Low noise onboard bass eq

[emosms]

Hi, I am looking for a onboard bass eq circuit.
Priorities, in that order:
1. Low noise, particularly when you turn up the treble to the max
2. Low power consumption (battery powered).
3. As simple as possible...

[emosms]

This is my current EQ:


And this is an active pickup blend, the mix goes to the EQ:

There is hiss when I turn up the EQ treble. Haven't tested yet if the hiss will go down, if I remove the J201 pickup blend..

So the hiss might be due to the blend circuit, but I need it, otherwise the blend pot does nothing.
The blend pot on my more expensive bass (lower hiss noise from the onboard circuit) does absolutely nothing (passive blend).
We have 1:1 blend at mid position and neck or bridge pickup as soon as you slightly go off the mid position.

This is a simple 2 transistor schematic for EQ:

I can rework it to 3 band EQ, but I can't evaluate by the circuit if it is going to be a low noise or a noisy one...

[J M Fahey]

1) Hiss is a fact of life, you can lower it but it never disappears.

Both discrete circuits you posted are somewhat crude and don´t expect them to be noisless, by any means.
There is also some signal loss, which works against you.

Your best bet is to find an Op Amp based Bass Preamp, and build it using low noise Op Amps.

2) Texas Instruments is making very good low noise ones, for about $2/$3 or so, while your current preamp most probably uses 50 cent TL072

Not bad, in fact the Industry Standard today, but over 20 years old, we have better today.

Noise will be 1/2 to 1/4 of what you have today, it will not *disappear*.

[emosms]

So u suggest a discrete solution can't be quieter than a proper op-amp?

It would be easier to design I guess.
I was playing (like a lame hobbyist) with electronics, guitars and basses and I thought the hum was the arch enemy. Not until I managed to finish a bass guitar amp/ cab with a tweeter and the hiss stepped in ...

Always dreamed about being able to get bright sound, capable of reproducing hi-fi like studio quality slap tone.
(Not that I don't like vintage, organic and warmer sound, P-bass tone, e.t.c.)

[g1]

What is your other bass that doesn't have as much of a hiss problem?

[emosms]

It is also a rather budget one - Sire M2:
https://sire-usa.com/products/m2-5st

The noiser one is some AliExpress stuff - PHX.
I won't touch the Sire, but the PHX is heavily modified.
This is the topic I deal with the diy amp hiss (it has a preamp valve).
https://music-electronics-forum.com/...ss#post1010204
There is a picture of the Chinese bass.
Seems the hiss is much worse with the Chinese/ DIY onboard and with a compression HF driver that I swapped for a 5" midrange (plays up to 10k).

Diy stainless steel bridge and brass saddles.
(Unfortunately, the brass saddles don't have as much of an effect on a bass guitar, compared to a strat with brass saddles).
String through mod - don't hear improvement in the sustain and tone .

I wound alnico pole humbucker pups @home (2 poles per string) and added the active pickup blend I insist on, that the Sire is missing. The original pups are quite bland cheap ceramic pups worth nothing.

The alnico is kind of impossible to distort, or rather compresses large signal pretty nicely (f.ex. plucking the strings as hard as you can) and gives a slight vintage sound.

So whatever 'quieter' onboard I put up, it should incorporate active pickup blend and 3 band EQ (as the knobs layout is).

I forgot there is also a bass boost circuit.
The home build pups used thick wire that can't accommodate a lot off windings, they lack some low end but are balanced bright (no shrill).
I will try to avoid that in the new onboard build, thus reducing circuitry and hopefully the hiss.
F.ex. having the bass EQ (low shelf) from 0 to +9/12 db end to end and no attenuation.

I also plan to have the treble not as a high shelf, but a fixed band moderate Q factor, to minimize hiss
(I just suspect the Chinese EQ treble is a high shelf, haven't tested)

[J M Fahey]

So u suggest a discrete solution can't be quieter than a proper op-amp?

It would be easier to design I guess.

It can be done, but not easier.

There are discrete Op Amps with better than normal performance, I would call them anything but "simple"

This one just emulates a humble 741, can´t imagine a high performance one.

While Texas Instruments offers you state of the art Technology for less than 3 bucks.

[emosms]

Is the simulation software 'noise analysis' realistic?

I understand it is rather pointless, but I have an idea to simulate two similar circuits and compare the noise density.

1. Quad op-amp
- 2 op-amps as individual pickup buffers
- input buffer op-amp after the blend pot, tone stack, output op-amp.

2. Ultra minimalistic discrete version, each op-amp substituted by ONE transistor...

[J M Fahey]

No, it is not useless at all.
I ever use simulators but results should be close to reality.

To find what you want, go to Mouser, search for "Op Amps" (they have thousands) , then add desirable parameers to narrow the search until yu are left with less than a dozen, then pick one or two you like.

Here I already reduced search to: "Op Amps, 4 channel, less than 2 mA current consumption, discard a couple which are "Automotive use" (not sure what that means)", select by noise.

Here best was 3.3nV /sqrt Hz which is nice.

https://www.mouser.com/c/semiconduct...pply%20Current

repeat search with the parameters you like.
Basically you want lowest noise and lowest current consumption.

2 mA for a quad is fine considering a standard TL072 eats 3.5mA for a pair.

Knowing these parameters (I suggested Mouser because their "parts selector" is impressive), not much need for simulation, Software will work with the noise number you give it, so ...

Your preamp is relatively "simple" because it does no need to do anything extreme: buffer each pickup, maybe provide *a little* gain, 1.5X, or 2X Max (battery power limits headroom). mix them, apply some EQ.

[pdf64]

1) Hiss is a fact of life, you can lower it but it never disappears.
...
TL072

Not bad, in fact the Industry Standard today, but over 20 years old, we have better today.

Nevermind 20 years, I seem to recall first tinkering with TL072 back in the mid 80s!
Hiss is one fact, 'time flies' is another

[Mick Bailey]

There's an interesting section in Sompbox Cookbook regarding opamp noise. There are some surprising figures that show a TL072 isn't anywhere near as noisy as you'd expect. I've recently been experimenting with IC swaps in a preamp designed around TL072s that had a fair amount of hiss. I ended up back with the original ICs as the noise wasn't from the opamps, but from the rest of the design.

My hifi preamp uses TL072s with no detectable hiss and it has a much greater bandwidth than would be necessary for an instrument preamp.

My only reason these days for using anything else for music projects is the need for rail-to-rail 5v microprocessor compatible opamps running off a single supply.

[emosms]

Still haven't done any testing.
I suspect the J201 in the particular circuit may cause hiss.
The bass is not here to physically test.
Neither put it up in simulator (I use Proteus, cause of the pcb layout functionality).

Anyway, it would worth to substitute all my ugly flying boards with a quad op-amp design.

Now I have a chain of boards..
- J201 buffers - transistor bass boost (don't have the schematic here) - the stock onboard EQ.

I don't know how to implement some bass correction to correct the pickups response.
A guy suggested that I actually lower the highs (smth like high shelf attenuation) instead of bass boost.

But it might also be that the pickup input stages have some gain and bass boost (some circuitry around the op-amp feedback). Then the pickup blend pot. I don't know if it would interact and mess up the boost setting when I turn the pot.
Then the 3 band EQ in between two op-amps.

The point is to accomplish all with a quad op-amp. I can first run it with some tl074, then eventually swap it.
But a DIP package on a socket would limit the choice of higher performance op-amps.

[Mick Bailey]

The point is to accomplish all with a quad op-amp. I can first run it with some tl074, then eventually swap it.
But a DIP package on a socket would limit the choice of higher performance op-amps.

My preference is to use dual opamps as there is often more choice than quad. SMD opamps can be mounted on a DIP adapter board to make both packages interchangeable in sockets.

[J M Fahey]

TL072 is a KILLER Op Amp, no wonder it became the Industry standard.

I would search others only in special situations, such as rail to rail with very low supplies as mentioned anbove or , say, Instrumentation (Lab measuring) amplifiers.

For Guitar stuff?
As Dave Ramsey says, "better than I deserve"

[emosms]

Moving very eclectic on these projects, now stuck on a side one...

Whatever the op-amp is, 2x2 or a quad, dip or soic package, I looked through few specs and seems the current draw is given per op-amp.
So there won't be any difference if I use a quad or 2 doubles I guess, same current draw