My first guess was going to be "cab" ...possibly bad
cable/connection...but since it isn't I'll just bump
your thread...
Hopefully one of the gear heads here may have a
solution for ya
Good luck
Peace Ed

Thanks!

Hey, Marty,

So, you're running the speaker-out into the board?
That would be pretty unusual; most sound guys
would take the line-out and plug it into the
board.

If the line-out sounds good, but the speaker-out
sounds bad, no matter what cab you plug it into,
this means that the preamp section is good, and
the power amp section is not.

Kelly

Yeah Kelly, sorry; I should have been more specific. I am actually running preamp out to the board, and it sounds fine, not speaker-out to the board...that WOULD be unusual.

I think your power amp in the head must be shot. Like Kelly said, the preamp must be good. The distortion is possibly due to being vastly underpowered. That's why when you run into the board (using the PA power amp) you get a better sound. The Peavey is just getting a boost from your PA amp(s).

I think it's worth a shot to look into.

Bo

I'm guessing that head would be of a fair vintage & I'll add a vote for the power amp section, perhaps the power supply capacitors.

Knowing how the head+cab performs at very low volumes might help a diagnosis. Also how the problem occurred; was it fine one week then lousy the week after?

The volume control basically has no effect on the bass sound output..it is just a barely-audible, distorted, nasty tone. Nothing that I do, i.e. gain, volume, eq, seem to change it in any way.

I used to run the head and cab together, and did so for about 3 years. Then I just started bringing my head to shows, running out of the preamp into the board, and leaving the heavy cab at home. After a couple years of that I had a bigger show come up (opening for .38 Special:)), so I dusted off the old cab, only to find that I had this problem. Basically, I have no idea when it happened or if it was "fine one week then lousy the week after". I wish that I did know.

Sounds like a crispy-crittered power amp to me. :)

Have you tried a different speaker cord? If so like others said it's your power amp section. I don't know the head but, assuming its solid state the first thing you check are the output transistors ESPECIALLY on a Peavey. If you have a multi-meter and those kind of skills. Older Peavey amps are notorious for taking out output transistors. Most of the time that's all it is. But, once in a while it is something else that takes them out. I found this out fixing an old CS-800. I replaced a bad output transistor and plugged it in for a test. It burned a whole in the top of the transistor and sparks were flying four feet above my work bench! So, take a look at the other components and make sure there's not a cooked resistor or something. If you see swelled capacitors theyre bad. Being an old head it could just be cold solders. Rule of thumb test all the large components. If it's big, test it. If you don't have those kind of skills time to take it to the shop.

Dave

yes, my thought would be to check all cables...bad cables can build up resistance or the soldering on the connectors can start to "break up" and cause a very distorted sound. As previous post(s) stated if you have done this, then amp needs checked out.

Thanks Dave. I have tried another speaker cord, and another one, just to make sure. Man, that would've been great.

I think that I'll tear into it tonight and start testing "all the large components". I will keep you all updated as to what I find out.

Thanks again, everyone.

Yep, let us know how you make out. First thing I do is just take a good look at everything. You would be surprised how many things I fix just by having a look at them. A discolored resistor, a spot on the board where things look like they are getting hot, swollen caps all point to a potential problem.

Dave

I had a friend tell me that by running the amp line-out to the sound guy, and not having it under a load (not having it plugged into a cab), I probably burned up the amp. Could running it without having it hooked up cause this? It sounds ridiculous to me.

No Marty that wouldn't hurt anything. I've never heard of anything like that before. Soundmen will run power amps and only use one side of them at times. It doesn't hurt it, you don't need a load on it. I've spent countless hours recording with my head on without a cab hooked up to it. I even fell aspleep one night and had it on all night.

Dave

That one surprises me Dave...
I always thought that to run your amp you needed a
load (ie.cab) plugged into it....or something would
cook
I guess one learns something everyday from AB....
Peace Ed

If that were the case Eddie no head would EVER have a pre-amp out. Guys will use a head as a pre-amp for years and unlike Marty will plug it in and it will work. When you are fixing an amp you want to do it without a load on it first. If you were fixing a really low quality amp it may oscillate and with something like a cheapy stereo amp you may want to put a heavy load on it for testing. But, the amps used in music shouldnt have such a problem. I have been laying down rough tracks for our next CD onto a four track. I have a speaker hooked up to one of my Crown Macro-tech 600. I'm only using one side of the amp and I've had it hooked up like that for months! The other side of the amp is still working fine. A power amp is basically two separate amps in one until you bridge them. That amp has had no load on it at all for months! Now there is still power going to the amp circuit I'm not using. So, solders can still go bad and caps can blow, but it won't be because there is no load on it. I've read through my Crown manual. There are many warnings in there but NONE that say "DO NOT OPERATE EITHER SIDE OF THIS AMP WITHOUT A LOAD"! I have a juke box in my shop. I'll be more than happy to disconnect the speakers from it and let it powered for a week straight 24-7. That has a power amp in it just like amps in any piece of music gear. I promise you when I hook the speakers up in a week that amp will still be working.

