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Permalink Reply by Mark Bliss on November 14, 2011 at 7:19pm

Well I am confused!

The headphone connection of the amp is an output, so the mic cant be used there, but as far as the mic not working at the instrument input, maybe some more info on the type of mic you are attempting to use?

Also, most amp circuits will shut off the speaker output if something is plugged into the headphone out jack.

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Permalink Reply by Jim Marksberry on November 14, 2011 at 7:24pm

Well, right now I am using a computer mic called a quick shot. I had a regular and loned it out, last time I saw it. Guitar, (Bass) works fine in the input jack. I had to put an adapter on the mic but I know it is working OK as I plugged a set of computer head phones into the amp and had to use it. The amp is fairly new.

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Permalink Reply by Mark Bliss on November 14, 2011 at 7:36pm

"but I know it is working OK as I plugged a set of computer head phones into the amp and had to use it."

 

I take this to mean you know the AMP works with headphones? Still lost here.

 

But I suspect you might have a mic with such low output it wont operate plugged into the amp input? It should work.

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Permalink Reply by Jim Marksberry on November 14, 2011 at 7:40pm

I am beginning to think you may be right. I was referring that the adaptor is working when I plugged the headphones into the amp output jack, but the mic didn't work in the input jack using the same adaptor.

I would still like to have a mic jack in that amp, that's why I wondered if the headphone jack could be converted.

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Permalink Reply by Mark Bliss on November 14, 2011 at 7:49pm

Ok, now I am on board!

Obviously you need to try a different mic! I havent run into this problem before, but I have never tried to use a computer mic either. Condenser mics can be quirky things though.

I guess the headphone jack could be disconnected and wired as an additional input, but then you might wish you still had the headphone output.

To me the simplest and most useful solution would be a splitter for the input, but then you might wish you could set the levels individually..... I reckon a little inexpensive two channel mixer might be the ticket here. What you are really wishing for is a two channel amp for Christmas.....

Hey, anybody got any cheap rigging ideas for Jim here?

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Permalink Reply by Jim Marksberry on November 14, 2011 at 7:51pm

He he, I don't think anyone will get me an amp for christmas or a mic, by humbug!

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Permalink Reply by Ron "Oily" Sprague on November 14, 2011 at 8:38pm

Jim,

 

One issue seems to be, to which Mark Bliss is referring, and which is what it looks like in your pic (unless that is a headphone cable), is that you can't plug an input device (your mic) into an output jack (your amp's headphone OUT jack). The other issue may be with your mic, specifically, its impedance. Most mics are low impedance, but some cheaper ones are high impedance; most guitar / bass input jacks are designed to accept high impedance inputs from... guitars and basses, which are high impedance devices. Plugging a low impedance source (your mic, maybe?) into a high impedance load (your amp's guitar / bass input channel jack) can result in a severe impedance mismatch, which can mean very weak or no signal, resulting in...no sound. The matching of the impedance in ohms of the source device to the load device is actually important for good signal transmission.

 

WARNING: the following can get very deep and confusing very quickly; I'm just scratching the surface here:

 

Is your mic equipped with a 3-pin XLR, 1/4" or 1/8" pin male connector on the cable end? If the XLR, then Radio Shack sells a $17.99 XLR-1/4" low-Z to high-Z adapter / transformer, that can allow you to plug a standard mic (say a Shure SM58 or 57, for example) into a gutiar amp's input jack, so the mic can be used as a PA. I have had one of these puppies for over 20 years, which works great if I have to plug in one of my stage mics into a mixing board with only 1/4" input jacks, or someone's small guitar amp for use as a temporary PA.

 

If your mic is a computer mic, these typically have a 1/8" pin male connector, and some of them come with a 1/8" - 1/4" adapter. Computer mics are typically (but not always) high impedance devices, so you'd think you could just plug it into your amp's guitar jack and get usable signal (I just checked out your Quick Shot: an extremely high impedance electret condenser mic). But it depends on what high (or low) impedance means. Here again, if the impedance differences between mic and amp are too great, you get either lots of noise, or no signal.

