Diamante -a discrete medium power opamp

[mymindinside]

Hi Russ,
i am interested in building this amp, but would like something thats portable.
in the photo attatched to your post the setup is powered by 2 9v batteries. is this feasible as a permanent solution. how long do the batteries last, since its biased for class a i suspect not very long....
thanks, and cheers to a good design using readily available transistors!

[mymindinside]

Oops sorry, just read through your earlier posts,
you mentioned that one could run it from battery. Would any component values change based on an 18v battery supply?Two 9v batts in parallel

[Russ White]

Originally posted by mymindinside
Oops sorry, just read through your earlier posts,
you mentioned that one could run it from battery. Would any component values change based on an 18v battery supply?Two 9v batts in parallel

I think you mean in series

No no component changes at all, in fact thats how I first tested it. It works great.

[Russ White]

The battery life will depend on the bias level you choose.

The nice thing is, this amp should perform very well even without much bias.

You should get great performance even with the output stage biased to just a few (2-3) milliamps.

[mymindinside]

Yeah, series it is, ok thanks a lot for the info...

[Russ White]

I have updated the circuit to revision 1.1.

I simplified the CCS and Cascode voltage refences. This eliminates one transistor and makes it easier to use the same parts for different bias levels.

I also changes some component values to make transistor matching even less critical (it never was very critical), and to make the amp less prone to thermal runaway at high bias.

Suggested bias is to measure around 30mv at the emitter resistors (R1-R6). This will get you about 3ma bias per device. (9ma total) The amp will do fine well into about 60mv bias. The driver Qs will get a bit warm though.

Here is a picture of my prototype of the Rev 1.1 layout.

Schematics and PDS are in the zip file which can be found
HERE.

We will post a new BOM too.

Have fun!

:EDIT: Ignore the fact the the silk screen in the photo reads Version 1.0, its really 1.1

[zeonrider]

Hold on Mr White, I, don't began with 1. one.

You will wait for first BOM.

Regards zeoN_Rider

[BrianDonegan]

Here is the V1.1 BOM

[Russ White]

I knocked this together in a couple hours, it should work well for prototypes.

Cheers!
Russ

[error401]

I got bored and did some simulation on this design tonight. It looks excellent. I used a 32R dummy load in my simulations, and included all optional components, except the output resistor/inductor. No parasitics were simulated. Here's the data:

Frequency response is ruler flat out to about 1MHz, -3dB at 10.46MHz. THD is 0.0007%, with the first harmonic at about -100dB. Slew rate is about 75V/uS (rise time to 2V is 27ns). There is a single cycle of ring on the rising edge of a 10KHz square wave, overshooting by about 0.2V above, recovering to 40mV below and settling immediately.

With a 1K load, THD improves to 0.0003% (-112dB first harmonic), and the settling behaviour with the square wave is a little nicer.

If anyone wants to see the plots I can generate them...

Looks like a very nice design Russ, thanks for sharing with the community!

Do you have any recommendations for SMD transistor substitutions? I guess BC850/860C would be appropriate, they seem to have the same specs?