Dave

Right on Dave.....
I've never been a gear head...hell,I can barely
hook up my home stereo....and any
electronics(TV,DVD) that comes in the
house,Jacquie hooks them up.
:P
I just never knew that and always assumed....tho
I'm sure I heard it somewhere before.....possibly
concerning tube amps...dunno
Anyhoo....thanks Bro
:)
Peace Ed

LOL! Poor Jacquie!

Yes I was just discussing that with Dave. Don't hook a tube amp up without a load. I'm talking solid state amps! Marty has a solid state head and a tube amp never really crossed my mind until Dave said something about it. You can run a solid state head without a load as long as you want without doing damage. But, you're still playing that Cavin R600 head? Now correct me if I'm wrong but that head is solid state with a small tube in the pre-amp section? If that's the case you don't need a load. I guess some of that old school metallity spilled over from the tube days to the solid state era.

Damn I'm just trying to help Marty get his amp fixed and end up in "One of those discussions"...hehehehe!

Dave

lol
Yeah...don't worry about Jacquie
She'd beat me if I tried hooking that stuff
up.....and less headache for me that way
:P

Yep...still running the Carvin...so far,so
good....and yes,solid state with a tube
emulator in there
All I know is I get what I want with it
:P

I dunno what makes it tick...all I know is when I
plug into it,she goes nicely boom....thump
thump....boom
lol
Peace Ed

LMAO! Eddie I'm just redneck at heart. Please don't go getting all technical on me with terms like "boom....thump thump....boom" LOL! You're getting WAY over my head Eddie!

: )

Dave

LOL
Maybe I was talking about Jacquie
;)
Hahhahaha
:P

LMAO! Well, it certainly explains why you've been with her so long....LOL!

; )

Dave

Here this is perfect!!! I just got a new Peavey PV-900 power amp. Most juke box manufacturers have quit building amps and are using music power amps in there juke boxes now. So I have a bunch of these amps in juke boxes. This is right from the PV-900 manual.

"operation above 4 ohms per channel and even open-circuit conditions can always be considered safe, but sustained operation at load below 2 Ohms could result in temporary amplifier shut down do to the thermal limit circuitry"

Meaning running it without a load can always be considered safe.

Dave

Thank you.

Ed,

The speaker completes the circuit; no speaker, no
circuit, therefore, no damage.

The problem comes in when there is a
circuit, but the resistance is too low. Kind of
like revving the engine in your car when the
transmission is in neutral.

Kelly

Thanks Kelly.....
Good info to know
Peace Ed

It sure WILL if it's a tube output stage.

I have done a LOT of reading on this topic over the last couple of days, and it seems like this is a topic of heated debate. The general consensus, however, tends to be that a.)It IS okay with a solid-state amp, and b.)It is definitely NOT okay with a tube amp.

I don't get what the debate would be about.

The consensus happens to be correct this time.

His is solid state. But, that's a good safety tip and I guess I should always throw in the disclaimer when it comes to tubes. When I talk amps I talk solid state. I keep forgetting that some have yet to embrace the remarkable new invention by Bell Laboratories called a transistor on December 16, 1947.

You want to know what is incredibly stupid with tube amps? They could put a dummy load on it! That would just make too much sense. Why go through the expense of a resistor that would prevent tube death and the frying of the transformer! I guess the money is in parts so why prevent something so easy to prevent when you can sell a guy new tubes and a transformer. But, I digress.

Dave

Dave, I know you'd know that but I added it Just In Case someone read it & . . .

I hear ya on the dummy load, but that'll add complexity to the circuit; a jack that'll 'switch' between real & dummy loads or a relay affair. Plus the load should take the full output power, or are you thinking a smaller wattage resistor would serve? It'd be an interesting mod, & a good idea.

Yeah, but that's still a good thing to include when talking amps. I'll be sure to do so from here on out. I would feel horrible if someone with a tube amp was recording without a speaker and cooked it.

Here's a DIY dummy load I found:

Build a Guitar Amp Dummy Load

Here's a schematic on how to build a 200watt attenuator: Attenuator

That's a lot more complex than it needs to be. But obviously I'm not the first one who had this idea.

Marshall made a "Power Brake". But, there's a bunch of stuff out there. Just google "Dummy Load For Tube Amps" and you'll get plenty of reading material. But, if it's me I'm talking to an engineer before plugging a dummy load into a vintage amp.

Dave

Nice links; good info. I like the analogy that went kinda like "running a tube amp without load is like running a car with the wheels jacked off the road".

Buddy raises a good point as well where you can get away with a 16 ohm load on an '8 ohm rated' output. I'd still design one for 8 though; ranges you from 4 to 6.

Yeah the big one in the 2nd link is a pretty busy circuit. Were I going to do this I'd just build one for 1/10th power & see how that worked for output level. I'd be inclined to use more smaller wattage resistors to keep the cost down, & in a format that gave lots of room for cooling.