vacuum tube active stepup for moving coils revisited

[Paul Birkeland]

It would be really nice if it could be used with tape heads too.  Please keep us in mind!  I would love to get another 10 to 20 dB before my Eros tape.

Dan, or team, can you answer this please?

IIRC, most tape heads are going to put out a few mV, and the Tape Eros is optimized for this signal level.  You have to remember that the Eros circuit can be overdriven, with the Tape Eros probably not wanting to see more than 2-3mV.  If your tape head is putting out 1mV, you would need to burn off nearly all of the signal out of the active step-up not to overdrive the Eros and end up with a lot of extra distortion.  This would maybe net you 3-6dB, and certainly nowhere near 10-20dB. 

Extra gain from the Eros would have to be obtained by a 3rd stage, a step-up transformer, or a fresh set of tape heads.

-PB

[johnsonad]

Hmm... Thanks PB.

[Paul Joppa]

To comment further, tape heads vary in voltage sensitivity and optimal impedance. All our tape head preamps are designed around a moderately high output tape head (250mH IIRC) with something in the vecinity of 100kohms load impedance. Really high impedance heads (500-1000mH) have some treble limitations, and low impedance heads are optimized for solid-state preamps. If you have a low-impedance head which you are committed to, then something like what we're looking at can make it work with all-tube electronics, but it adds a stage, so (in my humble opinion) it's better to use a high-impedance head with tubes if you can.

[Doc B.]

FWIW I was doing demos all day today and had digital, phono and tape all running. My Nagra has a fairly high output head. The output from the single ended RCAs of the Repro, which would be the same output level as an Eros, was WAY louder than the phono with the new active step up, or the DAC. Like 10 dB or more. So I'm inclined to suggest that you might want to look for a higher output playback head.

[johnsonad]

My 1/4" 2 track Flux Magnetic head has plenty of output. It's the 1/4" 4 track stock Otari head I would like a few more dB of gain out of for old comercial tapes. I can live without it but it would be nice. John French wasn't able to find a higher gain head that would work with the Otari.  It's been a while since I asked him and maybe I'll try again. Maybe a Nagra head will work....

[Doc B.]

You might ask Greg Orton if he would make a 1/4 track head. He has made them for me in the past. You might be able to specify the inductance. The 2 track head is 200mH IIRC. More inductance usually means more turns and thus higher output.

[johnsonad]

Thanks Dan. I'll shoot him an email.

[Doc B.]

Today PB has duplicated the existing stepup, with the single change being the use of triode wired 7788s instead of 6C45Pis. We will compare the two tubes and see which makes the most sense sonically. It should be possible to set the kit up so it's reasonably easy to change from one to the other with a little bit of socket rewiring.

[ironbut]

Hey Aaron,

IIRC, in the early days (months?) of the Tape Project forum, Mike Paschetto (Mikey on this forum) had JFR switch out the heads of his Technics to some 400mH Tascam heads which he found to be more "tube friendly".
When you contact John French, you might ask about that. I would guess that if he was able to get those heads into the Technics headblock, getting one into an Otari with and outboard tube pre should work (maybe John is assuming you're using the stock playback electronics?).

Just went back and took a gander at the post I was referring to and I was wrong-wrong-wrong!
Here's what he actually got,..

1/4 track playback head, Panasonic RPB-065 (560mHy, 400 ohm DCR)

[johnsonad]

Hi Steve, thank you very much for that! I'll shoot John an email tomorrow. That must be the head Dan had mentioned to me in the past.

[Mikey]

IIRC, in the early days (months?) of the Tape Project forum, Mike Paschetto (Mikey on this forum) had JFR switch out the heads of his Technics to some 400mH Tascam heads which he found to be more "tube friendly".
When you contact John French, you might ask about that. I would guess that if he was able to get those heads into the Technics headblock, getting one into an Otari with and outboard tube pre should work (maybe John is assuming you're using the stock playback electronics?).

Hi Gang,

Here's the link to that archived post from the old Bottlehead forum:

http://db.audioasylum.com/mhtml/m.html?forum=bottlehead&n=111455

[ironbut]

Hey Mikey!
I was hoping this thread would flush you out of the bushes.
Man,..2006! So that was before the Tape Project forum.
Kinda scary!

[johnsonad]

John says they haven't been available in a long time. Thank you all for the help!

[Doc B.]

OK, to get this back on track, PJ, PB and I spent yesterday afternoon working on the noise floor. It's very low, but we want to get it just a bit lower so it can work with really low output MC carts that are down below .3mV. We came up with a scheme that brought the noise down 3dB and have another one planned that we hope will give us another 1.4 dB of noise reduction. Bit by bit.

It sounds really good.

[denti alligator]

Shee-hut, even if you don't get it that far down it's pretty impressive. Looking forward to this.