Designing for 12AT7 preamp

[benoit]

i'm not trying to fight at all!
I'll stop posting on this topic
best of luck on the build i'm sure the client will be very happy!

I didn't think anyone was trying to fight, just looked like one of those threads that was about to escalate for no reason. You were making the thread a better place - even if Bob didn't take all your suggestions there's still a lot the rest of us can take from it. Leaving just cements a rift. I bet if you asked Bob, he'd say he meant no offense in what he said (though he's free to correct me if I'm wrong). Anyway, I'd love to hear more of your ideas discussed if you've got more.. no need to jet over misunderstandings. It's not really my business, I guess, but I just hate to see things go like this.

[Structo]

I didn't really pick up on that either. [IMG:37:15]http://i23.photobucket.com/albums/b392/ ... /dunno.gif[/img]
Lets keep this a friendly place, please?

[Bob-I]

Thx everyone, I appreciate everyone's input and if I offended anyone, I apologize.

I rejected 2 ideas, the alternate tube because I have a fairly good stash of NOS 12AT7's, and the grid leak input because the input impedance my friends design wants to see is 1M. I'm sure these ideas are great, but not for this amp.

Any suggestions are greatly appreciated.

http://www.sweettoothband.com/temp/Acou ... _Schem.jpg
http://www.sweettoothband.com/temp/Acou ... Layout.jpg

BTW, this isn't a client, I'm not in this as a business, just a hobby. Since my friend will be (hopefully) putting these into production I'm avoiding using his name but I hope that everyone's input helps him out, the economy has dried up his business.

[billyz]

looks like an interesting project. I have always liked the 12AT7 in certain uses. I find they work very well in Line stage applications, never did care for the sound in a low level preamp stage though.

More typical circuits would have the plate load resistor at 68K and the Cathode resistor at 470K for the 12AT7. Plate Voltage around 290VDC. yours looks more like a 12ax7 circuit type.

good luck.

[Bob-I]

More typical circuits would have the plate load resistor at 68K and the Cathode resistor at 470K for the 12AT7. Plate Voltage around 290VDC. yours looks more like a 12ax7 circuit type.

good luck.

I'm still debating about Rp, I wrote in 82K but I plan to test with 68k and 47k as well. 470K for Rk seems excessive though, did you mean 470R?

[billyz]

More typical circuits would have the plate load resistor at 68K and the Cathode resistor at 470K for the 12AT7. Plate Voltage around 290VDC. yours looks more like a 12ax7 circuit type.

good luck.

I'm still debating about Rp, I wrote in 82K but I plan to test with 68k and 47k as well. 470K for Rk seems excessive though, did you mean 470R?

MY BOO BOOO, you are correct, 470 ohm not thousand ohm on the cathode.

[selloutrr]

a really cool feature would be dual reverbs one long and one short to blend dual sends dual returns and a master reverb volume so you could drive the reverb hard then turn down the wet dry mix. think ampeg reverb-o-rocket and fender princeton reverb. it would really help set depth in the picking and mask any weird top end in the pickups or the playing. just cause you can afford a guitar doesn't mean you can play it lol as well as smoothing out fret squeeks and giving back a more natural acoustic tone when used lightly and then well more extreme if desired. you could easily wire each reverb true bypass so if it's not inserted it wont effect the tone. and make it foot switchable.

If you had dual reverb and a tremolo it would be a very close analog version of an acoustic simulator.

add a tube DI xlr and 1/4" preamp out / FX loops (Active send return) and power amp in.
it's not needed for an acoustic amp but it you added a boost on the foot switch and swapped out the first or second gain stage for a 12ax7 you would have a pretty awesome new age country amp! it would make a bitch'n sweet slide guitar amp! mate it with a pair of Altec 417-8H, JBL K120, or a single EV 12L or EV 15L extension speaker that would be hot! you could really play on the comsumer at that point and cover it in a tooled leather.
multi output ohm taps. a cool feature might be to have a 1/4" send and return on the reverb section so you could use the amp as a reverb tank.

i was thinking your friends pickup system might be 1m but most others aren't so if he was to compare pickups you would need to make the input impedance selectable either a push pull volume pot or toggle it would be neat to have a 3 way toggle so you can do 1M then slightly higher (fishman's imp) and then higher or one carbon Fishman one metal film fishman to add texture. dual inputs with an A/B/Y selector

[Bob-I]

a really cool feature would be dual reverbs one long and one short to blend dual sends dual returns and a master reverb volume so you could drive the reverb hard then turn down the wet dry mix. think ampeg reverb-o-rocket and fender princeton reverb. add a tube DI xlr and 1/4" preamp out / FX loops (Active send return) and power amp in.

Interesting...

i was thinking your friends pickup system might be 1m but most others aren't so if he was to compare pickups you would need to make the input impedance selectable either a push pull volume pot or toggle it would be neat to have a 3 way toggle so you can do 1M then slightly higher (fishman's imp) and then higher or one carbon Fishman one metal film fishman to add texture. dual inputs with an A/B/Y selector

Hmm...That's an excellent thought.