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Old 26th September 2012, 05:43 AM   #1
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Default Options for guitar amp

Hello, this is my first post.
I have an electric guitar, a practice amp (washburn BD8K), a small PA amp (realistic MPA-20) and two 8inch speakers (In homemade box) How can I use all of these together? I have a few ideas:
1. mic guitar amp to PA amp
2. use speaker as mic to PA amp (with proper circuit to match mic input)
3. use attenuator between guitar amp headphone out and PA mic input
4. connect guitar amp headphone out to PA line level input
5. custom wire guitar and PA amp to work together (anything goes... where did I put that soldering gun?)
The guitar amp is only 8 watts, but has a gain switch for overdrive. The PA amp is 20 watts and has 1/4 inch mic input and RCA line level input.
Any suggestions?
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Old 26th September 2012, 03:10 PM   #2
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Location: in half space
Going direct into a PA usually sounds pretty bad, as the guitar speaker is a fair share of the tone. So, I'd suggest micing the guitar amp.

However, since the speaker is part of the tone, if you want to be louder and sound better, your best bet would be to invest in a real 12" guitar speaker. 8 watts into a ~98dB speaker is surprisingly loud.

Warehouse Guitar Speakers | Warehouse Guitar Speakers
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Old 26th September 2012, 07:05 PM   #3
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Keriwena, good point about a bigger efficient speaker (I am very experienced with speaker building) I can get a decent 8 inch guitar speaker very cheap (closeout sale... parts express) and maybe also use the smaller speaker from practice amp with a crossover. Just for fun, I'll try wiring my two 8 inch speakers and see if 8 watts can drive them.. if so, then I'll add the smaller speaker with a capacitor (I also have a handwound coil I can add)
Does anyone know if there is a way to tap into the preamp section of the practice amp? Can I do this and send output to line level input on PA? If this is possible, can I run both the practice amp and PA at same time (both sharing preamp output)? I can't find a schematic of the guitar amp (BD8K) and don't know if preamp/main amp are one board. Is the gain/overdrive part of preamp, or does the whole setup work together?
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Old 27th September 2012, 10:52 PM   #4
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I opened up the practice amp... doesn't seem to have preamp, just simple design so no way to "tap into" it. I did try hooking up my two 8 inch speakers (parallel for 4 ohms) and it was weak using "clean" setting (but it is weak with original speaker anyway) On "boost" setting it sounded great! The little original speaker couldn't handle higher volume with boost, but my two 8's handled it with ease. I've decided to get a single 8 inch guitar speaker for the practice amp, but still have no solution if I want "clean" sound. Is there any way to convert PA amp for guitar? Any simple circuit I can build to do this? I got this thing for free, so I can "hack" into it... no worries. Maybe I should post this question to amp forum?
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Old 28th September 2012, 05:08 AM   #5
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Location: Jackson,michigan
Yes, There are many guitar Preamp circuits available that you could build to use with a PA amp is it is just an amp.
A guitar preamp will modify the signal from your guitar to a tone of your liking and then run that into the PA amp.
If you are using PA type speakers then you may want to turn down the highs quite a bit.
Using a Amp Cabinet Simulator filter is also another way to get a good sound as well.
It all depends on what kind of sound you are after and what kind of equipment you are attempting to use.
So more details would be nice.

I have a little Park amp that the 8" speaker didn't last long to my abuse and I now have it hooked to two very old 12" jensen's and it now has a killer sound that is quite loud as well!!
I was thinking that 4 of those Peavey 8" from Parts Express would make a nice little guitar cabinet for small amps like my Park.

http://www.parts-express.com/pe/show...number=299-202

If your amp uses a chipamp it could be easily worked with as my Park uses a TDA2030 chipamp and is rated about 15watts or so.
And the pinouts for them is easily found on the web.

But that is plenty loud using my 12" as Keriwena pointed out you want to have a high efficiency rating especially with a smaller amp.

