid PSU. In year or so when the warranty has run out I will open it up and see what the values are and maybe replace. I still have not been able to source the schematic from the manufacter.
I am going out later today for more parts shopping locally at the surplus store where I seem to be best able to find parts. I thought I found an additional source a few days ago. I decided to price a few items they carried against the general prices I have already been finding. They want to charge $6.00 for a 470uF 200V Nippon electrolytic cap which is $0.75 new in surplus store. What a rip off place, no wonder they do not even publish their prices, not even for their regular inventory stock. So it is back to being patient and sourcing as some parts come available.
The case/heatsink are my biggest challenge to find or make, otherwise I could make a pair of modules starting now. I am itiching to build, but only have 90% of what need.( ( (
Regards,
John L. Males
Willowdale, Ontario
Canada
13 May 2006 08:00
quasi said:
Your secret is safe with me quasi.
lol lol lol .... No need for the crash helmut Quasi. I already assumed a non-electrolytic would be better, but boat anchor I did not want.
I was unaware that Bi-Polars were really just two electrolytics in one package.Am I to assume the 0V DC potential, at worse 100mV, means I am safe choosing a capacitor with a working voltage of even 6.3V for C7? When one uses a electrolytic the - side faces signal ground or the + side for C7?
From your comments I will source the best quality electrolytic I available without much difficulty. The new commerical receiver I happened to pick up for $80.00 a few months ago sadly uses electrolytics even where one could use non-electrolytics. Still it sounds very respectable with 2SC5200/2SA1943 ouput stage, the 2SB649A and 2SD669A drivers and a torid PSU. In year or so when the warranty has run out I will open it up and see what the values are and maybe replace. I still have not been able to source the schematic from the manufacter.
I am going out later today for more parts shopping locally at the surplus store where I seem to be best able to find parts. I thought I found an additional source a few days ago. I decided to price a few items they carried against the general prices I have already been finding. They want to charge $6.00 for a 470uF 200V Nippon electrolytic cap which is $0.75 new in surplus store. What a rip off place, no wonder they do not even publish their prices, not even for their regular inventory stock. So it is back to being patient and sourcing as some parts come available.
The case/heatsink are my biggest challenge to find or make, otherwise I could make a pair of modules starting now. I am itiching to build, but only have 90% of what need.
( ( (Regards,
John L. Males
Willowdale, Ontario
Canada
13 May 2006 08:00
pejinm said:
Miodrag,
If you are using a "standard" standard multimeter it may not have a RMS rating over 400Hz, or 60Hz for that matter. That will likely skew the actual vs what meter measured. How much will be a function of meter's specs. Of course given a 1KHz signal the extent of the skew should not have had the 8V vs more like 50V reading I suspect you were looking for.
What wattage is the 10 ohm "dummy load? Is it a ceramic wirewound resistor?
Regards,
John L. Males
Willowdale, Ontario
Canada
13 May 2006 09:53
Hi Quasi,
Thanks for reply,
Yes, I own a oscilloscope but the amp is not clliping even at full gain and I still get 19V peak to peak.The level at input is about 1V p to p. I haven't tested the amps yet with some other preamp, I will do that very soon. Til then I will check my work another dozen times.
Hi John,
Thanks for reply,
The resitor is ceramic 10ohm 10 watts.
Regards,
Miodrag Pejin
P.S. I hope to find error very soon...
Thanks for reply,
Yes, I own a oscilloscope but the amp is not clliping even at full gain and I still get 19V peak to peak.The level at input is about 1V p to p. I haven't tested the amps yet with some other preamp, I will do that very soon. Til then I will check my work another dozen times.
Hi John,
Thanks for reply,
The resitor is ceramic 10ohm 10 watts.
Regards,
Miodrag Pejin
P.S. I hope to find error very soon...
Miodrag,
I am not sure what others do for a "dummy" load, but you may want to consider a more capable resistor/load. I suspect going for one large wirewound may not be best approach due to the larger inductance that may carry with it. If you take a larger value, say 200 ohms at 10 watts, and parallel 20 of them that should reduce the inductance one 10 ohm ceramic (wirewound) resistor has while increasing the power handling and still give you 10 ohms. In fact more resistive 10 ohms I believe than the one wirewound ceramic resister you are currently using. I am doing this strickly on the math. Others can confirm if the math in fact results in the real world mostly resistive "dummy" load for amplifier testing.
