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Old 1st March 2010, 08:59 PM   #1
tmblack is offline tmblack  United Kingdom
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Default Passive NAB Tape Preamp?

Has any tried building a reel to reel tape preamp?
My old Sony machine has real old components that generate a lot of hiss and loss of high frequency response.
I was thinking of using a high performance op amp such as the LME49720 and a passive EQ design.
Perhaps eventually a tubed unit for the ultimate sound and conversation piece.

Tom
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Old 4th March 2010, 10:30 PM   #2
studeb is online now studeb  United States
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go to the tapehead.net forum, or the bottlehead forum
they have diy tape head devices
basically a phonoe pre without the RIAA
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Old 22nd September 2010, 10:07 AM   #3
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Quote:
Originally Posted by tmblack View Post
Has any tried building a reel to reel tape preamp?
My old Sony machine has real old components that generate a lot of hiss and loss of high frequency response.
I was thinking of using a high performance op amp such as the LME49720 and a passive EQ design.
Perhaps eventually a tubed unit for the ultimate sound and conversation piece.

Tom
Have you started your project ?
I am thinking about doing the same thing, i started with power supply rebuilding but now i am faced with calculating the complicated Eq filters. I am looking for help on this part.
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Old 26th September 2010, 09:24 PM   #4
cbdb is offline cbdb  Canada
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Quote:
basically a phonoe pre without the RIAA
Not really. Pro decks have EQs to set, which varies with the kind of tape and tape speed. And you will also need a notch filter to take out any residual bias tone.

You also need gain and impedance matching, so passive is not possible.
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Old 26th September 2010, 09:37 PM   #5
cbdb is offline cbdb  Canada
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Here is an example.

Notice the various EQs used in the repro amp.
Attached Files
File Type: pdf AmpexAG300_schematics.pdf (158.2 KB, 166 views)
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Old 27th September 2010, 05:07 AM   #6
studeb is online now studeb  United States
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you are right, i should have said "like a phono pre but with a different eq"
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Old 27th September 2010, 06:08 AM   #7
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@cbdb : What impedance matching are you talking about ? Are you talking about the playback head impedance ?
My ideea is to build a flat response head-amp with a passive high-cut filter for the bias frequency.
After this gain stage i want to connect the Eq stage.
I think this would eliminate the playback head impedance problem.
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Old 29th September 2010, 05:44 AM   #8
cbdb is offline cbdb  Canada
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Quote:
Are you talking about the playback head impedance
Yes. Sorry, reread the first post. Originally though it meant totally passive. Looks like your on the right track. If you search the net you can find lots of pro ccts to use as a guide. Why not include the Low pass filter in the head amp, you will probably have to limit its bandwidth for stability anyways.
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Old 29th September 2010, 07:13 AM   #9
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By passive i understand connecting the filter network from the signal line to the ground. Pure passive cannot be done.
But i prefer connecting the filter network on the op-amp.
The thing is i cannot find on the nets what i am looking for.
If anyone has a tested schematic i am asking them to post it.
I will post mine here shortly.

I would also like an opinion on an artifact i encountered. I have run some tests, i fed the recording head a sine wave and measured the output on the playback head's output ( trough an op-amp ). I am getting a capacitor like effect ( like adding a cap from the signal line to ground ) on the sine. Is this from the tape ?

I am also thinking about a way to calibrate the EQ according to the tape's output. I own a Technics MC deck that performs such a calibration before recording and sets the EQ, gain and bias accordingly with exceptional results.
I will study the Technics schematics to see if i could use their system for the reel tape player.
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Old 1st October 2010, 08:57 PM   #10
cbdb is offline cbdb  Canada
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I am also thinking about a way to calibrate the EQ according to the tape's output.
You need a calibration (reference) tape that has tones at a specific magnetic flux density (level) to align the head and cal your repro (playback) levels and EQ. Once repro is calibrated you can align the rec head and cal the record electronics (bias as well as EQ) for the tape your using. Once thats done, Pros usually put tones (100 1k 10k) at the head of a new tape and use these to check/adjust playback if it doesnt match the reference tape, which it should at first, but over time these levels may drift (tape is lossey over time).

Last edited by cbdb; 1st October 2010 at 09:02 PM.
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