GGG Distortion Plus - Some Basic Questions.

[RacerR]

Hello - 1st post on this forum, and I'm currently building my first DIY pedal - a GGG Dist kit.

I have a couple of what I hope are really simple questions - all refer to BOM (Version 2009October25) and the Layout doc (Version 2008November20):
    1. What affect do the optional components C8 and D8 have on the circuit/sound?  Maybe I missed it somewhere, but I don't see any description of this in the GGG docs.
    2. I'm having trouble identifying C5 (a 10pF ceramic cap).  In the kit, I have two ceramic caps to choose from - the smaller one labeled only "100", the larger one labeled "25k IKV", not sure which is the correct cap for C5.
    3. I am using the same capacitor type on both C3 and C7 (this is a film cap, .001uF - marked "102").  The BOM is not completely clear, is this the correct cap for C7?

Thanks for helping a newbie out, any information provided is appreciated.

-R

[Bill Mountain]

Please post which schematic you're referring to.  I just looked at the GGG D+ schematic and I saw no C8 or D8.

If I had to guess without seeing the schematic they may be for polarity protect and power filtering which are usually good things to have.

[deadastronaut]

hi and welcome..

as bill said, c8 and D8

c8 100uf is for power filtering/smoothing..

D8 is for reverse polarity protection..

these are optional...but i would add them anyway, just in case your  psu is moody, or someone decides to put the wrong 9v adapter on it..

it will have no effect on the sound, its just precautionary..

hope this helps. have fun.

[RacerR]

Thanks Bill - yeah, that is interesting - they are not shown on the Schematic.

They are shown on both: BOM (Version 2009October25) and the Layout doc (Version 2008November20), and listed as "Optional".

Also - I had some additional questions, but I hit refresh while putting this together so they didn't post... I've corrected it and my initial post has been updated.

Thanks again for the speedy reply.

-R

[Bill Mountain]

Hello - 1st post on this forum, and I'm currently building my first DIY pedal - a GGG Dist kit.

I have a couple of what I hope are really simple questions - all refer to BOM (Version 2009October25) and the Layout doc (Version 2008November20):
    1. What affect do the optional components C8 and D8 have on the circuit/sound?  Maybe I missed it somewhere, but I don't see any description of this in the GGG docs.
    2. I'm having trouble identifying C5 (a 10pF ceramic cap).  In the kit, I have two ceramic caps to choose from - the smaller one labeled only "100", the larger one labeled "25k IKV", not sure which is the correct cap for C5.
    3. I am using the same capacitor type on both C3 and C7 (this is a film cap, .001uF - marked "102").  The BOM is not completely clear, is this the correct cap for C7?

Thanks for helping a newbie out, any information provided is appreciated.

-R

1.  Has hopefully been answered.
2.  The 100 is most likely the 10 pF cap. (101 would be 100pF, 102 would be 1nF, 103 would be 10nf, 104 - 100nF, etc.)
3.  Both C3 and C7 are 1n (.001uf-102)

Does this help?

[Bill Mountain]

http://www.elecraft.com/Apps/caps.htm

This might clear some stuff up for you.

[RacerR]

Thanks DeadAstronaut - I'll definitely include C8/D8.

D8 is easy to identify, I should be able to use the same type (1N914) as D1 and D2.  

C8, should be easy enough to ID since all Electrolytic caps are pretty clearly labeled.

Thanks.

-R

[RacerR]

Thanks Bill - I think that covers it.

I should have this thing finished up tonight or tomorrow - the build seemed pretty straight forward and I'm optimistic about the pedal working.

I'll post an update when it's done.

Thanks again.

-R

[RacerR]

http://www.elecraft.com/Apps/caps.htm

This might clear some stuff up for you.

Thanks Bill - that's very helpful.

-R

[Bill Mountain]

Welcome to the addiction!

[R O Tiree]

...D8 is easy to identify, I should be able to use the same type (1N914) as D1 and D2...

The object of that diode is to try to clamp the reverse voltage across the circuit to 0.7V (which will do little if any harm) while the battery is trying to drive it at 9V the wrong way round (which will do very bad things to your circuit). To loosely paraphrase RG (Google geofex polarity protection), it's a battle between your battery and the diode. The battery will get hot and the diode will get VERY hot. After only a short time, the diode will probably blow, allowing the full 9V the wrong way through the circuit. It's really only designed for when you're being a muppet and trying to connect the battery the wrong way - dead easy to spot and soon sorted out. Connect a PSU the wrong way and it'll probably be a few seconds until you realise it, by which time the damage is probably done.

A 1N914 is a small signal diode, and cannot take very much current. It therefore will not last very long at all when driven hard. You'd be better off with a more beefy 1N4001.

That said, a MOSFET and 1 resistor will provide fool-proof polarity protection. As will an NPN, a PNP and 4 resistors. Again, Googling geofex polarity protection will take you to a couple of articles that RG wrote some years ago that are easy to understand and cheap and simple to incorporate into your designs. Again, to paraphrase, there should be one of these in every wrapper.

[RacerR]

A 1N914 is a small signal diode, and cannot take very much current. It therefore will not last very long at all when driven hard. You'd be better off with a more beefy 1N4001.

Thanks, that makes a lot of sense to me.

I only have the components from the kit to work with right now though, it looks like there are 3 diode types to choose from: 1N914, "BAT 46", and some 1N34A germanium diodes.

