Hello everyone, I need to design a very low noise headphone amplifier with the following characteristics:
headphones: Vic Firth Sih2 datasheet
Sound pressure level 102db +/- 3 db (1mw at 1kHZ)
maximum power 100mw
Impedance 32 ohms +/- 15%
Conditions:
my questions are:
can these ICs work with a single supply (9V Battery) ?
Can they reach the maximum power of the headphones? I need to at least reach 110db SPL
I have already tried with different ICs, (TDA2822, TDA7052, PAM8403) but the result is very noisy, mainly white noise and RF noise in some occasions.
I have a EARS Headphone test jig from miniDSP, to do the tests and measurements Link
I really appreciate your comments and suggestions.
Thanks
Leonardo
headphones: Vic Firth Sih2 datasheet
Sound pressure level 102db +/- 3 db (1mw at 1kHZ)
maximum power 100mw
Impedance 32 ohms +/- 15%
Conditions:
- The circuit is powered by a single 9V battery.
- Candidate ICs: OPA1688 or OPA1622 (I read suggestions)
- the input of the amplifier will be connected to an AD9833 (Programmable Waveform Generator IC) datasheet
my questions are:
can these ICs work with a single supply (9V Battery) ?
Can they reach the maximum power of the headphones? I need to at least reach 110db SPL
I have already tried with different ICs, (TDA2822, TDA7052, PAM8403) but the result is very noisy, mainly white noise and RF noise in some occasions.
I have a EARS Headphone test jig from miniDSP, to do the tests and measurements Link
I really appreciate your comments and suggestions.
Thanks
Leonardo
9v is within the specified data sheet values and so should be fine. Remember that the circuit must be suitably configured for single rail use (as with any opamp).
They should do. You only need around 1.8 vrms across 32 ohms for 0.1 watt dissipation. That should be acheivable on a 9 volt supply.
I've used the TDA2822 in the past and found it excellent.
Remember the OPA opamps you mention are in VSOM packages (very small outline) and are not really diy friendly for most users of them.
They should do. You only need around 1.8 vrms across 32 ohms for 0.1 watt dissipation. That should be acheivable on a 9 volt supply.
I've used the TDA2822 in the past and found it excellent.
Remember the OPA opamps you mention are in VSOM packages (very small outline) and are not really diy friendly for most users of them.
@Mooly thanks for your quick response!
Do you think it is better to split the 9v with some IC like LM27762?
that is the last one I've tried, it works well as an amplifier, but in Standby (without input) the background white noise is notorious.
no problem with this, i have experience in SMD
Do you think it is better to split the 9v with some IC like LM27762?
The AD9833 has only a 10bit DAC inside, giving around -60dB quantization noise. I would posit that's where the noise is coming from, not the amp chips.
I built this circuit with a TDA2822M, without connecting anything to the input. and with the volume at minimum (pulldown to GND) and connecting the headphones white noise is heard.
Not necessarily, there is nothing wrong with AC coupling and single rail if done correctly.
This is where it gets subjective. Sensitive h/phones may give a slightly audible hiss but it would still be pretty low. You have to remember the TDA chip is a small power amp capable of driving speakers and so the hiss you hear would be similar to connecting h/phones directly to other power amps. To cut the hiss would need the addition of a series resistor to the 'phones.
The opamp circuit is neither one nor the other. It may be quieter but on the other hand a 32 ohm load connected directly to the output will restrict maximum voltage swing. So again a small resistor may be needed.
I have tried with 100 ohm resistors and with 220 ohms and the noise decreases, but it is still present.
Sorry for my ignorance but how does a cell phone, for example, when you connect the headphones and absolutely nothing can be heard?
Its very difficult to say without actually hearing how loud it is and also looking with a scope to see if anything else is going on. I would have though a 220 ohm should make it essentially silent as that is getting to the sort of series value you might use with a 40 watt amp.
The phone I have no idea about tbh. Could it be muted when there is no audible wanted signal... I really don't know on that one.
The phone I have no idea about tbh. Could it be muted when there is no audible wanted signal... I really don't know on that one.
I really appreciate your time.
I can measure the input and output of the amplifier and show you the result on Monday.
maybe that's my solution, mute the output until I need it.
I'm designing a portable audiometer, everything is solved except the amplifier.
How could I mute the output of a tda2822 that doesn't have a volume control?
Or do you recommend another IC?
The trouble is that its all relative. Without hearing it for real it is difficult to put figures on it. A scope check would show if something else was going on though with the TDA chip.
It's not easy. You would need a noise gate of some sort and a mute (like a speaker relay but probably using a small solid state MOSFET version ). That brings a whole bunch of other problems though such as slight step change on the output as it mutes and unmutes.
Perhaps just try an opamp version (with any common opamp initially) and see if it is a lot better than the TDA.
My first project published here on DIYA is a headamp made with a OPA1622. this chip has been designed to drive headphone, it give very good results : https://www.diyaudio.com/community/threads/ampcasq-an-opa1622-integrated-headamp-project.304684/.
My amp can operate on a 9V battery but as said by Mooly it's certainly much simpler to power the OPA1622, and input buffer, with single 9V supply and to have AC coupling.
Regarding the noise you encounter with the AD9833, it is very likely coming from the AD9833 itself and the microcontroller with drive the chip... You tried to install a strong Low Pass Filter after the AD9833 and program it to output a tone within the passband of the LPF ? If noise level is reduced then this is digital noise.
My amp can operate on a 9V battery but as said by Mooly it's certainly much simpler to power the OPA1622, and input buffer, with single 9V supply and to have AC coupling.
Regarding the noise you encounter with the AD9833, it is very likely coming from the AD9833 itself and the microcontroller with drive the chip... You tried to install a strong Low Pass Filter after the AD9833 and program it to output a tone within the passband of the LPF ? If noise level is reduced then this is digital noise.
I already have a pair of 1688 and 1622 in my mouser shopping cart, I am waiting for more opinions to know if I buy another one
the noise i hear is in the amplifier circuit alone, with nothing connected to the input. a faint white noise.
The TPA6120A2 is a nice amp indeed, but it's pretty power hungry. It wouldn't be my first choice for a battery operated headphone amp.
BUF634A + OPA1656 in a composite amp is a nice combination. You could also use the OPA1656 by itself (or two in parallel if you want higher output current).
I haven't played with the OPA1688 but it looks like a nice opamp on paper. The OPA1622 is nice, but hard to solder by hand. There is a pretty inexpensive evaluation module (EVM) for it, though. One of those with a pair of 9 V batteries would make a nice headphone amp.
Tom