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Post by morbe on Feb 7, 2012 9:03:20 GMT -5
Oh please forgive me. I feel like im pestering the older brotjer types around here but i noticed that radio shack sells a velleman 7watt monio audio amp. Not sure how loud it gets im sure not so loud, but i wanted start building and modding pedals amd would like a low wattage amp amp to test them out. Right now im using a power i pod dock that works okay, but its my duaghters. So i saw this kit online and a 1.5 watt at radio shack. Im sure i can scratch the rca jacks and replace them with 1/4 inch jacks to make it a.guitar input. Right? I would love to see if i can put.in some kind of tube pre amp i have an old pre amp tube hanging around, bit i know this is not possible. I really just need something to amplify a guitar signal and since the age level for this is 12 years and up why not? Its not a diy tube amp but its a start!
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Post by reTrEaD on Feb 7, 2012 9:13:00 GMT -5
Oh please forgive me. I feel like im pestering the older brotjer types around here but i noticed that radio shack sells a velleman 7watt monio audio amp. Not sure how loud it gets im sure not so loud, 7 watts is LOUD if the speaker(s) is efficient. So i saw this kit online and a 1.5 watt at radio shack. Im sure i can scratch the rca jacks and replace them with 1/4 inch jacks to make it a.guitar input. Right? Your guitar might not have enough output to fully drive the amp. You might need to add a preamp. |
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Post by morbe on Feb 7, 2012 10:16:53 GMT -5
They have those too i just need get study up on how to get them connect to each other. But they have a guitar pre amp kit. Is there a way to build a tube pre amp? Or is that getting into the realm of danger? The amp + guitar preamp will cost about 30 - 40 bucks and with speakers more! Almost the price of a used amp on CL, im not trying to reinvent the wheel so im telling my self its a learning tool with benefits.
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Post by morbe on Feb 7, 2012 12:03:43 GMT -5
So they sell.them separatley and the amp needs to connect to the mains and the guitar pre amp is powered by 9 volt batery is it possible to some how to connect the pre amp to the power supply? The power supply in the insructions are for i think a 12v ac 6va transformer and a 1.5a 50v rectifier bridge. Im sitting here scratchy my head wondering what this all means and wondering if this may be unsafe to learn with. It seems relativly low in volts and stuff?
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Post by reTrEaD on Feb 7, 2012 12:28:41 GMT -5
Is there a way to build a tube pre amp? Yes. But tubes require a substantial amount of current for the heater. If you were planning to run from a battery, this can be a budget buster in terms of battery life. Also, tubes run from a low voltage supply tend to sound pretty crappy. A plate supply of about 100v would be a better. Using FETs for the preamp would be the best choice, imho. |
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Post by morbe on Feb 7, 2012 14:08:07 GMT -5
Yeah, for a simple amp. I can get the 7 watt amp but it requires a power transformer but it calls for 8-18vdc/0.5a couldnt i just find an ac adapter that puts out 8-18dc with the required amps and splice it in. Instead of getting out put transformer and a rectifier. I have tons of ac adapters. I also want to plug the pre amp directly to this power source. Which is in the same voltage and amperage range. They have a pre amp here in town but it has no tone controls. Is.this a hard.thing to add?
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Post by JohnH on Feb 7, 2012 14:37:14 GMT -5
This seems like a good project. Is this the amp module:? www.vellemanusa.com/products/view/?id=350529It will be great for home use, but note that the 7W is so called 'music power', and will be at max supply voltage into a 4 Ohm speaker. Amps are better defined by RMS output, (you can look that one up, to save me from explaining it wrongly!), where it says 3.5W into 4 Ohms, or more likely 2W into 8 Ohms, and less if you use lower power supply voltage. Still useful though. The amp is quite sensitive, but has a bit too low an input impedance for direct guitar use. But a simple preamp will sort that out, and I also suggest FET's or opamps as a base for it. Check out this site for ideas: www.runoffgroove.com/articles.htmlBut as a first pass to get it going, one JFET buffer with volume control will get you started with a clean amp that you can play. guitarnuts2.proboards.com/index.cgi?board=schem&action=display&thread=4595Put the volume contral after the buffer (instead of before it), at about 100k log. John |
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Post by morbe on Feb 7, 2012 18:28:30 GMT -5
Well thats the amp i got a universal preamp i plan to use. Im plan on playing with it to get it to work i need to find an old ac adapter for 12vdc and atleast .5A
Ill figure something out. I have tons of old adapters if i can find the ideal adapter it will run both devises, now all i need is a speaker. I have wood to make a case for it all. Im a bit worried that there is no ground for the adapters i mainly only have 2 prong adapters. It doesnt need to be that loud its just so i can test pedal mods and pedals i plan to build.
