my power amp ic of my amp always blowing

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Re: my power amp ic of my amp always blowing

Postby ppluis0 » 14 Jan 2019, 12:29

ballfire wrote:if i cant find the part causing the distorted thing on the output ..i guess im gonna trace it down but it will take me too long.


Hi ballfire,

If you have or can borrow an oscilloscope is easy to figure at which pont in the amp the distortion starts.

Meanwhile, you can measure the DC value at each output pin of dual op amps. If the entire amplifier has split supplies then the pins 1 and 7 of each IC must be rest at 0V without signal.

If there are DC present in that points there indicate a defective chip.

Cheers,
Jose
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Re: my power amp ic of my amp always blowing

Postby phatt » 14 Jan 2019, 12:33

Well you could tell us the *NAME* and the *MODEL* of the amp.
If it's a brand name amp there is likely a schematic on the net.
google it.

I doubt anything is failing in the preamp,, try to understand you have a 10WATT power chip and it will distort at low SPL. So clean head room is very limited, just keep the gain down to play clean.
Because they are not loud it is easy to get to max power without hurting your ears, so hence distortion seems to happens early.
Now if you plug the same preamp into a 100Watt poweramp driving a quad box you would only get distortion at ear splitting high volume as they have heaps of Clean headroom before they distort.

Note; although the data sheet states it can produce 25Watts it is nowhere near that good as it can only do that into a 4 Ohm load.

Always look for the Wattage @ 8 Ohms as that is a more realistic power rating. in the case of TDA2040 it's 12 Watts @ 8 Ohm.
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Re: my power amp ic of my amp always blowing

Postby ballfire » 15 Jan 2019, 01:29

ppluis0 wrote:
ballfire wrote:if i cant find the part causing the distorted thing on the output ..i guess im gonna trace it down but it will take me too long.


Hi ballfire,

If you have or can borrow an oscilloscope is easy to figure at which pont in the amp the distortion starts.

Meanwhile, you can measure the DC value at each output pin of dual op amps. If the entire amplifier has split supplies then the pins 1 and 7 of each IC must be rest at 0V without signal.

If there are DC present in that points there indicate a defective chip.

Cheers,
Jose



yeah ..im gonna check those op amps...thank for the advice..



phatt wrote:Well you could tell us the *NAME* and the *MODEL* of the amp.
If it's a brand name amp there is likely a schematic on the net.
google it.

I doubt anything is failing in the preamp,, try to understand you have a 10WATT power chip and it will distort at low SPL. So clean head room is very limited, just keep the gain down to play clean.
Because they are not loud it is easy to get to max power without hurting your ears, so hence distortion seems to happens early.
Now if you plug the same preamp into a 100Watt poweramp driving a quad box you would only get distortion at ear splitting high volume as they have heaps of Clean headroom before they distort.

Note; although the data sheet states it can produce 25Watts it is nowhere near that good as it can only do that into a 4 Ohm load.

Always look for the Wattage @ 8 Ohms as that is a more realistic power rating. in the case of TDA2040 it's 12 Watts @ 8 Ohm.
Phil.



good day ..

my amp name is XTREK GX30 AMP a 30 watt amp..theres no schematic on the internet..i google it many times...its a china made amp i think.. the original power amp ic of it is LM1875T but theres no more available in our electronics shop here..only TDA2040 is available

i dont trust anymore online ordering because they sent me defected products it cost me too much and i have no money to order in USA it cost me too much penny..

its okey for me now my amp is stable atleast this time i can play my guitar..i dont mind if i lower down the wattage into 20 watts...its okey for me..

i used the former 8 ohms speaker from LM1875T..and its the same output it produced and its loud also but the bad side theres a fuzzy background when shifting to clean mode..

or maybe i install it t with 4 ohms only speaker??

thanky you for the advice again...
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Re: my power amp ic of my amp always blowing

Postby deltafred » 15 Jan 2019, 11:01

No wonder you have been blowing output amplifier ICs, the absolute max voltage for the TDA2040 is 40V total (+ and - 20V), for the LM1875T it is 60V total.

Internet fault finding can only be as good as the information supplied. Had you told us in post #1 that you had substituted a different amplifier IC we would have arrived at this point a lot sooner.
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Re: my power amp ic of my amp always blowing

Postby ballfire » 16 Jan 2019, 02:07

deltafred wrote:No wonder you have been blowing output amplifier ICs, the absolute max voltage for the TDA2040 is 40V total (+ and - 20V), for the LM1875T it is 60V total.

