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High Pitch sound coming from My Peavey Pro 40

Started by jmccorkle1222, August 31, 2011, 02:59:30 AM

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jmccorkle1222

Amp: Peavey Studio Pro 40
speaker: 12 inch - Studio Pro Speaker

Problem makes this sound: http://www.youtube.com/watch?v=BX7Ar3Z-oTo

Problem: When ever i try to get the amp to give more volume, Useally past 6 on a scale of 1-10, It produces that high pitch sound familiar to the youtube link i posted above. Also I can get it higher but i have to Lower the Saturation effect, or lower the gain... Then the volume knob can go up ( But in reality it is louder on a lower volume setting with the gain and saturation up )

Known Problems:

- The power chord that plugs into the wall from the amp is a replacement which does not have a ground on it. its just a 2 prong plug in, but the original power chord had a ground ( 3 prong ) power chord. Im not sure if this would cause the problem because the amp is still getting all the power it needs. The Ground is just a safety measure correct?

- Also My amp has 2 wires that go to the 12 inch speaker from the top part ( Amp ) . And the
Amp has 2 metal clips coming down. One of the wires goes straight up to the inside of the amp. But the other wire is wrapped around the other metal clip coming down from the top amp. ( im guessing these 2 wires are the positive and negative that sends the electrical signal to the 12 inch speaker ). So i know a signal is getting through or else the amp would not play anything out of the speaker.

Please this is very important to me, Guitar is my life and the only thing that keeps me sane. Please help me out so i can fix this amp. Hope this explanation is better

teemuk

#1
Most commonly I have heard this type of squeal when there is no

- Proper HF decoupling cap in opamp power supply

or

- Proper HF negative feedback cap in high gain stage

Production amp surely has them but there's always a chance of cold solder or component failure rendering them non-functional.

Oscilloscope might become usable: there's really no way to tell why the amp oscillates except by actually measuring things up or alternatively finding something visibly bad from inside that would explain why oscillation has started.

I have never heard of amps squealing due to lack of safety ground (low frequency hum perhaps but never squeal) but since it's a quick and easy test to verify whether the lack of safety ground is the culprit or not and recommendable "upgrade" anyway I'd recommend trying it first. After that it gets substantially more difficult and involves venturing inside the amp with proper measurement tools to locate the source of oscillation.

jmccorkle1222

Thanks for the input guys, i will replace the cord to a 3 prong cord. If this doesnt fix the problem should i open the amp and look inside?

Den.

The two speaker wires both absolutely must be soldered.  The blue speaker wire ( - neg ) goes to the pin closest to the front of the amp.  The yellow wire ( + pos ) is soldered to the pin closest to the rear of the amp.  Here is a link to the Studio Pro 40 operator's manual: http://peavey.com/assets/literature/manuals/studiopro40.pdf

Enzo

DOn't plug any instrument into the amp.  Now turn the amp up.  Does it still make the sound?  Or does it ONLY do it with an instrument plugged in?

If an instrument must be plugged in for it to happen, go ahead and plug one in, but tirn the volume control on the instrument to zero.  Does it still make the noise?

If the amp can make the noise by itself, then I'd say the amp has a problem, and I'd start with the solder at the input jack.  If turning the instrument volume to zero kills the noise, then the likely cause is your pickups.

jmccorkle1222

#5
Hello guys,

Thank you all for your input it is much appreciated! I am currently trying to get my music out to everyone i can and one of the things i need for that is a reliable amp :)

To the guy above me. The high pitch noise still exist at higher volumns even without the guitar plugged in. so it cant be feed back from the guitar.

Also since the speaker is playing, how is it gonna get better if i solder the wire onto the metal from the amp? Wont it stay they same just more sturdy ? instead of ****** rigged?

Thanks guys willing to do anything to get this amp fixed right now. The guy above be said something about working with the input , what exactly do you mean?

PS : Hope i don't offend you guys with anyway i put my words, i am taking all you have giving me in, and i respect all of your ideas.

