Help with modifying Circuit please

[sonolink]

Of course. Thanks for checking. I've had a few smokey missiles in the past hehe

 

[sonolink]

Hi again,

A quick and dumb question please, as I suspect I wired the pots the wrong way around But before rewiring them I'd like to be sure...
To have an increase in Gain, I should read a decreasing resistance on my DMM as I turn the pot clockwise, right?

So if I look at the pot with the shaft up and the pins looking at me, and I number them 1 to 3 from left to right, I should connect GND to pin 1, and the input and output to the other two pins (in doesn't matter in which order), right?

Ok, that's 2 questions
Cheers
Sono

 

[abbey road d enfer]

To have an increase in Gain, I should read a decreasing resistance on my DMM as I turn the pot clockwise, right? 

Depends where your DMM is connected...

[/quote] So if I look at the pot with the shaft up and the pins looking at me, and I number them 1 to 3 from left to right, I should connect GND to pin 1, [/quote] That's the case with most potentiometers, yes

and the input and output to the other two pins (in doesn't matter in which order), right?
[/quote] It certainly does matter! The wiper is generally the middle pin.

 

[sonolink]

Sorry if I didn't explain myself properly. What I meant to say was:

-if I want an increase in gain I should connect the pot so that I have a decrease in resistance right?

It certainly does matter! The wiper is generally the middle pin.

Ok. I would've thought so and always thought one was the input and the other the output but I've checked several schematics and some places the input on pin2 and others on pin3, and if I connect the DMM terminals to pins 2 and 3 either way around I get the same resistance reading...

I also noticed that on the layout I draw the pots connections differently than on the schem but then again some people count pin numbers left to right and others the opposite way... 

A bit confusing innit??

Cheers
Sono

 

[abbey road d enfer]

Ok. I would've thought so and always thought one was the input and the other the output but I've checked several schematics and some places the input on pin2 and others on pin3, 

You may see input on wiper (pin 2) particularly on some Gibson guitars, but also in some cheap mixers.

and if I connect the DMM terminals to pins 2 and 3 either way around I get the same resistance reading...[/quote] That's correct.

 

[sonolink]

You may see input on wiper (pin 2) particularly on some Gibson guitars, but also in some cheap mixers.

Ok. I'll connect GND to pin1, input to pin 3 and output to the wiper then

Cheers
Sono

 

[sonolink]

I've built a PSU for the little beast. It should be fed with 9V/1A and provide 2 lines of HV (190VDC) and a 6VDC line for Heaters. I get everything ok except that one of the HV lines reads aprox 80VDC instead of 190 like the other one.
Any ideas as why this could happen and where to begin looking?

Thanks a lot
Sono

 

[abbey road d enfer]

I've built a PSU for the little beast. It should be fed with 9V/1A and provide 2 lines of HV (190VDC) and a 6VDC line for Heaters. I get everything ok except that one of the HV lines reads aprox 80VDC instead of 190 like the other one.
Any ideas as why this could happen and where to begin looking?

Do you mean HV1 is lower than HV2? I would think it's normal since HV1 has a 10k resistor in series. If you draw 10mA from this rail, the voltage drops by about 100V.

 

[sonolink]

Mmmm makes sense....but there must be something wrong in my build. When I first built and tested the PSU, before building the pedal, I had 190V on both HV terminals and could adjust more or less voltage with the pot...looking at the schem I thought the problem would be somewhere after the fuse (bad 47uF cap) but what you say also makes sense....but I didn't dream the test readings so this is a bit confusing

This is the original schem:

I'll check the components, solder joints and connections to make sure they're ok and hope that fixes it

Cheers
Sono

 

[abbey road d enfer]

This is the original schem:

Can't read it; way too small.

 

[sonolink]

Sorry. here you go:

 

[abbey road d enfer]

Sorry. here you go:

Clearly, if you have 190V at HVA, you can't have 190V at HVB, unless the current draw is zero.

 

[sonolink]

Ok. I've reflowed some joints and rechecked and now all seems fine except for one thing: when I put my DMM between say HV1 and GND the voltage slowly drops down. If I disconnect the DMM terminals and reconnect them the voltage is back up to 190v and drops down slowly again. This doesn't happen at the Heaters terminal. There a get steady 6V...
This happens with no load.
Is that normal?

Cheers
Sono

 

[abbey road d enfer]

Is that normal?

Yes; check Ohm's law.

 

[sonolink]

Check Ohm's law.

Ok. I'm not very good at this but I'll try
Ohm's Law states V=I*R
So, if Resistance is a constant, voltage is slowly dropping because current is diminishing?
But I still don't know why this happens. Maybe because there is no load connected? But then, why is it not happening on the Heaters terminals?

Cheers
Sono

 

[abbey road d enfer]

Ok. I'm not very good at this but I'll try
Ohm's Law states V=I*R
So, if Resistance is a constant, voltage is slowly dropping because current is diminishing?

The voltage drops, but because there is a capacitor it takes some time; this time is governed by the current draw and the capacitor value.

Maybe because there is no load connected?

When you connect your meter, it draws some current, admittedly very small, so it takes a long time to discharge the capacitor.

But then, why is it not happening on the Heaters terminals?

Because the voltage is regulated.

 

[sonolink]

The voltage drops, but because there is a capacitor it takes some time; this time is governed by the current draw and the capacitor value.

I told you I wasn't very good at this.....
Mmmm I see... I thought that the cap would hold the charge since the circuit is connected but I can see it's a silly thought since that wouldn't be very useful...
So, if the current draw is bigger the cap wil discharge quicker and when completely discharged will just conduct like a wire so to say, until the current draw stops or diminishes, giving it time to recharge.....or something like that?
In other words, because the cap blocks DC it will charge unless there is a current draw?

Because the voltage is regulated.

Of course...the 7806...silly me...

Thanks a lot for your explanations and excuse my inquisitiveness 
I hope I can finish the build this evening

Cheers
Sono

 

[sonolink]

So I finally got some time to get to build this little beast
I plugged it into a sound card (Hi-Z input) but I get a huge steady signal (I haven't heard it, only got a visual on the meter). My guess is I have some bad gnd connection or massive gnd loops. I have shielded all the signal path (well I tried anyway) The shielded cables are the purple and blue ones. They are connected to GND only on one end. Maybe it's not worth shielding ALL the path?


https://postimg.cc/nMBRGbm7

Thanks
Sono

 

[DaveP]

The DC coupled cathode follower is crucial to the best sounding amps as that article will explain....do not change it!

DaveP

 

[sonolink]

The DC coupled cathode follower is crucial to the best sounding amps as that article will explain....do not change it!

DaveP

Sorry, what do you mean? What article?