Trying to build guitar amp

[markbernard]

I saw a couple of cool projects and wanted to combine them. A simple guitar amp at https://makezine.com/projects/make-09/the-5-cracker-box-amp/ and a pickup for an acoustic guitar at https://makezine.com/2011/12/20/collins-lab-diy-contact-mic/. To start with I am concentrating on the amp to try and get it working. I didn't try the one in th cracker box article because I couldn't find a rhestat for under $20. So I searched around for alternatives. One of the ones I tried is http://www.circuitbasics.com/build-a-great-sounding-audio-amplifier-with-bass-boost-from-the-lm386/. Another one is http://www.instructables.com/id/Portable-Guitar-or-iPod-Amplifier-Amp-9v-LM3/.

So far I haven't been able to get any of them to work. My main question, while I try to work this stuff out, is are these the correct designs to use for what I am trying? I am testing them with an electric guitar and a 4 ohm speaker salvaged from a computer speaker.

[markbernard]

I finally got one to work. This one https://www.instructables.com/id/From-Schematic-to-Protoboard-Building-a-Simple-LM3/. So I guess these kinds of designs are correct for this application. Now I just have to search to figure out how to reduce the hum.

[BradC]

Now I just have to search to figure out how to reduce the hum.

https://kinman.com/model-products.php?pid=4&products=Stratocaster&group=Named%20Sets

Welcome to the rabbit burrow that is guitars and hum. They all hum unless you are playing a battery operated amplifier while sitting in a Faraday cage. Ground loops, shielding... you have a lot of fun in front of you.

[Brumby]

Welcome to the rabbit burrow that is guitars and hum.

Yep.   Google "Humbucker" for one approach.

[Benta]

The original Stratocasters were horrible at picking up hum. Later models got the humbuckers, but at the same time lost a lot of brilliance. It's a compromise, sometimes you have to live with the hum. A radio-shielded room and a battery-powered amp will solve the problem 

[b_force]

In fact, it's actually bizarre that they don't use a balanced signal (or even phantom powered)
That way you would have a lot less noise problems.
All to safe a few pennies.

[Electro Detective]

EMG active pickups (battery powered) have been killing hum for decades AND are not wired to the earth ground shield on the guitar, 
so unlikely you'll get noise or zapped, even by a DIY amp going south

People with Stratocasters concerned with hum and buzz should put their 5 way toggle switch to position 2 or 4, rather than blow money fitting humbuckers

If your amp still hums after my suggestions, it's electronics troubleshoot frustration time      (or get out grandad's dusty sledge for a few swings)  

[BradC]

In fact, it's actually bizarre that they don't use a balanced signal (or even phantom powered)
That way you would have a lot less noise problems.
All to safe a few pennies.

Not saving pennies. SFA of the hum comes from anything that would be "improved" with a balanced signal. Pos 2 & 4 on a Strat can give some hum cancellation but unless that mixed out of phase sound is the one you are after it sounds pretty naff. Pos 2 is no substitute for a stinging bridge pickup sound.

Fender dabbled with humbuckers on the Tele Custom Deluxe but they were not great unless that flat sound was what you were after. They tried humbucking single coils in the form of the "lace sensor". They are a peculiar sound. Not humbucker nor single coil. Very particular early 90s kind of sound. They then made a good chop at copying the Kinman for their later "noiseless single coils". If it's a Strat sound you are after though, you just need to deal with the the hum, although the Kinmans are pretty good to my ear.

It's all subjective anyway, but mixed positions on a Strat are no substitute for a bridge or neck alone. A nice mod is an additional switch to give you neck and bridge to get that Tele twang. Not humbucking though unless you play with your phasing.

[markbernard]

Thanks for all the info guys!

This is the guitar I have http://www.musiciansfriend.com/guitars/washburn-house-of-blues-electric-guitar-package. Cheap but gets the job done. It has 2 single coils and a double coil pickup.

I get the hum even with the guitar unplugged and with gain at 20.

[b_force]

With a balanced signal I am referring to noise in general.
If you're running long cables (which you particularly do with a guitar), single ended wiring is asking for a lot of trouble.
The rest of the professional world uses proper balanced equipment.

About humming.
The main problem is not the 50/60Hz humming, but one octave higher.
The 50/60Hz hum can easily being filtered away (notch or highpass), since the lowest note on a guitar is around 82.41Hz
With DSP techniques it's actually not so difficult to remove an hum as well, but for a lot of guitar players that's a no go.

Thanks for all the info guys!

This is the guitar I have http://www.musiciansfriend.com/guitars/washburn-house-of-blues-electric-guitar-package. Cheap but gets the job done. It has 2 single coils and a double coil pickup.

I get the hum even with the guitar unplugged and with gain at 20.

If you mean that's also with the cable unpluggend there is something wrong with the amp.
Probably grounding issue

[markbernard]

No. I am using the jack as a switch to turn on the power. So the cable is plugged in. But even when I remove the jack and just run power through the amp with no input, I get a loud hum. I don't mind having some hum, I would just like to get the level down a little.

Thanks.

[b_force]

I don't know how much gain you're making, but a like I said, a lot of times it's paying better attention how you ground the thing.
Also, just double check semi-loose (solder) connections etc.

[markbernard]

It is currently on a breadboard. I am using the lowest gain(20). However I am powering it at 12v with a computer power supply. I just tried it with a 9v battery and the hum has now dropped to an acceptable level.

Thanks very much everyone.

[Electro Detective]

Thanks for all the info guys!

This is the guitar I have http://www.musiciansfriend.com/guitars/washburn-house-of-blues-electric-guitar-package. Cheap but gets the job done. It has 2 single coils and a double coil pickup.

I get the hum even with the guitar unplugged and with gain at 20.

