Transistor gain/volume question in my Blue Warbler. Please help. :(

[midwayfair]

Hey, folks, I'm trying to balance the output between modes in my Blue Warbler. This seems like something I should be able to work out on my own, but my brain is pretty fried from the weekend, and I'm short on breadboard space at the moment. Plus it seems like a simple thing

This is the dry path, which is similar to the Magnavibe with some different values (Q1 is any high-gain silicon or Darlinton):



Now, I've built five of these for friends and a couple for myself, and while there's a small difference in volume between the modes, it wasn't enough to bother me (and I use it in a band setting). However, Jacob Kokura built one of the PCB prototypes and described the volume drop as much more severe (there's nothing wrong with his build otherwise).

The tremolo mode is a collector follower with a small input cap. The vibe mode oscillates between the same collector follower and an emitter follower with a much larger output cap. The result is that the vibe mode sounds louder.

Here's my question:
Would changing the emitter or collector resistor(s) balance the volume between modes better? It seems to be that dropping the 2.2K would shunt some more signal to ground from the emitter's signal, and ought to increase the gain coming out of the collector at the same time, right? Or would that just make both modes louder?


Also ... it has to be a really, really minor change. It doesn't have to be the absolute BEST solution, but it can't be something that involves adding parts or hacking the PCB. I'm trying to help avoid a really bad situation here.

[slacker]

As long as the thing is biased properly, the signal at the emitter will always be essentially the same level as the input, so you can't change that without adding extra parts. Your idea should work, if you make the collector resistor bigger the output from the collector will be bigger.

The volume of the trem will depend on the minimum resistance the LDR gets to, this might be why your builds work fine and someone elses has this problem, the type of LDR used could make a difference. You might be able to tweak the volume by changing something on the LFO side as well, for example making the LED brighter may reduce the resistance of the LDR enough to solve the problem.

[midwayfair]

Thanks, Slacker.

Common sense is now telling me that it's not really possible to fix it -- the tremolo mode will always be slightly quieter than the vibe mode.

[JohnForeman]

Jon,
I really want to build one of these but my skills are not up to speed when it comes to understanding the schematic and vero.  I'm confused by the LDR and LFO 'components'.  It would be great if you could do a video showing the board and explaining the vero and components and how you've constructed it..
Keep up the great work..
John