I wanted my system to be simple. I have only one supply, +/-35V.
I need gain preamp. I can built it by opamp, but it will need another supply, +/-15.
So, I think about building gain preamp using chipamp, like TDA7294 so I dont have to provide another supply.
Has anyone built chipamp as gainpreamp? Or it is not suitable at all for small signal gain preamp?
I need gain preamp. I can built it by opamp, but it will need another supply, +/-15.
So, I think about building gain preamp using chipamp, like TDA7294 so I dont have to provide another supply.
Has anyone built chipamp as gainpreamp? Or it is not suitable at all for small signal gain preamp?
Why not use 7815/7915 regulators from main PS to give you the voltage you want for preamp power supply? I know some of the others may try to give you reasons not to do this but the big boys have been doing it for years so why can't you? After all we are only talking 4 to 6 parts. 2 regulators, 2 output caps and maybe 2 bypass caps. Seams simple enough to me.
Later BZ
Later BZ
. . . but still there isn't a technical reason not to do it.
One can always discuss the normal hifi/audio quality issues, but simply and technically there shouldn't be anything against it. You must however look in the technical specs of the opamp to see, if it can handle, whatever you wish it to do. Diagrams, please . . .
One can always discuss the normal hifi/audio quality issues, but simply and technically there shouldn't be anything against it. You must however look in the technical specs of the opamp to see, if it can handle, whatever you wish it to do. Diagrams, please . . .
My candidate for this is LM1875, because it is small chipamp, only TO-220 size. Just download the datasheet, I found some thing that maybe a problem if I use it as opamp.
In Xover, the opamp is only used as buffer, the -input is connected to output.
1. The LM1875 datasheet said that it is stable for gain 10 or more. Is this mean this LM chip cannot be used as buffer (-input tied to output)?
2. The datasheet also said about possibly ringing with capacitive load. In Xover, it is always capacitive load
3. The bias current is 70mA. Hmmm.... If the supply is +/-25V, then it will dissipate 3.5W? At first I think I can use chipamp without heatsink, if only used as opamp. But this dissipation certainly needs heatsink.
I just look at the LM1875 datasheet for a glance and has found this 3 obstacle if I wanted to use it as opamp.
It is not possible to use chipamp as opamp?
In Xover, the opamp is only used as buffer, the -input is connected to output.
1. The LM1875 datasheet said that it is stable for gain 10 or more. Is this mean this LM chip cannot be used as buffer (-input tied to output)?
2. The datasheet also said about possibly ringing with capacitive load. In Xover, it is always capacitive load
3. The bias current is 70mA. Hmmm.... If the supply is +/-25V, then it will dissipate 3.5W? At first I think I can use chipamp without heatsink, if only used as opamp. But this dissipation certainly needs heatsink.
I just look at the LM1875 datasheet for a glance and has found this 3 obstacle if I wanted to use it as opamp.
It is not possible to use chipamp as opamp?
lumanauw said:
It is possible, but no advisable.
A preamp's chip should have several capabilities that no power amp chip has: it should work in class A (if possible), it should have a large bandwidth gain and it should have low distortion.
If you look again, the MOX articles are based on a discrete op-amp, which should even be better than a monolithic chip.
You can use the +/-35v you have and filter/lower it to a voltage you can feed into +/-18v or +/-24v regulators, to power your preamp ICs.
Or you can go discrete and power it higher.
Carlos
Its quite true. Opamps are designed for its uses, chipamps also designed for certain purpose.
But very curious what will be the sound, if we use chipamps in the place of opamps. Will it result in something drastic in sound reproduction?
People in audio are known to use strange things. Some tube that are not inteded for audio use, can produce very good audio power amp. Nelson Pass uses Lateral mosfet, which the factory said is not suitable at all for audio. Gammut amp uses single gigantic mosfet (industrial mosfet) for its output. Mr.Pass himself has conducted strange experiment with opamps, using tons of it (I forget, is this lead to power amp, or just very powerful preamp), and experimented to put 10K resistor from opamp's output to negative rail, to force the opamp to work in class A.
Just wondering. Has anyone tried chipamp for opamp?
Is chipamp has stability like opamp, so it can be treated like opamp purpose (like make buffer with chipamp, gain=1)?
The OPAs (541, 548, 549...) are stable at gains of 1.
But using them for a pre?
Have you though of the PSU requirements of doubling the number of chips?
Much less work and much cheaper, and much better to use a good signal op-amp.
Or no op-amp at all, adjust the gain on the chiamp.
But I tend to prefer the GainClone with a pre, or at least with a good input (op-amp) buffer.
Sounds just that little better to me, believe it or not.
But using them for a pre?
Have you though of the PSU requirements of doubling the number of chips?
Much less work and much cheaper, and much better to use a good signal op-amp.
Or no op-amp at all, adjust the gain on the chiamp.
But I tend to prefer the GainClone with a pre, or at least with a good input (op-amp) buffer.
Sounds just that little better to me, believe it or not.
lumanauw said:
Three reasons
1. Cost The chip amp will cost more that a good low level opamp.
2. Distortion Almost a any low level opamp will have better distortion performance that a chip amp in that application.
3. Noise Good high performance opamps have a much lower noise floor than a chip amp.
Just because an ideas goofy doesn't make it bad, but it doesn't make it good eather.
Later BZ
No, not really. I have done the parallel opamp thing for headphone amps but more that that and the size of the circuit board starts to become a problem. To get 1 watt out of TLO72s for example would require about 25 chips or 50 opamps in parallel per channel.
Its best to use a part for it's intended purpose and range of operation. The designers made the part that way for a reason.
The trick is to choose the best part you can find and then use it in the most suitable way for that part. That's the secret.
Later BZ
Its best to use a part for it's intended purpose and range of operation. The designers made the part that way for a reason.
The trick is to choose the best part you can find and then use it in the most suitable way for that part. That's the secret.
Later BZ
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