Bass Tube Pre-amp Project VU Meter Help

[rwyarbrough]

I hope this hasn't been covered before and I'm not off topic for my first post here. Conducted a search and really didn't find anything that addresses some of my questions on this topic - so here goes:

I've built a few electronic projects, enough to want to give an attempt to build a tube bass preamp to drive a Carvin HD1800 I have. The prices for new and used mass produced ones seem awful high to me and I really don't need all the bells and whistles. I just want a clean preamp (low noise that is) with a input and output meter with the added warmth tubes bring to the mix.

I have found great schematics for the preamp itself, so I feel good about that, the question comes in in reference to the VU meters. Call me anal, but I would like to have two meters on my preamp. One for the input signal strength coming out of the bass into the preamp to keep from over driving the preamp and one for the output signal strength to the power amp to keep from over driving the power amp.

Does anyone know where I can find schematics for accomplishing that? I would assume that the circuitry would be different due to the amplification involved to the signal, but I am not versed in the fundamentals and theory involved in measuring signal strength let alone attaching a VU meter to measure it.

To add to the mix, I am nostalgic and love the look of the old style analog VU meters, which I want to use. Not sure how that impacts the circuit design for both signal measurement meters. A digital readout would be REALLY cool, but seems like I would be getting off track of my simple design and keeping the cost down with that. Worst case, I guess I could settle for LED VU meters or no meters at all, maybe a light that turns on at a threashold/peak if the analog VU meter undertaking is too much, but if possible, I really want to use analog VU meters.

Thanks in advance for any input, direction, links, or schematics for using analog VU meters or digital readouts in my bass preamp project.

[Enzo]

If you just want eye candy, meters are great. I think however - just my opininion - that as a practical matter, this may not be as useful as you think.

"VU" meter has a specific meaning. You are talking in general about just a level meter. The meter measuring units would be rather arbitrary really.

Your guitar is not likely to overload the amplifier input. SLapping and popping can send huge transients through an amp, but an analog meter won;t tell you when that happens and whether clipping has occured. Your erars will tell you right now if you are overdriving anything.

To set up some meter to tell you if you are getting into overdrive territory, you would first have to know what those levels were. What amount of signal does it take at each stage to overdrive the next? If you are building this preamp, then only you can tell that.

Then there is the meter drive. Your guitar pickups won;t be able to drive a meter directly unless it is a pretty sensitive one. You may have to create a simple meter drive circuit to buffer the signal from wherever, and present it on the meter. An op amp or two would handle it.

[Mike Dark]

Check this out LM3916 - Dot/Bar Display Driver

Should be a good starting point...