Shaka tube OD

[m_charles]

Hi there. Been a while but thought I'd give another project a go.
Simple question.

Before I dig into this, can someone confirm for me that this schem is solid (or confirm it if you have built)?

Appreciate the help.
Thank you,
-Charles

[PRR]

How can you doubt Aron, Gus and Rob?

However there is no value given for the Bias pot.

[m_charles]

Haha. Because they are all cursed with being humans.

How can you doubt Aron, Gus and Rob?

However there is no value given for the Bias pot.

Haha. Because they are all cursed with being human.

I believe I saw somewhere that 25k will get the job done. Looking at the circuit it makes sense to me. Just never used tubes before so trying to anticipate problems.

[aron]

10K apparently! Been so long....
https://www.diystompboxes.com/smfforum/index.php?topic=35011.msg245694#msg245694

[willienillie]

Dummy question time.  How is that opamp biased?  (And why isn't it a TL071?)

[swamphorn]

Dummy question time.  How is that opamp biased?  (And why isn't it a TL071?)

The op amp is biased with the 470 kΩ resistor to ground. The circuit runs on a bipolar ~12 V supply. There seems to be no reason to use a TL072 in this schematic, though you might be well-served to add a buffer somewhere between the second stage and the volume control--perhaps between the tone and volume potentiometers. Otherwise the volume control will load the second stage substantially with the wiper of the tone pot away from ground. That said, I haven't tried this circuit myself; maybe the interactivity is part of the design?

[PRR]

TL071 is the same price as TL072, and more likely in your shoe-box. The extra 3mA power is negligible next to the tube's power.

I too thought 10k loading 100k was odd. It may be "the tone!!", or it may be that the 10k could be a 100k and be happy.

[willienillie]

The circuit runs on a bipolar ~12 V supply.

Yeah, duh, bipolar.  I knew there was something simple and obvious that I was overlooking.  Ignore me, carry on, etc.

[m_charles]

We still have one important unanswered question, haha. Anyone built it? How'd it sound? 

[aron]

Hahaha my link that I posted has 2 sound samples.

[amptramp]

If you don't have a capacitor to ground from the bias pot slider, you will get feedback around the first tube stage through the 10K grid resistors.  It may help, it may hinder but it will not be neutral.