DIGI 125 REVISITED

[NanoFarad]

Hi everyone, due to utter boredom i desided to build some amps for fun. I wanted to start from a quasi complimentary amp designed by forum member WhiteDragon but later i thought why not begin with a simple classic design like DIGI125 (ETI, MAY 1989). I hve drawn a schematic based on the original design with very few modifications like bootstrap, zobel etc.

 

[Bone]

Not HiFi but a nice amp nevertheless. Ive built a couple of these using the original circuit.

 

[NanoFarad]

Any suggestion regarding the modification i made?

 

[lineup]

Refreshingly simple amplifier.
Bootstrap is a considerable improvement.
Nice!

 

[lineup]

If I should suggest some change:
1. Drivers in output should be BD139/BD140.
2. Change output devices to some TO-220 transistors.

 

[NanoFarad]

Here is the updated schematic. I changed drivers to BD139/40 and reduced bootstrap plus feedback cap value to 47uf. I dont have good TO-220 outputs except MJE3055/2955 but i hve some good old A1941 C5198 in TO-3PN package.

 

[wahab]

I posted this in another thread, do the same and THD will be considerably lower.

 

[NanoFarad]

I already made some changes and there's many ways for improvement but i want to keep the design as simple and original as possible. Vanishing THD isn't my goal & for that much better designs are available.

Regards

 

[wahab]

That s not only THD, PSRR will improve accordingly, so no need of giant capacitors in the PSU;
anyway do the way you like it, you are the end user after all.