StratoBoost- Strat Fattener

[DougH]

Here's something I threw together over the weekend. It's a tweak to the internet schems for the Hornby Skewes treble boost that have been floating around. I chose the in/out caps to fatten up my strat and give it a nice "round" neck pup sound. Also, tweaked the bias to use a 5k "volume" pot (like a rangemaster) instead of the fixed 3.9k resistor. (Some like a 100k pot on the output but that increases the Zout too much for my taste.) The guitar volume control is your friend with this one and can sweep from a wide range of clipping to clean without it getting too thin. In fact, just turn it on and leave it on- you'll like it. Use whatever PNP transistor you have lying around- Si works good too.



http://www.aronnelson.com/gallery/main.php/v/DougH/booster/StratoBoost.JPG.html

[joegagan]

looks, great, doug.  now all you need is a layout that fits in a strat output jack cavity, and a hearing aid battery.

[DougH]

Thanks Joe.  Give it a try on the breadboard and see what you think. I'd be curious to hear your thoughts.

[John Lyons]

Now, where to find an 80uf cap. 
Have to try it out Doug.

[user]

Quick question: Would an ac128 work with this?

[petemoore]

  What's the 128 like in a Stratobooster ?
 It's all about leakage and gain, then leakage and gain, then the sound it actually makes if made to work.
 "Should work'' might turn to "will work'' with the measured specifications on the Ge candidate transistor.
 See GEO for the Hfe/Leakage testjig.
  Or just build it with a socket, and get the 'right' transistor.
  There are many varieties of AC128 and the vary all over the map, even ones from the same batch.
 

[user]

thanks man.will try..

[DougH]

Now, where to find an 80uf cap. 

(Pssst... I actually used 2 47u's in parallel. Pass it on..) 

[DougH]

Quick question: Would an ac128 work with this?

When it comes to Ge transistors, just find one with acceptable leakage (or buy them pre-tested) and don't worry about the part number. I hope I made it clear that just about any PNP transistor (Si or Ge) should work in this thing.

[slacker]

I gave this a try using a silicon PNP and it's a nice little booster, plenty of volume and a bit of grit that sounds really nice overdriving an amp and backing off the guitar's volume pot cleans it up nicely. Does what it says on the tin, fattens up a strat nicely
I tried flipping the relevant bits and using an NPN silicon as well and that sounded just as good.

[DougH]

Thanks for trying it out and reporting results. 

I tried NPN with an earlier configuration and it didn't sound as good- and it really shouldn't have made any difference. Never could figure that one out. But haven't tried it with this one. Glad that worked out too.

An Si 2n5087 sounds good in this too, and will give it a little more treble.

[Joe Hart]

Now, where to find an 80uf cap. 

I have been messing around with a circuit based on the Hornby Skewes and I used a 50uf cap, and to be perfectly honest even omitting it was a VERY subtle difference. At least with my slightly modified circuit. So I doubt that exactly 80uf is all that critical.
-Joe Hart

[Paul Marossy]

Does what it says on the tin, fattens up a strat nicely

Sounds like something you would read on the label on a can of weight gain powder mix for Strat pickups.  

[Gus]

10K base to ground with a 1K emitter.  Almost any Ge or Si will bias up with this circuit.

10K(10K || (hfe x ( re) ||68K is the real input, (1K is bypassed with the 80uf so that is removed at guitar frequencies) ) is a heavy load for the pickups and tames the highs: However this circuit has gain and the input cap adjusts the high pass input filter so it is a balancing act of gain vs loading vs highpass.

[petemoore]

  I guess with Si's the process is sufficiently accurate enough to make the mirror circuit [negative ground] work at least very similarly.
 

[DougH]

a heavy load for the pickups and tames the highs

My only complaint about this is it is a smidgen dark. But that is with my hardtail strat, which is kind of dark sounding anyway. Would love to try it with a "normal" strat with a tremolo block. I bet it is plenty bright then.

[DougH]

Here's a cool mod idea to try with this thing. One of the issues I have with it is with the guitar vol maxed, it's pretty mid-peaky. It's a cool sound in a way, very resonant and "feedback-y", but not really exactly what I want out of it. I sort of prefer the sound with my volume rolled down to 8-9. So you can put a series resistor on the input to flatten out the mids some. Better yet, bypass the series resistor with a small cap, a la the treble peaking filters on a Marshall amp. This gives it a little treble boost, and should restore some of the "natural" sound of the strat.

I have not tried it yet, but it looks really good in the circuit sim. The frequency contour of it with the guitar volume maxed looks more like it does with the guitar volume turned down (with treble leaking- 130k/.0012u in series in my case), and should be a little more consistent over the travel of the volume control. It looks like a 22k/.0068u is a good place to start. I'll report back after I actually try it and if it works I'll mod the schematic. Won't get to it until tomorrow night.

[joegagan]

bypass the series resistor with a small cap

now you're speaking my language. .002 silver mica for me , please.  haven't had time to build it but i plan to soon.

[DougH]

I looked at it again Joe, and I think that .002 would work well with a resistor somewhere around 100k. I had my pot taper on the guitar vol screwed up in the sim and I think it's going need a larger resistor than 22k. I'm looking for roughly the same freq response I got with the original circuit and the guitar vol on 8.5-9, with just a little more gain. 100k on the input might create too much noise, though. Anyway, it's going to be fun to experiment with it.

[DougH]

This is showing a lot of promise.   So far 22k and .022 to .047 is sounding really good. Wow, cool!