Duocast is doing Weird Sounds - Video

[Thomasyoung]

Hi All,

Really wanted to have your help on this issue with my Duocast, is doing weird sounds with the volume pots at noon, already tried to change the transistors but the problem stays the same.

Here is a video and a picture for better understanding and hopefully someone can help me to cross check the problem.

Thank you very much
Best Regards
Nuno

 

[Thomasyoung]

The AC125 has a maximum voltage rating of 32v. The LT1054 has a maximum voltage rating of 15v.

So what should I change ?

 

[chris.knudson]

Nothing. The transistor can handle the voltage, and the IC would have already fried if you put more than 15 volts across it.

 

[Thomasyoung]

Nothing. The transistor can handle the voltage, and the IC would have already fried if you put more than 15 volts across it.

Ok but the IC LT1054 is on build documentation from PedalPCB.
Could you point me one that will works?
Thank you

 

[chris.knudson]

Yeah, that's what I'm saying -- you're not putting that much voltage across it. Even though your circuit has 27 volts on it, the IC isn't seeing that voltage.

 

[Harry Klippton]

That IC is the charge pump. It's putting out 27v. You don't power it with 27v

 

[chris.knudson]

What voltage are you powering the pedal with?

 

[chris.knudson]

Could you point me one that will works?

The LT1054 is fine.

 

[Erik S]

Took a quick look at mine compared to your photo. Didn’t spot any value differences, but I do have my trim pots set much higher. Does it sound any better if you crank those up?

 

[Thomasyoung]

What voltage are you powering the pedal with?

With a standalone 9V power supply, connected only with this pedal
This one: https://fuzzmonster.dk/en/shop/acce...diago-micropower9-9v-dc-1000-ma-power-supply/

Took a quick look at mine compared to your photo. Didn’t spot any value differences, but I do have my trim pots set much higher. Does it sound any better if you crank those up?

Thanks Eric: If I turn the trim pots higher is even worst, normaly I keep then in the middle, but already tried several combinations.
The thing is the weird sound only happens at 27V and when the Low level is set at noon (11h/13h), and the Gain and low cut above 12 O`Clock.

This issue is drive me crazy, I am almost start to disassembled the transformer (Jumper from 1 to 6) and some components to see if I can found what is happening. Already take off the socket from Germanium transistor and solder directly on the board but nothing.

If someone can help me will be so great
Thanks for all the comments and support that you´re providing.

 

[chris.knudson]

With a standalone 9V power supply, connected only with this pedal

Then the LT1054 is fine -- I wouldn't power it at 18v though. It has an operating range of 3.5v-15v.

 

[Thomasyoung]

Hi @hamerfan @Harry Klippton @MichaelW @KR Sound @music6000 @chris.knudson

Problem solved by myself, but thank you for all your comments trying to help me.

I was working on this issue for 1 Week and half, and for somehow I tested the pedal with many different power suplies and even 9V bataries.

One of my old 9V bateries the pedal didn´t do this weird sound, only new bateries OR Power Supplies, so I tried to add a 470Ohm resistor on +DC and the sound only do at 3Óclock só added a 1K resistor and Voilá this weird sound disappeared, I was so happy, I think this happens with some old fuzzes that the circuit add a 470Ohm resistor. In this case was a 1K resistor. I think the problem is that the pedal was feeding to much mA on DC.

Solution attached