Crowther Hotcake Voltages (WORKING)

[patrick398]

While i'm waiting for a new chip for the Mutron III build i thought i'd throw together a Crowther Hotcake. All fires up and works but doesn't sound great and i have a feeling (perhaps wrongly) that the IC isn't biased correctly. The voltages just look off to me but i defer to someone with a greater knowledge and understanding. All the pots work as they should but it sounds like the circuit can't handle how much gain there is. It sound ok-ish with the gain rolled all the way back but sounds worse and worse as it's increased and with it maxed it's super shitty, spluttery, no sustain, farty nonsense. Only changes to the circuit i've made are two 47nf caps in parallel instead of the 82nf. B50k pot wired backwards instead of C50k and A100k with a 100k resistor wired across it instead of A50k.

https://postimg.org/gallery/3g4nqg3bk/

Here are the pesky voltages:

DC JACK - 9.72
Pin 1: 0.12v
Pin 2: 6.74v
Pin 3: 3.69v
Pin 4: 0.00v
Pin 5: 0.12v
Pin 6: 7.47v
Pin 7: 0.08v
Pin 8: 0.00

Thanks!

[patrick398]

Working off this by the way
http://tagboardeffects.blogspot.co.uk/2012/02/crowther-hotcake.html

[Kipper4]

Go to the
What to do if it doesn't work section please.
We need more info.
What ever chip is in there the voltages look wonky.....
Who knows.
Schematic?
Build substitutions?

[bluebunny]

Are you counting your pins correctly?  Should start with pin 1 top left and proceed counter-clockwise.  Pin 7 is power, so 0.08V is completely wrong (whereas 7.47V looks in a more reasonable ballpark).  Have you made the two tricky track-cuts obscured by the 1M and 82K resistors?

[bluebunny]

Schematic?

This one?



Edit: ignore the relay switching stuff in the bottom-left.

[patrick398]

Sorry i thought i'd covered most of the info but here's the list. Yeah i'm counting Pin one at top left, pin 5 bottom right etc. All track cuts were made, 10 in total. I'm going to go probe around the 220R resistor, not sure why pin 7 isn't getting enough juice

1.Name of the project: Crowther Hotcake

2. Vero Layout: http://tagboardeffects.blogspot.co.uk/2012/02/crowther-hotcake.html
3. Pictures: https://postimg.org/gallery/3g4nqg3bk/

4.Substitutions: Two 47nf caps in parallel instead of 82nf cap. B50k wired backwards instead of C50K. A100k with 100k resistor instead of A50k.

5. Negative Ground.

6. Distortion sounds nasty, especially in higher gain settings. Spluttery, no sustain, unharmonic distortion.

7: IC (TL071) Voltages: See above

Thanks!

[patrick398]

Pin 7 is getting 8.08 not 0.08, can't read my own writing haha

[bluebunny]

Pin 7 is getting 8.08 not 0.08, can't read my own writing haha

That's more like it!   

Hmmm...  "Spluttery"?  Check the 82K/100K voltage divider that supplies V_REF to pin 2 (measure at the junction of the two resistors, or at the top of the 10uF cap).  The voltage at pin 2 looks too high: your signal can only swing less than a volt "upwards", but has room to swing ~6V "downwards".  This will sound like "splutter".

BTW, B50K wired backwards is a no-op.      (B50K is linear.  Backwards linear is still linear.)  You may have meant A50K wired backwards...

[patrick398]

On closer inspection it looks like a may have an 8K2 in there instead of 82K...that would certainly account for a higher voltage eh. I'll whip it out and get a 82K in there pronto. Thanks so much!
Also i think i've confused myself with the pots, i'll double check them too haha
Thanks again 

[patrick398]

MY GOD THAT SOUNDS GOOD!
Thanks so much guys!

[Kipper4]

Can you now post the new voltages for anyone else searching and finding this thread please.
You should be getting around 5v on pins 2,3,6
pin4 0v
Pin7 9v
If I remember right I built this some time ago or a version thereof. Nice mild overdrive right?

[bluebunny]

MY GOD THAT SOUNDS GOOD!

Good news!   

[patrick398]

Absolutely!

DC Jack: 9.72v

IC (TL071)
Pin 1: 0.13v
Pin 2: 4.38v
Pin 3: 2.12v
Pin 4: 0.00v
Pin 5: 0.13v
Pin 6: 4.38v
Pin 7: 8.09v
Pin 8: 0.00v

It's got a really nice range. Gain rolled all the way back has a nice clean sound to it that breaks up slightly when you pick harder. Has really mid OD and fully cranked it's bordering on fuzz. I love it! Just waiting on the C50k pot to arrive, presently a lot of the gain is bunched up in the last 10% of pot rotation.

Thanks again for your help. Theres no way the Mutron III debug is going to be this simple haha

[bluebunny]

I might have to give it a try myself...

Thanks again for your help. Theres no way the Mutron III debug is going to be this simple haha

Let us know exactly when you're tackling this one.  We'll all disappear on vacation...   

[Kipper4]

"Thanks again for your help. Theres no way the Mutron III debug is going to be this simple "

That's as maybe but you won't know until you get power to it Patrick.
Have faith.

[patrick398]

Let us know exactly when you're tackling this one.  We'll all disappear on vacation...   

*Makes solder bridge, burns self with iron...books flight to Acapulco* 

That's as maybe but you won't know until you get power to it Patrick.
Have faith

Sometimes it feels like putting together a jigsaw puzzle where all the pieces fit but the picture's still wrong.

[thermionix]

Okay, time to display my ignorance here.  I see a single opamp, no clipping diodes, where does the dirt come from?  Just overloading the opamp via the feedback loop?  Is that a dumb question?  Would the sound change pretty dramatically between a TL071 and an LM741?

[Katt]

Ok I've never used this forum before and it's very confusing, so bear with me.
I am also following the Tagboard layout for the Crowther Hotcake http://tagboardeffects.blogspot.com.au/2012/02/crowther-hotcake.html
I've built the circuit but all it does currently is oscillate; each pot changes the pitch, my guitar's volume knob also effects the pitch.
I've measured some voltages and I'm getting:
IC (TL071CP)
Pin 1: 0.00V
Pin 2: 0.13V
Pin 3: 0.00V
Pin 4: 0.00V
Pin 5: 0.00V
Pin 6: 0.11V
Pin 7: 0.00V
Pin 8: 0.00V

D1 (8.2V Zener)
Anode: 0.00V
Cathode: 8.29V

Someone please help 
much love

[bluebunny]

Welcome, Katt.

At first, I would say you have no power to your 071.  But you have ~8V at the Zener cathode, and that's the same node as pin 7 - so I'm a bit confused.  Either a typo or it's time for pictures!  Top and bottom please. 

[Katt]

Welcome, Katt.

At first, I would say you have no power to your 071.  But you have ~8V at the Zener cathode, and that's the same node as pin 7 - so I'm a bit confused.  Either a typo or it's time for pictures!  Top and bottom please. 

thanks for the reply. And thanks for pointing that out... it doesn't make sense! It prompted me to retest my IC and I got wildly different results, but the sound has stayed the same. How odd - perhaps I was on the wrong setting of my multimeter.
Pin 1: 0.14V
Pin 2: 4.54V
Pin 3: 4.11V
Pin 4: 0.00V
Pin 5: 0.13V
Pin 6: 4.40V
Pin 7: 8.23V
Pin 8: 4.00V

Here are pics of the board.
https://i.imgur.com/o5YkCIP.jpg front
https://i.imgur.com/o0OUtFM.jpg back

I've also double checked the resistor colour codes to make sure they are the correct values. they seem to be.