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Old 24th December 2012, 11:22 PM   #1131
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The second CCS is ingenious, but adds a number of parts. I'm guessing what you want is something that will give predictable current across builds without adjustment so Jfets are out. CCS diode?
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Old 28th December 2012, 12:32 AM   #1132
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I applied some cosmetic changes to the schematics for convenience - enjoy!
Attached Images
File Type: png circlofon.png (45.6 KB, 455 views)
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File Type: asc circlophone.asc (9.3 KB, 15 views)
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Old 28th December 2012, 02:53 AM   #1133
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Miniature Circlophone spotted! Thanks!
With 20+20VDC, your R21 at 33K should probably be closer to 27K. Your two zeners, 12v+12v=24v, probably sounds fantastic; however, it should technically be just 1 of 1w 20v zener so that the 2N3019's are both running at the same temperature. At this low voltage, you can show the outputs as MJE3055, which are in more convenient TO220 size packages. BC560C's can be used for input pair. The RF blocking +input RC is missing. R20 is fascinating because I haven't seen it before. The input load is missing. The approximately 150u power caps are missing. Either the NFB cap or the offset trimmer accessory, is missing.
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Last edited by danielwritesbac; 28th December 2012 at 02:56 AM.
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Old 28th December 2012, 03:47 AM   #1134
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R20 ensure that global gain doesn't fall below 2 at 12MHz. I'm sure it tries anyways! In any case it gives some phase slack that may help stability, but it really depends on the amp.
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Old 29th January 2013, 10:04 PM   #1135
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Default Compensation optimizations

Quote:
Originally Posted by Elvee View Post
The compensations have been optimized for 2N3055's, and if you use very different transistors, there might be some slight differences in the dynamic behaviour: with 2N3772 or 2N6259's, the slew rate is somewhat decreased.
Elvee, have you any basic rules to determine suitable compensation value ranges to be sure about circuit is not that far from its actual performance? I mean, I need such an advice like "increase/decrease these compensation (R and C respectively) values if these transistors contain this feature". I tend to use variety of transistors in terms of Ft, gain, noise level etc. and I'm curious about my amp's actual performance.

Thanks.
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Old 30th January 2013, 01:46 PM   #1136
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It is practically impossible to give general rules: there are too many factors to take into account: the VAS, drivers and OP can have Ft's and capacitances varying widely (in a ratio exceding 100:1 for the OPs), and each combination will have its own optimal values.
By contrast, the DC conditions are easy to compute, and the noise has no influence on components value.

I recommend you make a test, and if you see something is wrong you can try to correct it by altering the values.
Normally there is no risk of instabilities causing destruction (don't connect a speaker until everything is fine though)
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Old 31st January 2013, 07:08 PM   #1137
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I have simulated Darlington output version respecting the schematic at post #16. I used TIP142 and BDV65B libraries that i found at internet. I measured collector currents of Q5 and Q6 servo transistors and simulation shows 20-40 pico amperes per transistor besides 10-13 mA in standard version. If those such low current levels in simulation are realistic, I think that servo transistors must behave problematic in these conditions. For example, Ft of Q5 and Q6 must drop to excessively low levels.

I adapted my CFP pcb to standard version and I plan to share without attempting to build it. I'm working on a simplistic darlington version pcb and my concern mentioned above is related with this work.

Note: I will check the schematic again immediately to be sure for 120R's (R3 and R6) are there.

Last edited by terranigma; 31st January 2013 at 07:16 PM.
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Old 1st February 2013, 09:33 AM   #1138
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by terranigma View Post
I have simulated Darlington output version respecting the schematic at post #16.
Did you notice that this schematic is completely upside down? Supplies are reversed, transistor polarities are reversed, etc

If you missed one thing, nothing will work just like the symptoms you describe.

Alternatively, post your asc file for a check.
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Old 1st February 2013, 04:39 PM   #1139
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Quote:
Originally Posted by Elvee View Post
Did you notice that this schematic is completely upside down? Supplies are reversed, transistor polarities are reversed, etc

If you missed one thing, nothing will work just like the symptoms you describe.

Alternatively, post your asc file for a check.
I got figure it out. Input LTP alignment was wrong. After correction, measurements became realistic. I attached asc file anyway. When I use on-semi bdv65b spice model distortion level becomes remarkably high comparing TIP42 model below. Maybe it's related with insufficient model. I appreciate to take your opinion about on-semi BDV65B model file, because I plan to use authentic Philips BDV65B's in this project.

I'm also trying to find a good alternative for PNP servo transistors. Despite lack of Philips BD140's official CoB value, it seems to best to use it under 80V power supply conditions. For above power supplies, 150V/200mhz 2sa1360 seems fit despite its extremely low output capacitance (2.5 pF) if it adequate to solder a 8-10pF capacitor to its C-B legs.
Attached Images
File Type: png screenshot.png (60.9 KB, 272 views)
Attached Files
File Type: asc circlophone-Darlington.asc (8.7 KB, 40 views)
File Type: zip TIP142.zip (1.2 KB, 23 views)

Last edited by terranigma; 1st February 2013 at 04:49 PM.
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Old 1st February 2013, 07:26 PM   #1140
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by terranigma View Post
When I use on-semi bdv65b spice model distortion level becomes remarkably high comparing TIP42 model below. Maybe it's related with insufficient model. I appreciate to take your opinion about on-semi BDV65B model file, because I plan to use authentic Philips BDV65B's in this project.
Strange things happen with this model: it looks like half transistor, half darlington. Perhaps it has to do with the integral B-E resistors (real or simmed, I have no idea).
Shown below is the Vbe of the Op transistors.
We see that during their theoretically inactive part of the cycle, only the input transistors must be active because the Vbe is at 0.55V, with an Ic of 190mA.

Why not, that depends on the ratio of internal resistors.

But when the current becomes larger, anomalies appear: when the input transistor's current is insufficient, the voltage should jump to the next Vbe to catch up.
But what we see here is an arch of sinusoid, following linearly the output current.

This is quite strange and unexpected.
If the real component actually behaves like that, the THD will effectively jump to 0.025%. But I suspect that the parameters of the (probably single) transistor have been manipulated to look like a darlington, and in this case the approximation causes the strange behavior.


Quote:
I'm also trying to find a good alternative for PNP servo transistors. Despite lack of Philips BD140's official CoB value, it seems to best to use it under 80V power supply conditions. For above power supplies, 150V/200mhz 2sa1360 seems fit despite its extremely low output capacitance (2.5 pF) if it adequate to solder a 8-10pF capacitor to its C-B legs.
Many video output transistors could fit, some BF4xx or BF8xx. If their capacitance is too low for self compensation, an additional cap could be added.
The 2N5401 could probably also be used.
Attached Images
File Type: jpg Darling.jpg (152.2 KB, 239 views)
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