joan2 and mikek,
Indeed I have heard comments regarding this topology like the one you posted. However, if you can see in the pic, the amp is only constructed in a piece of wood (poor grounding), very thin wires, very small filter caps and so on but the amp is still running well. The heatsinks are small and for others it may seem inadequate but at zero volume they are cool. I am keen in watching for any hum, offset, oscillation and others beside music.
I have completed my leach amp months ago and was very pleased with it's sound but I feel it lacks punch at low freqs. Any neighbor that hears my leach amp becomes amazed that it sounds vivid and clear but all of them have the same observation, it's like something is missing.
Anyway, after I save enough money for a chassis and other accesories I think I will move on and find other amps to build. Isn't that what diy is all about, yes?
Best regards,
JojoD
Indeed I have heard comments regarding this topology like the one you posted. However, if you can see in the pic, the amp is only constructed in a piece of wood (poor grounding), very thin wires, very small filter caps and so on but the amp is still running well. The heatsinks are small and for others it may seem inadequate but at zero volume they are cool. I am keen in watching for any hum, offset, oscillation and others beside music.
I have completed my leach amp months ago and was very pleased with it's sound but I feel it lacks punch at low freqs. Any neighbor that hears my leach amp becomes amazed that it sounds vivid and clear but all of them have the same observation, it's like something is missing.
Anyway, after I save enough money for a chassis and other accesories I think I will move on and find other amps to build. Isn't that what diy is all about, yes?
Best regards,
JojoD
Shorter nfb path at HF.
By including the entire amplifier in the feedback loop at all frequencies you are just asking for stability troubles.
Suggestion -> Make a connection to the opamp output and use this for a proportionally greater percentage of the feedback signal with increasing frequency, instead of only from the final output stage. At normal audible frequencies though, the percentage of feedback from the opamp output can be quite low.
Someone else will have to suggest a starting value of R&C for this.
By including the entire amplifier in the feedback loop at all frequencies you are just asking for stability troubles.
Suggestion -> Make a connection to the opamp output and use this for a proportionally greater percentage of the feedback signal with increasing frequency, instead of only from the final output stage. At normal audible frequencies though, the percentage of feedback from the opamp output can be quite low.
Someone else will have to suggest a starting value of R&C for this.
Jojo,
Graham (Circlotron) is absolutely right, and knows a great deal about power amplifier design.
I second his suggestion. The first thing would be to add a small capacitor, silver mica is best, between the output of the IC and the inverting input. Start with 22pF and work up. This will pull more feedback from the IC alone with increasing frequency; you can reduce the feedback commensurately from the output stage by increasing the size of the 33pF cap across the feedback resistor, but to start out I'd leave it unchanged.
Secondly, the CFP output stage has a tendency to oscillate, particularly on the negative rail. Oscillation costs resolution and makes the outputs pretty hot, risking incineration through cross conduction. This can be eliminated by using a double emitter follower, that is, a conventional output stage with beefy drivers (2SC4793/2SA1837) and outputs (2SC5200/2SA1943).
Thirdly, there are very few ICs which will cope with 40V positive and negative rails, and since they are expensive you need to consider this. This is the reason most input and voltage amp stages of power amps with +36V rails and higher use discrete components.
Hope this is helpful,
Cheers,
Hugh
Graham (Circlotron) is absolutely right, and knows a great deal about power amplifier design.
I second his suggestion. The first thing would be to add a small capacitor, silver mica is best, between the output of the IC and the inverting input. Start with 22pF and work up. This will pull more feedback from the IC alone with increasing frequency; you can reduce the feedback commensurately from the output stage by increasing the size of the 33pF cap across the feedback resistor, but to start out I'd leave it unchanged.
Secondly, the CFP output stage has a tendency to oscillate, particularly on the negative rail. Oscillation costs resolution and makes the outputs pretty hot, risking incineration through cross conduction. This can be eliminated by using a double emitter follower, that is, a conventional output stage with beefy drivers (2SC4793/2SA1837) and outputs (2SC5200/2SA1943).
Thirdly, there are very few ICs which will cope with 40V positive and negative rails, and since they are expensive you need to consider this. This is the reason most input and voltage amp stages of power amps with +36V rails and higher use discrete components.
Hope this is helpful,
Cheers,
Hugh
Been watching this topic with some interest...wonder if anyone can make the PCBs and sell em out...I am willing to pay for a few...coz I can't make PCBs myself...anybody can teach me an easy no-frills way?? Seems a bit messy to me...anything that is messy doesn't agree well with my parents...I'm still 14...lolx....interests in bikes and amps have already burned a hole in my pocket~!!!
"Thirdly, there are very few ICs which will cope with 40V positive and negative rails, and since they are expensive you need to consider this. "
Why?
The output stage is running with a voltage gain of X4, the opamp is on ±15V. Looks fine for 200W/4R the way it is.
Circlotron's comments are on the money.
