Helo friends I am building class Ab Amp using this schematic Do i need some changes for better performance?
Thanks In Advance...
Thanks In Advance...
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The design itself is defining the quality. It looks workable but its not a great design in the scheme of things. I would recommend using lower supply rails seeing as TIP41/42C's are used as drivers and VAS stages. 70 volts in total -/+35 is more than enough.
The fixed bias arrangement isn't great but you would have to build it to see what sort of bias current you get and how stable it is.
The fixed bias arrangement isn't great but you would have to build it to see what sort of bias current you get and how stable it is.
Hi Zohaib
I am a little bit concerned about the bias-configuration:
You have 2 diodes drop plus the voltage over R7 compared to 3 base-emitter drops though the output stage.
This may - depending on the exact characteristics of the the 1N1007's and the base-emitter of Q1, Q3 and Q4 - give you a very low idle current.
So low in fact that cross-over distortion could give you problems.
You may consider adding a diode and a trimpot across all the diodes for idle current adjustment.
Cheers, Martin
I am a little bit concerned about the bias-configuration:
You have 2 diodes drop plus the voltage over R7 compared to 3 base-emitter drops though the output stage.
This may - depending on the exact characteristics of the the 1N1007's and the base-emitter of Q1, Q3 and Q4 - give you a very low idle current.
So low in fact that cross-over distortion could give you problems.
You may consider adding a diode and a trimpot across all the diodes for idle current adjustment.
Cheers, Martin
This looks like a circuit not to be built, but one to teach the basics of an amplifier. It's performance would not be very good. Will it amplify? probably.
Have you simulated this in SPICE?
Have you read Self and Cordell?
Have you analyzed other well understood schematics?
No RF filter in input
IPS, no current mirror, no constant current source
VAS, no Constant current source
Fixed bias, no thermal compensation
Severally limiting voltage to the IPS.VAS. Excessive rail resistors
No adjustment for DC offset
Questionable compensation methods
Very poor PSRR
No protection circuits, DC, power, thermal...
No muting
Why the small power supply cap on the negative rail?
1N4007 may not be the quietest diode choice
100W through only one output pair? Not a good choice by far.
Why are R15 and R11 not the same.
So, yes many many changes for quality. How much power you want is up to you.
You have also not included the power supply nor anything on the physical layout and construction which can have large effects on the quality.
Have you simulated this in SPICE?
Have you read Self and Cordell?
Have you analyzed other well understood schematics?
No RF filter in input
IPS, no current mirror, no constant current source
VAS, no Constant current source
Fixed bias, no thermal compensation
Severally limiting voltage to the IPS.VAS. Excessive rail resistors
No adjustment for DC offset
Questionable compensation methods
Very poor PSRR
No protection circuits, DC, power, thermal...
No muting
Why the small power supply cap on the negative rail?
1N4007 may not be the quietest diode choice
100W through only one output pair? Not a good choice by far.
Why are R15 and R11 not the same.
So, yes many many changes for quality. How much power you want is up to you.
You have also not included the power supply nor anything on the physical layout and construction which can have large effects on the quality.
Thanks For Huge Explanation Yes You Are Right This Is Not A Good Circuit For Build. There are Lot Of Changes To Do with This Schematic.
I Am Using 35v AC Transformer with it...
Thanks Mooly... Now I Come To Know That This Is Not A Good Circuit For Amplifier So I Will Try Another Design for My Project.,.
Thanks For Reoly
Thanks For Reply Martin I Have Not Design This Circuit My Self I Just Want To Make npn outout transistor amplifier So I Just Download It From Internet I Think This Is very Poorly Design Shematic With fixed Bias..
Can You modify It For me With diodes and Trim port For Perfect Output with Good Sound Quality I am Using 35v AC Transformer
I don't think that is a lot better, Zohaib. Several points to think about:
1. No obvious need for 33 ohm on right side of input pair.
2. No emitter degeneration on input pair- this pushes the high frequency response up, needing a big compensation capacitor (150pF ios getting on a bit) and leading to generally poor slew rates.
3. You have been advised to think about the bias. The circuit is far from optimum. You need to considerone of three options :
4. The two diode and resistor bias is so old hat and should be replaced by a Vbe multiplier, preferably with a pot to adjust the bias.
5. TIP42/43 are not good drives IMHO. They are ~3MHz and are better suited as low/medium power output devices.
6. The 2SC3280's are fast devices and are better driven with faster drivers.
You may have some problems stabilising a fast driver and fast output stage in the PNP/NPN configuration, which could require base stopper resistors but you have got stopper capacitors in your diagram.
