The Velvet Glove Experiment

[will queue for free stuff]

The Velvet Glove is the working name of a circuit I have "cabbaged" together.
(The name is a contraction of an old expression....an iron fist in a velvet glove).
There are two reasons I have assembled these pieces.
One, it has many elements that are popular, and will generate interest.....when it's
finished I hope it will be a unique and chunky overdrive, with a reliable octave up effect.
Two, I am not yet to the point where I can take snippets of circuits I like, and
successfully integrate them. By posting this experiment I hope that others in the same position
as well as myself can benefit by getting advise from more experienced builders.
To the schematic.......

The first thing I should do before I go any further is thank those people whose circuits I am
borrowing heavily from.
Firstly, B Tremblay from Runoffgroove. The first section here is from the tube reamer, a simplified version of the tube screamer
runoffgroove developed.
Secondly, the octave up effect is from the Foxx tone machine. Not sure who to thank for that one.......J D Sleep?  Thanks JD.
Thirdly, what I have labelled as presence, is the work of Jack Orman at AMZ.  Thank you sir!
Lastly, the LM386 and Marshall tone stack section is lifted from the Krank Distortus Maximus layout in the Gallery.
So thanks to Magnus Nordbye and Aron Nelson.
THE EXPERIMENT.
  I haven't breadboarded this circuit and I'll try to refrain from doing so
until all changes are made on paper.  The idea is to work out the circuit using
mathematics and experience and learn along the way.
Here's hoping it works!

So the first question is this; will the octave up section of the circuit work?
Secondly, how is this circuit properly coupled together?
By that I mean, what logical steps should be taken to assemble the circuit?
Thanks to any and all that are willing to help out.

[Perrow]

I have very little knowledge and experience with building and designing electronics, but I've read somewhere else about unused op amps (or part of op amps) and I think this will be an interesting read.

Anyway, it looks like an ambitious project, good luck.

[will queue for free stuff]

Perrow,
Thanks, that's a start.  A good link too.
I'm not sure it applies in this case though.......
Anyone else with more experience with the TL074 care to weigh in?
Craig.

[Earthscum]

not sure about the intent with D4, but as it is, it is reverse biased, and would need a large signal to turn it on... reason being that the cathode is connected to your voltage reference, while your anode is connected to your ground, through the 100k resistor.

Also, your voltage reference on the first OP amp should have some kind of resistor.

So, looking at the FTM section, take it out. I would try something based more around Gus Smalley's Octave Up Sick Box or something like this. It's a better start than trying to convert something like the Tone Machine to work with OPAmps.

[will queue for free stuff]

David said,

your voltage reference on the first OP amp should have some kind of resistor.

Thanks, your absolutely right!
I rechecked my notes and there should be a 1M resistor in there.

not sure about the intent with D4

The intention was to isolate the octave up rather than have it bleed back into the circuit.
I have to say I always second guess myself with the orientation of diodes.
That being said, I like the 'something like this'.
It would easily be integrated with the unused portion of the IC.
Thanks for taking the time.
Really good stuff.

[amptramp]

R5 and C5 should move form the op amp output to the inverting input.  Looks like the same story with R11 and C9.  I haven't seen anything else, but this is just from a quick glance.

[will queue for free stuff]

Thanks Ron,
Could you explain why these components are better located on the inverted input side?
While I know they act as filters, is it critical they filter the signal after the feedback matrix?

By the way, my intention is to redraw the schematic regularly with the changes that have been discussed

Thanks again Ron.

Dave, (Earthscum),  I was just sketching 'something like this'.......
Is this your design?
Can you explain how the circuit works (gets an octave up effect)?

[arawn]

Just a thought, but you may want the tone section before the 386 section. Pasive tone controls have a tendency to kill output! 

[anchovie]

Just a thought, but you may want the tone section before the 386 section. Pasive tone controls have a tendency to kill output! 

The 386 has a massive output signal anyway so that tone stack will actually help attenuate it to a useable range - it is lifted from Krank's commercial pedal after all and I don't think anyone has ever complained that the DM is too quiet!

I would suggest that this circuit does need to go on the breadboard. That 386 has pins 1 and 8 shorted to set it at maximum gain and no amount of mathematics is going to tell you if it will sound good with that front end going into it. It might fizz, squeal or completely destroy all of the tone that you've created before it. Though, if this is the case, you could always replace the jumper with a fizz/squeal/destroy switch!

[earthtonesaudio]

I would suggest learning the basics about op-amps before you proceed.

Once you know the most basic info, learn the "golden rules" of a general purpose (ideal) opamp:
1. The inputs are the same voltage
2. Through the use of feedback, the output does whatever is necessary to ensure #1.

Check out GEOFEX.com and read the stuff about op-amps.  Also I think there's a good tutorial about them on The Tone God's website.


I'm not trying to be patronizing, I just think it's more useful to learn the right way first, rather than explain how to fix the mistakes in the schematic.

[will queue for free stuff]

The Updated schematic:


Alex wrote,

I would suggest learning the basics about op-amps before you proceed.

Once you know the most basic info, learn the "golden rules" of a general purpose (ideal) opamp:
1. The inputs are the same voltage
2. Through the use of feedback, the output does whatever is necessary to ensure #1.

Check out GEOFEX.com and read the stuff about op-amps.  Also I think there's a good tutorial about them on The Tone God's website.


I'm not trying to be patronizing, I just think it's more useful to learn the right way first, rather than explain how to fix the mistakes in the schematic.

Your point is well taken.
However, the point of the 'experiment' is to learn this in the context of a circuit that has interesting possibilities.
After all, if I have no intention of pursueing an EE degree at this late point in my life, the only possible motive I
have for learning the basics of op-amps would be to achieve an effect I cannot otherwise.

I haven't taken offence, I understand your point, but I think I'll soldier on.
If it becomes a blog about learning how to patch a circuit together.........so be it.

[earthtonesaudio]

Now, then.  That updated schem is so vastly improved that I think you can disregard my advice and be just fine.   

The only error I see now is that IC2C and D's noninverting inputs should go to VR instead of GND.  Some op-amps can work from the ground rail but not the TL07x series.  Change that and it should work.
One additional suggestion (and it's a minor one) would be to put a cap somewhere between IC2D and IC1.  It should work as drawn but the LM386 will be happier without a positive DC bias at its input.

[DougH]

After all, if I have no intention of pursueing an EE degree at this late point in my life, the only possible motive I
have for learning the basics of op-amps would be to achieve an effect I cannot otherwise.

Since when does spending a few minutes learning how an op amp works equate to "pursuing an EE degree"?!?

If you were installing a shelf you would want to learn how a hammer or screwdriver works, first. Doesn't mean you're "pursuing being a housing contractor".

Saying you don't want to "pursue an EE degree" when confronted with looking up basic info is basically saying, "I can't be bothered with it myself, I want all you 'EEs' to look it up for me and just give me the information."

[will queue for free stuff]

Doug,
Is there anything that I can say here that won't piss you off?
My point was this, necessity is the mother of invention.
In my OP I tried to communicate that I was trying to learn how to assemble a circuit
from various bits and pieces.
I did attempt to say I did not want to be spoon fed.
I am not opposed to reading.
I do however require some context or point of reference
so that what I am reading makes sense.
Apparently you are a fan of Agatha Christie who said, and I'm paraphrasing....
'Necessity is not the mother of intention.....laziness is.'

PS My wife wants to thank you for curing me of any desire to build a stompbox.

[DougH]

If you really want to know how op amps work, here is a good place to start:

http://www.tpub.com/neets/

Take a look at modules 7 and 8.