low voltage hi gain tube pedal attemp #8,876,345

[zambo]

SHO>12ax7 both stages with 100k plate and 1k5 cathode .0022 coupling caps>12au7stage 1 same plate and cathode resistor > eq> 12au7 stage 2 same plate 4k7 cathode resistor .01uf out cap to 50K master volume.

48 volts on the tube plates. SHO is IRF510 mosfet with source grounded. Gain knob is 1M between SHO and V1 and is V1 grid to ground reference. EQ is mar$hall type. I am still trying to piece together the schematic. Not the best at drawing those. Its really a pretty simple build though.

Graphica by sharpie

[zambo]

Here is a single coil guitar into it. for all you strat types. I wish i could lay a strat right but whatever. you will get the idea. 

[iccaros]

so this is a SHO infront of a dual caster? do you get a lot out of the EQ?

[zambo]

Pretty much except its got 48v on the plates and more standard amp type gain stages with a proper cathode resistor etc. and all the caps are different values and its got grid stoppers. Surprisingly the eq is pretty darn effective. A very tunable pedal so far. FOR DAYS OF BOOST! LIKE WEEKS OF BOOST! I used it as a preamp for the power amp in on my peavy and it was really cool. It could use some more eyes and builds etc. to really refine it but i think its a good low voltage hi gain pedal for all the valvecaster crew that want to step it up a bit but dont want to deal with 100v + etc. 48v is still intimidating but not to bad. The eq and stuff just makes it cool. I would make a version with the SHO switchable as a boost to the tubes as well. So you would have a global on/bypass switch and then a just tubes/tubes + SHO boost as well. Am drawing the schematic now. Pretty much done, just needs proof read. Care to look at it? You and PRR always find the stuff i miss!

[iccaros]

always willing to help, this may be an interesting turn, as I am completing one pedal with a  12au7 and a 6au6, and looking at one with 2 12ax7's and was thinking today it needed a transistor boost in-front, so this may be in the direction I am looking at already

[mth5044]

Nice!

...I have that poster.

[zambo]

You have an Occupy Oakland poster? for reals?

[Ronan]

Sounds very good. 48V at the plate or 48V all up as a power supply? I guess you've already tried 12AT7 in various postions...sounds v. good, well done.

[zambo]

Thanks. Its a 9v supply to the whole pedal including the SHO. there is a voltage pump that puts 48v to the plates separate from everything else. I tried ax at and au in all positions. I like ax in the first position and au to drive the eq. it just seems to sound the best so far. totaly subjective though.

[zambo]

  here is the schemo I drew up. If anyone has any corrections that need to be pointed out etc. please say something  I dont have a real good layout for this. I followed a linear layout that matches the schematic. kind of how you would build a tube amp on eyelet board. it works. A pcb would be way smaller and probably better. I used sheilded wire for the longer runs from jacks to switch etc. no oscillation issues as of yet.

[iccaros]

do you need the 470K grid stoppers, I would think 10K would do the trick, well maybe not after the MOSFET. I have some IFR 610 and I like the 7660s instead of the 1044 because it is fine with 12v. with 12v you could run the tubes in parallel for heaters.
http://www.ebay.com/itm/10pcs-ICL7660S-ICL7660-7660S-Voltage-Converter-Intersil-SOP-8-/270933479001?pt=LH_DefaultDomain_0&hash=item3f14e4ce59#ht_1057wt_1163

[zambo]

I used the 470k stoppers because I wanted to roll off the highs a bit. I figure after the sho the tubes are just getting pounded and probably some grid conducting going on there. Space charge and low voltage have a lot of bass and excessive highs as well. Works great with one or two stages but after that it gets mushy and fizzy sounding so I was compensating for that as well with the small caps and big grid stoppers. Kind of leaves the mids to get amplified the most. when you compound all that with typical clean channel topology and settings ( less mids and tons of bass and shimmering highs ) it makes for a messy sounding pedal. This one isnt perfect by any means but i think its closer to what I am trying to achieve. I would love to see what you come up with.  I think the boost in front is a good thing. Havent tried any other voltage pumps etc. besides the 1363 and didnt want the 200v in a pedal that isnt mine. this one is sold. i think a 12 volt supply and around 80 to 100 volts on the plates would scream. I know you wouldnt need the boost in front at that point but i think it sounds pretty cool. you could probably drop one tube and just have a SHO > Gainstage > eq >Gainstage setup and that would be pretty sweet.

[iccaros]

got ya, I am almost done with my pedal, then I can start bread boarding yours..

[zambo]

the sign of a true junky! Cheers!

[brett]

Hi
Great clips.
I don't know too much about these amps, but I would have thought that inter-stage 'bleed' caps to ground would give nice, controlled roll-off of highs.  They would need to be small - barely a nF - because of the high plate resistance. That would allow smaller grid stoppers (10k to 47k), for less noise (10x less) and less signal loss (4 to 8x less).
V1a (for noise), and V2a (for signal) would be places that I think would benefit, then maybe V1b (noise and signal).
On the other hand, your system for bass roll-off (small inter-stage caps) seems nice and efficient.
congrats.

[iccaros]

the sign of a true junky! Cheers!

I think I am done with mine, a 12AT7 with a 6au6 running at 24v. May have some tone issues, and I need to get a 100K pot as 250K seems too big for 6au6.

So I am ready for a new hit to ease my addictions. 

[zambo]

@ Brett. I should try taking the stoppers out or making them smaller . I usualy dont use them at all. Just thought i would try this method. I do like it better than bleed caps to ground or plate resistor bypass caps. I use 500pf for that when i do. I didnt even think about the noise factor, but this pedal does have a lot of hiss when the gain is cranked. I will try and switch them out to lower ones of 100k or so to see about the effect it has. Thanks!

@ Icarros - try puting a 250k resistor from pin 1 to 3 on your pot. I will become a 125k if I am not mistaken? would love to hear that pedal!

[mth5044]

You have an Occupy Oakland poster? for reals?

Haha yeah. I live in Davis.. they were giving them away at the farmers market for some reason.

I have a Davis one as well from when the students got pepper sprayed.

[zambo]

How random and cool is that?! I was playing at The Stork Club that first friday when they were giving them away.

[iccaros]

you asked Greg
This is has some bad audio, the amp with the pedal put the phone mic into overdrive, making is sound really muddy, once its turned up.. I am adjusting some things and will get  a better video.. Maybe I'll have Greg play the guitar so it sounds better.  

this one may be better.. lowered the amp to a really low volume, 1 on pre and 1 on master... kills some tone from pushing a speaker past a watt, but the phone liked it better.. it was 10pm so I am tired.. please forgive me..