I'm no expert but...
Looks like someone forgot to update the component values to ones that will work.
Feedback is taken from the protection circuit - a connection from there to the output would be appropriate. As is you've got a comparator except that there is virtually no current in the differential because the load resistors are too high.
The 100 pf feedback cap means your low frequency limit is above the audio band. 100 K and 100K means once you get in band you'll have a gain of 2 if the feedback is properly connected.
The Vbe multiplier isn't correct - as drawn it is a diode connected transistor in series with 100K. The CCS is trying to sink 6 mA - (too low for a VAS) and the VAS Q will be saturated by the excess base voltage due to the LTP load. This means the 100K in the "Vbe multiplier has almost rail to rail voltage across it. This tries to blow the outputs. I'm not sure if the protection circuit will prevent blowing outputs or not - it is missing a reference to the output.
You'll probably want to add a predriver to ensure enough current drive capability.
35V rails are enough to get maybe 100V peaks, but this is more of a 60W size supply. One pair of MJL21194/3 will do fine unless you plan to make
Try Mike B's Symasym if you have a 35V supply.
Looks like someone forgot to update the component values to ones that will work.
Feedback is taken from the protection circuit - a connection from there to the output would be appropriate. As is you've got a comparator except that there is virtually no current in the differential because the load resistors are too high.
The 100 pf feedback cap means your low frequency limit is above the audio band. 100 K and 100K means once you get in band you'll have a gain of 2 if the feedback is properly connected.
The Vbe multiplier isn't correct - as drawn it is a diode connected transistor in series with 100K. The CCS is trying to sink 6 mA - (too low for a VAS) and the VAS Q will be saturated by the excess base voltage due to the LTP load. This means the 100K in the "Vbe multiplier has almost rail to rail voltage across it. This tries to blow the outputs. I'm not sure if the protection circuit will prevent blowing outputs or not - it is missing a reference to the output.
You'll probably want to add a predriver to ensure enough current drive capability.
35V rails are enough to get maybe 100V peaks, but this is more of a 60W size supply. One pair of MJL21194/3 will do fine unless you plan to make
Try Mike B's Symasym if you have a 35V supply.
There is enough for adequate current drive there; but as BobEllis mentions, there are some serious problems.
The 100K resistors in the diff amp are way too big, and the one on the right hand side shouldn't even be there, it should just be tied straight to the positive rail.
I use 6mA current sources in some of my large designs as the VAS without any trouble here.
Otherwise, all of the above mentioned faults are definitely there. Having no feedback loop is definitely going to make things bad to start with... You'll likely see some mad DC at the output if you actually fire this circuit up.
BobEllis: You must mean 100W peaks and not 100V peaks?
At most you'll be getting 70 or so watts for 8 ohms... A set of 45V rails is more what you want for 100W to 8 ohms. And one pair of the specified output transistors will do it like Bob mentioned.
The 100K resistors in the diff amp are way too big, and the one on the right hand side shouldn't even be there, it should just be tied straight to the positive rail.
I use 6mA current sources in some of my large designs as the VAS without any trouble here.
Otherwise, all of the above mentioned faults are definitely there. Having no feedback loop is definitely going to make things bad to start with... You'll likely see some mad DC at the output if you actually fire this circuit up.
BobEllis: You must mean 100W peaks and not 100V peaks?
At most you'll be getting 70 or so watts for 8 ohms... A set of 45V rails is more what you want for 100W to 8 ohms. And one pair of the specified output transistors will do it like Bob mentioned.
Hahahaha, you crack me up... I was thinking something to that order myself.
Maybe I should be a bit more helpful too.... Perhaps a resistor in the 2.2K to 10K range and you'll be then in the ballpark. Or a current mirror? Those do make life easy and can have some nice benefits, but don't get carried away like I do.
Maybe I should be a bit more helpful too.... Perhaps a resistor in the 2.2K to 10K range and you'll be then in the ballpark. Or a current mirror? Those do make life easy and can have some nice benefits, but don't get carried away like I do.
Hi,
It looks like the poster has re-drawn the circuit for our benefit and forgotten to change the components and left out a few connections.
The VAS current is OK @ 6mA. It could go even lower with all that current gain in the driver hFE~100 to140 and output ~30 to50.
The LTP could go a lot lower than 6mA try 2mA. There is nothing wrong with the resistors in BOTH collectors of the LTP, it helps keep the operating conditions for both halves the same. Keep in mind that the other half (inverting) operates as an amplifier just as often as the non-inverting side.
The IV protection circuit is missing two resistors on each half. That shown has a poor protection locus.
Add the missing resistor in the upper leg of the Vbe multiplier base side.
It looks like the poster has re-drawn the circuit for our benefit and forgotten to change the components and left out a few connections.
The VAS current is OK @ 6mA. It could go even lower with all that current gain in the driver hFE~100 to140 and output ~30 to50.
The LTP could go a lot lower than 6mA try 2mA. There is nothing wrong with the resistors in BOTH collectors of the LTP, it helps keep the operating conditions for both halves the same. Keep in mind that the other half (inverting) operates as an amplifier just as often as the non-inverting side.
The IV protection circuit is missing two resistors on each half. That shown has a poor protection locus.
