THE ENGINEER'S THUMB... At last, a better compressor!

[stevie1556]

I think I've got all the components for this build already (need to double check) so I'll attempt to get it built over the next few days. After I've finally finished my Spark Gap!

[R O Tiree]

Does it have to be a BC327 for Q1? Or will a 2N3906 do?

[PRR]

> Or will a 2N3906 do?

Yes.

[R O Tiree]

Thanks, Paul. I had a good look at the datasheets and they look very similar indeed... thought I might have missed something.

[PRR]

This part must have these specs or better:

Vbe @ 4mA under 1 Volt (typ 0.7V and reliable)
hFE over 10 (typ >100)
Vcbo over 4V (typ >20
leakage Ices under 1uA (typ <100nA)
fT over 1KHz (typ >100MHz)
or Tr under 0.1mS (typ <100nS)

You sorta can't buy a small PNP transistor this bad. Better is fine. Infine hFE is as good as hFE=25. More than 4V breakdown is fine (within limits, Vcb and hFE trade-off, a 4,000V BJT would have low hFE (but you can't find one)). There's no infinite fT but a GHz part is fine.

If you can tell NPN from PNP by smell (or tester) then you can rob old toys and appliances.

> BC327 ..Or will a 2N3906 do?

We all use the same parts but sold under different registries. In america, JEDEC "2N". In europe the "BC" numbering is common. Japan has the "2SC" etc system. Merlin is in England so his jellybean PNP is a BC. I use 2N2222 for everything, except PNP, so I try to remember which 2N390? is P-flavor. BOSS et al plans are full of 2SC parts. Very likely they all now come from one Chinese fab which puts the different numbers on as they are loading the ships to each corner of the world.

[earthtonesaudio]

...If you can tell NPN from PNP by smell...

[Kipper4]

This is my next build. The lm13700 chip should arrive anyday now. Plus the BC327 too.
I have a few dumb questions. I just want to check i have it right in my head while at the planning stage rather than when populating the board.
(basics, I will be using perfboard not vero. I will be using 2 x TL072's. I havent as yet tried vero although it seems popular among builders here and i cant even contemplate etching my own boards at this point in my pedal building hobby)

Q1 do i attach all the points marked 4.5v to pin 7 of U2:B ( i'm using the schematic from the pdf of Merlin B's)
Q2 do all points marked 9V attach to the little arrow marked 9v in the top left hand corner of the power supply section of the board  or do they go to the point marked 9v at the end of link 2?
(i'm assuming its the power supply section because its seperate from the rest of the schematic and that seems to be the norn)

I do alot of assuming since i have no real education in EE. It's mostly served me well. Feel free to correct me and educate me please.
Oh and the other thing is i guess i dont need to include jumpers since i'm not using an etched board or vero.
Thanks for the help

[midwayfair]

Q1 do i attach all the points marked 4.5v to pin 7 of U2:B ( i'm using the schematic from the pdf of Merlin B's)
Q2 do all points marked 9V attach to the little arrow marked 9v in the top left hand corner of the power supply section of the board  or do they go to the point marked 9v at the end of link 2?
(i'm assuming its the power supply section because its seperate from the rest of the schematic and that seems to be the norn)

I do alot of assuming since i have no real education in EE. It's mostly served me well. Feel free to correct me and educate me please.
Oh and the other thing is i guess i dont need to include jumpers since i'm not using an etched board or vero.
Thanks for the help

You connect all points marked 4.5V ... together. You connect all the points marked 9v ... together.

You'll almost definitely need jumpers, but the reason the jumpers appear in Merlin's schematic is that he used Eagle (most likely) for the board layout, and you need to put jumpers in the layout for them to appear in the board layout.

If you want to save yourself some trouble of making the layout, my perfboard layout is a couple pages back.

[Kipper4]

And very good the perfboard layout is too.
As long as my colourblind eyes dont play tricks on me i should be ok with that.
Thanks again John.
Just for future referance though where are the voltage point. (just so i understand whats going on a bit better)
Thanks

[midwayfair]

Hey folks, I can't edit my post a while back. There was a mistake in my layout with the position of the cyan jumper. It didn't prevent the pedal from working, but I forgot that layout I posted was on my website and not my dropbox. Here's the updated/corrected perfboard layout. (If a mod sees this and they can edit the picture out of my previous post, that would be great.)

https://dl.dropbox.com/u/9878279/Jon%20Patton%27s%20layouts/Engineer%27s%20Thumb.pdf

[deadastronaut]

as a complete dumbass..

could someone put the 13700n's relevant pin numbers on the schemo please?..i'd like to bread it, and try those pot+switch mods too

also is it better to use 2 dual op amps...or 1 quad?..hmmm...

[midwayfair]

could someone put the 13700n's relevant pin numbers on the schemo please?

They're in the build document file, the one that has the etching layout and bill of materials (http://www.freewebs.com/valvewizard2/engineersthumb.pdf).

[deadastronaut]

aha cheers man.....

[bluebunny]

could someone put the 13700n's relevant pin numbers on the schemo please?..i'd like to bread it, and try those pot+switch mods too

Ah, I think Jon may have gone in there first.  This is the snippet I was going to suggest:



(Or to use the "other" side of the 13700, read 16, 14, 13, 12 for 1, 3, 4, 5.)

Edit: two days away from a PC, and I gotta learn to type and mouse faster!

[deadastronaut]

thats the one...nice one!..

[garcho]

also is it better to use 2 dual op amps...or 1 quad?..hmmm...

It's almost always easier to breadboard with two duals, IMO. Less jumping.

[Kipper4]

This is One fine compressor. It does a great job without being to squishy. Sure its noticable when it's on from bypassed.
I tried to make the 9v supply only switched on when the input jack is in. That didnt work.
The treble booster switch i will ammend next time to an on the board switch as John has done. So its optional when opening the box but to be honest i cant see me switching it off and on all the time.
I think this will be the first project i actually box up. I got my first 1590B at the weekend. I'll try to get a step drill this week.
Thanks Merlin for the excellant design.
Thanks to John and everyone else who helped guide me along the way and for all the guys who helped me debugg it too.
Next project.
millenium bypasses for my previous pedals and next future move on all project a protection diode in case of reverse polarity.

I really like the millenium bypass by the way. Are there anythings it wont work with?
Do you guys use it as a matter of course?
Is there a way of using millenium bypass with an input jack ground switch for use with batterys?

[garcho]

I think this will be the first project i actually box up.

Next project. millenium bypasses for my previous pedals...

I really like the millenium bypass by the way... Do you guys use it as a matter of course?

Millenium bypass is fantastic. However, since its adoption, the once-expensive 3PDT foot switch is now relatively cheap, and judging by pictures on this forum, by far, the most common way we wire up true bypass with an LED indicator. There are ways to wire your pedals without true bypass that certainly have their own merits, but starting with a 3PDT is the way to go (common, easy, cheap).

There are many threads and examples of bypass wiring on this forum, but try using a search engine instead of the forum's built-in search function. Here's an example.

[Mike Burgundy]

Is there a way of using millenium bypass with an input jack ground switch for use with batterys?

http://www.geofex.com/Article_Folders/Mill2extn/mil2plus.htm

[deadastronaut]

okay, i numbered the pins, and lost the millenium too..and just made it easier on my eyes (which are pretty f.....d).....3pdt for me!..

just put this here for reference..(hope merlin doesn't mind my schemo tinker. .)

i'll have a play around on breadboard later..