12ax7 12au7 preamp

[Bengali]

Hi,

please refer to schematic for this pcb:

tube 12AX7 12AU7 preamp pre-amplifer golden plated pcb | eBay

What kind of gain does this produce? Should the Pot be 100K?
Any ideas on the values to better optimize? Seems like simple build with
the pcb.

Thanks for any info on it

[revintage]

20dB. Don´t build it!

[Rodeodave]

What's wrong with it?

[DF96]

Really strange design! It starts with a high gain high impedance valve (12AX7) but then throws away the gain by using strong degeneration and a relatively low anode resistor. Having done this, the sensible thing to do would be to follow with a CF but this uses another similar stage. The resultant high gain and high output impedance then has to be tamed by using feedback. Not enough feedback to really suppress higher-order products, though.

It looks like a valve circuit designed by someone brought up on BJTs.

[revintage]

It looks like a valve circuit designed by someone brought up on BJTs.

[Merlinb]

The PCB and basic topology is usable though. There's nothing to stop the OP using an ECC82 or ECC81 as an alternative, and either eliminating or changing the cathode degeneration and feedback loop. You could even ignore the second stage and arrange the first stage as a cathode follower for a unity gain buffer. Would make an neat and simple platform for a beginner to play with.

[cjkpkg]

spend some time at TUBECAD and study the different aikido, cathode follower, and other topologies discussed there.

I learned a heck of a lot by doing so and ended up ordering a simple 5687 aikido preamp kit. I am also a repeat customer because his products are proven, very good quality, and support is wide in this forum.

Not saying the preamp link you posted is bad - BUT if you are just starting out I would hate to see frustration come out of a build if you are.

The manuals have all kinds of good information too since his circuits allow for tube rolling with minor resistor value tweaks.

People have very good luck with using tubes like the 6dj8, 6h30, 6cg7, 6n1p to name a few. A gain that seems to generally work well for hi-fi ranges between 5 - 15 at most.

For a typical preamp a pot value of 50K or 100K should work just fine. I typically use Alps 100K stereo pots available at mouser. A stepped attenuator in that value range would be nice as well.

[Gobble]

Originally Posted by cjkpkg

spend some time at TUBECAD and study the different aikido, cathode follower, and other topologies discussed there.

I learned a heck of a lot by doing so and ended up ordering a simple 5687 aikido preamp kit. I am also a repeat customer because his products are proven, very good quality, and support is wide in this forum.

I am looking for a preamp for my MyRef Gainclone and see-sawing between the Grounded Grid and Aikido.

I heard a borrowed GG in my setup and funnily (and wonderfully) it made everything in between the CD and speakers disappear. Then I've had little luck in finding good 12AU7s amongst many NOS I tried so want to move away from 12AU7s. Also the Aikido promises to be cheaper.

How would you rate the Aikido on delivering excitement and ability to lift veils from the music?

---G0bble

[Bengali]

yeah, I confess, I bought it.

I don't have intimate knowledge of all the topologies,yet.
I've built several aikido's though.

I figure some one here would have a great circuit to replace
the original one if it's really that bad. The board is nice enough to
make mods.

Thanks

[cjkpkg]

It is the only preamp I have built where I do not feel the need for any kind of equalization. I have built some op-amp pre's and a Pass JfetBOZ. In my opinion what is recorded at the source is what comes over the speakers.

The aikido sounds just as good with a 6W SE amp as well as a MOSFET amp like a Pass F5. The beauty is being able to swap input tubes to fine tune the gain. I typically roll between 6CG7's and 6DJ8's depending on the power amp.