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Post by morbe on Feb 7, 2012 22:20:07 GMT -5
So I found a 12v power adapter that I can use and its 2 amps out put is in DC. Im putting my stuff together but Im a bit worried that I had to cut the tip off. I was going to get a 13.5v 1amp plug to use. I asked a guy at the local electronics store intertex and he said that its not lethal that I would feel a shock like a 9 volt battery to the tongue. but its would hurt worse because its a 13.5 volt. I'm just worried that when I plug in my guitar amp play through it, all that stuff is going to pass right through me and kill me. What are the odd of that happening? by the way I got a decent book at radio shack called teach yourself electronics. Its pretty decent.
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Post by morbe on Feb 8, 2012 11:17:54 GMT -5
Im good i have a better understanding of this. The project is a go will have pics and hopefully sound clips soon. I plan to build a chassis. I have a speaker being donated. Im plan to test swapping out the trim pot in the preamp with a potentiometer to see if i can get it to work as a gain. Since my amp will have volume. Im looking outside the web to see if there is a way to connect a make shift tone knob. If any of you guys have any schematics for an add on tone knib i sure would love to take a look at it. Thanks everyone. Still worried that my amp wont have a ground but im not too worried about it.
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Post by ashcatlt on Feb 8, 2012 14:11:23 GMT -5
As long as the wall wart is outside of the amp chassis there's not much to worry about. Something would have to go way wrong in order to get AC line voltage to your guitar. They always say "it's not the volts, it's the amps that kill ya", but actually I think it's the power (volts x amps). 13.5V @ 2 amps will hurt a little, but unless you've got other serious problems (pacemaker?) you will survive.
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Post by morbe on Feb 9, 2012 1:13:03 GMT -5
I built the amp it was easy from set up to clean up it took about 4 hours. I thought that the preamp stage would give more but I'm not sure yet as the speaker I was using Im sure was not the ideal speaker, it was part of a stereo system we used to have. any how here are some pics.  The electronic kits actually came in a clear case. I used this to make a prototype case, Of course I plan to make a mini head out of it.  Not sure if the speaker was the correct to test with. but this was just to make sure it worked.  Here is a video its not the greatest but Im still learning how to work the preamp and volume to dial in tone especially since it doesnt have tone knobs. I know it sounds awful but getting a great sounding amp was never the object, the object was to build a working amp.  |
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Post by JohnH on Feb 9, 2012 3:29:04 GMT -5
morbe - sincere congrats on getting it to work, and I think your recording shows some promising tones. When you get into the distortion part, is that the preamp giving you a driven sound, or are you just clipping on the power amp?
When tou get a guitar speaker fotr it, it will sound even better.
I know that is just a quick prototype to test it, but I like the random point to point wiring! and the drilling of the holes using a 45 Magnum!(that clear stuff can crack I think)
cheers
John
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Post by morbe on Feb 9, 2012 8:52:33 GMT -5
Thanks, its really hard to tell where the distortion is comming from. I have no i dead what the ohms on the speaker that was used. So as of right now it could be the electronics clipping out, the speaker distorting, or the preamp. I did notice that the pre amp has to be very low because it does clip out easy. Not to mention 7 watt amp i think in the specs says it starts to distort @ 2% not ideal for a guitar but i will get a hold of real guitar speaker and test it to see what happens
Im not done, i dont plan to keep in in the plastic box. I plan to make a mini head out of wood. Once i get he sound and get real wires as these came from a canabalized rca cabled meant for hd. Dont worry they were replaced with hdmi cables. I also plan to ad an led and power switch. Maybe a fuse but probably not a fuse.
Thanks again. Now im officially hooked on music, guitars, amps, tone and now elecronics.
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Post by JohnH on Feb 9, 2012 14:24:12 GMT -5
What is the preamp module? is it intended for guitar? Most likely the distortion, if it is not intended as part of the design of the preamp, comes because the input of the power amp is being pushed too hard. The specs say it has a sensitivity of 40mV, and the guitar itself can put out seveeral hundred mV, and probably the preamp does too. It may need a couple of resistors to make a voltage divider between preamp and power amp. In the meantime, you could try just turning your guitar volume down to make a small signal, then you can turn the power amp volume up.
