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Willow's picture
May 2017
6 days ago

I looked at a friend's guitar amplifier which wasn't working, the problem was clearly (because it fell off) a broken IC (TDA2030AC).

After replacing it, the amplifier started working again but when I was taking some measurements I made a short-circuit and burned it.

When I replaced the TDA2030AC again, the sound was very soft and distorted. I checked the datasheet and the circuit is a bit different than the recommended implementation. Some resistor and capacitor values are different, but it's a dual-supply non-inverting configuration.

The strange thing is that while making contact between pins 2 and 3 with my fingers it sounds fine. And the same occurs with a resistor between about 100 to 500 kohms (see red line in my diagram). Even if that solution works, I would like to understand what's going on and if there is likely another part of the circuit damaged.

I've post the circuit (excluding the rectifier and pre-amplifier) in the attachment.

And this is the reference circuit in the datasheet: http://www.kynix.com/uploadfiles/pdf9675/TDA2030AH.pdf (Figure 13: typical amplifier with split power supply)

I would appreciate any clarifications, thanks.

 

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rocktastic's picture
Dec 2008
4 days ago

mmm. Just a guess but maybe the 220k between pins 4 & 2 is missing or has a much higher value (no negative feedback). Are you able to look with a 'scope? Where does the output at pin 4 sit?

G_Point's picture
Nov 2015
12 hours ago

Possibly there is chip defect or oscillation. R1 100kohm and C7 values are wrong - read table 7. R3 normally must be ≥1mohm for magnetic pickups (minimum 500kohm), and ≥5mohm for piezo pickup(s). Figure 1 shows optimal regimes except for R3 value for guitar (input impedance).

 

bluezhawk's picture
May 2012
14 hours ago

You said - the problem was clearly (because it fell off) a broken IC (TDA2030AC)

Did this IC literally crumble into pieces? I've seen this happen in various circuits due to being overheated from excessive current and just replacing it won't solve the larger issue

You also stated that some of  the resistance value is different - again, this can happen due to excessive current flow when a circuit malfunctions. It doesn't have to be a dead short but something is breaking down and the changed values are causing the IC to have a higher output

My guess from looking at the diagram is that your speaker coil is beginning to breakdown. That's the only "load" that the IC is connected to. I'd hook another speaker to it or a dummy load of 8 ohms (or whatever the spec is) and try replacing the IC again.

You should also desolder one end of all resistors & caps in that circuit and raise that end out of circuit so you can test the values without any interference from circuit. This is the only way to get a true reading of their values. Circuits of this nature rely on precise voltage levels and if a resistor has changed value, then the IC won't operate as designed