power noise parkg10r amplifier

[rainman38501]

i recently bought a park/marshall g10r! everything functions properly and the guitar sounds are normal. but the amp has a constant noise that is present from the moment you power it on.it sound like a tv channel that has no signal...ya know that annoying static sound! it does this with or without anything plugged into it.it gets louder if you turn up the gain or volume, but all the pots and reverb work perfectly.so you hear he guitar and the static.you can adjust anything on the amp and it does not affect the static sound.ive deduced that this is power noise. i replaced the two 35v/2200uf caps in hopes that it was a filtering problem! but no change. this amp uses the TDA2030 IC chip and various smaller ic's on the simple board.i was thinking of changing this tda 2030 ic chip just cause its so cheap! do any of you senior techs think im on the right track or do you have any other suggestions. i did find the schematic on this forum.....thank you, and no thanks to marshall co.who has not responded to my numerous requests as of yet!! anybody want to give this a go?????? thanks

[Enzo]

You can turn the noise up and down with the volume, but you can adjust anything on the amp without affecting the noise. Well, which is it? You can turn it up and down or the controls have no effect?

You have a noisy part, most likely a semiconductor, and most likely among them a noisy op amp IC. (The little square 8-legged things.)

TV station off the air noise is called white noise or hiss. It does not involve your filter caps. FIlter cap problems result in hum.

The TDA2030 power amp IC is always connected to your speaker, so if it were noisy, you couldn't turn the noise down with the volume.

I would bet my lunch money it is one of the small op amps. Types like TL072, 4558, 4560, 4580, etc. They are indeed cheap - three for a dollar - and there are not many of them in this tiny amp.

The PG10R and MG10 are listed on my dealer site, but no schematics are included. In a commercial shop, we would not usually need one.

If you have a scope, look at pins 1 and 7 of the op amps and see where the noise exists.

[rainman38501]

g10r issue

i meant that the frequency of the hiss, as you say, does not change when you adjust the pots or plug in a guitar.it will get louder or softer as you adjust gain and volume respectively!sorry for the spoof, im a novice at electronics repair but my older friend, who is a tech, says i have good instinct but i know just about enough to get electricuted!!!lol.i will investigate the small ic's that you mentioned!dont have a scope but for the price i think ill just replace them all! thank you for your time and it is greatly appreciated!R.T.

[Enzo]

Let's keep the conversation here in the forum, please.

The part is a TL072, regardless of what-all is printed on the thing. That is a VERY common IC. SO are the 4558 ICs.

MAy I suggest stay away from the NTE stuff. If the guy can actually cross to it, you still wind up paying a lot more for your parts. ANY electronics part house should have these. Your parts guy probably does and doesn;t know it. What all these are is Dual OpAmps in an 8-leg DIP package.

For example go to Mouser.com and enter TL072 in the search window. That 0 is a zero, not the letter O. The first one in the list of finds is what you want. There are several others. If you want, click on amplifier ICs among the results, also click on the "stocked" box, and scroll over to package select and chose PDIP8. You should see about 9 choices ranging from 50 cents to a dollar.

4558 was very common, now more likely to see 4580 in circuits. Again at Mouser.com enter 4558 in search, then select semiconductors, amplifier ICs. (And always check the stocked box unless you also want to know what they don;t keep around.) Scroll right to chose package and choce DIP-8 or PDIP-8. Same thing, but listed separate.

We refer to 4558, but each IC maker adds some letters, so the 4558 will be one of these:
BA4558
KA4558
RC4558
NJM4558
MC4558
And probably others. They range from 30 cents and up. Pick one, not critical.

Your NTE guy probably needed the extra letters.

You could also do the same search but for 4580 and find some more choices, but 4558s are cheap and they work.