You do not want to use a screaming fast opamp in this circuit, a NE5532 is about right. If the opamp is slower than the output stage it will contribute to the loop stability.
Why?
The output stage is running with a voltage gain of X4, the opamp is on ±15V. Looks fine for 200W/4R the way it is.
Circlotron's comments are on the money.
You do not want to use a screaming fast opamp in this circuit, a NE5532 is about right. If the opamp is slower than the output stage it will contribute to the loop stability.
Re: reminds me of daniel meyer
Ahh, yes. The Tiger amp was the first amp I put together. Tiger Amp _Popular Electronics_,1972 The Tigersaurus was detailed in Radio Electronics, I believe, in 1974. It used MJ802 and MJ4502 output transistors like the Tiger, but it also used an unusual "slave" method of passing the speaker drive current through 2 parallel output transistors in series for each supply rail--4 outputs per rail total.
Ahh, yes. The Tiger amp was the first amp I put together. Tiger Amp _Popular Electronics_,1972 The Tigersaurus was detailed in Radio Electronics, I believe, in 1974. It used MJ802 and MJ4502 output transistors like the Tiger, but it also used an unusual "slave" method of passing the speaker drive current through 2 parallel output transistors in series for each supply rail--4 outputs per rail total.
Ulp, DJK, I missed that. Didn't have values on the schematic and didn't realize the gain was only four.
You are quite right, and thank you for pointing it out.
My point about using a double emitter follower is still true; this configuration is more stable than the CFP, though stability is helped by configuring with gain.
Cheers,
Hugh
You are quite right, and thank you for pointing it out.
My point about using a double emitter follower is still true; this configuration is more stable than the CFP, though stability is helped by configuring with gain.
Cheers,
Hugh
You meant NE5534 not NE5532 right? the NE5532 is a dual opamp and the amp uses a single opamp package right?
I will doing just that in my next prototype. However since I'll just use a single cap from opamp output to the inverting input, can I just solder it directly underneath the pcb?
Graham noted to use RC for this feedback, can you please show me how?
Keep the comments and suggestions coming please...
Thanks,
JojoD
"Ulp, DJK, I missed that. Didn't have values on the schematic and didn't realize the gain was only four."
I guess I was lucky, I saw the values on the PC layout.
"My point about using a double emitter follower is still true; this configuration is more stable than the CFP, though stability is helped by configuring with gain."
That's exactly what Bryston did on the old 3B/4B
http://www.geocities.com/atticoftreasures1/4b.html
This seems to work well:
http://homelf.kimo.com.tw/skychutw/ampzilla/schematics/ampzillaIII_sch.gif
McIntosh uses this topology with Q13, Q17 set up for a voltage gain of X5 and Q21, 22, 23 as followers.
They run the CFP in class A and don't seem to have any problems with oscillation. The outputs run virtually class B.
Hugh would probably like the front end, it has a single diff pair with a resistor as the current source, the second voltage amp (VAS) also uses a resistor as the current source.
Mine sound great and are going on 25+ years now (MC2120).
"You meant NE5534 not NE5532 right? the NE5532 is a dual opamp and the amp uses a single opamp package right? "
If you use a NE5534 you must remember to compensate it for unity gain. I'm lazy, I use a NE5532. The second section always comes in handy for a filter, balanced input, etc.
I guess I was lucky, I saw the values on the PC layout.
"My point about using a double emitter follower is still true; this configuration is more stable than the CFP, though stability is helped by configuring with gain."
That's exactly what Bryston did on the old 3B/4B
http://www.geocities.com/atticoftreasures1/4b.html
This seems to work well:
http://homelf.kimo.com.tw/skychutw/ampzilla/schematics/ampzillaIII_sch.gif
McIntosh uses this topology with Q13, Q17 set up for a voltage gain of X5 and Q21, 22, 23 as followers.
They run the CFP in class A and don't seem to have any problems with oscillation. The outputs run virtually class B.
Hugh would probably like the front end, it has a single diff pair with a resistor as the current source, the second voltage amp (VAS) also uses a resistor as the current source.
Mine sound great and are going on 25+ years now (MC2120).
"You meant NE5534 not NE5532 right? the NE5532 is a dual opamp and the amp uses a single opamp package right? "
If you use a NE5534 you must remember to compensate it for unity gain. I'm lazy, I use a NE5532. The second section always comes in handy for a filter, balanced input, etc.
Here is my amplifier's schematic:
Sorry for the quality of the schematic, it's under development.
Sajti
An externally hosted image should be here but it was not working when we last tested it.
Sorry for the quality of the schematic, it's under development.
Sajti
The file is small (53k).
Here is the link to my schematic:
http://www.freewebs.com/mccheese/MJL300_2.gif
I hope it works.
Sajti
Here is the link to my schematic:
http://www.freewebs.com/mccheese/MJL300_2.gif
I hope it works.
Sajti
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