[millerdog]

Tangent, your tutorial is not like cmoy's article in a neophytes eyes. Using a dual opamp makes the project very simple to construct and complete. Compared to cmoy's schematics, which to me is for the expirienced, your tutorial is childs play.
If I compare your completed board with the one in his article...to a greenpea like me, the differences are obvious. No slight to cmoy in anyway implicated.
I was wondering if building the amp with two separate channels would help me with more difficult projects such as a Gillmore?
We all gotta start somewhere right? Would that be the next step?
md

 

[tangent]

Going with single-channel opamps would help hone your DIY skills, but only because it would force you to think about the layout and such instead of just copying my layout.

If your goal is a practical education in electronics, you'd be better off just taking my parts list and ignoring the Assembly and Tweaks sections of my tutorial.

If you just want to build an amp and have a reasonable chance of getting it to work on first power-up, by all means, follow my tutorial verbatim.

 

[millerdog]

Sir!
Your first sentence answered my question.
I thought I had made it clear that I had already assembled the cmoy via your excellent tutorial.
As a side bar, if I hadn't followed your tutorial, I probably wouldn't have had the faintest clue on where to start on more complicated projects. If I may express myself in the vernacular: You are da man!
I guess now I will attempt the dual channel thingy and try to figure out how to place it on a proto board.
Thanks(or: what have you gotten me into?), Tangent!
md

 

[tangent]

Glad to be of help. But may I suggest that you aspire a little higher? Instead of building a second CMoy just to force yourself to come up with a layout on your own why not try for an upgraded CMoy. How about this:

- Standard CMoy amp circuit, using either a higher-spec dual or a pair of high-spec singles

- Buffered power supply of some sort -- TLE2426, BUF634, etc.

- Bigger caps all 'round. 470uF per side in the power supply at least, and 0.22uF input caps at least (maybe up to 1.0uF).

I mean, you don't want to end up with just a second version of what you already have, do you? Or maybe you do -- here's a second idea: try to cram the stock CMoy circuit down as tight as you can go. My personal record is a 5x22 section of protoboard (measured in holes -- so 0.5" by 2.2"). Others have beaten that record, in particular forum member Sijosae. Go dig up some of his older posts -- they're truly inspriring.

 

[millerdog]

Take it easy Tangent Sensei!
I am having a hard enough time looking at the original design, wondering what is going on. I am going to have to consult my cousin who is an EE.
I read the thread about rolling the op amps...got the Analog Devices kit...now how to get the DIPs?
Buffered power supply? Like the SR70 Blackbird...way over my head!
Caps...okay that I can handle...more storable voltage right?
Luckily I made three proto boards with jumpers in case I ran into problems...caps? I can deal with that. I am a greenpea, but wouldn't boosting the caps at the power supply suck more juice from the battery?
Sheesh!
Now I just gotta make another order at digikey. If you are suggesting tweaks that are not listed on your webpage, perhaps we should start a new thread.....so that others can learn too!
md

 

[tangent]

Quote:

Take it easy Tangent Sensei!

Center your mind, my student. The path to audiophile nirvana lies through the Cmoy and beyond, even unto the mystical lands of Jung and Shockley. Meditate upon this wisdom, child. Aaaaahhhoooooohhhmmmmmmm......

Quote:

I am having a hard enough time looking at the original design

At risk of having you think I'm continuing the mystical nonsense too far...the CMoy is both simple and complex. It took me a couple of months to wrap my head around the interactions among all the parts. Let it come to you in its own time -- ignore what you don't understand now, and latch onto anything that looks like a fact and then investigate it. The pieces will all fall into place one by one until one day it will all snap into place in your mind and you'll start sneering about how trivial the circuit is.

(The irony is, if the CMoy is so trivial, why does it take N months to figure it out?)

Quote:

got the Analog Devices kit...now how to get the DIPs?

One word: BrownDog (or is that two words?)

Quote:

Caps...okay that I can handle...more storable voltage right?

Ummmm, sort of. Capacitors store "charge", like a battery. You can charge them up to a particular voltage, and you can discharge them into a load, giving a particular amperage. The larger the power caps, the bigger the charge reservoir, which keeps the op-amp fed when it needs lots of current quickly. If the battery can't keep up with the op-amp's demands, the power caps start discharging until the battery catches up or the op-amp's demands ease up. Bass is the biggest consumer of current in an amplifier, so larger power caps improve the deepness and tautness of the bass line.

The signal caps (C1 in the amp section) are an entirely different ball game. Best to leave that one until later -- stick with the default value or maybe a bit bigger and just take it on faith that it needs to be there and that it does useful things.

Quote:

wouldn't boosting the caps at the power supply suck more juice from the battery?

When you turn the amp on, the battery does have to put out a lot of current for a short time to charge the power caps up. The bigger the caps, the longer they take to charge up. Then when you turn the amp off, the caps discharge to ground through the power supply's resistor divider. In between these two stages, the caps are just acting as charge reservoirs -- discharging a bit as necessary and charging back up when the load eases. Caps aren't perfectly efficient, of course, but it's not worth worrying about.

