Peavey MACE hiss problem

[Colas LeGrippa]

Hola amigos, long time no see !


A friend of mine brought me a Peavey MACE guitar amplifier ( 6 X 6L6's ), SS preamp.
The amp plays but there is a loud hiss comin'out of it. To me, it's not a heater, bad cap or grnd issue, because I never heard such a noise. I have swapped the 6L6's, same problem. Any tip ?


Thanks


Colas LeGrippa

[shooter]

SS preamp

Does the amp have a line out, or pre out?  if so, see if you hear it there.

[tubenit]

For those of you  who may not know Colas,  check out his video of impersonating Alvin Lee at Woodstock!  GREAT playing and performance!

I've heard Colas play some Johnny Winter also that was incredible.

https://www.youtube.com/watch?feature=player_embedded&v=rQb0OoCR1vI

With respect, Tubenit

[tubenit]

Does the amp have a line out, or pre out?  if so, see if you hear it there

I agree with this idea.  You could run the preamp into another amp's power section to see if hiss  is there.

OR .......... run another amps preamp into this amps' power section.

Maybe trying that will isolate where the hiss is coming from?  I don't know enough about solid state components to offer good advice to you.

With respect, Tubenit

[PRR]

Hiss is usually the small tubes, not the big tubes.

Noting what the knobs do to the hiss helps to narrow down which stage it is.

[whoops]

The hiss is probably from the preamp section.
Or from the solid state Phase inverter circuit.


Like other members said, you should separate the section first. It's easy on this amp since you have on the back Preamp Output and Power Amp Input jacks
Connect the Premp Out  to another amplifier or power amp, is the hiss there?
Connect another known non hissy preamp to the power amp section, and check for the hiss also, is it there?
Then you will know which part of the circuit is the hissy one

The amplifier has a lot of different inputs do all of them hiss?

Record the noise and show us, could also be a video, then it's easier to know what type of hiss/noise you're having.





 

[Colas LeGrippa]

Cool, Tubenit, it's been a long time since I watched this video LOL, with the wig....
Thanks for your replies. I think the hiss comes from the preamp too, I'll try to isolate where it comes from and will get beack to you. I don't feel like replacing transistors one after another till the problem goes away....


Have a good day........AND A GOOD YEAR TOO ( no, not the tires...)


Colas LeGrippa

[whoops]

Cool, Tubenit, it's been a long time since I watched this video LOL, with the wig....
Thanks for your replies. I think the hiss comes from the preamp too, I'll try to isolate where it comes from and will get beack to you. I don't feel like replacing transistors one after another till the problem goes away....


Have a good day........AND A GOOD YEAR TOO ( no, not the tires...)


Colas LeGrippa

Well if it's the preamp use a signal probe, if you don't have one it's easy enough to do, there's plans for one in the Hoffman site.

If the hiss comes from the power stage then it's easier to solve.

[Colas LeGrippa]

Happy new year !


I hate transistors amplifiers but finally I got rid of the hiss problem.
Was coming from de preamp, as I thought. Two tube driver transistors no. 65837 ( 2n3439) defective.
Customer happy, me happy, and year happy.......
I got to develop good troubleshooting methods with transistors. Too often I refuse to repair ss amps cause they scare me to death....


Thanks for the tips.


Jack

[shooter]

cause they scare me to death....

A 40volt poke is WAY nicer than a 400v poke
transistors from an audio troubleshooting point are basically like tubes, signal goes in the middle, comes out the top
The older metal ones typically had the "can" as the output, walk your scope can to can til things started looking bad, backup, fix.

new ones, loaded with uP and LSI, SMT, throw out!, no, scrap, they have some gold

[whoops]

Happy you solved the problem.

You shouldn't be scared of troubleshooting transistor circuits, the same skills apply.
Like shooter said at least is less dangerous than working on a Tube circuit.

The only thing is that normally solid state amplifier circuits can have more components, are PCB based and everything is smaller so it's not as easily accessible as a Turret or Eyelet board with big components.

Unfortunately I don't have an Osciloscope so I use a Signal/Audio Probe, insert music at the input and probe before and after each component. I was able to repair a lot of different amplifiers with this method. I'm sure with an Osciloscope then I would have more options.

Normally in solid state amplifier I find the odd open resistor, or shot capacitor. Hissy or farting transistor, Burned Output transistor.
Sometimes the molex connectors or whatever they're called, the multicable connectors that connect the different pcb's have bad contacts or make intermittent connections, sometimes I prefer to cut the connectors and just solder the wires directly to the pcb's.

[Colas LeGrippa]

When i say that ss circuits scare me to death, I mean that replacing small transistors on a new technology pc board is not easy. Fear of overheating the thin copper circuit or close components even with appropriate tools. The old Peavey Mace is much more easy cause at that time the pc boards were more solid and spacey.


Thanks


Colas leGrippa

[Platefire]

Just a little info, Gary Rossington of Lynyrd Skynyrd to my understanding uses a Mace to this day that started back in the 70's. I owned one I got new in 79 but never bonded with it---it was heavy as a twin%>/

Glad you got it rolling again. Platefire

[Colas LeGrippa]

thanks buddy