No Reverb in a Peavey Mace

[gfxbss]

Hey there,

Picked up a Peavey Mace this weekend for $100.

Not bad for the price, could badly use some new tubes.....

My only real issue is that the reverb doesn't work. I have checked and replaced the pot, but still nothing. This amp has a Solid State Preamp and a Valve Power amp. That being said, there are no preamp tubes to replace for the reverb.

Any ideas?

Here is the manual which includes a schematic.

Thanks guys,

Tyler

P.S. the raw URL is www.peavey.com/assets/literature/manuals/80347000.pdf

just in case of my link not working. ;D

[ashcatlt]

Simple stuff first.

Have you checked to be sure that the reverb pan is connected? Check both ends of both (send and return) cables.

[gfxbss]

Ahh, I forgot to mention that I did check that. When I purchased the amp and noticed that the verb wasn't working, I pulled out my screwdriver and pulled the tank real quick to see if I would be lucky enough to have a simple one.

Thanks Ash,

Tyler

[gfxbss]

alright next round of updates......

I took the tank back out just to have another look. The RCA cables connecting the tank to the amp were giving me erratic readings on my DMM. I replaced the cables and can now hear the springs vibrate if the tank is bumped(good call ash)..... so apparently there was an issue post tank output.

However, the verb is still not working. I can hear the tank rattle, but nothing if playing a guitar. So, this must mean that I also have an issue pre-tank.

All help is greatly appreciated.

Thanks, guys.

Tyler

[sumgai]

Tyler,

Some amps, and I don't recall what's the case for the Mace, but some amps have equal length cables for the reverb tank. If they're reversed, then all is lost. Actually, you'll still hear some output from a good shaking, but no signal from the guitar - just as you've described so far.....

Next step: How about the footswitch, did you get one, and is it plugged in during your testing? The reverb should work without it being plugged in at all, according to the schematic.

Third step: If you have another amp with a similar tank (not exactly alike, just similar), then swap the tanks between the two amps. Does the suspect tank work in the known-good amp? Does the known-good tank work in the suspect amp?

(If you don't have such an amp handy, how about one of your bandmates? It'll only take a quarter hour to test it all, and put everything back together.)

Fourth step: Assuming the tank is good, you'll need to pull the amp chassis out of the cabinet and check both ends of each cable with your DMM. Also at this time, give everything a good look - visual inspection is a mighty handy tool, one should develop a good eye for details. Possibly a crummy solder joint, or a crimp-on connector that slips over a post, that may have fallen off, there's a number of ways for things to go hayware in a simple fashion.

Finally: All the simple stuff has been checked. It's time to get dirty.... Do a voltage check around the two transistors that drive the tank, and the two that recover its signal. (Called the Reverb Return on the schematic.) You should see all the voltages they call out, plus or minus no more than 10%. Be Careful! You aren't measuring high voltages here, but you're still within arm's reach of some killer joltage - Be Careful!

If you've gotten this far and still no joy, then let's talk......

HTH



sumgai

[ChrisK]

Try measuring the reverb pan coil resistance using the amp end of each RCA cable (do unplug both first).

They should be a few hundred to thousand Ohms (I'm guessing).

If open or shorted, there you are. It's easier than swapping stuff.

[sumgai]

Chris,

Jul 24, 2009 19:07:21 GMT -5 ChrisK said:

Try measuring the reverb pan coil resistance using the amp end of each RCA cable (do unplug both first).

They should be a few hundred to thousand Ohms (I'm guessing).

If open or shorted, there you are. It's easier than swapping stuff.

True enough.

Although you did say "the amp end of each RCA cable". The manual for this model shows both front and back images, and sorry to say, I don't see any such jacks. Although, it's possible that they are on the under-side of the chassis, and the manual simply "forgot" to mention them.....


Tyler,

Chris's suggestion can still be carried out if you simply substitute a standard stereo "patch cord" (with suitable RCA plugs), then you can take a reading.

HTH



sumgai

[gfxbss]

Hey guys,

Sorry I took so long to get through this.....

Been having some other issues with the amp, but nothing that some new tubes and speakers didnt fix.

SG,

The Mace does have different length cables, but I had already removed them so I just have to run swap tests to figure out when it works.....

No foot switch, after this I will probably ask to see if you guys have any ideas on how to make one....(the automix switches are a bit hard to come by).

I swapped the tank with another that I thought worked. However, I tested both tanks w/ a DMM, and neither of them seem to be working according to that....

