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EricHaven
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PostSubject: Using a practice amp as a preamp   Sun Jan 24, 2010 1:02 pm

So, just because I get bored easily, I was trying to figure out if there was a way to use a smaller practice amp as a preamp going into a power amp. I have this little 20 watter that I got on eBay for around $50 sometime last year, but I hardly ever use the thing. It sounds great, though! It has a volume, bass, mid, treble, an 8" speaker, headphone out, and even a built-in compressor. So I got to thinking, "Since this little beast sounds so good with just the little 8" speaker, I wonder if it could be ran through my power amp?"

I used Linda's Behringer guitar amp as the guinea pig, since my rig is all at Andy's studio, and Linda's amp has splitting jacks that allow you to access the power amp section. Now, I know full well that there is a significant difference in the impedance values of a headphone out and speaker out, and the front end input of an amplifier. But I wanted to start out easy to see what would and wouldn't work. So I first tried running the headphone out into the power amp of Linda's Behringer. As I expected, it did work, but not without a lot of noise. So, just for laughs, I clipped the speaker wires, and ran them to a jack into the power amp. Same results, only louder. Then I remembered that several years ago, I used to use a Whirlwind Direct Box that allowed you to run an amplifiers speaker level down to line level, so started thinking about the possibility of wiring up a simple circuit. A quick web search yielded this:

http://www.epanorama.net/circuits/speaker_to_line.html

I love quick, cheap, and simple, you know? Wink

A quick trip down to Radio Shack, and about $5 later for the parts. Voila'! I wired up the circuit. I then hooked it up the the speaker leads of the little amp, and plugged a cord between it and the power amp. And what do you know? The thing actually works! The noise fell away to practically nil, and the little practice worked perfectly as a preamp!

So if anyone of you Guys has a little practice rig and a power amp source, and you want to have a little fun working on a project, then I think this one's a winner. It was really cool to do something that I wasn't even sure could be done!

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PostSubject: Re: Using a practice amp as a preamp   Sun Jan 24, 2010 8:29 pm

yo man ... thats awesome.

i've found some of my most interesting things this way ... "i wonder what would happen if ...???"

if you get tired of lugging around the box with the 8" speaker, chek out the rack mount space issue i solved in my preamp posting in the new toys section. you could rip that small amp outta the box and mount it in something else ... maybe theres room in your current amp head? thats what my guitar player has ... an old marshall ss amp in a valvestate case (with the face ripped off) with a mic preamp mounted inside (and more wires everywhere). people see it and laugh at him ... then he starts playing it.

just ideas, just ideas.
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PostSubject: Re: Using a practice amp as a preamp   Mon Jan 25, 2010 7:13 pm

Yeah, I'm going to bring the little amp over to Andy's shop so he can help me rip the case apart. I'd like to get my hands on a cheap two unit rack that I can mount the thing in.

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PostSubject: Re: Using a practice amp as a preamp   Mon Jan 25, 2010 7:42 pm

EricHaven wrote:
I have this little 20 watter that I got on eBay for around $50 sometime last year, but I hardly ever use the thing. It sounds great, though! It has a volume, bass, mid, treble, an 8" speaker, headphone out, and even a built-in compressor.

What model/brand is it? I'm looking for a cheap, good sounding practice amp, as I'm going off to college next year and obviously will not be able to take my 100 watt with me.
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PostSubject: Re: Using a practice amp as a preamp   Mon Jan 25, 2010 7:55 pm

yo eric !!!!!!!!!!!!!! bounce

2 rack mount space case .........

http://www.carvinguitars.com/products/single.php?product=SV2
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PostSubject: Re: Using a practice amp as a preamp   Tue Jan 26, 2010 4:54 pm

Oops! Let me clarify, MadMike. Laughing Although, that is a great deal on a case!

