What would be quieter - INA134 or a non-super-expensive transformer like Hammond 109T or Triad Magnetics SP66 with shield (or some other transformer - I know nothing about them)?
This would be for the XLR input of a high-gain guitar preamp so my focus is noise and not frequency response or THD. If the difference in noise floor is 10db, that is going to be amplified 10000x so I'm wondering if a transformer would actually be noticeably quieter in this scenario. Or would the EMF pickup actually contribute more noise than the INA134 input resistors?
Any help would be appreciated.
Mike
This would be for the XLR input of a high-gain guitar preamp so my focus is noise and not frequency response or THD. If the difference in noise floor is 10db, that is going to be amplified 10000x so I'm wondering if a transformer would actually be noticeably quieter in this scenario. Or would the EMF pickup actually contribute more noise than the INA134 input resistors?
Any help would be appreciated.
Mike
To answer my own question - from reading Small Signal Audio Design by Douglas Self page 345 (and section 14.1), it sounds like INA134 would actually add significant noise. So I bought some old BeyerDynamics 1:1 600 metal can transformers for about $25 USD each. Now I just have to figure out the best way to wire them up.
Even after amplifying it 10,000 times? In a high gain guitar preamp there is noise. That is unavoidable. The question is, will I hear less noise using a studio grade input transformer or the INA134?
I suppose the only way to really know is to test. I have the chip. When I get the transformers I'll do a comparison.
I suppose the only way to really know is to test. I have the chip. When I get the transformers I'll do a comparison.
I'm taking a line level signal from another piece of equipment like a compressor or some effect or whatever and then running that over a balanced line into a high gain preamp unit I'm building. That line-level input would come in through the transformer, buffered and fed into the high gain preamp. The signal gets amplified by 3 tube stages with a gain of about 20 or so each which is 20 x 20 x 20 or about 8000 times. Then it get's attenuated and routed back out at line level using DRV135.
The point is to add tube character, overdrive or outright distortion to the signal. Two channels for a stereo effect. And there will be a phase switch on one channel.
The point is to add tube character, overdrive or outright distortion to the signal. Two channels for a stereo effect. And there will be a phase switch on one channel.
Right. High gain guitar amps clip. Actually there are frequency dependent RC networks and attenuation that goes on between the stages so it doesn't clip 8000 x. But it does clip or at least compress a lot. That's the point.
But it doesn't clip noise. It just amplifies the hell out of it. So I'm assuming that any reduction in noise at the input will be noticeable. Thus the question.
But it doesn't clip noise. It just amplifies the hell out of it. So I'm assuming that any reduction in noise at the input will be noticeable. Thus the question.
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