Hugo
Looks very nice!!!
Don't we need the gate resistors of 220 ohms against parasitic oscillation?
Since you would go with Mosfets, I might try with Darlington.
JH
PS. I do not remember. What made your op broken?
Looks very nice!!!
Don't we need the gate resistors of 220 ohms against parasitic oscillation?
Since you would go with Mosfets, I might try with Darlington.
JH
PS. I do not remember. What made your op broken?
jh6you said:
Don't know about the gate resistors. But I'll add them and look at the results
The opamps blow up when R5/6/7/8 were turned up too high...
I guess 😉 RO was involved too. It all went so fast.
/Hugo - smoke is finally gone now...'in the lab'
Bernhard said:
And I try bananas
Somewhere there is a thread from someone who is trying with only opamps. Can't find it now, but I wonder what the progress is.
Added some 220 R's to the gates and it looks like nothing is smoking' for the moment.
/Hugo
Trying only with Opamps
That would be me. Still in the thinking and beating it up in a sim stage. Should be moving into a "smoke in the lab" phase soon as I have gotten every freind who could satisfy TI for the sample program to send off for some 541's and 549's. No one seems to offer the CFB's in samples - except for some new chips - one of which looked very interesting except for an extra buffer stage that you could not get around. That might not have been a problem, but with my skills, it seemed to be. So I will buy these.. and hope I don't toast them.
Several issues have rasied their ugly head - the limited reference notes to using the CFB opamps in the audio range. It seems that the app notes that I have found have focused on using these in video amps and drivers and such. ( I am willing to bet there are some old ones out there somewhere... it would be wonderful if there was a library of old application notes.)
The notes scream about issues of ringing and wild overshoots when cascading these opamps - strongly indicating the need to operate the power stage opamp at unity (or close to it). This then brings in the limitation of -/+ 15 V powersupplies - the voltage swing is pretty low with no further gain.
I have also decided that I don't want to have two transfo, so I will be using some method to go from 30v to 15v. Given the general simpleness of the powersupply for the OPA549 and the gainclone concept, I have decided that I need either an isolated DC/DC (expensive) or a pretty stiff regulated supply for the CFBs. Still looking for suggestions here.
But nonetheless, once the parts all show up, I will start tinkering. The three amigo's work in the descrete phase has kept me facinated.
That would be me. Still in the thinking and beating it up in a sim stage. Should be moving into a "smoke in the lab" phase soon as I have gotten every freind who could satisfy TI for the sample program to send off for some 541's and 549's. No one seems to offer the CFB's in samples - except for some new chips - one of which looked very interesting except for an extra buffer stage that you could not get around. That might not have been a problem, but with my skills, it seemed to be. So I will buy these.. and hope I don't toast them.
Several issues have rasied their ugly head - the limited reference notes to using the CFB opamps in the audio range. It seems that the app notes that I have found have focused on using these in video amps and drivers and such. ( I am willing to bet there are some old ones out there somewhere... it would be wonderful if there was a library of old application notes.)
The notes scream about issues of ringing and wild overshoots when cascading these opamps - strongly indicating the need to operate the power stage opamp at unity (or close to it). This then brings in the limitation of -/+ 15 V powersupplies - the voltage swing is pretty low with no further gain.
I have also decided that I don't want to have two transfo, so I will be using some method to go from 30v to 15v. Given the general simpleness of the powersupply for the OPA549 and the gainclone concept, I have decided that I need either an isolated DC/DC (expensive) or a pretty stiff regulated supply for the CFBs. Still looking for suggestions here.
But nonetheless, once the parts all show up, I will start tinkering. The three amigo's work in the descrete phase has kept me facinated.
Re: Trying only with Opamps
No reason at all why we can't use a common emitter output stage (as presented here) to get a couple extra volts out the deal. Cascading op amps? Whose advocating that?
People seem to think there is something magic or exotic about CF, when in fact it is a very traditional approach. I've seen lots more tube circuits using this topology than otherwise.
