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Class D Switching Power Amplifiers and Power D/A conversion

Problem with TPA3118 module and its preamp
Problem with TPA3118 module and its preamp
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Old 11th November 2018, 04:28 AM   #1
elrengofa is offline elrengofa  Argentina
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Join Date: Nov 2008
Default Problem with TPA3118 module and its preamp

Hi, i'm Facundo from Argentina.
I'm trying to make a small guitar head using a tpa3118 sanwu module, using a simple circuit as a preamp.

I've already tested the module with other sources of sound like differents guitar stompboxes or floor multieffects (like line 6 hd500, fractal ax8, axe fx rack unit, etc). All theese units worked flawless

But when i use an analog preamp, like a fetzervalve from runoffgroove if i hit hard the strings of my guitar, the class d module gets into protection (it makes a hard and loud "click" per second)
http://www.runoffgroove.com/fetzervalve.html

i'm thinking that may be there is a problem with the input signal of the class d module. So, i've removed one SMD resistor, to let the input gain in 20db. It worked a little bit better, but still have the "protection" issue.

i'm using the same power source, a notebook charger, 24v 4A for the preamp and class d module.

What i am doing bad?

The preamp sounds gorgeous, i love it, but i cant trust on it if i have to "play softly"
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Old 11th November 2018, 07:49 AM   #2
FauxFrench is online now FauxFrench  France
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Location: The mountains, calm and quiet.
It seems you are having too much input signal to the TPA3118 amplifier module. A guitar has got a huge dynamic range.
You may try to put a volume potentiometer in-between the pre-amp and the TPA3118 module. I know very little about use with guitars and perhaps it is normal to use a dynamic limiter to remove the worst transients.
Voltwide seems to know a lot about the use of guitars with TPA3118 amplifiers.

Last edited by FauxFrench; 11th November 2018 at 07:54 AM.
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Old 11th November 2018, 10:30 AM   #3
voltwide is offline voltwide  Ireland
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You'd better insert a soft limiter between pre-amp and TPA3116 input. You may have a look at this thread

the trAmp - my latest and smallest guitar amp
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Old 11th November 2018, 06:58 PM   #4
StevieF is offline StevieF  India
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That looks very nice voltwide. I've not used an analog based preamp into my tpa3118 yet, havent had any trouble with a zoom multieffect unit so far. I did make the gain selectable via a toggle switch between ~25db & 30dB range, no hiss related issues after that mod.

These work nicely for me into an 4ohm speaker of 40W, i power the tpa with 12V 2A, it gets loud for practice. It sounded much better after changing the smd electrolytic caps to a higher value & voltage rating.
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Old 11th November 2018, 08:30 PM   #5
voltwide is offline voltwide  Ireland
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I am playing now DIY guitar amps fitted with TPA3118 for several years on stage and on rehearsal. On stage I use a Celestion Century 12 inch neodriver - all in all there is enough power to play with a real drummer.
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Old 18th January 2019, 02:21 PM   #6
elrengofa is offline elrengofa  Argentina
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Join Date: Nov 2008
sorry for late response.
i've made some corrections to my preamp.
The fetzer valve is still being feeded with 24v, but i put a buffer with a tl071 working at 9v via a LM7809. That enhanced the problem when i remove the SMD resistor on the power amp board. It's nearly solved. If i use the board as it comes (around 34dB input gain) still get the "click" protection sound.
its weird because i've made one time ago and that problem was not there. So... mistery

Thanks for all your answers! and sorry for my English
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Old 18th January 2019, 04:06 PM   #7
voltwide is offline voltwide  Ireland
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How many ohms does your speaker have?
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tuby or not tuby, that is here the question!
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Old 18th January 2019, 04:08 PM   #8
elrengofa is offline elrengofa  Argentina
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Ive tried with 8 and 4 ohms!
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Old 22nd January 2019, 01:44 AM   #9
elrengofa is offline elrengofa  Argentina
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Join Date: Nov 2008
i'm still having the "protection" or clicking problem. If i remove the 100k SMD resistor the problem goes away, but just because of the change in the input gain settings.
i just dont understand why is this happening.
i'll try with another preamp. But didn't expect any changes... im just stuck there
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Old 22nd January 2019, 01:07 PM   #10
FauxFrench is online now FauxFrench  France
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Join Date: Dec 2017
Location: The mountains, calm and quiet.
Quote:
Originally Posted by elrengofa View Post
i'm still having the "protection" or clicking problem. If i remove the 100k SMD resistor the problem goes away, but just because of the change in the input gain settings.
i just dont understand why is this happening.
i'll try with another preamp. But didn't expect any changes... im just stuck there
Section 7.3.4 of the TPA3116D2 datasheet mentions power limitation and may be relevant for this case. Can you see if such a power limitation has been implemented? Check if the PLIMIT-pin (pin 6) is directly connected to the GVDD-pin (pin 7) or if if the PLIMIT-pin has a voltage lower than the GVDD-pin. Next, check if the PLIMIT-pin is well decoupled to ground by at least 1uF. If this decoupling is missing, a temporary spike may cause the “clicking”.

The correct functioning of a TPA3116 amplifier is described by that it can provide a rather distortion-free sine-wave of about 1KHz, with nominal output loading, at the output until the supply rail causes “clipping”. Such can be tested if you have access to an oscilloscope. The problem with the present setup is that we do not know if the problem relate to the TPA3116 amplifier or the “fetzer-valve” (the first time I have heard that word).

It seems likely that a 24V feed “fetzer-valve” (a single-FET amplification stage) can saturate the input of the TPA3116 amplifier. As a simple experiment, try to connect two 1N4148 diodes, coupled in anti-parallel, across the input terminals of the TPA3116 amplifier. Such 1N4148 diodes will act as a signal limiter and may remove the “clicking” but may introduce some distortion at high levels.
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