My recommendation is to read Self's Blameless design and adapt that for NPN only output.
1. No obvious need for 33 ohm on right side of input pair.
2. No emitter degeneration on input pair- this pushes the high frequency response up, needing a big compensation capacitor (150pF ios getting on a bit) and leading to generally poor slew rates.
3. You have been advised to think about the bias. The circuit is far from optimum. You need to considerone of three options :
- changing the PNP/NPN output stage so that the PNP emitter connects to the NPN collector and then to an "emitter" resistor, or at least adding a small resistor, typically a tenth of the base resistor of the NPN output (that is to say 10 ohms) in series with the emitter of the PNP. But then you run a risk of latch-up unless you have some means of limiting the current in the VAS transistor.
- adding a second 100 ohm resistor in series with the PNP and a second "emitter" resistor in series with the collector of the NPN and connecting the two with a diode such as a UF4002 to make a more balanced output stage
- or 3, move the emitter resistor to the collector of the NPN and connect the emitter of the PNP to it.
4. The two diode and resistor bias is so old hat and should be replaced by a Vbe multiplier, preferably with a pot to adjust the bias.
5. TIP42/43 are not good drives IMHO. They are ~3MHz and are better suited as low/medium power output devices.
6. The 2SC3280's are fast devices and are better driven with faster drivers.
You may have some problems stabilising a fast driver and fast output stage in the PNP/NPN configuration, which could require base stopper resistors but you have got stopper capacitors in your diagram.
My recommendation is to read Self's Blameless design and adapt that for NPN only output.
Look at this schematic https://www.diyaudio.com/forums/solid-state/236256-retro-amp-50w-single-supply-42.html
Apex AX6 is much better throught out with fewer parts. With 70 v rail & MJ15003 output transistors my build got 70 w/ch 8 ohms 5 seconds.
Will work with TIP41c/42c drivers, but sounds a lot better on high frequencies like top octave piano with MJE15028/29 drivers. Use VAS ft 20 mhz or above. MJ15028 again. Page 42 is my build with pictures. Other pages show a board layout. Mine was point to point with output transistors remote from the driver board. MJ802, MJL3281mjl 4281 MJL21194 would also work for output transistors. 2sc5200 would be safe for a little less wattage than the MJ15003 etc.
Apex AX6 is much better throught out with fewer parts. With 70 v rail & MJ15003 output transistors my build got 70 w/ch 8 ohms 5 seconds.
Will work with TIP41c/42c drivers, but sounds a lot better on high frequencies like top octave piano with MJE15028/29 drivers. Use VAS ft 20 mhz or above. MJ15028 again. Page 42 is my build with pictures. Other pages show a board layout. Mine was point to point with output transistors remote from the driver board. MJ802, MJL3281mjl 4281 MJL21194 would also work for output transistors. 2sc5200 would be safe for a little less wattage than the MJ15003 etc.
Thanks bro But I Have Not lot Of Knowledge About Amplifiers There For I Always Came Here For Any Kind Of Solution You All Guys Have Great Knowledge About. Electronics And You Always Helped Me Thanks..
Thanks I Have Seen Your Schematic Apex Ax6 Thats Good But I Am Confused With Bias??
Here is where you will learn the basics about amplifiers:
Robert Cordell Engineering Audio Power Amplifiers
Douglas Self Audio Power Amplifier Design Handbook
or for the math heavy theory, Marshal Leach Introduction to Electroacoustics and Audio Amplifier Design
You can look for posts and WEB sites from folks like Nelson Pass, John Curl, and Jan Didden. Oh, don't forget Ron Elliot, Elliot Sound Products.
Then download whatever version of SPICE is available to you. I expect it is available to you. I use LTSpice.
Yes, your second "version" is a bit better. But, do you understand why each change may be better?
There are many ways to get something done. The actually smart folks I mention all have slightly different approaches. Even me, with my very limited experience, have my preferences. For example, I tend to like MOSFET outputs.
When you get in deep and understand the differences, it gets quite fun. You don't get much just copying a design.
Here is one I was playing with when I was first learning. Not finished and I have even more "hindsight" and would change it quite bit if I were to build one. (no claims if it would actually work, so do not build it!) But it is a fairly strait forward design covering the basics. You can also find schematics for well respected amps, everything from the Aragon, Music Fidelity, Creek, Quad, Parasound, and many more. All different for different reasons. Informative to see the differences.
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You are getting there, but you should be considering better transistors for the VAS/CCS and drivers.
Indianajo suggested MJE15028/29 and that is a good choice for the drivers.
For the vas/CCS you should think about devices like 2SC3503/KSC3503 and 2SA/KSA1381.