With that guitar, if wired correctly at the factory, you should have no or minimal hum at switch positions 4 (mid and neck pups) and position 1 the humbucker at the bridge

With some guitars (not all) position 2 may give you the same result as position 4, only if the humbucker coils are a split wiring arrangement.

Anyway, before you continue further I would strongly suggest you try the guitar and cable plugged into a working amplifier (friend or shop) to ensure they are both working perfectly and noise free,

otherwise you will end up between ROCK and a hard place   

i.e. that's THREE sources of possible hum and noise that you need to eliminate, starting with the guitar and cable

Once done you may find the amp build behaves better and that's all you have to concentrate on. 


OTOH, if you like drama and frustration      please ignore the above   

[markbernard]

Thanks.

I already have an amp for it. And there is no hum in the amp (maybe a very small amount). I am just trying to build a more portable one as well as to learn.

I did find this http://howtodosteps.blogspot.ca/2017/04/lm386-amplifier-circuit-schematic.html. He claims to have gotten rid of almost all the hum. The video shows that the hum disappears. I just don't know if what he did is possible and he is just pulling everyone's leg.

[Brumby]

I hope this post is unnecessary - but I feel it should be said...

Just promise us one thing ... if you ever see someone offering a "tip" on how to cut out hum by snipping the earth connection inside anything ... DON"T DO IT.

It may well fix the hum problem - but that won't be any good to you if you get electrocuted.


As difficult and frustrating as it may be - spend the time to find the cause and fix it, safely.

[Electro Detective]

I hope this post is unnecessary - but I feel it should be said...

Just promise us one thing ... if you ever see someone offering a "tip" on how to cut out hum by snipping the earth connection inside anything ... DON"T DO IT.

It may well fix the hum problem - but that won't be any good to you if you get electrocuted.


As difficult and frustrating as it may be - spend the time to find the cause and fix it, safely.

Cutting any earth ground to defeat noise that should not be there is similar to the goings on in the movie 'Deer Hunter',

it's russian roulette.. musician style...   

[mrpackethead]

In fact, it's actually bizarre that they don't use a balanced signal (or even phantom powered)
That way you would have a lot less noise problems.
All to safe a few pennies.

My ovation elite LX in deed does.   Its not cheap.

[Buriedcode]

Almost all 'hum' from guitars comes from the pickups, namely single coils, although humbuckers *can* hum, it is just greatly attenuated because of the nature of the pickup (two back-to-back single coils).
After that its improper grounding of the metal on the guitar and/or the socket/jack.

I would stick to the bridge humbucker for testing, so any hum you pickup will most likely be from your cable or your breadboard setup (its going to be breadboard..).  Nothing much can be done about the hum single coils pick up.

[b_force]

If you just want to test the amp, simply short the input (maybe with a termination resistor)
Standard procedure.

[dmills]

Tip for anyone doing work inside a guitar, put a class Y cap of maybe a nF or so in series with the bridge earth connection, it wont stop a tingle but will make that live guitar, lips meet earthed mic experience rather less toe curling.

Not something that should ever be needed and not something that is going to make that fault safe (Metal pot shafts and jacks), but it would have saved several lives back in the day.

Regards, Dan.

[markbernard]

Thanks for all the replies everyone.

I would definitely rather not mod the guitar. So I'll keep working on the circuit some more. It is quite a bit better with the 9v battery. I'll also try using just the the humbucker.

[markbernard]

Well I solved a large part of it. I had my inputs reversed. I had pin 3 to ground and pin 2 as the input from the guitar. Once I reversed them it cleaned up a lot more. Even at 200 gain.

Now it's my A string is the worst. It cause a lot of distortion when plucked loudly instead of softly. The low E is next and the other four are pretty good.

[markbernard]

After some experimentation I figure out a couple of gain resistors to use (instead of a trimmer). I need a 560ohm for my 4ohm speaker and I need a 1Kohm for my 32ohm headphones. I also added a 1000uF capacitor on the bypass and that reduced the string buzz. I now have no more hum than my store bought amps and only a little more buzz. I'll post the schematic soon in case it will help anyone else.

[markbernard]

I was able to get both the speaker and headphones working with a single gain resistor of 1k. I think that sets the gain around 73.

I have attached the schematic if anyone is interested.

[Audioguru]

But even when I remove the jack and just run power through the amp with no input, I get a loud hum.

Maybe your power supply produces the hum, try powering the LM386 amplifier with a battery that produces no hum.

It is currently on a breadboard.

Each row of contacts and each of the messy long wires all over the place on a solderless breadboard is an antenna that picks up hum from electricity that is all around it. Use a compact pcb or stripboard instead.

You have a 4 ohm speaker. The datasheet of the LM386 shows that it works well with an 8 ohm speaker. A 4 ohm speaker produces more heat in the LM386 than output power.

[HB9EVI]

Hi there; my first post here so far and some recent experience:

After years of more or less not using my Fender, I decided to build a midi-controlled loop switcher for my stompboxes and a the same time to reconstruct the whole guitar setup. I removed the stompboxes from the piece of wood they were fixed all along with an old Zoom 2020 and the midi pedal. This board was connected by more than 5m long cables with the the patchpanel on the rack where the midi-controlled DSP-FX are mounted. The guitar itself was connected to the rack's patchpanel - so all together there was far over 10m cable between guitar and the first stompbox. Long time not aware about the capacitance of that long cable chain, I was always disappointed about the setup's sound; so patching the guitar directly to the new built loop switcher with an active hi-Z input amp was real revelation - crisp and brillant sound like never before, and in the end much less noise and hum too. Being aware about coxial cable capacitance as a ham, I oversaw this issue on my guitar setup totally.
The lesson after all is to never forget considering the lenght of your cables in the guitar setup if sound's poor and noise/ham are bugging.

vy 73
Pascal