Replaced the cables and cleaned up a few solder joints, also replaced the pot but still nothing.

Checked all four reverb transistors and all of the numbers are reading normal.....

Also, the "amp end" of the RCA reverb cables do go to the underside of the chassis.

Thanks and let me know if you need any more info.

Tyler

[sumgai]

T,

You won't be able to use a DMM to read continuity between the input and output jacks of a reverb tank. The reason being, there are a pair of transducers, one at each jack, which are used to magnetically couple the audio signal to the physical springs. The input is like a tiny speaker, the thing that looks like a small transformer is really just a coil with it's metal core large enough to wrap around the spring supports (at just the right place along the spring). The magnetic field generated by the coil excites (forces vibrations upon) the springs. At the output, the vibrating spring excites the magnetic field of the coil, in turn producing a small voltage - just like a guitar pickup!

While a transducer's coil might go bad (you can use your DMM to do a continuity check for this), it doesn't usually do so. Where things go bad is most often the spring breaks loose inside of the pointed solder joint that holds it. Don't attempt to put it back with your own soldering iron, the factory uses a very costly jig to keep things exactly lined up during assembly - the chances of you getting the same results are pretty slim.


Having two tanks go bad at the same time is a bit strange, although not unheard of. But now you understand why I suggested that you take the tank (and now your spare tank too) to another known good working amp, and not rely on just one test. Sure, it takes more time and effort to do this, and it seems like doubling the effort, but it eliminates all doubts about what works, and what doesn't. End of story, troubleshooting wise.


And nice catch on the underside-of-the-chassis RCA jacks, truly the manual doesn't show them. Go figure.

HTH



sumgai

[gfxbss]

SG,

Wanted to let you know that I haven't forgotten. I am trying to find time to head up to my favorite shop. They said that I can pull the tank out of one of their old peaveys and pop in one of my tanks....

Ill let you know the outcome when I get a chance.

Tyler

[gfxbss]

SG,

Finally got a chance to go and test the tanks....

All is well with both tanks. Worked fine in the other amp.

any more ideas?


thanks,

Tyler

[sumgai]

Tyler,

OK, so you've done all the usual things an owner can do, and you've done some DC voltage checks, now what?

Time to enter Stage Two, signal injection. This is actually a two-way deal - you'll both inject and detect a signal, albeit with different equipment.

Step one is to make sure that the two Reverb Return transistors are actually passing a signal on to the rest of the amp (the driver and power amp stages). You do this by simply touching the open end of the RCA cable that is plugged into the Reverb Return jack. Easy, no? You may need to turn up the Reverb control, but start with it all the way down - most such circuits are very sensitive, but you never know, so you might as well play it safe (for your ears, if nothing else).

That takes care of the "injection" part - you just substituted your ability to detect hum right out of the very aether, putting it into the amp where we'd normally expect to see a Reverb signal. If you got quite a bit of hum, you know that this stage is good. If not, you know where to focus your efforts. (It won't be as loud as if you'd done this at the input jack, but it will be loud enough to give you an "aHa!" moment. )

In case that was good, we'll need to "detect" if the Reverb driver stage is doing its job. The easiest way to do that is to simply take the output from the Reverb Send jack, and run it back into the Reverb Return jack. Now you know why I had you test the Return jack first - you need to know that it's good, before you can blame/exhonerate the Send jack. To this job properly, you must avoid overdriving the Return jack. Connect the two jacks (their center conductors, of course - they already share the signal return line) with a 220KΩ resistor. If they're close enough, just tack-solder the resistor in place. You could also solder some RCA plugs to the resistor's leads, bend those leads, and then insert said resistor into the jacks properly, as if it were a cable.

All of this will basically test the AC capabilities of the two Reverb stages - you've already tested the DC voltages. In the technical vernacular, you've localized the problem. Providing that one or the other stage is bad, you're now set to isolate the problematic part(s). Get back to us with your results, please.

HTH




sumgai

[gfxbss]

@!#$

The amp has now completely lost the effects channel. This means that the amp is down to one channel(since series and parallel are actually a mix of the normal and effects channel). Also, this means that the reverb will never work until this channel is up and going.

Now, since the normal channel still works fine(the tone is a bit thin sounding but it has since Ive owned the amp). I am thinking that this must be an issue in the solid state preamp of the mace.

Wanna continue to help?

Thanks,

Tyler