Internet fault finding can only be as good as the information supplied. Had you told us in post #1 that you had substituted a different amplifier IC we would have arrived at this point a lot sooner.



good day..

i resorted to TDA2040 and i have no choice..i thought its ok to feed the power amp ic tda2040 a 28volts but i failed..so i follow the advice of phatt to change it to 12-0-12 transformer and it works..but last night again when im playing it..as i put the volume incerease suddenly the output became tingy or twangy and lost its fatiness..i think its busted again..

im using the former 8 ohms speaker 10'inch ...is this the problem???should i change it to 4 ohms only???because of the 8 ohms speaker the output became twangy???

thanks pls advice...or i will throw now this crap amp to garbage
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Re: my power amp ic of my amp always blowing

Postby deltafred » 16 Jan 2019, 11:21

You were not running the output IC at 28V, you were running it at 56V (+28 0 -28 gives 56V total).

Why it has blown again after changing to a 12 0 12 VAC transformer I have no idea, but as I said before internet fault diagnosis can only be as good as the info provided.

Please measure the voltage on the output IC power supply pins. You are assuming that your 12 0 12 VAC transformer is what it says on the label and as an old engineer and mentor told me when I was an apprentice "Never assume!".

ballfire wrote:should i change it to 4 ohms

No, running a 4 ohms speaker will stress the output amplifier more than 8 ohms.

There is the possibility that there might be a a fault with your speaker which is putting too much load on your amplifier when you turn the volume up (voice coil shorting to the magnet).

One thing at a time, remove the now faulty IC and measure the voltage on each of the supply pin pads.
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Re: my power amp ic of my amp always blowing

Postby ballfire » 17 Jan 2019, 01:33

deltafred wrote:You were not running the output IC at 28V, you were running it at 56V (+28 0 -28 gives 56V total).

Why it has blown again after changing to a 12 0 12 VAC transformer I have no idea, but as I said before internet fault diagnosis can only be as good as the info provided.

Please measure the voltage on the output IC power supply pins. You are assuming that your 12 0 12 VAC transformer is what it says on the label and as an old engineer and mentor told me when I was an apprentice "Never assume!".

ballfire wrote:should i change it to 4 ohms

No, running a 4 ohms speaker will stress the output amplifier more than 8 ohms.

There is the possibility that there might be a a fault with your speaker which is putting too much load on your amplifier when you turn the volume up (voice coil shorting to the magnet).

One thing at a time, remove the now faulty IC and measure the voltage on each of the supply pin pads.



good day..

thanks man for the reply...whatever you are sir thanks for the great advice..

you know im debugging repeatedly this amp for 1 year then it never return back the old mojo tone of this amp..

before it broke ..i like this amp very much because theres something in it makes my diy pedals really roar mostly distortion..
last year it just suddenly busted up and became tingy output..im frustrated of this amp..i try everything in it to fix it but..i dont know what the hell happening inside of it ive check the resistor and everything..everything..

now last week i decided to change the transformer to 12-0-12 as advice..and change the power amp ic to TDA2040 because the former chip is not available..the amp power up and the the mojo tone came back im very glad it returned..but last tuesday night when im playing
the problem returned..damned fuck ..

last night because im really furious now what supposed to do i change the power amp ic with new TDA2050 and it work!!!! and the speaker i install it with new one a 100 watts 8 ohms..because theres no available 30 watts on our place..the amp works the mojo tone again back atleast.....

this morning when i plugged to see if its okey ..im shocked there a loud hum when i plugged the cable to my guitar on ti..but theres a signal output when im strumming my guitar ..when i touch the cable plug to the input it disappear..damn i think it has a jinx or something...

any advice sir....
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Re: my power amp ic of my amp always blowing

Postby deltafred » 17 Jan 2019, 10:15

A hum that disappears when you touch something is often caused by a bad ground connection. This might be on the guitar or the amp or even the mains supply.

First check the obvious things.

guitar Lead.
Make sure your guitar lead is good. With your multimeter check for resistance of the screen and tip connections between the jack plugs. The resistance should be almost zero ohms, especially the screen connection. Not related to your fault but worth doing for completeness - check for any continuity between the tip and screen (on either jack plug). This should show a very high resistance, ideally open circuit.

Guitar bridge ground connection.
Plug a guitar lead into your guitar and measure from the screen connection on the lead to the bridge of your guitar. This should not read more than a few ohms.

Mains ground connection.
Try your amp in a mains outlet in a different room. It could be that your ground connection on the mains outlet you are using is faulty. If this is the case the mains wiring needs to checked at by a competent electrician.

If your amp has a separate mains lead try a different lead (if possible). If you don't have a spare lead then check the continuity of the ground connection with your multimeter. It should read very close to zero ohms.

If it does not have a separate mains lead then check the continuity of the ground form the power plug to the chassis. This should be very close to zero ohms.