The reason I caution the "dummy" load to handle more power is at 8V RMS and 10 ohm load that only represents a resistive power of 6.4 watts. Right not you are not going to blow that 10W resistor, but once you get above about 12 V RMS you likely reach beyond of the headroom and short duty cycle you can subject the 10W resistor to before it starts to smoke or break down. I do not know the exact point this will happen, but the point is with a PSU of +-72 and accounting for rail losses, that will likely result in about +-41V RMS at the rails, ie 82 RMS. You are expecting about 140W at 10 ohms resistive, less due to inductive wirewound ceramic resister. I doubt you will be able to drive the amp to clipping before the 10W fails. I may be wrong here. Others with more real world experience can comment furether on this.
I am still newish to all this, so please have others with more experience to validate my points of theory and how well this translates to real world for a short duty cycle clipping test for the power rating of your amp modules. I have lots of theory I have absorbed (see quasi I absorb the answers to those question of you and others on form along with my reading ), but at same time there is a vast amount of theory, not to mention experience, others here have.
I just wanted to bring this you just in case. I tend to always wear safety glasses just in case something blows up and take other precatutions. Just something I practice as I do pick up lots from surplus stores. No major poofs yet, but I err on safe side. I also really like the quasi method to set bias as ity reduces risk of putting $$ into smoke, not to mention the other risks that exist if one does nto use reistors in place of fuses on initial power up.
I am sure the experts here will help you solve the issue for you. Some things just take time and patience
Regards,
John L. Males
Willowdale, Ontario
Canada
13 May 2006 15:01
13 May 2006 15:10 Typo corrections
I am not sure what others do for a "dummy" load, but you may want to consider a more capable resistor/load. I suspect going for one large wirewound may not be best approach due to the larger inductance that may carry with it. If you take a larger value, say 200 ohms at 10 watts, and parallel 20 of them that should reduce the inductance one 10 ohm ceramic (wirewound) resistor has while increasing the power handling and still give you 10 ohms. In fact more resistive 10 ohms I believe than the one wirewound ceramic resister you are currently using. I am doing this strickly on the math. Others can confirm if the math in fact results in the real world mostly resistive "dummy" load for amplifier testing.
The reason I caution the "dummy" load to handle more power is at 8V RMS and 10 ohm load that only represents a resistive power of 6.4 watts. Right not you are not going to blow that 10W resistor, but once you get above about 12 V RMS you likely reach beyond of the headroom and short duty cycle you can subject the 10W resistor to before it starts to smoke or break down. I do not know the exact point this will happen, but the point is with a PSU of +-72 and accounting for rail losses, that will likely result in about +-41V RMS at the rails, ie 82 RMS. You are expecting about 140W at 10 ohms resistive, less due to inductive wirewound ceramic resister. I doubt you will be able to drive the amp to clipping before the 10W fails. I may be wrong here. Others with more real world experience can comment furether on this.
I am still newish to all this, so please have others with more experience to validate my points of theory and how well this translates to real world for a short duty cycle clipping test for the power rating of your amp modules. I have lots of theory I have absorbed (see quasi I absorb the answers to those question of you and others on form along with my reading
), but at same time there is a vast amount of theory, not to mention experience, others here have.I just wanted to bring this you just in case. I tend to always wear safety glasses just in case something blows up and take other precatutions. Just something I practice as I do pick up lots from surplus stores. No major poofs yet, but I err on safe side. I also really like the quasi method to set bias as ity reduces risk of putting $$ into smoke, not to mention the other risks that exist if one does nto use reistors in place of fuses on initial power up.
I am sure the experts here will help you solve the issue for you. Some things just take time and patience
Regards,
John L. Males
Willowdale, Ontario
Canada
13 May 2006 15:01
13 May 2006 15:10 Typo corrections
Hi Ahmad,
Yes the first power on is still stressful for me too.
First make sure that there is no connection from the heatsink to the FETs.
Insert the fuses then using a meter measure across the power inputs to ground to make sure they are high impedance (just in case there is a simple mistake.
All being well remove the fuses and insert the 100 ohm resistors (5w), connect your leads. Check your connections (reversed leads will hurt the amp).
Pray and turn on....