I meant the actual metal chassis that houses the unit itself. Like this, only not costing an arm and a leg:

http://snpi.dell.com/sna/images/products/mlrg/A2057581.jpg

Most rack chassis I find cost around $75 to $125 to begin with, and there is NO way that I'm going to throw this little amp into something that costs so much.

Does anyone happen to have a two unit piece of broken rack gear they would be willing to part with for next-to-nothing?

Speaking of the amp KS, it's branded by some company called Precision Instruments, but don't bother trying to find them on the web. They are one of a kajillion companies from overseas who make cheap gear for resellers on eBay to list. I think I paid about $50 for mine back in October of 2008. A quick search on eBay shows that there are a few different bass practice amps starting at around $60 or so.

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PostSubject: Re: Using a practice amp as a preamp   Tue Jan 26, 2010 7:11 pm

gotchya ....

lemme take a look around.
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PostSubject: Re: Using a practice amp as a preamp   Tue Jan 26, 2010 7:42 pm

Thanks, Bro! Wink

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PostSubject: Re: Using a practice amp as a preamp   Tue Jan 26, 2010 7:46 pm

cheapest applicable i found so far ......

http://www.parts-express.com/pe/showdetl.cfm?partnumber=320-820&source=googleps

i've bought from them before ... decent company. lotsa cool stuff.
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PostSubject: Re: Using a practice amp as a preamp   Tue Jan 26, 2010 7:51 pm

wow!

again ... they want so much money ... basicly for a metal box!

its that word ... "vintage". vintage doesnt make it better. vintage makes it cost more. its still a metal box!

i saw a d.i.y. blog about using an old computer case. i would bet a company by you that does computer refurbs might have some scrap you can use.
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PostSubject: Re: Using a practice amp as a preamp   Tue Jan 26, 2010 9:58 pm

Thanks MadMike! That is a cool chassis, but it lacks rack ears. I want to be able to rack mount the thing.

I have looked for a surplus place around us, and it turns out that we are in such a remote area that there isn't a whole lotta market for recycled 'pute stuff. Just my luck. Rolling Eyes

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PostSubject: Re: Using a practice amp as a preamp   Tue Jan 26, 2010 10:31 pm

Have any friends who are good at working with sheet metal? Very Happy

That's an awesome solution to your dilemma, man! How cool is that...
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PostSubject: Re: Using a practice amp as a preamp   Wed Jan 27, 2010 4:31 pm

Well, it wasn't meant as a solution for my dilemma, but the funny thing is that is exactly what it's turning into. It's like our earlier discussion regarding using amps with simpler controls, and how much I dispise EQ's on amplifers. This little guy only has the bass, mid, and treble controls, which is perfect! Nice and simple! And if I need more tonal range, I can still go to a pedal EQ. Plus it has a compressor built in already! Wink

As for my never-ending quest for the perfect dirt, I have been making my drummer crazy with all of my different tonal experiments, as he is also our recording engineer. So one day last week, he opens up a case that he had and tosses a Line 6 POD 2.0 at me. My eyes popped out of my head! He goes "you wanna try messing with this thing?" I was like "hell, YES!" Laughing BTW, here is what the POD looks like:

http://cachepe.samedaymusic.com/media/quality,85/brand,sameday/Moto_POD_Hi_Rez-93a8c5c64f06f0389707082c86c47aae.jpg

I don't know where he gets all of his cool toys, but it's fun to try them all! He also pulled out a Korg A5 bass pedalboard that I tried out, and it was OK, but nothing really too exciting: http://www.chrisguitars.com/korg-a5bass.jpg

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PostSubject: Re: Using a practice amp as a preamp   Wed Jan 27, 2010 8:45 pm

again ... back to that vintage word.

eric ... you said that korg isnt anything too exciting.

youre right. its a dinosaur and fairly pedestrian.

... but it sez korg on it!

