Lovetone Brown Source

[mikeb]

Well done, and belated apologies for the error in my protel-tracing.  :oops:

Mike

[RickL]

Okay, so I rebuilt my Brown Source according to the schematic analogguru posted and while it is working better, it's not quite there yet.

The gain control has an noticable effect, the tone control works and I can get sound in each position of the tone select switch. However...

I'm not getting any distortion. I get a buffered version of the input at the collector of Q1 but it looses most of it's volume on the other side of C3. If I lift C3 from it's connection to the 220R resistor (or lift the resistor from it's connection to pin 5 of the opamp) I get full volume again. The volume is boosted again by the opamp (volume is back up again at the output of the opamp, controlled by the drive pot) but obviously not enough to be clipped by the diodes. Both the transistor stage and the opamp gain stage appear to be working so why the volume drop when they're connected?

Also, the last three positions of the tone select switch don't seem to have much variation in tone. Particularly, I can't hear any difference between positions 2 and 3. Since these two positions just put either a 33n or 22n cap in parallel with another 33n cap I wonder if one of them should be 10 times larger (330n or 220n) or if the fixed 33n should be 3n3.

FWIW I tried a 100k pot in place of the 25k drive pot and it didn't make any difference. There isn't any noticable gain with the pot set above about 25k.

[Processaurus]

In analoguru's schematic, the 33nf cap in the feedback loop of the first opamp stage looks much too large to me,  all the audio fequencies are probably passing through it rather than the clipping diodes.  For instance, looking at a tube screamer clipping stage, the cap in the feedback loop is about 1000th the size of this capacitor, and is just for filtering out RF.  They may have used a bigger capacitor, like 330pf or 3300pf to start filtering the treble out, to make it BROWNER, but the 33n capacitor would filter every frequency that made its way into the circuit.

I'm glad there's interest in this project, I just ordered ma switches for this one.