I used to have a Fender Vibro Champ and I mounted one of my Sunn 10" drivers in that thing and what a world of difference it made!
I kept it that way for many many years until one day I had three of them hooked to it in parallel and fried the output transformer.
Opps......You live and learn !!! He,he,he,he

jer

Last edited by geraldfryjr; 28th September 2012 at 05:16 AM.
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Old 28th September 2012, 07:08 PM   #6
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geraldfryjr, could you give examples or link for circuits? Do you mean for the "preamp" to be connected to mic input, line level input, or wired in another way?
I forgot to mention, but the two 8 inch speakers are actually home stereo woofers. I have them in a huge box with a "slot port", and I have some smaller speakers I can add for more highs. They sounded great! Not too much "bite", but good smoothness and bass. Hey, great deal on those peavey 8 inch... don't buy them all... leave one for me About my small practice amp: are you suggesting upgrading the IC for more power? Does that mean I finally get to play with my soldering gun? I miss building my own circuits... it's been years. Ramsey has some really easy affordable kits... have you looked at these? Last thought: I'm interested in the Digitec Bad Monkey. Could it be used with the PA amp? I couldn't find schematic of the PA amp, just parts list. MPA-20 originally had transistors, but mine seems to be newer model with ICs. I can post photo of inside if that will help (it looks brand new... low milage)
I hate to admit it, but I'm very strapped for cash... that's why I'm messing around with these silly ideas. Hope to build my own guitar amp from scratch someday.
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Old 29th September 2012, 10:30 PM   #7
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I should have explained something: I have some friends that will be here for a few months. They all play... acoustic/electric guitar, drums, and keyboard. I need a quick solution... by the time I get a decent guitar amp they will be gone. We just want to have fun and jam! That's why I just need a quick fix. By the way, I'm very intersted in a tube amp
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Old 29th September 2012, 11:35 PM   #8
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Location: Jackson,michigan
Typically preamps have a line level output.

Don't woory about me buying up those peavey speakers, Get as many as you want !!
I am set on guitar stuff right now.

Posting a picture of what you are trying to work with would help a great deal.
There is a possiblity of replacing the chipamp to one of a higher wattage providing that the power transformer is big enough and the voltage is right.
I had thought about doing this with my Park amp, But I don't need to really, since I got my big rig running again and It sounds just fine with the two Jensen 12's hooked to it.

There is a couple of really good threads on some preamps in this forum.
As I had stated before, you can also build a copy of just the preamp stages of a commercial amp of your liking.

Like this,

Tube pre into a solid state

My two favorite amps are the Marshal 8100 valvestate and the Peavey Renown 400.
Both preamps are made from opamps with the exception of one tube in the Marshall.

This DIYer's thread had the same thing in mind using a LM4780 dual chipamp which has two LM3886's on one die,

LM4780 Guitar Amp Question

I have had both amps as the Marshall had gotten stolen.
I used to run it through an ART Power Plant straight in to the board when recording and sounded sweet in some headphones as well.

For tubes I would like to duplicate an all tube Marshall TSL or AVT2000 or JCM2000 preamp stage as I was never quite too crazy about the JCM 800 amps.

Here is a goolge search for "diy guitar preamps" images page,

diy guitar preamps - Google Search

There is a ton of stuff out there to choose from!!!

I have read a lot of good reports about this one,

Infinity: New DIY Universal Guitar Preamp Day !!!

And can be breadboarded very quickley as PCB are easy to make as well.
It just depends on your skill level.
I started doing this kind of stuff when I was 13 back in the late 70's, So it is very easy to do.

Rod Elliott has some great stuff on his site as well with a huge wealth of info,

ESP Projects Pages - DIY Audio and Electronics

Ask and you shall recieve,

diy guitar preamps - Google Search

Enjoy !!!

jer

P.S. Here is another cool thread of the PAIA Preamp,

PAiA stack-in-a-box guitar preamp kit

This is very similar the Valvestate design only Marshall powers the tube with a High voltage B+.

Last edited by geraldfryjr; 30th September 2012 at 12:05 AM.
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