The Box Wrecker....Two tube preamps in paralell into one poweramp.

[zambo]

Ok, I got the prototype into a working state this morning. Its ugly and it hums but it does work and the volumes are working independently of eachother and you can differentiate the tones somewhat. I will post a video as soon as I can get one on here. I started with the trainwreck express preamp built all the way through the phase inverter ( just the top half ) on one side and what was supposed to be a matchless hot box on the other. I didnt like the cathode follower as it does not invert the signal 180 like the other tube stages and therefore i would have ended out of phase with the wreck circuite so.....i just put a slightly tweaked big muff tone knob after stage three with a master right after it and then ran it into stage four for a recovery stage. Its not really a hot box now....as a matter of fact i dont really know what it is. Most of the cathode resistors are a similar value though. All of this is running on 9 volts until I can get a smps to work. If that doesnt work I will do the usual voltage multiplier and run about 45 volts or so. When I figure out how to post pictures i will draw and upload a schematic of sorts. until then I will see about some video footage with an explanation. Cheers, Greg

[zambo]

first vid sound sample.    http://www.youtube.com/watch?v=878vtOgvPDE            The hum is incredible....got to work on that.....voltage is only 9 volts so its not as gainy as I like it yet. They seem to be in phase. Any idea why they would hum so bad? Its almost like a capacitor issue. the hum kinda has a volume swell after I stop playing....interesting...thoughts anyone?

[maarten]

Is your 9v power supply strong enough to provide all of the current? Did you buffer the supply with a larga capacitor? Check whether the voltage on your plates is going down when you're playing and coming back up when you stop....

Maarten

[zambo]

yeah, I am using a 1.7 amp supply. Heaters are 150 ma per tube and I think the tube plates are drawing less then 10 ma each for sure so I should have a ton of juice left. Am using a 330 uf cap from + to - on the dc input. It might be the 900 feet of wire hanging out randomley in the air on my desk.....lol. I am going to try and clean up the design and put it in some kind of chassis to work on it as soon as I get some more tube sockets and decent caps.

[merlinb]

yeah, I am using a 1.7 amp supply.

But is it voltage regulated? If it is, then the hum is probably due to stray pick up and should clear up once you put it all in a metal box.

[DougH]

Yeah, I'm guessing the hum is due to the long wires and lack of shielding in your prototype setup. As Merlin mentioned, make sure your voltage is regulated, especially the heaters if they are DC.

[EATyourGuitar]

since you have experience, I'll ask you. do you know how to make a trainwreck pre in a pedal? has this been done before. I know the trainwreck amps are famous for the line of caps in parallel but I dont know if thats on the pre or the power.

[zambo]

If you are asking me, I just built an express pre in a pedal..its pretty easy as far as I can tell...    http://www.youtube.com/watch?v=T-sNT_xjJ9E   . I am not very experienced though. there is a schematic in this thread    http://www.diystompboxes.com/smfforum/index.php?topic=87343.0. just build the preamp section all the way through the top half of the phase inverter. You will end up with four gain stages using two complete 12ax7's. I ran mine on 45 volts with pretty good results. I think it would start to get magic at about 125 volts though.

[zambo]

oh yeah i almost forgot. I watched the interview with KF and he used all solid core wire in his preamps...if that matters.

[zambo]

Dear Diary,
Today I shortened up some leads and added a marshall style tone stack that I designed on the tone stack calculator! What a sweet device that thing is! I replaced the 220k  treble pot with a 1megA . I also used a 50kb for the mid. The eq is very interactive and somewhat like the trainwreck eq. Most of the hum has gone since I cut off the 2 input/output jacks I quit using. Next I need to try the a/b/y the heck not swithing on the front. I also plugged into the power amp section on my hot rod deluxe. Very nice. Aron and Doug, If you like the less gainy bluesy fusionish sounds try the wreck design at 9v with 12au7s. If you do this paralell trip, same thing applies. I am getting a very nice tube overdrive sound with plenty of highs and bass from both channels. It is loud enough on 9 volts to drive the fender power amp nicely. Will update with vids when I try higher voltage on plates. I will try for better sounding vids too.