So forge ahead, fearless amplifier designers...
That's B.S. "Current Feedback" op amp (misnamed: they really mean that the open loop gain is dependent on the impedance of the network attached to the - input) are very stable stuff, but also very fast.Sawzall said:
No reason at all why we can't use a common emitter output stage (as presented here) to get a couple extra volts out the deal. Cascading op amps? Whose advocating that?
People seem to think there is something magic or exotic about CF, when in fact it is a very traditional approach. I've seen lots more tube circuits using this topology than otherwise.
So forge ahead, fearless amplifier designers...
Hugo
Ref. to your latest circuit. It seems that the 10 ohms of R0 is too small, compared with the sizes of R15 and R16. If we have the balanced input signals of +1V and -1V, for example, total 2V will occur across R0, i.e. 200mA will flow through R0. This means that 185mA (after deduction of maximum 15mA allowed to the inverting inputs) should go through R15 and R16, and for this, about 200V (impossible value) should happen across R15 and the same voltage across R16. Otherwise, the op amps would be toasted.
Looking forward to your opinion...
JH
Ref. to your latest circuit. It seems that the 10 ohms of R0 is too small, compared with the sizes of R15 and R16. If we have the balanced input signals of +1V and -1V, for example, total 2V will occur across R0, i.e. 200mA will flow through R0. This means that 185mA (after deduction of maximum 15mA allowed to the inverting inputs) should go through R15 and R16, and for this, about 200V (impossible value) should happen across R15 and the same voltage across R16. Otherwise, the op amps would be toasted.
Looking forward to your opinion...
JH
jh6you said:
There is a big chance that you are correct here, but none of the simulations I did is pointing me in your direction. 😉
But tomorow I will be back, having 2 brand new LM's (I can toast again).
/Hugo
Please read all 🙄
What is the absolute minimum voltage across the base bias resistor ? 0,65V ?
In case of mosfets, is it the gate voltage ? 3 V ?
Does it need more bias current for more power or just higher rail voltages ? Does the circuit leave classA operation on high voltage swings if the bias current is too small ?
What would be better, 2SJ55 and 2SK175, IRFP240 and IRFP9240 or just ordinary MJXXXXX ?
I have an incredible idea which depnds on the answer of the third question. 😎
What is the absolute minimum voltage across the base bias resistor ? 0,65V ?
In case of mosfets, is it the gate voltage ? 3 V ?
Does it need more bias current for more power or just higher rail voltages ? Does the circuit leave classA operation on high voltage swings if the bias current is too small ?
What would be better, 2SJ55 and 2SK175, IRFP240 and IRFP9240 or just ordinary MJXXXXX ?
I have an incredible idea which depnds on the answer of the third question. 😎
Bernhard said:
1) Silicium 0.6V
2) Between 3.3V and MAX 20V, but between 3 to 5V in audio.
Third question I can't answer...
4) 2SJ55/2SK175 are too old I guess. I would try IRxxx. These are most used by Passlab products and these guys seem to know what they do. 😉
Don't leave us uninformed about that idea!!! Dare you!!
LennyK said:
It works, when simulated.
Lenny
Hi Lenny,
This is a nice drawing and maybe something for JH to answer your question.
He's trying to make the 741's work, with no success till now.
Don't ask me if it's an X, personally I think it rather looks like a double-X. 😉
/Hugo - will go for triple-X, good Belgium Beer.😉
Is it possible to built this amp by using only N-channel fets like IRF240 ?
May be some DIY-darlingtons ?
Special greetings to Gdansk, the second best Place in Poland best is Warszawa.
May be some DIY-darlingtons ?
Special greetings to Gdansk, the second best Place in Poland
best is Warszawa.
Bernhard said:
That's exactly what I'm trying to figure out too! (N-fets)
I guess we will have to change polarity somewhere, and phase also. Just a guess.
Till now, I simulated with both P- and N-channels.
/Hugo
I suggest you solve your problems with the complementary parts before looking for additional trouble.
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