Tonestack help, please.

[Peter Snowberg]

The resistance of the controls takes care of grounding the gate so no need for another gate grounding resistor.

If you test this out, you should also experiment a bit with the coupling cap going into the 386. It will make a huge difference. With no stack, a smaller cap is a good idea there to limit the bass; once you have a stack in there you'll probably find that a larger cap will suit you better.

The classic fender stack is like balancing on a high wire. Take any component or characteristic too far in any direction and it doesn't sound that good. It's quite a stretch to take something designed for a 38K input impedance and drive it with 1K. Some adjustment is necessary as you found out with the 33K slope resistor. Compare the Marshall version and the input impedance it sees with your design now. I think you should also try cutting the connection between CCW end and wiper of the mid pot, reconnecting the mid cap to the wiper (as per the Marshall version). You may also want to try upping the treble cap too.

Since the speaker and the guitar figure heavily into the results, also give the BMP tone control a shot. You may find that the Baxandall stack works better for clean sounds, while distortion will generally benefit from some kind of mid-cut.

The tone world is a big place.... explore as much of it as you can before settling in any single spot.

Happy searching,
-Peter

[javacody]

Well, before I added the tone stack, I had a great chimey, fendery sound that is completely gone now. Would adding another buffer get me that back?

Should I add that the guitar I'm using is an alder bodied (see pics here http://www.mycgiserver.com/~javacody/project/index.jsp) strat style guitar with Fender Custom shop 69 pups?

[Peter Snowberg]

That will return some of it, but remember that a "stack bypass" control is a very nice hotrodding mod too. There's a reason for that.

Take care,
-Peter

[javacody]

Also, there is no coupling cap going into the 386 (currently), should there be one? I thought I would replace this with the tone stack?

[Peter Snowberg]

A JFET buffer stage should be capacitively coupled one way or another. The tone stack accomplishes this for the first stage, but if you add another buffer after the stack, that one should get a coupling cap too.

If you draw schematics the "regular" way, in each stage of the circuit, you should have DC flowing from top to bottom (really bottom to top, but that's another issue ), and you should have AC flowing from left to right. Capacitors block DC so just trace the lines until you run into one and that will show you where AC is able to flow.

Take care,
-Peter

[Ansil]

If you draw schematics the "regular" way, in each stage of the circuit, you should have DC flowing from top to bottom (really bottom to top, but that's another issue ), Take care,
-Peter

lol.. dont' get the guys brain fried here.. lol  i know what you mean i think most all diyers know about the flow of electrons in a circuit.. but some dont' ever believe it.. i dont' know why.. but my professor in collleg never wanted to beleive it..  but he understood it.. so i guess that was all that mattered..  

[javacody]

OK guys. I don't get the humor, so as hard as it is to not make easy sport of me ( :lol:  ) Please try to control yourselves.  Where the hell do I start learning all of this stuff?

[Ansil]

there is a ton of research on the web..  i can't really tell ya where to start as i started playing with voltages that should have killed me and most definately could have over 20years ago..  i started learning theory in highschool  and went to engineering school in my college years.

electrons flow from the negative side of the source to the positive side.  

basically there is a shortage of electrons on the positive side so when you hook up crap to it.. they try to go over and fill up that gap.  

not really trying to poke fun we all learn new stuff everyday. somtimes twice in one day..!!!  lol.  but if we have no humor then we have no life.  

[Peter Snowberg]

OK guys. I don't get the humor, so as hard as it is to not make easy sport of me ( :lol:  ) Please try to control yourselves.  Where the hell do I start learning all of this stuff?

I'm certainly not trying to make sport of you in any way. I still stand by the top to bottom or bottom to top for DC and left to right for AC flow being what you want to look for. I made the comment in parenthesis so that if you wanted to know more, I could point you towards it. If you didn't want to know more, the description would make sense, given the 'classic' view of power.

The top to bottom flow is what the "classic teachings" on power describe. Power comes from the + side and flows to the - side. Long ago, things like schematic symbols were described which is why diodes look like they point from + to -. LEDs and transistors followed suite because of precedence. At the time people said, "well if electrons is what we're talking about here, they're negative, so they must be flowing to the negative potential and away from the positive potential, thus giving current flow".

The trouble is that this contradicts what the materials science crowd sees in very simple experiments. If you apply power to two iron nails and put them in water, the negative nail will be eaten away as the iron atoms are ripped off of it and travel towards the positive nail. The direction of the actual power flow is reversed from the schematic symbols.

(two related terms here are "anodizing", where the anode gets new atoms bonded to it, and "cathodic protection", where a negatively charged piece of metal is introduced to a system so that it will get eaten away before the equipment it is protecting.)

Later still, the concept of electricity was elaborated on as a force that moves at the speed of light (just like gravity), rather than the simple transfer of electrons from molecule to molecule. This got the name "electromotive force" and that's what the E in Ohm's law equations stands for.

From here it starts to get really contradictory, and funky. I just googled the basic question "what is electricity" and got this page as result #1. It's not complete, but it does a pretty good job of setting the stage end explaining some of the contradiction.

http://amasci.com/miscon/whatis.html

I don't like the idea of anybody holding back with information (unless it's a proprietary design). If I know something that I can pass along, I am only too happy to do so. I hope that everybody does the same, otherwise I stop learning pretty fast except from my own limited experience. I never make a statement without the willingness to expand on it.

