Fishman Prefix preamp

[lowell]

Technically this is an amp so I'm posting it here.

I'm trying to figure out of this pickup/preamp is putting out the correct amount of signal.

Here's the manual - https://www.fishman.com/wp-content/u...User-Guide.pdf
and at the bottom it says:

nominal input -20dBV
nominal output -12dBV

So my question, being that I've yet to be able to fully comprehend decibels and the various scales, what kind of ac voltage should I be seeing on my meter? My meter, I realize, will be telling me RMS.

Thanks!

[lowell]

Ofcourse this all depends on what the transducer itself is putting out... but, any experience or opinions appreciated regard the transducer AND the preamp itself.

[lowell]

Anyone have a service manual or schematic for one of these Prefix Blenders? The pcb says Version 3 on it. I'm guessing they don't provide this information, nor do they sell just the pcb. They want you to buy a new unit for $300+. Lame. Gonna look up the SMD ICs in here and see if anything looks obvious regarding circuit tests.

[MarkusBass]

A set of useful converters is available here: calculator volt to dBu and dBV

[lowell]

I'd need to know the pickup output (preamp input) to calculate output though correct? Seems as though there's 8db of Gain.

[MarkusBass]

I'm trying to figure out of this pickup/preamp is putting out the correct amount of signal.

I'm not sure what exactly is the problem with this preamp. Instead of calculating the gain, you can simply plug the guitar cable into an amp and check it by ears. I assume it uses a piezo transducer which often fail. But you can check the microphone (whether it provides sufficient signal).

Mark

[lowell]

Markus I've definitely done THAT

The issue is that the under saddle transducer is low output and the mic is either too low to be heard or not working at all.

I checked how true the saddle was and sanded it back to being straight and level on the bottom. Still same.

[TimmyP1955]

-20dBV is 100mV. -12dBV is 250mV.

[lowell]

Thanks do you have a reference for this? A url? I believe you, would just like to read more.

[g1]

Here's one:
dB dBu dBFS dBV to volts audio conversion digital - calculator volt to dBu and dBV dB mW SPL dB decibels 0 dBFS - convert dB volt normal decibels relatioship relation explanation analog audio absolute level true rms convertor converter decibel to dbf

[lowell]

Dare you to memorize that webpage. What YEAR was that built?

[MarkusBass]

Dare you to memorize that webpage. What YEAR was that built?

This is the same link I posted in post #4. Why do you ask for the year it was built? It may surprise you but the information posted there is still valid and it will be valid even in the next year

If you want to know more, go to wikipedia and search for "decibel": https://en.wikipedia.org/wiki/Decibel#Voltage

Mark

[TomCarlos]

Fishman schematics are nearly impossible to find. As suggested, you need to "compare" - meaning have you tried another Piezo, have you used that same Piezo with a different preamp system, compare this system to another. I have a Fishman Presys that I used as a project and that seems to put out more volume than my Taylor ES 2. So it is all relative. Tell us this... if you do a side-by-side of your system (Piezo and Preamp) and compare that to something different, do you have the same volume, half volume, hardly any volume?