Anyone successfully built a EQ pedal with LA3600?

[nguitar12]

Data sheet here: http://pdf.datasheetcatalog.com/datasheet/sanyo/ds_pdf_e/LA3600.pdf

Everything seem simple.  Resonance Frequency can be determined by capacity value.
What else is needed in order to convert it into a guitar pedal?

[Johan]

Buffer on the input.
J

[nguitar12]

Buffer on the input.
J

Hi do you mean this?



Can this circuit be used?

[Johan]

Yes. But you don't need c2 since the eq already has a capacitor on its input

[nguitar12]

Yes. But you don't need c2 since the eq already has a capacitor on its input

It seem simple then
I always heard about input and output buffer but I never know why they are needed.
What are they for?And why output buffer is not required for this circuit?

Thanks so much

[R.G.]

I always heard about input and output buffer but I never know why they are needed.
What are they for?And why output buffer is not required for this circuit?

Input buffers are needed for pedal effects because they may be driven by a passive pickup electric guitar. The pickups on these are heavily inductive, and so they become high impedance at higher frequencies. So if they have to drive low impedance inputs, the treble is loaded down more than the bass, and the sound gets dull. A buffer with an input impedance of around 1M is generally accepted as eliiminating this effect.

Output buffers are needed when you reasonably may have to drive a low impedance load. This is generally not the case for guitar pedals, but can be in some circumstances. There is no substitute for knowing the details of what is being driven.

An output buffer is not needed for this circuit because as the datasheet shows, the output is taken from the output of an opamp, which is in general quite low in impedance already.

Note that the IC contains one opamp, five separate transistors, and some resistors. Exactly the same thing can be done with a dual opamp and five discrete transistors. Oddly enough, this doesn't save you much room on a PCB.

See  http://www.geofex.com/article_folders/eqs/paramet.htm for some info on EQs and a seven band EQ with a similar IC, the KA2223, and then the layout of both the KA2223 and an opamp/transistor layout of similar circuits at http://geofex.com/Article_Folders/EQs/greqs.gif

[nguitar12]

I always heard about input and output buffer but I never know why they are needed.
What are they for?And why output buffer is not required for this circuit?

Input buffers are needed for pedal effects because they may be driven by a passive pickup electric guitar. The pickups on these are heavily inductive, and so they become high impedance at higher frequencies. So if they have to drive low impedance inputs, the treble is loaded down more than the bass, and the sound gets dull. A buffer with an input impedance of around 1M is generally accepted as eliiminating this effect.

Output buffers are needed when you reasonably may have to drive a low impedance load. This is generally not the case for guitar pedals, but can be in some circumstances. There is no substitute for knowing the details of what is being driven.

An output buffer is not needed for this circuit because as the datasheet shows, the output is taken from the output of an opamp, which is in general quite low in impedance already.

Note that the IC contains one opamp, five separate transistors, and some resistors. Exactly the same thing can be done with a dual opamp and five discrete transistors. Oddly enough, this doesn't save you much room on a PCB.

See  http://www.geofex.com/article_folders/eqs/paramet.htm for some info on EQs and a seven band EQ with a similar IC, the KA2223, and then the layout of both the KA2223 and an opamp/transistor layout of similar circuits at http://geofex.com/Article_Folders/EQs/greqs.gif

Thanks. very detail. Actually I did read this page before. I decide to use LA3600 because the circuit is much more simple. As for the input buffer. How can I set the input impedance ?



Not many component can be adjust in this circuit.

[R.G.]

As for the input buffer. How can I set the input impedance ?
...
Not many component can be adjust in this circuit.

In the circuit you show, the input impedance is the parallel combination of the two 1M bias resistors, or about 500K. To get higher, you make them bigger, in equal proportion. This makes the thermal noise a bit worse.

While that circuit will work, That circuit is not what I would use.  I would make a bias voltage by using two 10K resistors between +9V and ground, and a 10uF capacitor from the junction of the two 10K's to ground. Then I would run a single 1M resistor from the junction of the 10k's to the + input of the opamp. This approach can be quieter, and is the starting point for even more advanced techniques for making it even quieter.

[nguitar12]

As for the input buffer. How can I set the input impedance ?
...
Not many component can be adjust in this circuit.