The discharge to ground at power off is technically wasteful, but as long as you're not turning the amp on and off a hundred times a day, this loss is also ignorable.

 

[millerdog]

OH you shriveled green white haired big eared sensei!
I understand the caps in the power supply.
Now C1 in the amp section....since those are the line ins...I suppose they are uh..storing the uh..input from the inputs...then sending them out to the opamp.
I know nothing about circuits...why is that grounded through the resistor?
I can see why the outputs have resistors...but why do the inputs have both caps and resistors?
Unless they are there to uh....regulate the inputs...I know nothing of these op amps as you can see.
Tangent/Yoda sensei,
I am beginning to feel the force!
md

 

[tangent]

Okay, you asked for it -- tried to warn you, I did....

The input resistor has one main function, and two side effects. One is to set the input impedance of the amplifier. The lower the input impedance, the harder your source has to work, and the higher it is, the more chance for noise to get into the system. 100K is a reasonable balance between these two. The input resistor needs to be larger than the pot's total resistance, for reasons I'm still not 100% sure of. (It's been explained to me, and I've seen what happens when you violate this rule, but I don't yet understand what's really going on.)

The input resistor also adds a current bias to the op-amp's +IN. With FET input opamps you can ignore this issue. It matters with bipolar-input opamps.

The other side effect is that in combination with C1 it forms a high-pass filter. More on this later.

C1's function is to block DC from getting into your amplifier. (DC cannot pass through a capacitor -- only AC gets through a cap, which is why the caps in the CMoy's DC power supply circuit are "across" the rails, not inline with them.) Your headphones want to amplify signals that are precisely centered around 0V DC -- imagine a sine wave, with 0V DC as 0 on the Y axis, and the sine wave split exactly in half across that 0 line. If there is a DC component within the amplification chain, that sine wave gets shifted up or down. If the shift is bad enough, it can fry your headphones. At best, it just won't sound good.

Now for the unfortunate consequence of adding this cap: a cap inline with a signal followed by a resistor to ground is called a high-pass filter. That means that it passes frequencies that are higher than some cutoff. The filter's cutoff is not sharp -- it rolls off pretty gently. With CMoy's default part values, the filter's "corner frequency" is about 16 Hz, which means that the signal level coming out is -3dB lower than the signal level going in. (If you don't understand how a decibel scale works, now's a good time to go out on the Net and find some good tutorials.) -3dB is an easily audible drop. For trained ears, -1dB is on the edge of audibility -- the filter's -1dB point is 31 Hz, well into the bass audio range. Further, an RC filter like this shifts frequencies around, which "smears" the bass.

If you increase R2 or C1, the corner frequency moves down. You can find the corner frequency with the equation 1/(2*pi*R*C). So, if C1 is 0.47uF and R2 remains at 100K, the corner frequency is about 3.4Hz. Much better.

 

[millerdog]

Sensei, I flunked precal four times...mostly because I never showed up for class..formulae...oh my!
The input resistor is R2.
when you mean not across the rails. you mean there are the resistors between them?
I understand the sine wave and parabola...
I think I need an explanation on corner frequency...I know dbs..they are uh...exponential...whatever..
When you say 16 hz corner freq..is that frequency coming out of the line out? No, that's lame...
Explain rc filter?.
Okay, the caps and resistors are filters.
I wonder why you didn't list C1 at .47uF in the first place. Or even as an alternate. I would have tried it.
md

 

[tangent]

Quote:

when you mean not across the rails. you mean there are the resistors between them?

I'm talking about the power caps, how they go from a rail to ground, vs. being in line with the signal like the input capacitor is. If the power caps were in line with the V- and V+ lines, no current would flow, and no voltage would get through the caps from the battery. Caps block DC voltage, and pass AC voltage.

Quote:

Explain rc filter?.

R = resistor, C = capacitor. This high-pass filter on the CMoy amp's input is an RC filter.

Another try at explaining this:

Imagine that we've constructed a high-pass filter with a "6dB per decade" rolloff below 1kHz. If you pass a 1V 1kHz signal through this filter, it will pass through unscathed. Below 1kHz, signals get attenuated. At a 10x lower frequency -- 100 Hz -- the voltage level has dropped by 6dB. 6dB is a factor of 2, so voltage is now down to 0.5V. Drop frequency by another 10x to 10Hz, and you halve the voltage again -- 0.25V. And at 1Hz, voltage is 0.125V through this filter.

Is this clear?

Quote:

I wonder why you didn't list C1 at .47uF in the first place

All kinds of reasons. One of which is that I didn't want to put a discussion like this one in an article for beginnners.

 

[millerdog]

Okay,
I am beginning to sense what the rc filter is all about. The sad thing is, I have no idea about how to adjust it.
I am(ohoh) assuming that the hz you are talking about is audio?
Okay, if I input uh....1000hz...the voltage drops...how do I compensate?
Up the capacity of the caps? No, that is lame too.... Lower the resistance of the resistors to allow more voltage?
man, i am just guessing
md

 

[tangent]

Do you hear a bass rolloff? If you do, then use that equation to find out how to adjust the filter. If you aren't hearing a bass rolloff, then sit back, and enjoy the amp. It will work perfectly fine with the default part values.