Add the missing resistor in the upper leg of the Vbe multiplier base side.
Quite simple, R3/4/6/12 can NEVER be 100k.
You seem only to have 100ohms and 100kohms. An amp does not work that way.
Also, you are missing a resistor from T6 base to R10. You are missing a connection between output and emitters of T7/8.
The emitters of t9/10 need to be connected with a resistor.
R12 is way too big, r10 is way too small.
The whole schematic is competely flawed and can never work.
Also, it's nuts to have 3 output pairs with a supply voltage of +/- 35v. Even a single pair of MJL21194/3 will be "bored" driving a 4ohm load.
R3/4 need to be carefully calculated, 100k is way too big, driving T1/2 into reverse bias.
R6 sets the gain of the amplifier to a stunning 1:2.
Shall i continue ?
Mike
You seem only to have 100ohms and 100kohms. An amp does not work that way.
Also, you are missing a resistor from T6 base to R10. You are missing a connection between output and emitters of T7/8.
The emitters of t9/10 need to be connected with a resistor.
R12 is way too big, r10 is way too small.
The whole schematic is competely flawed and can never work.
Also, it's nuts to have 3 output pairs with a supply voltage of +/- 35v. Even a single pair of MJL21194/3 will be "bored" driving a 4ohm load.
R3/4 need to be carefully calculated, 100k is way too big, driving T1/2 into reverse bias.
R6 sets the gain of the amplifier to a stunning 1:2.
Shall i continue ?
Mike
Hi Pro,
without actually counting the components, I guess 95% of the components have the wrong value.
The circuit cannot work as posted.
There are missing links between stages.
The circuit cannot work.
There are components in the wrong place.
The circuit cannot work.
There are components missing.
The circuit cannot work.
Bin it and start again with a known good design. Oh, keep the MJL21193/4s and MJE15031/2s
without actually counting the components, I guess 95% of the components have the wrong value.
The circuit cannot work as posted.
There are missing links between stages.
The circuit cannot work.
There are components in the wrong place.
The circuit cannot work.
There are components missing.
The circuit cannot work.
Bin it and start again with a known good design. Oh, keep the MJL21193/4s and MJE15031/2s
I hope not to be nearly as pessimistic as the others...
This circuit resembles that of something that works very well.
Simply put, some of the most key parts of the circuit are completely incorrect.
I would really recommend something to the extent of a Rod Elliot project 3A for you. It's not much different from what you're after, and trust me, it -does- work.
Project 3A
This circuit resembles that of something that works very well.
Simply put, some of the most key parts of the circuit are completely incorrect.
I would really recommend something to the extent of a Rod Elliot project 3A for you. It's not much different from what you're after, and trust me, it -does- work.
Project 3A
Re: Project 3A
Hi Duo,
Not without some leanings toward instability:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=88256&perpage=10&pagenumber=1
Cheers
ps: end of that thread: put a 0.1 cap across the bias transistor C-E; possibly put a small(ish) capacitance across the feedback resistor...
Hi Duo,
Not without some leanings toward instability:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=88256&perpage=10&pagenumber=1
Cheers
ps: end of that thread: put a 0.1 cap across the bias transistor C-E; possibly put a small(ish) capacitance across the feedback resistor...
Hi,
much better.
Now we can be more useful to you.
Is C4 needed?
C1 will remove too much bass, good as a mid or treble amp, but could be increased to 1000uF.
Signal ground is missing from the top of r3. Connect the RCA barrel (using the screen) to this and then connect this to audio ground (you need two PCB holes next to the non-inverting input connection) with a 0.5sqmm wire.
Try to research IV protection the scheme you have here is not good, but ALL the components you have are in the correct place, some resistors are missing.
much better.
Now we can be more useful to you.
Is C4 needed?
C1 will remove too much bass, good as a mid or treble amp, but could be increased to 1000uF.
Signal ground is missing from the top of r3. Connect the RCA barrel (using the screen) to this and then connect this to audio ground (you need two PCB holes next to the non-inverting input connection) with a 0.5sqmm wire.
Try to research IV protection the scheme you have here is not good, but ALL the components you have are in the correct place, some resistors are missing.
Hi
Change R6 to 1K and R11 to 22K , that way you will have lower offset and in that case the C2 100 uF capacitor become enough.
Put a100 ohms resistor between the bases of the output transistors.
Don't use a polarized capacitor in series with the 10 Ohms resistor in the Zobel network, use a plastic one.
Cheers
Change R6 to 1K and R11 to 22K , that way you will have lower offset and in that case the C2 100 uF capacitor become enough.
Put a100 ohms resistor between the bases of the output transistors.
Don't use a polarized capacitor in series with the 10 Ohms resistor in the Zobel network, use a plastic one.
Cheers
provyf said:
The schematics has a lot of funny values of resistors. NFB is taken from the wrong point and this mean that, even resistor values was correct (and they aren't), amplifier will be in a open NFB state, i.e. steadily looked up on one of two supply rails and not working at all.
Trash this schematic and pick a new one from somewhere. This appear to be designed by a one which don't understand as a solid state amplifier work.
If you wil, look on the web for Leach Amplifier and start from here at least for dimensioning correct values of components
Piercarlo
PS - Sorry for my english but is not my main language.
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