Bass guitar effect pedal (need help)

[ReCoC]

Hello everyone.
As you can see this is my first post here and i need your help on this one:

I've built an envelope filter for my bass guitar which i found here. It works just fine except for one little thing. The output signal is lower than the input so i tried to find a way to amplify the output signal. I searched on the internet and found this guitar amplifier. I built it and intergrated it into the envl. filter's box. Connected the filter's otuput to the amp's input and the amp's output to the box'es output jack. I also connected the amp's 9V input along with the filter's 9V input and use this 9V power supply. So i turned it on but nothing changed. I think the amp is ok although i didn't try it on it's own.

Have you got any ideas\suggestions on that?

thank you in advance

 

[audioguru2]

Hi ReCoC,
You have a bass guitar but the amplifier circuit has an input capacitor value so small that it cuts bass frequencies below about 1600Hz and is half power at 320Hz.

Increase the value of the capacitor 22 times to get some bass.
Also, the gain pot is wrong, it is supposed to have a capacitor in series with it. You don't need it anyway because the gain is 20 without it.

It doesn't need a 25 ohm reostat to waste battery power. Use a 1k pot and a 10uF output capacitor.

View attachment 39820

 

[ReCoC]

Also, the gain pot is wrong, it is supposed to have a capacitor in series with it. You don't need it anyway because the gain is 20 without it.

It doesn't need a 25 ohm reostat to waste battery power. Use a 1k pot and a 10uF output capacitor.

What is the differnce between the 25 ohm reostat and the 1k pot? Why is the reostat wasting battery power? Wouldn't the smaller capacitor (10uF) cut the bass frequency on the output as well?

 

[audioguru2]

What is the difference between the 25 ohm reostat and the 1k pot? Why is the reostat wasting battery power?

Turn up the volume and hold your guitar near the speaker for a loud fuzzy sustain. The LM386 will be feeding 0.5W to heat the 25 ohm reostat and heat itself with 0.29W. The battery current will be 88mA and a little 9V battery won't last long.

Do the same with a 1k pot and the battery current will be only 3.5mA which is less than the idle current of the LM386. The little 9V battery will last a long time.

Wouldn't the smaller capacitor (10uF) cut the bass frequency on the output as well?

220uF into 25 ohms has a half power frequency of 29Hz. Full power above 145Hz.
10uF into 1k has a half power frequency of 16Hz. It goes much lower. 16Hz is the heartbeat played at the beginning of Pink Floyde's Dark Side of The Moon song. You feel it instead of hear it. ;D

 

[ReCoC]

ok thanks a lot! I'll try it on monday because i forgot both circuits at work  :-[

two more things. Where will it be better to put the amp, before or after the filter? if i put the gain control can it be used as an overdrive?

thanks again man

 

[audioguru2]

Where will it be better to put the amp, before or after the filter? if i put the gain control can it be used as an overdrive?

You will like it both ways. Use a switch to select which way.

 

[ReCoC]

You will like it both ways. Use a switch to select which way.

interesting idea. will it have any noticable difference to the sound?

 

[audioguru2]

will it have any noticable difference to the sound?

Of course it will if the little amplifier or the filter are overdriven. If the power amplifier is overdriven instead then it won't make any difference.

 

[ReCoC]

wait a minute. I missed something here. ???

So do I or do I not put the gain pot? And will it give me an overdriven sound? If i don't use overdrive, will it make any difference if I put the amp before or after the Envelope filter? The overdrive is a second priority. I mostly care that the bypassed signal is same loudness with the one after the effect.

ps. The amp will be in the same box with the env filter and will be switched on and off as one.

 

[MP1]

ReCoC,
You don't want to use the LM386 output to go into the input of your BASS amp. The overload is not good for the input section of the amp. The LM386 also does not make a good distortion unit. It clips too much.

Just increase the value of the input cap on your effect pedal so that it is allowing the low frequencies to pass. This is where you are losing some of the amplitude. If you still need amplification, change the feedback resistor on inverter a2c in the effect circuit. The R13 and R7 ratio determines amplification. If this does not help, add an amplification stage like a2c right after a2f. Note that this will invert your signal again, so you will want to add two if this is a problem. You can use a larger ratio between the input resistor and the feedback resistor to increase gain.

MP

 

[ReCoC]

Could you please be more specific? Exactly what values should I put and where exactly?
If I use the LM386 output to go into the input of the effect without the distortion?

 

[audioguru2]

If I use the LM386 output to go into the input of the effect without the distortion?

The article with the LM386 shows a high input impedance FET buffer from the guitar to the LM386 amp.

If you play strongly then the high output from your guitar could overdrive the FET, the input of the LM386, the output of the LM386, the circuitry in the effects unit or the power amplifier. Overdrive creates distortion that is called "fuzz".

 

[MP1]

Overdrive creates distortion that is called "fuzz".

...or it can also cause damage to the circuit. Uncontrolled or uncalculated overloading is actually harmful and might sound great for a few minutes.....then poof!  :'(

LM386 is not an input stage. It is a power amp chip. It has no place in the input stages of effects or amplifiers. Connect a speaker to it and use as a practice amp if you must use it for something.

MP

 

[ReCoC]

LM386 is not an input stage. It is a power amp chip. It has no place in the input stages of effects or amplifiers. Connect a speaker to it and use as a practice amp if you must use it for something.

MP

I see...

Well then please tell me exactly which resistors, capsitors, etc I have to change and what values should I replace them with? I'm not that good at electronics :-[ so you have to explain me with little more details....  ;D

 

[MP1]

Since you are using an effect that is not even meant to be used with your instrument, you will need a little experimentation to get by with the least amount of changes. If you would like to experiment with the values, I would start with changing the value of C2 and C3 to 1 micro farad or even to 2.2 micro farad. Then try the effect again. This might be all that you need. If you still need amplification, the next step is to change R13 to 470K. Again, you should try the effect before going further.
If you are still not there, tell me what you have resolved and what you have not. For example, you might have good amplification with not much effect. In this case, you would need to fix the amplification values in the threshold and attack part of the circuit.

MP