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Author Topic: Pedal Hiss?  (Read 560 times)

ddpiax7

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Pedal Hiss?
« on: June 18, 2021, 08:27:58 AM »
Hello all,
Recently I built a cool amp based off of a kit I purchased off of eBay from a place in Florida called Valkits. Great little amp, if you give it a push….it uses a jfet as a buffer amp with signal being taken off the source side, so zero gain, but lower impedance, into a baxandall stack into a tl071, into a tda2030a. I added a jfet preamp using a j201, with a drain voltage of about 6 volts after a 22k resistor with 12 VDC fed from a Milwaukee M12 cordless tool battery! I also added a dc to dc 12 volt to 9 volt Amazon “converter” which is just a regulator, for a source of pedal power. It works and sounds fantastic, but with my pedals ran from the same supply as the amp, I get a constant white noise hiss. You can’t hear it with signal present but it’s really annoying! When I switch pedal power to an independent source, the hiss isn’t there! Any good noise filter suggestions?

Jazz P Bass

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Re: Pedal Hiss?
« Reply #1 on: June 18, 2021, 07:53:23 PM »
https://www.vakits.com/14-watt-single-channel-audio-amplifier-kit-1344
Stupid question: why did you knock down the 12Vdc battery to 9Vdc?

ddpiax7

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Re: Pedal Hiss?
« Reply #2 on: June 20, 2021, 08:11:34 AM »
Not for the amplifier, just for effects pedal power. The amp is still at 12 Vcc

Jazz P Bass

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Re: Pedal Hiss?
« Reply #3 on: June 20, 2021, 09:48:21 AM »
Oh.
But the converter is what is making the pedals hiss?
Not the amp? (with the pedals powered from the converter)

ddpiax7

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Re: Pedal Hiss?
« Reply #4 on: June 21, 2021, 06:58:44 AM »
No, not at all. When I power it from a separate source of 12 vdc there’s no issues. It’s only when they share the common source battery.

Jazz P Bass

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Re: Pedal Hiss?
« Reply #5 on: June 21, 2021, 12:54:48 PM »
I would not think that it's the battery's fault.
More likely it's the dc to dc converter.
Do you have access to a scope to find what frequency the hiss is?

ddpiax7

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Re: Pedal Hiss?
« Reply #6 on: June 24, 2021, 07:07:14 AM »
It’s got nothing to do with the converter, I put it on another 12 vdc battery and the pedals were quiet. I’m going to try a few things, but thanks for the interest!

Pete

phatt

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Re: Pedal Hiss?
« Reply #7 on: June 25, 2021, 02:13:41 AM »
If the Hiss is only present when using the converter then logic tells you there is a very good chance it IS the converter.

Be aware, If it's a Switchmode type DC/DC converter then it's a fair bet that is the source of the noise. In which case it's highly likely the converter is introducing hash as Smode setups are notorious for bleeding HiFeq crap into Audio gear.

If so you may be better off building a simple Analog regulator, i.e. using an LM7809 reg chip.

Also please consider that the explanations you give make sense to you because it's in front of you,,, we are not there so it's often hard to make out what exactly you mean.

Phil.

joecool85

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Re: Pedal Hiss?
« Reply #8 on: June 28, 2021, 10:44:26 AM »
If the Hiss is only present when using the converter then logic tells you there is a very good chance it IS the converter.

Be aware, If it's a Switchmode type DC/DC converter then it's a fair bet that is the source of the noise. In which case it's highly likely the converter is introducing hash as Smode setups are notorious for bleeding HiFeq crap into Audio gear.

If so you may be better off building a simple Analog regulator, i.e. using an LM7809 reg chip.

Also please consider that the explanations you give make sense to you because it's in front of you,,, we are not there so it's often hard to make out what exactly you mean.

Phil.

I agree it is most likely the SMPS (switch mode power supply).  Sometimes you can add some filter caps to remove this noise - it depends how bad it is.  Worst case you can always go with an analog regulator like Phil mentioned - I just hate how inefficient they are.

Here are some good ideas for how to set up your filtering: https://www.we-online.com/web/en/electronic_components/news_pbs/blog_pbcm/blog_detail-worldofelectronics_107484.php
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