Q6 may be triggering on high level signals.
Make R14 ~30% to 35% of R11. i.e. 30r or 33r
If you still need degeneration of 47r, then add the missing resistance as an extra resistor above the base tapping.
Add a collector load resistor to Q7 to limit dissipation if overloaded at input.
Try 1k6, or 1k8 to power ground.
C3 seems to be enormous, is this to stop full oscillation?
Similarly C1 is far too big. 10uF bi-polar electrolytic will pass all your bass, or use two 22uF polarised electrolytic back to back.
Make R14 ~30% to 35% of R11. i.e. 30r or 33r
If you still need degeneration of 47r, then add the missing resistance as an extra resistor above the base tapping.
Add a collector load resistor to Q7 to limit dissipation if overloaded at input.
Try 1k6, or 1k8 to power ground.
C3 seems to be enormous, is this to stop full oscillation?
Similarly C1 is far too big. 10uF bi-polar electrolytic will pass all your bass, or use two 22uF polarised electrolytic back to back.
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Thanks for your reply
I applied your suggestions and here it is :
1- I lower down the R14 to 33ohms and it burn Q7 and then positive fuse
2- add 1.6k between the collector of Q7 and ground (problem still there)
3- lowering down C3 to 36pf reduced that oscillation significantly (but there is still some left)
4- I also reduced C1 to 10uf bi polar
Now here's the new output signal :
Reducing R14 from 47r to 33r is increasing the open loop gain.
That increases the feedback and increases the oscillation.
This is confirmed by your fuse blowing and confirms that the amplifier is very close to full oscillation.
As a temporary solution increase Q11 degeneration to 60r until you get on top of this instability problem. Now split R14: 33r to the -ve supply rail and 27r to Q11 emitter.
Tap Q6 base in to the junction between 33r & 27r. (you could use two 33r instead.)
Go back to 70Vdc supply rails.
I am not any good at this instability solving, so this next suggestion is a (bad) guess: Try changing Q11 from kse340 to a much faster device.
Ic ~ 100mA to 150mA, Vce0 ~ 150V to 200V, P ~ 5W to 10W, fT ~ 100MHz to 300MHz
and it needs to remain reasonably fast at the current you choose to pass through it.
Can our AC circuit experts come in and suggest solutions?
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I did this and here's the output signal :
An externally hosted image should be here but it was not working when we last tested it.
the tops of that oscillation look like they are flat topped.
Are you driving the amplifier to near clipping?
reduce the signal by 40dB and test again in steps of 6dB from that -40dB level.
See when the oscillation starts.
Try going back to the low level signal and adding on a 1nF cap to the output. step the signal.
Are you driving the amplifier to near clipping?
reduce the signal by 40dB and test again in steps of 6dB from that -40dB level.
See when the oscillation starts.
Try going back to the low level signal and adding on a 1nF cap to the output. step the signal.
Turns out that the problem was from Power Supply as I'm using SMPS to run this amp
when I connect the amp to 50Hz transformer I get a completely clean waves in output
when I connect the amp to 50Hz transformer I get a completely clean waves in output
An externally hosted image should be here but it was not working when we last tested it.
that tells you the amplifier is intolerant of HF artifacts on the power supply.
You need to make the amplifier more tolerant.
Have a good look at the filtering on the supply rails, especially the HF and MF supply rail decoupling fitted to each stage of the amplifier.
Posts 40 & 44 show no decoupling. This is a serious failing/bad design of the schematic. Where did it come from?
You need to make the amplifier more tolerant.
Have a good look at the filtering on the supply rails, especially the HF and MF supply rail decoupling fitted to each stage of the amplifier.
Posts 40 & 44 show no decoupling. This is a serious failing/bad design of the schematic. Where did it come from?
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it's kind of coming from Bob cordell's book with some changes I made
this amp works great and I've used it but with about 200w power before for a long time without any problem
R.Cordell discusses supply rail decoupling and shows where it needs to be added.
Why did you omit all of them?
Reading your various reports of operating problems I cannot agree with you that your amplifier "works great".
Hi,
As per my earlier post, if your amplifier is as per the thread circuit design, you have the input pair transistors incorrectly connected.
All designs in Bob Cordells book have the degeneration resistors connected to the emitters.
You have the transistors connected incorrectly.
Regards,
Shadders.
yes you're right
I drew the schematic wrong
Q2 & Q3 collector and emitter should be reversed
Exact Schematic from cordell's book
An externally hosted image should be here but it was not working when we last tested it.
Crazy Amplifier
Hi BadBoy,
I call your project as Crazy Amplifier as it gave you some crazy test results.
The Bob Cordell schematic is just a reference to study and understand amplifier behavior.
Could you tell me (us) the purpose of this project? It is just for fun or it have a commercial direction.
Did you make PCB for it?
There is lots of things you can improve and change the DHT from near 3$ to an impressive 0,003%
I am looking forward to read your answer.
Ronaldo
Hi BadBoy,
I call your project as Crazy Amplifier as it gave you some crazy test results.
The Bob Cordell schematic is just a reference to study and understand amplifier behavior.
Could you tell me (us) the purpose of this project? It is just for fun or it have a commercial direction.
Did you make PCB for it?
There is lots of things you can improve and change the DHT from near 3$ to an impressive 0,003%
I am looking forward to read your answer.
Ronaldo
i'm building a 400w rms amp to drive my subwoofer
i've used this amp but with less output power (about 200w) for a couple of month
I ran them for a long time at full power and never once have problem with it
I don't know what do you call a good amp and how an amp satisty you
please tell me the problems with this amp so I could improve it
I did everything that here have been said and some of them even make the amp even worse and unstable
I'll be happy if you tell me the amp problems
Simulation Proposal
Badboy,
Thank you for your answer.
I use to listen one amplifier I projected more than 10 years ago. I could get the maximum from my old B&W DM604 speaker.
My one is a good amplifier and was based in gain-bandwidth product. I used the Leach Book as reference to project this old amplifier and also used informations from some patents in audio.
I am attaching the simulation of your circuit and my circuit version with corrections and changes.
It was done with LTSpice, so you can download and test my changes. Here in the forum you can find all data and information to learn to use it as I did.
I asked about PCB as the decoupling depends from your layout. My simulation schematics do not comply it. If you change this circuit and make a new PCB I wonder to have a free pair. I am also Eagle user.
Regards
Ronaldo
Badboy,
Thank you for your answer.
I use to listen one amplifier I projected more than 10 years ago. I could get the maximum from my old B&W DM604 speaker.
My one is a good amplifier and was based in gain-bandwidth product. I used the Leach Book as reference to project this old amplifier and also used informations from some patents in audio.
I am attaching the simulation of your circuit and my circuit version with corrections and changes.
It was done with LTSpice, so you can download and test my changes. Here in the forum you can find all data and information to learn to use it as I did.
I asked about PCB as the decoupling depends from your layout. My simulation schematics do not comply it. If you change this circuit and make a new PCB I wonder to have a free pair. I am also Eagle user.
Regards
Ronaldo
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