If all that fancy stuff about Fets really grabs you the have a looksee here;
    http://www.till.com/blog/archives/2004/12/interesting_lin.html

IMO, No matter how slick you make it look/sound most of this stuff tends to miss the point.

Distortion of active commponents is only one small part of a very big picture.

My attention would be aimed at tone shaping of each each and every stage from input to speaker.
exact replication of a troide will sound rather boring with a flat response.
Another thing worth noting;

Impedances dramatically alter when driving Valve amps into OD/comp/dist.

I'm not clever enough to give exact exacts but I can give a classic example of this effect.

If you ever find yourself in front of a really old model Marshall (not the crap sold now)
Then play at *Low volume (2/3)* and tweak the tone controls around. You know, turn knob play turn knob play, try every possibility.
*Pay very close attention to How much the tone control effects the sound.*

NOW crank the Volume to 7/8/9.
Go back and start turning the tone knobs again. 
If you've never done this,,You will be quite dumbfounded at how little effect the controls now have. (they are almost not working anymore)

THIS is part of the mojo magic of those old valve amps.
Better qualified folk might like to explain the details but from my understanding it's the loading effect of *High Impedance, High volatage* circuits.
From what I've read the *Internal impedances* dramatically fall when the whole circuit is under load. This changes the the *Tone shape* Hence also alters the colour of the distortion produced.
This phonomina happens to all the old valve amps, just very noticable in Marshalls.

Back to SS Emulation; IME You can achive quite stunning results just by a few simple tone tricks using basic SS circuits.
BTW, if it interests you my circuits produce the above mentioned quirk much like a Marshall rig.

Well lets just say I'm *more* than happy.
Phil.

Try a guitar speaker or any full range speaker.
You will have a far better chance of success
Phil.

Hi Enzo,
            Arrh good to know I'm not alone,
I also have spent many times head down bum up inside industrial rubbish bins.

Hi my name is Phil and I am addicted to salvaging every last bit of value from any old VCR/ AudioCassette, you name it if it's got electronics inside it and it's in a bin I just can't help myself.

A chap in Auz put me onto super cheap high voltage Electro caps.
Those use once, throw away cameras have a 80uF/330Volt cap inside them.
Handy for tube circuits.
Most camera shops just throw them in the bin,, if you ask they will gladly hand them over for FREE!! (you will also gain a collection of AA cell Batteries)
Just be warned some caps still have a charge, an they hurt like hell when they bite you!!
I admit I'm speaking from experience, ouch!
(actually it's the first time in 40 ish years I've been bitten by a HV Cap.
My arm pained for a good half hour,,Maybe I'm getting sloppy in my old age)
From King of the junk pile,
Phil.

Just did some quick simulations.
With or without *diodes* the waveform is identical?

With 100k Drain R's the circuit will be asymetrical anyway, So I don't quite get it.
A tad confusing artical to read.

Also all those pedals have Cabsim inbuilt and judging by the clips at *AMT* those cabsims are in use the whole time. I admit it does sound good.
(JCM 800 very nice)

*mensur*,
can I ask, was there a point to this post?
Have I missed the point? LOL.

IMO Any dist will sound more convincing through a good cabsim.

Having built whole Fet preamp circuits with 3SK30A Fets running from 37VDC I will simply say that there not all they are cracked up to be.

The best use I found for Fets was the mu booster type pedal Which I still use BTW.
Cheers Phil.

Hello autir,
               Teemu's book may help to broarden your understanding of these issues.
If I remember he covers the problems you mention.
Well worth the read,, heck it's free mate.
(You can download it here on this site)
Phil.

Whoops.
Oh I see what you mean.
Don't mind me,, carry on.
Phil.

Whould it not be simple to check the wire colour on the *Speaker output socket*?
Tip is usually the hot +positive wire.
Phil.

Hi autir,
               It's called a *Case* or grounded Metal chassis.
Phil.

