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Passive IEC equalization for tape playback --
Passive IEC equalization for tape playback --
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Old 1st March 2020, 01:17 AM   #1
jackinnj is offline jackinnj  United States
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Passive IEC equalization for tape playback --
Default Passive IEC equalization for tape playback --

I was asked if "His Majesty's Noise" layout could be use for tape playback:
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File Type: png RIAA_Schematic.png (8.7 KB, 64 views)
File Type: png RIAA_Results.png (7.7 KB, 66 views)
File Type: png IEC_Schematic.png (8.7 KB, 65 views)
File Type: png IEC_Results.png (8.6 KB, 65 views)
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Old 1st March 2020, 01:43 AM   #2
kevinkr is offline kevinkr  United States
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Passive IEC equalization for tape playback --
I am working on something similar for my current phono stage design. I can't tell if this is 35us or 70us EQ as the resolution of the graph is insufficient to determine the -3dB point.

Not sure why you are not just using first constant at ∞ and a step network at 35us/70us.. (The added second cap?)

I have a lot of 2 track machines and will do something with one of them.

Cool...
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Old 1st March 2020, 02:15 AM   #3
jackinnj is offline jackinnj  United States
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Passive IEC equalization for tape playback --
Quote:
Originally Posted by kevinkr View Post

Not sure why you are not just using first constant at ∞ and a step network at 35us/70us.. (The added second cap?)
MBE somebody would prefer NAB, the equations which Lipshitz developed for the "1C" network can be pressed into service -- I gotta drive 450 miles tomorrow but will put them out on Monday.

edit -- phono and RIAA are something I have a bit of experience in -- this was an effort to help someone out.

Last edited by jackinnj; 1st March 2020 at 02:19 AM.
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Old 1st March 2020, 02:45 AM   #4
PRR is offline PRR  United States
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How many IEC EQs are there?? How many do you need?

I picked 3180uS and 50uS as common values. A play-any-tape preamp will need switching.

In your plan, C3 R10 define a 2Hz low-cut. R2 C2 define a 155kHz treble-cut. These may be needed for amplifier happiness(?) but is not really "equalization".

I get other values for the EQ parts. R1 seems 2X too big? These values are close enough to put in a sim. I am quite sure the Cs should be rounded to available values, and the Rs re-figured (you can buy R many more sizes than you can buy C). If C1 is 330nFd then R1 is 9.650k.
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File Type: gif IEC-EQ-1-42.gif (21.2 KB, 53 views)
File Type: gif IEC-EQ-2-42.gif (54.4 KB, 17 views)
File Type: gif IEC-EQ-3-42.gif (83.5 KB, 17 views)
File Type: gif IEC-EQ-4-42.gif (8.3 KB, 21 views)
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Old 1st March 2020, 02:54 AM   #5
jackinnj is offline jackinnj  United States
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Passive IEC equalization for tape playback --
Quote:
Originally Posted by PRR View Post

In your plan, C3 R10 define a 2Hz low-cut. R2 C2 define a 155kHz treble-cut. These may be needed for amplifier happiness(?) but is not really "equalization".
C3 and R10 are just elements of the next stage 6922/6DJ8 stage -- this is, after all, hived off Stu's "HMN".

Thanks for your comments and elucidations.
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Old 2nd March 2020, 03:19 AM   #6
PRR is offline PRR  United States
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The "real problem" with passive IEC is that it "can" go up-and-up to zero frequency. With NFB EQ this is easily done. With pure passive it may force HUGE midband loss, depending how you define "subsonic". If we pick the lower limit as 10Hz we need over 40dB of loss in the EQ, which means over 40dB of gain in the stage before the EQ to avoid the second stage adding hiss. 40+dB gain *may* get us into midband overload.
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Old 2nd March 2020, 02:53 PM   #7
jackinnj is offline jackinnj  United States
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Passive IEC equalization for tape playback --
Yes, I changed T3 to 7950uS, T4=35uS, T5=100nS (you can probably eliminate T5.) Mid-bass response is down 20dB @390Hz.

Of course, SY's "His Majesty's Noise" uses a 1:10 step-up transformer to effect balanced input and balanced output -- if this is valuable to reel-to-reel I don't know.
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