Piezo Preamp + Mute True Bypass + Clean Boost + DI Box

[brazuca_nz]

One more thing (sorry about the amount of questions).

I am also trying to integrate the Booster in this schema. Some considerations:

• I want to use the same Vref and Vin for all opamps in the circuit.
• When the booster is OFF, the audio output is that from the pre-amp, when it is ON, it must only boost the signal (in this case there is a gain control that allow the boost to be from 0dB to +15dB, in theory)

Here is the schematic:
https://postimg.cc/v1Dh9NwG



I built and connected both circuits to test and I notice that:

• When the booster is OFF, the sound is that from the pre-amp, as I wanted, but it is weaker than it was before I connected the booster.
• When the booster is ON, the LED lights up and there is a small voltage drop in both Vin and Vref (0.5v more or less).
• The booster isn't boosting the signal, only adding noise to it and, furthermore, the gain pot atenuates the sound when it should only be unit gain (0dB).

What am I doing wrong?

Thanks!

[antonis]

• When the booster is OFF, the sound is that from the pre-amp, as I wanted, but it is weaker than it was before I connected the booster.

That's due to PREAMP_OUT connection to BOOSTER_OUT..
(voltage dividing effect..)

see post #9 for proper connection:

• When the booster is ON, the LED lights up and there is a small voltage drop in both Vin and Vref (0.5v more or less).

Try a bigger value for R15 (and R12)..

• The booster isn't boosting the signal, only adding noise to it and, furthermore, the gain pot atenuates the sound when it should only be unit gain (0dB).

Place a 1M (or so) resistor between U2A pin 3 and V_REF..
(as it is, C2 kills the signal from PREAMP_OUT..)

P.S.
Place 10 to 100 nF ceramic caps between pins 4 & 8 of op-amps, as close as possible to ICs..
U2B unused amp should be properly wired..
(pin 5 to V_REF and pins 6 & 7 shorted..)

[brazuca_nz]

see post #9 for proper connection:

Ohh many thanks! I finally got it (I guess).

I made the adjustments you have said (except the LED resistor, I kept it on 1K).

Here is the result, is that right?

[antonis]

Here is the result, is that right?

I think so..

Just add a 100k to 1M (the lower the better) pull-down (anti-pop) resistor to GND after C10, wherever convenient..
( C10/R14 junction is the preferable point but it should also be OK either on R14 right leg or on SW3 lug 1..)

e.g.



To be honest, I don't like "bare" Zeners being across power supplies..
100R resistor has dual role here:
It serves both as Zener over-current limiter and supply HPF (together with C1, the value of which might be raised up to 470μF for more effective ripple smoothing, although op-amps PSRR is large enough..)




P.S.
Also, a 100pF ceramic cap across U1B pins 6 & 7 should prevent potential high-pitch oscillations..

[brazuca_nz]

Okay!

Here are the modifications. I also wanted to use the unused op amp from the booster and I found a good use for it: to check if the battery needs to be charged. The circuit I got from ChatGPT so I don't really know if it is right haha. In theory it has two voltage dividers, one for the battery (3.7v / 2 = 1.85v) and another dividing the 9V to get a reference voltage of 1.65v, that is the half of 3.3v (when the battery needs to be charged). Does that make sense?

Then I light the RGB led RED if it needs to be charged, BLUE if it is charging and GREEN if it doesn't need to be charged.

Other than that the circuit remains pretty much the same, I added the resistors and the diode you mentioned.

Cheers!

[FiveseveN]

The circuit I got from ChatGPT so I don't really know if it is right haha

Yes, hilarious.
Is your goal to learn things like how to make an op amp comparator (the battery check) or to rely on AI to do the thinking for you and pray it works?

[brazuca_nz]

Yes, hilarious.

Thanks!

[PRR]

Using a 3.7V battry to check your 9V battery is...... interesting.

True, when I check my "12V" car battery I sometimes(*) rely on the 9V batt in my DMM. Not as reference, but it sure gets goofy when the DMM batt is down to 6V and bits are lost.
(*)When I have my doubts I check with the $10 passive needle-meter. Tends to work or not-work (burnt), no middle ground.

[brazuca_nz]

Using a 3.7V battry to check your 9V battery is...... interesting.

It is actually the same battery (18650 li-ion) that is boosted to 9.1V by the LX-LCBST module. Since I am using the other side of the op amp that is already fed by 9.1V, I need to divide that voltage to compare it to the 3.3V threshold.

Here are some simulations (I changed the values and slightly modified the circuit):
LED off - 3.4V in the battery


LED on - 3.3V in the battery


I will make a prototype to test it. I understand there is another way of creating the reference voltage by using a Zener diode, but I don't know if that would work with the op amp being fed by 9.1V. Is it a better option?

[antonis]

Is it a better option?

Yes..!!

[brazuca_nz]

Is it a better option?

Yes..!!

I didn't notice this was a URL, but I googled this circuit a little bit and, based on the smallest Zener I have (3V), I got this circuit. It works on the simulator:

(Led ON when battery voltage <= 3.3B and led OFF when it is > 3.3V)

[brazuca_nz]

Chnging the subject back to the pre amp, I was still in doubt between the Barcus Berry 3000A clone and Rod Elliot's Charge Amp, so I made the 2 of them and recorded the same song intro on both, the result, for my ears, the Charge Amp wins, it is brighter and clearer.