You have now gone for complementary outputs, but you can improve the design by using just one resistor between the output bases, you don't need separate ones. Whether you add a capacitor as well is debatable. Self suggests using one; often a moderate value helps with stability but a lower resistor value does not have the charging/discharging effects of a capacitor but increases driver dissipation.
But you still have the basic slew-inducing input stage, and now the compensation capacitor is 330pF! Whether that is even needed with a slow TIP VAS is questionable, but is likely to limit the audio quality at the top end.
And, your three-diode bias is not optimum. You should use a Vbe multiplier of some description.
Do read up on Self's blameless design ... you are making your way there slowly. I'm sure his original Wireless World/Electronics World articles may be available on line perhaps on Electronics World web site or Self's.
Finally, it appears you are aiming at a 4 ohm speaker for 200W.
Not sure that a pair of output devices will be enough. I use a set of 3 pairs for 100W into 8 ohms.
This is due to the need for good second breakdown protection.
You should really read up on these things if you want to progress.
Self and Cordell's books are strongly recommended if you can't read Self's articles from the mid-1990's.
Indianajo suggested MJE15028/29 and that is a good choice for the drivers.
For the vas/CCS you should think about devices like 2SC3503/KSC3503 and 2SA/KSA1381.
You have now gone for complementary outputs, but you can improve the design by using just one resistor between the output bases, you don't need separate ones. Whether you add a capacitor as well is debatable. Self suggests using one; often a moderate value helps with stability but a lower resistor value does not have the charging/discharging effects of a capacitor but increases driver dissipation.
But you still have the basic slew-inducing input stage, and now the compensation capacitor is 330pF! Whether that is even needed with a slow TIP VAS is questionable, but is likely to limit the audio quality at the top end.
And, your three-diode bias is not optimum. You should use a Vbe multiplier of some description.
Do read up on Self's blameless design ... you are making your way there slowly. I'm sure his original Wireless World/Electronics World articles may be available on line perhaps on Electronics World web site or Self's.
Finally, it appears you are aiming at a 4 ohm speaker for 200W.
Not sure that a pair of output devices will be enough. I use a set of 3 pairs for 100W into 8 ohms.
This is due to the need for good second breakdown protection.
You should really read up on these things if you want to progress.
Self and Cordell's books are strongly recommended if you can't read Self's articles from the mid-1990's.
This bias is controlled by the stack of 2 diodes and 27 ohm resistor between the two driver emitters. Actually I use a 100 ohm pot instead of a 27 ohm resistor. I mounted the 3 parts above the output transistors heat sink to pick up the heat & collapse the voltage when hotter. You can see them in the picture on p 42. I paralleled the pot with a 3rd diode in case the wiper of the pot let go. You short the wiper of the pot to one end. I set the idle bias current to 20 ma which is 40 mv across one of the output emitter resistors. I have a lower O.T. .51 ohm emitter resistor too.
The schematic of post 15 has 12 transistors instead of 6, and more resistor. Possible if you have a circuit board, a lot more trouble point to point with wire on bare board. Plus with any of the split supply versions, you make one iffy solder joint that lets go later, the output goes to +rail or -rail and tears your speaker suspension or overheats your speaker winding. The speaker capacitor amps that problem is solved by a $3 3300 uf capacitor. Other DC on speaker protection schemes have 6 to 8 times the part count. Those 6 extra transistors of post 15 increase resistance to rail voltage variation, which I solve by a 1 transistor 1 diode regulator on my rail voltage. 30 or more wires to lay on a point to point bare board.
Your post #14 has complimentary outputs instead of quasi-comp. I can't hear the difference on speakers with harmonic distortion >20 db below signal. (Peavey SP2(2004)) My comparison amp to the AX6 is a Peavey CS800s, that specifies HD at .03% full power. No speaker cap, no input cap, full-comp, no difference @ 1 W in my music room. Note 2sc5200 2sa1943 are 1.2A safe operating area @ 80 v parts. Not as tough as 1.5 A 80 v soa MJ15003 or tougher output transistors listed post 11. Don't try 2sc5200 at 75 W/ch for 5 seconds from 70 v rail as I did my unit. Note my transformer is very still. The advantage of all those extra transistors in post 15 is it allows a cheap undersized transformer to sound good for a short time. My transformer is 75 v 6.75A continuous.
