Trainwreck Preamp Pedal..built it.Sounds good. Has one mega problem...need help!

[DougH]

No problem at all doing that. The easiest way is to plug into the fx return if you have a loop. You won't like the sound in bypass as the low Z input of the loop will load the guitar pup and make it sound very dull. It will not be very loud, as you have no preamplification in that case. And I agree that you probably don't want to run your pedal through a guitar amp preamp- all the extra gain and EQ will mess with its sound in a bad way, exaggerating all the gain/EQ you already have in the pedal.

[sst4270]

Greg,

I'm very interested in this build. I've built a number of TW's (all varities: Express, Liverpool, Rocket) I'm in the process of building something very similar to yours except into a Class D power amp section (50W) to make it very lightweight yet giggable. The whole thing will be going into a 8" cube head and weight approximately 7lbs.
You mentioned "4 preamp gain stages" The Express only has three (not including the gain of the phase inverter). Did you add a fourth gain stage to simulate the PI?

If so could you explain how? Also I can assure there is no problem with posting your circuit here... I'm positive the guys over at TAG would really appreciate seeing this as well!

Please keep the updates coming.

Regards,

Steve

[sst4270]

BTW: I'm running mine at full voltages using a "very small" toroidal transformer to step 12VAC up to about 200V.

[zambo]

I will see if i can figure out the posting part. I did simulate the pi and all i did was run a cap from triode three anode over to grid on triode 4 with 110k resistor on plate and whatever cathode resistor the schematic shows . 470 in series with 10k i think. I really tried to follow the schematic as close as I could. Only the voltage difference. What transformer did you use and does it power the heaters as well? How many milliamps does it need ? I love the idea of having the full voltage ( or closer to it ) in a pre amp and the versatility of using different power amps for different gigs. I have a push pull 2 x 12au7 amp for about 2 watts, a 6k6 amp at about 2.5 or 3. next I would like to build a 5e3 power section with 6k6's in pp/p for about 7 or 8 watts . What I need is the right transformer to get about 250 volts plus heater voltage. How small is the toroidal?

@ Doug. I thought that was the answer, I just get scared of testing things with lots of volume or voltage....Kind of a sissy that way. I plugged into the preamp section as well and it sounds good if you roll the treble and bass off of the amps eq and just hammer the input from the pedal. The master on the pedal that i added is running at about 8 or 9. Thanks for your help btw!
I am still getting a little scratch on my volume pot. Should I use a bigger cap? I have .047 in there now.

[sst4270]

Greg,
It's not complete yet because I'm in the process of etching the boards.
However, here's a link to the transformer I'm using:
http://www.alliedelec.com/search/productdetail.aspx?SKU=4400191
This is more than enough to handle the current through the tubes.
I got the idea from this project:
http://www.el34world.com/projects/tube_box.htm

Using a 12VAC power supply (wall wart) you power the secondary side of the toroid to get your HV.
Also you tap off the 12VAC power supply into a rectifier to get 12VDC > LM7812 regulator > to pins 4 & 5 of the tubes.
I've seen this same technique used on several production tube pedals. EHx for example.
I'll post a thread as it nears completion.
(Work has been slow as I recently had shoulder surgery.)

It sounds like you created a cathode follower for your fourth stage which I believe acts as a buffer. (which is good for going into the power amp but only about unity gain, so you have 3 three gain stages as I initially thought. Still plenty of gain though as you've discovered since the Express preamp circuit is pretty hot.)

*I'd recommend 0.1uF for your input cap.

BTW: I'm building a Rocket preamp not an Express which has the cathode follower already.

[sst4270]

Here's a link to the layout I made:
http://www.aronnelson.com/gallery/main.php/v/diyuser/sst4270+-+layouts/tube-preamp.pdf.html

I've since changed it to be on one single board instead of two in order to simplify assembly, but none of the components have changed.
(I may go back and include holes for the addition of an input cap in case I need it)

The output will feed directly to the input of a 50W Class D amp. And the whole thing will fit into a hammond 1444-12 chassis.


-Steve

[zambo]

nope its not a cathode follower. Its just another gain stage. The other side of that triode would invert the signal for the Pull part of the push pull section but since i didnt need that it worked out nicley to use the one half of the pi as a gain stage ( which it appears to be) on the schematic. Cathode follower takes signal off the the cathode right? This stage it is still taken off the anode and through a cap to the the output jack ( or a master volume in my case). I couldnt get those links to open but I woll try again tonight after band practice. I think I am going to build a 9 or ten watt se amp with this pre at original voltages. I ordered this trans for power. Its a hammond with these specs. 270EX 118VA, sec. 275-0-275, DC ma 125, Fil.#1(rct) 5.0v @ 3a, Fil.#2(htr) 6.3v @ 4.0a.
That should be enough for two ax7's and and el34 or 6l6 right?

[Paul Marossy]

Sounds nice in the right hands. 

[sst4270]

Greg,

Yes, you're right. I misunderstood from your previous post. I thought you were tapping off of the cathode.
I may try to incorporate that extra stage into mine as well.

well you won't need the 5.0V unless you're going to use a tube rect. and 4A for a single EL34 or 6L6 heater plus a couple of 12AX's should adequate.
And the 125mA for your HV should also be plenty.

Steve

[zambo]

Sweet, I want to make something close to "the little monster" if i can. I think I can I think i can.....

Thanks Paul!

[DougH]

So let me get this straight- you built the whole PI and are just using half of it? Tapping off of that to a master volume?

That's interesting... And that explains why it sounds so good too. I tried a TW pre into a S/E amp before and it was kind of so-so. The pre by itself does not deliver much gain. But the PI is the key to the sound of this amp methinks. And that's reinforced by your video.

[zambo]

yeah as it looks to me it goes stage one into eq, stage two into stage three with no loss, three into four wich would be pi but also functions as a gain stage. so two tubes works out perfect.

[DougH]

So you just wired up half of the PI stage using your leftover 1/2 triode?

[aron]

Sounds good to me. Nice playing!!!!

[sst4270]

Something like this:

[DougH]

Yeah, that's what I figured. You won't get the negative feedback injected into the PI like in the amp, but it sounds like it works just fine. I'm seriously thinking of trying this.

[zambo]

I am really liking this thing a lot! Yeah i just used the leftover triode like you said Doug. It seems to be a good thing. I wired the eq wrong or...I am not using enough voltage to have the eq function properly ( I think I messed it up though ) so I have another one mocked up to test different voltages on. As soon as I get some better caps I am going to try 200 volts again. My smps whines when I dont load it with enough work so i though what if...i built two running in parallel with an fx loop before any of the gain stages. I could run my wah and chorus delay whatever fx on one half and run the other dry. put the 1 meg master volume right before the last triode stage ( pi stage). I should then be able to mix the signals as desired and run different eq or gain settings. as long as the signals are not out of phase it shouild work right? Would the master volume before the last triode stop them from interacting with each other ( i.e. side a volume affects side b as well ?). I have always wanted to try this. I love bi-amping but hate carying two amps. Any thoughts?

[aron]

Greg, you have the little monster schematic???

I like that amp!

[aron]

I did a search for little monster and I found a post where this guy got to play a real dirty little monster. I started reading and something sounded familiar..... uh....

http://www.ampgarage.com/forum/viewtopic.php?t=39&view=next&sid=05f06d75a5dca0cc24256f9d48e58a9a

[zambo]

@ Aron- ok that is just funny stuff there! Great info too! I am fascinated with this amp. It really screams make me into a pedal!!!!