That's not an all-in-one link to understand electricity and all the associated concepts, but hopefully it will help. If you have any more questions about it, I will only be happy to pass along what I have learned.

Take care,
-Peter

[javacody]

I just started reading, but its starting to remind me of Zen Buddhist teachings.    How can an atom be moving and standing still at the same time?

[Peter Snowberg]

LOL! (to bad there isn't a little buddha smiley)

The universe is more Zen than we can commonly accept.

We are all one.

(the question is one what?)

Om Mani Padme Hum.....
-Peter

[javacody]

If you test this out, you should also experiment a bit with the coupling cap going into the 386. It will make a huge difference. With no stack, a smaller cap is a good idea there to limit the bass; once you have a stack in there you'll probably find that a larger cap will suit you better.

Peter, when you talk about a larger value for the coupling cap, how large is large enough? 0.1uF? 1uF? I would prefer to stick to film caps for anything that effects tone, and I have one film cap (I think its film, its a rectagle) rated at 1 uF.

Also, regarding the Fairchild 2N5457, how would the resistors in my buffer have to change to set the bias on this guy? Would the 10k trimmer be large enough?

[javacody]

Well, regarding the cap question, I found the following (which really should be in the FAQ if you ask me, hint hint)

http://www.diystompboxes.com/sboxforum/viewtopic.php?t=2945&highlight=coupling+capacitor+bass
and
http://www.diystompboxes.com/sboxforum/viewtopic.php?t=3813&highlight=coupling+capacitor+bass

I'm going to try a 0.1 uF cap, and if that doesn't give me enough bass, I will go with a 1 uF film cap.

Next, in another bout of self-reliance (  ) I am going to do a search on that FET and see if I can find a data sheet on it.

[Peter Snowberg]

That post was a good find Javacody. It's now in the FAQ along with a bunch of other R.G. gems.

If you want more bass, but you want to keep the character of a film cap, you can always use two caps in parallel.

For the 2N5457, if you are still taking the signal from the source, try eliminating the drain resistor (short it) and use a 4.7 in series with a 10K pot (set at 50%) for the source. If you want more gain, add a cap across the source resistance. Try .68uF for a Marshally tone, and 22uF for a full spectrum to be more Fenderish. You can always toss a 10uF in there and see how you like it. Really low values like 0.1uF will boost higher treble.

Take care,
-Peter

[brett]

In response to the 4.7k + 10k trimmer suggestion for a 2N5457....  That will probably work for a 2N5457, but maybe not for other JFETs.  I find that some JFETs with low Vgs(on) values (ie <-2V) require fairly small drain resistors.  Others, such as J201s will need more than 14.7k.
e.g. an MPF102 that I have with Vgs(0.1mA)=-2.6V needed Rdrain ~ 4kohms, and a 2N5457 with Vgs(0.1mA)=-1V needed Rdrain~19kohms.  

Approximately...Rdrain = 33k * exp(0.84*Vgs)  where Vgs is the gate-source voltage for Ids ~ 0.1mA.

[Gary]

Ansil said:

"a 5k pot on the 386 is redundant.. you dont' need more than 2k and you wont' get all of that. out of it.. pins 1 and 8 have a resistor in between them in the chip.. it is only 1.35k to set the gain at 20 anything less more than 1.35k will not do jack crap"

Ansil,

I guess you didn't notice the parallel resistance of the pot and the internal resistor.  Your suggested 2k pot will only give about 800 Ohms at the lowest gain setting.  Considerably hotter than 20X gain.  The listed 5k pot will give you a little over 1k at the minimum gain setting.  A little closer to 20X than the 2k pot.

The way this pot works is by the parallel resistance between the pot and the internal resistor.  Aside from that, have you tried the 5k pot?  I did.  It worked the best of the readily available RS parts for taper and range.  All designs on RunoffGroove are tested and proven to work before posting.  Actually, we do a double test.  B Tremblay and I both prove the circuit and critique and modify it before he posts.  We are trying to do the DIYers a favor and prove a design to work as advertised before people waste their parts on a "pipedream" sketch/schematic.

Posts like yours have caused a recent slow-down of my sharing of ideas/designs.  I am tired of freely giving ideas only to see postings like that.  I doubt you've tried the pot.  It seems to me you just want to add your two cents.  That's fine.  Add your two cents on someone else's stuff.  Better yet, add your two cents to your own stuff.  I think most people would appreciate that.  That would be a lot better than the spreading of mis-information.

"Preach" on.

[javacody]

Please help me verify this:

I'm thinking the capacitance of the lm386 is 50k, right? So to figure out what cap I would like, I use the following formula:

F = 1 / (2 * 3.14 * R * (C / 1000000))

I'm looking for something between 60 and 70 Hz so if I use 50k for R and a 0.047uF cap for C I get the following:

F = 1 / (2 * 3.14 * 50000 * (0.047 / 1000000))

Which gives me an F of 67.75985905949316

Am I missing anything?

Also,  thanks for the clarification Gary. The little gem design works great . I just didn't have the technical knowledge to explain how the pot was working, I just knew it was. I was hoping you or B Tremblay would drop in and clear it up. Addionally, when I was having trouble getting my buffer working, it was looking at the schem for the Little Gem MKII that gave me the idea to switch the signal out from the drain to the source.

Brett, I'm not sure I follow? Peter was talking about removing the drain resistor altogether and placing the trimmer on the source.