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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kevinkr

Administrator
Paid Member
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...
 
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.
 
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PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com
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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PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com
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.
 
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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