Marsha

[JakeFuzz]

[soundcloud]http://soundcloud.com/jakefuzz/marsha[/soundcloud]

This thing sounds sick! Here is the link to the original build report.

http://www.madbeanpedals.com/forum/index.php?topic=4670.0

I was initially getting a huge amount of parasitic noise. I insulated all of the input and output lines with the small coaxial cable SB sells and it works beautifully now. The pre-amp was built to the normal channel specs. I settled on a balance between the two channels but I think I could lower the treble bypass cap on the gain a bit (it is at the bright channel's stock 500pF). The lower gain sounds are pretty bright and aggressive but I kind of like it. What do you guys think? It loves to be boosted from the front end and the last phase inverter approximation adds a very fair amount of drive. I ordered a few different preamp tubes to try as the ones currently in are cheapo junkers I pulled from my buddies amp.

The demo was done with an Epiphone goldtop with P-90's through a Fender Twin Reverb. I've got some minute tweaking to do with it but I am amazed at how awesome this thing sounds.  

[nzCdog]

friggin awesome!  

Delicious overdriven tones and great saturation... liked the rangemaster factor too

[alanp]

Gnarly.

[JakeFuzz]

Thanks guys!I thought you'd like this one Corey, we need more tube pedals here!

A few thoughts on this build:

The higher gain sounds are little fuzzy and bassy sounding. I am sure this is because of the low bass cut of the 330uF cathode bypass cap and the first coupling capacitor (22nF). Low gain is a little bright and I am sure it is because of the 500pF gain bypass cap. Somewhere on the gain knob there is a sweet spot with just the right balance. I am wondering if I should try lowering the first coupling cap to around 10nF and the bypass cap to 200pF. That would even out the EQ on the gain pot. I kind of like it how it is now but it could be interesting to switch it up.

[JakeFuzz]

And the schematic as it is right now. Hopefully it is large enough to read...

PS: The filament regulator is actually 12 volts, not the 15v that it says in the schem, whoops!

[nzCdog]

Thanks for this... was hoping to see the schemo

[alanp]

Is there any particular reason you went with DC heaters, rather than just 12V AC?

[JakeFuzz]

Is there any particular reason you went with DC heaters, rather than just 12V AC?

Actually AC heaters was what I wanted to do to cut out that second rectifier and get a little more filtering on the power supply. I just wasn't absolutely sure about it and I saw a very similar project schematic over at Hoffman amps that used regulated DC for the heaters. I just went with that. I am sure you could run it at series AC 12 volts but I figured this had been tried and tested. I think I actually emailed him asking why he decided to use DC but I never got an answer.

[JakeFuzz]

Another question for everyone. If you were to build another pre-amp besides this one, which amp would it come from? I would say an AC-30 or a 5F6 Bassman. I don't know how different they would sound though.

[timbo_93631]

Yeah, probably something EF86 based.  They are so microphonic in a combo, less in a head, but in a dedicated pre like that you could really isolate that tube.  "Juicy" tone.

[JakeFuzz]

Yeah, probably something EF86 based.  They are so microphonic in a combo, less in a head, but in a dedicated pre like that you could really isolate that tube.  "Juicy" tone.

That's a great idea! Or you could do like a normal/bright channel switch and switch between an EF86 and 12ax7 input stage...

[gordo]

I love the sound of this thing!  I'd really like to see a '86/12AX7 two channel version too.

[JakeFuzz]

I love the sound of this thing!  I'd really like to see a '86/12AX7 two channel version too.

Thanks! I really like it too. I just put new tubes in and it sounds even better. Without question my new favorite overdrive.

I am really considering doing a tagboard version of the AC30 pre. I don't quite understand the EF86 input stage though. The only thing driving the EF86 is the guitar signal, does this mean that the saturated sounds are from the EF86 driving the phase inverter? I was thinking that the great saturation came from cascading EF86 stages but the AC34 schematics show just a single EF86 section going straight into the long tail phase inverter. Tagboard and cap cans are the way to go with this one, it will look much nicer. 

[timbo_93631]

Here is the 18watt.com layout  and hand drawn schematic of an 18watt lite with EF86 pre driving a 12AX7 PI: