5 Band Tone Stack Help

[Box_Stuffer]

I found this 5 - band EQ diagram , but the host page had no mention of what the values of the pots should be. I have seen many EQ schematics and a lot of them use either 100K or 24k pots, so I put this together using all 100k pots and a 10k pot at the end for level. I have a 2n2222 boost in front with a gain of 20 and 100nf caps in and out. 

It sounds pretty good, but I would like a little higher highs and a bit lower lows. I am just starting to experiment with complex tone control. How would you guys set this up?

[antonis]

I put this together using all 100k pots and a 10k pot at the end for level. I have a 2n2222 boost in front with a gain of 20 and 100nf caps in and out.

Could you plz post a schematic..??
('cause 10k level pot might load Tonestack output and BJT boost might need to be configurated as summing amplifier..)

[PRR]

I found this

That doesn't even look right.

There ARE good multi-band EQ plans around. Don't jump on the first (apparently) clear one you see.

[Box_Stuffer]

I put this together using all 100k pots and a 10k pot at the end for level. I have a 2n2222 boost in front with a gain of 20 and 100nf caps in and out.

Could you plz post a schematic..??
('cause 10k level pot might load Tonestack output and BJT boost might need to be configurated as summing amplifier..)

At first I tried to make this and I could not make it work.




It is pretty vague on the definition of "pre-amp" but it recommends something with a gain of 20-30. It said that  100mV signal in would be attenuated to around 10mV signal out. So I used TransistorAmp as a template and made a boost as close to that as I could with what I have on hand.




I wasn't hearing much change in the sound when turning the pots, so I applied the same boost to the front of the previous tone stack and added the 10k "level" control on the end. It works okay for a first attempt, but I'm sure it could be better.

I would like to get into some more complex examples, but they use ICs that I don't have yet and also the sliders are expensive and that is if you can even find the values that you need.

[antonis]

At first I tried to make this and I could not make it work.

This is another kettle of fish..
It's a Wien network and needs "isolation" between its ends..
(low impedance driver and high impedance next stage input..)
In fact, it works well when going into a summing amplifier..

P.S.
See example below:

[antonis]

I have a 2n2222 boost in front with a gain of 20

If you refer on the CE amp posted, it hasn't gain of 20 even with infinite load..
(it hardly exhibits a gain of 13.5..)

Considering Collector resistor is effectively set in parallel with the parallel combination of all tonestack pots/resistors, it might exhibit a gain of less than unity (dependent on pots settings..)

[Box_Stuffer]

I have a 2n2222 boost in front with a gain of 20

If you refer on the CE amp posted, it hasn't gain of 20 even with infinite load..
(it hardly exhibits a gain of 13.5..)

Considering Collector resistor is effectively set in parallel with the parallel combination of all tonestack pots/resistors, it might exhibit a gain of less than unity (dependent on pots settings..)

If I use a summing amp at the output, do I still need a boost in front to push the signal through all the pots? Would it still need a "pre-amp" at all?

[antonis]

If I use a summing amp at the output, do I still need a boost in front to push the signal through all the pots?

As long as summing amp exhibits some gain (proportional to tonestack loss), no..

But you'll need a low impedance driver (e.g. a BJT buffer..)

P.S.
A dual op-amp should serve both for in & out driving purposes..

[GibsonGM]

Stuffer, what Antonis is getting at is that you need a transistor buffer (or one made of other parts, like an opamp) in front of the circuit.    This will act like a bridge between 'what comes before' and the tone controls, which as you are reading, suck up a lot of juice.  This is called "insertion loss", which you need to overcome (using the buffer).

A buffer is a current source (not a voltage source).  It is like a big pot of current sitting there, and the signal controlling it allows that current to DRIVE the following 'stuff', without interacting with the circuit before it.

In the second post, 'preamp' was doing this job.  probably half-heartedly, too! 

It is easy to add an input buffer to one of these tone circuits, followed by a summing amp.  You could even make them first, and start by adding 1 tone control and testing it - then another and so on.    The two circuits isolate what you're doing between them, which is a good thing 

Like the man said - if you use a DUAL opamp, one amp can be configured for the buffer, and the other for the summing amp!

[Box_Stuffer]

Stuffer, what Antonis is getting at is that you need a transistor buffer (or one made of other parts, like an opamp) in front of the circuit.    This will act like a bridge between 'what comes before' and the tone controls, which as you are reading, suck up a lot of juice.  This is called "insertion loss", which you need to overcome (using the buffer).

A buffer is a current source (not a voltage source).  It is like a big pot of current sitting there, and the signal controlling it allows that current to DRIVE the following 'stuff', without interacting with the circuit before it.

In the second post, 'preamp' was doing this job.  probably half-heartedly, too! 

It is easy to add an input buffer to one of these tone circuits, followed by a summing amp.  You could even make them first, and start by adding 1 tone control and testing it - then another and so on.    The two circuits isolate what you're doing between them, which is a good thing 

Like the man said - if you use a DUAL opamp, one amp can be configured for the buffer, and the other for the summing amp!

Cool. Thanks. I have a lot of EQ schematics downloaded and some have the opamp method you are describing. I just havent tried them yet. Some of them use the LA3600 IC , which I do not have yet. I found this Electro Harmonix Diagram that is what you are describing - I think. Would I need n opamp for each band?




And here is a similar one with no buffer, but a transistor for each band.

[GibsonGM]

You don't need a 'fancy' or hard to find opamp to get your buffer and summer; a good old TL072 would work well! 

The buffer in your first pic would work, and in the "Multi Tone' type circuit the R15 thru R21 would be taken to the input of a summing amplifier made with the other opamp section (look up 'opamp summing amplifier' for more about them).  In fact, look up 'opamp buffer' and just throw a quick guitar tone control (or volume pot!) after to get a sense of what's going on!


The transistors in R.G.'s simple, easy graphic EQ are doing something else; they're acting a 'gyrators', simulating inductors.   I'm assuming the insertion loss is designed to be low enough to not need a buffer, and the opamp at output is giving some gain. 

[antonis]

What Sir Mike said..



P.S.
I'd lower original circuit resistors/pots values by a factor of 10 (at least) and raise caps values respectively..