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Old 14th November 2012, 04:24 PM   #131
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Hi Line up checkout Class i
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Old 14th November 2012, 10:21 PM   #132
Struth is offline Struth  Canada
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Hi Guys

Lineup, in my circuit Q5 and Q6 control bias. They symmetrically control both halves of the circuit.

The series combination of the emitter resistors in the output stage has a constant current through it set as approximately 700mV/2Re. So, if you set Re=330mR, then you have 660mR total. The idle current will be 700mV/660mR=1A - actually 60mA higher.

I only need low power, so running class-A does not incur a high heat penalty with the +/-12V supplies.

With the bias cap in place, you can set the class-A output to any arbitrary value you like, despite having much higher supplies than would be needed for that power. The cap allows higher drive to occur and the circuit goes to class-B - I believe Self would say AB here.

The refinements you've made with the triple-EF and capacitive load handling are great! There are countless variations that can be made of this circuit and nearly all will be top performers.

Note that "m" is "milli". 330mR is what some right as 0.33R. Similarly, the 33mF cap is more often written as 33,000uF.

Have fun
Kevin O'Connor
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Old 15th November 2012, 07:17 AM   #133
lineup is offline lineup  Sweden
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Thanks, Kevin.
So far I have only tested this LU Power Buffer
with standard Class AB with bias set to 100mA in MJL3281A/1302A.
The use of these output devices is because I know I have good models.

I just tested THE BEST VERSION so far in my SPICE.
I was get stuck with THD 0.00016% at 1 Watt.
It seemed impossible to get lower.

The Cure was to change to other transistors.
I had used only BD139/140 and 2SC2240/SA970.

Now I use 2SC4793/SA1837 and 2N5551/5401.
Voila!!!
The nice numbers are almost frightening.
THD 0.00006% at 1 Watt

I show here the new and best version with new transistors.
Of all versions I prefer TRIPLE EF output.
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Old 15th November 2012, 07:37 AM   #134
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Quote:
Originally Posted by lineup View Post
Now I use 2SC4793/SA1837 and 2N5551/5401.
Voila!!!
The nice numbers are almost frightening.
THD 0.00006% at 1 Watt
Bravo lineup

The same THD number jkuetemann got in post #121

As homemodder said for unity gain buffer that's not so very surprising THD, as complete amp should incorporate voltage gain stage with its own anomalies to correct too. Try to sim something like global CFB symmetrical amp. Hopefully phase margin and OLG bandwidth will show us something special too.
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Old 15th November 2012, 07:50 AM   #135
lineup is offline lineup  Sweden
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I did a 20kHz test. For 1, 4, 9 Watt so far.
The numbers are promising:
THD 20kHz
04 Vp, 01 Watt THD 0.00022%
08 Vp, 04 Watt THD 0.00072%
12 Vp, 09 Watt THD 0.00119%


Regarding how fast. The last version above is -3dB at well above 10 MHz.
So some little input filter is probably a good advice .......

Lazy Cat,
can you point me to 'global CFB symmetrical amp'.
I might try this.
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Old 15th November 2012, 03:19 PM   #136
Struth is offline Struth  Canada
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Hi Guys

The 2N5550/5400 pair have been industry standards since the late 1970s or early 1980s. They are used in many of the best production amps. Some details of their specs are unexciting but their linearity is excellent, producing a balanced distortion spectrum.

Most of the solid-state amps I've built in the past twenty years have been for guitar or bass. In that environment, and because I also use these BJTs in kits related to tube equipment, the high voltage capability of the MPSA42/92 is convenient. They have a pretty flat gain over a wide current range. Again they have some unspectacular characteristics, as well, but are also quite linear devices as Self demonstrated.

Since Toshiba introduced the 2SA1302/2SC3281 and 2SA1306/2SC3298 pairs, I have only used these and similar for hifi amps and drivers in guitar amps. Some of the latter had TO-3 devices since they were the fashion of the day and easy to acquire. Everything has gone to TO-247 and TO-264 for outputs now, which are a convenient package. It is a good thing that Motorola licensed the Japanese technology so they could improve their line of fairly good devices. The MJL21193/94 are pretty much MJ15024/25 die in a TO-3P case. The MJL1302A/3281A are renumbers 2SA/2SC to appease US buyers loath to buy foreign-numbered product.

I assumed you were using BDs instead of better devices out of convenience - you already them or you already had the sim models. It is no surprise that the numbers are better with the more linear devices.

Matching of devices will lower THD and help with DC offset. Device parameters and matching can be made less critical with emitter degeneration in place. The use of Rs instead of CSs pretty much eliminates DC offset based on current imbalance of the CSs and provides a very balanced rise/fall of supplies while maintaining low offset.

Leach suggested a GBW of 8-10MHz is a reasonable range for an amp to have low TIM and otherwise good performance. The LU buffer is in that ball park, so no need to try to make it faster as that is just asking for critical layout problems.

Have fun
Kevin O'Connor
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Old 15th November 2012, 03:26 PM   #137
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I begin to like you very much Kevin ....all very well said ...
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Old 15th November 2012, 03:35 PM   #138
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Even though what you said Kevin is the mother ..and basis for a lot of reasonable things there is actually many variables that worth looking at .

A BC 547 for example next to Mpsa XX will also depend on the ""way"" you operate them ...Harman Kardon runs 60 volt drivers ( for example ) at 59.9999 volts and then if current is not enough put two of them in parallel ...which actually plays quite fine and measures even better ...still to my understanding its a very bad practice ...

kind regards
sakis
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Old 15th November 2012, 04:11 PM   #139
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Sakis I would not say its a bad practice at all, it depends on where the part is used and how. I always use fast parraleled drivers instead of one big slow one like mje15032 series. Harmon know exactly what they doing.

Those BDs are exceptional as drivers although limited by Vce and SOA, two of them can be used in parrallel and they peform better than those toshibas at their max Vce especially at frequencies higher than 1Khz and lower powers.

Lineup is simulating not measuring, reality could be very different. His spice models for the BDs could be incorrect as well as the other models too.
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Old 15th November 2012, 04:22 PM   #140
lineup is offline lineup  Sweden
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I love to ba able to measure, homemodder.
But I have nothing to do this with.
I have had in the past when I lived in another place.

No doubt reality check with measuring the amplifier can give some unpleasant surprises.
But SPICE is not all bad.
Some people here use both sim and real stuff.
Even if they can measure they can checkup and find problems using SIM.

I am waiting for that guy, that will build ....!!!!
And I am confident in the circuit will work.
How well nobody knows for the moment.
But even guesses can be good.
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