I don't see the "BAT 46" used in the other pedal versions which can be built from this Kit, so I'm not sure why it's included.   Is the "BAT 46" an appropriate diode for use in D8 ?

Also - does anyone know the value of the ceramic cap from the kit labeled "25k IKV" ?  I'm not finding it with Google searches.

Thanks.

-R

[R O Tiree]

Definitely not - it's a Schottky diode with a Vf about the same as a Ge diode (1N34A). Their Vf is approx 0.25V @ 1 mA If to 0.45V @ 10mA If, with an absolute max current of 150mA and a max power dissipation of 150mW (so 16mA @9V), so they'd be even worse off than a poor little 1N914 trying to do the biz. And don't use the 1N34As either - they're becoming like hens' teeth these days. Nip down to your local electronic parts store and see if they have anything in the 1N400X series (the higher the last digit "X", the more current they can cope with)

I've just looked at the files at GGG and D8 is clearly marked as a 1N4001 on the layout. That means it should be in the kit. Those diodes are black with a silver band painted around one end. That said, they also say in the BoM that D8 can be either 1N914 or 1N4001. I've repaired quite a lot of pedals for people that used a 1N914 in that position. I've repaired only a few that had a 1N4001.

That cap is probably (?) a 25pF. The "K" denotes its tolerance (+/-10%) and the "IKV" is probably "1kV", which means it's good for 1000V. If that cap appears to be a spare one, then I guess it could be used instead of the 10pF if you find you don't like the sound with the smaller cap.

[Govmnt_Lacky]

Just for informational purposes.

The original MXR Dist + used 1N270 germanium diodes for the clipping section   

[RacerR]

Gvt Lacky - I noticed there are Germanium diodes on the the original MXR boards, I was wondering about that.  Since this is my first DIY pedal build, I decided to stick with the GGG kit instructions.

Out of curiosity, would the 1N270 be a direct replacement for the 1N914 in this circuit?  I just ordered a handful of each germanium type (1N270 and 1N34A) - so I'll have some options to experiment with once they get here.

I have my board populated except for C5, C8, and D8.  I'm going to Radio Shack tomorrow to pick up a 1N4001 for D8; once I have that soldered, I'll mount and solder C8.

I have a question about C5:  What do most people here use?  I've read that some people find the sound a bit too harsh on the high/treble side with the 10pF cap in C5, and the "fix" is to bleed out some high end using a 25pF cap (or higher) in C5.

I'm putting this information together as I find it, sorry if the questions are a bit newbish.

Thanks.

-R

[R O Tiree]

Not newbish at all, Racer - in fact you are getting to grips with this stuff really fast. You're also noting what people have said in this thread and (a) taking the advice and (b) taking time to read and research for yourself elsewhere (a rare quality). Keep throwing questions... there will be someone here who's seen it, heard of it and even some who were around when it was invented or helped design it.

1N914 in your kit is a small-signal silicon (Si) diode with a Vf of about 0.7V. You'll also see 1N4148 very often in schematics, as these 2 are pretty much identical for our purposes.

1N270 is another small-signal germanium (Ge) diode, very similar to the 1N34A in your kit, with a Vf of about 0.3V, so 1N270 would be the relplacement for 1N34A. You'll also see OA90 and OA91 elsewhere.

1N400X series are Si diodes capable of passing a much higher current than things like the '914, so you often see this series being used in amplifiers, for example, to rectify AC. Again, a Vf of about 0.7V

C5 - try 10pF first. if not good, whip that out and try the 25pF. If still a little harsh, put the 10pF and 25pF together to make 35pF (caps add when they're in parallel, unlike resistors which add when they're in series). You might be able to get 2 leads down each hole in the board for C5... if not, solder one cap in and then try to solder the other one to the first one's legs.

A note on de-soldering and re-soldering... The solder you buy is impregnated with something called "flux". This stuff seems almost magical and does several things. It helps the solder flow, cleans at least some of the corrosion off leads, PCB pads, etc, and joints made with enough flux in there are shiny and neat and are very quick to make as well, which is good for your self-esteem and also the parts you are trying to solder. The downside is that the more you heat a joint the more the flux burns off. Joints made without enough flux are dull (crystalline, which is generally bad for solder joints), blobby, and take ages to look even vaguely right, which leads almost inevitably to overheating of the parts (bad) and/or overheating of the pads and traces on the PCB (and once they lift up and break off, it's a devil of a job to hack it about and re-create the tracks using stub-ends of wire... messy and unreliable). So, while you're at RadioShack, get some flux and some de-soldering braid or a de-soldering pump - braid wicks up molten solder and it's cheap, whereas a pump is more expensive but a lot quicker to use. I use a pump almost exclusively, but there are those who wouldn't touch one with a bargepole. So, apply some flux to the joints you are about to de-solder, nip in with the iron to melt one joint, pop the pump in right next to the iron tip and trigger it (or apply the braid if you're using that) and you will have got rid of almost all the solder in that joint. Repeat for the other joint. You might find that there's a tiny bit of solder left in the joint... you might be able to tease it apart with needle-nose pliers, but it's probably best to just touch the iron to each joint in turn to keep the solder molten as you remove the part. Let everything cool down again and then re-solder.

[RacerR]

FYI - this pedal went together well, and it sounds like it should.

Thanks everyone, for all the info.

-R