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M2 inspired balanced output preamp idea
M2 inspired balanced output preamp idea
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Old 20th February 2019, 07:26 PM   #41
Mark Johnson is offline Mark Johnson  United States
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M2 inspired balanced output preamp idea
Norwood's good for 200mA. Tucson is only spec'd to 35 mA. Rolling your own design using THT might select the OPA633 in DIP8, as the final output drive.
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Old 20th February 2019, 07:56 PM   #42
woofertester is online now woofertester  United States
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Quote:
Originally Posted by indra1 View Post
Pin 1-2 connection will draw > 50ma at 20Hz for 20Vpp output. Needs a buffer with enough grunt.
Correct. Good prediction.

For 10v p-p out, the -3dB frequency is 16.5 Hz. This is not bad for a $6 transformer. At 10 v p-p, there is no visible distortion.

As you predicted, for 20v p-p out at 20 Hz, the sine wave is visibly distorted.

So, if max p-p voltage out is needed at low frequencies, this is not a good solution.

But, you have to consider that acoustic music played at realistic levels does not contain vast amounts of 20 Hz. The cheap buffer boards driving the Edcor as a preamp may sound just fine for many applications. It is probably not a good idea for Dub Step music at a night club at 120 dB.
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Old 20th February 2019, 08:06 PM   #43
Zen Mod is offline Zen Mod  Serbia
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M2 inspired balanced output preamp idea
for that you don't need amplification

just Variac

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Old 20th February 2019, 08:10 PM   #44
woofertester is online now woofertester  United States
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Originally Posted by Zen Mod View Post
for that you don't need amplification

just Variac


I think I may want a SUSY pumpkin preamp.
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Old 20th February 2019, 09:07 PM   #45
indra1 is offline indra1  Indonesia
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Originally Posted by woofertester View Post
... For 10v p-p out, the -3dB frequency is 16.5 Hz. This is not bad for a $6 transformer. At 10 v p-p, there is no visible distortion....
Good, let's worry about 20Vpp at 20Hz later. Edcor still has the PCW or the WSM 600/15k that will cut it. Time to start finding out what the PC 600/15k needs to sing well in circuit.
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Old 20th February 2019, 09:40 PM   #46
woofertester is online now woofertester  United States
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Originally Posted by indra1 View Post
Good, let's worry about 20Vpp at 20Hz later. Edcor still has the PCW or the WSM 600/15k that will cut it. Time to start finding out what the PC 600/15k needs to sing well in circuit.
I agree. The cheap-o buffer boards are probably good enough to drive the Edcor in a balanced preamp configuration for real-world music.

I like to measure things so I went further and measured the Edcor for voltage swing and for bottom octave behavior.

No problem getting the Edcor to swing 100V p-p undistorted as low as 50 Hz. Below 50 Hz, and above 10 V p-p, there is visible distortion regardless of output impedance of the driver. So, I conclude that the distortion is core saturation.

This preamp idea would be to drive my Aleph 30 which would be driving an array of midrange speakers that will have a 100 Hz crossover making behavior below 50Hz not so important.

Thank you all for the inputs and suggestions. They were all helpful.
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Old 20th February 2019, 09:48 PM   #47
woofertester is online now woofertester  United States
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50 Hz 100V p-p output
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Old 20th February 2019, 09:49 PM   #48
woofertester is online now woofertester  United States
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20 Hz 68V p-p
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Old 20th February 2019, 10:43 PM   #49
Zen Mod is offline Zen Mod  Serbia
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M2 inspired balanced output preamp idea
don't use force , use a bigger hammer
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Old 21st February 2019, 12:19 AM   #50
indra1 is offline indra1  Indonesia
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I modified Scott Wurcer's model for the PC600/15k with your measurement and sim a driver idea.
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