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Old 13th July 2011, 12:28 PM   #91
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Quote:
Originally Posted by Elvee View Post
Could be the C suffix, I mainly used unsorted ones, without suffix.

Anyway, 140mA is large enough for the circuit to operate properly, nothing to worry about.



If you're happy with the sonics, and the amplifier looks well behaved, that's sufficient.

But more generally, squarewaves are a useful tool to quickly uncover hidden issues, like marginal stability, insufficient internal bias currents, etc.
The squarewave behavior has little relation with the sonic performances, but it highlights any weakness in the design, like poor decoupling or compensation, inadequate wiring, unsuitable Zobel, etc.

You don't need a full feature function generator: for a buck or two, you can improvise an excellent generator on a scrap of veroboard, with a CMOS oscillator, see an example below

Looks promising.
Undoubtedly, that little tool will come in handy many times in the future, so I will have to build one when I can.

Thanks.
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Old 13th July 2011, 01:38 PM   #92
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hello people,
nice to see a functioning amplifier
I'm currently in development a similar power amplifier. I do not know if you've noticed it(sub4668). One of my fears is the switching on.
On your amplifiers, a strong turn-on is caused at the output?
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Old 14th July 2011, 01:55 PM   #93
Elvee is offline Elvee  Belgium
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Originally Posted by moschfet View Post
hello people,
nice to see a functioning amplifier
I'm currently in development a similar power amplifier. I do not know if you've noticed it(sub4668).
Nice circuit. The bandwidth and slew-rate must be impressive with the individual P-P drivers for each MOS.
Something isn't clear for me: why did you include a single cascode transistor, Q8?
Q5 sees a large static voltage, but the dynamic excursion is tiny.
On the other hand, Q4 sees the full output swing (a little more in fact).
I would think it would benefit more from the cascoding.

I would also be concerned about thermal stability. I see no obvious control or compensation mechanisms.
It would be a good idea to perform a thermal analysis in LTspice before you run the risk of frying real transistors.

Quote:
One of my fears is the switching on.
On your amplifiers, a strong turn-on is caused at the output?
Topologies like ours (same sex OP transistors) are inherently superior in this respect to more conventional complementary topologies.

In a classic complementary amplifier having an active VAS loaded by a passive CCS (or a bootstrapped resistor), the CCS becomes active before the VAS (or more rarely the opposite) when the amplifier "wakes up", causing a positive thump at the output, followed by negative "aftershock", when the charge accumulated by the capacitor in the NFB network is restored.
In principle, the overall NFB should minimize this effect, but if the amplification chain isn't fully active yet, the thump remains.

In principle, fully symetrical complementary designs should adress this problem, but the symetry of complements is mostly an illusion, and the small diffferences between the positive and negative sides is sufficient to cause a large thump, because of the high current gain of the output stage.

On the other hand, circlo designs like yours and mine rely on a horizontal symetry rather than a vertical one, and thus have both halves waking up with almost perfect synchronism, minimizing unwanted output excursions at power-up.
These excursions are further controlled by the NFB as soon as it becomes active, and in the case of the Circlophone, the bias servo also helps control the behaviour of OP transistors, even at an early stage of the powering up.

Note that even if the PA is silent at power up, the preamplifier might still inject its own disturbances.
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Old 14th July 2011, 03:15 PM   #94
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Quote:
...why did you include a single cascode transistor, Q8?
Q5 sees a large static voltage, but the dynamic excursion is tiny.
On the other hand, Q4 sees the full output swing (a little more in fact).
I would think it would benefit more from the cascoding.
The cascode at this point is easy to implement and ensures the same quiescent current performance.
Q4 have only to sweat at very high levels. There would be too complicated to add a cascode.
Quote:
I see no obvious control or compensation mechanisms.
Q10 is thermally connected to the MOSFET.

Quote:
In principle, fully symetrical complementary designs should adress this problem
My amps are usually symmetrical and turn on all soft. So my concern.

Quote:
On the other hand, circlo designs like yours and mine rely on a horizontal symetry rather than a vertical one, and thus have both halves waking up with almost perfect synchronism, minimizing unwanted output excursions at power-up.
These excursions are further controlled by the NFB as soon as it becomes active, and in the case of the Circlophone, the bias servo also helps control the behaviour of OP transistors, even at an early stage of the powering up.
Thank you for your explanation. I hope the amp will works fine
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Old 14th July 2011, 08:55 PM   #95
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Both channels up and running. More to update later.

I have some parts to change on the first channel. Used different type capacitors on second channel in some places and I feel it sounds better. I want both channels to be as similar as possible. Have the same 140mA draw on the positive 18V rail. No oscillations at all with these 4MHz MJW21196's.

I still can't get over how "fast" the amp sounds. When snare hits for example, it has great attack and just seems very fast for lack of better words. Dynamic.

Is anybody else building? Oh well, at least I will enjoy mine for the moment. I think others need to build. I'm loving the sound so far. It's delicious!

Soon I will have it on the proper supplies (still only using 2,000uF/rail, +-18V), and the proper speakers.
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Old 15th July 2011, 01:43 PM   #96
Elvee is offline Elvee  Belgium
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Originally Posted by odysseybmx414 View Post

Soon I will have it on the proper supplies (still only using 2,000uF/rail, +-18V), and the proper speakers.
With the MJW21196's and the heatsink you use, you could very easily double the supply voltage.
You just need to increase R21 to 56 or 68K.
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Old 15th July 2011, 03:41 PM   #97
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Originally Posted by Elvee View Post
With the MJW21196's and the heatsink you use, you could very easily double the supply voltage.
You just need to increase R21 to 56 or 68K.
I was going to ask about foregoing the use of the regulator boards and just using about +-33V. So, which value would be better, 56 or 68K?

Thanks!
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Old 16th July 2011, 06:17 AM   #98
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56K would be closer to the design goal for 2x33V, but it isn't that critical at all, and I made tests between 15V and 45V without modifying anything.
Not something I would recommend though, but it shows the tolerance of the circuit.

One thing I forgot to mention, if you use 33V supplies, the zeners should have a total voltage in that region: 2x15V or 16V, or 1x30V or 33V (1.3W for a single).
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Old 16th July 2011, 08:04 AM   #99
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Quote:
Originally Posted by Elvee View Post
Some news:

I have tested (in sim) the idea of replacing the zeners with a resistor.

The result is disappointing: the change in linearity is insignificant, and for the worst.
It looked like a good idea in theory, but it doesn't deliver, and if there is no improvement in sim it's probably not worth testing in reality.
In addition, it would probably upset the compensation and degrade the dynamic performances.
Replace the two Zeners with one NPN in cascode?
I mean w. base referenced to output...

Q6 already rides one emitter (Q11) below the output,
both Q5 & Q6 should then see same collector voltage.
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Old 16th July 2011, 11:40 AM   #100
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Originally Posted by Elvee View Post
56K would be closer to the design goal for 2x33V, but it isn't that critical at all, and I made tests between 15V and 45V without modifying anything.
Not something I would recommend though, but it shows the tolerance of the circuit.

One thing I forgot to mention, if you use 33V supplies, the zeners should have a total voltage in that region: 2x15V or 16V, or 1x30V or 33V (1.3W for a single).
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