Any one have a good tape head amp schematic

[chopdr230]

Hi there dose any one have a good schematic for a tape head amp ? I already have the bottlehead seduction
amp but don't want to convert it for tape use and i cant afford the repro amp and love building my own stuff but i cant find a good schematic any where . Also when are single tapes going to be available i would like to try one first be for i make the jump for the subscription . Thanks so much AL

[Ben]

I am sure, if you dig you can find something on the internet
but under a phono pre-amp. I know some pre-amps like Dynaco, had tape in
but I don't know what voltage levels.
I still favor a two stage amp, with a single stage of gain from the heads
in the deck to the main amp a few feet away. I wonder if transistors have
matured so a good front end is possible? +- 18 Volts do not make for great
tube designs. Regardless of what you find,
unless you have the free time to experiment, you may save more money in the long run buying doc's new design, once he stops playing with his toys.

[PJ]

:^) Sorry, could not resist. You have a Seduction; the schematic is in the manual and the modifications to convert to IEC are on the web site. If you want to embark on such a DIY project, the Bottlehead forum is full of helpful people. We've always had a strong DIY and learning focus, so helping people get past kits to doing their own projects is just another part of the learning community. (Yes, I stole that phrase from Peter Senge!)

[Ben]

I too favor a little better preamp than the the seduction. For me
a little better, is a tube design say using 12AY7's ( gain of about 33 per
stage) and then a driver tube other than the one  they use.
This is  3 triode stages.  Zener diode regulation[1]
and no CCS's.[2]  PS. I am cheap too, I use 10 cent green leds for bias but...[3]

How ever I take it there are more factors in designing a low noise, non-cost cutting
modern design than I can think of. A diy project is a one off item, the seduction
and other bottlehead products are nice designs and good value for your money.
The doc has the resources to tweek the equipment, for quality sound, and for
now I TRUST his judgment. I can always upgrade later for better sound from my
deck, right now finding any R2R 2 track music that I like is hard.
Ben.

[1] Or tube regulation. Transistors require a heat sink that is a pain
to isolate from +300 volts.
[2] You want a load line 90 degrees from the bias point of your tube.
Horizontal is not always the best.
[3] Spend my money on big 100 uf poly-caps

[PJ]

I too favor a little better preamp than the the seduction. For me
a little better, is a tube design say using 12AY7's ( gain of about 33 per
stage) and then a driver tube other than the one  they use.
This is  3 triode stages.  Zener diode regulation[1]
and no CCS's.[2]  PS. I am cheap too, I use 10 cent green leds for bias but...[3]

...

[1] Or tube regulation. Transistors require a heat sink that is a pain
to isolate from +300 volts.
[2] You want a load line 90 degrees from the bias point of your tube.
Horizontal is not always the best.
[3] Spend my money on big 100 uf poly-caps

Agreed that one can do better than Seduction, which was always intended as an entry-level design.

The 6DJ8/6922 has a low enough plate impedance to drive a moderate-length cable directly so that two stages can suffice. Most other tubes will as you say require an additional stage.  For the Progressive Engineering phono preamp I did just what you have suggested - switched to 6N1P for the gain stages, and added a direct-coupled cathode follower for low output impedance, along with a shunt regulated power supply. In our experience, cathode followers are pretty decent if they have a good shunt-regulated power supply; otherwise they have been problematic. A 12AY7 would be a good candidate; like the EF86 it's a tube designed for small-signal audio.

An improved Seduction would have a shunt regulated power supply. We've done it experimentally and the difference is quite audible. It would require a new power transformer and supply of course. In fact we had planned to make such a thing, but it got replaced by the EF-86 based design after we listened to the Repro Amps.

Incidentally, we did build a test box with stereo cathode followers and six different shunt regulator circuits, including Zeners and gas regulator tubes, in order to chose what configuration to use in the Bottlehead products.

A couple points of information about the designs: In addition to lower distortion at large signal magnitudes (admittedly, not that significant for these tiny signals) a good current source plate load provides some 50dB of power supply noise rejection, so I continue to prefer that configuration. We use old-technology low efficiency red LEDs because their dynamic resistance is especially low, and they are very quiet.

[Scott D. Smith]

So, I'm curious-what was the favored configuration for the shunt regulators?

--Scott

Incidentally, we did build a test box with stereo cathode followers and six different shunt regulator circuits, including Zeners and gas regulator tubes, in order to chose what configuration to use in the Bottlehead products.

A couple points of information about the designs: In addition to lower distortion at large signal magnitudes (admittedly, not that significant for these tiny signals) a good current source plate load provides some 50dB of power supply noise rejection, so I continue to prefer that configuration. We use old-technology low efficiency red LEDs because their dynamic resistance is especially low, and they are very quiet.

[docb]

The hybrid regulator that we use in our kits is the one that worked best for us. It uses an LM431 stacked under the triode, and when used with a CF it is bypassed to keep the noise down. Similar circuits can be found in the July 1999 issue of Tubecad Journal.

[Ben]

Well I am glad you had good luck with solid state, I have never had
good luck with any of the tube-cad ideas. $%#! new parts today, don't
even come with magic smoke any more, sigh. That includes PENTODES
and new transformers for me as well. I need Robbie the robot to state
'Danger Will ..." .  I'll stick to triodes,glow tubes,Si diodes and 5 watt zeners,
they work for me the best, as well as home for the cheap green led bias.
-.19 volts seem to be the best bias for me.