Baldringer - Dual Drive

caspercody · Post by **caspercody** » 05 Mar 2013, 20:27

@Bajaman - Did you do any more with this circuit? Just wandering what you might have found.

Thanks
Rob

bajaman · Post by **bajaman** » 06 Mar 2013, 01:25

no
gave up on it

cheers
bajaman

caspercody · Post by **caspercody** » 07 Mar 2013, 14:55

@Bajaman.. Thanks for getting back to my question!!! If you do not mind, I have a couple of questions on what you think. I bread boarder it and got no sound. I used the schematic for the Rust driver as a base (mostly because it is the only circuit I can find that was inverting op amps). If you look at the attached file, I bread boarder it basically the same way, but inserted the Baldringer stage in the gain stage op amp. I used a audio probe and got signal up to one side of the C2 cap. But on the other side of C2 cap (the side that goes to the Baldringer stage) I got nothing. The Baldringer schmatic shows the (+) op amp going to ground, but I connected it to the voltage divider voltage??

Thanks
Rob

caspercody · Post by **caspercody** » 07 Mar 2013, 15:02

Here is the patent file on the Baldringer circuit, in case you do not have it anymore.

jonasx26 · Post by **jonasx26** » 08 Mar 2013, 14:32

Some Music man amplifiers use a similar technique. See attached schematic.
Also, similar/related technique used in this app-note, page 3; http://www.thatcorp.com/datashts/dn03.pdf

I experimented with this some years ago.
Wasn't all that different from standard diode clipping, which isn't surprising as the transistors function as diodes with adjustable Vf and softer 'knee'.

Making the clipping frequency-dependent as in the patent might make things more interesting though. Probably worth investigating if you're into distortion/overdrive-stuff.

caspercody · Post by **caspercody** » 08 Mar 2013, 14:40

Thanks for the information!

jonasx26 · Post by **jonasx26** » 08 Mar 2013, 15:11

caspercody wrote:The Baldringer schmatic shows the (+) op amp going to ground, but I connected it to the voltage divider voltage??

All grounded points in the Baldringer patent must be connected to the 4.5V reference ground.
Also, reduce the two 100k resistors to something like ~4.7k-22k and add a ~22µ-100µ capacitor from the divider voltage to ground. Should increase your chances of making it work.

caspercody · Post by **caspercody** » 08 Mar 2013, 16:55

What point would be the "4.5V reference ground" (looking at the Rust schematic)? Would it be the same ground point shown on the schematic as 4pin? I thought that point would be just the common ground of the circuit? Would a bi polar power supply be needed?

I have always wondered what is the difference in using different resistor values to make the voltage bias point?

Thanks for your time and help
Rob

jonasx26 · Post by **jonasx26** » 08 Mar 2013, 20:12

caspercody wrote:What point would be the "4.5V reference ground" (looking at the Rust schematic)? Would it be the same ground point shown on the schematic as 4pin? I thought that point would be just the common ground of the circuit?

The reference ground would be at the junction of the two 100k resistors. Pins 5 and 3 of the op amp is connected to it.
Ground is usually in the middle of the supply voltage. This box has a 9V supply, which makes ground inside this box 4.5V.
Outside the box, ground can be something else. Another box might use a +/-9V supply, which means ground would be 0V inside that box.
Ground is not a number, it's just a reference-point. As long as you've got coupling caps at the input and output, you can call whatever voltage ground and reference all signal within the box to that voltage..

caspercody wrote:Would a bi polar power supply be needed?

Probably not. But the reference point needs to be low impedance (stable, not fluctuating when loaded (sourcing/sinking current)) to all signals connected to it.
The two 100k resistors work in the rust driver. But not in this application..

caspercody wrote:I have always wondered what is the difference in using different resistor values to make the voltage bias point?

I could probably explain it pretty well in Swedish, even though I've had some beers

But as for now, R.G. Keen explains it better than me here; http://www.geofex.com/circuits/biasnet.htm

Baldringer - Dual Drive [traced]