Op-amp Big Muff bias question

AndersonCouncil · March 14, 2018, 03:07:26 PM

In building this circuit I accidentally omitted R18, the 820K resistor. It makes sort of a cool gated sound without it so I thought I could put that resistor on a switch. Is there any harm being done to the IC Chip when it's out of the circuit? Is this a viable way to get that gated sound?

Here's the layout i used:

GibsonGM · March 14, 2018, 03:12:37 PM

Nope, switch away! And welcome to the forum.

R18, with R14, are applying a bias voltage to the "+" input pin of the 741. When you lift it, you're basically rectifying your signal, clipping part of it. Hence the gating sound.

AndersonCouncil · March 14, 2018, 05:01:30 PM

Awesome. Thanks for the quick reply!!

antonis · March 15, 2018, 08:00:02 AM

Quote from: GibsonGM on March 14, 2018, 03:12:37 PM
you're basically rectifying your signal, clipping part of it. Hence the gating sound.

SEMI-rectifying, I woud dare to say, Sir..

(or else, you should say "hence the OCTAVE sound"..

P.S.
Just a tease from a 27^oC sunny place to an unkown temp snowstorm..

duck_arse · March 15, 2018, 10:19:47 AM

you could put some different, low values on that switch, might shift your tone around a bit. I'm just posting this, so I can add ......

QuoteP.S.
Just a tease from a 27^oC sunny place to an unkown temp snowstorm..

yeah, me too. [can't remeber the UNIcode for the degrees sign, either.]

BetterOffShred · March 15, 2018, 10:48:52 AM

Unicode! Alt+248

°-°
247°

I am about to build a op-amp BM finally so I may try this switch idea

thanks

GibsonGM · March 15, 2018, 03:37:15 PM

Instead of a switch, you know...you could put a 1 Meg pot, wired as a variable resistor! Then you could dial in your own bias setting!

27C? Where I live, it is often more like -27C

But it is a lot of fun in summer!

antonis · March 16, 2018, 06:54:42 AM

Quote from: GibsonGM link=topic=119892.msg1120800#msVDCg1120800 date=1521142635
27C? Where I live, it is often more like -27C

<spam on>
So you don't have to spend money for power devices big cooling ribs/fins..

<spam off>

About Pot variable bias..
I made it once upon a time (but for an FET Gate bias) and worked very well as a distortion Pot alone with cascaded FET amp..
(but awfully with following phase splitter + octave modulator..)

GibsonGM · March 16, 2018, 07:18:46 AM

Cooling is not a problem in the US Northeast, Antonis! No heat sink required.

I have to be careful or my beer will freeze...

Now I want Anderson to replace his resistor with a pot, and make a sound sample!

PRR · March 17, 2018, 01:28:22 AM

> But it is a lot of fun in summer!

Both weeks.

> Cooling is not a problem in the US Northeast

No; but I put in A/C anyway. Lot of people on the coast do. So much that they had to bodge and finally upgrade the distribution power to the island; too much summer A/C load. So much that for a while they ran turbo-generators just for a few days each summer. It gets pretty damp. "Wet bias".

GibsonGM · March 17, 2018, 09:08:26 AM

Best 2 weeks of the year, Paul, you know it. If it wasn't, the black flies would stay home. And just enough time to get the wood in for next year...

So the AC is just for humidity? It's never hot or humid enough in the mountains to miss having it. 2 days of 90, when we go down to the river. Other than that, the ever-present wind takes care of any overheating issues

duck_arse · March 17, 2018, 09:49:29 AM

Quote from: GibsonGM on March 15, 2018, 03:37:15 PM
Instead of a switch, you know...you could put a 1 Meg pot, wired as a variable resistor! Then you could dial in your own bias setting!

27C? Where I live, it is often more like -27C But it is a lot of fun in summer!

we are having 39 metric UNIalt+248's tomoz. also, alt+248 don't work here. control-shift-u00b0, like this °.

bluebunny · March 18, 2018, 07:53:02 AM

Quote from: duck_arse on March 17, 2018, 09:49:29 AM
we are having 39 metric UNIalt+248's tomoz. also, alt+248 don't work here. control-shift-u00b0, like this °.

I just use superscript "o". Works like a charm. It's 0^o here right now with a couple inches of the white stuff, so in usual UK style, the world will freakin' stop.

EBK · March 18, 2018, 11:17:20 AM

Quote from: bluebunny on March 18, 2018, 07:53:02 AM
Quote from: duck_arse on March 17, 2018, 09:49:29 AM
we are having 39 metric UNIalt+248's tomoz. also, alt+248 don't work here. control-shift-u00b0, like this °.

I just use superscript "o". Works like a charm. It's 0^o here right now with a couple inches of the white stuff, so in usual UK style, the world will freakin' stop.

Here we just put 'F' after all our temperatures once we figure out how to type the degree symbol. Even an abbreviated expletive helps to vent the frustration. It's 44

°

F

here right now. See, I feel better already.

GibsonGM · March 18, 2018, 11:38:58 AM

Yes, such as "It was 6F this morning, and is 18F now. Lovely March we're having..."

PRR · March 18, 2018, 10:14:01 PM

I had 69F on the porch today.

In a plastic bottle in the sun. (The LCD thermo needs a damp-shield, that porch gets 20 minutes sun at most.)

In the shade scarcely 26F. That plus sun let the snow soften to re-freeze even harder. The 105 pound dog is walking on top.

duck_arse · March 19, 2018, 09:43:39 AM

the temp here has plummeted today, we only had 30 of the metric degrees. brrrrr.

also - big muff, opamps, and bias.

antonis · March 19, 2018, 09:51:27 AM

You insist to ignore Marc's suggestion for superscript degrees symbol, despite CGS/MKSA/SI or whatever system, Stephen..!!
(it isn't very polite, don't you think..??)

duck_arse · March 19, 2018, 09:55:54 AM

I don't think the foreigners will understand them, antonis. watch:

°°°°°°°° °°°°°°°° °°°°°°°° °°°°°°

there, 30 degrees.

vigilante397 · March 19, 2018, 09:56:30 AM

It's been about 40° F in the morning when I head out for work, but by the time I get home it's usually 75° F with a nice breeze

I'll enjoy it while I can, as in a month or two the Mojave desert will be reminding me what's what.

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Op-amp Big Muff bias question