In the circuit you show, the input impedance is the parallel combination of the two 1M bias resistors, or about 500K. To get higher, you make them bigger, in equal proportion. This makes the thermal noise a bit worse.

While that circuit will work, That circuit is not what I would use.  I would make a bias voltage by using two 10K resistors between +9V and ground, and a 10uF capacitor from the junction of the two 10K's to ground. Then I would run a single 1M resistor from the junction of the 10k's to the + input of the opamp. This approach can be quieter, and is the starting point for even more advanced techniques for making it even quieter.

It is the better buffer you just mentioned?

This circuit is quote from the same website. Quite strange that he is using 1/2 tl072 instead of 071 in this circuit. Does it matter?

[R.G.]

It is the better buffer you just mentioned?

Conceptually, yes.

This circuit is quote from the same website. Quite strange that he is using 1/2 tl072 instead of 071 in this circuit. Does it matter?

No, not at all. In terms of electrical performance, there is no significant difference in using a single opamp versus half of a dual with today's well-made dual opamps.

[nguitar12]

It is the better buffer you just mentioned?

Conceptually, yes.

This circuit is quote from the same website. Quite strange that he is using 1/2 tl072 instead of 071 in this circuit. Does it matter?

No, not at all. In terms of electrical performance, there is no significant difference in using a single opamp versus half of a dual with today's well-made dual opamps.

Great, I am just worry different op amp will need a bipolar supply, which is what I don't want. I will try to build it. Thanks for everyone who had helped .

[Aryo rock]

Yup I build this equalizer week ago. But actually I bought this circuit from electronic store couple years ago for around 3 buck. The circuit is stereo but I only using one side and rehousing it into pedal. Sound is good, it can boost and cut around 10 -12 decibel I guess.  One thing I change is cap for high freq, because I need around 4-6 Khz.

[vigilante397]

I just finished the GGG 6-band EQ. Super easy build, great sounding pedal. The only part that gets a little messy is offboard wiring of 6 pots (7 if you use the external gain control like I did). Great circuit though.

https://www.generalguitargadgets.com/projects/18-eq/46-6-band-graphic-eq

[PRR]

There's already a perfectly good bias source on the LA3600 (see data).

Tap that to bias the TL07x buffer.

Also take the buffer's power from the 180r+47uFd power filter for the LA3600.

Now both chips track (within a few mV) so for a "much more simple" build you can omit the input cap into the LA3600's networks.

However for guitar it would be wise to add a little series resistance on the input, to protect against various things.

[roseblood11]

...and add the second half of the TL072 as a gain stage at the output.

But what about sound quality? How noisy is the LA3600?
I guess a clone of the Boss GE-7 that uses high quality parts would sound better. A bit more complex, but who cares?

[nguitar12]

Yup I build this equalizer week ago. But actually I bought this circuit from electronic store couple years ago for around 3 buck. The circuit is stereo but I only using one side and rehousing it into pedal. Sound is good, it can boost and cut around 10 -12 decibel I guess.  One thing I change is cap for high freq, because I need around 4-6 Khz.

Great. Can you share your cap value? I have trouble calculating them.

[nguitar12]

I just finished the GGG 6-band EQ. Super easy build, great sounding pedal. The only part that gets a little messy is offboard wiring of 6 pots (7 if you use the external gain control like I did). Great circuit though.

https://www.generalguitargadgets.com/projects/18-eq/46-6-band-graphic-eq

Thanks but I want to keep my build as simple as  possible.

[nguitar12]

There's already a perfectly good bias source on the LA3600 (see data).

Tap that to bias the TL07x buffer.

Also take the buffer's power from the 180r+47uFd power filter for the LA3600.

Now both chips track (within a few mV) so for a "much more simple" build you can omit the input cap into the LA3600's networks.

However for guitar it would be wise to add a little series resistance on the input, to protect against various things.

Thanks. It seem that this will be the finally schematic to build. Thanks again for your effort on this.
Should C1 be changed into 10uf to allow more bass end going through?
Also no cap is needed between pin6 of tl072 and input of eq stage?

[PRR]

> Should C1 be changed

100nFd into 1 Meg is below 2Hz. Far-far below any musical bass.

[nguitar12]

> Should C1 be changed

100nFd into 1 Meg is below 2Hz. Far-far below any musical bass.

Thanks, sorry for my noob question