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Author Topic: Old newb questions  (Read 3321 times)

dogbox

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Old newb questions
« on: December 20, 2020, 04:42:04 PM »
Hey guys, haven’t been here in a while or played around with electronics and electric guitars for couple years. Been on an acoustic odyssey lol. Feel like I’m starting from scratch again. Dragged out my MIM strat and red knob superchamp..thats downstairs in the man cave and too loud for the living room.

I was wanting to build myself a small stereo coffee table guitar amp. I have seen plenty of cheap amp boards on ebay, pre soldered with surface mount components with stereo 3w output. That would do me, anything much louder would annoy the missus, and we don’t want that ;) and I don’t want make a real amp with power transformer..i don’t do AC.

I need a preamp...but before I get to that stage I have some really obvious things that I don’t know/ forgotten.

1. Could I just use an effects pedal as a pre?
My intuition says no because guitar amps have an input stage ( i remember that part)

2. Would pedals work directly into a line level inout if i placed a DI box between pedal and amp? What would it sound like? Would a cabsim pedal or amp in a box work?


3. Is there a schematic on here or elsewhere that gives a simple clean channel, with maybe basic tone controls that you could point me to, that may be suitable for these ebay amps. Fetzer valve was one i used in the past and I remember Phil(Phat) had some great preamp designs floating around here. Would there be a way to modify one of those to work with the ebay amp?

4. Should I stay away from those chinese prepopulated boards on ebay, and build a proper deigned practice amp? If the latter option, Which one?

5. If it was Ok to have a preamp board ( that i would perf) and the ebay amp side by side in a box, and i didn’t need a D/I circuit in between, could I use a single 9/12v wall wart to power both boards, or would I need a seperate supply for both pre and power amp?

Am i barking up the wrong tree with the D/I box..i just remember having a need for a DI box when plugging into my mixer years ago..sounded terrible without it, and it had line level inputs. When it comes to electronics I know enough to be dangerous. I can solder ok and use a dmm. I used to build pedals 10 years ago, then had sporadic forays back into electronics but only limited understanding. Sorry for the dumb questions, and rambling in advance

Looking for your input
steve

Loudthud

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Re: Old newb questions
« Reply #1 on: December 21, 2020, 12:31:09 AM »
You can probably use an effects pedal as a preamp, but not all will be suitable. You don't need a DI box as long as the pedal has enough output to drive the power amp. A wall wart is a good choice for a power supply as long as it has enough current capacity for the power amp. It should be enough for both preamp and power amp. Both circuits can be built into the same box.

A WORD OF WARNING: If the power supply does not have a safety ground, you will probably have hum on the output of your amp. In addition, you may get a mild to moderate shock if you touch someone playing another amp when you both are touching your guitar's strings. BE SAFE, GET A POWER SUPPLY WITH A SAFETY GROUND !

flester

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Re: Old newb questions
« Reply #2 on: January 21, 2021, 04:20:53 PM »
Did you make any progress on this? If you are like me, such projects happen over months rather than days. I have had good results with pedals straight into a power amp module. The Kemo amp modules are durable and stand up to soldering better than very cheap ones. 

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edvard

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Re: Old newb questions
« Reply #3 on: January 23, 2021, 02:05:12 AM »
Hey guys, haven’t been here in a while or played around with electronics and electric guitars for couple years. Been on an acoustic odyssey lol. Feel like I’m starting from scratch again. Dragged out my MIM strat and red knob superchamp..thats downstairs in the man cave and too loud for the living room.

I was wanting to build myself a small stereo coffee table guitar amp. I have seen plenty of cheap amp boards on ebay, pre soldered with surface mount components with stereo 3w output. That would do me, anything much louder would annoy the missus, and we don’t want that ;) and I don’t want make a real amp with power transformer..i don’t do AC.

I need a preamp...but before I get to that stage I have some really obvious things that I don’t know/ forgotten.

1. Could I just use an effects pedal as a pre?
My intuition says no because guitar amps have an input stage ( i remember that part)

As Loudthud said, it depends.  A chorus pedal?  No.  A 5- or 10-band EQ with boost?  Yes.  Some dirt boxes are full-fledged preamps in themselves, consisting of a gain control, multi-band tone control, and output volume.  That's about the bare minimum for what you'd want in a preamp, even a clean one.

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2. Would pedals work directly into a line level inout if i placed a DI box between pedal and amp? What would it sound like? Would a cabsim pedal or amp in a box work?

You don't need a DI between a pedal and a line input.  One thing that pedals are very good at is taking your high-impedance guitar input and producing a low-impedance output, which more-or-less is compatible with line level inputs.  A standalone cabsim would work well after your preamp if you want some color to the sound that more resembles a "real" amp, or you could get one of the Tech21 "Character" series or Joyo pedals that simulate amps.  They are a preamp and cabsim all in one.

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3. Is there a schematic on here or elsewhere that gives a simple clean channel, with maybe basic tone controls that you could point me to, that may be suitable for these ebay amps. Fetzer valve was one i used in the past and I remember Phil(Phat) had some great preamp designs floating around here. Would there be a way to modify one of those to work with the ebay amp?

Any preamp with at least 2-band tone controls (bass & treble) and a volume or output control will work.  The only mod you may need is to make sure the output is low-impedance, but I don't think that's a problem with most schematics you can find here and elsewhere.  You can message Phatt, he's still around; I'm sure he won't mind at all sharing anything that might help.

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4. Should I stay away from those chinese prepopulated boards on ebay, and build a proper deigned practice amp? If the latter option, Which one?

Use what works for you.  I'd say if you get a small stereo amp or kit that you plan to run regular hi-fi speakers with, then definitely a cabsim as mentioned before will help the sound, especially with headphones.  The same stereo power amp hooked up to a bona fide guitar speaker is not all that different from any production Solid State guitar amp.

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5. If it was Ok to have a preamp board ( that i would perf) and the ebay amp side by side in a box, and i didn’t need a D/I circuit in between, could I use a single 9/12v wall wart to power both boards, or would I need a seperate supply for both pre and power amp?

As long as the power supply has enough juice to run the power amp and then some, you'll be fine.  Say you have a circuit or amp module that's 10 watts; you'd need something that was at least between 10 and 15 watts, and some will even say don't run the amp with anything less than 2X the power demands of your amplifier.

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Am i barking up the wrong tree with the D/I box..i just remember having a need for a DI box when plugging into my mixer years ago..sounded terrible without it, and it had line level inputs. When it comes to electronics I know enough to be dangerous. I can solder ok and use a dmm. I used to build pedals 10 years ago, then had sporadic forays back into electronics but only limited understanding. Sorry for the dumb questions, and rambling in advance

A D/I box would be useful if you are simply plugging your guitar into something low-impedance with no pedals or preamps at all.  If you know how to build pedals, you already know all you need to tackle this one, it's just a bigger box with a speaker.  I don't think your questions are dumb at all.

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Looking for your input
steve