snow day parts substitution/flabulance

[neve1272]

can the building blocks of that pedal be applied to to other preamps say sunn orange marshall ect. sort of like changing the caps and tone stacks?
after reading the build doc i got so exited i thought there would be like opto compressor /overdrive or some thing, not a amp in a box .... my favorite

i worked very hard trying to pedalize my favorite amp......and it never worked , was cool overdrive and that is about all

i found this muamp and it seems really cool by its self im not sure if it could be subbed as a gain stage  in those tube to fet type circuits
in any case thank you jon and brian. this shot to the top of my list, i can not wait to build this.

[HKimball]

That mu-valve looks like the one on the former Thor circuit over at runoffgroove (replaced by the thunderbird) and the booster part of the Paul Cochrane fat boostered if I'm not mistaken.

I don't know very much but the Thor (and the jfet Vulcan by Joel davisson) use a similar layout for q1 and q2 (where q2 is primarily the gain providing transistor if I'm not mistaken, which is totally possible and indeed even likely) to Jon's snow day overdrive (and the ROG umble now that I think about it, but of course these all use differing bias and cap setups).

Because of the bjt buffer at the end of the circuit I've wondered myself if one could make a higher gain version similar to cascading the ROG omega into two other fetzer valves but I don't know enough about the MOSFET section to know what other components you'd need to change. Or even if it would sound good or like a hot mess (the omega is a 30-35db boost so I imagine you'd get a ton of overdrive including hard clipping from the fets unless the gain was way down)

You can still see the Thor circuit at http://www.runoffgroove.com/thor.html even though the link isn't on the main page any more from what I can tell.

As far as the mu-amp as a gain stage, I mean I'm sure it's possible I just wouldn't know how to be honest.

The beautiful thing about the snow day tone stack is how simple it is - if you want to add a more traditional b/m/t toneatack you'd have to do it right after q1. From the schematic it looks like there's a cap for treble bypass but other than that not a whole lot in the way of stuff.

So I've spoken long enough - I'm sure Jon or Brian will answer the question instead of just contemplating how wonderfully versatile this circuit can be.

[midwayfair]

Huh, I thought I had replied to this a few days ago ...

Re the mu amp (in addition to the other circuits already mentioned):
Rob Henry's Blues N Metal pedal uses a couple of them cascaded.

A lot of Catalinbread's circuits used it. Including one based on Orange Amps (the SCOD, I think). I was pretty sure Jubal81 had done a PCB for that one and a couple other Cbread pedals. Jubal also has at least one original design that used it -- he had a pedal that had like four distortion circuits in it, one of which was a JFET drive with mu amps.

I used RG Keen's version of it in the Clipper Ship, but not really as a distortion element (as a boost).

There's not really a great way to sub it into one of the stages in the Snowday. It needs a bias voltage with power filtering and a couple extra components to work really well.

Just my opinion, but if you're going to try to use it in something, put it EARLY in the circuit to overdrive another transistor, or you can do it like I did where the signal is clipped to a safe level ahead of time. I don't think it does pleasant things to a signal that's large enough to hard clip the JFETs, though Rob Henry made it work. Also, you might be interested in knowing that it can be done with pretty much any type of transistor with some small changes. If you want to delve into that, read RG Keen's article on the SRPP (http://www.geofex.com/Article_Folders/modmuamp/modmuamp.htm) and Jack Orman's article on the Mini Booster.

As far as emulating a different amp with the Snow Day topology (or just emulating amps in general):

HKimball hit the nail on the head in that the tone stack falls after the equivalent of Q1 on most preamps. You'd end up needing a lot of components off board to accomplish this. I'd suggest breaking out the breadboard and a copy of the orange amp schematic you're thinking of and seeing what changes need to be made in the preamp first, so you can know if it's worth hacking up bits of the board. The tone control placement in the Snow Day was actually taken from the Cut control on a Vox (but it did what I needed it to where it's currently placed, something to keep in mind when you're copying an amp -- duplicating what's going on with the original isn't the only way to make the right thing happen).

It would also be worth comparing the preamp voltages (which should be noted on the manufacturer's schematic) to see if any of the tubes are biased cold or hot. You can compare that to your biasing of the FET stages. The biasing of the transistors is kind of important for getting closer to emulating tubes. So while the Mu Amp above might give you a lot of gain without fuss, when it clips, it won't necessarily have the right harmonic structure. See the Fetzer valve article for more info on that.

Also, if you increase the gain BEFORE Q3, you will most likely need to adjust the compression circuit to avoid over-compressing (something I'd be worried about copying an Orange amp ... they don't strike me as "bendy").

The Snow Day has gain to spare without even changing any parts, so you CAN use the current topology to get Marshall-style levels of distortion. Aside from the most obvious things like biasing Q1 and/or Q2 to a lower voltage (you can try setting Q2 to 1/3 supply to get something very ranchy out of it) to drive Q3 harder, you can also change Q3 to a J201. You can also lower or even jumper the feedback limiting resistor in series with the MOSFET clippers (it's a 33K) -- you could even replace Q4 with a BJT instead of the MOSFET; a BJT might actually be a little closer to an EL tube (or maybe I'm misremembering and they're closer to beam-tetrodes ...). You can also solder a 22uF cap across the source resistor of Q4 to double its gain. (As if the pedal isn't loud enough already! You might want to readjust that 10k/10k divider on Q4's drain if you do this.)

I'm just going to put some further reading on emulating tube stages/tube "soft" clipping of various sorts down here (these are just from my Snow Day notes, by no means is this an exhaustive list of what when into it):

http://runoffgroove.com/fetzervalve.html and the Supreaux Deux, Azabache, and Britannia articles
http://www.diystompboxes.com/smfforum/index.php?topic=106405.msg963073#msg963073
http://www.sugardas.lt/~igoramps/article68/article.htm (er ... that one's in Russian, sorry!)
http://www.diystompboxes.com/smfforum/index.php?topic=103129.0
http://www.diystompboxes.com/smfforum/index.php?topic=93817.0

And keep different power supplies/charge pump set ups handy while breadboarding ... J201s on 9V can be similar levels of gain with different dynamic ranges compared to 2N5457 on 18V, or MPF102 on 27V!

Huh, I think this potst

[neve1272]

http://www.diale.org/triode.html
  i have no idea how that math works   

      thanks jon that is a metric ton of info for me to digest
for 1 i was worried that the bass that some of these different  amps introduce (the input caps and others being to high) would affect the compression.

   when i would breadboard j201 fezer would distort to quickly and mpf102 would sound cool but not have the gain
and the more gain stages the harder time i had biasing the breadboard.
       Now muamps were great for biasing but way to much gain. voltage dividing the signal down between them seems the wrong ...thinking..
that was my experience trying to bread board my amp.

thank you for the links and responding
    im waiting on the board mounted switch and the 12v zener to come in the mail to really hear this, then its all ready to go. I am super jazzed , these really are my favorite pedals