VOX AGA-70 Owners / Experience?

mlejeune · #1 10-26-2016, 06:50 AM

I have a very lightly used Vox AGA-70. Both microphone inputs are acting intermittently and often will drop out completely for no apparent reason. I was wondering if anyone with this amp has had similar experience. If so have you had it fixed? Both guitar inputs seem to work fine. I like the amp and my preference would be to get it fixed. There was one attempt to repair the amp already under extended warranty but this did not solve the issue. At the time I thought the issue was with one input but now it appears to be both.

If anyone has similar issues and has any guidance or insight, it would be greatly appreciated.

SpruceTop · #2 10-26-2016, 10:48 AM

I have a VOX AGA-150 but I've only used a microphone with it once and didn't have a problem. Are you running a dynamic or a condenser mic into your VOX AGA-70 channels? I'll try running my Shure Beta 58A through both channels to hear if anything drops out.

mlejeune · #3 10-26-2016, 11:05 AM

Good question. The mics I've been using are Shure SM-58 and PG-57. I've mostly used the mic on the clean channel but when that channel starting dropping in and out on the weekend, I switched to the tube channel and discovered it was dropping out too. Thanks for the help!

SpruceTop · #4 10-26-2016, 03:06 PM

What you've got are dynamic mics, so they don't need phantom power. I just tested a Shure Beta 58A dynamic in both channels of my AGA-150 and both channels work fine with no dropouts.

Let me suggest you try another microphone cable with your mics to see if the problem remains.

Also, you might want to "exercise" all switches and knobs by sliding and turning them back-and-forth several times just in case some corrosion has set in.

Let us know how you make out and Good Luck!

mlejeune · #5 10-26-2016, 05:26 PM

Yeah, dynamic mics so not an isuue with phantom power. I've tried switching cables and still an issue.

Turned on the amp tonight and one channel took a bit of time to come on and the other one didn't come up at all. I had hunch from all of the different things I've been trying and plugged the guitar channel in and unplugged it and the mic channel came back on loud and clear and stayed that way for the evening. I know this doesn't make sense but it "seemed" to work. More testing required.

mlejeune · #6 10-30-2016, 06:35 AM

OK. So it does seem that if the mic input is not working and I plug and unplug the guitar input, that it seems to either fix or improve things. I'm pretty sure that the guitar input blocks the microphone input when it's plugged in. But I don't understand why what I'm doing is affecting the mic channel in a positive way. I'm hoping to eventually get this repaired. Any thoughts?

SpruceTop · #7 10-30-2016, 08:01 AM

According to the VOX AGA manual, the mic input is disabled when you plug a guitar into the guitar jack on the same channel. Do you find that when plugging-in or unplugging the guitar that it takes very little force to do either? I'm wondering if there is an intermittent short-circuit due to worn guitar jacks? Try the following by first making sure you have nothing plugged into any of the jacks on the rear of the amp: Plug-in both a microphone and guitar into the same channel and listen to what happens as you plug-in and withdraw the guitar plug several times. Talk into the mic or play music from a speaker as you do this to hear what the mic is doing. Once the guitar is plugged-in, wiggle the plug and see if you get crackling or noise of some sort. Also, do this after the guitar plug is withdrawn slightly away from full insertion. I'm wondering if the spring-contact arms in the guitar jacks are worn? Your problem seems to be guitar-jack related but it seems strange that both channels are affected unless you've used both channels a lot. Please keep us informed on your efforts.

mlejeune · #8 10-30-2016, 03:41 PM

Thanks for your help SpruceTop. There are several points of resistance when inserting and removing the guitar jack on both channels. The amp has seen very little use so it's not likely worn jacks. Maybe they are not worn enough?

No significant crackling when the guitar plugs are inserted fully or partially. The sound on the mic channel simply cuts in and out fairly smoothly when the guitar is plugged in and out.

Plugging something in and out of the guitar input seems to fix things going forward after the amp is powered up but right now I wouldn't depend on this amp in a live situation.

How's your experience with the 150 been? I like this amp other than the aforementioned issues.

gretsch4me · #9 11-01-2016, 08:14 AM

Both the AGA70 and 150 use a 12AX7 preamp tube in the mic channel if I remember correctly. Sounds like a tube issue from what's being described.

Sent from my SM-G900W8 using Tapatalk

SpruceTop · #10 11-01-2016, 11:50 AM

Quote:

Originally Posted by gretsch4me

Both the AGA70 and 150 use a 12AX7 preamp tube in the mic channel if I remember correctly. Sounds like a tube issue from what's being described.

Sent from my SM-G900W8 using Tapatalk

The tube listed for the AGA amps is a 12AU7 (ECC82), which is similar to the 12AX7 (ECC83) but I don't know if they're interchangeable. His 1/4-inch instrument inputs work okay. It would be simple enough to change the tube, though, to hear if that corrects his intermittent mic problems.

BruceShaffstall · #11 10-19-2017, 11:03 AM

I have recently Purchased a slightly used Vox AGA 70 and I notice something strange with the Tube Preamp channel.

(I had an AGA 30 years ago and this one is acting different)

I plug into the Tube channel with the Guitar and turn on the amp and get no sound. Wiggle the chord, nothing, try a different chord and guitar input and nothing.

I leave the amp turned on and then take out the 1/4 in guitar chord and hear a snap from the speaker. I plug it back in and the tube preamp channel now works fine.

Questions: Is this normal?
Is the tube going bad and needs a jolt to start?
Is there something wrong with the Guitar 1/4in jack?

Any other suggestions?

I expect to be able to simply plug in the guitar and then turn it on and as soon as the Tube warms it should work, but that is not what is happening