One-Bottle Preamp

[NewYorkDave]

I'm sorry I forgot about the rest'a yuz who were building one-bottles and two-bottles. My memory ain't what it use'ta be.

Kevin, my 12AV7s came today, too... Like yours, they're all RCAs. I guess we both placed our orders on "RCA Day" at Antique. :thumb:

Kingston made a good point about the "gremlins" which can arise due to the wide bandwidth of the 12AV7. I was wrestling with this over in the "Small Line Amp" thread on the Drawing Board. Layout is important, and you might even have to use small grid stoppers to dumb down the tube a little bit. I'm sure part of my problem came from the fairly careless layout of the breadboard; I usually know better but like everyone else, sometimes I get lazy.

 

[Consul]

My one-bottle project is waiting for me to stop forgetting to order another larger chassis and the remaining caps I need. :wink:

Dave, would a 12" x 6" x 2" chassis do the trick for both channels plus power supply, or should I go for some more room? Thanks!

My view of PCBs: Well, I do like to have them, as they make things so much easier, but I won't run to the hills in the absence of one. If all else fails, perfboard works. :green:

 

[khstudio]

Hey Dave,
Could you post a quick sketch of a layout you think would work best?
It might save others & myself a few headaches? I do have a general idea of how things should be.

The reason I'm asking is I'm going to do it Fender style with the eyelets & board. If that's too much trouble maybe just a few basic rules for the less experienced :green:

Thanks

 

[cannikin]

I'm still waiting for my Cinemag output transformers.... :?
definitely not dying

 

[pstamler]

Just ordered my 12AV7's -- ten of 'em. A couple or so will go in the general direction of one of Dave's mic pres. A couple may wind up in a phono preamp.

Peace,
Paul

 

[NewYorkDave]

Darren,

12" x 6" could work with careful layout but if bigger is an option, go for it. You wanna keep that PSU away from the preamp circuits.

Kevin,

Are you building a one-channel job or two? Power supply in the same box or in a separate box?


Paul,

Funny coincidence, just this morning I was thinking that with all the AV7s I've accumulated, I should look into using them in an RIAA preamp for vinyl-to-dig transfers. I like the simple circuit that used to appear in the back of the RCA tube manuals, but it would have to be adapted for the differences in i/o capacitance, plate resistance and so on between the AX7 and AV7.

 

[khstudio]

2 channel, 1 box, internal power.

Kevin

 

[Consul]

Thanks, Dave. I guess I'll keep looking.

 

[pstamler]

[quote author="NewYorkDave"]Paul, Funny coincidence, just this morning I was thinking that with all the AV7s I've accumulated, I should look into using them in an RIAA preamp for vinyl-to-dig transfers. I like the simple circuit that used to appear in the back of the RCA tube manuals, but it would have to be adapted for the differences in i/o capacitance, plate resistance and so on between the AX7 and AV7.[/quote]

A few years ago I wrote an article in audioXpress outlining a passive EQ circuit that could go between any two amplifiers with flat response, and talked about optimizing the network given variations in output impedance of amp 1 and input capacitance of amp 2. A one-bottle for each amplifier, set to a gain of between 28 and 30 dB depending on your cartridge's output, and you'd be set. Or make a feedback pair of 1/2 each of a 6SL7 and a 12AV7; still two tubes per channel but arranged differently. Oh, and the RIAA can be switched around for non-RIAA records, if you're into that.

I wouldn't do the RCA circuit; the open-loop single tubes aren't all that clean.

Peace,
Paul

 

[kiira]

Hi Paul is there an RIAA stage you like a lot? My best friend asked me to build him a pre and he has a lot of very nice 6sl7s and 6sn7s so it would be nice if it used them... I'll do the output stage with them as well. He wants it to use transformers for headphone output too.

thanks,

Kiira

 

[Freddy G]

Here's my layout for Dave's two bottle pre:
http://home.cogeco.ca/~lothar/twobottlelayout.jpg
This is a layout using a turret board.
What do you all think? Does anyone see any problems with this?
Cheers,
Freddy

 

[pstamler]