If there is no smoke check your voltages across the 100 ohm resistors.
Good Luck
Yes the first power on is still stressful for me too.
First make sure that there is no connection from the heatsink to the FETs.
Insert the fuses then using a meter measure across the power inputs to ground to make sure they are high impedance (just in case there is a simple mistake.
All being well remove the fuses and insert the 100 ohm resistors (5w), connect your leads. Check your connections (reversed leads will hurt the amp).
Pray and turn on....
If there is no smoke check your voltages across the 100 ohm resistors.
Good Luck
Hi Ahmad,
before you connect up for the first time!!
Wire a mains rated light bulb in series with the primary of the transformer.
You can wire this as a plug then the bulb and it's own socket and then a three pin socket for the untested equipment.
Then just switch on and the bulb should flash very briefly and go out. This indicates that the transformer is drawing a small current.
If you equipment is faulty the light may glow after switch on or may be bright. Both these conditons indicate that the transformer is drawing significant current. This could be normal, but it is on and you can start measuring voltages until you have proved it is operating correctly or there is a wiring or component error.
The bulb virtually eliminates the risk of blowing up faulty equipment. You may still damage miswired components but almost no risk to life from explosions.
Be safe wire up a light bulb.
before you connect up for the first time!!
Wire a mains rated light bulb in series with the primary of the transformer.
You can wire this as a plug then the bulb and it's own socket and then a three pin socket for the untested equipment.
Then just switch on and the bulb should flash very briefly and go out. This indicates that the transformer is drawing a small current.
If you equipment is faulty the light may glow after switch on or may be bright. Both these conditons indicate that the transformer is drawing significant current. This could be normal, but it is on and you can start measuring voltages until you have proved it is operating correctly or there is a wiring or component error.
The bulb virtually eliminates the risk of blowing up faulty equipment. You may still damage miswired components but almost no risk to life from explosions.
Be safe wire up a light bulb.
Hi Quasi,
I found out from datasheet of 2sc2240 that they have lower dc current gain than 2sc1845.
Is it possible that this can reduce amp power?
Is it safe to increase the value of R17(33k feedback transistor) to 47k to rise the amp gain?
Thanks in advance for reply!!!
Regards,
Miodrag Pejin
I found out from datasheet of 2sc2240 that they have lower dc current gain than 2sc1845.
Is it possible that this can reduce amp power?
Is it safe to increase the value of R17(33k feedback transistor) to 47k to rise the amp gain?
Thanks in advance for reply!!!
Regards,
Miodrag Pejin
AndrewT said:
Andrew,
The grades available from my text notes file I have been carrying about as I go parts shopping from some time and sourced from the datasheets are:
(2) 2SC1845 - T1, T5, NPN (Long Tail Pair), Low Noise, Vceo(V) 120, Ic(A) 0.050, PD(W) 0.5, fT(MHz) 50, hFE 200-1200 P 200-400 F 300-600 E 400-800 U 600-1200 (2SA992 complimentary)
Alternate - 2SC2240, Toshiba, Low Noise Vceo(V) 120, Ic(A) 0.10, PD(W) 0.300, fT(MHz) 100, hFE 200-700, NF(db) 4 (2-6) (2SA970 complimentary)
* 2SC2240GR, Toshiba, Low Noise Vceo(V) 120, Ic(A) 0.10, PD(W) 0.300, fT(MHz) 100, hFE 200-400, NF(db) 4 (2-6) (2SA970 complimentary)
** 2SC2240BL, Toshiba, Low Noise Vceo(V) 120, Ic(A) 0.10, PD(W) 0.300, fT(MHz) 100, hFE 350-700, NF(db) 4 (2-6) (2SA970 complimentary)
I left the other info in my notes just in case you need it. This is a straight copy/paste from my project notes text file for quasi's amplifier.
I hope this is the information you are looking for Andrew. I do not have hFE sample measurements for either of the 2SC1845 or 2SC2240 handy. I can tell you the few I sampled in the store before I bought a number of them was they were all in the >300hFE range. I was using the hFE function of your average run of mill multimeter. I will be building a hFE tester later to help match hFE's more closly for each module I build to test at the currents the devices will be operating at.
Regards,
John L. Males
Willowdale, Ontario
Canada
14 May 2006 21:25
14 May 2006 21:27 Typo Corrections