Hello
I use the ESP Project 113 Headphone Amplifier in my diy master section of my mixing console (D&R Dayner) and it sounds and works really good.
U1A (and U1B) are a OPA2134.
1. Is it correct that opamps with a FET input like the OPA2134 have no DC offset at their input?
2. So can I omit C1L (and C1R) in the circuit of the ESP Project 113? (There is no DC from the source)
Thanks in advance for helping me out
Cheers
Beerzel
I use the ESP Project 113 Headphone Amplifier in my diy master section of my mixing console (D&R Dayner) and it sounds and works really good.
U1A (and U1B) are a OPA2134.
1. Is it correct that opamps with a FET input like the OPA2134 have no DC offset at their input?
2. So can I omit C1L (and C1R) in the circuit of the ESP Project 113? (There is no DC from the source)
Thanks in advance for helping me out
Cheers
Beerzel
Attachments
Hey thanks, that was quick 🙂
Do you mean its fine when I don't measure any DC at its input or that its always fine exept when there is DC from a source at its input?
Cheers
Beerzel
Do you mean its fine when I don't measure any DC at its input or that its always fine exept when there is DC from a source at its input?
Cheers
Beerzel
What he meant was that if there is no DC on the input (before C1L or C1R capacitors), then you can safely remove those capacitors and put a bridge instead. Also, make sure that the output of the device you are connecting to this amplifier's input does not have any DC on its outputs.
Bottom line, if you'll be connecting various devices to it, it's better to have those decoupling caps there, or you might end up frying your headphones, the amplifier itself or both. Be careful if you're going to ditch them.
Bottom line, if you'll be connecting various devices to it, it's better to have those decoupling caps there, or you might end up frying your headphones, the amplifier itself or both. Be careful if you're going to ditch them.
OPA134, OPA2134 and other JFETs have usually low offset.
A few mV.
Non-JFET opamps can get offset from the resistors, but this is not true for JFET.
It is not usual to have offset problems fom OPA2134.
A few mV.
Non-JFET opamps can get offset from the resistors, but this is not true for JFET.
It is not usual to have offset problems fom OPA2134.
Ok I see, thanks. Makes sense that when there is DC, it will be amplified directly to the headphones which seems quite unhealthy...
But in my case it seems to be save:
At the mixbus output stage I have a transformer with two secondarys. One split goes to the output where I connect the AD Converter. The other split goes to the monitor section (with a coupling cap) and also directly to the headphone amp, so I hear the ''sound'' of the Sowter transformer while mixing :-D.
I wanted to omit the cap at the headphone amp to have a place, straight as possible, to listen to the mixbus. So great, my dreams come true ;-)
Cheers
Beerzel
But in my case it seems to be save:
At the mixbus output stage I have a transformer with two secondarys. One split goes to the output where I connect the AD Converter. The other split goes to the monitor section (with a coupling cap) and also directly to the headphone amp, so I hear the ''sound'' of the Sowter transformer while mixing :-D.
I wanted to omit the cap at the headphone amp to have a place, straight as possible, to listen to the mixbus. So great, my dreams come true ;-)
Cheers
Beerzel
It will even be OK for low amounts of DC.
Its AC feedback so the DC wont get amplified.
You will just get same DC out as in.
FET input amplifiers have extremely low input bias current and input offset current, which are two factors that can determine input DC offset. They still have input DC offset voltage however, depending on how well the input stage is matched or trimmed.
In your input circuit, with the capacitor, this bias current will flow through 23kΩ to create an offset voltage. So, a bipolar op amp like a 5532 with 200nA input bias current would generate 4.6mV of offset, not a huge amount, but more than the 0.5mV typical voltage offset of that amp. By contrast, an OPA2134 has 5pA bias current, producing 0.115 microvolt of offset in addition to its 0.5mV offset voltage. So, with high DC input impedances, input bias currents can be significant DC error sources.
As was said before, this circuit does not amplify DC, so eliminating the 1µF input capacitor will be fine with an OPA2134.
In your input circuit, with the capacitor, this bias current will flow through 23kΩ to create an offset voltage. So, a bipolar op amp like a 5532 with 200nA input bias current would generate 4.6mV of offset, not a huge amount, but more than the 0.5mV typical voltage offset of that amp. By contrast, an OPA2134 has 5pA bias current, producing 0.115 microvolt of offset in addition to its 0.5mV offset voltage. So, with high DC input impedances, input bias currents can be significant DC error sources.
As was said before, this circuit does not amplify DC, so eliminating the 1µF input capacitor will be fine with an OPA2134.
Thanks for all this info, helped me and I learned a lot.
Just curious now: Is it C2L and/or C3L+C4L that won't let the DC to be amplified? If it is just C2L, what are C3L+C4L there for?
Cheers
Beerzel
Just curious now: Is it C2L and/or C3L+C4L that won't let the DC to be amplified? If it is just C2L, what are C3L+C4L there for?
Cheers
Beerzel
- Status
- Not open for further replies.