Slowish devices all over the place. 120 watts from a pair of 2N3055'2/2SC5200's? Zero bias of the power devices? This amp is a no-go!
Best regards!
Best regards!
You need +-50V to get 100w with 8 Ohm.
A normal 2n3055 only specs up to 60v. That is +-30v.
I am talking about the power supply voltage. The output voltage swing will be less than that. I use 80% overhead.
A normal 2n3055 only specs up to 60v. That is +-30v.
I am talking about the power supply voltage. The output voltage swing will be less than that. I use 80% overhead.
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It’s just another bastardization of the circuit in post #6, which is an oversimpified BGW.
People do run 2N3055’s on +/-40V all the time. That doesn’t make it a good idea. Sometimes it works. Sometimes it doesn’t. And usually the people trying to do it are least equipped to do so, or understand why it goes bang on them. C5200’s can - at least real ones - and give 100 or so watts on 4 ohms. That doesn’t make the circuit any better, though. You’d be better off with the MJE340/350 VAS in post 6, even if you opted for this output stage.
People do run 2N3055’s on +/-40V all the time. That doesn’t make it a good idea. Sometimes it works. Sometimes it doesn’t. And usually the people trying to do it are least equipped to do so, or understand why it goes bang on them. C5200’s can - at least real ones - and give 100 or so watts on 4 ohms. That doesn’t make the circuit any better, though. You’d be better off with the MJE340/350 VAS in post 6, even if you opted for this output stage.
Question is if anybody needs 100 Watt or more.
My designs almost never go beyond 25 Watt.
Sometimes stays on 10 Watt ...
My designs almost never go beyond 25 Watt.
Sometimes stays on 10 Watt ...
Some people hold parties. Some people have 75 db 1w1m speakers and listen to 72 db dynamic range music. That is CompactDisc max. I've heard more dynamic range in band performances I played in. If there was a recording media that could reproduce that. MP4? Besides 126 high school students on stage blowing away there was an antiphonal brass section in the balcony of ~20 college students. Procession from Parsifal? My LP of the performance was stolen.
I own 98 db 1w1m speakers but have carried them out on the front porch for 4th of July before. 1812 Overture. Turn it up! Speaker limit 500 w AES. Amp limit 240 W/ch RMS. Inside SP2 are fine for solo flute at 1/8 watt. Input op amp was NJM4580.
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Who wants to try this?
Current Dumping with OPAMP. All the resistors and inductance are tuned for NE5532. Those values just happen to cancel out all the distortion, WITHOUT any bias current.
Current Dumping with OPAMP. All the resistors and inductance are tuned for NE5532. Those values just happen to cancel out all the distortion, WITHOUT any bias current.
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I can't find my breadboard. 😕
I might try this in the upcoming holiday.
I might try this in the upcoming holiday.
The TL071 has phase-reversal, so is a dangerous component to use in a power amp. A single transient spike might lock the output at the rails in worst-case scenario...
Actually the TL071 is one of the more well behaved types for input stage use. Keep the input current under fault conditions under 4 mA and all is well. I’ve tried more advanced versions (OPA2604) that sound just fine - but the first hint of amplifier clipping blows the op amp. TL071 will take being run to clipping all day, generating large differential inputs, and smile. My go-to is the LF412 for amps with abuse potential. The second op amp in the package is useful in other ways.
You really don’t want any power amp input stage potentially exposed to guitar amp output jacks or mains voltage. It will blow non-op-amp amps just as easily, or wreck your precious hand matched input pairs even if it survives. So how do you prevent that? Use another op amp (totally separate package) to do the balanced/unbalanced conversion, and it’s output will never exceed +/-13V. Even in you manage to blow it the worst that can happen is sending 13V to the speaker.
The only real issue with the 071 is it’s lack of drive capability. It works well driving a common emitter small signal stage. Not quite well enough driving common base, and won’t directly drive big power followers. It will drive EF2’s just fine, up till you need more than 10 mA of base current. There are times when that’s just not enough.
You really don’t want any power amp input stage potentially exposed to guitar amp output jacks or mains voltage. It will blow non-op-amp amps just as easily, or wreck your precious hand matched input pairs even if it survives. So how do you prevent that? Use another op amp (totally separate package) to do the balanced/unbalanced conversion, and it’s output will never exceed +/-13V. Even in you manage to blow it the worst that can happen is sending 13V to the speaker.
The only real issue with the 071 is it’s lack of drive capability. It works well driving a common emitter small signal stage. Not quite well enough driving common base, and won’t directly drive big power followers. It will drive EF2’s just fine, up till you need more than 10 mA of base current. There are times when that’s just not enough.
So you think the TL071 doesn't have phase reversal? That's provably false of course. And any opamp with phase-reversal in a negative feedback loop has the possibility of locking up since phase reversal turns negative feedback into positive feedback. You can design around this, but its something you have to consider as a designer.
In practice it won’t reverse if the feedback resistor is large enough to limit the input current to +/-4 mA when/if the speaker output goes to either rail. You could drive the positive input too hard from a low Z source but you shouldn’t be doing that anyway. That will blow up a fancy discrete stage.
Here is an input structure that will prevent that. R28 is 1/10 watt resistor to burn out if a roadie plugs a 75 w bass amp in the input of the M-2600. Excess current goes through diodes to power supply until burnout. Most of the feedback is through a 25 uf e-cap. There is a 4.7k direct feedback resistor. U2 is a CA3094 operational Transconductance amp. Overdrive compression. Listening to this now.
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I can't do anything with the term “Phasenumkehr” in the context of the actual physical processes in the semiconductor, especially in the context of the correct use of integrated operational amplifiers, that's true!
If you are so convinced, then we may have the most common and obvious problem of all time: a linguistic misunderstanding!
Let's just read what the source of the /your interjection writes in her book ISBN 978-0-240-52177-0 on page 128:
"
It is a quirk of this Device (the TL072) that the input common-mode ranges does not extend all the way between the raild.
If the common-mode voltage gets to within a couple of Volts of the V - rail, the op-amp suffers phase reversal and the inputs swap their polarities.
There may be really horrible clipping, where the output hits the bottom rail and then shoots up to hit the top one, or the stage may simply latch up until the power is turned off.
"
[Douglas Self; Small Signal Audio Design]
There is really no need for anything else on this topic. I myself have been using the TL071, 072, 074 regularly for over 37 years, it can be found in countless of my circuits - to this day flawlessly, without the miracle of Self's warning ever occurring in practice.
Any user who knows what a p-channel jFet is can explain and imagine what could really happen physically and electrically.
Nevertheless,
thank you very much for your advice Mark T.
kindly,
HBt.
👍.
That's exactly how it is. Only the chosen terms reverse and phase are extremely unfavorable, for a German species of my kind. But we all know what we have to avoid in use and read the data sheet for our component.
@lineup
The conclusion must be: one can justifiably use operational amplifiers as IP stages in a PowerAmp, that's it.
HBt.