A little trouble shooting help needed with my Muff build

[plexi12000]

^^^ yep-- heard that.   i'm gunna have to pull up the board.  there are two caps....where there might be a problem.....that i can't use my audio probe because they are flat/flush down on the PCB.

i'm thinking maybe i shouldn't do that---LOL   might be better to leave some lead exposed, just for situations like this.   Baah!

[Astronaurt]

forgot to ask you Asronaurt....what muff did ya build?

I built mine based off of kitrae's site here:
http://www.kitrae.net/music/big_muff_guts.html#Circuit

which I think has the specs of the '73 Ram's Head?

Added some modifications myself like socket-able diodes and a trimpot in series with each set of diodes to limit current through them(It's fun to dial in, but totally unnecessary), mostly the same circuit as the Triangle though.

[plexi12000]

cool!  love the muff!

[aron]

The audio probe is audio -- just listen to the input section of each stage. Start from the beginning and work your way through the circuit. You will find the problem very quickly. Listen to the base of each stage and see if the signal is being amplified correctly and that it sounds correct.

[plexi12000]

thanks aron--  i put the probe together and been trying it out.  is it normal for some parts of the signal path to be "louder" than others? or does that indicate trouble?

[PRR]

> is it normal for some parts of the signal path to be "louder" than others?

We ultimately want to get from a teeny-tiny guitar signal to a honking-big loudspeaker signal. That can't be done in one stage. That's why most audio boxes are multiple stages.

Like growing trees from seeds. First you get a half-inch sprout, then a 6 inch baby, and so on to a 70 foot tree. If you run a tree nursery you will have trees in all stages. You expect the tree to be bigger in each older row. However if you prune-back for better shape, the trees will be smaller at that point. Still the overall trend should be bigger at most stages.

In audio we DO do some heavy pruning. Clippers and tone controls can cut-down a bunch. But amplifying (growth) stages are so cheap that we soon get signal level back up.

{EDIT- typo}

[plexi12000]

Thanks PRR! --i understand.  -just like the signal in a tube amp!

[rocket8810]

> is it normal for some parts of the signal path to be "louder" than others?

We ultimately want to get from a teeny-tiny guitar signal to a honking-big loudspeaker signal. That can't be done in one stage. That's why most audio boxes are multiple stages.

Like growing trees from seeds. First you get a half-inch sprout, then a 6 inch baby, and so on to a 70 foot tree. If you run a tree nursery you will have trees in all stages. You expect the tree to be bigger in each old row. However if you prune-back for better shape, the trees will be smaller at that point. Still the overall trend should be bigger at most stages.

In audio we DO do some heavy pruning. Clippers and tone controls can cut-down a bunch. But amplifying (growth) stages are so cheap that we soon get signal level back up.

geez paul, i always love the things you and R.G. say in addition to the help you give. but, man this is the best damn thing i've read in a long time. hands down the best way to think about designing and effects.

i printed this up and put it on on work bench along with the commandments and rules R.G. posts periodically.

[PRR]

> man this is the best damn thing i've read in a long time

Hmmm. That's the problem when you "know too much". The basics become so "obvious" that we never mention them.

The main reason we love electronics is "amplification". Many aspects to that (oscillators, computers), all variant Amplifiers.

I wrote a long essay about development of Audio, the Telephone, before and after amplifiers (not forgetting the carbon microphone). Then the power went out, PC crashed. Oh, well, TL;DR.

Seeing the wonders that amplifiers had wrought in speech (call your Mom long-distance, Public Address systems), the guitarist wondered if he could be boosted to be heard in the Big Band.

The acoustic guitarist puts-in say 10 Watts of arm-effort to get 0.1 Watts of air-energy into the room. Such inefficency is common in audio. In fact to get the same 0.1 Watts of sound energy with a loudspeaker we probably need 10 Watts of electrical wiggle.

The standard guitar pickup outputs 0.000,000,1 Watts, 0.1 micro-Watts. (Figuring 0.1 Volts and 100K load.)

We want to *amplify* that microWatt to at least 10 Watts to equal a hard-worked acoustic guitar. And more than that, or it is hardly worth buying and dragging the gear around.

So we want a power gain of about 10 Million. (This can be apportioned as a voltage gain of around 100 and a current gain of about 100,000.)

A single electronic amplifying device has a power gain maybe over 1,000, but by the time we get it all biased-up and coupled-to source and load, maybe only about 100.

So we need about four such devices. (100*100*100= 1 million, a bit shy; 100*100*100*100= 100 million, a bit in excess.) Well-honed 3-stage guitar amps exist-- Fender Champ (Epi Jr). 5-stage designs are also found (5F6a Bassman).

Soon after you get over the thrill of "louder!", you start asking to change the flavor. More bass? Not without more amplification. The benefits justify the cost. The tubes (transistors) don't know bass from treble, so we amplify everything then use passive parts to cut-back the stuff we want less of. (More bass is really treble cut plus amplification.) Then your buddy wants to share your amp, but mixing is usually lossy, so more amplification needed. Then you discover that amplifier overload gives some of the musical emphasis that singers and sax players get naturally when they push their instruments, a rise of overtones which does not happen much on strings. Such overload limits your output, so you want more amplification after a clipper.

That Fender Champ is a good example of a "complete audio system". It takes a very-teeny but very-important signal (your fine fingerings), boosts it up and modifies it to do "useful work" (fill a small room with big sound). Here's a rough listing of the signal levels throughout a Champ, and a picture:

First stage: 0.1V in, 5V out
Tone network: 5V in, 1V out
Second stage: 1V in, 15V out
Power tube: 15V in, 200V out
Transformer: 200V in, 4.5V out


The trend is mostly-up, but sometimes down.

> is it normal for some parts of the signal path to be "louder" than others?

Yes. In a tube amp the end may be *2,000* times bigger than the beginning. Your main amp does the heavy-lifting of boosting the weak pickup signal into a big speaker signal.

When we "add" stuff to the basic guitar amp, such as pedals in front or effects in a loop, we usually do not want THAT much added amplification. But a simple boost/cut tone control typically needs a gain of 10 to make-up tone-control losses. A wide-range Fuzz typically boosts up to 100 times (or more) before brutally cutting-down.