The 2sc3503 and 2sa1381 mentioned in post 16 were not available in the US market. Nor 2sc4793 2sa1837. All 2sc 2sa available here are ebay, likely counterfeits. The TO220 case 20 mhz GE D44R4 VAS I'm using on AX6 sounds fine on top octave piano & tinkly bells. Dynaco used a 2n5320 VAS in TO5 case with 50 mhz, which also worked well once the crossover problems of that amp were sorted out by the djoffe mod. I have one 2n5320 surviving on my ST120, which channel sounds the same and is a little louder than the AX6 channel.
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I don’t know how many times we’ve got to keep saying this (sounds like i’m back in the 80’s scratching on turntables here): Don’t use TIPs for drivers. Don’t use TIPs for VAS. I don‘t care how refined the circuit is, they WILL compromise it. No, the original 2SC3503’s are not available anymore BUT the KSC’s are (if they are in stock). In a circuit like this, matching gain rank does not matter, so they don’t need to be both D or E. The best drivers to use in this application are the MJE1503x series. Again, since things are not terribly critical - you CAN mix and match voltage rank to get an NPN and a PNP that are in stock. Still 1000X better than using TIPs!!!!!! ANY modern Japanese driver pair will work if you can get them. The Jap types will also work in the VAS position.
TIPs are absolutely the worst possible choice for the VAS stage. I want to wring the neck of whatever idiot started suggesting them - and now it’s propagated all over the world. There is a temptation to use MJE1503x types instead, but the truth is they are really too big. Fast enough, yes, but there is still too much capacitance to drive. Large enough that you can often get away without the compensation capacitor - but the internal capacitance is nonlinear and causes distortion. You are far better off with the proper SIZE transistor, and a fixed cap from collector to base. If you can’t get the proper types, at least use the MJE340/350. They are small enough, fast enough, and they ARE available on the gray market If that’s ALL you’re limited to. And they WILL work - Better than MJE1503x, and 1x10^6 X better than TIPs. With the usual caveats about fakes, of course. Back when you could get discarded CRT TV sets by the side of the road, the video output transistor (usually a NPN TO-202 not a typo) was PERFECT. 300 volts, about half an amp, low capacitance and VERY linear. Not as much gain as 2SC3503 but you can’t have everything. I salvaged every one I could get. Of course, it limited you to a boot strap drive with a PNP input stage, but that DOES work. Sometimes these types will show up on the gray or surplus markets because nobody wants them, and you can get a deal.
TIPs are absolutely the worst possible choice for the VAS stage. I want to wring the neck of whatever idiot started suggesting them - and now it’s propagated all over the world. There is a temptation to use MJE1503x types instead, but the truth is they are really too big. Fast enough, yes, but there is still too much capacitance to drive. Large enough that you can often get away without the compensation capacitor - but the internal capacitance is nonlinear and causes distortion. You are far better off with the proper SIZE transistor, and a fixed cap from collector to base. If you can’t get the proper types, at least use the MJE340/350. They are small enough, fast enough, and they ARE available on the gray market If that’s ALL you’re limited to. And they WILL work - Better than MJE1503x, and 1x10^6 X better than TIPs. With the usual caveats about fakes, of course. Back when you could get discarded CRT TV sets by the side of the road, the video output transistor (usually a NPN TO-202 not a typo) was PERFECT. 300 volts, about half an amp, low capacitance and VERY linear. Not as much gain as 2SC3503 but you can’t have everything. I salvaged every one I could get. Of course, it limited you to a boot strap drive with a PNP input stage, but that DOES work. Sometimes these types will show up on the gray or surplus markets because nobody wants them, and you can get a deal.
Oh, now I’ve got to take that particular statement BACK. I remember the ”high end” Gallien-Krueger bass guitar combo amp I had to rebuild once - that used MJ15022 in the VAS position. Yes, that is worse than a TIP41.
MJ15032 has more capacitance than a MJ15028 as a 250 v part. Both are 30 mhz Ft parts. Guitar amps don't have to amplify higher than 7000 hz. Most males are deaf above that point anyway. I'm not. I used earplugs.
I tried fairchild TIP41c/42c & TIP31c/32c as drivers. They had much worse highs than the 2n53202n5322 on the other channel. MJE15028/29 sound the same.
Apex AX6 suggests MJE340 for VAS. Main reason I don't, the original MJE340 has no Ft spec. TIP32c in a TO126 case would qualify, and probably that is what NTE & NJ semi *****semi etc sell.
I tried fairchild TIP41c/42c & TIP31c/32c as drivers. They had much worse highs than the 2n53202n5322 on the other channel. MJE15028/29 sound the same.
Apex AX6 suggests MJE340 for VAS. Main reason I don't, the original MJE340 has no Ft spec. TIP32c in a TO126 case would qualify, and probably that is what NTE & NJ semi *****semi etc sell.
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