What types of caps for tone benders?

[svirfnebli]

Hey all,

Im working on my first pedal. I'm so excited!! I've got my first couple of builds worked out in my head. My first build is going to be a Tonebender MKII. Then my second building is going to be a Tri-Tonebender, with all three tone bender circuits inside (MKI, MKII, and MKII .. but not 1.5). Im not building for sale, just for myself.

So my question is is.. looking at the schematics I can see that there are several different caps in the circuit.. How do you determine what type of caps (film, ceramic, PIO, etc) for each position? Do you just look at what is out there and copy that? I'd like to build fairly historically accurate and money isnt an object for parts. Hell I spent a fortune to get the Mullard OC81D's.

Does anyone have any advise for this? Are there some good stripboard layouts for these?

Matt

[petemoore]

MKII, and MKII .. but not 1.5). Im not building for sale, just for myself.
  So my question is is.. looking at the schematics I can see that there are several different caps in the circuit.. How do you determine what type of caps (film, ceramic, PIO, etc) for each position?
  Voltage rating, never exceed rated voltage, this seems to apply mostly to electrolytics or larger value caps running at <12v.
  Do you just look at what is out there and copy that?
  I read GEO and find the capitor query satisfaction page, then used film capacitors, or new. Could be a copy, mostly just by personal choice, Poly film for the values they provide which is usually <4uf or something.
  I'd like to build fairly historically accurate and money isnt an object for parts.
  It seems like I'm always finding out just how accurate history is, just make it a 2009 - 2010 build, that should be close enough.
  Hell I spent a fortune to get the Mullard OC81D's.
  Does anyone have any advise for this? Are there some good stripboard layouts for these?

[petemoore]

  Does anyone have any advise for this?
  Choose transistors for leakage and gain, see GEO technology of the Fuzzface. I had some biasing issues as well with Q1, IIRC a Ge with 'some' leakage is required for a good bias as shown, otherwise low leakage is a +.
  Swapping transistors in the 3 postitions with various gains allows reshaping the gain structure, try a low-ish gain FF Q1 transistor [Q3 in a tonebender].
  Are there some good stripboard layouts for these?
  Check Layouts, or someone may chime in with a link.
  I'd choose one with trimpot for Q3 collector resistor. Otherwise, fascilitate Q3c resistor adjustment for bias of the FF circuit portion [Q's 2 and 3] of the Tonebender, any FF tricks apply there, maybe build so a 100k can be easily added to a [long-legged] 100k feedback resistor to make it 50k, see YaFF at AMZ, and take a look at the other 1001+ FF texts/diagrams.
  Consider a 'perfbread' build, something with a 6 or 8pin IC socket for the transistors, perhaps more socket-age for this's and that's's like input/output caps,  bypass cap, adjustment of Q3c resistor, that '470' ohm or so, usually shown horizontal, on the top of FF schematics, larger values = more output, influencing where the volume control tends to reside/the settings change the series resistance at the output etc., or breadboard.
  Then populate the permanent board with the selected values.     
  From a purely historical, sound perspectives approach..."What-zit-goin-inta?"..is exponentially more important than capacitor material used [it's a Fuzz circuit], otherwise their values are important.
 
   
 

[Electric Warrior]

here you go:



the original used metallized polyester film caps. Might be hard to find NOS Iskra caps with the right values.

Here's how David Main biases his Tone Benders: http://stompboxes.co.uk/forum/viewtopic.php?f=6&t=3229&hilit=room+temperature&start=10
He's using the trim pot not for Q3's collector resistor, but for Q2's. Interesting read. He explains what to listen for.

And on this thread you can find the only two OC81D-MkII gut shots I'm aware of: http://dam.10.forumer.com/viewtopic.php?t=502&postdays=0&postorder=asc&highlight=oc81d&start=15  nice reference. The unmarked metal can transistors in the other "OC81D"-units turned out to be some type of Impex transistors..