(madmike wipes the drool from his chin)

i'de love to have that A5. for me ... thats vintage!
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PostSubject: Re: Using a practice amp as a preamp   Wed Jan 27, 2010 8:47 pm

How did you like the POD's dirt, Eric?
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PostSubject: Re: Using a practice amp as a preamp   Thu Jan 28, 2010 8:35 pm

LOL! I did forget to mention anything about the results, didn't I? Laughing

It's actually quite cool! I still have to mess with it a little more, but it was cake to quickly dial up a great distortion tone. Honestly, it is as close as I have come to a Grunge tone as of now.

MadMike, I totally hear you. The Korg is a rather vintage piece, but I wouldn't hold my breath. I don't expect Doug to let me buy the thing! Laughing But if I decide it isn't for me, do you want me to ask him what he might want for the thing?

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PostSubject: Re: Using a practice amp as a preamp   Fri Jan 29, 2010 6:10 pm

shure ... why not.

lemme go search for some specs on the thing ...........

i'm saving some nickles for an electro harmonix bass micro synth .... aside from the moog and the dinosars with the extra pickup i gotta mount on the bass, its the one that seems the most impressive.

the boss synth effects on the gt-10b processor are cool but not practical. they dont work too well with even the preamp or cabinet modeling and distort way too much. i need a separate better unit.
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PostSubject: Re: Using a practice amp as a preamp   Fri Jan 29, 2010 6:14 pm

wow! that korg is a dinosaur .... its a processor with 5 effects.

its like ... easier to just carry 5 pedals.

altho korg makes me drool ... this thing would be rendered useless by me. thanx anyway eric.
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PostSubject: Re: Using a practice amp as a preamp   Fri Jan 29, 2010 7:45 pm

No problem, Bro. Wink

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PostSubject: Re: Using a practice amp as a preamp   Sat Jan 30, 2010 11:13 am

Sounds kinda like those Ibanez units from the 80s with three or more of their effects (like EQ, chorus, TS9, etc) all in one cheap, plastic enclosure...


Last edited by Chowderboots on Sat Jan 30, 2010 12:11 pm; edited 1 time in total
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PostSubject: Re: Using a practice amp as a preamp   Sat Jan 30, 2010 11:42 am

Yeah, that's pretty much the deal, Bro. Wink

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PostSubject: Re: Using a practice amp as a preamp   Sat Jan 30, 2010 12:11 pm

Rad. Getting one of those would be fun for a little bit. I think you can see Dave from Maiden using one in the Beast Over Hammersmith footage.
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PostSubject: Re: Using a practice amp as a preamp   Wed Feb 03, 2010 1:43 pm

Final test results. Wink

I brought over my little franken-practice-amp-thing to Doug's studio last night to give it a whirl as a recording preamp.

Dud. Sleep

Way too flat sounding, noisy as heck, and simply not functional. But it was an interesting experiment, and Doug got a good laugh out of seeing the thing! Laughing

BTW, a correction on my earlier post. The Korg that Doug brought out for me was not the A5, but is actually the A4:

http://www.zikinf.com/_gfx/matos/dyn/large/korg-a4-bass.jpg

And we took the time last night to dial up some killer tones for me using the Korg, as well as the aforementioned Line 6 POD. But I shall elaborate in a new thread. Wink

So my experiment at making a preamp from a little practice amp is completed.

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PostSubject: Re: Using a practice amp as a preamp   Wed Feb 03, 2010 3:55 pm

well ... i dont know about completed ... or at least my version of complete when i try to make some outdated, just about worthless, pos work for what i need and it fails.

you must sacrifice it to the gods of bass! smash it! burn it! melt it! have a mosh pit on it!

... or you can just be ok with sticking it in the back of a closet and never using it again. personally, i like my way better.

ok, ok ... that korg a4 is more of an animal. it has more effects for being a smaller of a sequential model number ... the a4 has more than the a5???

would be interested in fiddeling with it to determine the quality of the synth effects ... i was trying to state earlier about the boss and what i want ... good tracking; tracking is the correct word. i doubt this korg has good tracking.

still, all the reviews i read, the electroharmonix bass microsynth has the best tracking.
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