Use a bigger value pot.  Durh!!!  it should be obvious.
BTW, You just got the best answer you could ask for from JMFahey,,, now if you want to spend the next mindnumbing 4 years
at teck colledge just to get the maths sorted then go for it mate,,,
Meantime 5 minutes work to swap out a couple of pots will tell you the right value.

In the case of your situation  ( I Assume ?*)   You are taliking about a  * Master Volume for a *PowerAmp module*?
Then most are not ever high enough Imp to cause concern.
So take a 100k pot and don't concern yourself with trivia maths that is niether here nor there.
Phil.

Quote from: E on March 24, 2010, 01:19:29 PM
Home etched PCBs are great, but they can take a lot of time and indeed money. You could also use perfboard, which done well can be almost as good (and it doesn't make a difference to the finished product) or even wire wrapping (i think it has a better name, just can't think of it at the moment), which can actually be used as a permanent solution while still allowing you to quickly fix any mistakes.

http://www.stevechamberlin.com/cpu/about/

But yeah, if you use perfboard or PCB then it's usually an idea to try it out on a breadboard first. Not entirely sure how to lay it out, i could do with a bit of help in that area too.

Hi E,
        Just get a breadboard and start building simple circuits. With Opamps it's hard to blow them up even if you wire it wrong,,, the beauty of working with low voltage devices
Some of the more exotic circuits can go fut but by the time you start messing with them you will have learnt enough to know how to avoid disasters.

I just finished building a *Zombie Chorus Pedal* .
I built and tested 3 different circuits in a very short time to see which ones worked and which ones where just trouble.
The *John Hollis* one worked straight up and only needed minimal tweaking.   Only took a week ,, thanks to the use of BB 
Have fun with it, Phil.

Quote from: heineken on March 25, 2010, 09:11:13 PM
okay. sourcing a new transformer as we speak.
If I wanted to have a clean channel as well as a gain channel, can I do this with one LM3886 Stereo kit? Seems like I should be able to, but I've been wrong before.
and I believe I've read before you could take most overdrive/distortion pedal schematics and turn them into a preamp? I was thinking either a Krank distortus maximus or the Dr. Boogey as my high gain channel, both of which I've found the schematics and veroboard layouts. do you need to make any major adjustments to them? I'm sure it's probably already been covered somewhere in this forum, I hate coming along late in the game.

Hi heineken,
                    You can have multiple preamps with only 1 Poweramp, You just have to sort out how you want to switch between the channels.
Unless you are a relay building guru building such circuits can really slow progress.

IME, it's a lot easier to have a totally seperate unit for preamp/s as that can be a self contained floor unit seperate from PowerAmp.
My reasoning is simple,  any channel switching can be done with direct (mechanical) switching which makes design simple.
(Of all the amps I've repaired more than 50% of issues are in relay type circuits that switch something via a remote pedal.
This fancy relay circuitry is only needed because ALL the controls are in the Amp,,,
Soooo if all the preamps are on the floor unit and most poweramp unit don't need any controllers then why make life hard. 
Just build all the preamps and switching arrangements inside one dedicated floor unit.

Yes a lot of pedal circuits can/are built into a preamp circuitry But I strongly advise you to Bread board test it all first.
It took me a few years of frustration and failed circuits before I caught onto the realisation that no matter how simple some of these
mix an match may look,,,,.a LOT them will no doubt  be a waste of solder and time. Hint trust me I've been doing this for over 30 years.

Of all the stuff I've built (seemed like a fantastic to good to be true circuit at the time) only about 5 circuits have been seriously useful.
Does that make Me a bad designer,, or am I just refusing to except crap circuits? LOL

Poweramps (especially chip ones) there is not much to tweak and most of them don't colour the tone greatly
BUT with all Preamps there are just so many different ways to effect a change to Tone/ Dist/ OD/ Crunch.
So when you read the blab on some of these sites with schematics and build instructions be warned you are taking on someone else's opinion
of what constitutes a fantastic sound.
And will it work with your Guitar /Amp / Speaker /musical style. 
In my experience ,,it's a big gamble to etch a board,, build it ,,,and have it all magically come together.
but it's possible no doubt.
I've got a whole bottom draw chock full of dud PCB's that will end up as land fill no doubt.