 

A commonly used definition for low to high impedances is:

 

Low = 50 - 600 ohms

Medium = 600 - 10k ohms

High = 10k - 100k ohms

(k=1000)

 

Also important is whether the cabling to the mic is balanced. Balanced is better, because it offers better noise rejection. Pro or semi-pro mics typically use balanced XLR connectors and cabling. Cheaper mics typically used unbalanced cables, and are, hence, noisier.Unbalanced high impedance mics are also highly dependent on cable length. They can easily lose over 50 percent of their signal = transmitted voltage (typically in the high frequencies) with a cable length of only 6 feet or so, depending upon their impedance rating.

 

RE Converting your Silvertone amp headphone jack to a mic jack:

 

As Mark says, there is probably a "cut-off" circuit in the headphone OUT jack that disables the amp's internal speaker when anything is plugged into that jack. I have an amp that has this same feature, whcih is useful for playing your amp in through headphnees the wee hours without waking up the household. If you have plugged your mic into the headphone OUT, you will get no sound. Converting the headphone OUT jack on your amp to a mic IN jack is NON TRIVIAL, and basically means redesigning the circuitry inside the amp. Unless you are really good with a soldering iron, and know your amp's electronics inside and out (which I doubt, given your question - not being mean, jsut sayin'), I wouldn't attempt this.

 

I understand you are on a limited income. However, I will still make a purchasing suggestion: for around $175 new ($130 used) at your local Guitar Center, you could pick up a 5-watt, battery-or wall wart-powered Roland Stereo Mobile Cube. I have one of these, and it has become one of my favorite small practice amps. The beauty of it is that it has separate, switchable, guitar, keyboard and mic inputs, with 2 4" stereo speakers, and allows for simultaneous guitar and mic inputs with separate volume controls for each channel. I have used this onstage with my daughter in front of 1000 people in her school gym for a talent show a couple of years ago, and it was loud enough at 3/4 volume for both the acoustic-electric I played and her singing voice to be heard through a standard SM58 vocal mic. Here's a coupla pics:

 

 

 

 

I hope this helps,

 

Oily

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Permalink Reply by Jim Marksberry on November 14, 2011 at 9:02pm

The picture you see is the headphones pluged into the jack, the one on the left is the guitar jack. I understand what you mean and really it would be no problem rewiring the headphone jack to the input jack but I dought I will do that. I think the best is to purchase a standard mic and rethink other parts of it. I live along in the country so I don't worry about bothering other people. It was just and idea. Another thought is to get another jack and wire it to the input and leave the headset alone.

I sold off all my music equipment a few years back thinking I was done, piggy backs and mics, the whole shebang. Just thought maybe get into CBG's for fun.

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Permalink Reply by Ron "Oily" Sprague on November 14, 2011 at 9:30pm

Jim,

 

Ah. I wondered. Sounds like what you really want / need is something that can provide both guitar and mic input at the same time. That's why I recommended the Mobile Cube. But there are other ways. Yeah, a standard vocal mic could help, but you'll still need something to plug it into. You could try one of the small Danelectro, Fender or Vox mini-amps for around 40-50 bucks, or you could  build a CBG amp using an LM386 chip for about the same price, and use that as a vocal amp. You could also try the Y-splitter method, getting a dual 1/4" or 1/8"  female input cabled to a single 1/4" male output (I remember the garage band teens in my neighborhood in the 60's doing this, running both a guitar and a vocal mike through the guitar amp input, because they only had one amp between them - the sound ends up pretty muddy,  with weird alternating sounds as the varying voltages from the guitar and the mic hits the amp, but it does work - I did the same thing surreptitiously with my parents' then-high-end stereo cabinet when I started learning to play and sing in the mid-70's). Problem is, both the guitar and mic will be pretty quiet, and you can get soem feedback issues this way, as well.

 

Yeah, I hear you on "getting into CBGs for fun." I have now spent several hundred dollars on parts, "must have, 'cause it will make said job easier, tools," and even several CBGs made by other people. Truly, it's an Addiction.

 

But I can stop whenever I want.

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Permalink Reply by jim on November 15, 2011 at 12:58am

The adaptor your using is stereo for your headphones, and your trying to use it in a mono input jack.

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Permalink Reply by Mark Bliss on November 15, 2011 at 1:38am

Ah, now theres something I hadnt considered, and is a likely culprit! If the adapter is mismatched for the input receptacle..... There you go.

And of course Oily makes some very good points as well, the impedence mismatch issue for one, but the limitations of a band aid solution as well will cause a whole 'nuther set of issues!

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