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Author Topic: A wish: New tape preamp: Desire  (Read 3521 times)

Offline Ben

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A wish: New tape preamp: Desire
« on: September 06, 2008, 11:04:41 AM »
This is what desire ...  A combo seduction and  the foreplay line driver
in a single small box.  The main reason is I don't think I will have room for
both the seduction and foreplay and my deck all in the same corner of the room
when I do decide to upgrade. I suspect other people also may have the same problem, a small amount of room for the tape deck and amps.
Set 45,Open baffle speakers,Otari 5050,,Pioneer DV-79AVi DVD/CD/SCAD player

Offline PJ

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Re: A wish: New tape preamp: Desire
« Reply #1 on: September 09, 2008, 12:12:05 AM »
Well, I see that Doc has not mentioned the Bottlehead R&D plans yet. But they come close to addressing this issue, so I'll put up a few remarks.

The Repro Amp has three stages, as has been noted. The first two stages (EF86 and 6DJ8/6922/7308) have 20dB more gain than the Seduction, and the third stage adds another 12dB plus the ability to drive balanced 600 ohm lines. There is also an unbalanced output after the second stage. Of the 20dB extra gain in the first two stages, 10dB goes to extending the bass flat to 17Hz vs. 50Hz with Seduction for IEC tape equalization, and the other 10dB goes to greater gain for the less sensitive tape heads. Getting this much gain from an EF86 is pretty tricky, and for the best performance you do want to find some prime examples of the EF86.

For some time we have been working to produce a phono (RIAA) preamp kit using just those first two stages. For RIAA applications we'll shoot for only 10dB more gain, since the bass issue is not a problem with RIAA. That gives us more latitude with respect to EF86 selection. Obviously it will be more costly than the Seduction, but less than the full-fledged Repro Preamp. Even when it comes out, it may be some time before we have a tape head modification for it that we are entirely happy with (i.e. incorporating the deeper bass of a full IEC implementation). But we are working to provide a higher-gain option. The first prototype has been evaluated, and the second version is being designed. I can't say when it will be available, because we don't know how many more versions will be needed.
Paul Joppa
Bottlehead R&D

Offline Ki Choi

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Re: A wish: New tape preamp: Desire
« Reply #2 on: September 10, 2008, 11:44:12 AM »
Hi PJ,

Thanks for your clear explanation.

"50Hz with Seduction for IEC tape equalization"

Is there a graph that shows Seduction's frequency responses below 50Hz for the IEC tape eq., ideally in comparison to the big boy?

Ki
Ki Choi

Offline Ben

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Re: A wish: New tape preamp: Desire
« Reply #3 on: September 10, 2008, 03:29:16 PM »
Well for me, my Full Range Speakers only go down to 55hz so I don't have a
real worry about anything lower. I really depends on your system you have.
I plan to upgrade slowly, get the basic system R2R and a few tapes. Later I plan
to upgrade to the seduction+foreplay system.
My only real gripe about the current system is you don't have a pre-amp for
the heads in the R2R, but go straight in the seduction.
Set 45,Open baffle speakers,Otari 5050,,Pioneer DV-79AVi DVD/CD/SCAD player

Offline PJ

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Re: A wish: New tape preamp: Desire
« Reply #4 on: September 10, 2008, 04:38:08 PM »
I tried to attach a plot of the gain in the bass, showing the IEC specification, the Repro amp, and the Seduction, but I could not get it to work. I'll post it in the Bottlehead forum in case anyone wants to see it before I get this software here figured out.

Note that the IEC spec calls for infinite gain at zero frequency; this is because a constant tape flux level produces a signal whose magnitude is proportional to frequency. The NAB standard calls for boosting the tape flux level below 50Hz so that the tape preamp can have finite gain. IEC does not do the boost so that the tape won't be overloaded. That means the bass response can be set by the preamp, and no standard is set for that. Since Seduction is only two stages and gain is limited, we chose to use 50Hz which is the same as NAB tape (and RIAA phono) equalization standards. For those rare occasions where there is significant energy that low, this means 3dB down at 50Hz and about 6dB at 30Hz. Obviously, speaker response and room effects will have a very large influence as well on what you hear.
Paul Joppa
Bottlehead R&D