TDA2003 practice amp help needed

[MartyMart]

http://www.alldatasheet.com/view.jsp?Searchword=TDA

Here's the DATA sheet for the TDA, my circuit is almost the same as the
main test circuit listed there.
Mine is a "kit" that was given to me by someone who never got around to
using it ( a hobby that didn't work out I guess !! )
It's built and is working but here's my problem :
The specs I have say that the amp is expecting to see around 50mV/150Kohm
"Plain ole" guitar at the fromt end is causing the amp to "distort" - in a
not very nice way.
I have a 10k pot at input, which has to be almost "off" to give me a clean
signal .... but then almost NO volume !!
Using a pedal upfront with its volume on almost "zero" also helps, but
again there's no volume anymore.

Do I need to build an ic based "buffer" to reduce my gtr signal enough
to solve this ?
In which case would it be a non-inverting circuit and how much "gain"
should I reduce by, to hit this circuit properly ?
It's designed to see a small signal from a tape/CD player I guess.

Any help/pointers would be great !

Marty.

[Ge_Whiz]

I'm assuming the wiper from your 10k pot feeds into the input capacitor, C1. Isn't it just a case of adjusting the voltage divider at the input by putting a resistor in series with the input, say 100k, reducing the maximum signal by a factor of ten? Or am I missing something, sorry?

If the only undistorted signal is one that is too soft, then you would seem to have a problem with the amp itself. A gift, you say, from somebody who never used it? Hmmm...

:!:

[MartyMart]

I'm assuming the wiper from your 10k pot feeds into the input capacitor, C1. Isn't it just a case of adjusting the voltage divider at the input by putting a resistor in series with the input, say 100k, reducing the maximum signal by a factor of ten? Or am I missing something, sorry?

If the only undistorted signal is one that is too soft, then you would seem to have a problem with the amp itself. A gift, you say, from somebody who never used it? Hmmm...

:!:

Yeah its a "cheap" kit on a PCB, but seems OK !
So just a 100k at the input will do it ?
Thats good news, I thought I'd have to tack on something a bit more
complicated !!
Thanks,

Marty.

[Ge_Whiz]

Well, 100k or thereabouts. If you think about it, the resistor + pot becomes something like a 110k pot of which you can only use the first 10k of the range.

[Mark Hammer]

Author - redundant posting

[Mark Hammer]

I'm a little puzzled.  The circuit you're using is based on (I assume not too different from) the one in the appnotes.  That circuit, in turn, is not too different from a crowd of other power amps based on the TDA2030, 2040, and 2050, all of which are regularly used as the power stages in just about any commercial solid-state amp under 30W you would care to name.  THOSE power amp stages are, in turn, generally preceded by very generous gain stages, and all of that is AFTER whatever boost is applied before the plug goes in the amp's jack.  So, notwithstanding the fact that, yes, guitars put out heftier signals than voice mics or phono cartridges, I'm puzzled as to why the circuit would distort so readily and obviously.  My own feeling is this may have less to do with attenuation than you think.

Take a look at some of the Marshall valvestate or Fender Frontman amps, or some of the lower power Crate amps, all of which often use the TDA2030.  They may have some ideas in there.

[beens]

I dont know if you have seen this but it might help you if if I have understood your problem correctly..

http://photobucket.com/albums/v324/caseyseffectpage/Amplifiers/?action=view&current=fenderampclone.jpg

[David]

You're not the first to encounter this.  Clay Jones and Lone Star Johnny have complained about this amp chip as well.  I had also been considering building a power amp around this chip (till I lucked out and found a powered monitor).  You might try sticking a GEO "Adjusticator" in front of your TDA because it can attenuate.

I used to have a schematic for a Marshall that used a TDA2030.  The link is now dead.

[MartyMart]

Hmm, I dont get it !!
The 100k resistor at input "does" reduce the input level so that I dont get
any amp "break up" but of course, the thing is now very quiet !!
Perhaps this little circuit is just "bad" and as its a PCB, its not possible to change the layout much, so I'll build that little amp that was
posted ( thank you ) as it looks a bit different to this.

Marty  :?

[David]

Marty:

How are you powering it?  I'm wondering if perhaps you're running out of headroom.  IIRC, the datasheet specified voltage from 8 to 18VDC.  I would think your headroom would improve as you got closer to 18.  Also, are you heatsinking your amp chip?

[MartyMart]

Marty:

How are you powering it?  I'm wondering if perhaps you're running out of headroom.  IIRC, the datasheet specified voltage from 8 to 18VDC.  I would think your headroom would improve as you got closer to 18.  Also, are you heatsinking your amp chip?

Hi,
12v regulated PSU at the moment and its got a large "bolt-on" heat
sink.
I can't get the schemo on-line though I have one printed, it looks a little
"simple" 4x resistors and 6 caps.
I'll try the little 8 watt amp thats in this thread, I'm only getting about
2 watts before nasty "crunch" so its a bit useless !!
I may also be able to power it with 16.5 volts .....
Thanks all,

Marty.

[David]

You could always try this one:

http://www.zen22142.zen.co.uk/Circuits/Audio/tda8.htm