Adapting the Wampler Basic Overdrive

[timkenyon]

@antonis - You got me this far

[PRR]

Some times I feel like a useless member..

The original schematic had two errors, at least.

Every "do this!" seems to add another error. And at this point I don't know what plan is "newest".

We all want to be helpful but sometimes the OP should desk-check before posting.

[antonis]

@timkenyon:

1. We always bias non-inverting input (+)..
Connecting V_BIAS to non-inverting input via a high value resistor is only necessary for non-inverting configuration..
(when signal comes into non-inverting pin)

2. We always connect NFB loop to inverting input (-)..
(unless we want some kind of oscillator..)

The above said, could you plz make a final schematic..??
(in which we might deal with items values and not proper arrangement..)

[WoundUp]

Brian and those vids are the main reason I started buying stuff to try and build them for myself. I just, wish I knew enough to understand what you guys are talking about lol. Or what Brian is talking about most of the time.

His latest vid on the Bluesbreaker pedal is another that easily goes over my head when he starts getting technical.

[ThermionicScott]

Some times I feel like a useless member..

I feel like that at work sometimes... I'll try to diagnose a software problem, and due to my chatty nature, the process of following a couple dead ends on the way to the actual root cause and solution is very visible.  Don't sweat it.   

[timkenyon]

As requested - here is the updated schematic:

@PRR - the reason I'm posting schematics is (a) I am not experienced in this stuff and need the feedback to learn, (b) I have no facility (prototyping materials) to desk check, and (c) I get wicked tunnel vision on a project and need other pairs of eyes to spot errors.  These are all things that are in progress.

[duck_arse]

the cap before the tone pot is shown backwards.

antonis - you put 47uF across the bias pot wiper. why so much?

[timkenyon]

The cap before the tone is backwards on the original schematic, so it was copied over.  I've seen other similar schematics with a non-electrolytic cap, so I would check this out in prototyping.

[PRR]

.....I have no facility (prototyping materials) to desk check....

Sorry. I'm dating myself.

"Desk check" is for computers when computer time was EXPENSIVE. Pencil and paper, go through the code and check what the computer would do at every step.

https://www.techopedia.com/definition/18825/desk-check
https://en.wikipedia.org/wiki/Rubber_duck_debugging

Circuits are really more complicated. But still you could see that in the Reply #25 plan, the opamp output is probably now following the BIAS voltage (finally) and so is about midway up a positive supply. The output network must sit very close to zero. Then the DC voltage on C6 is positive to the left. Is that what the drawing says?

When computer time was $10/minute, or if working large power systems with $1000 caps, an hour of desk-check could save much more than an hour's worth of desk time.

[antonis]

antonis - you put 47uF across the bias pot wiper. why so much?

No particular reason..

Just followed "original" design value for Vref..

P.S.
IMHO, it should be of much higher value 'cause of pot potentially extreme setting but let it be..

[timkenyon]

@PRR - I can confirm that the original schematic I followed (from which this is derived) does have C6 oriented the way I have it here.  I've also seen overdrives where this capacitor is non-electrolytic to the same value.

@antonis - I'll start with a 47uF capacitor in that spot with the potentiometer and change its value upwards and see what happens once the stuff I intend to order for breadboarding finally arrives.

Thank you all, again, for the patience and the input.

[antonis]

I'll start with a 47uF capacitor in that spot with the potentiometer and change its value upwards and see what happens once the stuff I intend to order for breadboarding finally arrives.

So far as V_BIAS is only involved in TL082 bias, you can even omit it..

To be honest, 47μF cap value isn't our primary problem here..
(I'd dare to say, not even a secondary one..)

[timkenyon]

Ummm... ok - what is the primary problem?

[antonis]

Hmmmm... Let's say we've already mentioned it..

The above said, could you plz make a final schematic..??
(in which we might deal with items values and not proper arrangement..)

[timkenyon]

Check post 23 - that's the most up to date schematic I have, there have been no revisions since.

[antonis]

In which C6 insists to be reversed placed... 

[timkenyon]

I have replied previously on this thread that this is how the capacitor is drawn in the original diagram.  There are also schematics of other OD/Dist pedals I've seen with a non-electrolytic capacitor of the same size in this position.  I have also stated that this would be something tested out on breadboards.

You're honestly telling me that folx can't look past it being the wrong way around?

[antonis]

You're honestly telling me that folx can't look past it being the wrong way around?

I'm trying to tell you that it's more plain & easy to talk about any particular FINAL schematic..
(or else, we could maintain your initial one and keep in mind any changes suggested and oraly verified..)

[timkenyon]

I'm not someone who copes well with insinuation or hints as I tend to miss them or misunderstand - so my preference is for directness, even to the point of blunt honesty.

In that spirit - post 25 (and now 36) contained the most up to date schematic I have for the pedal [the only difference being the orientation of C6].  Whether or not this is the *final* version depends entirely on how the rest of the replies on this thread goes.

[duck_arse]

I'm not someone who copes well with insinuation or hints as I tend to miss them or misunderstand - so my preference is for directness, even to the point of blunt honesty.

In that spirit - post 25 (and now 36) contained the most up to date schematic I have for the pedal [the only difference being the orientation of C6].  Whether or not this is the *final* version depends entirely on how the rest of the replies on this thread goes.

in that spirit, follow the volts, and not the mistakes. your bias divider pot sets a bias voltage, more positive than ground by X.XX volts, and that 1M [image too small for squints] resistor applies that voltage to the (+) non-inverting input of the opamp. the opamp will do what it's told, and follow that voltage through to its output. so now the output pin is also sitting some amount of volts more positive than ground.

now connect your capacitor, say it is un-polarised, non-polar, direction doesn't matter. the opamp end of the cap is, as stated, some volts above ground. the other, outer end of the cap, you can follow, has a direct DC path through the tone pot, etc, until it can see ground itself, that is 0 volts, that is 0 volts above ground. so one end of the cap is more positive than ground, and the other end is effectively ground.

now replace the not polarised cap with a polarised one, which wants the (+) terminal to the more positive voltage, relative to its (-) end.

you can do this on the bench, and simply measure the voltage either end of C6, but we can tell you now what you will find.