The speaker is unlikely to be causing distortion, its just that the full-range tone of a hifi speaker doesnt sound good with electric guitar, unless you play very cleanly.
Once you get it running with clean output at good levels, there are heaps of circuits for getting a nice distortion if you want it.
John
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Post by morbe on Feb 9, 2012 15:40:43 GMT -5
Yeah, im thinking about taking the pre and out and see what happens. I have a pa speaker but i dont want tear up a good guitar cord for the 1/4 inch male end just to test it. Im looking for a tone knob schematic to add. The preamp chip is UA741M its out put is only 1k ohm i wonder if thats jacking things up.
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Post by ashcatlt on Feb 9, 2012 16:19:52 GMT -5
Schematics would make this much easier to discuss! I'd almost be surprised to hear that you got them with these "paint by numbers" kits, though.
A high-cut tone control can be wired exactly the same way you'd do on a guitar, though values will need to be tweaked a bit.
Does this speaker you're using have a separate tweeter? Can you open the cabinet and disconnect that? It will probably help quite a lot.
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Post by morbe on Feb 9, 2012 17:59:47 GMT -5
Yeah, the schematics came with the kit. Of course i didnt need them. Though i should have studied the board in order to learn how to apply a schematic to a bread board than and actual icb.
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Post by reTrEaD on Feb 9, 2012 20:37:33 GMT -5
Yeah, the schematics came with the kit. Of course i didnt need them. Just because you don't need schematics to accomplish building a kit doesn't mean you don't need them now, to have a discussion about understanding how to best use the circuit and/or make changes to it. Does this speaker you're using have a separate tweeter? Can you open the cabinet and disconnect that? It will probably help quite a lot. Good call. In addition, the overall gain the overall gain is probably a bit much and I suspect the input impedance of these circuits will be a little low for guitar use. |
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Post by ashcatlt on Feb 9, 2012 21:25:59 GMT -5
I thought he said the preamp was meant for guitar. OTOH, if we're looking to lose treble along the way, a "too low" input impedance might actually help the cause.
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Post by reTrEaD on Feb 9, 2012 23:30:57 GMT -5
I thought he said the preamp was meant for guitar. He said "universal", whatever that means... OTOH, if we're looking to lose treble along the way, a "too low" input impedance might actually help the cause. It might, particularly with a "dirty" amp. Less harmonic content in the input signal would make the distortion simpler and less fizzy. But if we're going for a decent sounding clean amp, decimating the highs at the input is not so good. |
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Post by morbe on Feb 10, 2012 8:26:52 GMT -5
I took the pre amp out for now. But im getting a lot of noise, like when i touch the strings i can hear a lot of crackle and pops but not too bad after you initially touch it, it doesnt hurt nor do i see sparks fly. Maybe im just super observant but when i turn it way up you hear that typical hum but when i touch the tuning keys to ground, ie. The metal frame of my garage door opener the hum went away. I dont expect any here to answer this but i thought ground caused noise, ghats why some amps have a ground lift. any my set just has a simple 2 prong wall wort no ground, i just left is that the noise was just some kind of electrical hum that was in the grounds and when i connected it to source.of.ground if found a place to go.
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Post by morbe on Feb 10, 2012 8:32:56 GMT -5
On the lighter side the amp alone was more than enough juice to power the guitar. I was using my test guitar an old beat up Kramer Ultra. Strat style guitar. Its decent more than enough for what i want to do with it. Just test pedals i plan to build. It sounds good at about volume level 5. It starta to break up quite quickly after that, but its rated to handle 7watts at 4ohms but the speaker i was using was only 8ohms. The univeral preamp is just a simple booster. Hey! Maybe i can turn it into a boost pedal! Any way here is a new.  |
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Post by reTrEaD on Feb 10, 2012 9:02:07 GMT -5
I dont expect any here to answer this but i thought ground caused noise, ghats why some amps have a ground lift. No. Proper grounds do not cause noise. Improper grounds can cause noise. That's why some amps have a ground lift. any my set just has a simple 2 prong wall wort no ground, i just left is that the noise was just some kind of electrical hum that was in the grounds and when i connected it to source.of.ground if found a place to go. lol wut? |
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Post by morbe on Feb 10, 2012 9:12:00 GMT -5
Lol i dont understand it either, intersting expiriment though. Just excuse me im still learning.
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