About a year ago I ran across this preamp on the Wired State forum. Has anyone ever heard of / listened to this preamp?

Mark

Where is this monster, if you please?

Yerz,

Poinz

I found out some more about this unit since my last post.

First, it's available in the U.S. from Vacuum Tube Valley for around $350. I think this was originally a kit sort of affair from the guys on the Wired State forum, based in the Phillipines. No kits now I'm thinking. I got surprisingly little information from the Wired State forum.

A fellow from VT Valley wrote me and it seems like the thing is very nicely wired inside: Black Gates, high quality resistors, all that. This USA version is of course 110V compatible.

The problem for me was there are only 2 inputs. Since I run a tuner, phono, and a CD...it was not feasible for me.

Currently the guys at Wired State have what looks like a Tono 300B project going on. Worth checking out. Looks nice, but I'll stick with my 2A3 based amps.

I do have a photo of the Tono Preamp somewhere and if you're really, really interested I could send it to you offline.

I'm shopping around a bit for preamps -- or might be content if I could just get my Foreplay 2 a little more quiet. Then I could forget about something new.

Others under consideration are the Foreplay 3 and Hagerman's (hagtech.com) "Clarinet". Both look pretty nice and are supposed to be quiet.

Mark

The problem I had with all the regular circuits was too much gain (and thus too much hum/noise gain), and not enough drive (without a cathode follower). I fixed this by using a simple, linear circuit with a small power tube. This baby has a gain of ~4.5, Zout of 200Ω, bandwidth (+0, -1dB) of 8Hz to 300KHz (!), and hum+noise low enough to be difficult to measure with a lab millivoltmeter, about 0.1mV.

The number-of-inputs problem is solvable with any circuit. I do this too, because I can source a nice silver-contact toggle switch for about six bucks, where an equivalent quality rotary is about forty with a nice knob.

I'm going to put this project up on my site in the next couple of days, but if you want to look at it right now, The Owner's manual is up at:

http://www.AudioTropic.net/AudioTropicMobiusUsersManual/UsersManual.html

All the technical details are in there.

Aloha,

Poinz

As Cartman would say: "That's Hella-Kewl !"

I love not only the looks but the simplicity of the whole thing. And , for once on the Internet, there are excellent diagrams / schematics that are easy for even a rookie like me to follow.

Tell me more about the selector switch for $6 and also this main transformer. I'm not familiar with the company.

Regards,
Mark

It's all there. Go look at the parts list. If you can live with two inputs (a toggle input switch), the switch is an ElectroSwitch DPDT center-off toggle from Digi-Key whose part number is listed. The main tranny is an Amveco toroid, likewise, which shifts for the princely sum of ~$15 in onesies-twosies. If you need your several inputs, use the Elma 04-1261 from Percy, $34 (plus the knobbie of yer choice); it's a dandy.

Go look at the parts list, confoun' you. I spend hours making these things up and verifying that they're accurate.

I'll have a better expo of this piece on my site in a day or two, but meanwhile,

Yer Obeediyunt Servunt,

Poinz

Will take a better look at all this! Like I say it's very refreshing to see plans that are so well thought out.

More questions to follow from me, no doubt.

Regards,
Mark

OK, some preliminary questions:

1) On the first schematic, in the lower left corner, there's a tube pin out shown for a 7BZ? I'm not understanding why it's shown. I thought this preamp used (4) 6AQ5 tubes.

2) Is a 6AQ5-A tube acceptable to use?

3) How does the wiring run from the power supply side (right side) to the audio side (left side)? There must be a bottom or something I cannot see in that middle section where the four tubes are located? And the wiring runs underneath that?

Thanks,
Mark

2) 6AQ5, 6AQ5A, 6AQ5W/6005 that I have gotten are all exactly the same (from the same manufacturer).  It seems to me that the 6AQ5W/6005 are a little less microphonic and a little more uniform in their characteristics; it's probably a selection thing.  I'm trying to decide if they sound better or not.  I think maybe slightly.

3) Bless you, my man.  You know, not one person in four ever flashes on that little detail of the implementation.  I am a forty-year maker of musical instruments, aircraft, sailing yachts, and this stuff.  The umbilical wiring (B+, circuit ground, chassis ground, heaters) runs through the chassis wall.  I will bring one of these to your house, and with a magnifying glass you will not find how I did it.  You have just appeased my (considerable about this stuff) vanity, so if you beg me, maybe I'll tell.

Yer admirer,

Poinz

Gee, I'd much rather come to your place to see how that umbilical wiring runs from one section to the other since I see you live in beautiful Hawaii! It's still cold here in Pennysylvania!

I'm guessing you split one of the long pieces (the back one) lengthwise, run a groove or grooves with a router make a space to house the wiring, run the edges on the jointer to clean them up, then glue the two back together? That's how I'd do it. Practically invisible if done carefully.

So, that middle section is indeed open all the way to the tabletop, then? And, all you see is the tubes? Cool idea! I love the looks of this preamplifier.

I also like the fact that the transformer is cheap, and the hum level is very low. I found 5 or 6 good 6AQ5's in my tube stash too. The fellow who used to sharpen my saw blades was a TV repairman and he gave me a bunch of his pulls.

I may try to build one of these with your help. I've never built any electronics from scratch, only kits. Lots of speakers, but no electronics. Presently, I use the Bottlehead Foreplay 2 preamp. I like it just fine, but I can't seem to quiet it down.

I forgot to ask what beautiful tropical wood you were using? Koa?
Wish I had a barn full of it.

I understand now about the pin out diagram for the 6AQ5's. I didn't know they had a certain number code too...7BZ. I guess I thought each numbered tube just had it's own pin out diagram.

All the best,
Mark