Fuzzy audio from mic input on Akai?

[gac]

Hey everyone,

I own an Akai GX-620 and am just trying to bring it up to speed and correct all the issues it has.

The current one I'm dealing with (besides replacing the tape counter belt) is this fuzzy, almost distorted audio I'm getting when I try plugging a mic into the mic input.

I'm not sure how common this is or if it's a serious thing. I'm praying it's easy to fix or I'm just missing something.

I've tried the line in / line out on the back of the machine and that works fine, so I'm able to send audio back and forth between my tape machine and my computer. However I'd like to experiment with recording directly to the tape itself.

I can post an audio clip if need be to better describe what I'm experiencing -- but I hope this is enough for someone in here to know what I'm talking about and have a solution to the fuzziness/distortion.

Sincerely,
GAC

[Somnium7]

Do you have or know of a source for the schematics?

[gac]

I'm not sure where I can find any... does anyone out there know?

The booklet I got is very basic and cheap and doesn't offer any explanations of the internal workings.

Hopefully someone out there might be familiar?

GAC

[Tim Gillett]

I believe those Akais had faulty preamp transistors. I certainly had to replace them a few times myself in various models.

I read on a website not long ago some guy sells the exact original part number trannies, but I never bothered. Replacing them with garden variety low noise npn's seemed to do just fine. There are two per channel.

A tech could do it for you, and a good one should be able to do it without the schematics. It's a bit of a cramped circuit board as I recall but not too hard to do.

Just be aware, the preamps are hardly stellar in performance even when working as new. You might be better off using a small mixer and plugging into the line in of the Akai, saving the expense and trouble of the repair.

Tim

[gac]

Thanks Tim, I'll probably leave that one alone for now... but I'm glad I have a good idea of what the problem is now. Thanks again,

GAC

[Dr ZEE]

GAC,
is it "fuzzy loud and ugly" or "fuzzy weak"
Is the "fuzziness" consistently the same, or comes and goes?
Is it exactly the same "fuzz" on the left and on the right channel?

What exactly microphone do you use. Did you try different mic(s) (if you have them)?

just wondering.

[gac]

hey dr zee,

i actually just tested it again and it was my mistake-- the mic volume on the tape machine was at maximum to compensate for the mic gain being so little since i didnt run a preamp through. so it was really just the white noise of the tape machine at max volume. its just odd that it overpowered all of my mics to that degree!

it sounds fine now with a preamp and/or using other instruments that naturally have more gain.

but now i have another issue-- i dont know if i should start a new thread for it-- but i only get a signal from the mic right channel and none from the mic left channel. what might be wrong here?

GAC

[Dr ZEE]

I don't know.
First make sure you get it set right. Check "track selectos" push-switches, then make sure that you actually adjust the level (there are two knobs for mic L and R on the same shaft. Do they both turn as you turn the top one? Turn both of them ALL THE WAY counterclockwise first).
If you are doing everything right and still no go for one mic channel, then the mic preamp may be 'dead', which could be a one dead transistor sort of problem (just guessing, ???????). Could be fixed if you up to it, also could be pain in the neck to do it yourself.

[gac]

Hey Dr Zee,

Both track selector buttons are pushed...

After some tweaking with the volume, i noticed that the mic left channel DOES work... but, it fuzzes in and out depending on how you sensitively you turn the volume knob. as if some connection might be loose perhaps? and the audio is very distorted as well.

when i run any signal through it, it sounds like it's dying, and any note or sound played rolls off before its completed.

i could record the audio if it'd help explain more.

i'm not sure what to guage from this... is this a dead transistor?

GAC

[Dr ZEE]

So does the Right Channel Mic works fine when using the same mic with no problems at all? So you have this fuzz problem only with left channel mic input? Correct?

Originally Posted by gac

, it fuzzes in and out depending on how you sensitively you turn the volume knob.

Do you get this fuzz and distortion while you actually turning the mic record level knob? Or do you mean that the fuzz and distortion "comes in" if (and only if) you turn the level to the a certain point (or pass that point) while there's no fuzz/distortion below that point.
Or is this problem completely random and comes in and out at any level regardless whether or not you are touching anything, sort of acting on its own ?
I am trying to sort out potential problem with the level adjustment potentiometer, it may need cleaning.
Also take a close look at the mic jacks (well, as close as possible), just a guess here, but there could be bad contact there (dirty contacts or even broken)

[gac]

The right channel works perfectly, using the exact same mic setup. No problems at all.

As for the left channel, theres fuzz and distortion when i turn the knob. There's also fuzz and distortion when I talk into the mic. However, when silent, or not touching the knob, there's no fuzz or distortion.

I cant tell much from the mic jacks... they look fine, but I could be wrong... anything in particular I should be looking for?

- GAC

[Dr ZEE]

If you hear scratches or sound gets 'distorted' while you actually turning the knob , then the potentiometer may have problem. If it's not defective/broken, then it can be dirty (oxidized). You can try cleaning it and see if it'll help (which may NOT be the case ).
To do so you need a contact cleaner (or so-called control cleaner) and you'd need to open up the machine to access the potentiometers to be able to spray the cleaner inside the potentiometer. I'd imagine you need to get inside from the back of the machine. If you don't feel comfortable doing that, then just leave it alone.
Also it may not be the problem, so at the end all you get is spent time anscrewing-screwing minus few buck for cleaner .
However, it's a good thing to have a contact cleaner around when you dealing with electronics, connectors etc, so if you feel like doing so you can purchase Contact/Control cleaner at RadioShack (it's ten bucks):
http://www.radioshack.com/product/in...entPage=search
it may actually look different on the shelf in the store from that picture in on-line catalog, but the same catalog number (64-4315).
Or visit : http://www.deoxit.com/,