One-Bottle Preamp

[kiira]

Foo. I got carried away as usual with this and added too much stuff.. it was supposed to be a single bottle pre.

I'm un-doing mine and putting it in a little bit bigger enclosure. I don't have room for the output xformer and the input has to be pretty small to fit. This way I can use one of the larger input xformers I have and space things out a bit more and have better hum control. heh well I'll use the other box for a DI maybe.

Kiira

 

[CJ]

Once you have this built, you can do mods very easily, since the pwr suply and chassis are all done, and the tube socket is there, you can do many things with this test bed.

so leave some room.

 

[skipwave]

My next One-Bottle is going to be modular with seperate power supply box and main chassis, a lot like the prototype.

The power will be carried to the circuit via 4 pin XLR type connector, because the box I'm using already had this jack in addition to the XLR in and out. I'm wondering if I have any use for the fourth conductor. Let's see, B+, HT, ground. Heater will be 12VDC.

All of the filtering will be done in the PS box, so I think I only need to carry one ground from the audio circuit. Thoughts?

 

[CJ]

put a resistor and cap in the box. last filter should be in the box so ps rejection is good.

 

[skipwave]

Yes sir. I will use the fourth conductor to carry the neg of that filter cap back to the power supply ground. The audio ground and the PS ground only get tied together at one point in the PS box.

 

[NewYorkDave]

No, the audio ground is the power supply ground. Use a ground buss that follows the signal; the cap in the last stage of B+ filtering should be in the preamp box and be connected to the B- buss at the same point as the cathodes of V1A/V1B--not back at the PSU box! You want the B- buss to physically resemble the way I drew it on the schematic. It should lead back to the rectifier with the filter caps connected to it in order, and the input filter cap and the rectifier connected at the same physical point on the buss.

The B- buss and the chassis ground should be kept separate but for one point only. And a good place to do this is at the "beginning" of the B- buss, at the first filter cap/rectifier grounding point.

Be careful with using a 4-pin XLR, since that's also a standard connector for low voltage supplies and things could get ugly if it fell into someone else's hands. If you must use it, I suggest you connect your 12VDC heater to pin 1 (negative) and pin 4 (positive). That's the Sony standard, the usual configuration for use of the 4-pin XLR as a power connector. Use the inner pins for B+ and B- and the shell for chassis. And, for reasons of safety, definitely use a male connector on the preamp and a female on the PSU.

 

[Consul]

So my parts from Mouser came in...

First off, I'm amazed at how small the 47uF/450V 'lytic caps are.

Second, I was only able to order some of the caps from Mouser, since I couldn't understand what the hell their website was trying to tell me. I did manage to find one of the film caps I needed, though. Then I rummaged through my partsbox and found another: the .022uF coupling caps. Granted, the ones from the partsbox were actually .025uF, but I didn't feel like splitting hairs. I had largely forgotten about which ones I ordered from Mouser.

Guess which ones?

I need a better way to know what I already have.

Third, I'm a little worried that the Bud box I got (an 8" x 6" x 2") might be a bit too small for the power supply and two preamps. It would be fine if I were not using the output trafos, but now I'm not so sure. I still have a box I can build the PS in separately if I have to.

Thank you for this project and all the wonderful advice, Dave. We all appreciate it.

 

[skipwave]

[quote author="NewYorkDave"]No, the audio ground is the power supply ground.[/quote]

That all makes sense now. Thanks!

 

[Consul]

Okay, this is probably a really stupid question, but I'd like to make sure.

A 1/4" stereo jack can serve as a balanced output jack, correct?

Just making sure...

 

[kiira]

[quote author="Consul"]Okay, this is probably a really stupid question, but I'd like to make sure.

A 1/4" stereo jack can serve as a balanced output jack, correct?

Just making sure...[/quote]

oh.I know this.

yes.

Kiira

 

[kiira]

[quote author="Consul"]Okay, this is probably a really stupid question, but I'd like to make sure.

A 1/4" stereo jack can serve as a balanced output jack, correct?

Just making sure...[/quote]

oh.I know this.

yes.

Kiira

 

[Consul]

Thanks, Kiira! I was pretty sure of that, but better to be informed and only look a fool, you know? :guinness: :thumb:

 

[CJ]

Use a mono jack also.
Bill Y shoulder washer.
Then, run a lift sw from the G wire.
cj

speakin of G, I heard a band on KHUM last week called the Dead KennyG's. :razz:

 

[kiira]

[quote author="Consul"]Thanks, Kiira! I was pretty sure of that, but better to be informed and only look a fool, you know? :guinness: :thumb:[/quote]

No problem. I know a few answers to dumb questions. :razz:

Kiira

 

[Consul]

Grrr...

I got the tube sockets from Purchase Radio, and the tubes fit them, but they won't actually slide it without significant force which I chose to avoid for now. They are bakelite sockets, and I'm afraid I may still have to order away for some ceramic sockets. Maybe I can find one store that still sells those and tunable coil forms, then I can kill two birds with one stone.

I was able to get some of the rest of the caps I need. I'll still need to order away for the remainder. I'll pitch them in with the parts order for another project so I'm not paying more for shipping than the actual parts.

EDIT: Nevermind, Newark's web site is 100 times easier to use than Mousers. I think I'll just go there from now on.

Thank you all, especially you Dave, for your help!

 

[NewYorkDave]

That's a not-uncommon problem with new mini tube sockets: contacts too tight. You can "deflower" them by pressing the tip of a straight dental pick into each hole. A sewing needle would work too, but just be careful not to hurt your hands--perhaps use pliers to hold the needle.

 

[Consul]

Thanks, Dave! I swear that that did occur to me. Honest. :green: :wink:

 

[pstamler]

[quote author="NewYorkDave"]That's a not-uncommon problem with new mini tube sockets: contacts too tight. You can "deflower" them by pressing the tip of a straight dental pick into each hole. A sewing needle would work too, but just be careful not to hurt your hands--perhaps use pliers to hold the needle.[/quote]

A wooden toothpick is also good, and is safer, just in case some capacitor someplace held onto its charge.

As is so often the case in this world, a little lubrication is also useful; treating the tube pins with DeoxIt, then PreservIt (cleaning them off with a Q-tip in between) helps.

Peace,
Paul

 

[kiira]

[quote author="pstamler"]

A wooden toothpick is also good, and is safer, just in case some capacitor someplace held onto its charge.

[/quote]

heh, I learned that forever working on my deluxe reverb. Good thing it wasn't the V4 :?

Cailube works well but is pretty pricey.

Kiira

 

[kiira]

[quote author="CJ"]Once you have this built, you can do mods very easily, since the pwr suply and chassis are all done, and the tube socket is there, you can do many things with this test bed.

so leave some room.[/quote]

put it in a better box... much bigger.