hi i am trying to build an amiplifier with both balanced and unbalanced inputs using the drv134 and ina103 chips, but i can't get it to work. what i did was basically use the schematics that were published on the datasheets
drv134:
http://www-s.ti.com/sc/ds/drv134.pdf
page 8, figure 1
ina103:
http://www-s.ti.com/sc/ds/ina103.pdf
page 12, figure 12
...and connect the outputs of the drv134 directly to what would be the xlr input in the ina103 datasheet. what is happening is that the outputs of the drv134 have a strong negative dc voltage and that is making the ina103 get stuck and showing the negative supply voltage in it's output... i don't know why the 47u capacitors don't block it... they are polarised and i am not using phantom power, has this got any relationship?
is there something wrong that i am doing?? or should it work?? i checked the connections but maybe I missed something... what should i do????
and even better, does anyone know a way in which i can make the balanced and unbalanced entries work at the same time? this is optional, by the way. but if someone could show me how to feed an unbalanced dynamic microphone into the ina103 i would appreciate it very much. and if it uses the drv134, even better.
thanx
drv134:
http://www-s.ti.com/sc/ds/drv134.pdf
page 8, figure 1
ina103:
http://www-s.ti.com/sc/ds/ina103.pdf
page 12, figure 12
...and connect the outputs of the drv134 directly to what would be the xlr input in the ina103 datasheet. what is happening is that the outputs of the drv134 have a strong negative dc voltage and that is making the ina103 get stuck and showing the negative supply voltage in it's output... i don't know why the 47u capacitors don't block it... they are polarised and i am not using phantom power, has this got any relationship?
is there something wrong that i am doing?? or should it work?? i checked the connections but maybe I missed something... what should i do????
and even better, does anyone know a way in which i can make the balanced and unbalanced entries work at the same time? this is optional, by the way. but if someone could show me how to feed an unbalanced dynamic microphone into the ina103 i would appreciate it very much. and if it uses the drv134, even better.
thanx
To start with I think you are using the wrong chip for the second stage, which should be INA134 instead of INA103, which is a mic preamp. Try the circuit in Figure 2 of the DRCV134 datasheet.
The same circuit, with the gain setup set to the minimum, should work with the 103 too. But you should take two precautions:
1) Use a large bipolar capacitor (2000uF at least) to DC block one end of gain resistor.
2) Use a blocking capacitor at the output, just in case.
If not you should have at least 50mV of output offset.
The signal of the 134 might be too large anyway, even if you can attenuate it, so you better use the mating receiver chip.
Carlos
The same circuit, with the gain setup set to the minimum, should work with the 103 too. But you should take two precautions:
1) Use a large bipolar capacitor (2000uF at least) to DC block one end of gain resistor.
2) Use a blocking capacitor at the output, just in case.
If not you should have at least 50mV of output offset.
The signal of the 134 might be too large anyway, even if you can attenuate it, so you better use the mating receiver chip.
Carlos
First off, the INA103 should be what you're taking your mic into.
While it is probably possible to use the INA 103 single ended, this is going to be tricky if you're also going to use this with phantom powered mics. (I assume you know that you can't use an unbalanced mic with phantom power.)
Also, since unbalanced mics usually operate at a higher impedance than balanced mics, the input impedance of the mic pre will be too low for an unbalanced mic.
Your best bet would be to use an inline hiZ/loZ unbalanced/balanced transformer if you really need to use an unbalanced mic with this. Shure makes these, you can also pick them up a Rat Shak.
While it is probably possible to use the INA 103 single ended, this is going to be tricky if you're also going to use this with phantom powered mics. (I assume you know that you can't use an unbalanced mic with phantom power.)
Also, since unbalanced mics usually operate at a higher impedance than balanced mics, the input impedance of the mic pre will be too low for an unbalanced mic.
Your best bet would be to use an inline hiZ/loZ unbalanced/balanced transformer if you really need to use an unbalanced mic with this. Shure makes these, you can also pick them up a Rat Shak.
this is what I am trying to do:
dynamic (unbalanced) or condenser(balanced) mic->mic preamplifier ->power amplifier
so what you are basically saying is that the INA103 will work well only with balanced inputs, since phantom power might harm a dynamic microphone. so the only solution might be to build some preamplifiers for unbalanced mics and other for a balanced mic. (one mic preamp for the condenser mic and one for the dynamic)
if that is the case i want to know if you guys have seen any high quality unbalanced mic preamp... i know there are a lot of designs out there but i would like your informed opinion about it
or reccomend me some chips... i thought that the INA103 could work as well with the unbalanced mics, perhaps connecting the +Vin directly to ground or something like that.
thanx for all the help.
dynamic (unbalanced) or condenser(balanced) mic->mic preamplifier ->power amplifier
so what you are basically saying is that the INA103 will work well only with balanced inputs, since phantom power might harm a dynamic microphone. so the only solution might be to build some preamplifiers for unbalanced mics and other for a balanced mic. (one mic preamp for the condenser mic and one for the dynamic)
if that is the case i want to know if you guys have seen any high quality unbalanced mic preamp... i know there are a lot of designs out there but i would like your informed opinion about it
or reccomend me some chips... i thought that the INA103 could work as well with the unbalanced mics, perhaps connecting the +Vin directly to ground or something like that.
thanx for all the help.
lulu said:this is what I am trying to do:
dynamic (unbalanced) or condenser(balanced) mic->mic preamplifier ->power amplifier
so what you are basically saying is that the INA103 will work well only with balanced inputs, since phantom power might harm a dynamic microphone. so the only solution might be to build some preamplifiers for unbalanced mics and other for a balanced mic. (one mic preamp for the condenser mic and one for the dynamic)
if that is the case i want to know if you guys have seen any high quality unbalanced mic preamp... i know there are a lot of designs out there but i would like your informed opinion about it
or reccomend me some chips... i thought that the INA103 could work as well with the unbalanced mics, perhaps connecting the +Vin directly to ground or something like that.
Perhaps you should first get a bit acquainted with mic types before you make a preamp. There are too many big questions you are doing which you should get to know about.
A professional balanced dynamic mic probably won't suffer any harm even if the phantom power is applied. In any case you should put a switch to power the phantom supply, if possible per channel.
You can plug a low impedance unbalanced mic in a balanced input, but you will have to build an adaptor cable with two resistors inside. The input should be standardized for balanced connections, and use the adaptor to connect the other mic.
There are no high quality unbalanced mics, only reasonably good. If you want quality you should buy a balanced mic. A balanced mic into an unabalanced input, if the cable is not more than 10 meters long, will work fine. All balanced mics are low impedance, and you should pick one.
Carlos
Even if you configure the INA103 to operate single ended (probably just need to connect the inverting input to ground through a big capacitor) the input impedance of the circuit will be too low to use with a guitar. The whole point of the INA103. INA163, and INA217 chips is to implement a circuit that would otherwise require 3 opamps with only one chip.
It's easy to build preamps for unbalanced mics and guitars with just one opamp.
It's easy to build preamps for unbalanced mics and guitars with just one opamp.
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