[quote author="kiira"]Hi Paul is there an RIAA stage you like a lot? My best friend asked me to build him a pre and he has a lot of very nice 6sl7s and 6sn7s so it would be nice if it used them... I'll do the output stage with them as well. He wants it to use transformers for headphone output too.[/quote]

You can do a feedback pair composed of a 6SL7 followed by a 6SN7, set for a gain of about 25 (cartridges with a 5mV output) or 30 (cartridges with a 3.5mV output). Follow that with a passive RIAA network, follow that with another feedback pair, same design, same gain. 2 tubes/channel. On the 6SL7, use 2.2k resistors on the cathode; not as quiet as one would like, but they keep the feedback resistors reasonable. (52.3k for the 25x gain, 63.2k for 30x).

The audioXpress article talks about tweaking the RIAA network for the actual characteristics of the feedback pairs. Sorry to keep coming back to it, but the article describes the pesky little details that don't fit into a post here. It's in the Dec. 2001 issue of audioXpress.

For headphones, he'll want a volume control; I'd find a 100k stereo audio-taper pot, connect its outputs to cathode followers (maybe made from a 6SN7) and a pair of transformers.

Subsonic filtering is also an issue, and one I haven't finished working out when it comes to tubes (opamps are easy).

Peace,
Paul

 

[ciminosound]

That Riaa talk reminded me of something I saw before. Check this out.

http://www.geocities.com/TimesSquare/1965/phono.html

 

[Brown Note]

http://img97.imageshack.us/img97/1439/onebottlelayout8nw.jpg

Here's my layout for the one bottle. The dashed lines are jumpers beneath the turret board. The numbers on top correspond to tube pins. I'm hoping this component layout is fine and the problems I had before are entirely related to embaressingly sloppy wiring.

-ben

 

[khstudio]

how are you guys making out with this... layout wise?

 

[Freddy G]

I think I found a power transformer that I can use for 2 channels of Dave's 2 bottle pre with phantom power.

It's a Hammond 369AX:
40VA
125-0-125 / 100ma
6.3V CT @ 2A
50 VAC bias tap

What do you guys and gals think? Can I use this?
Cheers,
Freddy :sam:

 

[kiira]

[quote author="Freddy G"]I think I found a power transformer that I can use for 2 channels of Dave's 2 bottle pre with phantom power.

It's a Hammond 369AX:
40VA
125-0-125 / 100ma
6.3V CT @ 2A
50 VAC bias tap

What do you guys and gals think? Can I use this?
Cheers,
Freddy :sam:[/quote]

Hi Freddy... yep I think you can - with a bridge rectifier and taping off the center tap you'ed end up real close, at least I did.

Kiira

 

[Nadege]

Hi NYDave

I'm totally new at DIY so I've some question for you regarding your one bottle design . I'm confused about power transformers.

Wich one will you recommend for this design:

http://groupdiy.twin-x.com/albums/userpics/10031/onebottlepsu.pdf

I don't really understand how it's wired nd how it's working. Maybee your advice could be usefull for me to understand the process of the power suplly.

I'm also wondering what's the "pilot lamp" DS1 in the schematics and why it's used for.

Thanks for your help.

 

[Kingston]

[quote author="Nadege"]I don't really understand how it's wired nd how it's working. Maybee your advice could be usefull for me to understand the process of the power suplly.

I'm also wondering what's the "pilot lamp" DS1 in the schematics and why it's used for.[/quote]

Google power supply 101, and study how AC gets converted to DC. That NYD schematic basically has a full wave bridge rectifier and smoothing caps to get good quality 300V DC from the raw AC of the PSU transformer (rated like in the schematic).

Have a look at these power supplies, http://rpm.fi/rpm/21-0-Welter-powerformers-en.htm

I used the N1 for two channels of two bottle preamp with phantom. If you build only one channel of one bottle pre, you can use a lot smaller PSU transformer.


The "pilot lamp" is just a small light for you to see that the preamp is on. You don't actually need to put it there. It's just for the looks. (and for you to see that the unit is powered)

 

[Nadege]

Hi Kingston,

thanks for the answer it's really helpfull.