Preview On New Discrete OpAmp

i've just replyed to yoru email
sorry for the delay

Finally I found time to stuff and test the prototype. Works like a charm! I think Fabio will do a board run, if anyone needs Gerbers let me know and I'll see what I can do.

Within the next weeks I'll write a detailed documentation with parts list, stuffing instructions and application notes. For the time being here a temporary parts list: [removed]

Samuel

Great news! Looks like there will be more DOA building going on in the future.

One question though - what are you using for inductors? I didn't see them on your parts list.

Wow!

another DOA! life just gets better and better . . .


Wonderful news. ican;t wait yo try.


ANdyP :thumb:

What are you using for inductors? I didn't see them on your parts list.

Click to expand...

Thanks for pointing this out--completely forgot them. I updated the parts list. Any standard HF inductor with low resistance and reasonable resonance frequency should work in place of the part I indicated.

Samuel

Hey Samuel, I´m not trying to be smart, but you have to take a look
at the M-100 from former NTP in Denmark ( you can find it at Gyraf´s
resources) and tell me what your improvements are?! I can answer one for my self; M-100 runs in class B which I think is a pity because its a wonderful sounding amp if you not strain it; thats-no heavy load under 5-10kohms.
Cheers, Bo

You have to take a look at the M100 from former NTP in Denmark and tell me what your improvements are!

Click to expand...

Perhaps let's say it like this:
* substantially lower voltage noise
* class A drive up to 600 ohm
* input protection
* output short-circuit protection
* improved high-frequency PSRR
* higher open-loop gain (and thus lower distortion)
* lower unity-gain transit frequency (and thus improved stability)

I do not pretend to have any significant invention in my design; it's all about compromises and that's a compromise I like. It is very easy to improve the performance in many respects if you give up the simplicity of these designs and add a few more parts, but that's not what I wanted here.

BTW, I measured the input offset voltage of the first prototype yesterday and found--much to my surprise--that it is below 1 mV. Either I've been lucky or these Toshiba transistors are extremely consistent and SPICE predicts the quiescent conditions very well.

Samuel

We are about to make some boards of Samuel DOA, check here:

http://www.groupdiy.com/index.php?topic=14712&postdays=0&postorder=asc&start=0

:guinness:
Fabio

I uploaded the first revision of the documentation: [removed]

More to come ASAP! Please report errors and typos...

Samuel

Samuel, great work and documentation, thanks alot.
looking forward to the pcbs :thumb:

Very exciting! Excellent documentation. Can't wait to see the remaining subjects completed. Samuel, how can a Swiss write such good English? :grin:

Hey Samuel, i made a breadboard of this your nice OP,but I have some trouble.
The slew and therefore freq resp. is poor.
I get neg. peak when the square curve goes down, upwards its very slow.
I´ve messured the idle current and they are fine, just as you predicted.
The outp.offset is about 0,8V. The MPSA 18 has about 950 as hfe.
I took away the C2+R8 and it became a figure of 5 better in responce.
I´ve followed your fine desciption but I cant get it work properly.
What to do?
Cheers Bo

At which gain/configuration did you test the opamp? Can you measure the voltage drop across R3, R4, R6 and R7 and post them? It looks to me as if one of these resistors could have a wrong value, at least it would explain the large offset and the asymetric slewing.

Removing C2/R8 will of course make the amp unstable at low gains.

Samuel

I uploaded the latest revision of the documentation: [removed]

Samuel

-my mistake, I thought I checked evry...
the fault was that the 1k6 never was connected,you pointed me into the right direction. Thanks! So now it reeds 8,2 mV !! offset with gain 1 and 10kohm in the feedback loop. ´This is a fast amp and it reeds square wave above
100kHz but it rings and it could be wise to compensate.
It still has a ringing and an overshot of about 10% mostly on the negative side. (measured at 10kHz.)
Soon I´m gonna listen to it as well.
Cheers Bo

Glad it worked out! Check the simulated impulse responses in the new documentation. With my board and test gear they are pretty close to what I measure.

What happens when you short the 10k feedback resistor? 10k is a bit high in value as it will start to decrease stability together with the rather large capacity of the input transistors.

DC offset should go down as well, I guess.

Samuel

Yeh, fine information! I tested shortening the 10k in feedback loop.It
didn´t like that,but when I was around 3kohm it measured really well.
When I came less then 300 ohms it did tend to get nervous. Maybe
cause I´m still in breadboard-land.
Cheers Bo

[quote author="Samuel Groner"]I uploaded the latest revision of the documentation:
SGA-SOA-1_documentation.pdf

Samuel[/quote]
Thanks, nice to have all the info compiled and as thorough as this.

I was able to finish a new revision of the documentation which includes a mic pre circuit in the app notes: [removed]

Samuel

Well done!! :thumb: