Question about the TychoBrahe Octavia

[smccusker]

The first schematic for this pedal that I found was the one on this site by Justin Philpott, so I went and bought all the components and sat tight on them for a little while. Then I found the GGG schematic, which I would like to build instead so my question is this, can I use the transistors I bought for Justin Philpotts schematic (MPS-A18, and 2N3906) for the values in the GGG circuit (2N5807 and 2N5088), as far as I can tell, both the MPS-A18 and the 2N5807 are NPN and the 2N3906 and 2N5088 are PNP.

Anyway, any help would be greatly apreciated.
-Sam

[phillip]

That schematic that you saw at GGG is for the modified negative ground version of the pedal (the original was positive ground).  I would use the transistors that are listed in the GGG schematic...2N5087 for Q1 and 2N5088 (or 2N4401) for Q2 and Q3.

MPSA18 and 2N5088 are NPN

2N5087 and 2N3906 are PNP

By converting the circuit to negative ground you can use the same power supply with all your modern negative ground effects (Boss, Dunlop, EH, Ibanez, etc.).  In order to convert the circuit to negative ground, the NPN transistor in Q1 had to be replaced with a PNP (in this case a 2N5087).  Then the two PNP transistors in Q2 had to be replaced with a pair of NPN (2N5088s in this case...I've also used 2N4401s).

Hope this helps!
Phillip

[smccusker]

Ahh whoops, you're right.
Damn, so I wouldn't be able to sub two MPS-A18s for the 2N5088s?

[phillip]

hmm the MPSA18 actually might work pretty well...maybe a tad on the gainy side, but then again that might be a good thing in the Tyco circuit

The MPSA18 and 2N5089 are basically interchangeable with almost no differences...the 2N5088 is just slightly lower gain.

Phillip

[smccusker]

Ahh cool, well thats a bit of a relief, I didn't really want to have to buy a bunch of new parts (since for some reason transistors seem to be hard to track down in Australia).

[smccusker]

I just did a rough perfboard layout for the Octavia, would someone please be able to give me some feedback on it (its the attempt I've ever done of designing a layout from a schematic)? I'm sure I've checked everything, but I've been at it for a while, so a fresh pair of eyes is always helpful. I used Runoffgroves template for the 371 hole Perfboard, and cannibalised some of his other layouts for component graphics.
Any feedback will be greatly appreciated. Hopefully I can start on this tomorow morning

EDIT: I forgot to mention I based it off the GGG schematic.

[onboard]

Nice layout - and correct.

I'll run a search, but I'm curious why C7 & R14 are *after* the volume pot...seems like I read that order is irrelavent in a series network  -  so the output cap and 4.7M :shock: resistor could go before the pot and eliminate a wire.  Unless there *is* a reason for the order.

[smccusker]

Oh really?
I just put them after the volume pot because thats thats what the schem said, and also the way it was wired up in the GGG layout.

Thanks for your feedback!
-Sam

[smccusker]

Just thought I'd bump this to see if anyone else had any comments or suggestions. I haven't started building it yet because the closest electronics store has been closed for the last few days for stocktake, I might try and treck out to one of the others later today, or tomorow.

EDIT: I noticed that the 22uf capacitor that connects to the ground on my layout should actually be 220uf.

[robotboy]

When you confirm that this layout works, could you send me a PM? I want to build the octavia as well, and this looks like a nice layout.

[smccusker]

yeah absolutely!
I'm just starting it now.
Wish me luck everyone!

[smccusker]

Okay so I just finished a build from my layout, but when I plugged it in, there is no signal when the pedal is not bypassed. I thought I might have missed a connection on the signal path, but its all there. I checked the orientation of the caps, transistors and diodes and they're all correct. I used 2 MPS-A18 transistors and 1 2A3906 instead of the dual 2N5088 and single 2N5087, but i should be getting atleast some sort of signal from that shouldnt I? even if its not correct? that's the only reason why I can see there would be a problem, unless it's with my layout
I guess all I can do is take a break, have dinner and come back to it with fresh eys. Its a bummer when things dont work first time around though.

[smccusker]

I made an audio probe and the problem SEEMS to be with the transistors. Like I said before, I subbed different Transistor values, but I thought there should still be some signal?
But Im not even getting hum or anything through.
Anyone got any ideas?

EDIT: I followed the signal path and I'm getting signal after all three pins on the first transistor (though it doesnt sound any different) and the signal seems to stop after the second transistor (the first NPN) any thoughts?

[tungngruv]

First, I'm not great at debugging but..... I checked your layout to the GGG and I did notice that on GGG's layout, the signal goes from Q2 B to Q1 C to R5(220K) to R6(220R) to C3(.001) to ground. Your layout has the signal the same up to R6(220R) where it goes to ground instead of through C3, then ground. I'm not sure if this will make any difference though in my limited  :oops:  knowledge. Also, I always wire up the DPDT with one outside pair together, the inside pair are jack in and out then the outer pair the in and out from the board. Obviuosly inputs are on same side as are the outputs. Not questioning your ability, but I've made that mistake a couple times. Hope you get it working as I want to perf this up also.

[phillip]

Nice layout - and correct.

I'll run a search, but I'm curious why C7 & R14 are *after* the volume pot...seems like I read that order is irrelavent in a series network  -  so the output cap and 4.7M :shock: resistor could go before the pot and eliminate a wire.  Unless there *is* a reason for the order.

The 4.7M resistor (R14) is on the "outside" of C7 to serve as a pulldown resistor for the output.  If it were placed on the inside of C7 the circuit would have a fairly loud "pop" when it's switched on and off because of leakage from that capacitor being shifted across the contacts of the bypass switch.

Also note that in the original Tycobrahe Octavia, there was no output capacitor (or pulldown resistor) on the circuit output.  The output in the original Octavia comes from the "wiper" lug of the 500KA volume pot.

Phillip

[smccusker]

First, I'm not great at debugging but..... I checked your layout to the GGG and I did notice that on GGG's layout, the signal goes from Q2 B to Q1 C to R5(220K) to R6(220R) to C3(.001) to ground. Your layout has the signal the same up to R6(220R) where it goes to ground instead of through C3, then ground. I'm not sure if this will make any difference though in my limited  :oops:  knowledge. Also, I always wire up the DPDT with one outside pair together, the inside pair are jack in and out then the outer pair the in and out from the board. Obviuosly inputs are on same side as are the outputs. Not questioning your ability, but I've made that mistake a couple times. Hope you get it working as I want to perf this up also.

Ahh you're right, I beleive the connection from the B of Q2 should come BEFORE the 220o and .001 capacitor, as well as the resistor being oriented incorrectly. Theoretically, since current takes the path of least resistence, i could be sending the signal straight to the ground, which would certainly explain why i'm not getting anything at the other end of the signal path. Oh and by the way I'm using a 3pdt, using the GGG wiring method, not DPDT like on the octavia layout.

Anyway I'll fix it up and see how that goes.
Thanks again!

[smccusker]

I fixed the orientation and ordering of the 220o resistor and the 0.001 cap, but I was still getting no signal, so I probed around and found that i was now getting signal all the way upto the output capacitor, so i tried a few different wirings between the output cap, pulldown resistor and the signal out, until i realised that i had foolishly run the ground to both legs of the resistor, so anyway i fixed that up, but ever since then is has been making these really cool (but not exactly the desired effect) oscilations when there is no signal coming from the guitar. however if i turn my tone knob all the way down the oscilation disappears (but doesnt change pitch at all). My offboard wiring is pretty awful because i havent boxed it up yet, so would i be right in assuming that it may be the reason for the oscilation? (if i touch the hot lug on the input jack i can hear the radio)

Also, when the pedal is running, the signal is reaaally @#$%ing loud. like to the point where to listen to it at a slightly above bearable level, when the pedal is bypassed the clean signal is almost inaudible, would that be to do with the transistors that i used?

Anyway, apart from those two things the pedal works as it should, and i can get some absolutely face shredding tones from it. As soon as i clear up those problems and house it up, this pedal is definitely making its way into my setup.

I'll also fix up my layout and post it again for those who are interested.

Thanks to everyone who helped me out on my second, and slightly more problematic build
-Sam