opa1692 is 4.2nV/sqrt(Hz) for 0,65mA Vs 4.5nV/sqrt(Hz) 2mA for opa1678. But nothing comes free, opa1692 got way higher current noise, wich is not a big deal until source is >10-20kohm , wich is not the case here.
(correct me if i'm wrong
)Thanks for all the input on this, I've been (slowly) considering it all.
Originally, when I started this post, I was just thinking about replacing the current opAmp in my circuit (the OPA2134), but since then, I've been also considering replacing the JFETs with opamps, simply because they are getting harder to buy now... my local electronics store is out of stock and has been for awhile. Also, the inconsistency in their power draw is not overly appealing- it's extra work to test all the IDSS's, etc. And I'm also now thinking about the option of adding three more piezos (for a total of six), so I'm looking for the absolute lowest power draw here.
The OPA2145 is looking the most appealing for the buffer stage (if "stage" the right word to use here)... due to the low power draw and the FET inputs. Does anyone have insight on if this OPA2145 will also work equally well as the gain opamp in my circuit?
This could very well be a bad choice, but would the LT1352 work for the buffer section? It has very little power draw and the datasheet mentions that it's good for buffer circuits, but doesn't mention anything about audio buffers in particular. Also is not rail-to-rail, so maybe the headroom will suffer? https://www.analog.com/media/en/technical-documentation/data-sheets/1352_53fa.pdf
Yes, I guess it seems that 2mA might be too high. I haven't tested any of these low power SOIC opamps yet (as I've been swamped with other work lately), but if they can do the job (which is basically, keeping at least the same audio quality that I have now) with lower power, then I'll go for them.
Originally, when I started this post, I was just thinking about replacing the current opAmp in my circuit (the OPA2134), but since then, I've been also considering replacing the JFETs with opamps, simply because they are getting harder to buy now... my local electronics store is out of stock and has been for awhile. Also, the inconsistency in their power draw is not overly appealing- it's extra work to test all the IDSS's, etc. And I'm also now thinking about the option of adding three more piezos (for a total of six), so I'm looking for the absolute lowest power draw here.
The OPA2145 is looking the most appealing for the buffer stage (if "stage" the right word to use here)... due to the low power draw and the FET inputs. Does anyone have insight on if this OPA2145 will also work equally well as the gain opamp in my circuit?
This could very well be a bad choice, but would the LT1352 work for the buffer section? It has very little power draw and the datasheet mentions that it's good for buffer circuits, but doesn't mention anything about audio buffers in particular. Also is not rail-to-rail, so maybe the headroom will suffer? https://www.analog.com/media/en/technical-documentation/data-sheets/1352_53fa.pdf
Surface mount versions of FETs are available MMBFJ201. Changing these for opamp would change sound.
TL0x opmaps are not rail-to-rail, so less headroom on output.
Surface mount is actually easier to assemble than TH if you stay away from the smallest footprints and use small iron tip. Blob one pad and keep heated. Slide part into place with tweezers to anchor first pin. Flux helps. Acid type must be washed off with water.
TL0x opmaps are not rail-to-rail, so less headroom on output.
Surface mount is actually easier to assemble than TH if you stay away from the smallest footprints and use small iron tip. Blob one pad and keep heated. Slide part into place with tweezers to anchor first pin. Flux helps. Acid type must be washed off with water.
I would definitly go for LT1352 if dip package and low power is a concern. Passinwind has used it as others in on board bass preamp designs.
From datasheet, and the few i understand, it's stable with capacitive loading (good point for long cable). You add gain before it in your shematic, so it will definitly be happy as buffer. Gain stage before will give it the input swing needed for it to keep it slew rate way high enough.
From datasheet, and the few i understand, it's stable with capacitive loading (good point for long cable). You add gain before it in your shematic, so it will definitly be happy as buffer. Gain stage before will give it the input swing needed for it to keep it slew rate way high enough.
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Thanks @spladski for the info. Good to know that surface mount can be even easier with the right tools. Regarding the FETs and their sound, I've actually tried an opamp as a buffer before and I thought it sounded as good, maybe even a touch "cleaner" (which I like in this case). It was an OPA604... which has FET inputs I believe, but I think the power draw is not great, relatively speaking.
@papasteack just a heads up that in my situation the cable length is not an issue as I'm installing the circuit directly in the guitar. Also (and I don't want to presume anything) in my schematic, I have the buffer stage before the gain stage, not after... unless you are looking at it differently somehow?
@papasteack just a heads up that in my situation the cable length is not an issue as I'm installing the circuit directly in the guitar. Also (and I don't want to presume anything) in my schematic, I have the buffer stage before the gain stage, not after... unless you are looking at it differently somehow?
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