madbeanpedals::forum

Projects => General Questions => Topic started by: SirEgno on October 02, 2020, 06:58:23 AM

Title: Need help with zener diode
Post by: SirEgno on October 02, 2020, 06:58:23 AM
Hi all,
I'm building a preamp pedal based on sunn O))) beta bass.
My idea is to use different input voltage (9 or 18v), so I'm planning to use this schematic as "power section":
(https://i.postimg.cc/3WHzmzsJ/PSU.png) (https://postimg.cc/3WHzmzsJ)

I tested the circuit without any chip, and with 18v input the DMM shows 17,8 volts.
Am I doing something wrong?
Title: Re: Need help with zener diode
Post by: cooder on October 02, 2020, 07:48:22 AM
Where did you source the zener diode? I think I recently had some funky ones from Tayda... ordering those values form Mouser now.
Title: Re: Need help with zener diode
Post by: SirEgno on October 02, 2020, 06:48:39 PM
I bought them from musikding.
Is there a way to test a zener diode?
Title: Re: Need help with zener diode
Post by: Scruffie on October 02, 2020, 07:39:56 PM
CLR, a zener isn't a regulator.
Title: Re: Need help with zener diode
Post by: SirEgno on October 02, 2020, 09:45:12 PM
I don't remember the source, but I read that the 5817 should act as a resistor.
in fact the DMM shows about 50 ohms. Is it not correct?

I've seen this schematic used in many project. That's why I omitted the CLR.
Title: Re: Need help with zener diode
Post by: cooder on October 02, 2020, 10:01:54 PM
Quote from: SirEgno on October 02, 2020, 09:45:12 PM
I don't remember the source, but I read that the 5817 should act as a resistor.
in fact the DMM shows about 50 ohms. Is it not correct?

I've seen this schematic used in many project. That's why I omitted the CLR.
It certainly has a bit of voltage drop that matches what you read with DMM.
Title: Re: Need help with zener diode
Post by: Scruffie on October 02, 2020, 10:36:24 PM
They do act as a resistor... under the right conditions, the resistance will vary with voltage and current across it.
Title: Re: Need help with zener diode
Post by: SirEgno on October 04, 2020, 06:07:31 PM
Got it. the zener is not the best solution, better a 7815 and "passa la paura".
BUT... I have only one 7815 and it doesn't work. It became hot and in output I measure 0.peanuts volts.