Off topic technical question

noacronym · Apr 2, 2013

Thank you for allowing this post to remain. I have a technical question related to electronics and post it here because I think I know of a few folks who can answer me most correctly (insert my respect here). I would like to ask anyone who knows how to draw me up a little circuit to divide the signal from an HP 200 ABR into stereo so that I can run the signal into the inputs of tape recorders to align their circuits and heads. Typically, the line in would be 0db or .775 volts. But I do not know what kind of little resistor/capacitor arrangement I would need to fabricate. The HP ABR has a 600Ω output. I am providing a page from the manual. Thank you.The power output as listed in the HP 200 ABR manual is 1 watt or 24.5 V into a 600 ohm load

tkamiya · Apr 2, 2013

Hi,

If the source (your signal generator) can generate that much power, then I'd use something like 1:100 attenuator for 600 ohm unbalanced for L and R channels and tie the input side together. Attenuators will provide the necessary isolation as well as reducing the massive power into your equipment.

There is no need for capacitors as there is no DC components to block out.

noacronym · Apr 2, 2013

Thank you but I wouldn't know how to draw up such a schematic. I'm capable of reading schematics but not designing them.

tkamiya · Apr 2, 2013

This is what I would do....

Each attenuator has an input impedance of 1200 ohm, output impedance of 600 ohm, and loss of -20db.
Since the input is in parallel, it will match the 600 ohm impedance of the source.

I found an online calculator for the resistor values.

tkamiya · Apr 2, 2013

Oh, by the way, I would suggest using metal film type resistor. (see, it's FILM related!)

noacronym · Apr 2, 2013

Thanks friend. I'll whip up one of those that you just designed. Of course I'll have to go toRadio Shack, which doesn't sell electronics any more, and get the closest values I can and depend on the output control on the HP get my .775. I just didn't know how to split the signal and get all the impedences right. I knew the HP would overpower my tape recorder straight off the HP outputs. Looks like with your help I can move on to using this HP instead of generating my signals in Adobe Audition and taking my signals off the sound card. I still need to do some tests and make sure the HP is still putting out flat from 20-20,000. It might not. But if I can get it to generate my signals, I'll be happy. Still looking for a Leader LMV 181a or 185. Using a digital multimeter to calibrate my scope for converting db's to millivolts is a real pain. Thank you sincerely, again.--HTF

noacronym · Apr 2, 2013

By the way all this most certainly is related to photography. If you are listening to music while doing darkroom work, it's incorrect darkroom procedure if it isn't originating from a reel to reel tape deck. Just not done in polite photographic circles.

ic-racer · Apr 2, 2013

Personally I'd just use that signal generator to set the meters to read "0vu" and do it one meter at a time (not splitting the output). Then use the test tape to set playback levels adjustment and then set record levels based on your calibrated meters.

noacronym · Apr 2, 2013

ic-racer said:
Personally I'd just use that signal generator to set the meters to read "0vu" and do it one meter at a time (not splitting the output). Then use the test tape to set playback levels adjustment and then set record levels based on your calibrated meters.

I thought about that, but VU meters ate not necessarily flat. You can depend on an accurate reading at 400hz, or a thousand--maybe a few thousand. But I wouldn't give a nickle for any reading a VU meter gave me at 16,000. I work VERY HARD on a flat response from my tape deck jobs, even if they don't pay. Most of them have heads that won't even give 12,000 any more. You have to know where you are on needed flatness of signal strength every second. Guess what--I caught the sound card of my computer not being flat for me last week. My Tek 2335 100mhz scope doesn't lie.

Trask · Apr 3, 2013

By the way all this most certainly is related to photography. If you are listening to music while doing darkroom work, it's incorrect darkroom procedure if it isn't originating from a reel to reel tape deck. Just not done in polite photographic circles.

Shades of Gene Smith! Didn't he ship a record player and a bunch of records to the South Pacific when he was out photographing WWII? Of course, he also used tape recorders extensively when back in NYC -- wired up his whole apartment building, and managed to record jazz luminaries along the way. What a guy....

noacronym · Apr 3, 2013

tkmiya, I would like to thank you for your help on this matter. The only thing that would make me happier is knowing how you did that. I've been in radio (electronics) for a long time, but some things elude me, being self-taught I guess. Impedance matching and impedance calculations just seem to stymie me. I wish I knew how you did that. Thank you.

E. von Hoegh · Apr 4, 2013

noacronym said:
tkmiya, I would like to thank you for your help on this matter. The only thing that would make me happier is knowing how you did that. I've been in radio (electronics) for a long time, but some things elude me, being self-taught I guess. Impedance matching and impedance calculations just seem to stymie me. I wish I knew how you did that. Thank you.

It's not a matter of being self taught. It's a matter of being unsystematic and not very thorough, Henry.

Dead Link Removed

http://www.ece.rutgers.edu/~orfanidi/ewa/ch12.pdf

noacronym · Apr 4, 2013

E. von Hoegh said:
It's not a matter of being self taught. It's a matter of being unsystematic and not very thorough, Henry.

Dead Link Removed

http://www.ece.rutgers.edu/~orfanidi/ewa/ch12.pdf

I won't take offense at that. Thanks for the links. Upon skimming through I see some math that's over my head. But then a lot of things I've studied were over my head at first. They don't usually stay that way for long.

Peter Simpson · Apr 4, 2013

If you can't find what you need at Radio Shack, try Digikey.com.

lacavol · Apr 7, 2013

What kind of tape recorder are you calibrating and also what tape are you using. The tape speed also has a great deal to do with frequency response. Anything below 30 ips will have a roll off of the higher frequencies and the low frequency bumps are also changed with tape speed as it depends on the wavelength which is speed dependant. The bias also comes into this the same as film you have to get into the linear portion of the tape. The tape has a toe and shoulder also. Tape is not that precise at least in the maths, which is also what makes it's properties more desirable.

Also you might want to go here: http://home.comcast.net/~mrltapes/

The technical papers are great as most are published by the AES and IEEE. They also sell calibration tapes, which are expensive these days. Jay McKnight is one of the people who set the standards for the recording industry.

noacronym · Apr 7, 2013

lacavol said:
What kind of tape recorder are you calibrating and also what tape are you using. The tape speed also has a great deal to do with frequency response. Anything below 30 ips will have a roll off of the higher frequencies and the low frequency bumps are also changed with tape speed as it depends on the wavelength which is speed dependant. The bias also comes into this the same as film you have to get into the linear portion of the tape. The tape has a toe and shoulder also. Tape is not that precise at least in the maths, which is also what makes it's properties more desirable.

Also you might want to go here: http://home.comcast.net/~mrltapes/

The technical papers are great as most are published by the AES and IEEE. They also sell calibration tapes, which are expensive these days. Jay McKnight is one of the people who set the standards for the recording industry.

Presently I'm on this Teac A4010GSL. The original ferrite heads had lost their high end. Replaced with used metal heads and got flat to 16,000--so that's not too bad. I use my MRL 200nwb/m tape for aligning playback, then set up my recording head on a Tek 2335, injecting tones from Adobe Audition, till I get my HP generator going.

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