Crate V3112 Troubleshooting

[Sarsipius]

Hi everyone,

I'm new here and was looking for some ideas troubleshooting my Crate V3112. I turned it on the other day and got this nasty hum. It hums even if the volume is all the way down.

Here is a sample of the hum. Hum.m4a

I have checked all tubes on an Orange VT1000 Valve Tester. They all show good.

As I read a few other places I plugged a guitar in the line in on the back of the amp and the hum is gone and the guitar can be heard loud and clean. This pretty much rules out the output tubes and high voltage supply right? Putting the problem in the pre-amp section?

I have tracked down a schematic that seems to match the amp. crate_palomino_v32.pdf and been trying to work through it but haven't got anywhere with it.

I have measured everything on it I can find that was marked VDC but I guess I don't know exactly what I'm looking for. v3112 voltages.txt


If anyone can assist in removing the gremlins from this amp I would appreciate it

[drewl]

Okay, you tested the power amp and it seems good.
Hum is coming from the pre amp.

You can try swapping out the pre amp tubes, one at a time to see if it is something simple.

Does it have reverb? I forget. If so, does reverb control have an effect?
Try unplugging the tank.

[Sarsipius]

Thanks drewl,

I have swapped tubes around and put in new tubes. No change. I will check the reverb situation in the morning and report back. I think it was working but have had it turned down while trying to figure this out. Thanks for your ideas.

[g1]

It looks like the tubes in the power amp section have AC heaters, but the preamp tubes use DC heaters. Check for ripple on the preamp heater supply and op amp supplies. (+/-14.7V and +/-12.9V supplies)

[Sarsipius]

drewl: I checked the reverb and everything works as it should. Unplugging the tank had no effect.

g1: Thanks for pointing out that tubes 1 & 2 have DC heaters. I didn't think of that or even pay attention to that part of the schematic. I will take some measurements as soon as I can. My old scope gave up and my new one will be in on Friday.

Thanks again guys.

[SoulFetish]

Hi everyone,

I'm new here and was looking for some ideas troubleshooting my Crate V3112. I turned it on the other day and got this nasty hum. It hums even if the volume is all the way down.

Here is a sample of the hum. [ATTACH]40284[/ATTACH]

I have checked all tubes on an Orange VT1000 Valve Tester. They all show good.

As I read a few other places I plugged a guitar in the line in on the back of the amp and the hum is gone and the guitar can be heard loud and clean. This pretty much rules out the output tubes and high voltage supply right? Putting the problem in the pre-amp section?

I have tracked down a schematic that seems to match the amp. [ATTACH]40283[/ATTACH] and been trying to work through it but haven't got anywhere with it.

I have measured everything on it I can find that was marked VDC but I guess I don't know exactly what I'm looking for. [ATTACH]40288[/ATTACH]


If anyone can assist in removing the gremlins from this amp I would appreciate it

You got a V30? That takes me back! I had one of those and it was the amp that made me realize that every Crate does not suck. I loved that amp... but enough retrospective.

Right away I can tell you that the Hum you posted is a wonderful example of what 120Hz sounds like.
I have the schematic for a 3112 including Transformer Specs, Power Supply, Output Stage, and Preamp. I'll track 'em down and post them when I can.

[mozwell]

sch attached for V3112 which has DC heaters for the first two valves, and for VC3112, which has AC heaters

You have a V3112, so as G1 said, check the pos & neg 12.9VDC supplies (ie across C44 and C43), check with your meter on DC volts and AC volts, do this with the preamp valves in place as we want the normal load on the power supply for this check.
Also check the pos & neg 14.7V supplies for the op amp, if you get ripple on the supply on the op amp, that may be the cause of the hum & your valves could be fine. IC2 is just before the send socket, so it could be the source of the noise, power supply ripple could cause the hum you hear.

It could be the soldering on C23, C24, C26, C26, C43 or C44, or one of these capacitors could be faulty, especially if they are old. If you end up replacing one of them, i would do them all as you have the amp opened up anyway.

If IC2 is in a socket & you have a spare one, its easy to swap it out & see if the IC is the problem, or if you don't have a spare, remove IC2 and carefully link pins 1 & 3 on the ic socket. If the hum goes away, then it is either the IC or the power supply for the IC.

[SoulFetish]

Moz, you beat me to it! These are great suggestions and Good places to start. 120Hz (or 100Hz to the reast of earth) screams power supply ripple to me.
So, Sarsipus, do what Moz suggested, these are some areas to check into and I'd be surprised if these don't at least expose the problem.

The V30 schematic looks to be the same one that I have as well, but I'll post this one also because it includes the specs and design for the power transformer and it may be of interest to some.

Crate V30 - 3112 schematic & transformer.pdf

[Dave H]

g1: Thanks for pointing out that tubes 1 & 2 have DC heaters. I didn't think of that or even pay attention to that part of the schematic. I will take some measurements as soon as I can. My old scope gave up and my new one will be in on Friday.

Use your scope in differential mode (or use a DMM) to measure ripple on the DC heaters. The -H pin isn't at ground potential so you don't want to short it to ground by connecting the scope ground to it. It shouldn't blow anything up in this case because they have used 100R artificial centre taps (why have R60,61 and R79,80?) but it would if they had used the real centre tap.

[PboRich]

Just found this forum, just found this thread and just joined.

I currently have a CRATE V3112 (US Made cream tolex) on my bench for recapping the pcb is out and a schematic in hand. First thing I noticed is that C32 and C57 appear to be switched on the schematic, as they are currently located on the pcb in reverse order and the amp has never been touched before I opened it up.

Anyone have experience with recapping these things? Also, I read elsewhere that someone had done some mods to make it sound like a Dumble(?) is that even remotely possible?

Thanks in advance,
Rich

[g1]

If the unit was otherwise working, replace parts as they are in the unit. The schematic is probably wrong, or for a different revision.

[Enzo]

My parts list doesn't even go up as high as C57. I see C32 is a small cap across a rectifier, wherr is the other?

[g1]

My parts list doesn't even go up as high as C57. I see C32 is a small cap across a rectifier, wherr is the other?

In post #7, there is a VC3112 schematic that has a C32 and C57 as supply filter caps. Maybe that is the schematic he meant.

[Enzo]

Ah, didn't realize there were multiples.