Please report back with your findings.
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Re: my power amp ic of my amp always blowing

Postby ballfire » 18 Jan 2019, 03:16

good day..

i found the problem the wire that connects to the ground chassis from the mainboard was losen up..and i screw it tightly the hum is gone now..


last night i checked the pre amp section everything okey..and i found out all this one year of debbuging the power amp section the real problem...i should focus on this section..and checked it regularly to avoid tone failing on the output...

the speaker is newly installed and work fine even its 100 watts i just lower the volume for avoiding overloading..the transformer 12-0-12 is stable and..now everything functioning well..im gonna observed this for 1 week if something happend..

thanks for the advice sir.and to those other people who help me
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Re: my power amp ic of my amp always blowing

Postby deltafred » 18 Jan 2019, 11:10

Good to hear you have got it working again. :D
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Re: my power amp ic of my amp always blowing

Postby ballfire » 19 Jan 2019, 05:32

deltafred wrote:Good to hear you have got it working again. :D



good day ...


I checked the new voltages of my amp last night..
is this right voltages??? please justify ....
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Re: my power amp ic of my amp always blowing

Postby plush » 19 Jan 2019, 11:05

ballfire wrote:
deltafred wrote:Good to hear you have got it working again. :D



good day ...


I checked the new voltages of my amp last night..
is this right voltages??? please justify ....


To me it looks like something is drawing too much current from the 2nd node.
The voltage there should be around 12 volts (not 10) and the voltage drop over 220 ohm resistor should be 4 volts, not 6.
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Re: my power amp ic of my amp always blowing

Postby phatt » 19 Jan 2019, 15:07

Those 220 Ohm resistors are now too large a value,, for the lower supply voltage,,you need to reduce them.
too late to think to night,, but at a guess start with 100 Ohms.
Just keep lowering till you get down to 12VDC.
The zeners can no longer regulate as the input voltage is lower.

The preamp chip may be able to run on +16/-16 rails,, check the data sheets.
Some of these small amps don't even use a Zener just a drop resistor.
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Re: my power amp ic of my amp always blowing

Postby ballfire » 21 Jan 2019, 03:10

phatt wrote:Those 220 Ohm resistors are now too large a value,, for the lower supply voltage,,you need to reduce them.
too late to think to night,, but at a guess start with 100 Ohms.
Just keep lowering till you get down to 12VDC.
The zeners can no longer regulate as the input voltage is lower.

The preamp chip may be able to run on +16/-16 rails,, check the data sheets.
Some of these small amps don't even use a Zener just a drop resistor.
Phil.


yesterday sunday..

i debugged it as always...i removed the two 220 ohms resistor and resolder it again on the board ..then check the reading and i found the voltage on the 12 volt zeners returned to 12 volts supply..not 10 volts only..

but i saw some schematics it should be 100 ohms in place of that 220 ohms resistor..but it works now on 220 ohms..im confused here???

anyway my amp is working now...
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Re: my power amp ic of my amp always blowing

Postby phatt » 23 Jan 2019, 03:01

Well it might read 12Volts with no signal but the moment you turn up the volume that power chip will draw current and the voltage after the 220 R resistors will drop and the Zener will no longer be able to regulate as they need at least a few volts above the reg voltage to work.
You could replace the 220R with 100R but hey if it works and sounds ok then leave it. [smilie=a_whyme.gif]
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Re: my power amp ic of my amp always blowing

Postby ballfire » 23 Jan 2019, 05:34

phatt wrote:Well it might read 12Volts with no signal but the moment you turn up the volume that power chip will draw current and the voltage after the 220 R resistors will drop and the Zener will no longer be able to regulate as they need at least a few volts above the reg voltage to work.
You could replace the 220R with 100R but hey if it works and sounds ok then leave it. [smilie=a_whyme.gif]
Phil.



yeah ..youre right man..i checked the voltage last night..its really crazy the voltages on opamp on preamp section on pin 8 the voltage was 9.o8 v , on pin 4 the voltage was 12.0v..it really crazy..is not balance and it creates loud hum..maybe its also the cause of tingy twangy output of my amp..??

i guess im gonna change the 220 ohms with may be 100 ohms..what wattage can i use on 100 ohms???

thanks man..damn youre really good on amp repair.and the others great advice..

hooray to you all people yeah cool... :D

im gonna check the voltage after i change those parts..lets what will happend..
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Re: my power amp ic of my amp always blowing

Postby phatt » 24 Jan 2019, 08:43

As it's only opamps after those drop resistors then 100 Ohm/1 watt would likely be fine.
you can leave the originals in place and parallel them with another 220 Ohm which brings it back to 110 Ohms. :thumbsup
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Re: my power amp ic of my amp always blowing

Postby ballfire » 25 Jan 2019, 08:41

phatt wrote:As it's only opamps after those drop resistors then 100 Ohm/1 watt would likely be fine.
you can leave the originals in place and parallel them with another 220 Ohm which brings it back to 110 Ohms. :thumbsup
Phil.



i changed the 220 ohm resistor into a 100 ohms 1 watt the voltage got high to 12volts now as the zener diodes regulate them right..

yeah youre right i should lower them down this drop voltage resistors..

i learn a lot on this forum..thanks to everybody..

I MEAN IT..THANKS TO EVERYBODY HERE..THUMBS UP TO THIS FORUM.. :)
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