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Old 4th February 2018, 12:22 AM   #4121
sq225917 is offline sq225917  United Kingdom
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I've. Built with the bom parts, 2140 and opa627BP. There's no audible difference though I suspect the 627 is more stable over temp range. It doesn't really matter once it's up to temperature.

Swapping the 1m resistor for a 5m, slows the servo operation. If your input stage is very well matched this will improve the bass, better tonality, more solidity.
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Old 4th February 2018, 09:54 AM   #4122
FdW is offline FdW  Netherlands
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A slightly faster servo may be beneficiary in (more than) two ways.
1: 10...20Hz servo's remove low frequency rumble Rumble (noise) - Wikipedia
2: 10...20Hz servo's lower 1/f (flicker) noise Flicker noise - Wikipedia
3: ...

Actually I should have said 100ms...50ms servo

Last edited by FdW; 4th February 2018 at 10:04 AM.
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Old 4th February 2018, 10:04 PM   #4123
AVWERK is offline AVWERK  United States
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I thought Curl suggested a slow servo so as not to influence the whole frequency range but it has been a few years

Regards
David
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Old 5th February 2018, 08:11 AM   #4124
FdW is offline FdW  Netherlands
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Yes, and I oppose that, I think 50...100ms is best.
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Old 5th February 2018, 08:26 AM   #4125
FdW is offline FdW  Netherlands
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Current servo 413mHz
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File Type: png Paradise R3 Servo 413mHz.PNG (83.4 KB, 277 views)
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Old 12th February 2018, 07:55 AM   #4126
avinunca is offline avinunca  Europe
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Quote:
Originally Posted by hesener View Post
Hi ste, the input transistors are running at 3mA each, in the circuit the VCE is around 14V. The DCA75 can be set from 3V...9V, so I would go for 9V. Most important is that all mesure the same, the VCE is not so important.
I compared results with different test voltages. I was surprised by the effect of Vce. If for instance, matching were done with a Peak DCA-55, there would be quite a difference in hFE between PNP and NPN sides at operating voltage. I maintained temp around 24C and repeated with other 337/327

BC327 DCA-75 curves at 9V ,3mA =hFE 483, Test function (DCA-75) = hFE 440, Test function (DCA-55) = hFE421

BC337..................ditto ....................444 ....................ditto ..................434...................... ditto ...............422

I am rather late to the party and I'm sure this must have been discussed previously. I am only on p400 of MPP!
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Old 19th February 2018, 12:07 PM   #4127
avinunca is offline avinunca  Europe
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Assuming I am using the DCA-75 curves correctly, many Paradise builders having matched transistors using the DCA-55/75 test function apparently have poor matching between pnp and npn transistors at normal operating voltage.
I set my tester to produce one curve in hFE vs Vce=9V and read value at Ic=3mA.
BC327 hFE increases much more than BC337 hFE with higher Vce
It appears the circuit design effectively compensates for some 10% or greater mismatch between BC327 and BC337 even in the input stage. Being in the process of building this amplifier I would appreciate any clarification that would help me with transistor selection.
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Old 19th February 2018, 05:42 PM   #4128
sq225917 is offline sq225917  United Kingdom
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Yes lots of people probably have God awful matching and aren't seeing the full performance of the circuit.
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Last edited by sq225917; 19th February 2018 at 05:48 PM.
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