**Removed racially insensitive term**

phatt

Hi jmccorkle1222,,
No don't be worried about upsetting the good people here.
Sorry if I came across like a ranting ol fool,, but hey Safety First.

*Enzo* probably means the input jack may have a cracked solder pad which maybe causing issues.

Whoever replaced the power cord may have unknowingly caused something to come apart and the squeal may have nothing to do with the power cord repair but there is a fair chance something has happened during that repair.

If you are not savvy to the internals of Amps and you don't know how to wire up a power cord correctly then there is a very good chance you need help.

If you have a camera, May I suggest either taking some pics of the power cord wires entering the amp and maybe some clear internal pics as well that way the good people here can show you how to connect things in a SAFE manner.

Re Speaker wires.
Some of these Amps have a floating output where neither speaker wire should be grounded to the chassis. Needless to say there are some gotchaz inside for the novice.

I find it disturbing that the person who fixed the cord may have messed up not just the circuit but also did not consider the EARTH.

In my mind the EARTH connection comes first,, fixing the other issue comes after safety.
Phil.

jmccorkle1222

Once Again, thanks to everyone that has helped me this far! I Will be posting pictures of my amp later on today. But i wanted to post something that is a little odd..

Today i was messing with the amp to try to understand more of what the problem was. So i decided to turn the  Pre Gain all the way up and the High Equalization ( Which are the 2 settings that effect how high and low i can go without getting the High pitch noise on the Post Gain ( Volume ) )  But something odd happened.. The pitch slowly got higher as i increased both the settings... then when i hit 9-10 the high pitch sound went out and i couldnt hear it anymore! Obviously the setting was very high in treble so i don't wanna be stuck with these settings or the really low ones. It seems like i either must have these setting on very low or very high??? What could this possibly be!! It seems like the Post Gain is ok but its these 2 settings that are giving me the problem!

Also guys, i know im new here, and hope im not a bother... Thanks for all your help!

J M Fahey

QuoteThe pitch slowly got higher as i increased both the settings... then when i hit 9-10 the high pitch sound went out and i couldnt hear it anymore!
That does not mean you *cured*it, rather that you can't hear it, because it goes supersonic.
Try plugging a shorted plug in the input jack.
If it does not affect the high squeal, it's an internal problem which I'm afraid may be quite hard to solve.

jmccorkle1222

Like i have said It does it even without anything plugged in, Going to take the amp apart tommarow and take some photos and see what i can do!

jmccorkle1222

#10
Hey guys, sorry for the delay! Life has been a *s!!t* load.

So i ended up going to my dad who is a electrician.. He ended up replacing that crap 2 prong cord with a 3 prong grounded cord exactly how its suppose to be done. And it looks great! When we were inside looking at the circuit board on the amp, he said he didnt see any fried parts, and the high pitched noise might be a a electrical problem that is getting amplified but didn't exactly know what it would be. We also attached the jerry rigged wire from the 12 in speaker back to the inside of the amp like it was supposed to be.

But the problem didnt fix from replacing the cord , and making sure a ground there for the amp...

Im totally lost and im not sure what to do! I got to clean 1 of pots out cause one has a little scratch around 1-2 on the post gain knob... but idk where to go from here.. If you guys need any information ill try my best to supply it..

I play for my church and other little gigs, and would just love it to have a reliable amp! and i know this amp can be that! i just love the tone too much to give up on it.

Thanks again guys, for all your help!

Enzo

There is a limit to what we can do from here, for you there with the limited tech skills.  SOmetimes , you just need to bite the bullet and take the amp to a repair shop.

Peavey has authorized repair shops all over God's green acres, but really, this is not a complex amp, and any competent amp tech can service it.  Peavey will send the schematic to anyone who needs it.

One of the theories presented is that the amp is oscillating above the audio band.  Only way to tell this is to scope the amp, or use an RF probe.

mitch88

See my recent post about reverb tank.  For the instant cure you need to wrap the reverb tank in a vinyl bag and reinstall it with new rubber grommets.

mikeskory

This is the exact problem I'm hearing on a customer use is the year 2017. Did you get this fixed?