It's rewarding long term but you do need to have the patience  when things don't go as planed.
Phil.

The white wire would normally go to the other end of trans Pri?

Coming from the black mains wire through switch> turns into Yellow wire which runs through Thermal sensor back to FUSE>
The Fuse > (left side is Yellow wire)
From the *righthand side* of fuse follow the tracks back Through to the transformer,,
which WILL ulltimately leed back to the *White wire in power cord*

You need a pen and paper drawing the circuit as you go untill you arrive at the trans windings
\which looks like it maybe blue and black Going Down through the hole.

( I guess the other 3 wires comeing up *Red- Red/Yellow stripe-  Red* are the *Secondary* wires.)

Don't assume anything,, Visual checking as well as using the continuity testing.
Don't concern yourself to much with blue things,, likely mains suppression caps,, usually wired across the primary switch.
You need to develop the ability to work from schematics ,, not just rely on ever changing colour coding on some obscure PCB.
Phil.

Quote from: J M Fahey on March 23, 2010, 01:08:01 AM
For design work I have used for the last 40 years the original, 1920 technology breadboard, that's to say a piece of wood with some nails and bare copper wire ground, +B and -B lines.
In fact I use brass wire for its stiffness and nobility.
The cost is nil, I can have as many as I want, but the *REAL* advantege is that parts are *soldered* and firm.
Of course I don't cut parts legs and they are reusable.
The technique is strong enough as to survive onstage (for 1 night testing, not for touring)
I like protoboards for IC work, problem is that I'm halfway through a project and I must rush to buy another for a new one.
I have a shelf with a few of them, with unfinished experiments; so the wood and nail breadboard ends up being the preferred embodiment.

I might have guessed,, LOL.
The story reads like a mad professor movie,, all that is missing is those big *Knife switches* hanging off the wall, humming with electrons waiting to leap out when the switch is thrown.
I did read of a chap who builds with the dead bug assy,,, all components upside down using an unetched PCB  as a ground plane and 10 meg R's as stand offs.
I guess  as long as we all have fun in the end.
Phil.

Quote from: Minion on March 22, 2010, 06:35:12 PM

Quote from: phatt on March 22, 2010, 08:49:37 AM

Quote from: Minion on March 21, 2010, 12:59:27 PM
I personally built my First circuits by designing and etching my own PCB"s which is a great thing to learn if you plan on building a lot of your own Custom projects but it is an art within it"s self ........ There are several free PCB design programs out there and tutorials on how to etch your own PCB"s then all you need is to know how to read a schematic and a Datasheet properly and you can start .....


Cheers

Yep I did that for a while ,,,till I realised it was painfully slow.
A bread board makes lite work of it all as you can quickly weed out all the hickups and worms.
THEN commit to PCB.
Phil.

I found the opposite to be true for me, I made far more mistakes when breadboarding than when PCB designing (I have a hard time adjusting from looking at the top of the board to the bottom of the board , the mirror image thing really screws with my Dislexia ) and I found I could design and etch a PCB in no time at all and end up with a better looking product .....

But I know a lot of poeple who swear by them so 2 each his own ....

Cheers

Kool mate,    Phil.

Hi Zappa,
Chassis is ground ,,no use measuring that
What ever colour wires come from the power cord and which also run to the Power Tr's *Primary* winding.
Measure the mains voltage on those two wires,, Remember this is the mains supply side which can kill!!

*With power off and unplugged* A visual Check for fuse, Pwr switch and *Earth to Chassis*
Ground/Earth is normally Green or green /yellow,,, so obviously the other two wires will have AC mains potential between them.
While the powers off follow the continuity tests already mentioned.
Phil.